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LOAD REDUCTION PLANNING TOOL (LRPT) V2

1. R worksheet that was created when guidance in selecting a maintenance effort level for a scenario the patches were incorrectly When all of the fields are populated click the Calculate C button to saved make the appropriate return the runoff coefficients C for each patch The runoff coefficient changes in the Patch Data Input values for treatment BMPs that have been adjusted for performance Table and save the patches again decline over time are shown below the Initial runoff coefficients Cj After the C values are calculated the user can save the patch data by clicking the Save Patches button A separate worksheet tab is created that stores the patch data each time the Save Patches button is clicked e g Patches1 The runoff coefficient values and all of the other patch information must be filled in when the user saves the patches Complete the PATCH DATA Input table in the LRPT spreadsheet by filling in the highlighted cells The HYDROLOGIC ROUTING Input Table requires the user to specify the percent contribution from each source patch to each receiving patch The routing Input Table matrix is automatically populated when the user clicks the Save Patches button for the previous input table The source patches are listed along the top row and receiving patches are listed along the left hand column Scroll down to the bottom of the table to see the offsite routing and the routing totals
2. IF Porous pavement PP Treatment BMPs Biofilter BF Undeveloped areas with natural vegetation pervious surface subjected to minimal maintenance and little to no localized foot traffic Other Names Dry Well Infiltration Trench Roof Drip Line Rock Lined Channel etc Porous asphalt Pervious concrete Grass pavers Modular blocks etc Grass swale Grass filter strips Rain gardens Vegetated buffer strips Bioslopes etc Description Land surface modified to sustain maximum infiltration rates typically consisting of vertical excavation of native soils and filling with coarse drain rock prefabricated infiltration units or other highly permeable material Infiltration features are implemented to reduce volumes generated from adjacent impervious surfaces A durable pervious surface overlaying a crushed stone base that stores rainwater and allows it to infiltrate into the underlying soil Porous pavement includes an underlying reservoir to increase infiltration rates Local stormwater is typically not routed to a porous pavement surface but rather constructed to minimize the volume of stormwater generated and routed downgradient from a previously impervious surface Footprint can vary but is typically used to replace parking lots or other impervious surfaces A pervious substrate with dense native and or maintained vegetation coverage 28096 Biofilter designs such as rain gardens can augment de
3. DOCUMENTATION LOAD REDUCTION PLANNING TOOL LRPT V2 FINAL GUIDANCE ONONATURE ecosystem science design A TOOL TO ESTIMATE THE WATER QUALITY BENEFITS OF PARCEL SCALE RETROFIT PROJECTS IN THE TAHOE BASIN aan Baduetian Danaina Taal ft riu S arhnieal ann cardfsumeemncefvecmmant Load Reduction Planning Tool LRPT v 2 Technical and User Guidance Document CONTENTS LIST FIGURES e i LiSt OF ADIOS 228s e dier UR O HERR HORE ERR cies ERRORI ORI HIERO ede E ESSI D EDS NER ROTE ii Executive Tnra HH 1 DAP EOC Prol Ton HP 1 2 SUC MID 2 EXCI nr icibiisolrer e e 4 4 Theory and Methodology inr rtr etr nr a ree Fri nt a hee iR era hene ri Pega ra Feo SRL ER YA 4 LI 4 LUE Tai eip joe ET 17 STEP 1 Specify Parcel Boundaries ecce entr eere eet E ei aa reete dete rad reete leta eines 18 STEP 2 Define Scenario and Site Condition essssssssssssseeseeeeeee nennen nenne ennt enne ennt nn rennen enne 18 STEP 3 Delineate Patch Boundaries and Hydrologic Linkages ceccescesseeseeeeeeeeeeeeeaeteeeseesaeeeaeeeeeteesaeeeateneeee 19 STEP 4 Assign Hydrologic Routing Contributions ceceeescecesecceeeeeseeeceeceeseeeaeeaecseecs
4. Lake Tahoe A guide for building and landscape professionals and presented as the example in the tutorial to assist new users in applying the tool to an actual parcel Should LRPTv2 be used for parcel retrofit planning or potentially be integrated into parcel retrofit permitting requirements future versions of LRPT could be developed to incorporate user feedback and address some of the known limitations and potential improvements listed below 1 TheLRPT is a reasonable and simple methodology to estimate the relative water quality benefit of parcel retrofit projects in the Tahoe Basin The accuracy of the LRPT annual loading estimates from any specific redevelopment site is likely limited Rather the methodology applies fundamental hydrologic routing principals and focuses on preserving the relative accuracy of the water quality benefits of different urban land use improvements that are commonly implemented in the Tahoe Basin While the pollutant load estimates generated are unlikely to accurately represent actual loads for a specific year the LRPT method is expected to reliably differentiate the relative water quality benefit across parcels and different redevelopment scenarios To the extent possible LRPT algorithms are based on and consistent with PLRM thus increasing confidence that outputs from LRPT on the parcel scale align with PLRM estimates on the urban catchment scale The accuracy of LRPT results are in part dependent upon the jud
5. claimed by the user The users should download the Calculation Spreadsheet available at www trpabmp org to calculate storage properly and ensure the treatment capacity ft of each Treatment BMP is properly sized and exceeds the contributing runoff ft from the source impervious area Porous Pavement The ability of porous pavement to store and infiltrate runoff is controlled by the vertical reservoir depth and void space of material beneath the surface Rather than the user determining the storage in inches of runoff for porous pavement the LRPT calculates the storage for each porous pavement patch independently as a function of porous pavement vertical reservoir depth and void space as provided by the user Eq 6 PP S in Z in VS 96 Eq 6 Where PP S is the porous pavement storage in Z is the vertical reservoir depth in and VS is the void space of the reservoir beneath the surface 96 as input by the user 1 00 0 90 0 80 0 70 0 60 0 50 0 40 0 30 Annual runoff coefficient C 0 20 0 10 0 00 Treatment BMP annual runoff coefficients C determined by PLRM simulations of hypothetical Treatment BMPs based on TRPA BMP sizing criteria www trpabmp org for seven meteorological grids representative of Lake Tahoe urban areas 2NDNRTURE LLC 0 80 1 00 1 20 1 40 1 60 1 80 2 00 Treatment BMP storage inches of runoff from contributing impervious area Met
6. natural vegetative cover parking lot sweeping and other BMPs to reduce the annual source of sediment and nutrients generated from the site Tier 1 A constructed BMP that accepts attenuates and treats urban stormwater Treatment BMPs are implemented to reduce pollutant loads in stormwater by either removing pollutants and or by reducing surface water volumes LRPT focuses on 3 different types of Treatment BMPs that are typically installed on commercial or residential parcels to capture and retain stormwater to reduce runoff transported off site Infiltration features porous pavement and biofilters Treatment BMP Treatment BMPs are intended to provide a sink for urban pollutant loads and a Treatment BMP condition is defined as a continuum of the pollutant load removal capability of a Treatment BMP Treatment BMP condition is considered to be at benchmark following Treatment BMP installation and or after adequate maintenance As pollutant loading and treatment occurs condition during subsequent storm events the condition of a Treatment BMP gradually declines 2NDNATURE et al 2009 LRPT quantitatively incorporates the expected decay in water quality performance of the Treatment BMPs as a function of maintenance frequency identified by the user 9 REFERENCES 2NDNATURE Environmental Incentives and Northwest Hydraulic Consultants 2009 BMP RAM Technical Document Lake Tahoe Basin Prepared for the U S Army Corps of En
7. which should total 100 for each column Click the Save Routing button to save the hydrologic routing network currently displayed in the table If the user has not saved the patches currently displayed in the patches table an error message will appear when the user clicks the Save Routing button If this occurs return to the patch data input table and save the current patch configuration before clicking the Save Routing button LRPT creates a new worksheet tab with the routing data every time the Save Routing button is clicked e g Qcalcs1 Double check the site diagrams to ensure that routing directions and contributions have been correctly assigned for each patch as incorrect routing can lead to incorrect runoff and loading calculations Hydrologic Routing Contributions Troubleshooting If information is changed after the routing is saved delete both the worksheet tabs with the current patch data Patches and the routing configuration Qcalcs Re save the Patch Data Table make the appropriate changes and re save the Hydrologic Routing Input Table Assign routing by specifying the percentage of runoff from each source patch to each receiving patch gt Save Routing IM1 IM2 Receiving Patch IM3 IM4 IM5 IF1 IF2 IF3 offsite N Offsite Runoff offsite S offsite E offsite W Flow Routing Check Source Patch IM1 IM2 IM3 100 100 100 v 100 100 100 Complete the HYDROLOGIC ROUTI
8. BOUNDARIES AND HYDROLOGIC LINKAGES For step 3 examine the diagrams in Figure 9 You will use the information from this step to populate the LRPT Input Tables in step 5 LRPT relies on user delineation of patches of similar surface types and specification of hydrologic routing Patches constitute the physical area within the site where runoff calculations are made The sum of the individual patch areas equates to the total site acreage Mapping should be initiated in the office using GIS Google Earth AutoCAD or another mapping program with preliminary patch delineation conducted to the extent possible Engineering plans may also be useful in determining the location and sizing of Treatment BMPs for relevant scenarios The draft map should then be field verified at the site to confirm the existing conditions parcel delineation and identify flow directions from patch to patch Patch types should be labeled with the appropriate prefix listed in Table 1 of the User Guidance Attempts should be made to reduce complex geometries to simple polygons while preserving the site surface area In the majority of cases the visual distinction between various surface types and their relative permeability will be readily apparent but in some instances based on best professional judgment infiltration measurements or other means to gain additional information on the surface type and most appropriate annual runoff coefficient may be necessary One or m
9. and post improvements to better illustrate STEPS 1 4 offsite 7026 100 100 5 off E Site ONDNATURE LLC A8 a3N9SIS3G TEL 831 426 9119 FAH 8314267082 FLOW PERCENTAGE EXAMPLES FIGURE 8 wuuw endnaturellc com STEP 5 POPULATE LRPT INPUT TABLES AND RUN SIMULATION User guidance on how to populate the LRPT Input Tables is provided below Screenshots are provided as reference for each Input Table and in some instances the complete Input Tables may not be displayed below due to space limitations indicated by dashed arrow A detailed tutorial is provided as Appendix A using an example site to demonstrate the functionality of LRPT to the new user OPEN LRPT MS EXCEL FILE LRPT is a visual basic application implemented in a Microsoft Excel spreadsheet with the name LRPTV2 xlsm The program has been tested in the 2007 version of MS Excel and may not function properly in other versions of MS Excel due to changes in VBA from one version of Excel to another Users are permitted to change data in the Input Tables but the rest of the sheet is locked for editing and users cannot view the macro code that runs the application Both of these measures are intended to reduce the potential for users to unintentionally cause errors in the program LRPT is locked for editing so users should save it as a new file for each new site evaluation For LRPT to run users must ensure t
10. needles and other debris Overtime Treatment BMPs that rely upon infiltration are gradually clogged as pollutants sediment and other small grained material are introduced and accumulate in the vertical pore spaces that control infiltration rates and treatment capacity The rate of performance decline of a specific Treatment BMP is assumed to depend upon the runoff volume contributed to its footprint qn and the relative sediment loading rate of infiltrated volumes to the Treatment BMPs These two factors are presumed to dictate the rate of infiltration decline caused from clogging and occlusion of the Treatment BMP While the concept of decreased infiltration capability of a Treatment BMP is well accepted the actual quantification of the rate of decay or algorithms that relate the contributing volumes and sediment loading rates are very poorly understood It is also assumed that frequent inspections and regular maintenance will reduce the rate of performance decline and the implementation of extensive maintenance actions will restore infiltration capacity and overall Treatment BMP performance to initial i e benchmark condition Thus over time Treatment BMP runoff coefficients are expected to approximate the curves illustrated by solid lines in Figure 5a However there is a limited amount of existing knowledge and data available to quantify the cyclic decline and restoration of performance represented by the solid lines in Figure 5a or the identify th
11. not doing so results in circular flow See Figures 6 and 7 in the User Guidance Document for more information LRPT allows up to 30 patches to be defined for a scenario If the site requires more than 30 patches the user will have to divide the site and model the scenario as two Examine the site map in Figure 9 What are the patch types of surfaces accepting roof runoff On Figure 9B label the impervious patches with IM STEP 4 ASSIGN HYDROLOGIC ROUTING CONTRIBUTIONS Runoff from patches is controlled by three distinct components the rate at which water accumulates on the patch from direct rainfall and contributing patches the area of the patch and the annual runoff coefficient of the patch All patches accumulate water from direct precipitation Receiving patches also accumulate water that runs off adjacent patches as defined through hydrologic routing in the LRPT The LRPT user specifies the contribution of each upslope source patch to each down slope receiving patch Note LRPT assumes no runoff is generated from adjacent parcels i e offsite up gradient and routed to the site Water i e mass is conserved as runoff is routed through the parcel and across patches By defining the hydrologic routing of a parcel Treatment BMPs can be strategically placed to retain runoff generated from patches with relatively high annual runoff coefficients see Table 1 in User Guidance In Figure 11 all of the patches have been del
12. of infiltration rate 0 13 in hr o E 0 60 o 5 050 e 2 w 0 40 5 amp 0 30 0 20 0 10 0 00 0 00 0 25 0 50 0 75 1 00 1 25 1 50 1 75 2 00 Treatment BMP storage inches of runoff from contributing impervious area Figure 5b PLRM and SWMM estimates of the annual runoff coefficient increase as a result of 2596 5096 and 7596 decline in infiltration rates of a hypothetical Treatment BMP given a range of storage located in MET grid 847 East South Lake Tahoe The relative C reductions obtained from this analysis of MET grid 847 are used to extrapolate expected average annual C values for Treatment BMPs in other MET Grids based on maintenance commitment See Table 4 2NDNRTURE LLC A8 a3N9SIS3G TEL 831 426 9119 FAX 8314267092 LRPT MODELING OF MAINTENANCE FIGURE 5 www 2ndnaturellc com INFLUENCE ON BMP e VALUES effort commitment levels high moderate and low for the overall site in question Table 3 provides the definitions and actions assumed to be performed to meet the stated maintenance level of effort for each category Based on best professional judgment high moderate and low maintenance commitments have been linked to a 2596 5096 and 7596 decline in the initial infiltration rates respectively on average over an 18 year time period The results from Figure 5b were extrapolated to other MET grids by applying the adjustment factors to the initial C values of a Treatment BMP a
