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Limburg Soil Erosion Model USER MANUAL

1. e E 10new run el 9907 20nc un e Soli Il nuttest Type RUN File Size 445 KB ES E File name 9907 Ale und TT Une run T tm nun Dlm pu Files of type Run files run Cancel An example of a run file is given in the appendix It can be edited by hand but the variable names should not be edited because LISEM uses them to recognize the them Model options e No erosion runoff only all erosion calculations are skipped e Simulate main channels channel calculations are done additional maps are required e Channel infiltration ponded infiltration in channel using simple subtraction of a Ksat map The infiltration will stop if the storage given in mm is filled up Additional maps needed CHANKSAT MAP and CHANSTOR MAP NOTE this option does not work properly at the moment LISEM MANUAL version 2 x January 2 2002 51 Additional options A few parameters in LISEM do not need to be defined in a spatial way but as a single constant in the interface e Splash delivery ratio the relative amount of sediment that is splashed from the dry part of a gridcell to the wet part of a grid cell so that it can be transported The remainder of the splash sediment settles again as splash deposition e Manning s n grass strips a large Manning s n value is given here to simulate the friction of flow on a grass strip As the strip is generally smaller than a gridcell the surrounding Manning s n is given in the Manning
2. 6 2 4 Gully incision For each gridcell and timestep the processes above result in the water discharge Q kg m the corresponding gully width w m and the sediment discharge Qs kg The eroded mass of the soil is recalculated to a depth depending on the situation 1 Homogeneous soil only the depth d of the gully increases over the gully width w using the amount of flow detachment Df and the bulk density D of the soil d Df w dx D Note that these parameters are represented by maps that can be spatially variable only the depth is assumed homogeneous 2 Two layers in case the soil has a compacted layer with a higher cohesion e g a plough layer both the gully width and depth have to be adjusted In this case the gully often becomes shallow and wide because the sideways erosion is easier than the downward erosion This effect is not accounted for in the Q w relationship Thus the following system is devised if the depth of the gully reaches the second layer AND the water level in the gully still touches the first layer the flow detachment is divided over the walls and bottom of the gully as follows Df Ze wTM wm dx j 6 6 DI p GT CN wu ox where h is the water depth m Py is the wet perimeter m and Y and Y are the efficiencies based on the cohesions of the 17 and 2 layer The gully width w and depth d are increased according to Ww W Df fi ax p d d Dt jw dx p 6 7 The gully width cannot b
3. Subtraction of Ksat SE 2 3 1 Swatre Infiltration and soil water transport in soils are simulated by a solution of the well known Richards equation which combines the Darcy equation and the continuity equation E alae 2 4 e amp ES with K the hydraulic conductivity m s h the pressure matric potential m Q the volumetric water content mim z the gravitational potential or height above a reference level m t time s Using the soil water capacity C h d dh the slope of the soil water retention curve h the unsaturated flow equation is derived a Cz The Mualem Van Genuchten equations Mualem 1976 Van Genuchten 1980 can be used to predict the soil water retention curves and the unsaturated hydraulic conductivity which are needed to solve the equation above However LISEM does not use these relations directly but requires the user to define the water retention curves and the K h curves as tables The reasoning is that the measured curves hardly ever follow the Mualem Van Genuchten relations exactly but usually derivate near saturation of the soil Thus for the catchments soil profile types are defined and for each characteristic soil horizon and for each horizon tables with the measured K theta h relations are required The equations are solved by explicit linearisation using the so called Thomas tridiagonal algorithm see e g Remson et al 1971 The submodel operates with a vari
4. no3conv C data china 10m2 NO3conv map NutsNH4 nh4cont C data china 10m2 nh4cont map nh4solute C data china 10m2 nh4solut map nh4efficiency C data china 10m2 nh4eff map nh4sorp C data china 10m2 NH4sorp map nh4conv C data china 10m2 NH4conv map Nut sBD bulk C data china 10m2 bulkdens map Gully dem C data china 10m2 dem map gullyn C data china 10m2 gullyman map bulkdens1 C data china 10m2 bulkdens map gullydep C data china 10m2 soilDep2 map gullycoh C data china 10m2 coh2 map bulkdens2 C data china 10m2 bulkden2 map OutputNut outpsolut C data china res10m1 NPsol outpsus C data china res10m1 NPsus outpinf C data china res10m1 NPinf outnh4solut C data china res10m1 NNH4sol outnh4sus C data china res10m1 NNH4sus outnh4inf C data china res10m1 NNH4inf outNO3solut C data china res10m1 NNO3sol outNO3sus C data china res10m1 NNO3sus outno3inf C data china res10m1 NNO3inf outno3inf C data china res10m1 smul Output outrunoff C data china res10m1 ro outconc C data china res10ml1 cone outwh C data china res10m1 wh outrwh C data china res10m1 rwh outeros C data china res10ml1 eros outdepo C data china res10m1 depo OutputGul outguld CcC data china res10m1 guld outgulw C data china res10m1 gulw LISEM MANUAL version 2 x January 2 2002 64 outgula C data china res10m1 gula outgulf C data china res10m1 gulf outguldem C data china res10m1 dem OutputMC
5. IDs not necessarily sequential begin of file 1 O 0 1 O 2 Be O23 0 3 4 Lids 0 35 0 4 LG 6 1 0 95 1 8 S 0 d of le s NOTE LISEM assumes no logic in this table It will not check if a LAI of 6 is combined with a cover fraction of 0 7 2 3 Soil surface maps LISEM MANUAL version 2 x January 2 2002 38 This is a mixed catagory with maps that determine several processes infiltration surface storage overland flow veloccity In an agricultural catchment these maps are based on the landuse mostly or on a combination of landuse and soils Note that in a crop rotation cycle these values will change according to for instance crusting stage soil cover and tillage operation It also includes different tyoes of surface for which the processes are calculated separately N Surface resistance to flow expressed as Manning s n RR random roughness used here as the standard deviation of the micro relief heights do not use transformations to obtain a more normal distribution STONEFRC fraction of stones for which no splash erosion is calculated used only in this process CRUSTFRC fraction of the soil crusted On gridcells with non zero values the infiltration is calculated according to soil physical properties supplied by the user depending on the infiltration option chosen ROADWIDT width of imermeable roads for which no infiltration is calculated is used in all infiltration modules percalc m
6. Roughness RR Originally the depression storage in LISEM was based on the work of Onstad 1984 Using the same form of equation Kamphorst et al 2000 found R 0 88 n 221 MDS 0 243RR 0 010RR 0 012RRS 2 17 in which RR is the standard deviation of surface heights cm and S is the terrain slope They tested 6 different roughness indices but found that the standard deviation of the heights gave the best relation with MDS cm RR mm 0 10 20 30 40 50 MDS mm Figure 2 3 Non linear relation between RR and MDS Kamphorst et al 2000 based on 221 DEMs of 1m samples of a wide variety of surfaces The difference in sampling distance is caused by the application of different tools in the various countries Apart from the water available for runoff the roughness also determines width of the overland flow in LISEM Rather then taking the cell width dx the flow width and hydraulic radius is assumed linearly related to the fraction of ponded surface f in the cell The latter variable is related to the water depth at the surface h mm Jetten and De Roo 2001 fpa 1 exp ah 2 18 where a is an empirical factor between 0 04 and 1 8 for the roughness data set mentioned above Figure 2 shows that the factor a appears to be strongly related to RR in mm R 0 99 n 362 LISEM MANUAL version 2 x January 2 2002 14 a 1 406 RR 2 19 In which RR is in mm Figure 3 shows the increase o
