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Appendix _H_ Corridor Development
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1. Geographic Coordinate Long 73 279040 Lat 44 247495 Map Documentation and Notes Comments for Reac Quads Orthos Reach Attributes Imported for defining Stream Corridors Stream Type E k Aroup jc Major Channel Adjustment lt Reference Stream Departure No Towns Notes Calc Data Export Data Import Stream Type When one clicks on the button labeled Import Stream Type the following message is issued Continue with Import This will transfer data from the table StrmCorD at dbf to the attribute table for the Reach Point theme Continue The above simply provides a chance for the user to bail out if the button was inadvertently clicked Select No to quit the import function Otherwise click on Yes to continue For the Tools to import the data the table must be named StrmCorDat dbf and must be located in the BaseData directory If the table is not found the following error message is issued Revu dBase File Not Found BaseData directory of h geomorphology version3 B aseD ata The required table StrmCorD at dbf does not exist in the File selection ignored SGAT Version 3 VT Agency of Natural Resources H 17 Revision December 10 2003 Development of Stream Corridor Buffers in Step 09 If the table is found a check is made to ensure that the required fields are in
2. entered by the user in a Microsoft Access data base as part of the assessment process As a result the necessary data must be transferred from the data base into the attribute table for the reach point theme Each feature if present is buffered in accordance with the applicable parameters in the record selected from the buffer reference table These component buffers are then merged using specific rules to form the stream corridor This permits creating a stream corridor specific to the conditions of a given reach The implementation of the above has been accomplished in such a manner that it is for the most part transparent to the user Further the average user will not need to understand the details presented in this Appendix However for users who have specific needs or applications the information presented herein can be used to tailor the buffering procedure in arriving at specific stream corridor configurations This Appendix will provide detailed descriptions of the concepts introduced above However some background on relevant aspects of the Geomorphic Assessment is necessary These are presented in the next section SGAT Version 3 VT Agency of Natural Resources H 2 Revision December 10 2003 Development of Stream Corridor Buffers in Step 09 Related Background on the Geomorphic Assessment Process During the Phase assessment process the following data is captured for each reach e Stream type e Sensit
3. J N DefaultNY N Y k l m n o N DefaultNN N N p q r s t N Default u v w x y N Note Specific records for key values of Default with conditions appended can be omitted if the buffering requirements are the same as the overall Default record last record in the above table Note At a minimum each buffer reference table must have one record with a key value of Defaul and only values for the following fields DefaultBuf StreamCL MeanderCL ValleyToe and RequireVW All other fields would be blank The first column in the previous tables refers to a key The values for this field are simply formed by various combinations concatenation of the values in StrmGroup StrmType Departure and or Adjustment Access to a specific record will be by the value in the key field For each reach the Tools will construct keys in a pre determined order using data collected in either the Phase lor Phase Il assessments After a key is constructed an attempt is made to find a matching key in the buffer reference table f the key is found the associated buffering parameters are used to define the stream corridor for the reach If however the key is not found the next key in the pre determined order is constructed This process is repeated until the generic key of Default is constructed at which time the record from the buffer reference table having the same value will be used to obtain the buffering parameters Note It is mandatory t
4. Stream Corridor Buffers in Step 09 Concept of Application in the Tools Extension The concept of applications has been implemented in the Tools to permit certain functionality to be used for different purposes The following table lists the applications that have currently been defined Application Application Buffer Reference Table Access Level Applicatn BuffrTable AccessLvl Floodway Determination Option 1 FD Option 1 SysBufOpt1 dbf 2 Floodway Determination Option 2 FD Option 2 SysBufOpt2 dbf 2 Stream Geomorphic Assessment SGA SysBufSGA dbf 1 Note Floodway Determination Options 1 and 2 are defined in the Floodway Determination Technical Guidance document and Stream Geomorphic Assessment is defined in the Stream Geomorphic Assessment Handbooks These documents are available from the River Corridor Management Section refer to address on previous page The only difference between the applications as far as use of the Tools is concerned is in the development of stream corridors Step 09 This difference is implemented through the use of buffer reference tables The above table actually represents the contents of the system table SysApps dbf The field names in the system table are shown within parentheses in the column heading As illustrated in the table each application row is associated with a buffer reference table Once an application is selected the buffer reference tabl
5. This provides a more accurate reflection of conditions where the resolution of the source maps digital versions of the USGS topographic maps prevented a more detailed delineation of the valley walls Step 4 The buffer shown to the right illustrates the meander centerline buffered at 4 0 times the channel width For the stream geomorphic assessment application this buffer will be created only if both the valley walls and the meander centerline are present for a given reach Specifically if a valley wall polygon is not present that encompasses the entire reach the reach point and its neighboring upstream reach point then this buffer will not be created For Floodway Determination Options 1 and 2 a buffer will be created using the meander centerline regardless of the presence of valley walls For all applications Following creation Valley Walls Meander Centerline Surface Water Centerline Valley Wall Meander Centerline Surface Water Centerline of the meander centerline buffer it will be clipped by the valley walls Note This portion of Step 4is not shown In other words this buffer is not allowed to extend laterally beyond the valley walls SGAT Version 3 Revision December 10 2003 VT Agency of Natural Resources H 22 Development of Stream Corridor Buffers in Step 09 Optional Intervening Step If no meander centerline is present for a reach a secondary buffer may be creat
6. are required to make the hierarchy work SGAT Version 3 VT Agency of Natural Resources H 13 Revision December 10 2003 Development of Stream Corridor Buffers in Step 09 Decision tree for finding record in Buffer Reference Table for Stream Geomorphic Assessment and Floodway Determination Option 1 To use the diagram start on the very left and follow a decision path to the far right where the buffering criteria to be used have been identified Buffering criteria found Key TTsCFVS The decision tree identifies the hierarchical search implemented to find an appropriate record in a Buffer Reference Table based upon stream type IT slope modfier in stream type s confinement CF valley slope VS and sensitivity Class or other stream type grouping CCC If no record is found using the variations of those values an attempt will be made to find a Default record with the stream departure and major adjustment values If that fails the Default record will be used If there is no Default record an error condition is raised Buffering criteria found Key DefaultCF Buffering criteria found Buffering criteria found Buffering criteria found Found Buffering criteria found Found a Buffering criteria found Found Key TTs Found Key TT Found S AN ONNA Key CCCCFVS h o hy Found bo Sy My 0 o Sp Key Components o Sop Kay CCC TT Stream Type hr i b Found s S