13. post retrofit conditions by performing a sequence of steps summarized in Table 6 below LRPT STEP Description STEP 1 Specify parcel boundaries STEP 2 Define scenario and site conditions STEP 3 Delineate patch boundaries and hydrologic linkages STEP 4 Assign hydrologic routing contributions STEP 5 Populate LRPT spreadsheet and run simulation STEP 6 Repeat steps 2 5 for all desired scenarios STEP 7 Compare runoff and pollutant loads STEP 8 Generate LRPT summary report Table 6 LRPT user STEPs The following sections provide user guidance for successfully completing each LRPT step The accuracy of runoff values and associated pollutant load calculations by the LRPT increases as the hydrologic routing representation of the site approximates the actual drainage conditions It is critical that the user obtain the best available aerial photos engineering plans and topographic data as well as perform visual inspections of the site in order to delineate surface types patches and hydrologic routing paths as accurately as possible The user will need the site map before initiating STEP 1 below STEP 1 SPECIFY PARCEL BOUNDARIES The location of the parcel s to be improved must be determined The entire site boundaries where BMP retrofit improvements are planned should be determined using GIS AutoCAD or other mapping program site visits site surveys and or engineering plans The user needs to obtain th
14. remaining 10096 parking area MP1 unpaved on bare driveway 10090 soil offsite East 2NDNRTURE LLC A8 a3N9SIS3G TEL 831 426 9119 FAX 8314267092 PRE RETOFIT FLOW ROUTING FIGURE 11 wuu endnaturellc com POST RETROFIT PATCH DELINEATION AND FLOW ROUTING LRPT STEPS 3 amp 4 150 100 infiltration feature F 100 infiltration feature IF5 infiltration feature beneath deck as 100 100 Y 50 gt UENIRE I NUN QN _h_eoa enamaaonaon22 gt 22 PRI IA y IF2 terraced 100 305 ft2 slope native 10096 10096 vegetation Parcel Slope 4 3 remaining 10096 area MP1 IM5 driveway 10096 offsite East Iv o e z z 2NDNATURE LLC X TEL 891 426 9119 FAN 891 4267092 POST RETOFIT SITE PATCH DELINEATION AND FLow RoUTING FIGURE 12 wwwus 2ndnaturellc com
15. required to represent the flow characteristics If the site is sloped to the East as shown in Panel C two additional patches are required to avoid circular routing issues Figure 6c shows a typical peaked roof surrounded on three sides by turf and on one side by asphalt Note that the runoff from the roof is directed perpendicular to the roof apex independent of site slope assuming that the building is level If the site is sloped to the North as shown in Panel B only three patches are required to represent the flow characteristics If the site is sloped to the East as shown in Panel C an additional patch is required to avoid circular routing issues GROUP SURFACE TYPES INTO ONE PATCH Whenever possible it is advantageous to group multiple similar surface types into a single patch Grouping can be done when the patches to be grouped are 1 spatially close together 2 separated by other regions also having similar permeability and 3 the surfaces have the same drainage pattern direction Panel A in Figure 7a consists of five roofs surrounded by turf along with an area of asphalt The roofs can be grouped into a single patch having acreage equal to the sum of the acreages of the individual roofs Three patches as opposed to seven are required to represent flow characteristics if the site is sloped to the North as shown in Panel B An additional patch 4 is required to avoid circular routing issues if the site is sloped to the East as show
16. the Lake Tahoe TMDL Pollutant Reductions Opportunity Report Lahontan and NDEP 2008 Table 2 and land use specific testing in the Lake Tahoe Basin 2NDNATURE 2010 The LRPT includes three private land use types commercial CICU multifamily residential MFR and single family residential SFR based on the TRPA Land Use designation GIS layer Lahontan and NDEP 2008 To maintain consistency across redevelopment areas and scenarios the land use category selected to represent the site will be a single land use even for redevelopment projects that include mixed land use types The expected water quality impacts decline as the relative human population density and disturbance frequency declines thus the CRCs for each pollutant of concern are highest for commercial land use and lowest for single family residential parcels Land Use Type Pollutant of Concern Baseline CRC mg L Tier 1 CRC mg L 296 4 204 Residentia MR DP om oso Residentia sR DP 014 0130 w om om Table 5 CRCs for baseline condition and Tier 1 improvements for urban land use types Lahontan and NDEP 2008 Event mean concentration EMC has a very specific definition and associated calculation Lake Tahoe stormwater modeling tools have employed the term characteristic runoff coefficient CRC to represent the average annual concentration expected from a specific land use type and associated condition 3 TMDL EMCs for fine s
17. BA to estimate the potential pollutant load reductions from BMP retrofit projects in Lake Tahoe Basin on a parcel or multiple parcel scale The LRPT terminology and methodology is consistent with the Pollutant Load Reduction Model PLRM nhc et al 2009 the BMP Maintenance Rapid Assessment Methodology BMP RAM 2NDNATURE et al 2009 and other Lake Tahoe stormwater management tools Offsite The user must define a common outfall where the runoff generated from the site will accumulate and LRPT calculations are summed Typically parcel outfalls are not specific locations but rather the downslope boundary e g the north border of the parcel and termed in LRPT as offsite Offsite in LRPT is analogous to an outfall as defined by PLRM and the point at which average annual pollutant loads are estimated Patch Patches are used to spatially delineate the site for hydrologic routing A patch can contain multiple adjacent surface types that possess similar runoff characteristics to simplify site geometry Patches constitute the physical area within the site where runoff calculations are made The sum of the individual patch areas equates to the total site acreage Patches are characterized by the relative infiltration capability of the surface as represented by an annual runoff coefficient C Pollutants of These are fine sediment particles FSP 16 um dissolved phosphorous DP total phosphorous TP total suspended sediment
18. C ROUTING Input Table when the user clicks the Save Patches button in the PATCH DATA Input Table with source patches listed along the top row and receiving patches listed along the left hand column The user should systematically enter the hydrologic routing as represented on the site delineation map created for the respective scenario Once all hydrologic routing data entry is complete scroll down to the bottom of the table to verify the flow routing check totals are 100 for each column Use this calculation to identify and remedy any data entry errors Hydrologic Routing Contributions Troubleshooting If information is changed after the routing is saved delete both the worksheet tabs with the current patch data Patches and the routing configuration Qcalcs Re save the Patch Data Table make the appropriate changes and re save the Hydrologic Routing Input Table Assign routing by specifying the percentage of runoff from each source patch to each receiving patch Save Routing IM1 IM2 Receiving Patch IM3 IM4 IM5 IF1 IF2 IF3 offsite N Offsite Runoff offsite S offsite E offsite W Flow Routing Check gt Source Patch IM1 IM2 IM3 100 100 100 i v 100 100 100 Once complete click the Save Routing button to save the hydrologic routing network currently displayed in the HYROLOGIC ROUTING table If the user has not saved the patches currently displayed in the PATCH DATA table an error message
19. Grid 672 CSLT South Y Met Grid 238 West Shore 9 Met Grid 204 Tahoe City Met Grid 532 Kings Beach Met Grid 817 Incline Village 9 Met Grid 847 CSLT Stateline Met Grid 903 East Shore A8 a3N9SIS3G TEL 831 426 9119 F84 8314267092 wuuw endnaturellc com TREATMENT BMP ANNUAL RUNOFF COEFFICIENT AS Fl G U R E 4 FUNCTION OF STORAGE AND METEOROLOGICAL GRID 4 4 BMP MAINTENANCE COMMITMENT Y Treatment BMPs are intended to provide a sink for urban pollutant loads and Treatment BMP condition is defined as a continuum of the pollutant load removal capability of a Treatment BMP A Treatment BMP is considered to be at benchmark condition following installation and or after adequate maintenance 2NDNATURE et al 2009 It is known that some level of maintenance is required to maintain Treatment BMP performance over time and devoid of maintenance Treatment BMPs will approach non functional conditions Therefore the initial annual C value for each Treatment BMP is adjusted in LRPT to represent an average annual C value based on the users defined level of maintenance commitment for the site MAINTENANCE IMPACTS ON TREATMENT BMP PERFORMANCE It is assumed that adequate maintenance requires frequent observations and simple improvements to ensure BMP conveyance is operating i e the BMP is actually getting water during runoff events and the BMP inlets outlets and surface are free of pine
20. Maintenance Commitment pad Seasonal commitments Extensive Maintenance Frequency Rake and remove all leaves pine needles or other debris e The maintenance commitment and FALL when resources permit Continue as necessary to ensure schedule aims for the treatment minimal debris at surface of BMP prior to snow BMPs at the site to be in proper accumulation functional condition the majority of As snow accumulation recedes at least one inspection to the time e g gt 50 WINTER ensure BMP conveyance is operating i e getting water and free of pine needles or other debris SPRING LOW maintenance commitment requires Infrequent visual inspections of BMPs and no planned use of e Resources are limited SUMMER BMP performance monitoring or rapid evaluations Irregular inspections e Likely Treatment BMPs on the site will be in a failed condition for Lc FALL Rake and remove all leaves pine needles or other debris extended periods of time when resources permit e No formal maintenance schedule developed WINTER Infrequent visual inspections of BMPs and debris removal as Maintenance actions are primarily resources permit triggered by anecdotal observations at the site Table 3 Definitions of site maintenance commitment levels high moderate and low which includes completing the stated actions on the indicated frequency for all Treatment BMPs located within the subject site The user selects one of these 3 ma
21. NG Input Table by filling in the highlighted cells Explain why each column in the routing matrix should sum to 10096 Simulation results for each scenario are stored in the RESULTS SUMMARY Output Table The program will take up to 1 minute to run and when complete will display annual runoff and pollutant loading estimates for an 18 year simulation period Results Comparison gt Annual Pollutant Load Change kg yr P r Compare Runoff Change Initial Scenario Final Scenario FSP TSS Results ft yr BSO1 BSO3 2510 0 1 1940 1 4126 Click the Run Scenario button in the Results Summary Table What is your calculated pre retrofit runoff Q ft yr STEP 6 REPEAT FOR POST RETROFIT SCENARIO You are now ready to populate the LRPT with post retrofit scenario data The post retrofit design alternative has been completed and all necessary site information is provided in Figure 12 Review Figure 12 and notice where Treatment BMPs have been placed and how routing at the site has changed To save time an LRPT spreadsheet has been partially populated for you to reflect changes in the patches and hydrologic routing shown in Figure 12 Additional information to complete the post retrofit scenario e The source patch to infiltration feature IF2 is the roof IM2 and generates 31 cf of runoff The treatment capacity of IF2 is 23 cf e The pervious pavement surface PP1 has a reservoir depth of 5 inches and the media is fine gr
22. PT 1 INTRODUCTION The Load Reduction Planning Tool LRPT provides a way to estimate reductions in potential water quality pollutant loading associated with the proposed parcel scale implementation of Best Management Practices BMPs including redevelopment projects private parcel retrofits and single family BMP implementation in the Lake Tahoe Basin The LRPT could be used early in the planning process by planners developers and or regulators to identify alternatives and design modifications to reduce pollutant loads generated from a site The LRPT methodology is applicable to a much smaller spatial scale than the Pollutant Load Reduction Model PLRM and it is not intended to replace PLRM or other water quality planning tools approved by Lahontan Regional Water Quality Control Board RWQCB the TRPA or the Nevada Division of Environmental Protection NDEP Rather LRPT provides a First use of glossary Section 8 terms are bolded complementary approach to estimate the benefits of water quality improvements implemented on the parcel scale that can be used in situations where other tools are less appropriate A key component of any parcel scale improvement is the strategic placement of Treatment Best Management Practices BMPs to optimize hydrologic routing from impervious to pervious surfaces onsite As outlined in the TRPA Best Management Practices http www tahoebmp org a primary strategy to minimize runoff from resident
23. PT pervious patch annual runoff coefficients are adjusted as the q loaded to a specific pervious patch increases as summarized in Table 2 Remember q is the ratio of the total volume contributed from adjacent patches to the patch area see Eq 3a Thus for the same inflowing volume q will be larger for smaller patches and therefore accounts for the size of the pervious patch Maintained Compacted Severely compacted pervious Pervious pervious Qn Undeveloped ft yr UN MP cP SP C 0 04 C 0 15 C 0 25 C 0 50 Table 2 Adjustments to initial C values for pervious patch types see Table 1 based on q to eliminate large volumes of water infiltrated by relatively small pervious patches where the hydraulic loading from contributing patches is relatively large TREATMENT BMPS The Treatment BMP types definitions and descriptions relevant to the LRPT are provided in Table 1 Based on multiple PLRM simulations of the same sized Treatment BMP located in different locations within the Tahoe Basin i e using different meteorological grids it was determined that climatic conditions play a role in the runoff capture and treatment capability of an infiltrating BMP The initial runoff coefficient values assigned by LRPT use an empirical relationship between the Treatment BMP storage capacity and meteorological and soil conditions as unique by each MET grid Figure 4 These relationships were
24. TSS dissolved inorganic nitrogen DN and total concern nitrogen TN A durable pervious surface overlaying a crushed stone base that stores rainwater and allows it to infiltrate into the underlying soil Porous pavement includes an underlying reservoir to Porous increase infiltration rates Local stormwater is typically not routed to a porous pavement pavement PP surface but rather constructed to minimize the volume of stormwater generated and routed down gradient from a previously impervious surface Footprint of porous pavement can vary but typically is used to replace parking lots or other impervious surfaces Post retrofit condition The parcel s of interest in their post improvement condition that includes retrofit actions such as source control improvements erosion control improvement Treatment BMP installation etc At least one post retrofit LRPT scenario is required in order to compare improved to unimproved site conditions and estimate the associated load reductions as a result of actions Pre retrofit condition The parcel s of interest in their pre improvement condition prior to implementation of site retrofit actions including source control improvements erosion control improvement Treatment BMP installation etc Pre retrofit LRPT scenarios are required in order to compare improved to unimproved site conditions and estimate the associated load reductions for each post retrofit scenario Receiving
25. U and gt 15 Residential MFR Land use type Residential MFR C If parcel area is 1596 Commercial CICU and lt 15 Residential MFR Land use type Residential SFR The same land use type should used for both pre and post retrofit scenarios unless there is a significant land use designation change and a strong justification for a shift in the land use type as a result of redevelopment can be made Land use condition The user must determine if the scenario land use condition is either baseline or Tier 1 see Section 4 5 The site is expected to be modeled as baseline conditions that include minimal spatial application of TRPA parcel based BMPs to reduce sources and generation of the pollutants of concern sediment and nutrient species Baseline conditions are typical of 2004 private land use conditions prior to BMP retrofits and source control actions In most instances pre retrofit scenarios will be at baseline conditions Tier 1 improvements assume complete private BMP implementation per the certification requirements of the TRPA BMP program with respect to pollutant source controls as outlined at http www tahoebmp org Default aspx The Tier 1 improvements include stabilization of all exposed soils using native vegetation retaining walls driveway and human path paving etc to reduce the chronic source of potential sediment and particulate pollutants generated from the site Other pollutant source control measures that are required t