7. Roughness on Overland Flow and Erosion PhD Thesis Catholic University Leuven p 137 181 Takken Beuselinck L Nachtergaele J Govers G Poesen J and Degraer G 1999 Spatial evaluation of a physically based distributed erosion model LISEM Catena 37 431 447 Van Deursen WPA and Wesseling CG 1992 The PC Raster Package Department of Physical Geography Utrecht University http www pcraster nl Wendt RC Alberts EE and Hjelmfelt AT Jr 1986 Variability of runoff and soil loss from fallow experimental plots Soil Sci Soc Am J 50 730 736 LISEM MANUAL version 2 x January 2 2002 59 11 PARTNERS The LISEM project is an ongoing project with input of many organizations The model is constantly improved hopefully and expanded in EU projects The following institutions contribute or have contributed to its development The development is in charge of Dr Victor Jetten ATT Victor Jetten Rudi Hessel and Daniel Universiteit Utrecht van der Vlag Department of Physical Geography Utrecht University NL Cees Wesseling PCRaster environmental software Coen Ritsema Jannes Stolte and Simone van Dijck Alterra NL RESEARCH Ad de Roo JRC IT NITRE pm ebe pir EUROPEAN COMM THON a vy Gerard Govers Jean Poesen Jeroen KATHOLIEKE UNIVERSITEIT Nachtergaele Ingrid Takken Laboratory for Exprimental ______ Geomorphology Catholic University Leuven BE The Erosion research group
8. SA H 1 Hago 5 1 10097 In itration mm f 30 Geck time P min be A200 aen amp O00 Sutsee storage mm 23 00 Peak time Q min npon l riaa Lem 2 S 152 Mean K N OF h 4 dl ch AT Peak dacharge US EOD pea we phe d Ze ey en ge ny EE Aen E Discharge outlet imm amu Mats bal EN ail cy 600 gie A BEEN REESEN app d Surface erosion Channel erosion 200 en S d 12527 Sp etschfont 23 278 Flow datach bot E D ER E 1335 06 Flon detach font 5 016 Deposition ee 100 up 120 130 440 150 460 170 180 __ 956 991 Deposition ton GEIT Sed in flow ton tine ent 0 763 Sed in ilo Don k 4 00345 Mase bal er Bart F O Outet M O Subt oa fF Q Sed E Sed Cone 34 50 Discharge l s 1045 1 Avg soil oes kg ha E ime Pimm Ois Sed g l ERIA Total LCE br 22 Total sotasan sis 179 000 0 000 36 33 8 04 Te ue 179 250 O 000 35 86 88 35 we arning Preparing Mepe ues 317 179 500 0 000 35 40 29 69 aggregate stability values Si 0 0 found for those cells 376 179 750 p opp 34 04 en o LOS is used for splash detachment 219 180 000 nmn aaen en ap Starting Loop Infiltration method using MAST DE nfitration mode 9 2 Hydrographs and sedigraphs Hydrographs and sedigraphs of up to three locations usually the outlet and two subcatchments can be stored as comma delimited files that is one of the standard input formats of MS Excel extension csv see example below The nam
9. Unite d Agronomie de Laon Peronne INRA FR Institut National de la Recherche Agronomique ld Roy Morgan John Quinton Cranfie EUROSEM Institute of Water and nab hdd ena Environment Silsoe College Cranfield Silsoe University UK re Dino Torri Lorenzo Borselli Institute K IT for Soil Genesis and Ecology CNR ees CONSIGLIO NAZIONALE DELLE RICERCHE GES IT nan 3 Limburg Waterboard Roer en Overmaas Roer en Gol A A xi University of Amsterdam Physical x Geography UNIVERSITEIT VAN AMSTERDAM LISEM MANUAL version 2 x January 2 2002 60 APPENDIX The Run file All options and map names of a single run are stored in the run file which can be edited by hand These include the names and option for all LISEM types wheeltracks multiclass sediment etc Where no values are found default values are used The rainfall file and maps are stored with their full path names so they are linked individually and can be found in different directories e g infiltration maps for different seasons LISEM for WINDOWS run file Work Directory WorkDir C data china Input Map Directory C data china 10m2 Table Directory C data china 10m2 Rainfall Directory C data china Rainfall file p9907201 txt Output Result Directory C data china res10m1 Main results file res csv Outlet 1 file o0outt csv Outlet 2 file o0out1 csv Outlet 3 file o0out2 csv Erosion map er map Deposition map dep map Sim
10. are maps that give a flux or status at regular intervals or at timesteps chosen by the user type a series of timesteps in minutes in the user defined area Simply select the type of output you want Depending on the LISEM types chosen additional timeseries can be stored second list in picture below The maps are stored in the result directory given by the user in the Start screen The maps are stored as name0001 250 name0006 500 etc for the output at 1 min 15 seconds or respectively 6 minutes and 30 seconds In order to have compatibility with PCRaster which stores the maps by timestep number name0000 001 name0000 002 etc the store as PCRaster timeseries can be chosen Additionally the runoff can be stored in unit discharge I sec m flow width es Lisem for Windows wersion 2 0 jE q Sam HR r D Start l Basic maps Multiclass Output maps Simulation Additional tme series output maps Deion conc sediment concerbation g CidatatchnavesIOm wh wale height on surface mm C data chinawes Um reh water height on surface mm L data chinawes Un ens erop kal Lkdatachnavesl Orel deposition kal CAdatachinaes Om 1 1 1 14 4 E smul suspended sediment Hus class 1 mul CC kdatahchnaues Dm ke ane suspended sediment tls class 2 mul C datechnaves Om MM sp suspended sediment Iu class 3 mul data chnauezl Um L smu suspended sediment Mux class 4 mul CAdstsc
11. between rills and ephemeral gullies can often be heard from the side of soil erosion modellers First of all the need for such a distinction with respect to erosion modelling originates from the fact that some erosion models explicitly state that they only cover interrill and rill erosion e g USLE What falls beyond the scope of these models needs to be named and defined since it requires another model or modelling approach Concerning the erosion processes involved modellers often raise that rills and ephemeral gullies can be treated equally since the initiation of both linear erosion features require soil material to be detached and transported by flowing water LISEM MANUAL version 2 x January 2 2002 26 6 1 2 Summer and winter gullies The cross section criterion can be applied to classify both so called summer gullies in central Belgium shallow and very wide and winter gullies deep and narrow as ephemeral gullies figure 2 Figure 6 2 winter left and summer gully right in belgium photos Takken KULeuven EUROWISE has to be able to simulate both types of gullies shallow gullies that widen when more erosion takes place and deep gullies that deepen and stay narrow The difference is caused by the soil cohesion in summer the situation is often a seedbed above a more compacted layer and sideways erosion encounters less resistance and costs less energy 6 2 Basic principles EUROWISE is an extension of LISEM a f