7. effect any changes It is imperative that the buffer reference table referred to in a record actually exist in the SysData SGAT Version 3 VT Agency of Natural Resources H 5 Revision December 10 2003 Development of Stream Corridor Buffers in Step 09 directory If the buffer reference table does not exist an error message will be issued during the initialization procedure of the Tools extension and access to the functions will be prevented Note Additional verification of each buffer reference table is performed during this procedure If any errors are detected appropriate error messages will be issued Access to any functions will be prevented until such error conditions are cleared up Refer to the Section of the User Manual for the Tools entitled Initialization Procedure for a description of the error conditions As implied one can edit the SysApps db table to include additional applications If this is to be done adhere to the following rules 1 Any editing should not be performed while the Tools extension is active Always exit the extension click on Exit on the Setup Dialog before editing Do not modify any data for the existing records in the SysApps dbf table These applications are to be used for their intended purposes and have statutory or scientific basis Enter the name to be associated with the application into the Applicatn field Enter the name of a valid buffer reference table wh
8. if the valley toe feature is present see MeanderCL above If the value is N No then buffering of the meander centerline will be performed independent of whether a valley toe feature is present Key C 24 StrmGroup C 16 Adjustment C 1 StreamCL N 6 3 MeanderCL N 6 3 ValleyToe N 6 3 RequirevW C 1 Note The values in fields StrmType12 StrmType3 Departure and Adjustment are not used within the Tools These fields however must be present in the buffer reference table The Tools uses the existence of the fields Departure and Adjustment to specify use of the buffering decision tree for Phase II data i e for Floodway Determination Option 2 Using Phase IlI data associated with a given reach the decision tree identifies which record to use for obtaining the buffering parameters In addition these fields provide documentation for the value of the Key field If any of these fields are not used in forming the value of the Key field the value of the field should be left blank otherwise adhere to the format described in the table above SGAT Version 3 VT Agency of Natural Resources H 8 Revision December 10 2003 Key Default Key Default Key Low Mod ModYY ModNY High Default Development of Stream Corridor Buffers in Step 09 In the buffer reference tables the field StrmGroup can be used in a much broader sense than
9. key is matched Group designation for stream type e g sensitivity class For permissible values refer to the column Stream Group and its definition in the table presented earlier Stream Type designation First and second characters identifying Stream Class StrmType12 C 2 must always be present and Dominant Sediment Material if not present a dash must be used Stream Type designation Third and optional character identifying Slope Modifier StrmType3 C 1 if not present a dash must be used Departure c 1 Designation of existing stream departure from reference stream which at present is either Y for Yes or N for No If value does not exist use a dash Designation of whether existing stream is in major adjustment which at present is either Y for Yes or N for No If value does not exist use a dash Fixed distance for creating a default buffer around the stream centerline Value of DefaultBuf N 6 0 this field represents a fixed distance on either side of the stream with a total width of twice the value A value of zero will indicate this buffer is not to be used Channel width multiplier for defining a buffer around the stream centerline Buffer distance will be the value of this field multiplied by the channel width and will represent distance on either side of the stream with a total width of twice the product A value of zero will in
10. Stream Geomorphic Assessment Tools Appendix H Development of Stream Corridor Buffers Development of Stream Corridor Buffers in Step 09 Introduction Stream corridors are created in Step 09 by creating buffers around certain features and then combining those buffers in a specific manner The concepts of buffers and features are used from the perspective of Geographic Information Systems Features can be points lines or polylines which are a connected string of line segments or polygons enclosed or bounded areas A feature is a digital model or representation of an object in the real world As examples Points can represent such objects as fire hydrants signs reach points polylines can represent such things as road centerlines electric transmission lines stream centerlines and polygons can represent such things as town boundaries rivers lakes valleys Within the Stream Geomorphic Assessment Tools the Tools the predominant feature type is a polyline Stream centerlines meander centerlines and the valley walls are represented as polylines Note While valley walls are digitized and provided as polygons the toes of the valley walls are extracted from those polygons and used as polylines With the release of Version 3 of the Tools significant flexibility has been incorporated into the development of stream corridors via processing Step 09 This flexibility is based upon the implementation of the following concep
11. a will be required for developing and or refining the stream corridor calculations of Step 09 The data elements which are required are included in the lower right corner of the dialog for Step 10 If the fields shown on the dialog have values of N A then the import function has not been executed The operation for importing the data will be initiated by clicking on the mport Stream Type button The dialog for Step 10 with the relevant areas highlighted are shown in the figure on the following page SGAT Version 3 VT Agency of Natural Resources H 16 Revision December 10 2003 Development of Stream Corridor Buffers in Step 09 Part B Step 10 Data Entry Review of Reach Point Data Reach Point Theme Multiple Themes for this input created Select Theme Theme SOSRPts01 shp z to be used last one created shown first Reach Point Identifiers Vermont Id 0201000805 0001 Reach ID mdm gentoo Distance Id _ M 000 000 Reach Point Data Reach Point Type omw SS Channel and Valley boost Channel lt Units gt Valley ocatior 5 s Distance to Statt Too Feet Width 98 lt Feet gt Width 0 Length ES 2 Elevation foo Feet ng 6684 lt Feet gt Length l 0 Slope 0 00 lt Percent gt Slope J 0 00 State Plane Coordinates i F Sinuosity 0 0 lt Ratio gt Confinement l 0 437778 67 194434 96 Areas ed 0 60 Sq Miles ea 23 10 Sq Miles iles