26. aeeaeceaeceeeseesaeseaeseeeseeeeatenas 24 STEP 5 Populate LRPT Input Tables and Run Simulation nnne nnne 26 STEP 6 Repeat STEPS 2 5 for All Desired Scenarios eene nnne nennen nnne nnne nnne nnns 30 STEP 7 Compare Runoff and Pollutant Loads esses nennen netten innert trenes innen innen 30 STEP 8 Generate LRPT Summary Report eerta penatus n horno site hh 3s iiinn ERR Re Ra gn d eoe BER EN ERR RARE Rara daga uh 31 6 Programatic IritegratiO reiecta roe eee trei e Eae Pepe et nis sessi FL esa tabe be ee ssecdetteceacenabaceadtvasseatediebetaese 31 7 LRPT v2 Limitations and Next St ps iscissi anesini esu ra coecasscavevedevcudesceveudiacvavesccaviesdeveschanvevacs eR Sra Ex eoa ead 33 8 Acronyms and Glossary IRE ainainen aenn eea E aa E Eae dE E EAEEREN REE EAE Ea NNEGA 35 9 References c conet AERE aaan HR IER EE TER EE Aaaa aaa P EAE AE E Aaaa PEES a re Age ee RENE 38 Appendix A ERPT v2 Tutorial interiret e e E EE Ye ere e E re FER Ee aa Nea v Taa aN 39 LIST OF FIGURES Figure 1 Simple schematic showing hydrologic routing between two patches see 5 Figure 2 Hydrologic routing between three patches eesssssessesseeeeeeeennee nennen nennen nnne 7 Figure 3 Meteorological grids in Tahoe Basin ccsecesscceeececeeseceseceseeeceeaeeeaeeaeseaecseeeseceaeceaeseesaeeeaeseeesaeenatenas 8 Figure 4 Treatment BMP annual runoff coefficients eesssssssssssssese
27. ailed catchment scale validation of LRPT to improve our confidence in reasonable alignment of loading estimates with PLRM would be useful and require the application of LRPT on a large number of parcels within a specific urban catchment for comparison to PLRM outputs for the same catchment 8 ACRONYMS AND GLOSSARY LIST OF ACRONYMS BMP RAM C CRC Best Management Practice Maintenance Rapid Assessment Methodology Average annual runoff coefficient Characteristic Runoff Concentration Crediting Program Tahoe Basin Clarity Crediting Program EMC FSP LRPT LRWQCB NDEP PLRM TMDL GLOSSARY Event Mean Concentration Fine Sediment Particles lt 16um Load Reduction Planning Tool Lahontan Regional Water Quality Control Board Nevada Division of Environmental Protection Pollutant Load Reduction Model Total Maximum Daily Load Annual runoff coefficient C A value between zero and one that accounts for the fraction of precipitation and contributed runoff that is unable to infiltrate or evaporate from a given surface type on an average annual basis and therefore produces stormwater runoff Impervious surface types have high annual runoff coefficients whereas pervious surface types have relatively lower annual runoff coefficients Treatment BMPs in LRPT are assigned annual runoff coefficients calculated based on their storage capacity relative to the contributing impervious area to the Treatment BMP defined by hydrolog
28. avel with a void space of 2096 Open the spreadsheet file LRPTv2_trainingPost xlsm Complete the Patch Data Input Table and the Hydrologic Routing Input Table by filling in the highlighted cells the same way that you completed these tables for the pre retrofit scenario STEP 7 COMPARE RUNOFF AND POLLUTANT LOADS For each site a pre retrofit scenario and at least one post retrofit scenario are required A user can input multiple post retrofit scenarios in order to compare parcel improvements The user can compare various patch configurations and BMP types as different scenarios at a site to optimize design for the maximum water quality benefits Make sure that results are displayed for your pre retrofit and post retrofit scenarios in the LRPT spreadsheet Results Summary Table Move to the RESULTS COMPARISON Output Table in the LRPT spreadsheet To examine runoff and pollutant loading changes due to retrofit improvements select the user should select the pre retrofit scenario as the initial scenario and the post retrofit scenario as the final scenario With this configuration negative runoff and pollutant load change values indicate decreases from the initial to the final scenarios Use the pull down menus to select your initial and final scenarios for comparison and click the Compare Results button What is the post retrofit runoff Q ft yr What is the annual runoff volume change from the pre retrofit to the post retrof
29. being unable to provide well reasoned rationale for the importance of BMPs when faced with disgruntled residents who are unhappy with the requirement to invest in BMPs Training and use of LRPT will provide project review and private property BMP certification staff with the tangible understanding of the importance of well designed and maintained BMPs and will provide them with quantitative examples to reference With the ability to test different design options or levels of maintenance commitment LRPT will enable staff to experiment with more flexible BMP design alternatives which can allow them to accommodate the desires of residents related to particular areas on their property POLICY ALTERNATIVE amp CLIMATE CHANGE ANALYSIS LRPT provides a consistent platform to analyze how basin or municipality wide policies may play out at a site scale Planners and regulators are shifting the approach to address water quality issues through a focus on average annual load rather than strictly focusing on runoff frequency and concentrations This approach holds the potential to provide more flexibility for development and redevelopment activities that can result in economic benefits to the Tahoe Basin LRPT provides a conceptually simple means to analyze how different policies would result in requirements for typical retrofit projects Using this information planners and regulators can test their assumptions of the results of new policies at a site to i
30. ce LRPT can t calculate a contribution from a patch without first calculating the contribution to that patch from others Patch Data B Define patch charactistics beginning with patches at the top of the site e g receive only rainfall and no runoff from other patches PatchID IM1 IM2 IM3 Surface type Impervious IM Impervious IM Impervious IM Area An ft2 12 5 375 900 Storage of Treatment BMP S in Porous pavement reservoir depth Z in Porous pavement void space V Initial annual runoff coefficient C 0 820 0 820 0 820 BMP maintenance commitment adjusted coefficient C Calculate C values Save Patches The user selects the surface type from the pull down menu and enters the surface area of each patch in units of square feet by referring to the site diagram For porous pavement surfaces the user specifies depth and voids pace For biofilters and infiltration features the user specifies the storage as the quotient of the design volume and the source impervious area Infiltration Feature and Biofilter Storage inches rainfall Design Volume of Infiltration Facility ft Source Impervious Area ft 12 inches feet Troubleshooting If information is changed after patches have been The level of Treatment BMP maintenance effort accounts for decline of i saved the user should delete the their performance over the 18 year simulation period See table 3 for
31. cenario and the other for the post retrofit scenario Open the file named LRPTv2 trainingPre For LRPT to run users must ensure that macros are enabled in Excel 1 Open Excel 2007 and click the Office button in the upper left corner of the screen At the bottom of this menu click the Excel Options button Click the Trust Center button on the left Then at the bottom right select Trust Center Settings In the new window that appears choose Macro Settings from the sidebar and select Disable all macros with notification from the list of options that appear This option keeps macros disabled but notifies users when macros attempt to run allowing users to decide on a case by case basis which macros to enable Click OK to exit this window 4 Forthe new settings to take effect it will be necessary to close Excel and reopen it A security dialog box should appear beneath the Office ribbon the next time you attempt to run a spreadsheet that contains macros 5 When the notification appears click the Options button Choose Enable this content from the options that appear to allow macros to run within the current spreadsheet Click OK to close the window STEP 1 SPECIFY PARCEL BOUNDARIES The entire site boundaries where BMP retrofit improvements are planned should be determined using GIS AutoCAD or other mapping program site visits site surveys and or engineering plans The user needs to obtain the site address create a site ID determi
32. coefficient for the range of Treatment BMP storage values located within MET grid 847 Figure 5b Based on the results presented in Figure 5b the development team created 3 maintenance maximum runoff coefficient 1 0 extensive maintenance action Cow moderate range of C iign C for HIGH maintenance initial runoff coefficient i e benchmark effort Average annual runoff coefficient Time since BMP construction years HIGH maintenance effort MODERATE maintenance effort LOW maintenance effort _ BMP C value over time J BMPC value over time BMP C value over time Bee Average annual C value A Average annual C value Average annual C value Figure 5a Expected evolution of runoff coefficient as a BMP ages solid lines The runoff coefficient C can be reset by performing extensive maintenance actions on the BMP to return its performance back to benchmark conditions and more intensive maintenance results in a lower range of C values over time The LRPT categories of maintenance high moderate and low are used to represent the expected relative average annual runoff coefficient with the knowledge that the actual runoff coefficient varies but the pattern is predictable over time 1 00 0 90 initial infiltration rate 0 5 in hr 2596 reduction of infiltration rate 0 38in hr g 0 80 Z 50 reduction of infiltration rate 0 25 in hr E 0 70 7596 reduction
33. ction kg yr Baseline Average Annual Pollutant Load kg yr Improved Average Annual Pollutant Load kg yr Eq 2 4 THEORY AND METHODOLOGY The LRPT calculates average annual pollutant loads for 6 pollutants of concern by iteratively accounting the hydrologic routing of runoff across one or more parcels based on average annual precipitation site characteristics and site mapping details input by the user Annual runoff coefficients are assigned to estimate the fraction of runoff retained on patches of different permeability and treatment capacity on an average annual basis LRPT assigns the initial runoff coefficient for each Treatment BMP as a function of storage capacity and the hydrologic routing characteristics of the site for the benchmark condition The annual runoff coefficient for each Treatment BMP is determined based on the relative maintenance commitment as defined by the user for the site The annual runoff volumes for an 18 year time interval are integrated with the appropriate CRCs to estimate average annual pollutant loads for pre and post retrofit scenarios The difference in pollutant loads generated from the site between pre and a post retrofit scenario is the estimated load reduction resulting from implementation of BMPs on the site 4 1 HYDROLOGIC ROUTING The LRPT user delineates the parcel into discrete patches each with a unique runoff coefficient Table 1 The annual runoff coefficient defines the fraction of water intro
34. d on the patch delineation and hydrologic routing input by the user The methodology can be applied to parcels with various patch distributions and hydrologic routing patterns Runoff is calculated by iteratively quantifying the runoff from each source patch to each receiving patch working from up gradient to down gradient along the flow path Figure 2 displays three individual patches a house with a pitched roof A5 surrounded on two sides by a roof drip line Az which is embedded in a lawn A Hydrologic routing at this site begins on the roof where 50 of the runoff from A enters A and the remaining 5096 discharges to A All of the runoff 100 from A flows to A The total runoff generated from the parcel as outlined in Figure 2 is equal to Q4 Figure 2 Hydrologic routing between three patches 4 2 PRECIPITATION P The average annual precipitation P in yr at the redevelopment site is determined from long term datasets or pre compiled regional averages The LRPT uses the average annual precipitation for the PLRM metrological grid stations MET grid for 7 representative zones throughout Lake Tahoe generated from the SNOTEL long term meteorological stations Figure 3 The user selects the PLRM MET grid station that best represents the subject site The same annual precipitation value must be used for all LRPT simulations run for a specific site 4 3 ANNUAL RUNOFF COEFFICIENTS C The LRPT user delineates the parcel into discr
35. duced to each patch that is unable to infiltrate or evaporate expressed as a value between 0 1 see Table 1 Table 1 provides initial runoff coefficients that may adjusted for specific patches within LRPT based on sizing or site maintenance commitment to better represent average annual runoff coefficients Stormwater runoff from a patch is controlled by three distinct components the rate at which water accumulates on the patch from direct rainfall and contributing patches the area of the patch and the annual runoff coefficient of the patch All patches accumulate water from direct precipitation Receiving patches also accumulate water that runs off adjacent patches as defined through hydrologic routing in the LRPT Note LRPT assumes no runoff is generated from adjacent parcels i e offsite upgradient and routed to the site Water i e mass is conserved as runoff is routed through the parcel and across patches By defining the hydrologic routing of a parcel Treatment BMPs can be strategically placed to retain runoff generated from patches with relatively high annual runoff coefficients see Table 1 The annual runoff generated from patch n Q e g ft year is calculated as Q C P q A Eq 3a gt fo q o Eq 3b n Where C is the annual runoff coefficient for patch n unitless P is the precipitation rate e g ft year qn is incoming runoff from contributing source patches e g ft year A is the area
36. e Description Examples Initial Runoff Coefficient C Impervious IM Surface with very little infiltration capacity Impervious surfaces include concrete or asphalt such as paved driveway walkway parking area courtyard sidewalk etc Walkway sidewalk courtyard driveway etc made of brick cobblestone or other hard surface Typical roof or deck surface Severely compacted pervious SP A pervious surface with very poor infiltration ability Examples include unpaved parking area driveway road shoulder etc Areas with high automobile and or human disturbance Compacted pervious CP Drainage is moderate to poor high human disturbance and poor infiltration ability Poorly maintained pervious areas with high human or animal foot traffic and associated soil compaction e g foot paths surrounding buildings Intensely used areas of ballfield such as a baseball diamond infield or other compacted park or playground surfaces Maintained pervious MP Landscaped and or other maintained vegetated areas that have moderate to low human foot disturbance or traffic Maintained lawn surface where human foot traffic may be high but surface is well maintained e g golf course park lawn ballfield Maintained pervious topography is at grade with surrounding areas and not constructed to provide storage of runoff routed from surrounding surfaces Undeveloped UN Treatment BMP Type Infiltration feature
37. e assignment of percentage of flow across adjacent patch boundaries Panel C Patch 1 shares flow boundaries with i e is a source patch to both Patch 2 and Patch 3 Based on the length of the shared boundaries it is estimated 7096 of the runoff from Patch 1 is discharged to Patch 2 and the remaining 3096 is discharged to Patch 3 Patch 2 discharges 10096 to Patch 3 which in turn discharges 10096 offsite Panel D Patch 1 discharges 10096 to Patch 2 which discharges 10096 to Patch 3 Patch 3 discharges 10096 offsite Panel E Patch 1 shares flow boundaries with Patch 2 and the offsite region Based on the relative length of the shared boundaries the user estimates 7096 of the runoff is routed to Patch 2 and the remaining 3096 is routed offsite Patch 2 discharges 100 to Patch 3 which in turn discharges 100 offsite to the east The final product of STEPs 3 and 4 is a plan view map of the site scenario with a series of spatially distinct patches flow direction between patches and ultimately to offsite areas and percent contribution of flow from each source patch to each receiving patch The user will need to extract specific information from the site delineation map including patch surface type patch area ft the source to receiving patch flow links and relative flow percentages for input into the LRPT spreadsheet tool For Treatment BMPs additional sizing information is required Refer to Appendix A for a simple site example for both pre