12. calculated with various sub models according to the data available Available are the Holtan Beasley and Huggins 1982 and Green and Ampt Li et al 1976 equations for one or two layers or the SWATRE model a finite difference solution of the Richard equation Belmans et al 1983 Feddes et al 1978 The latter option includes vertical soil water transport and the change of matric potential in the soil during a rainfall event which can be examined by the user The input is in the form of maps with soil hydrological properties such as initial moisture content porosity and saturated conductivity For each layer maps are defined In case of the Richards equation a map with soil profile types is linked to a series of tables with values for humidity 8 matrix potential y and hydraulic conductivity K LISEM MANUAL version 2 x January 2 2002 8 The choice of infiltration model is mostly governed by the type of data available and the experience of the user It should be noted that the models do not give the same results Since initial water content and hydraulic conductivity are among the most sensitive input parameters of LISEM De Roo et a 1996b Jetten et al 1998 re calibration is advisable when a different infiltration model is used Currently the following models are available Swatre finite difference approximation of the Richards equation Holtan as in the Answers model Green and Ampt for 1 and 2 layers Morel and Seytoux
13. deposition in channels is treated in the same way as these processes on land There is no separate detachment equation LISEM although the stream power concept was initially developed for rills The same formulas are used but with the hydraulic radius velocity discharge and transport capacity are based on channel maps for corss sectional shape bed gradient and manning s n The detachment efficiency is calculated with the channel cohesion LISEM MANUAL version 2 x January 2 2002 A LISEM WHEELTRACKS to be done 4 LISEM MULTICLASS to be done 5 LISEM NUTRIENTS to be done 22 LISEM MANUAL version 2 x January 2 2002 23 6 LISEM GULLIES EUROWISE 6 1 Introduction In the MWISED project EU ENV4 CT97 0687 Modeling Within Storm Erosion Dynamics LISEM was extended to cope with the incision and formation of ephemeral gullies The model was presented under the name EUROWISE which is used here EJROWISE is synonym to LISEM gullies EUROWISE was designed not to need much more data for gully incision than the original LISEM Incision can be modelled in a physically deterministic way by using shear stress of the flow along the sides and bottom of the gully and compare it to the shear strength of the profile This would require a complete knowledge of the soil cohesion and variation of cohesion with depth and the capability of simulating the flow conditions in detail Although this can be done technically such a model is very dif
14. material The pick up rate for cohesive soil therefore needs to be reduced by a coefficient whenever C is less than T By definition Yis 1 deposition takes place i e when C is larger than T and when erosion takes place it is calculated as Rauws and Govers 1988 Y Umin Ue 1 0 89 0 56Coh 2 31 in which us and Umn are the critical shear velocity and the minimum critical shear velocity om SL and Coh is the cohesion of the wet soil determined with a Torvane kPa Cohesion by plant roots can be accounted for in LISEM by a second cohesion map that is added to the soil cohesion Note that dx is added because the unit length of a spatial element in a raster environment becomes the grid cell size The transport capacity of overland flow is modeled as a function of unit stream power Govers 1990 Tc d c w w 2 32 in which T is the volumetric transport capacity kg m 5 is the material density 2650 kom is the stream power calculated as flow velocity energy slope and w is the critical stream power defined by Govers 1990 for a fairly wide range of materials to be approximately 0 4 cm s c and d are experimental coefficients depending on the median texture d50 of the material This equation describes the transport capacity in rills In LISEM equation 9 becomes with V in m s and the sine of the slope S Tc 2650 c VS100 0 4 2 33 Note that currently LISEM does not distinguish in its algorithms
15. to the soil profile for wheel tracks The area where tracks are present are given in WHEELWID MAP Note that there are more maps to define wheeltracks HEADOUT MAP map with up to four cells numbered 1 to 4 de rest having value 0 When the option matric output is checked in the infiltration options of the input menu an ASCII table with matric potential for each layer at each timestep is created INITHEAD 001 INITHEAD 020 initial matric potential for each layer if for instance you have defined 6 layers in PROFILE INP there are 6 maps 001 to 006 The values are positive matric potentials in cm c Holtan Overton The Holtan infiltration model is a one layer empirical model The maps need no further description Note that the extra infiltration options wheel tracks crusts and grass strips are not implemented for the Holtan model LISEM MANUAL version 2 x January 2 2002 42 d Green amp Ampt 1 and 2 layers and additional surface types G amp A demands the hydraulic properties of the first layer NOTE that the soil depth is only of consequence if the option impermeable sub soil is checked meaning that the soil storage is limited to the product of the moisture deficit and the depth thetas1 thetai1 soildep7 If this option is not checked the soil is assumed of unlimited depth and at moisture content thetai1 for its entire depth Map name Contents Type Unit Range KSAT1 Saturated hydraulic conductivity scalar Imm h
16. 002 29 Figure 6 4 PCRaster contributing area from accuflux identical to variable A in the critical zone algorithms see text a patterns using the steepest slope and b patterns using the according the tillage direction However the implementation of the above algorithms in PCRaster needs a certain interpretation of the thresholds Firstly when the algorithms are implemented directly the critical area is calculated on a cell to cell basis That means that if a cell has a local slope angle that does not meet the criteria that cell may not be seen as a critical cell This causes fractioning of the critical zone It must therefore be assumed that once a gully starts forming it will not stop at a single location and continue downslope of that location simply because the local slope is not sufficient Therefore a more continuous zone has to be created Secondly the gully formation will not continue endlessly and the algorithms show a dominance of the drainage area A above the local slope S In reality gully formation may stop because the gradient at the bottom of the slope is low and deposition occurs This has been observed for the Belgium loess belt although not for the Mediterranean area The implementation in PCRaster is done as follows 1 A critical zone is made according to the algorithms 2 the map edge is excluded from the zone because the flow path created in PCRaster will consider the map edge as a boundary so often a gully will for
17. 30 C AT TRT 100 3 etc ASCRP C TRT 15 STIR REST TRT 30 C AT TRT name TBL in the soil above three horizons are defined each of them with seperate soil phyisical characteristics referring to the specific tables The horizons used here are 0 15 cm 15 30 cm and 30 100 cm The tables used for these layers contain 3 columns soil moisture content theta fraction pressure head h in cm and unsaturated conductivity k in cm day An example LISEM MANUAL version 2 x January 2 2002 41 0 01 4 86EH 24 1 95E 21 0 02 1 04E 07 1 64E 11 0 03 9 02E 05 2 12E 09 0 04 2 15E 05 3 63E 08 SSES etc 0 31 3 19EHE 01 6 74E 01 0 323 24338H401 9 89E 01 0 33 1 54E 01 1 54E 00 0 34 0 00E 00 5 69E 01 PROFILE MAP a map based on soils fields or a combination with ID numbers that are used to look up the corresponding soil physics tables in PROFILE INP PROFCRST MAP a map with ID numbers on those places where there is a crust to look up the soil profiles for crusted soils in the file PROFILE INP The areas that are crusted are defined in CRUSTFRC MAP There can be more crust profiles if there are for instance more crop types with a different developing surface Simply include more crust profile descriptions in PROFILE INP PROFGRAS MAP a map with ID numbers corresponding to the soil profile for grass strips The area where strips are present are given in GRASSWID MAP PROFWHL MAP a map with ID numbers corresponding