12. am corridors will be created using the Default record in the buffer reference table associated with the given application Any attempts to create stream corridors for the other applications will result in an error being generated in Step 09 and access to the buffer function will be prevented The data elements required for using the buffer reference table are collected during the Phase I and Phase Il assessment efforts These data elements however are entered into and maintained in a separate Microsoft Access data base An automated method for extracting the required data elements is provided as part of the interface to that data base Note Refer to the documentation for the Phase NII Access data base for instructions on performing the extraction When the extraction is performed from within the Access data base a dBase table named StrmCorDat db f will be created This table must be moved or copied to the BaseData directory Then the mport function available on the dialog for Step 10 can be used to transfer that data to the attribute table for the reach point theme The Import function is described in the section of the User Manual for the Tools extension pertaining to Step 10 A portion of that section has been incorporated below for completeness of this Appendix During Phase and Phase II of geomorphic assessment for a watershed a significant amount of data will be entered into a Microsoft Access data base A limited set of that dat
13. arture from the reference stream Note Sensitivity class stream group is disregarded Record 2 pertains to all other conditions of stream type Y3 regardless of slope modifiers sensitivity class departure condition or major adjustment condition Record 3 pertains to all other stream types in the sensitivity class Mod regardless of stream type departure condition or major adjustment condition Record 4 pertains to all remaining stream types regardless of sensitivity class departure condition or major adjustment condition In summary creating a buffer reference table requires that one define records from the most specific conditions using meaningful combinations of the data elements that require special attention After those have been defined records are defined on a more and more aggregate level Finally a default record is required to cover all remaining conditions SGAT Version 3 VT Agency of Natural Resources H 12 Revision December 10 2003 Development of Stream Corridor Buffers in Step 09 A Default record can be included for each combination of departure condition or major adjustment condition However a Default record must also be included without reference to those conditions The following table illustrates this concept Key Strm Strm Strm Depar Adjust Default Stream SCL Meander Valley Require Group Type12 Type3 ture ment Buf CL noMCL CL Toe VW DefaultYY Y Y a b c d e N DefaultYN Y N f g h i
14. ates contribution of the lower Southerly valley wall buffer to the stream corridor resulting from Step 7 The area is shown is that part of the buffer from Step 6 that falls on the opposite side of the stream centerline The contribution of upper northerly valley wall buffer to the stream corridor is shown on the right below Valley Wall Valley Walls Valley Wall Buffer Areas Contributing Valley Wall Buffer to Stream Corridor Areas Contributing to Stream Corridor Step 8 The following figure illustrates the combination of all of the contributing buffers from Step 5 and the two contributing valley wall buffers from Step 7 defining the composite buffer resulting from Step 8 Valley Walls Meander Centerline Surface Water Centerline SGAT Version 3 VT Agency of Natural Resources H 26 Revision December 10 2003 Development of Stream Corridor Buffers in Step 09 Step 9 As show below the composite buffer resulting from Step 8 is clipped to the sub watershed boundary This is performed to prevent overlapping stream corridors forming at sub watershed boundaries and to ensure that subsequent data LcLu and soils is properly calculated for a given sub watershed reach Step 10 It is possible that certain configurations of the features buffered will result in gaps or holes left in the composite buffer This could occur for example in very broad valleys or if the meander centerline or st
15. ble the sensitivity class is used to group stream types based upon similar characteristics Stream Group Sensitivity Class VL Very Low to Low LW Low to Moderate MD Moderate to High HI High to Very High VH Very High to Extreme EX Extreme The column under Stream Group represents the values for the field StrmGroup as used in defining a stream corridor via a buffer reference table These values may be used in matching data entered by a user during a geomorphic assessment to a key in a buffer reference table As a result the values must be consistent between those used during the assessment and the development of the buffer reference tables SGAT Version 3 VT Agency of Natural Resources H 3 Revision December 10 2003 Development of Stream Corridor Buffers in Step 09 Departure from Reference Stream Type Whether the existing stream type is a departure from reference stream type is at present a Yes No data element Major Channel Adjustment Whether a major channel adjustment is in progress is at present a Yes No data element Valley Slope The following table for Valley Slope categorizes streams using a range of valley slopes Valley Slope Group Designation Slope Range a Very Steep gt 4 b Moderate to Steep gt 2 but lt 4 c Moderate to Low gt 0 5 but lt 2 c Gentle lt 0 5 The column under Group represents the values used for the field VSGr
16. cluded and that the table can be edited The following error messages will be issued if problems are encountered Revu Incorrect dBase File Format D Table StrmCorDat dbf does not have one more of the required fields File selection ignored Revu dBase File Cannot be Edited another application or marked as Read Only File selection Table StrmCorDat dbf cannot be edited Table in use by ignored If no error conditions are detected the following fields will be created in the reach point theme O StrmType11 Stream Type The first character of the stream types assigned during the Phase l StrmType12 Stream Type The second character of the stream types assigned during the Phase l StrmType13 Stream Type The third character of the stream types assigned during the Phase I StrmGroup1 Stream Group The group designation e g Sensitivity Class assigned during the Phase I VSGroup The valley slope group assigned during the Phase based upon the slope of the valley line for the reach VCGroup The valley confinement group assigned during the Phase I based upon the confinement of the valley for the reach StrmType21 Stream Type The first character of the stream types assigned during the Phase Il SirmType22 Stream Type The second character of the stream types assigned during the Phase Il SirmType23 Stream Type The third character of the stream types assigned during the Phase IlI Sir
17. de the stream corridors may be different Warning The Phase Il assessment effort will most likely not be performed for all reaches For those reaches in which the assessment was not conducted the stream type imported will have a value composed of dashes In Step 09 any reach having a stream type value of dashes will not have a stream corridor created This will result in stream corridors being created only for those reaches in which a Phase Il effort was conducted This will only affect the FD Option 2 Floodway Determination Option 2 application SGAT Version 3 VT Agency of Natural Resources H 19 Revision December 10 2003 Development of Stream Corridor Buffers in Step 09 Steps used to Create the Stream Corridor from Component Buffers The figures in this Appendix are provided for the purposes of documenting the process data and themes used in creating the stream corridor buffer in Step 09 The essential themes are as follows Sub watershed delineation polygons Valley wall delineation polygons Meander centerline polyline and Stream Centerline polyline Note Refer to Appendix E of the Vermont Phase 1 Stream Geomorphic Assessment Handbook and Floodway Determination Technical Guidance for scientific concepts and reasoning behind the development of the stream corridor The following figure illustrates the basic themes used in creating Stream Corridor Buffers Valley Walls Meander Ce