38. e maximum water quality benefits Make sure that results are displayed for your pre retrofit and post retrofit scenarios in the LRPT spreadsheet RESULTS SUMMARY Output Table Use the pull down menus in the RESULTS COMPARISON Output Table to select the pre retrofit and post retrofit scenarios and click the Compare Results button to display the runoff and pollutant load reductions Negative runoff and annual pollutant load change values indicate reductions from the Initial Scenario to the Final Scenario Use a pre retrofit scenario as the initial and a post retrofit scenario as the final to examine runoff and pollutant loading changes due to retrofit design changes Results Comparison gt Annual Pollutant Load Change kg yr em Compare Runoff Change Initial Scenario Final Scenario 3 FSP TSS Results f yr BSO1 BSO3 2510 0 1 1940 1 4126 STEP 8 GENERATE LRPT SUMMARY REPORT The LRPT summary report detailing the water quality benefits resulting from redevelopment should include the Results Summary Table and Compare Results Table populated with the scenarios of interest The Compare Results Table should be accompanied by the site diagrams for each redevelopment scenario as produced by the user during STEPS 2 4 that include site delineation and flow routing as shown in the training exercise in Appendix A 6 PROGRAMATIC INTEGRATION DESIGN ALTERNATIVES COST BENEFIT ANALYSES amp PROJECT REVIEW Using LRPT site retrofit desi
39. e most sensitive factors driving the rate of increase of runoff coefficients In addition it is known that the appropriate maintenance actions and frequency for each Treatment BMP on a site will vary based on the factors contributing to performance decline inherent to a specific BMP While acknowledging the limitations stated above incorporation of Treatment BMP maintenance into the LRPT estimation is a priority to highlight the importance of these actions to sustain water quality improvements over time Therefore the LRPTv2 utilizes a simplified site based approach and applies a number of reasonable assumptions to estimate average annual runoff coefficients over a long time period based on the relative maintenance commitment specified by the user represented by the dotted lines in Figure 5a It is suspected that future research will improve our ability to quantify performance decay and recommend reasonable maintenance schedules for Treatment BMPs LRPT MODELING OF TREATMENT BMP MAINTENANCE In order to estimate the influence maintenance actions and associated frequency has on Treatment BMPs in LRPT the PLRM simulations of hypothetical Treatment BMPs of varying storage were used to translate a decline in the average annual infiltration rate into an increasing annual runoff coefficient Sequential reductions in the benchmark infiltration rate of 0 5 in hr were modeled using PLRM and SWMM to determine the corresponding increase in the annual runoff
40. e off or alternatives analysis PRIVATE PROPERTY BMP RETROFIT DESIGN amp APPROVAL Private property BMP site design recommendations and certification can be improved through the standard use of LRPT By equipping field staff with LRPT templates of typical site layouts they can quickly modify the standard templates to reflect actual site conditions This will increase the consistency of recommendations and provide a stronger basis for treatment BMP placement and design at a specific site than is possible from the multiple interpretations provided by different staff of how to apply recommendations in the TRPA BMP Handbook A frequent complaint of the private property BMP requirement is that property owners feel their property does not contribute to pollutant loading By providing loading information over multiple years LRPT will educate property owners of their overall contribution to lake clarity loss It will also link local residents to the achievement of basin wide load reduction goals called for in the TMDL and necessary to restore lake clarity STAFF TRAINING It is a challenge to train new staff to understand how specific BMPs and design alternatives relate to large scale threshold and TMDL goals This lack of understanding can result in inconsistent review comments and a lack of ability to articulate the importance of installing and maintaining BMPs This lack of detailed understanding and quantitative evidence can result in BMP program staff
41. e should they begin the iterative task of delineating patches and hydrologic routing linkages Rules for delineating patches 1 Pervious or impervious surface types that have permeability adjacent to one another can be lumped to simplify site delineation and hydrologic routing see Table 1 of the User Guidance for similar surface types 2 Each patch is a Source Patch every patch receives precipitation and is a source for runoff Runoff is routed to either an adjacent Receiving Patch or Offsite 3 Each patch has slope elevation or other characteristic that will determine routing of runoff generated from it to another patch or offsite 4 Begin patch flow assignments by starting at the highest elevation within the redevelopment site and work down gradient This means that the first patches defined will be those that do not receive runoff contributions from other patches i e are source patches only 5 Flow cannot be circular between patches Runoff is always one way and down gradient If runoff from Patch 1 flows to Patch 2 runoff cannot flow from Patch 2 or any patches connected hydrologically to Patch 2 back to Patch 1 6 Ifthe site appears to be completely flat identify offsite as the adjacent public right away e g city road or road surface and assume that direction is down gradient 7 The goal is to create the minimum number patches required to represent the overall hydrology of the site Do not subdivide patches unless
42. e site address create a site ID determine total site area in t and utilize Figure 3 to select the most representative MET grid for the site The MET grid is used by LRPT to determine average annual precipitation in yr and the annual precipitation is held constant for all LRPT scenarios conducted for the subject site STEP 2 DEFINE SCENARIO AND SITE CONDITION The LRPT estimates the average annual pollutant load reductions for pre and post retrofit scenario pairs based on differences in hydrologic routing general land use condition and the implementation and continued maintenance of Treatment BMPs on the site STEP 2 requires the user to define the scenarios that will be modeled in LRPT identify the parcel land use type determine the land use condition for each scenario as well as determine the future maintenance commitment level that will be implemented to ensure long term Treatment BMP performance as designed STEPs 2 5 must be completed for each scenario to be modeled in LRPT If improvements are planned and LRPT is being used to quantify the water quality benefits of one or more potential design alternatives the user should first complete LRPT for the existing unimproved site conditions and field verification of site delineation STEP 3 and hydrologic routing STEP 4 should be completed Post retrofit scenarios are then future design concepts for improved conditions to be implemented on the site in question If improvement have already been
43. e that both land use type and condition should be used to constrain the potential downslope water quality risk nhc et al 2009 2NDNATURE 2010 Current and future research will continue to improve the CRC dataset from residential commercial and other land use types over the typical range of conditions Future updates to the CRC values should be conducted in the LRPT calculations as new data becomes available The development of LRPTv2 required the transfer of a pollutant load reduction estimation methodology into a user friendly tool and user guidance to expand the audience and potential application of LRPT However there remain a number of technical concepts and critical decision points that must be evaluated and solved by the user to accurately represent the parcel loading particularly during the patch delineation and hydrologic routing determination of the site Use of LRPT by a new user will take time and effort and users should continue to critically evaluate both input and outputs from the tool to minimize user errors and misrepresentations of site conditions and perceived water quality benefits 6 Preliminary validation of LRPT was completed by simple area weighted comparisons of average annual runoff and pollutant loading estimates with PLRM outputs that are completed on larger catchment scale Given the use of PLRM to inform a number of the algorithms in LRPT close agreement of runoff and loading estimates is likely However a det
44. ediment were published as TSS lt 63um To remain consistent with other pollutant load reduction methodologies being developed for the Lake Tahoe Basin and with the primary pollutant of concern in Lake Tahoe urban stormwater the TSS lt 63um was converted to a likely event mean concentration of fine sediment particles by mass mg L 16 um Preliminary urban stormwater particle size distribution data provided by DRI to 2NDNATURE and particle converter xls file provided by UC Davis to 2NDNATURE indicate that on average 30 1 of the mass of particles lt 63um are within the range of 22um 63um The fine sediment lt 16um EMC for each land use presented in Table 2 were calculated by TMDL FSP TSS x TSS mg L x 0 699 FSP 16um mg L Condition is a simple way to quantitatively express the relative water quality impact of a set of general practices and the expected pollutant generation from urban lands In LRPT condition is expressed as an estimate of the average annual CRC for each respective pollutant generated from a specific land use type that is expected to be maintained at a certain relative condition There are two potential conditions for each land use baseline and Tier 1 Baseline conditions are typical Lake Tahoe 2004 private land use conditions where parking and paths on pervious surfaces result in soil compaction and erosion roof drip lines are bare soil fertilizer use is excessive and other conditions of a parcel prior t
45. ent on hand when beginning the exercise LRPT STEP Description STEP 1 Specify parcel boundaries STEP 2 Define scenario and site conditions STEP 3 Delineate patch boundaries and hydrologic linkages STEP 4 Assign hydrologic routing contributions STEP 5 Populate LRPT spreadsheet and run simulation STEP 6 Repeat steps 2 5 for all desired scenarios STEP 7 Compare runoff and pollutant loads STEP 8 Generate LRPT summary report PROTOCOLS What you need e 1computer with LRPT tutorial files The tutorial files along with a blank version of LRPTv2 called LRPTv2 are posted on the LRPT file sharing site http 2ndnature centraldesktop com 2nfilesharing doc 10276628 w LrptV2 along with the final LRPTv2 MS Excel File and the Technical and Guidance Document If this link is not active contact the TRPA Erosion Control Team to obtain documentation tool and tutorial e Microsoft Excel 2007 version e Hard copy of LRPTv2 Technical and User Guidance Document Final November 2010 e TAC training packet e Pen Pencil e Calculator EXERCISE INSTRUCTIONS You will use the diagrams provided to answer the questions and populate the LRPT spreadsheet The LRPT spreadsheet consists of 4 Input Tables and 2 output tables that will be populated as you progress through the 7 steps for the exercise You have two LRPT MS Excel files with the Input Tables partially populated You will use one file for the pre retrofit s
46. esseeeccssseeeesssseeesseeeestseeeess 15 Maintenance commitment level adjustment factors Y applied initial C values ees 15 CRCs for baseline condition and Tier 1 improvements for urban land use types 16 Steps implemented by user to complete LRPT sesseesseseeeeeee eene enne nennen nennen nnns 17 EXECUTIVE SUMMARY The Load Reduction Planning Tool LRPT estimates the potential water quality pollutant load reductions associated with the proposed parcel scale implementation of Best Management Practices BMPs including redevelopment projects private parcel retrofits and single family BMP implementation in the Tahoe Basin We present a new version of the tool LRPTv2 as a visual basic application for Microsoft Excel 2007 version that uses site specific data created by the user to reflect the spatial heterogeneity of surfaces in combination with a simple mathematical model that routes runoff across a parcel to estimate the average annual runoff from the site LRPTv2 includes a function to estimate performance decay of Treatment BMPs over time as a function of maintenance commitment The LRPT has been designed to be consistent and compatible with the Pollutant Load Reduction Model PLRM the Best Management Practices Maintenance Rapid Assessment Methodology BMP RAM and other Tahoe Basin stormwater tools to the extent practical This document provides a description of the techn
47. ete patch types that are used to represent the differing runoff characteristics that may be present on the parcel Table 1 presents the common surface types on commercial and residential parcels in the Lake Tahoe Basin The LRPT includes a number of functions to adjust the initial runoff coefficients Cj for pervious and Treatment BMP patch types to provide realistic estimates of average annual runoff coefficients and volume reduction capabilities over an 18 year time period Legend E PLRM Meteorological Grid SnoTel Weather Stations Bl Urban Areas z Lake Tahoe d San Francisco n NEVADA CALIFORNIA 2NDNATURE LLC LRPT user selects the PLRM meterological grid that best represents the climatic conditions of the redevelopment site of M interest su A8 aa3N9SISs3G TEL 831 426 9119 rav 8314267092 wuuw endnaturellc com LAKE TAHOE PLRM METEOROLOGICAL GRID FIG U R E 3 RUNOFF COEFFICIENTS Published runoff coefficients Caltrans 2003 Dunne and Leopold 1978 Davis and McCuen 2005 are displayed as ranges indicating their subjectivity to rainfall intensity antecedent conditions and surface area The initial runoff coefficients for typical impervious and pervious surface types were adapted from ranges in the published litera
48. f a patch receives runoff from anther patch the patch that it receives runoff from e g its source patch is listed earlier on the left side in the table This is an important rule to follow since LRPT can t calculate a contribution from a patch without first calculating the contribution to that patch from others Patch Data B Define patch charactistics beginning with patches at the top of the site e g receive only rainfall and no runoff from other patches PatchID IM1 IM2 IM3 Surface type Impervious IM Impervious IM Impervious IM Area An ft2 1275 3 5 900 Storage of Treatment BMP S in z z Porous pavement reservoir depth Z in 7 E Porous pavement void space V 2 E Initial annual runoff coefficient C 0 820 0 820 0 820 BMP maintenance commitment adjusted coefficient C Calculate C values Save Patches The user inputs each unique Patch ID selects the surface type from the pull down menu and enters the surface area of each patch in square feet from the scenario site diagram completed in STEPs 3 and 4 Troubleshooting If data in PATCH DATA Input Table is changed after Save Patches For Treatment BMPs patch types biofilters BF or infiltration button has been pressed the user should features IF the user must enter the storage Sn of each delete the worksheet that was created when the patches were incorrectly saved Treatment BMP by dividing the design volume of the infi
49. generated from multiple PLRM simulations for Treatment BMPs sized for a range of storage capacities 0 01 2 inches of runoff for 7 representative metrological grids within the Lake Tahoe urban areas The average annual amount of runoff generated from a Treatment BMP in LRPT is a function of storage inches MET grid of the site and the user s commitment to maintenance Infiltration Features and Biofilters The capacity sizing or storage for infiltration features IF and biofilters BF that are designed with detention storage is determined by Eq 5 by the user www trpabmp org Infiltration Feature and Biofilter Storage inches rainfall Design Volume of Infiltration Facility ft Source Impervious Area ft 12 inches feet Eq 5 Infiltration features are typically sized using Eq 5 with the recommended design standard in Lake Tahoe to retain 1 inch of rainfall generated from the source impervious area Similarly annual runoff coefficients for biofilters constructed to provide depressional storage and infiltrate volumes are determined based on the storage of each biofilter Eq 5 Onsite biofilters that are not constructed to provide surface water storage to detain stormwater are assigned an initial C value of 0 15 the same as maintained pervious patch types see Table 1 The LRPT assumes that the treatment capacity of each Treatment BMP included has been adequately designed to meet or exceed the storage inches of rainfall