18. 990 The kinematic wave is done over the Local Drain Directions map that forms a network which connects cells in 8 directions some cells may have a channel ditch gully for which a separate kinematic wave is done see fig 6 The cells that have a channel receive a part of the overland flow depending on the velocity Thus the velocity is considered the average velocity existing in the cell The channel is considered to be in the center of the cell so that the distance from the edge to the channel is 0 5 DX channel width The part of the water that flows into the channel is therefore f dt V 0 5 dx cw 2 25 The channel width cw in m can increase during the run if the channel is not rectangular and the water level in it rises In that case it cannot become larger than 0 9 of the cell width dx qland flow channel flow Figure 2 8 Overland and channel flow with LDD structure LISEM MANUAL version 2 x January 2 2002 19 2 6 Erosion and eposition Detachment modelling is based on a generalised erosion deposition as described by Morgan et al 1992 and Smith et al 1994 and is identical to the EJUROSEM model It is assumed that the transport capacity concentration of the runoff reflects a balance between the continuous counteracting processes of erosion and deposition Dp Erosion is sum of splash detachment by rain drops Ds and flow detachment by runoff Df The amount of sediment in suspension e is then calcula
19. AN the LDD map based on the channel mask alone This map can opnly have one pit that has to be the same as the pit outlet of the LDD A way to create this map is pcercalc lddchan map lddcreate dem chanmask map 1e10 1e10 1e10 1e10 CHANGRAD the gradient of the channel bed based on the channel mask alone A way to create this map is percalc changrad map slope dem chanmask map CHANMAN the Manning s n resistance to flow of the channel Usually this is not known and a literature value ditches with vegetation is assumed If the channel is used to simulate a thalweg the manning s n of the land use could be used n map see above pcercalc chanman map n map chanmask map CHANCORH the cohesion kPa of the channel bed resistance to flow erosion Usually this is not known and a literature value ditches with vegetation is assumed or of a concrete channel is simulated a very high cohesion could be assumed If the channel is used to simulate a thalweg the cohesion of the land use could be used coh map and cohadd map see above percalc chancoh map coh map cohadd map chanmask map CHANWIDT the channel bed width in m Because the channel shape is not necessarily rectangular the top width at water level and the hydraulic radius is calculated from the side angle and the water height in the channel This value should be smaller than the grid cell LISEM MANUAL version 2 x January 2 2002 45 width not more than 90 of the ce
20. After analysis it appeared that a second threshold is needed Nachtergaele 2001 when a critical area is defined according to the algorithms above the contributing area will soon dominate the analysis and all area towards the outlet will be seen as critical Thus a second threshold is needed to give a lower boundary that will make the gully formation stop For the Belgian loessbelt it was shown that no gullying occurred on the lower slopes and thalwegs when the slope angle decreased below 4 Below this angle deposition processes become dominant 6 2 2 Critical area analysis Implementation in LISEM Since the EUROWISE model uses raster maps created with the Geographical Information system PCRaster Van Deursen and Wesseling 1998 This GIS combines the regular spatial expression of any GIS with a modelling language that enables the analysis of flow of material over a landscape and is therefore very suitable for this work package The language follows simple rules that can be combined in a script a kind of macro that is executed with a compiler PCRCALC EXE In PCRaster a network can be generated from the digital elevation model DEM that defines the direction of flow over the landscape The network is called LDD the Local Drain Direction The LDD can be made directly from the DEM by using the steepest angle of flow see figure 1 To delimit critical areas the contributing area draining towards a given point has to be generated In PCRaster th
21. FPJ 7P DF with dr percolation or drainage rate mm h FP field capacity saturation The major advantage of the Holtan model over other infiltration equations is the use of cumulative infiltration instead of time as the independent variable This offers several advantages in catchment hydrology simulation Skaggs et al 1969 evaluated several infiltration equations and concluded so Using the Holtan equation difficulties are not encountered in computing the infiltration rate at any time during a storm event even when the water supply does not exceed the infiltration rate Furthermore because the Holtan model assumes a relationship between drainage and soil water content the recovery of infiltration rate as the result of a temporary interruption in rainfall can be predicted The major difficulty with the Holtan equation is the control zone depth DF Holtan suggested that the depth to the first impeding layer should be used If no impeding layer exists a value equal to 0 25 to 0 75 of the A horizon is advised Beasley amp Huggins 1982 Beasley and Huggins remarked that of all of the variables used in the ANSWERS model the DF is the least well defined and most arbitrary Huggins and Monke 1966 found that the effective depth was highly dependent on both surface condition crusting and the cultural practices used in preparing the seed bed De Roo and Riezebos 1992 also demonstrated the influence of crusting on the DF vari
22. LISEM Limburg Soil Erosion Model Windows version 2 x USER MANUAL DRAFT 2002 01 03 Victor Jetten si UCEL rg s Universiteit Utrecht Centre for Environment an Landscape Dynamics LISEM MANUAL version 2 x January 2 2002 2 Preface This is a first draft of the manual for the new LISEM for windows currently at version 2 1 It is a compilation of the website http www geog uu nl lisem on which you can find the latest information LISEM started out as an erosion model that simulates overland flow splash and rill erosion with some extra features More processes were added and the number of variables and choices in the interface became prohibitive because initially all combinations were allowed Therefore it was decided to have different versions of LISEM that essentially consist of the Basic version plus an extra set of processes S LISEM Basic the original LISEM including parallel infiltration through different types of surfaces inside a gridcell as well as grass strips and channels SE LISEM Wheeltracks the basic version plus the ability to treat semi permanent wheeltracks as a network of small channels S LISEM Multiclass the basic version with the erosion deposition changed to a multiclass system with 6 sediment classes causing spatial changes in texture composition LISEM Nutrients the basic version with the nutrient losses N and P in solution and in suspension absorbed to the clay particl
23. M MANUAL version 2 x January 2 2002 37 7 2 2 Vegetation maps Vegetation and or crops are mainly used by the interception and splash erosion processes in LISEM The maps are usually made by reclassifying the field boundary map vegetation influences also the soil cohesion for which a separate map must be defined see below Note that LISEM has never been tested for forest areas and should be used with care in these circumstances LAI leaf area index used to calculate the storage capacity of the canopy The value represents the LAI of the vegetated part of the gridcell For instance if a grid cell has a single tree with a LAI of 6 in it the LAI of that cell is 6 PER fraction of soil cover by canopy but also litter or other types of soil cover except for stones CH crop height used to calculate throughfall kinetic energy in the splash erosion part These maps can be made in similar operations if a table is available that has as the first column the id numbers of the landuse map units and in the other columns values for the LAI cover fraction and vegetation height the option matrixtable is needed because of the table layout conventions in PCRaster percalc matrixtable lai map lookupscalar landuse map 1 veg tbl percalc matrixtable per map lookupscalar landuse map 2 veg tbl percalc matrixtable ch map lookupscalar landuse map 3 veg thbl The table may look like this four landuse types with different