18. dicate this buffer is not to be used Channel width multiplier for defining a secondary buffer based upon the stream SCLnoMCL N 6 3 centerline when a meander centerline is not present A value of zero will indicate this buffer is not to be used Channel width multiplier for defining a buffer around the meander centerline Buffer distance will be the value of this field multiplied by the channel width and will represent distance on either side of the meander centerline with a total width of twice the product A value of zero will indicate this buffer is not to be used If no meander centerline feature is present for a given reach no meander centerline buffer will be created See also RequireVW below Channel width multiplier for defining a buffer from the valley toe in the direction toward the stream centerline Buffer distance will be the value of this field multiplied by the channel width and will represent distance on the side of the valley toe towards the stream centerline Buffers will be created using the left and right valley walls A value of zero will indicate this buffer is not to be used If no valley toe feature is present for a given reach no valley toe buffer will be created Permissible values are Y Yes or N No defining whether the valley toe feature must be present for a given reach to perform buffering of the meander centerline If the value is Y Yes buffering of the meander centerline will only be performed
19. e Adjustment DefaultBuf StreamCL SCLnoMCL MeanderCL ValleyToe RequireVW Low 0 5 N Mod 0 5 2 2 4 N Mod Y Y 0 5 3 3 6 N Mod N Y 0 5 3 3 6 N High 0 5 3 3 6 N 0 5 3 3 6 N To summarize e Selecting an application on the Setup Dialog establishes the buffer reference table that will be used in Step 09 Refer to the table on page H 5 e Inthe buffer reference table the presence of the fields o VCGroup and VSGroup indicate that Phase data and decision tree will be used o Adjustment and Departure indicate that Phase II data and decision tree will be used Let s take a close look at a single record in a buffer reference table Each record contains the buffering parameters to be used in creating a stream corridor The method for determining which record to be used or the decision tree will be presented subsequently SGAT Version 3 VT Agency of Natural Resources H 9 Revision December 10 2003 Development of Stream Corridor Buffers in Step 09 Buffering Parameters Each record in a buffer reference table contains the following fields DefaultBuf default buffering specifications used with the stream centerline StreamCL stream centerline buffering specifications MeanderCL meander centerline buffering specifications SCLnoMCL buffering specifications used with the stream centerline when no meander centerline is present ValleyToe buffering specifications for toe of valley wall and Require VW specificat
20. e to be used in Step 09 has been identified To establish the application to be used one first identifies the user type and then the application on the Setup Dialog The upper area of that dialog is shown below Stream Geomorphic Assessment Tools er 3 00 0 Setup Dialog Primary Functions User Type Watershed Group x Application SGA v User Access Type and Application Designation Select Application for which SGAT is to be used The user type must be established first because certain applications are restricted to certain user types Whenever the user type or application are changed on the Setup Dialog the selected values are entered into the system table named SysSystem dbf That table maintains the currently selected values Thus when you exit the Tools extension and subsequently re enter the extension the user type and application last selected will remain known In certain circumstances the user type and application may be pre defined and locked In these cases one will not be allowed to alter either setting This in turn pre determines the buffer reference table that will be used for determining stream corridors via Step 09 This is done so that those who will only be using one specific application such as stream geomorphic assessment will not have to be confronted with decisions that are not relevant to their work The records of the SysApps db table must be manually edited to
21. earlier the buffer resulting from Step 3 is allowed to extend laterally beyond the valley walls while the buffer resulting from Step 4 is constrained clipped off by the valley walls This can be seen in the figure below by the stair step appearance at the valley wall of the easterly portion of the buffer resulting from this step Valley Walls Meander Centerline Surface Water Centerline SGAT Version 3 VT Agency of Natural Resources H 24 Revision December 10 2003 Development of Stream Corridor Buffers in Step 09 Step 6 The figure below to the left is the buffer for the southerly valley wall and to the right is the northerly valley wall resulting from Step 6 These buffers are to be constrained by the valley wall delineation As a result the buffers shown below have been clipped off by the valley walls It is important to note that in more confined valleys the buffer created for one valley wall may extend laterally beyond the opposite valley wall Since these buffers are to be constrained by the valley walls the area extending beyond the opposite valley wall is also clipped off The following illustrates the valley wall buffers resulting from Step 6 in the same figure The overlap of the buffers is not illustrated SGAT Version 3 VT Agency of Natural Resources H 25 Revision December 10 2003 Development of Stream Corridor Buffers in Step 09 Step 7 The following on the left illustr
22. ed to illustrate the concepts implemented for Floodway Determination Option 2 and therefore Phase Il data Assume that there are six unique stream types Y1 Y2 Y3a Y3b and Z1 Keep in mind that experience may lead to the definition of new stream types These stream types are associated with stream sensitivity classes as follows Y1 and Z1 are Low Y2 and Y3a are moderate and Y3b is high Each stream type may be associated with a departure from reference stream type and may be experiencing major adjustment To provide the capability where each unique combination of the data elements could be assigned unique buffering criteria would require the definition of 72 records 6 stream types 3 sensitivity classes 2 departure conditions 2 major adjustment conditions Experience however indicates that only a few records are required The following table exemplifies a set of records Key Strm Strm Strm Depar Adjust Default Stream SCL Meander Valley Require Group Type12 Type3 ture ment Buf CL noMCL CL Toe WwW Y3bYY Y3 b Y Y 0 2 5 3 4 8 N Y3 Y3 0 2 5 3 3 8 N Mod Mod 0 2 5 3 3 6 N Default 0 2 5 3 2 5 N In the above example note that different buffering requirements not intended to be realistic are identified in each record The following describes each record Record 1 pertains to stream type Y3b Y3 with slope modifier appended when it is undergoing Major Adjustment and is a dep