50. gineers September 2009 http ndep nv gov bwaqp file bmp ram techO09 pdf 2NDNATURE 2010 Focused Stormwater Monitoring to Validate Water Quality Source Control and Treatment Assumptions Final Report Prepared for U S Army Corps of Engineers March 2010 ftp 2ndnaturellc com 2ndnature 2NDNATURE Reports Lake9620Tahoe PLRM 9620Refinement FinalPhasel Tech nicalReport pdf Caltrans 2003 Storm Water Quality Handbooks Storm Water Pollution Prevention Plan SWPPP and Water Pollution Control Program WPCP Preparation Manual March 2003 http www dot ca gov hg construc stormwater SWPPP Prep Manual 3 03 pdf Cobourn J Capp C A Cecchi S Ferry B Harrison E Jespersen J Hogan M Larson E Pulsifer M Widegren B and Daryl Witmore D no date How to install best management practices BMPs in the Lake Tahoe Basin Manual for Building and Landscape Professionals http www unce unr edu publications files nr 2004 EB0403 pdf Davis A P and R H McCuen 2005 Stormwater Management for Smart Growth New York Springer Books Dunne T and L B Leopold 1978 Water in Environmental Planning New York W H Freeman and Company Lahontan Regional Water Quality Control Board LRWQCB and Nevada Department of Environmental Protection NDEP Lake Tahoe TMDL Pollutant Load Reductions Opportunity Report March 2008 v 2 0 http www waterboards ca gov rwqcb6 water issues programs tmdl lake tahoe docs presentations pro repo
51. gment and experience of the user The user must use the best available information and data when dividing the redevelopment area into patches assigning patch types and determining flow routing percentages STEPs 3 and 4 The delineation of site patches may be subjective in some instances but the user should determine the number of patches and flow routing linkages based on the rules provided in the user guidance such that the overall hydrology of the site is reasonably represented Because the rules allow for subjective determination of patch boundaries and flow routing there will be variability in runoff and load calculations made by different users However the difference between LRPT estimates by two independent users on the same site is expected to be 1096 if the rules are rigorously followed The incorporation of maintenance commitment for the site into LRPT addresses the critical need for regular maintenance of BMPs to maintain performance within an acceptable range and is considered a valuable first step to incorporate the role of maintenance in a water quality benefit estimation tool However LRPTv2 uses an overly simplistic quantitative approach to estimating the decline in the infiltration capacity of specific Treatment BMPs over time The LRPTv2 approach ignores the inherent variability in the performance decay rates for different BMP types at different locations on the same site Different BMPs on a site are likely to respond differently t
52. gners can quickly develop several different layout and treatment design alternatives that will improve their ability to communicate trade offs with municipal and regional project reviewers Currently different municipal engineering staff and design consultants use different modeling approaches assumptions and file formats to evaluate stormwater treatment designs and runoff quantities This lack of standardization increases the cost of developing analyses and decreases the ability for reviewers to compare analyses from different parcels Further current methods to provide analyses of potential site retrofit alternatives generally only calculate volume for design storms which does not provide the more important water quality context of understanding of pollutant loading impacts over long term periods The standardization resulting from the consistent use of LRPT to evaluate stormwater pollutant loading for different parcel scale design alternatives will increase the consistency of analyses and improve the ability for reviewers to understand the analyses in the context of the Lake Tahoe TMDL and load based stormwater permits and Memoranda of Agreement LRPT will provide quantitative consistent and clear results that provide simple comparisons of how preferred design options address onsite runoff and loading issues This will provide robust information to substantiate redevelopment projects that significantly reduce runoff and pollutant loading from current
53. hat macros are enabled in Excel 1 Open Excel 2007 and click the Office button in the upper left corner of the screen At the bottom of this menu click the Excel Options button 2 Click the Trust Center button on the left Then at the bottom right select Trust Center Settings 3 Inthe new window that appears choose Macro Settings from the sidebar and select Disable all macros with notification from the list of options that appear This option keeps macros disabled but notifies users when macros attempt to run allowing users to decide on a case by case basis which macros to enable Click OK to exit this window 4 Forthe new settings to take effect it will be necessary to close Excel and reopen it A security dialog box should appear beneath the Office ribbon the next time you attempt to run a spreadsheet that contains macros 5 When the notification appears click the Options button Choose Enable this content from the options that appear to allow macros to run within the current spreadsheet Click OK to close the window 6 Save as a macro enabled MS Excel file xlsm and give the file a unique name reflecting the site evaluated The LRPT spreadsheet consists of four Input Tables and two Output Tables All user input for the LRPT is done on the worksheet labeled controlForm and new worksheets are dynamically created as the user saves data from the Input Tables Cells are annotated within the worksheet to help guide the user through t
54. he data input process POPULATE SITE INPUT TABLE The spreadsheet is designed to be used for a number of scenarios for a single site so a new workbook should be used for each new site evaluated Enter a unique Site ID for your site and select the appropriate MET grid from the drop down menu The average annual precipitation in inches per year is automatically populated in the field below the MET grid field Below this enter the total site area in square feet ecosystem science design LR PT Load Reduction Planning Tool E NONATURE Site Site ID 4BS004 Site Address 4000 Baker St MET grid Kings Beach 532 Average annual precipitation in yr 29 91 Total site area ft 15 000 POPULATE SCENARIO INPUT TABLE At the SCENARIO Input Table enter the information for a single scenario beginning with a unique Scenario ID and Scenario Type The Scenario Type field is selected from a pull down menu and specifies whether the scenario is pre retrofit or post retrofit The user then selects the appropriate land use type and land use condition for the specific scenario See STEP 2 for guidance If the scenario is post retrofit suggesting the installation of Treatment BMPs the user must designate the BMP Maintenance Effort commitment high moderate or low for all of the Treatment BMPs at the site See STEP 2 for guidance on selection The default BMP Maintenance Effort is LOW If the scenario is pre retrofi
55. hmark condition is a term defined in the BMP RAM 2NDNATURE et al 2009 and used to define a Treatment BMP immediately after installation or adequate maintenance Benchmark condition indicates that the specific processes relied upon for water quality improvement for a Treatment BMP are functioning at their best achievable condition Biofilter BF A pervious substrate with dense native and or maintained vegetation coverage gt 80 Biofilter designs such as rain gardens can augment depression storage to capture detain evapo transpire and infiltrate urban runoff Nutrient concentration reductions occur by fixing nutrients via biological processes The footprint of these surface types are larger than typical infiltration BMPs Biofilters constructed with depressional storage must include a relatively shallow slope Characteristic Lake Tahoe stormwater pollutant loading models PLRM and LRPT express the condition of an urban land use quantitatively as a characteristic runoff concentration CRC for pollutants of concern for lake clarity A CRC is a representative average annual concentration for a pollutant runoff of concern in stormwater runoff from a specific urban land use and its associated condition In concentration the LRPT the parcel CRC is combined with the average annual runoff generated from the site CRC to provide an estimate of average annual pollutant load for each pollutant of concern The land use types included i
56. ial private parcels includes placement and maintenance of highly permeable surface types infiltration features biofilters porous pavement etc to capture and infiltrate runoff volumes generated from impervious surfaces within the parcel Onsite infiltration of runoff reduces water volumes and pollutant loads to the local stormwater infrastructure The TRPA requires all developed properties to install BMPs that help improve water quality by reducing volumes generated from the site reduce soil erosion and capturing polluted water before it enters Lake Tahoe The LRPT requires the user to spatially delineate the parcel s of interest based on surface characteristics and define the associated hydrologic routing on the parcel in a format that can be directly entered into the LRPT spreadsheet tool LRPT estimates the average annual runoff generated from the site using a simple disaggregation of the surface and stepwise routing across the parcel that includes performance decay of Treatment BMPs over time as a function of the maintenance commitment specified by the user Average annual runoff estimates are combined with characteristic runoff concentrations CRCs for predominant land use types and expected condition to estimate the pollutant loads generated from the site for pre and post redevelopment conditions The pollutants of concern include in order of priority fine sediment particles FSP 16 um dissolved phosphorous DP total phosphorous TP
57. ic routing where they are located in the Basin and the maintenance commitment of all BMPs at the site as defined by the user Initial runoff coefficient as presented in Table 1 is calculated for all patches The initial runoff coefficient will be used for LRPT calculations unless 1 it is a pervious patch that is relatively small compared to area and amount of water routed to it In these instances the pervious patch initial C value is adjusted to eliminate large volumes of water being infiltrated by relatively small patches Table 2 or 2 it is a Treatment BMP The initial runoff coefficients determined based on storage and MET grid for all Treatment BMPs at a site are adjusted based on the relative maintenance commitment as defined by the user to better represent the average annual runoff coefficient expected over an 18 year time period Baseline land use condition There are two potential conditions for each land use baseline and Tier 1 The LRPT user determines the land use type and associated condition that results in the assignment of appropriate average annual CRCs for the pollutants of concern Baseline conditions are typical Lake Tahoe 2004 private land use conditions where parking and paths on pervious surfaces result in soil compaction and erosion roof drip lines are bare soil fertilizer use is excessive and other conditions of a parcel prior to BMP retrofits and source control actions Benchmark condition Benc
58. ical approach and methodology for LRPT calculations Section 4 detailed user guidance Section 5 and recommendations for future programmatic integration Section 6 An LRPT user follows a series of 8 STEPS to estimate the water quality benefits of parcel scale retrofit and improvement actions in the Tahoe Basin Table ES1 The LRPT requires the user to spatially delineate the parcel s of interest based on runoff characteristics and define the associated hydrologic routing on the parcel for each site scenario of interest The user populates the user friendly LRPT spreadsheet with information created during STEPs 1 4 to generate runoff volume and load reduction estimates for 6 pollutants of concern expected to be generated and transported offsite for each pre retrofit post retrofit scenario pair LRPT outputs can inform site retrofit design alternatives and Treatment BMP maintenance commitment levels to maximize the expected water quality benefits of parcel scale improvements LRPT STEP Description STEP 1 Specify parcel boundaries STEP 2 Define scenario and site conditions STEP 3 Delineate patch boundaries and hydrologic linkages STEP 4 Assign hydrologic routing contributions STEP 5 Populate LRPT spreadsheet and run simulation STEP 6 Repeat steps 2 5 for all desired scenarios STEP 7 Compare runoff and pollutant loads STEP 8 Generate LRPT summary report Table ES1 Steps implemented by user to complete LR
59. ical means for project proponents to address the concerns of municipal engineers and regional regulators related to the need to reduce pollutant loading and meet Lake Tahoe TMDL implementation milestones By reducing loading coming from specific parcels within a catchment the overall loading at the bottom of a catchment should be reduced However LRPT does not account for additional pollutant controls in place in a catchment downstream of the analyzed parcel thus the LRPT results cannot be directly used to determine load reductions on a catchment scale The consistency of the assumptions between LRPT and PLRM provides directly applicable information that can be used generally understand relative magnitude of runoff volume and pollutant load reductions expected from one or more parcels relative to the volumes and loads exiting the bottom of the respective catchment 7 LRPT V2 LIMITATIONS AND NEXT STEPS The LRPTv2 has been developed to meet the goals objectives and functions of the tool defined by the scope at the onset of this effort Tool development was conducted with limited resources and this initial version of the tool is ready for user testing and feedback Fall 2010 All of the components of the LRPTv2 have been implemented tested and refined given available resources and tool functional and improvement priorities A single residential parcel in South Lake Tahoe and is the example parcel in the How to install best management practices BMPs in
60. ies of spatially distinct patches and the flow direction between patches and ultimately to offsite areas The completion of STEP 3 will be an iterative process by the user The STEP 3 mapping should be initiated in the office using GIS Google Earth AutoCAD or other mapping program with preliminary patch delineation conducted to the extent possible Engineering plans may also be useful in determining the location and sizing of Treatment BMPs for relevant scenarios The draft map should definitely be field verified at the site to confirm the existing conditions parcel delineation patch sizes and identify flow directions from patch to patch One or more surface types can be lumped into distinct patches based on similar expected annual runoff coefficients i e permeability see Table 1 The user should focus the detail of parcel delineation on the location sizing and hydrologic routing of constructed Treatment BMPs as these are the features installed and maintained at the site to provide a water quality benefit downslope Impervious and many pervious surface types can be lumped into a single patch if 1 The surface types are identified to possess the same relative permeability see Table 1 2 They are adjacent or in very close proximity and 3 Consolidation of surface types simplifies site geometry while preserving the general hydrologic routing processes of the subject parcel Impervious surface types such as pavement roofs and brick s
61. implemented at a site and LRPT is being used to retroactively quantify the water quality benefit of the post retrofit actions the user should first complete the post retrofit scenario mapping and site delineation and then use best available site information to represent the pre retrofit site conditions that no longer exist Regardless of the order of scenario completion pollutant load reduction calculations require at least one pre and post retrofit pair to be entered into LRPT However the user can input multiple post retrofit scenarios in order to compare alternatives based on the estimated water quality benefits Land use type The user is required to identify the land use type of the parcel in question using the TMDL land use type categories LRWQCB and NDEP 2010 The user must consider the area of each land use type and its relative contribution to the overall parcel s In many instances parcels analyzed using LRPT may consist of mixed land use types Since condition of a private urban land use is assumed to be influenced by the relative density and frequency of human traffic if greater than 1596 of the parcel area is used for the higher traffic land use either commercial or multi family residential the parcel is designated as the higher impact land use type The rules for land use type determination are below A If parcel area is gt 1596 Commercial CICU then Land use type Commercial CICU B If parcel area is 1596 Commercial CIC