24. SIGS COTACHITICN ee Ee 19 2 6 2 Flow detachment and depoesiton 19 2 6 3 Channel detachment and deposition 21 3 LISEM wheeltracks si ccscatsvie dca wusdsserteeabadchddadsdivesenddd eudedestee 22 4 LISEM multiclass icsintoactadendseacadeadnondeanakdhauaeinieutwaiceeesadayebiaukay 22 5 Riol En EE 22 6 LISEM GULLIES EUROWISE ccecceccecceceeserseesetsensees 23 6 1 Jeder fer e RE 23 6 1 1 Ephemeral QUINGS eseri ap stew etree EE 23 6 7 2 Summer and wintergoulles ec ec ccc ccccceccsnecseccecececsueceuecsessuccecsesseeseecseesaees 26 62 Basic ere 26 6 2 1 Critical area analysis Deory 27 6 2 2 Critical area analysis Implementation in LISEM ccccccccceccsecceecseeceeeaees 28 6 2 3 Ephemeral gully formation rssi re A aa 30 OZ GUMVINCISTON eege eege 32 l THEINPUT DATABASE EN 33 LI PORASTE EE 33 LZ WRG IA DUC IAS ceraian E EE 34 1 2 1 EE Eeer 35 1 2 2 VEGCTANON Maps ER 37 ee EE 37 m24 ELE SCIALEO EE ee ees 39 7 2 5 ErOSiOn AepOSition related maps 43 E EE ee EE 43 7 3 Additional maps needed for EUROWISE cc eccecc ccc eeeceeeeeeeeeeeeeeeeeeeeeeneeeeens 45 7 4 FEE LAL FS gt WEE 47 LISEM MANUAL version 2 x January 2 2002 4 11 TAG INTC e 43 Speed DUTONS E e EE 49 SE e 49 BASIC Mla EE 51 Slftdei r 53 LISEM OUUU EE 54 Main output screen and totals cece ccc seceeceeceeceeteeseeeeeeeeeeeeeeecseseeceeseeseeeees 54 Hydrographs and sedigraphS ccccccceeceecceceeeceeeeeec
25. a china 10m2 crustfrc map compfre C data china 10m2 compfrc map stonefrc C data china 10m2 stonefre map InfilHoltan A C data china 10m2 A FP C data china 10m2 FP P C data china 10m2 P InfilExtra ksatcrst C data china 10m2 ksatcrst map ksatcomp C data china 10m2 ksatcomp map ksatgras C data china 10m2 ksatgras map InfilGA2 ksat2 C data china 10m2 ksat2 map psi2 C data china 10m2 psi2 map thetas2 C data china 10m2 thetas2 map 61 LISEM MANUAL version 2 x January 2 2002 thetai2 C data china 10m2 thetai2 map soildep2 C data china 10m2 soildep2 map InfilGA1 ksat1 C data china 10m2 ksat1 map psil C data china 10m2 psil map thetas1 C data china 10m2 thetasl1 map thetail C data china 10m2 thetail map soildep1 C data china 10m2 soildepl1 map InfilSmith ksat1 C data china 10m2 ksat1 map psil C data china 10m2 G1 map thetas1 C data china 10m2 thetasl1 map thetail C data china 10m2 thetail map soildep1 C data china 10m2 soildepl1 map InfilMorel ksat1 C data china 10m2 ksat1 map psil C data china 10m2 G1 map thetas1 C data china 10m2 thetasl1 map thetail C data china 10m2 thetail map soildep1 C data china 10m2 soildepl1 map InfilSwatre profinp C data china 10m2 profile inp profmap C data china 10m2 profile map profcrst C data china 10m2 profcrst map profwltr C data china 10m2 profwltr map profgras C data china 10m2 profgras map inithead C data china 10m2
26. able Huggins and Monke 1968 suggested that the DF for deep soils can be determined by the depth necessary for the hydraulic gradient to approach unity Skaggs et al 1969 computed the control zone depth for fallow soils from the initial soil water content ASM the soil porosity TP and the volume of water that had infiltrated F at the time the infiltration rate reached a constant value Psat Se 2 8 fi ASM TP with Fsa Cumulative infiltration mm at saturation A major disadvantage of this method however is that the DF variable is made a fitted variable instead of being physically measurable as the depth to the first impeding layer Nevertheless with this method Holtan s equation gave an excellent fit r 0 988 obtained using non linear regression to their experimental data The Holtan infiltration model incorporates a minimum infiltration capacity FC which equals the saturated conductivity Ks of the topsoil Because the Ks is always larger than zero the model always allows for infiltration even when the soil profile is saturated Thus using this sub model only Hortonian overland flow is simulated Saturation overland flow is not simulated Using the Swatre based sub models and the Green Ampt submodels one can simulate saturated overland flow LISEM MANUAL version 2 x January 2 2002 11 2 3 3 Green and Ampt Green and Ampt 1911 first applied the Darcy equation to the wetted zone in the soil assumin
27. able time increment depending on pressure head changes ou lt SE l NOTE SWATRE assumes that the nodes are not in the centre of the layers as is common but between the layers Thus the user specifies the depth to the bottom of each layer see section input database NOTE The average hydraulic conductivity between the nodes can be calculated either as a arithmetric average 0 5 sum of Ki and Ki 1 or as the geometric average sqrt Ki Ki 1 The choice is made in the user interface This has a large influence as the geometric mean LISEM MANUAL version 2 x January 2 2002 9 favours the node with the lowest K value and the K h relationship is nhighly non linear compare 0 5 1 0 01 0 5005 with sort 0 01 0 1 Figure 2 2 Data structure of the Swatre infiltration module table with depths soil IDs and painters to Gol inte PROFILE TAB Map with land units tables with soil physical data PROFILE MAP WEA DOW TRL beg it o 9 DL lG5 E2 9196 36 0 02 1 0901 11 E 1 0 03 1 00E 06 19E 12 WE HP RO TEL 15 lH RESTTAL 7 C ALLTEL 10 MES OO TAL is 0 31 2 99E 0 oDIED GR RESTTEL A 0 32 OO0E 00 25E 02 Hit OH AE LG ALL TEL eT AAA UU h Eu 2 3 2 Holtan method For areas without detailed knowledge of the soil physics different model versions with empirical infiltration equations can be used using Green amp Ampt and Holtan e g Beasley amp Huggins 1982 de Roo 1993 The Ho
28. al GIS but a generic programming language for dynamic landscape modelling If you are interested in using PCRaster for modelling purposes a distance learning course is available through the internet http ocraster geog uu nl mutate PCRaster is used in two contexts here 1 LISEM is largely built in a mixture of PCRaster commands and C 2 The modelling capabilities of PCRaster are used to create the input maps with one or more macros scripts LISEM is developed in an environment that is a mix of C and PCRaster libraries A large part of the source code is written in the macro language of PCRaster The advantage of this close integration is primarily for the model developer the PCRaster macro language includes a powerful calculator that is able to parse virtually any mathematical or logical equation Equations that are commonly found in erosion models can be typed almost literally from a text to include them into the model An example the Manning s equation can be written in PCRaster as a string that is given to a calculator the statements are translated to C at compilation V if n gt 0 R 2 3 sqrt max slope DEM 001 n 0 where V R DEM and n are raster maps and slope is the GIS operation to calculate the gradient from the DEM but it cannot be smaller then 0 001 The instruction is carried out for all cells in the raster maps As a precaution the logical if statement sets the Velocity to 0 where n is 0 The advanta