23. ed using the stream centerline as the selected feature The development of this buffer will be dependent upon the value of the SCLnoMCL field in the buffer reference table being used If that value is zero no secondary buffer will be created If however the value is non zero then it will be used as a channel width multiplier and multiplied by the channel width to form the buffer distance on each side of the stream centerline This buffer will not be constrained to fall within the valley walls and therefore may extend laterally beyond the valley walls This step is not illustrated The following represents the decision tree implemented for determining whether the secondary buffer on the stream centerline is to be created Decision Tree for Buffering of Meander Centerline RequireVW Create MCL Buffer Clip to VW MCL buffer created NO MCL a MCL CW Multiplier gt 0 MCL Present VW Present NO MCL buffer S created pe MCL CW Multiplier gt 0 SCLnoMCL MCL Present SCLnoMCL CW Multiplier gt 0 Create MCL Buffer Clip to VW Create MCL Buffer Clip to VW CW lt lt Multiplier gt 0 NO MCL buffer created Create secondary SCL Buffer SGAT Version 3 Revision December 10 2003 NO MCL oa H 23 Decisions shown on horizontal lines with positive true conditions taking the upper b
24. ering criteria found Tad Found Buffering criteria found Key TT Buffering criteria found Found 7 A rp h 485 Moy By een Buffering criteria found ML Shy Found bo oy Mp o Yo ep Key Components ay So y Key CCC TT Stream Type ey th Found Buffering criteria found s Slope Modifier Key Default DM n Found Buffering criteria found M Major Adjustment value D Stream Departure value Key Default Found CCC Sensitivity Class or group designation Decisions shown on horizontal lines with positive true conditions taking the upper blue branch and negative conditions taking the bottom magenta branch Rectangles at end of branch es identify Error J procedures values to be used as a result of See coe ALL decisions made SGAT Version 3 VT Agency of Natural Resources H 15 Revision December 10 2003 Development of Stream Corridor Buffers in Step 09 Import of Phase I Phase II Data Thus far the discussion has been oriented around the development and use of the buffer reference tables The data elements required to access these tables however will not be available until a set of export import procedures has been executed Until the export import procedures have been run the only stream corridor development that can occur will be for the stream geomorphic assessment application and Floodway Determination Option 1 And in those cases all stre
25. hat each buffer reference table contain a record with a key value of Default The presence of such a record in each table is verified during the initialization procedure for the Tools extension If no such record is found in any buffer reference table an error message is issued and access to the Tools extension is prevented The preceding has the following implications 1 The data collected from the Phase and Phase II assessments is entered and maintained in a Microsoft Access data base and must be transferred into the attribute table for the Reach Point theme The approach for performing this task is described in a subsequent section of this Appendix 2 The pre determined order in which keys are constructed must be carefully defined and followed in both the development of buffer reference tables and the search for a matching key in the Tools The pre determined order in which keys are to be constructed is defined through the decision trees shown on the following two pages When designing or implementing changes to records within a buffer reference table review the decision tree with respect to the order in which combinations of the data elements are used to form a Key The order from left to right represents the most sensitive and specific cases to the most general Identify where a new record should fit in the hierarchy Then take time to see if inserting that record will affect others and if so what changes or new records
26. ich will exist in the SysData directory into the BuffrTable field The format contents and use of buffer reference tables are described subsequently in this Appendix If the new application pertains to stream geomorphic assessment and is to be available to watershed groups enter a value of one 1 in the AccessLv field Otherwise enter a value of two 2 2 lt _ DA lt oOo a Once the editing has been completed and the referenced buffer reference table is copied or moved to the SysData directory the Tools extension will list the application on the Setup Dialog While in that dialog select the application After that the associated buffer reference table will be used during processing of Step 09 Buffer Reference Tables As described in the preceding section a buffer reference table is associated with each application A buffer reference table contains records that define the parameters to be used in creating buffers around specific features Features refer to the stream centerline meander centerline and valley walls During the development of stream corridors in Step 09 specific records in these tables will be retrieved based upon assessment data for a given reach There are two formats that may be used in defining a buffer reference table The format should be selected based upon the source of data to be used in defining the stream corridor for a reach The sources are o Stream Geomorphic Asses
27. idth and the resultant stream corridor will also increase laterally as one proceeds downstream Valley Walls Meander Centerline Step 1 Surface Water Centerline The figure to the right illustrates the default buffer This buffer is created using a specific distance of 100 feet to each side of the stream centerline and is not dependant upon the channel width This buffer is allowed to extend laterally outside of the valley walls Step 2 Valley Wall Meander Centerline The buffer shown to the right is the Surface Water basic stream corridor This buffer is Centerline created using the stream centerline with the buffer distance calculated as 2 5 times the channel width For this reach the channel width is 91 67 feet and the valley width has been calculated via Step 07 as 1426 43 feet As with the default buffer this buffer is allowed to extend laterally outside of the valley walls SGAT Version 3 VT Agency of Natural Resources H 21 Revision December 10 2003 Development of Stream Corridor Buffers in Step 09 Step 3 To the right is the Union i e combination of Step 1 and Step 2 of the default and stream corridor buffers In reaches such as the one shown the basic stream corridor will always be larger In upland reaches however the default buffer may be the more dominant buffer As indicated earlier the resultant buffer is allowed to extend laterally outside of the valley walls
28. ion that valley walls be present in order for any buffering to be performed on the meander centerline The above define the buffering parameters that are to be applied for a given reach The field Require VW is used to differentiate between policies used in calculating the stream corridor for stream geomorphic assessment from those for floodway determination For stream geomorphic assessment at present a buffer for the meander centerline is not created if valley walls are not present for the reach As a result all records in the buffer reference table for the stream geomorphic assessment will contain the value of Y for this field Values for this field will be N for all other applications The Tools has been developed such that stream corridor definition is composed of merging component buffers created using the following features Default Buffer fixed distance from stream centerline Stream Centerline multiple of channel widths Meander Centerline multiple of channel widths Valley Wall toe multiple of channel widths The Tools will develop each of the component buffers in accordance with the criteria in the buffer reference table for the designated application In addition the following rules will apply 1 Per the value for the field Defau tBuf a default buffer will or will not be created If the value is zero no default buffer will be created Otherwise a buffer equal to the value which represents a fixed d