62. ineated and routing contributions determined Review this figure and notice areas where patches are lumped and or defined and the specified flow routing directions contributions to adjacent patches Compare Figure 10 to Figure 11 and note the differences Which patches does patch CP2 contribute runoff to Which patch does runoff from most other patches flow to before exiting the site STEP 5 POPULATE THE LRPT INPUT TABLES AND RUN SIMULATION At this point you should have already populated the Site and Scenario LRPT Input Tables and saved the scenario You are now ready to populate the remaining input tables in the LRPT spreadsheet At the PATCH DATA Input Table the user specifies characteristics of patches that are used to calculate the annual runoff coefficient for each patch Each patch should have a unique ID that follows the naming conventions shown in Table 1 in the User Guidance e g IM1 for the first impervious patch The user should enter patches beginning from those at the uppermost elevation that only receive rainfall and no runoff inputs from other patches such as roofs The user fills in Input Table 3 from left to right with no blank spaces Patches to the right are down slope of patches to the left The user should ensure that if a patch receives runoff from another patch the patch that it receives runoff from e g its source patch is listed earlier on the left side in the table This is an important rule to follow sin
63. intenance levels that best represents the intended priority for maintenance at the site and LRPTv2 uses this information to calculate the expected average annual runoff coefficient C over an 18 yr time period Treatment BMP storage HIGH MODERATE LOW inches of runoff from maintenance maintenance maintenance source impervious area Yu Ym Y 0 01 1 00 1 01 1 02 0 05 1 03 1 08 1 12 0 10 1 07 1 16 1 27 0 20 1 13 1 34 1 58 0 25 1 17 1 43 1 77 0 50 1 34 1 94 2 98 0 75 1 44 2 47 4 63 1 00 1 42 2 61 6 02 1 25 1 42 2 64 6 85 1 50 1 45 2 35 6 92 1 75 1 99 5 80 15 22 2 00 1 91 5 14 15 02 Table 4 Initial C value adjustment factors Y each maintenance level of effort and storage of Treatment BMPs These data were used to create equations to allow the calculation of the maintenance adjustment factor for any storage value See Equation 7 for how the maintenance factor Y is used by LRPT to calculate the average annual runoff coefficient for each Treatment BMP at a site 4 5 LAND USE TYPE AND CONDITION CRC Lake Tahoe stormwater modeling tools have employed the term characteristic runoff coefficient CRC to represent the average annual concentration expected from a specific type of land use and associated land use condition nhc et al 2009 2NDNATURE et al 2009 The CRCs used by LRPT Table 5 have been estimated based on the published TMDL event mean concentration EMC values in
64. it projects in Lake Tahoe Basin on a parcel or multiple parcel scale The LRPT terminology and methodology is consistent with the Pollutant Load Reduction Model PLRM nhc et al 2009 the BMP Maintenance Rapid Assessment Methodology BMP RAM 2NDNATURE et al 2009 and other Lake Tahoe stormwater management tools Hydrologic routing Anticipated movement of stormwater runoff through the site Volumes are routed across the parcel by sequential patches along topographic and hydrologic gradients from high to low Patch Patches are used to spatially delineate the site for hydrologic routing A patch can contain multiple adjacent surface types that possess similar runoff characteristics to simplify site geometry Patches constitute the physical area within the site where runoff calculations are made The sum of the individual patch areas equates to the total site acreage Patches are characterized by the relative infiltration capability of the surface as represented by an average annual runoff coefficient C Source Receiving patch Terminology used with respect to hydrologic routing Patches contributing runoff to the site are termed source patches whereas those accepting runoff from source patches are termed receiving patches By definition all patches are source patches they all receive rainfall and discharge some fraction as runoff Not all patches are receiving patches Annual runoff coefficient C A value between zero and one that acco
65. it scenario Q ft yr What is change in FSP loading from the pre retrofit to the post retrofit scenario EXAMPLE SITE PRE RETROFIT taken from Cobourn et al M ox iuc Ho bana Aki Unvegeizied soi armand hause g unprotected drip lines FIGURE 9A C Capii valiy i 1404 Vaohickes rack acl onda get Tom upad deoa BEFORE IMPLEMENTING BMPS FIGURE 9B unprotected drip lines unprotected drip lines 50 10 zT compacted walkway unpaved Parcel Slope driveway 496 parking on bare soil E 2NDNATURE LLC A8 a3N9SIS3G TEL 831 426 9119 wuuw endnaturellc com FAH 831 426 7092 PRE RETROFIT SITE SCHEMATIC AND MAP FI G U R E 9 PRE RETROFIT PATCH DELINEATION LRPT STEP 3 150 unprotected drip lines unprotected drip lines 100 580 ft2 compacted walkway unprotected drip lines Parcel Slope 4 parking remaining area MP1 unpaved on bare driveway soil 2NDNRTURE LLC A8 GAN9ISAG TEL 831 426 9119 FAH 8314267092 PRE RETROFIT SITE PATCH DELINEATION FIGURE 10 www 2ndnaturellc com PRE RETROFIT FLOW ROUTING LRPT STEP 4 150 unprotected drip lines 10096 GP3 unprotected drip lines 100 o CP4 compacted walkway 10096 580ft2 unprotected drip lines 10096 Parcel Slope 496
66. lar flow See Figures 6 and 7 and guidance below LRPT allows up to 30 patches to be defined for a scenario If the site requires more than 30 patches the user will have to divide the site and model the scenario as two A number of example scenarios demonstrating the rules for determining patch geometries and assigning hydrologic routing linkages are included below to guide the user through STEP 2 The individual examples are deliberately designed to be simple and representative of features that will likely be encountered within any LRPT application with the goal that a complex site can be represented by a combination of simple examples AVOIDING CIRCULAR HYDROLOGIC ROUTING The following example illustrates the governing rules for assigning patches and hydrologic routing Figure 6a The example site has two surface types asphalt and turf Panel A If the site is sloped to the North Panel B only two patches are required to represent the flow characteristics Patches 1 and 2 both receive rainfall with runoff from Patch 2 routed to Patch 1 which in turn routes offsite offsite offsite Figure 6a Simple flow routing and patch delineation examples illustrating the consideration of site slope and number of patches necessary to properly delineate site and not circularly route water offsite offsite offsite T l l e I L2 Site eb slope A B Figure 6b Proper patch delineation for 3 surface types given si
67. ltration make the appropriate changes in the PATCH DATA Input Table and the press Save Patches button again facility by the source impervious area see Equation 5 For porous pavement PP patches the user specifies the reservoir void space VS and the depth of pervious pavement subsurface reservoir Zn and the storage is calculated by LRPT when the Calculate C values button is clicked When all of the fields are populated for all of the patches at the site click the Calculate C values button and LRPT will populate the runoff coefficients C for each patch If an error is discovered in the PATCH DATA Input Table simply make the appropriate change and click the Calculate C values button again The runoff coefficient values for Treatment BMPs that have been adjusted for the site maintenance effort are shown below the Initial runoff coefficients The user should ensure the runoff coefficient C values are calculated and all of the other patch information is complete and then save the patch data by clicking the Save Patches button A separate worksheet tab is created that stores the patch data each time the Save Patches button is clicked e g Patches1 POPULATE HYDROLOGIC ROUTING INPUT TABLE The HYDROLOGIC ROUTING Input Table requires the user to specify the percent contribution from each source patch to each receiving patch The matrix of patches is automatically created in the HYDROLOGI
68. n LRPT are single family residential SFR multi family residential MFR and commercial CICU Hydrologic Anticipated movement of stormwater runoff through the site Volumes are routed across the routing parcel by sequential patches along topographic and hydrologic gradients from high to low Land surface modified to sustain maximum infiltration rates typically consisting of vertical Infiltration excavation of native soils and filling with coarse drain rock prefabricated infiltration units or feature IF other highly permeable material Infiltration features are implemented to reduce volumes generated from adjacent impervious surfaces Initial Runoff See annual runoff coefficient Coefficient Land use condition is defined by the LRPT as the average annual state of a land use relative to downslope water quality A wide range of pollutant source controls are implemented on urban land land uses with the intention of improving land use condition and reducing the pollutant condition generation risk Examples of pollutant source control actions on private parcels include fertilizer application reductions and erosion control actions such as vegetation planting and maintenance bank stabilization or terracing LRPT includes two potential land use conditions baseline and Tier 1 Load Reduction Planning Tool LRPT version 2 A Microsoft Excel spreadsheet tool written in Microsoft Visual Basic for Applications V
69. n in Panel C OFFSITE REQUIRED FOR ALL PATCHES Figure 7b shows an infiltration feature BMP surrounded by turf Recall that each patch is a source patch that must route runoff to an adjacent patch or offsite If the site is sloped to the east as shown in Panel B three patches are required to represent the flow characteristics and avoid circular routing issues If the site is sloped to direct all Patch 1 runoff to the infiltration BMP then runoff from the Treatment BMP Patch 2 must be routed either to another patch Patch 3 that is hydrologically down gradient from Patch 1 or offsite should the capacity of the infiltration BMP be exceeded Panel C PATCH ID The user must assign each patch a unique identification code and label each patch directly on the site map for easy transfer into the LRPT worksheet The recommended nomenclature is the two letter ID indicating the patch type such as IM for impervious or BF for biofilter see Table 1 followed by sequential numbers for each patch type IM1 IM2 etc However the users are free to assign any short identification codes to each patch within the area of interest if it provides added clarity to the user and future reviewers offsite offsite MORE Sie See Site slope Figure 7a Grouping of surface types and patches to simplify site geometry yet preserve area and flow routing configuration offsite C __ gt Site T slope Figure 7b Delineation of c
70. ne total site area in ft and utilize Figure 3 in the User Guidance Document to select the most representative MET GRID for the site The MET grid is used by LRPT to determine average annual precipitation in yr and the annual precipitation is held constant for all LRPT scenarios conducted for the subject site 2NDNATURE ecosystem science design LR PT Load Reduction Planning Tool Site Site ID 4BS004 Site Address 4000 Baker St MET grid Kings Beach 532 Average annual precipitation in yr 29 91 Total site area ft 15 000 Examine the site diagrams provided in Figures 9 and 10 to complete the SITE Input Table Which direction will water drain from the site What is the total site area ft STEP 2 DEFINE SCENARIO AND SITE CONDITIONS The LRPT estimates the average annual pollutant load reductions for pre and post retrofit scenario pairs For each site of interest the pre retrofit scenario and at least one post retrofit scenario are required The user can input multiple post retrofit scenarios in order to compare alternatives based on the estimated water quality benefits The user specifies a unique ID for each scenario whether a scenario is pre or post retrofit the land use type and the land use condition Users can refer to the hypothetical situation description and the appropriate User Guidance sections for information on specifying land use type and condition A scenario also includes specification of a mai
71. nform how the policies can both practical and effective The LRPT outputs can also be used to communicate the expected results of new policies to constituents which will provide a tangible framework that can make policy debates more productive The ease of use of LRPT may also provide a cost effective means for project designers to evaluate the potential influence of climate change on loading from different design alternatives LRPT currently uses an accepted historic precipitation record The precipitation data file can be changed to a projected precipitation record that reflects a climate change scenario Designers and reviewers can use LRPT to determine the potential magnitude of change for a site design by comparing loading results using these two different precipitation records This information can inform design options to favor designs that perform well under both historic and projected future precipitation regimes LAKE CLARITY CREDITING PROGRAM RELATIONSHIP The Lake Clarity Crediting Program requires the use of PLRM or an equivalent continuous simulation to estimate catchment scale annual average load reductions based on planned water quality improvement actions which are the basis for defining the number of credits awarded Annual credit targets will be included in stormwater permits and memoranda of understanding and jurisdictions will be expected to meet these credit targets through any combination of pollutant controls LRPT is a pract
72. nt site should they begin the iterative task of delineating patches and hydrologic routing linkages Rules for delineating patches 1 Pervious and impervious surface types of similar permeability adjacent to one another can be lumped to simplify site delineation and hydrologic routing see Table 1 for similar surface types 2 Each patch is a Source Patch every patch receives precipitation and is a source for runoff Runoff is routed to either an adjacent Receiving Patch or Offsite 3 Each patch has slope elevation or other characteristic that will determine routing of runoff generated from it to another patch or offsite 4 Begin patch flow assignments by starting at the highest elevation within the redevelopment site and work down gradient This means that the first patches defined will be those that do not receive runoff contributions from other patches i e are source patches only 5 Flow cannot be circular between patches Runoff is always one way and down gradient If runoff from Patch 1 flows to Patch 2 runoff cannot flow from Patch 2 or any patches connected hydrologically to Patch 2 back to Patch 1 6 Ifthe site appears to be completely flat identify offsite as the adjacent public right away or road surface and assume that direction is down gradient 7 The goal is to create the minimum number patches required to represent the overall hydrology of the site Do not subdivide patches unless not doing so results in circu
73. ntenance commitment level for Treatment BMPs which provide a sink for urban pollutants As pollutants debris and other material are introduced during storms the condition of a Treatment BMP designed to infiltrate water gradually declines over time The LRPT simulations incorporate estimated Treatment BMP infiltration decay corresponding to declining condition over time but take into account adjustments in the decay rate by allowing the user to specify the Treatment BMP maintenance effort in the Scenario Table At the SCENARIO Input Table enter the missing information in the appropriate fields based the hypothetical situation described above and the sectiond of the User Guidance Document on land use and land use condition When all of the fields have been populated click the Save Scenario button A change in any of the SCENARIO Input Table fields will constitute a new scenario Users must enter a unique Scenario ID for each new scenario and click the Save Scenario button for each one Users may add up to 6 scenarios for evaluation with a single worksheet and should save additional worksheets to run more scenarios Scenario Scenario ID BSO2 BMP Maintenance Commitment Low Scenario Type post retrofit Land Use Type Residential_SFR Land Use Condition Tier 1 Save Scenario Complete the Scenario Input Table in the LRPT worksheet What information indicates the BMP maintenance effort level for this scenario STEP 3 DELINEATE PATCH