29. ame farea map Open Fiegofbpe PCRaster maps Umap ci Similar screen exist for the other categories Note that when the maps are not selected the mapnames are grayed out and not accessible e g swatre maps are grayed out when Green and Ampt is selected SWATRE options 1 minimum timestep to adjust for mass balance errors SWATRE calculates internally with a flexible timestep smaller than the timestep used in LISEM The timestep cannot become smaller than the value given here A smaller value gives greater accuracy Generally 1 sec gives sufficient accuracy NOTE in old LISEM versions older than version 1 60 this value was given in days because SWATRE was initially designed for daily timesteps This has been changed to seconds for ease of use In the run file this value is still in days to have downward compatibility 2 save matric head this option needs a map headout map that has numbered locations For these locations ascii tables are written with the temporal change of the hydraulic head during the run 3 geometric mean the average conductivity K between nodes is calculated as Kavg sqrt Kj Ki 1 else the average K is calculated as Kayg Ki Ki 1 2 NOTE the conductivity between the surface and the first node is always calculated with the geometric mean Feddes et al 1978 LISEM MANUAL version 2 x January 2 2002 SE 8 4 Output timeseries The results of LISEM can be stored in timeseries these
30. at raingauge 1 is 2 53 mm h From time 965 87 to time 1300 there is no rainfall Important The last time entered should be large enough to allow all runoff to reach the catchment outlet This time should be equal to or larger than the time at which the simulation is stopped specified in the interface Note the rainfall file is not in standard PCRaster format This format was an experimental format and is only used in LISEM It may change in the future LISEM MANUAL version 2 x January 2 2002 48 8 THE INTERFACE The five version of LISEM are contained in a single executable lisemwin exe When it does not exist a file lisemwin ini is created in which the last workspace Is saved LISEM opens with the following screen fee LISEM Windows version 7 0 i a n Lea e Big Ca Va et Kc E BR ee e 3 LISEM Basic Original LISEM runoff arid Enterit erosion GC E EE 3 LISEM Wheeltracks Simulation of semi permanent wheeltracks a Ta l E SI LSEM Muticlass f Simulation of multiple sediment classes gege si An a H EE the e Pie KE EC E E ys le Ap o Vd cb Ex ak ee in St Sek LISEM Nutrients kal CHcn of nutrient losses in runoff d t Se i Remedi os A ath Ni a pp ie a LISEM Gullies Simulation of ET gully formation E Pressing one of the buttons will generate a LISEM interface that only contains the options needed to run that particular version of LISEM The basic interface looks as follows ET Lisem for W
31. atrixtable n map lookupscalar landuse map 1 surface tbl percalc matrixtable rr map lookupscalar landuse map 2 surface tbl percalc matrixtable stonefrc map lookupscalar landuse map 3 surface tbl percalc matrixtable crustfrce map lookupscalar landuse map 4 surface tbl pcrcalc roadwidt map scalar if roads map neq 0 width 0 where surface tbl is a table such as used with the vegetation related maps and width is a value for the road width in m LISEM MANUAL version 2 x January 2 2002 39 7 2 4 Infiltration related maps There are currently 6 infiltration options in LISEM based on 3 different models Depending on the choice of the user in the interface a different set of input maps is needed no infiltration no maps needed SWATRE including crusts wheel tracks and grass strips Holtan Overton Green amp Ampt 1 and 2 layers and additional surface types e Morell Seytoux amp Verdin ON oO D a No infiltration The entire catchment is assumed impermeable Can be used for testing b SWATRE To operate the SWATRE infiltration module the user has to set up a series of maps and tables with soil physical properties that describe the profile max 20 layers of each land unit These can be e g soil type units or fields or parts of fields PROFILE INP when the SWATRE infiltration model is used LISEM needs a 3D structure of the soil This structure is described in the tex
32. between interrill and rill erosion In fact all erosion is assumed to be rill erosion although there are no rills defined as such Water simply flows from cell to cell following a drainage network see below Currently the definition of a separate rill network is under development and then rill and interrill transport capacity can be differentiated LISEM uses the median of the texture d50 as input to represent spatial variability of grain sizes The model calculates the corresponding coefficients a and b based on work of Govers 1990 D50 5 0 32 2 34 D50 5 300 C d NOTE originally these equations are valid for materials with a grain szie diameter larger than 32 u m There are two checks carried out in LISEM to avoid the calculation of an incorrect Df or Dp The amount of erosion or deposition in a timestep depends on the settling velocity Vs With a too large timestep it may happen that all sediment has already settled before the end of LISEM MANUAL version 2 x January 2 2002 21 the timestep Therefore the deposition is never more than the amount of sediment in suspension Dp min sediment Dp 2 35 In the case of detachment the amount of detached soil cannot be more than the remaining carrying capacity of the flow Q ihn m3 s Df T C Q dt 2 36 The net sediment in suspension is transported between gridcell with the kinematic wave 2 6 3 Channel detachment and deposition Erosion and
33. calc guldepth map scalar 0 01 normal 1 0 08 gives a map with a depth of 8 cm with a normal distributed noise that has a standard deviation of 1 cm GULCOHZ2 Cohesion of the second layer see the map COH MAP GULBDz2 see the bulk density map above LISEM MANUAL version 2 x January 2 2002 47 7 4 Rainfall data The file containing the rainfall data is in ASCll format and can have any name The rainfall file should have the following structure the second column is for explanation only and should be ignored in the real file Fixed text 1 indicates the number of RUU CSF TIMESERIE INTENSITY NORMAL 1 e raingauges name of gauge 1 if more gauges are station 1 present then put each name ona seperate line empty line required 0 000 00 00 indicate 60 mm hours rainfall intensity 20 00 60 00 from minute 0 to 20 250 0 00 00 If two or more rain gauges are used e g 3 referring to the numbers used in ID MAP the file should have the following structure RUU CSF TIMESERIE INTENSITY NORMAL 3 station 1 station 2 station 3 955 00 0 00 00 00 1 0 960 00 2 53 20 00 8 960 30 2 51 10 00 H 960 90 2 49 05 63 0 50 961 97 2 44 10 00 0 965207 222 6 02 00 16 1300 00 0 00 00 00 The first column is time in minutes The second column is the rainfall intensity in mm h of rain gauge number 1 the third column is the intensity of raingauge number 2 etc So from time 955 to 960 minutes the rainfall intensity
34. cros and even spatial models all commands given here are combined in a script so that the complete database can be constructed in one go The script can be downloaded from the website NOTE the map names given here are NOT compulsory but can be specified individually by the user in the interface However to enable compatibility with the older versions of LISEM the map names used here are the default names Also the extension map is NOT compulsory just convenient 7 2 1 Catchment maps The actual digital elevation model is not used in LISEM only maps derived from it This has the advantage that a number of important maps such as the surface drainage network called Local Drain Direction or LDD in PCRaster and Gradient are not automatically derived with GIS operations but can be supplied by the user LDD Local Drain Direction this map gives for each cell the direction of the surface runoff the number corrspond to a keypad on your keyboard 1 drainage to lower left 6 is drainage to the right etc the number 5 is reserved for the catchment outlet Note that this map cannot contain local depressions the entire catchment has to drain towards the outlet PCRaster provides commands that can automatically generate such a map with removal of the local depressions pits based on constraints given by the user In this case the LDD is based on the steepest slope The command is percalc ldd map lddcreate dem map 1e10 1e10 1e10 1e10 T