29. is buffer is not to be used MeanderCL N 6 3 Channel width multiplier for defining a buffer around the meander centerline Buffer distance will be the value of this field multiplied by the channel width and will represent distance on either side of the meander centerline with a total width of twice the product A value of zero will indicate this buffer is not to be used If no meander centerline feature is present for a given reach no meander centerline buffer will be created See also RequireVW below ValleyToe N 6 3 Channel width multiplier for defining a buffer from the valley toe in the direction toward the stream centerline Buffer distance will be the value of this field multiplied by the channel width and will represent distance on the side of the valley toe towards the stream centerline Buffers will be created using the left and right valley walls A value of zero will indicate this buffer is not to be used If no valley toe feature is present for a given reach no valley toe buffer will be created RequireVW Permissible values are Y Yes or N No defining whether the valley toe feature must be present for a given reach to perform buffering of the meander centerline see MeanderCL above If the value is Y Yes buffering of the meander centerline will only be performed if the valley toe feature is present If the value is N No then buffering of the meander centerline will be
30. istance on either side of the stream centerline will be created The value of the DefaultBuf field is to be in feet 2 Ifa given feature stream centerline meander centerline or valley wall is not present for a given reach that or those component buffer s will not be created 3 If the value in the buffer reference table for a component buffer is zero 0 that component buffer will not be created 4 Where a meander centerline is not present a second buffer will be created on the stream centerline where the channel width multiplier has been supplied in the field SCLnoMCL If however the value for the field SCLnoMCL is zero no buffer will be created 5 Ifa given feature is present and a non zero value is found in the buffer reference table for a component buffer a buffer will be created The value in the buffer reference table will be multiplied by the channel width for the reach to define the buffer distance The buffer distance represents the distance from the feature to the edge of the buffer i e on either side Note The default buffer is a fixed distance as specified in 1 above SGAT Version 3 VT Agency of Natural Resources H 10 Revision December 10 2003 Development of Stream Corridor Buffers in Step 09 6 Per the field Require VW in the reference table a buffer for the meander centerline will or will not be created if valley walls are not present 7 If a component buffer is created using the
31. ivity Class grouping of stream types e Valley slope and e Valley confinement During the Phase assessment process the following data may be captured for each reach e Stream type revision from or more detailed stream typing than conducted in Phase h e Sensitivity Class revision from Phase grouping of stream types e Whether the existing stream type represents a departure from the reference stream type e Whether a major channel adjustment is in progress The above data is entered into and maintained in the Phase I II Access Data Base on a reach basis for the watershed being assessed A brief description of the data elements follows Stream Type The stream type is a concatenation of up to three characters that generally defines the reach as described below Example C2b where C first character defines the class associated with the reach The class indicates certain characteristics of the reach such as entrenchment width slope etc 2 second character defines the dominant sediment material This character may not always be present as part of the stream type identifier especially during Phase assessment b third character is a slope modifier and categorizes the slope of the channel when the slope is different than that associated with the class This modifier may not always be present as part of the stream type identifier Stream Group Sensitivity Class As illustrated in the following ta
32. lope Modifier CF Confinement Group VS Valley Slope Group CCC Sensitivity Class or group designation Decisions shown on horizontal lines with positive true conditions taking the upper blue branch and negative conditions taking the bottom magenta branch Rectangles at end of branch es identify procedures values to be used as a result of ALL decisions made SGAT Version 3 H 14 Revision December 10 2003 Buffering criteria found Key Default Found i Ero 3 VT Agency of Natural Resources Development of Stream Corridor Buffers in Step 09 Decision tree for finding record in Buffer Reference Table for Floodway Determination Option 2 The decision tree identifies the hierarchical search To use the diagram start on the implemented to find an appropriate record in a very left and follow a decision Buffer Reference Table based upon stream type path to the far right where the TT slope modfier in stream type s stream buffering criteria to be used have departure D major adjustment M and sensitivity been identified Class or other stream type grouping CCC If no record is found using the variations of those values an attempt will be made to find a Default Butfeing crea found record with the stream departure and major adjustment values If that fails the Default record will be used If there is no Default record an error Key TTsDM fanaa condition is raised Found an Found Buff
33. lue branch and negative false conditions taking the bottom magenta branch RequireWV value is obtained from the buffer reference table for each reach A value of Yes requires that valley walls be present If valley walls are not present for a given reach buffering of the meander centerline is not be be performed VW Present identifies the fact that a given reach point and its upstream neighboring reach point are contained within a polygon representing valley walls i e valley walls are present for the reach MCL Present identifies the fact that a meander centerline is present for the reach This centerline need not pass completely through the reach i e it may extend only partly into a reach MCL CW Multiplier gt 0 The channel width CW multiplier for the meander centerline MCL is obtained from the buffer reference table for a given reach If the value is zero no buffer will be created using the meander centerline SCLnoMCL CW Multiplier gt 0 The channel width CW multiplier for the SCLnoMCL is obtained from the buffer reference table for a given reach This value is intended to be used to create a buffer around the stream centerline if no meander centerline is present If the value for SCLnoMCL is zero no buffer will be created VT Agency of Natural Resources Development of Stream Corridor Buffers in Step 09 Step 5 The following is the Union i e combination of Step 3 and Step 4 As stated