74. o pre retrofit Residential SFR Baseline 7 47E 03 3 24 6 10 BSO2 Run Scenario post retrofit Residential_SFR Tier 1 5 67E 03 2 63 5 26 BS03 Run Scenario post retrofit Residential SFR Tier 1 4 96E 03 2 05 4 69 STEP 6 REPEAT STEPS 2 5 FOR ALL DESIRED SCENARIOS In order to calculate the load reductions from a site improvement effort the pre retrofit scenario and at least one post retrofit scenario is required A user can input multiple post retrofit scenarios in order to compare parcel improvements The user can compare various patch configurations various Treatment BMP types and sizing and different maintenance commitments as different scenarios at a site to optimize design for the maximum water quality benefits The user obtains the runoff and pollutant loads generated for each scenario with the LRPT from the RESULTS SUMMARY Output Table In order to obtain the runoff and pollutant load reductions from a pre retrofit scenario and one or more post retrofit scenarios the user will view the RESULTS COMPARISON table STEP 7 COMPARE RUNOFF AND POLLUTANT LOADS For each site a pre retrofit scenario and at least one post retrofit scenario are required A user can input multiple post retrofit scenarios for one site in order to compare parcel improvement alternatives The user can explore the differences between various patch configurations BMP types and maintenance commitment levels as different scenarios at a site to optimize design for th
75. o BMP retrofits and source control actions Whereas Tier 1 assumes a number of pollutant source control PSC practices have been implemented on the parcel to reduce the application generation and or transport of pollutants at their source PSC include the reduction of fertilizer applications and the implementation of erosion control BMPs such as retaining walls path or driveway paving natural vegetative cover parking lot sweeping and other BMPs to reduce the annual source of sediment and nutrients generated from the site Tier 2 improvements were also estimated by Lahontan and NDEP 2008 and included extensive pollutant control actions banning of phosphorous based fertilizers and other advanced land management improvements For the purposes of LRPT v2 it is assumed that Tier 2 CRC values are not representative of likely private parcel conditions in the near future However future versions of the tool may include Tier 2 CRC values if field measurement validate that the associated CRC values are achievable on a long term basis The LRPT user follows a set of rules to define the land use type and associated condition of the site for each scenario Based on user inputs the associated CRC values for the 6 pollutants of concern see Table 5 are integrated with the average annual runoff volumes EQ1 to provide the annual pollutant loads generated from the site for a given scenario 5 LRPT USER GUIDANCE The user applies the LRPT methodology to pre and
76. o assume the scenario condition represents Tier 1 conditions include frequent sweeping of commercial parking lots fertilizer application restrictions and other actions that require long term commitment to the reduction in the sources of sediment and nutrients on the parcel If the redevelopment scenario is designed and managed to meet the TRPA BMP certification guidelines the scenario condition is expected to be Tier 1 BMP Maintenance Effort If the scenario is post retrofit the user must specify the maintenance commitment level high moderate or low for all Treatment BMPs located on the site See Table 3 for guidance on selecting the appropriate maintenance commitment level for each post retrofit scenario based on available resources and the relative priority of on going maintenance of all of the Treatment BMPs at the site Section 4 4 details the LRPT approach to modeling the effects of maintenance on Treatment BMP performance over time If the scenario is pre retrofit conditions maintenance is not incorporated into the LRPT calculations and the maintenance commitment selection is not applicable to the scenario STEP 3 DELINEATE PATCH BOUNDARIES AND HYDROLOGIC LINKAGES The purpose of STEP 3 is to obtain a spatial understanding of the redevelopment site delineate the site into discrete patches of similar hydrologic characteristics and determine hydrologic routing linkages The final product of STEP 3 is a plan view map of the site with a ser
77. o the influence of contributing surface area and the pollutant loading rate LRPTv2 lumps the maintenance effort for the overall site when it is likely that Treatment BMPs chronically accepting dirty water such as an unpaved driveway will clog faster than those accepting relatively clean water such as roof runoff While there is strong agreement that regular maintenance is necessary to maintain the infiltration capability of Treatment BMPs empirical data to support the rate of performance loss as a result of lack of maintenance is extremely limited Future research is necessary to improve our capability to quantify the water quality benefit and necessary frequency of maintenance to sustain pollutant load reduction expectations from Treatment BMPs In addition the stormwater quality improvement community needs to identify and implement practices that ensure adequate maintenance actions are performed on reasonable intervals to ensure long term sustained pollutant load reductions The land use CRCs for the pollutants of concern are based on the TMDL EMCs and limited land use specific water quality data The land use CRC changes from baseline to Tier 1 improvements are purposely modest as to not over estimate the water quality benefit of source control actions that require long term and continued implementation to provide the actual average annual water quality benefit over 18 years as estimated from the LRPT Tahoe Basin research continues to build evidenc
78. of patch n e g ft fiis the fraction of runoff that flows from source patch i to the receiving patch n unitless Q is the annual runoff from each contributing source patch i e g ft year Equation 3a is used to calculate the total volume of water generated from patch n by summing the amount of direct precipitation P and the amount of runoff contributed from each adjacent source patch qn The contributed volume is distributed evenly over the patch area A and adjusted by the annual runoff coefficient C to estimate the volume generated and routed downslope by patch n The LRPT iteratively accounts for water flow from source patches to receiving patches per the hydrologic routing defined by the user and ultimately calculates the amount of runoff discharged from the parcel An example of hydrologic routing between patches is shown schematically in Figure 1 Patch A corresponds to an impervious surface roof of a house surrounded by pervious patch A turf Both patches A and A receive precipitation at the same rate P Runoff generated from patch A is converted to a contributing rate q5 10096 of which is routed to patch A Runoff Q from patch A is determined by summing the precipitation P and contributing rate q2 and multiplying by the area and annual runoff coefficient for patch A P 1008 Q q 1 b A Figure 1 Simple schematic showing hydrologic routing between two patches Patch Typ
79. on of Complete BMP RAM evaluations annually If BMP infiltration resources SUMMER rate or other treatment process appears to have declined e Documentation of maintenance plan beyond acceptable levels perform extensive maintenance to that details extensive maintenance HIGH restore function prior to Oct 1 actions and schedules for individual Prior to October 1 and first significant winter rain rake and treatment BMPs F LL remove all leaves pine needles or other debris Continue as Extensive maintenance is performed necessary to ensure minimal debris at surface of BMP prior when BMP condition is fair and before to snow accumulation failure As snow accumulation recedes frequent inspections to 5 Roles of responsible parties are WINTER ensure BMP conveyance is operating i e getting water and ouine free of pine needles or other debris At least one inspection per spring to ensure BMP conveyance SPRING is operating i e BMP is getting water and free of pine MODERATE maintenance commitment needles or other debris requires v MODERATE e Some explicit resource allocations Complete BMP RAM evaluations every 2 3 years If BMP e Intermittent evaluations of SUMMER infiltration rate or other treatment process appears to have treatment BMPs declined beyond acceptable levels extensive maintenance e Treatment BMPs may underperform actions are performed to restore function or fail for short periods Infiltration BMP
80. onstructed Treatment BMPs must include downslope routing subsequent source patch of water should capacity of infiltration BMP be exceeded QNDNATURE LLC A8 aa3N9SISs3G TEL 831 426 9119 _ FAH 831 4257092 SITE DELINEATION EXAMPLES FIGURE 7 Wwww 2ndnaturellc com STEP 4 ASSIGN HYDROLOGIC ROUTING CONTRIBUTIONS The user estimates the percentage of flow across boundaries from source patches to receiving patches or offsite By definition each patch is a source patch and must therefore have a minimum of one flow connection to either an adjacent patch or offsite If there is only one flow connection then by definition the fraction of routing is 10096 If there are multiple connections the user must estimate the routing percentages between connected patches based on a combination of 1 topographic and structural data and 2 length of the shared boundaries between the patches The routing percentages are determined for each source patch and must sum to 100 Figure 9 illustrates the estimate of the percentage of flow across patch boundaries The user always begins with the upslope upgradient patch on the site and indicates the flow percentages directly on the patch delineated site map With the site sloped to the north as shown in Panel B 10096 of the runoff from Patch 2 is routed to Patch 1 In turn 10096 of the runoff from Patch 1 is routed offsite Figure 8 examples increase in complexity to illustrate th
81. ore surface types can be lumped into distinct patches based on similar expected annual runoff coefficients i e permeability see Table 1 in the User Guidance The user should focus the detail of parcel delineation on the location sizing and hydrologic routing of constructed Treatment BMPs as these are the features installed and maintained at the site to provide a water quality benefit downslope Impervious and many pervious surface types can be lumped into a single patch if 1 The surface types are identified to possess the same relative permeability 2 They are adjacent or in very close proximity and 3 Consolidation of surface types simplifies site geometry while preserving the general hydrologic routing processes of the subject parcel While on site the user should conceptualize the entire redevelopment site in a holistic manner by first identifying which portions of the site are 1 up gradient versus down gradient site slope and 2 which portions are raised or elevated above adjacent areas buildings structures etc Runoff will always flow from higher to lower elevations The user should consider hydrologic connections between the site and offsite areas are there storm drains or other conveyance features onsite that route directly offsite If there is an offsite BMP what is the hydrologic connection between onsite areas and the offsite BMP Only after the user has identified the overall hydrologic routing of the redevelopment sit
82. patch Terminology used with respect to hydrologic routing A patch that accepts runoff from a source patch es is termed a receiving patch Not all patches are receiving patches Runoff The rate volume time at which stormwater is generated LRPT estimates the average annual pollutant loads generated from a site termed a scenario Scenario The scenario types are either pre retrofit which is prior to site improvements or post retrofit The user is able to enter a number of post retrofit scenarios for comparison of the estimated load reductions for different retrofit alternatives on the same site Terminology used with respect to hydrologic routing Patches contributing runoff another Source patch patch or off site are termed source patches By definition all patches are source patches they all receive rainfall and discharge some fraction as runoff There are two potential conditions for each land use baseline and Tier 1 The LRPT user determines the land use type and associated condition that results in the assignment of appropriate average annual CRCs for the pollutants of concern Tier 1 assumes a number of pollutant source control PSC practices have been implemented on the parcel to reduce the application generation and or transport of pollutants at their source PSC include the reduction of fertilizer applications and the implementation of erosion control BMPs such as retaining walls path or driveway paving
83. pre retrofit conditions Further comparing the loading resulting from different alternatives in light of the relative costs for each alternative will enable project designers to identify when on site treatment is sufficiently difficult that off site improvements produce significantly greater load reduction benefits more cost effectively By using a long term hydrologic simulation and calculating loads LRPT provides results consistent with the PLRM which is used to calculated catchment scale load reduction and Lake Clarity Credits credits This consistency will allow municipal stormwater planners project reviewers and regulators to communicate using consistent terms and inform long term catchment and municipal scale planning to achieve credit targets TRPA and county project review staff will greatly benefit from the standard use of LRPT through faster and higher quality review and input to project plans and permits Requiring the analysis of loading from a parcel will provide a strong incentive for project designers to use LRPT as the most cost effective tool available for use in the Tahoe Basin To provide an additional incentive reviewers may give priority to projects with supporting analyses using LRPT and require a longer review period for projects that use non standard approaches More aggressively project permit requirements may be adjusted to require analyses using LRPT for all projects or for all projects that require any sort of trad
84. pression storage to capture detain evapo transpire and infiltrate urban runoff Nutrient concentration reductions occur by fixing nutrients via biological processes The footprint of these surface types are larger than typical infiltration BMPs Biofilters constructed with depressional storage must include a relatively shallow slope Initial Runoff Coefficient C Varies based on storage and MET grid Varies based on underlying reservoir depth and void space and MET grid Without depression storage 0 15 With depression storage varies based on storage and MET grid Table 1 Surface types and initial runoff coefficients for urban surfaces adapted from Caltrans 2003 Dunne and Leopold 1978 Davis and McCuen 2005 and verified using PLRM simulations on a 1 acre pervious surface with a range of hydraulic conductivity values Treatment BMP types and descriptions are adapted from BMP RAM definitions 2NDNATURE et al 2009 Initial annual runoff coefficients for Treatment BMP types are calculated by LRPT based on sizing and MET grid information provided by user The annual runoff coefficients used by LRPT calculations for pervious surfaces are adjusted for relatively small patches and Treatment BMP C values are adjusted based on user maintenance commitment Eq 4a x 4 7 rs Eq 4b Q CP q2 A Eq 4c The LRPT MS Excel spreadsheet tool provides the necessary accounting of stormwater runoff across the parcel base
85. r t v2 pdf Northwest Hydraulic Consultants nhc Geosyntec Consultants and 2NDNATURE 2009 PLRM Model Development Document Prepared for Lake Tahoe Basin Storm Water Quality Improvement Committee South Lake Tahoe CA Available for download as well as full source code and other supporting documents from www tiims org APPENDIX A LRPT V2 TUTORIAL PURPOSE Familiarize participants with the usability functions and outputs of LRPT The user should have the complete LRPTv2 Technical and User Guidance Document readily available for reference HYPOTHETICAL SITUATION A single family residential parcel in South Lake Tahoe is scheduled for retrofit improvements The site currently includes minimal TRPA parcel based BMPs to reduce sources and generation of the pollutants of concern sediment and nutrient species Based on recommended BMP practices and private parcel improvements one post retrofit alternative has been developed that includes a series of Treatment BMPs and source control improvements The site retrofit alternative will include a number erosion control actions to reduce the sediment generation from the site the removal of all non native vegetation and reduction of fertilizer use Post retrofit a detailed maintenance plan will be developed and resources allocated to ensure that Treatment BMPs continue to function at their full performance level You are tasked with using LRPTv2 to estimate the water quality benefits of the retrofi