35. e command to do this is ups map accuflux ldd map cellarea This command accumulates the cellarea over the network and gives therefore in each cell of the output map the cumulative area of all cells draining towards that cell so e g the value of the outlet of the catchment has the total area of the whole catchment above the outlet This is the PCRaster equivalent of the variable A in the algorithms above In an agricultural environment the direction of flow is often the tillage direction at least for a part of the year Takken 2001 in her work on the influence of tillage on runoff created a PCRaster script to generate automatically a valid LDD based on the tillage direction per field while including features such as headlands dead furrows and topography where necessary see Fig 3 It can be seen that the effect is very different the concentration zones follow the field pattern much more in the right hand image than in the left hand image Fig 4 The main concentration lines are formed by the four small side valleys The slope is calculated by taking the difference in elevation between a grid cell and the cell towards it drains divided by the distance Figure 6 3 PCRaster LDD maps for a 40ha catchment Limburg NL a drainage direction lines and slope grayscales according to the steepest slope and b according to tillage direction Note that the field boundaries are preserved LISEM MANUAL version 2 x January 2 2
36. e THETAS1 THETAI2 see THETAI1 scalar l see THETAI1 IPSI2 see PSI1 scalar em see PSI1 SOL DER see SOILDEP1 scalar mm see SOILDEP1 LISEM MANUAL version 2 x January 2 2002 43 e Morel Seytoux amp Verdin Not implemented yet 7 2 5 Erosion deposition related maps Erosion and deposition in LISEM is based on the deficit transport capacity capacity surplus equals deposition and transport deficit equals erosion The particles in flow have a settling velocity that is estimated by the settling velocity of the median fraction D50 in mu To calculate more sediment classes the LISEM MULTICLASS SEDIMENT version has to be used AGGRSTAB aggregate stability is used for the splash erosion It is the median number of the drops needed to decrease the size of the aggregates by half on a sieve LOWE test COH Cohesion of the soil kPa measured with a torvane The cohesion value is used in an empirical formula to decrease the transport deficit with a factor between 0 no erosion and 1 cohesionless soil COHADD Additional cohesion kPa to be added by the user to simulate the effect of plant roots on the soil strength Note that this is a calibration value as the Torvane test is not suited to measure the effect of roots D50 median of the texture of the soil um used to simulate the settling velocity This value determines strongly the depostion WARNING if water with sediment with e g D50 25 flows over a gridcell wit
37. e considered in soil erosion assessments an important erosional area and source of sediment within fields is being overlooked Foster 1986 The topography of most fields causes runoff to collect and concentrate in a few major natural waterways before leaving the fields Erosion occurring in these channels is what is known as ephemeral gully erosion Foster 1986 The ephemeral nature of this erosion feature results from the fact that ephemeral gullies are ploughed in and tilled across annually or more frequent therefore restoring the original hollow but leaving a potential zone for subsequent ephemeral gully erosion Poesen 1993 added to the view of Foster 1986 that ephemeral gullies may also form where overland flow concentrates along or in linear landscape elements e g drill lines plough furrows parcel borders access roads Definition wise incisions in linear landscape elements can be classified as rills since their formation is associated with the micro relief generated by tillage or landforming operations Haan et al 1994 However incisions in linear landscape elements are a form of concentrated flow erosion that will never develop in a standard USLE runoff plot used to quantify interrill and rill erosion According to the original idea behind the introduction of ephemeral gully erosion as a separate erosion class Foster 1986 it seems sound to consider incisions in linear landscape elements as part of ephemeral gully erosio
38. ecome larger than the grid cell width During the calculations the digital elevation model changes For each time step a new DEM is calculated in the dynamic loop of PC Raster This new DEM is derived from old DEM with subtraction of the erosion or addition of the sedimentation Changes in the DEM causes changes in local drain direction LDD which allows fluctuations in the stream pattern of the gullies LISEM MANUAL version 2 x January 2 2002 33 7 THE INPUT DATABASE The input database consists of a series of raster maps created with or converted to the GIS PCRaster Furthermore LISEM needs event based so called breakpoint data of rainfall intensity for one or more rainstorms Note that LISEM does not yet simulate evapotranspiration so that this is not taken into consideration when dry periods between rainfall events are calculated In the next sections you will find an overview of the input data and the commands needed to create them with PCRaster Note that a PCRaster script file is available from the website which generates the complete input dataset from a few basic maps 7 1 PCRASTER All input and output maps in LISEM are in the format of the PCRaster Geographical Information System PCRaster is a free GIS is produced by PCRaster environmental software and can be obtained through their website aster There you will find a complete list of functions research and coding examples and literature PCRaster is not only a norm
39. eedback loop is added whereby the simulated flow detachment is recalculated to a loss of soil volume and causes a decrease of the surface height in the digital elevation model This in its turn causes a change in local slope and flow path which influences the erosion in the next time step LISEM MANUAL version 2 x January 2 2002 2 The modelling of gully incision and formation takes a three step approach 1 An analysis of the landscape to determination likely locations of a gully as a result of one or more rainfall events called here critical areas These areas are selected on the basis of topographic features such as slope and upstream drainage area 2 The simulation of splash and flow detachment on a physically deterministic basis everywhere in the catchment using the principles of the LISEM BASIC 3 Incision and change in gully dimensions as a result of flow detachment inside the critical areas using an empirical discharge width relationship The rest of the catchment is assumed to have rill erosion only which is not causing gullying This is an extension of the code to simulate the incision in a 2 layer soil based on bulk density and cohesion and an empirical width discharge relationship 6 2 1 Critical area analysis theory The position of the gullies is determined as the areas where topological critical thresholds are exceeded The algorithms in this section are based on the work of Nachtergaele et al 2001 He found that e
40. eeeeeeseeeeeeeeeeeeseeseesaesaeeneeees 54 Erosion and deposition MANS EE 55 Hie LEE 56 Be 57 PANE ienei 59 APPEND EE 60 LISEM MANUAL version 2 x January 2 2002 5 1 INTRODUCTION LISEM the LImburg Soil Erosion Model simulates the hydrology and sediment transport during and immediately after a single rainfall event in a small catchment The model has been used so far in catchments between 10 and approximately 300 ha LISEM is built to simulate both the effects of the current land use and the effects of soil conservation measures The model was originally made for the Provice of Limburg the Netherlands to test the effects of grass strips and other small scale soil conservation measures on the soil loss In the Limburg project three catchments were fully equiped and monitored for 5 years by the local governement Waterboard Roer en Overmaas the Free University of Amsterdam Physical Geography Alterra and the Utrecht Universitfy Physical Geography Although it can be used for planning purposes it is essentially a research tool because of its complexity The philosophy behind LISEM ts that the model assumes nothing An example if a land use change is modelled there is no way of telling LISEM that it should change all the related variables because the crop is e g winter wheat and not sugar beet The user must change all appropriate variables him herself infiltration variables surface roughness Manning s n etc This gives the use