34. mGroup2 Stream Group The group designation e g Sensitivity Class assigned during the Phase Il Adjustment Whether a major channel adjustment is in progress Values will be Yes or No Departure Whether the existing stream type is a departure from the Reference Stream Type Values will be Yes or No The data from the import table named StrmCorDat dbf is then transferred into the attribute table for the reach point theme SGAT Version 3 VT Agency of Natural Resources H 18 Revision December 10 2003 Development of Stream Corridor Buffers in Step 09 Following import the values transferred from the import table will be displayed for each reach These values will include dashes to identify data not entered into the Microsoft Access data base Upon successful completion of the mport operation the Export function will include the above data fields In addition one can then create stream corridors for all applications with use of the data imported Warning It is possible that running Step 09 for the SGA Stream Geomorphic Assessment Phase and FD Option 1 Floodway Determination Option 1 applications following the import operation will create different stream corridors This will be dependent upon the structure of the buffer reference table associated with these applications At present the stream corridors will be the same however if modifications to related buffer reference table are ma
35. meander centerline and the valley walls are present for that reach component buffer will be constrained to fall within the toes of the valley walls l e the meander centerline buffer will be clipped off by the valley wall polygon if present 8 The final buffer will be the composite sum of the component buffers created as per the corridor delineations described in the assessment protocols Appendix E or the VTDEC Floodway Determination Technical Guidance 9 Any holes formed within the composite buffer will be removed to provide complete coverage A graphic example of the procedure used in developing the component buffers and the merging of those to form the stream corridor is provided at the end of this Appendix Accessing a specific record in a Buffer Reference Table The buffer reference tables and the logic or decision tree to access a specific record have been designed to permit the use of buffering parameters for very specific conditions and or configurations of a reach These conditions and configurations are identified during the Phase I and Phase Il assessment efforts If Phase data is being used certain combinations of the following data elements can be used to define buffering parameters Stream Type Stream Type slope modifier Valley Confinement Group Valley Slope Group and Stream Group e g sensitivity class If Phase II data is being used certain combinations of the following data elements can be
36. nterline Surface Water Centerline Valley Line Step 07 Note The valley line developed in Step 07 is shown for illustrative purposes only It is not used in the process for creating stream corridors Creating a stream corridor involves a ten step process of creating individual buffers around a specific feature stream centerline meander centerline or valley wall clipping a previously developed buffer to a specific feature and or combining previously developed buffers to form a composite buffer The steps are briefly described and illustrated in the following SGAT Version 3 VT Agency of Natural Resources H 20 Revision December 10 2003 Development of Stream Corridor Buffers in Step 09 Please note In this document references are made to the use of specific numbers for creating the individual component buffers These numbers identify a specific distance or channel width multiplier and are used for illustrative purposes only The actual numbers used in the implementation of the Stream Geomorphic Assessment Tools Tools may be different The channel width is calculated in Step 08 of the Tools A channel width multiplier is a number that is multiplied by the channel width to determine a buffering distance Since the channel width is based upon the drainage or watershed area above a reach point the channel width will increase as one proceeds from upstream reaches downstream Those buffers dependant upon the channel w
37. oup as used in defining a stream corridor via the buffer reference table Valley Confinement The following table for Valley Confinement categorizes streams using a range of confinement ratios valley width divided by channel width Valley Confinement Group Code Designation Valley Width Channel Width Ratio 1 NC Narrowly Confined gt 1and lt 2 1 SC Semi Confined gt 2and lt 4 2 NW Narrow gt 4and lt 6 3 BD Broad gt 6and lt 10 3 VB Very Broad gt 10 oe eee on The column under Group represents the values used for the field VCGroup as used in defining a stream corridor via the buffer reference table When using the Stream Geomorphic Assessment Tools Tools for floodway determination and for Phase of stream geomorphic assessment the data elements described above serve as the foundation for determining the stream corridor for each reach Step 09 in Tools The tables and information provided in this section were current as of the date of writing this manual For current and additional information on the data elements refer to the Stream Geomorphic Assessment Handbooks available from River Corridor Management Section Water Quality Division Department of Environmental Conservation Agency of Natural Resources 103 South Main Street Building 10 North Waterbury VT 05671 0408 SGAT Version 3 VT Agency of Natural Resources H 4 Revision December 10 2003 Development of
38. performed independent of whether a valley toe feature is present Note The values in fields StrmType12 StrmType3 VCGroup and VSGroup are not used within the Tools These fields however must be present in the buffer reference table The Tools uses the existence of fields VCGroup and VSGroup to specify the use of the buffering decision tree for Phase data i e for Assessment and Floodway Determination Option 1 Using Phase I data for a given reach the decision tree identifies which record to use for obtaining the buffering parameters In addition these fields provide documentation for the value of the Key field If any of these fields are not used in forming the value of the Key field the value of the field should be left blank otherwise adhere to the format described in the table above SGAT Version 3 VT Agency of Natural Resources H 7 Revision December 10 2003 Development of Stream Corridor Buffers in Step 09 Format of Buffer Reference Table for Floodway Determination Option 2 Field Name Format Description Format of Key field used for Floodway Determination Option 2 Various concatenations which may include values from StrmGroup StrmType Departure and Adjustment Refer to descriptions of these fields below and the discussion in the text regarding how a specific value is to be created and how a record will be retrieved A value of Default designates a default record which will be used if no other
39. r of records Each record is identified by a key and the key is a reflection of certain conditions that categorize a reach For example a key may reflect a specific stream type stream group designation e g sensitivity class valley confinement group and valley slope group SGAT Version 3 VT Agency of Natural Resources Hel Revision December 10 2003 Development of Stream Corridor Buffers in Step 09 Each record contains the parameters to be used in creating a stream corridor for reaches whose conditions are reflected in the key A specific hierarchy is implemented to combine the conditions of a reach in an attempt to find a record with a matching key in the buffer reference table This hierarchy is in the order of the most specific or highest sensitivity conditions to the most general The most general conditions are reflected in a record containing a key value of Default which reflects the general parameters for creating a stream corridor for the application associated with the buffer reference table Note All buffer reference tables must have a record containing a key with a value of Default The buffering parameters in this record will be used in the absence of finding any other record that meets the conditions of the reach Import of Phase I Phase Il Data The data necessary to define the conditions of a reach are not inherent in the calculations or derivation of data within the Tools This data is however