86. s presented in Table 4 LRPT integrates the maintenance commitment and the associated factor adjustment Y Table X and the initial runoff coefficient for each Treatment BMP using Equation 7 C C Y Eq 7 Where C is the annual runoff coefficient for Treatment BMPn unitless C is the initial runoff coefficient for Treatment BMPn based on storage and MET grid unitless Y is the factor adjustment to Ci based on user s maintenance commitment unitless The LRPT user is required to select one of three maintenance commitment levels of effort to perform Treatment BMP inspections and conduct extensive maintenance actions as required based on observational and or BMP RAM results Table 3 Based on the user input the average annual C values for all of the Treatment BMPs at the site are adjusted to reflect the maintenance commitment using equation 7 with higher C values corresponding to a lower overall maintenance commitment The maintenance frequency linkage to the absolute decline in infiltration rates are based on hypotheses and best professional judgment in LRPT and these estimates should be quantitatively improved over time Infiltration BMP Maintenance Commitment posa Seasonal commitments Extensive Maintenance Frequency Frequent inspections to ensure BMP conveyance is operating SPRING i e BMP is getting water and free of pine needles or other debris HIGH maintenance commitment requires e Adequate explicit allocati
87. see Table 1 and glossary for more details Treatment BMP condition Treatment BMPs are intended to provide a sink for urban pollutant loads and a Treatment BMP condition is defined as a continuum of the pollutant load removal capability of a Treatment BMP Treatment BMP condition is considered to be at its initial or benchmark condition following installation and or after adequate maintenance As pollutant loading and treatment occurs during subsequent storm events the condition of a Treatment BMP gradually declines 2NDNATURE et al 2009 LRPT quantitatively incorporates the expected decay in water quality performance of the Treatment BMPs as a function of maintenance frequency identified by the user Pollutants of concern These are fine sediment particles FSP 16 um dissolved phosphorous DP total phosphorous TP total suspended sediment TSS dissolved inorganic nitrogen DN and total nitrogen TN Land use condition Land use condition is defined by the LRPT as the average annual state of a land use relative to downslope water quality A wide range of pollutant source controls are implemented on urban land uses with the intention of improving land use condition and reducing the pollutant generation risk Examples of pollutant source control actions on private parcels include fertilizer application reductions and erosion control actions such as vegetation planting and maintenance bank stabilization or terracing LRPT includes t
88. seeeeeeeee nne enne 11 Figure 5 LRPT modeling of maintenance influence on BMP C values sse 13 Figure 6 Site delineation examples rrt beet eden HR o e ER S sa ini a ER Rh S AER Ra ean 21 Figure 7 Site cdelimeatiom examples err ete e RE ERE E des ue HERES e Ere apu gera des e ERE 23 Figure 8 Flow percentage examples cesecsesseesseeseseeesececsaeeeseeseeesenesesaeeeaeeceseeseanessaeessaeeeaeeseeseneeseeeeseaneres 25 Figure 9 Pre retrofit site schematic and map nnne nennen rentre nnne nnne nennen 49 Figure 10 Pre retrofit site patch delineation 0 2 eceesceecesseeeseteneceeeteeesseeeeeceaeceecseceaeseaessaeseeeaeeeaeseaeeeeeeneeeaees 50 Figure 11 Pre retrofit site flow routing sssssssessesseeseeenenne enne enne nennen nnne nhstnnsn nenne nennen eren nnei 51 Figure 12 Post retrofit site patch delineation and flow rOUtING cccccccesssccessseccesssecccssseeeessseeeessseesessateeeees 52 LIST OF TABLES Table ES 1 Table 1 Table 2 Table 3 Table 4 Table 5 Table 6 Steps implemented by user to complete LRPT cc cccccccsesssssesccesseessnsseeceesseeseseeeseessesesseeeeeeseeesaaes 1 Surface types and annual runoff coefficients for urban surfaces esssssssseeeeeeeeennnne 6 Adjustments to initial C values for pervious patch types based on Qn cesssscceesseceeesssecesssseceestseeeesses 8 Definitions of maintenance commitment CAtEQOLICS ccecccccesscccesssscc
89. t alternative for this site EXAMPLE RETROFIT SITE Figures 9 11 present the final maps and data the user will generate for each scenario during LRPT STEPs 1 4 Figure 9A is a schematic of the site pre retrofit and figure 9B is a plan view of the site The parcel is located in MET Grid 847 Figure 10 is the pre retrofit site map delineated into patches per LRPT STEP 3 and each patch has been assigned a unique ID Figure 11 is the pre retrofit site map delineated and hydrologic routing contributions STEP 4 noted for all connected patches Figure 12 is a post retrofit scenario map that includes both patch delineation and hydrologic routing contributions It is possible to develop and run a number of post retrofit scenarios to optimize retrofit design based on the water quality benefit as estimated by LRPT This parcel is the example parcel in the How to install best management practices BMPs in Lake Tahoe A guide for building and landscape professionals Cobourn et al This exercise will allow you to implement components of each of the LRPT STEPs to demonstrate the functionality of the tool LRPT STEPs 1 4 are inherently the most time consuming In the interest of time the exercise is structured so that you will complete components of STEPs 1 4 but the majority of the exercise focuses on interaction with the spreadsheet program This section contains references to Section 5 of the User Guidance so users should have the docum
90. t the BMP Maintenance Effort is not applicable to the user When all of the fields have been populated in the SITE and SCENARIO Input Tables click the button labeled Save Scenario A change in any of the SCENARIO Input Table fields will constitute a new scenario since they affect runoff and loading calculations in LRPT To enter another scenario change the appropriate field values and click the Save Scenario button Remember to create a new unique Scenario ID for each new scenario The user may create up to 6 scenarios for a single worksheet Scenario Scenario ID BS02 BMP Maintenance Commitment Low Scenario Type post retrofit Land Use Type Residential SFR Land Use Condition Tier 1 Save Scenario POPULATE PATCH DATA INPUT TABLE At the PATCH DATA Input Table the user specifies characteristics of the site patches that are used to calculate the annual runoff coefficient for each patch The user should refer to the completed site delineation and hydrologic routing map for the respective scenario to easily transfer the data into the PATCH DATA Input Table The user should begin patch entry with those at the uppermost elevation that are only source patches i e only receive rainfall and no runoff inputs from other patches such as roofs The user populates the PATCH DATA Input Table from left to right continuing from patch to patch as they progress downward in site elevation with no blank spaces The user must ensure that i
91. te slope differences gt offsite Site C slope gt offsite offsite roof apex offsite A I I j i Site slope Site B C slope Figure 6c Proper patch delineation for 3 surface types given site slope and patch elevation differences 2NDNRTURE LLC A8 a3N9SIS3G TEL S3TL4286 BT 9 FAH 8314267092 SITE DELINEATION EXAMPLES FIGURE 6 www 2ndnaturellc com If the site is sloped to the East Panel C and only 2 patches are incorporated the result is circular hydrologic routing which is not allowed red X a portion of the runoff from Patch 1 is routed across Patch 2 which in turn discharges back to Patch 1 A third patch is required to represent site hydrologic routing Incorporating a third patch as shown in Panels D F resolves circular routing issues green checkmarks The user has broad discretion when choosing the boundaries of Patch 3 it can be equal in size to Patch 1 Panel D much larger Panel E or much smaller Panel F All choices are valid In a more complex redevelopment scenario incorporating additional patches occupying what is now labeled as Offsite the user would consider which scenario Panels D F best fits with the additional patches Figure 6b provides an example with three patches as shown in Panel A turf asphalt and maintained pervious swale If the site is sloped to the North as shown in Panel B only three patches are
92. total suspended sediment TSS dissolved inorganic nitrogen DN and total nitrogen TN All pollutants are tracked and reported on an average annual mass basis LRPT outputs include four critical elements for each set of pre and post redevelopment scenarios 1 average annual runoff volume reduction ft yr 2 average annual pollutant load reductions kg yr and 3 user generated site diagrams illustrating the hydrologic routing through the site for both pre and post redevelopment scenarios The initial version of the LRPT was completed by 2NDNATURE LLC with Army Corps of Engineers funding in March 2009 and outlined the detailed step by step methodology for a user to follow to make load reduction calculations Using joint funding from the Army Corps of Engineers and the Tahoe Regional Planning Agency TRPA a number of technical improvements to the methodology and implementation approach were made and incorporated into a visual basic application operated from a user friendly MS Excel spreadsheet to automate load reduction calculations This is the technical and user guidance document for the LRPTv2 2 KEY TERMS The following key terms are used throughout this document A complete glossary and acronym list are included as Section 8 Load Reduction Planning Tool LRPT version 2 A Microsoft Excel spreadsheet tool written in Microsoft Visual Basic for Applications VBA to estimate the potential pollutant load reductions from BMP retrof
93. ture and were selected to represent average hydrological characteristics on an annual basis for sub parcel sized areas Table 1 The C values for pervious patch types were verified by PLRM simulations of a hypothetical one acre pervious parcel with a range of hydraulic conductivity values The C values for specific pervious patches in LRPT are adjusted if a specific patch is too small relative to the volumes routed to it see Pervious Patch Types below The C values for Treatment BMPs are calculated by LRPT and vary by BMP type BMP storage and the MET grid and user maintenance commitment for the subject site see Treatment BMPs below The assignment of specific annual runoff coefficients for surface types in LRPT rather than user selected ranges increases the consistency of LRPT pollutant load reduction estimates across users and scenarios PERVIOUS PATCH TYPES LRPT includes a function to avoid modeling the infiltration of a large volume of water within small pervious patches The volume of water potentially applied to a pervious patch is the sum of direct precipitation P plus all contributing runoff from adjacent patches qn see Eq 3a Using hypothetical PLRM simulations to route a range of impervious areas to the various pervious surfaces types in LRPT UN MP CP SP see Table 1 a relationship was created to increase the annual runoff coefficient of pervious patches that may experience excessive loading from contributing patches The LR
94. unts for the fraction of precipitation and contributed runoff that is unable to infiltrate or evaporate from a given surface type on an average annual basis and therefore produces stormwater runoff Impervious surface types have high annual runoff coefficients whereas pervious surface types have relatively lower annual runoff coefficients Treatment BMPs in LRPT are assigned annual runoff coefficients calculated based on their storage capacity where they are located in the Basin and the maintenance commitment for all Treatment BMPs at the site as defined by the user Offsite The user must define a common outfall where the runoff generated from the site will accumulate and LRPT calculations are summed Typically parcel outfalls are not specific locations but rather the downslope boundary e g the north border of the parcel and termed in LRPT as offsite Offsite in LRPT is analogous to an outfall as defined by PLRM and the point at which average annual pollutant loads are estimated Treatment BMPs Constructed BMPs that accept attenuate and treat urban stormwater Treatment BMPs are implemented to reduce pollutant loads in stormwater by either removing pollutants and or by reducing surface water volumes LRPT focuses on three different types of Treatment BMPs that are typically installed on commercial or residential parcels to capture and retain stormwater to reduce runoff transported off site infiltration features porous pavement and biofilters
95. urfaces are lumped during delineation and all are assigned an average annual runoff coefficient C of 0 82 see Table 1 Attempts should be made to reduce complex geometries to simple polygons while preserving the site surface area In the majority of cases the visual distinction between various surface types and their relative permeability will be readily apparent but in some instances best professional judgment infiltration measurements or other means to gain additional information on the surface type and most appropriate annual runoff coefficient may be necessary Although advanced computer software allows the locations of boundaries to be determined very precisely the user should employ best professional judgment in simplifying complex geometries While on site the user should conceptualize the entire redevelopment site in a holistic manner by first identifying which portions of the site are 1 up gradient versus down gradient site slope and 2 which portions are raised or elevated above adjacent areas buildings structures etc Runoff will always flow from higher to lower elevations The user should consider hydrologic connections between the site and offsite areas are there storm drains or other conveyance features onsite that route directly offsite If there is an offsite BMP what is the hydrologic connection between onsite areas and the offsite BMP Only after the user has identified the overall hydrologic routing of the redevelopme
96. will appear when the user clicks the Save Routing button If this occurs return to the PATCH DATA Input Table and save the current patch configuration before clicking the Save Routing button in the HYDROLOGIC ROUTING table LRPT creates a new worksheet tab with the routing data every time the Save Routing button is clicked e g Qcalcs1 Double check the site diagrams to ensure that routing directions and contributions have been correctly assigned for each patch Incorrect routing can lead to incorrect runoff and loading calculations Incorrect routing can lead to incorrect runoff and loading calculations Users should ensure that only one set of patch and routing worksheets are present for each desired scenario and delete unneeded sheets RUN SCENARIOS At the RESULTS SUMMARY Output Table the user obtains the LRPT runoff and annual pollutant load estimates for the 18 year simulation period for each scenario that has been entered into LRPT by pressing the corresponding Run Scenario button LRPT simulations will take up to a minute to run a simulation for a scenario and return results to the table so please be patient If needed the simulation can be terminated by hitting the Esc key Results Summary B Click the buttons to obtain results for each scenario Pollutant Loads kg yr Scenario Scenario Land 3 Scenario ID Scenario Type Land Use Runoff ft yr FSP TSS Use Type Ru Condition BSO1 Run Scenari
97. wo potential land use conditions baseline and Tier 1 Characteristic runoff concentration CRC Lake Tahoe stormwater pollutant loading models PLRM and LRPT express the condition of an urban land use quantitatively as a characteristic runoff concentration CRC for pollutants of concern for lake clarity A CRC is a representative average annual concentration for a pollutant of concern in stormwater runoff from a specific urban land use and its associated condition In the LRPT the parcel CRC is combined with the average annual runoff generated from the site to provide an estimate of average annual pollutant load for each pollutant of concern The land use types included in LRPT are single family residential SFR multi family residential MFR and commercial CICU 3 GENERAL APPROACH The user calculates average annual loads for the site for both baseline conditions pre redevelopment and planned improved post redevelopment conditions for the six Lake Tahoe pollutants of concern Characteristic runoff concentrations CRCs are assigned based on the user s selection of land use type and land use condition The average annual pollutant load is calculated with appropriate unit conversion factors not shown as Average Annual Pollutant Load kg yr Characteristic Runoff Concentration CRC mg L x Average Annual Runoff ft yr Eq 1 The estimated load reduction as a result of improvements is calculated as Estimated Load Redu

LOAD REDUCTION PLANNING TOOL (LRPT) V2

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