40. ream centerline makes a significant loop outside of the valley walls This step reviews the composite buffer and removes any holes island polygons The result is the stream Die yy And That s all folks JE gt SGAT Version 3 VT Agency of Natural Resources H 27 Revision December 10 2003
41. sensitivity class It can be used to relate stream types in any manner It is important however that whatever values are assigned to StrmGroup be consistent between field data collection and development of the buffer reference tables described herein Each buffer reference table must have a record with a Key value of Default This record will contain the general buffering parameters to be used if no other record can be found to match the conditions of a reach There are three buffer reference tables distributed with the Tools SysBufSGA dbf for use with the stream geomorphic assessment Phase based upon Phase I data SysBufOpt1 dbf for use with the Floodway Determination Option 1 based upon Phase data and SysBugOpt2 dbf for use with Floodway Determination Option 2 based upon Phase II data At the time of writing this Appendix the content of the buffer reference tables is shown in the following Buffer Reference Table for the Phase 1 Stream Geomorphic Assessment StrmGroup StrmType12 StrmType3 VCGroup VSGroup DefaultBuf StreamCL SCLnoMCL MeanderCL ValleyToe RequireVW 100 2 5 4 8 Y Buffer Reference Table for Option 1 of the Floodway Determination Procedure StrmGroup StrmType12 StrmType3 VCGroup VSGroup DefaultBuf StreamCL SCLnoMCL MeanderCL ValleyToe RequireVW 0 5 3 3 6 N Buffer Reference Table for Option 2 of the Floodway Determination Procedure StrmGroup StrmType12 StrmType3 Departur
42. sment Phase I or o Stream Geomorphic Assessment Phase Il The differences in the two formats are the presence of the fields o VCGroup and VSGroup for use with Phase data OR o Adjustment and Departure for use with Phase IlI data Only one of the above sets of fields may exist in a buffer reference table All other fields are identical in format and content The two formats for buffer reference tables are provided on the following pages SGAT Version 3 VT Agency of Natural Resources H 6 Revision December 10 2003 Development of Stream Corridor Buffers in Step 09 Format of Buffer Reference Tables for Stream Geomorphic Assessment Phase I and Floodway Determination Option 1 Field Name Format Description Key C 24 Format of Key field used for Stream Geomorphic Assessment and Floodway Determination Option 1 Various concatenations which may include values from SirmGroup StrmType VCGroup and VSGroup Refer to descriptions of these fields below and the discussion in the text regarding how a specific value is to be created and how a record will be retrieved A value of Default designates a default record which will be used if no other key is matched StrmGroup Group designation for stream type e g sensitivity class For permissible values refer to the column Stream Group and its definition in the table presented earlier StrmType12 Stream Type designation First and second charac
43. ters identifying Stream Class must always be present and Dominant Sediment Material if not present a dash must be used StrmType3 C 1 Stream Type designation Third and optional character identifying Slope Modifier if not present a dash must be used VCGroup C 3 Valley Confinement Group designation For permissible values refer to the column Group and its definition in the table for Valley Confinement presented earlier VSGroup C 3 Valley Slope Group designation For permissible values refer to the column Group and its definition in the table for Valley Slope presented earlier DefaultBuf N 6 0 Fixed distance for creating a default buffer around the stream centerline Value of this field represents a fixed distance on either side of the stream with a total width of twice the value A value of zero will indicate this buffer is not to be used StreamCL N 6 3 Channel width multiplier for defining a buffer around the stream centerline Buffer distance will be the value of this field multiplied by the channel width and will represent distance on either side of the stream with a total width of twice the product A value of zero will indicate this buffer is not to be used SCLnoMCL N 6 3 Channel width multiplier for defining a secondary buffer based upon the stream centerline when a meander centerline is not present A value of zero will indicate th
44. ts Application Through an application one establishes a linkage to a buffer reference table In effect an application can be associated with one and only one buffer reference table A buffer reference table however can be associated with any number of applications Buffer Reference Table A buffer reference table contains records that define the parameters to be used in creating buffers around specific features Features refer to the stream centerline meander centerline and valley walls There are two versions of the buffer reference table that identify the source of data to be used in defining the buffer for a reach The sources are o Stream Geomorphic Assessment Phase I or o Stream Geomorphic Assessment Phase Il Buffer Parameters Each record in a buffer reference table defines parameters to be used in buffering features These parameters establish the requirements for buffering as follows 1 Whether a specific feature will be buffered 2 The width of the buffer to be used for a specific feature 3 Whether a default buffer of a specified with around the stream centerline is to be used 4 Whether an alternate buffer using the stream centerline is to be developed when a meander centerline is not present and 5 Whether to ignore buffering the meander centerline if valley walls are not present Accessing a specific record in a Buffer Reference Table A buffer reference table can be composed of any numbe
45. used to define buffering parameters Stream Type Stream Type slope modifier Whether a major channel adjustment is in progress Whether the existing stream type is a departure from the reference stream type and Stream Group e g sensitivity class Note Remember the application selected on the Setup Dialog identifies the buffer reference table to be used The presence of the fields VCGroup and VSGroup in the buffer reference table establish the use of Phase Idata Or the presence of the fields Adjustment and Departure in the buffer reference table establish the use of Phase II data SGAT Version 3 VT Agency of Natural Resources H 11 Revision December 10 2003 Development of Stream Corridor Buffers in Step 09 To create a buffer reference table that contained all possible combinations of the data elements would involve creating literally hundreds if not more records This would be cumbersome potentially error prone and difficult to manage Instead a hierarchical method has been implemented for designing the buffer reference tables and for accessing specific records in those tables The method implemented recognizes that e Only a few reach conditions represented by specific combinations of the data elements listed above require special consideration for buffering and e Flexibility is required to add or alter specific buffering requirements for any combination of the data elements as the needs dictate An example is us
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