41. ephemeral gully development in a given watershed and measured suspended sediment concentrations at the outlet of that watershed for comparable rainfall events In other words ephemeral gullies do not only act as sediment sources but once established they also function as efficient sediment transport ways Despite the aforementioned arguments there still exists a small overlap between rills and ephemeral gullies For example when a slope shows several clear rills that concentrate gradually downslope and finally form a clear ephemeral gully Figure 1 where should the critical point between rill and ephemeral gully be placed It is clear that there exists a transition zone between rills and ephemeral gullies While an overlap between the two cognate concepts does not impede the existence of each individual concept problems may arise when assessing rills ephemeral gullies in the field In order to have an objective measure to distinguish rills from gullies in such dubious cases Poesen 1993 proposed a critical cross section of 929 cm2 or one square foot a criterion first used by Hauge 1977 Within this study this criterion was used to ensure that the data sets assessed in all study areas and by all persons involved are fully comparable Figure 6 1 Photograph illustrating a transition from rill to ephemeral gully erosion January 1998 Guadalentin south east Spain foto J Nachtergaele Finally questions about the true need for a distinction
42. er height h lt SDS runoff 0 h gt SDS runoff h SDS 1 exp h h SDS MDS SDS 2 21 In fact this resembles a Gaussian curve 1 exp x as is seen in figure 4 Seen ad H ad bes Ka Gel E 10 15 water height mm Figure 2 6 Increase of runoff height with with water height for different values of MDS and SDS increase with 5 mm intervals 2 5 1 Surface Storage in LISEM Version 1 63 and earlier Version 1 63 and earlier Storage in micro depressions is simulated by a set of equations developed by Onstad 1984 and Linden et al 1988 The variable Random Roughness is used as a measure of microrelief Surface storage in depressions is simulated by Onstad 1984 RETMAX 0 112RR 0 031 RR2 0 012RRS LISEM MANUAL version 2 x January 2 2002 16 with RET qax Maximum Depressional Storage cm RR Random Roughness cm S Slope gradient NOTE in the Onstad equations the RR is calculated using the method of Almaras 1967 who eliminated the extreme 10 of the surface height readings and takes the In of the values to normalise the dataset The rainfall excess rainfall overland flow interception infiltration required to fill all depressions RET Rain in cm is calculated using the equation Onstad 1984 RETran 0 329RR 0 073RR 0 018RRS Moore amp Larson 1979 identified three possible stages during a rainfall event a Micro relief storage occuring no
43. es SE LISEM Gullies EUROWISE the basic version with incision in a mult ilayered soil in certain areas that are prone to gullying according to an empirical landscape analysis Not all of the theory and descriptions are included in this manual yet only of the basic version and the gully version Victor Jetten January 2 2002 Reference Jetten V 2002 LISEM user manual version 2 x Draft version January 2002 Utrecht Centre for Environment and Landscape Dynamics Utrecht University The Netherlands pp 48 DISCLAIMER No warrenties expressed or implied are made that the computer programs described in this publication are free from errors or are consistent with any particular standard of programming language or that they will meet a user s requirement for any particular application LISEM MANUAL version 2 x January 2 2002 3 Contents 1 INC GO UCHON saareen OOO 5 2 LISEM BASIC Theoretical framework ccceceeceeeeeeeeeeees 6 2 1 Ela T ee e EE T Zoo aO NE 7 2 3 1 EEN 8 ZS AOAN NOT EE 9 23 9 Greenand AMDI rers E ey Seek ee wees 11 2 3 4 Morel Seytoux and Verdun 12 23 9 SUM ACI ON OF TKS Geiser EE 12 2 4 Surface definition on a sub gridcell level 12 20 Storage im Micro e ele EE 12 204 Surface Storage in LISEM Version 1 63 and earler 15 2 5 2 Overland flow and channel SOW 1c ccccccceccneececceeceesseececceessesseeeeesessesseenees 17 20 EFOSION ANG CDOSIMION EE 19 2 6 1
44. es tryO000 001 try0000 002 etc The runoff maps are optionally stored as discharge l s or unit discharge I s m The erosion positive values and deposition negative values maps are stored in tonnes ha LISEM MANUAL version 2 x January 2 2002 50 Simulation time Begin and end times of the simulation in minutes these have to be present in the rainfall file The timestep is in seconds be sure to make it not too large in general equal to the gridcell size in m A good rule of thumb is to use simulation intervals in sec that are 0 2 2 times the grid cell size in m Do not make it too small either this causes instabilities apparently A smaller timestep results in a higher peek because of a greater accuracy of the kinematic wave solution Output times Definition of output times to store the runoff timeseries There are two options give an interval e g every 4 timesteps or define individual timesteps Runfile list List of runfiles loaded with the load file button More files are added until the trashcan button is pressed and the list is emptied LISEM will start executing the runfiles one by one DOUBLE CLICKING on a runfile name will activate it and load the options stored in it The list of runfiles is executed from the file you double clicked to the end of the list You can select several run files in the file open window by holding shift or ctrl and pointing the mouse Open Look in 3 china
45. es of these files are specified on the LISEM start screen Below is the basic output If LISEM multiclass is chosen all suspended sediment classes are stored as separate columns LISEM MANUAL version 2 x January 2 2002 begin of file gn npu non Oged Cona min mp bh MLS Wert e Mett e H D E 1 25 19 4628 0 0 0 1 5 19 4628 0 0 0 1 75 19 4628 0 0 0 2 19 4628 0 0724395 0 00968105 0 2 ador 26 0608 0 794583 0 0718342 0 2 5 26 0608 1 28849 0 124497 0 24 15726 0608 2 4 56996 05 3 29806eEe 07 10 6319 a 260 0605 5 78236 05 4 033546 07 4 90999 3 25 50 9473 0 0129043 0 00328798 216 454 35750 9473 0 036197770 01088577 266 185 3s 5760 94 75 0 04080L1 0 0095 7 935 212 616 4 50 9473 0 0749616 0 010196 124 569 4 25606 2244 0 138133 0 0152438 102 085 OCC Example hydrograph data stored as comma delimited file 9 3 Erosion and deposition maps LISEM produces two maps that contain the erosion positive values and deposition 55 negative values in PCRaster format The names of these files are specified on the LISEM start screen The values are expressed in tonnes ha and represent the total erosion deposition in a gridcell including channels and or wheel tracks In case of multiclass erosion the values are the sums of the erosion and deposition of all the texture classes Note that It is not so easy to interpret these maps as material that is eroded somewhere in the catchment may de
46. es the amount of splashed soil that is transported through the air from the dry part of the gridcell to the wet part of the gridcell so that is can be transported This means that although most splash occurs on the dry part of the gridcell because of the exponential decrease of splash with water height only a part of it will be transported 2 6 2 Flow detachment and deposition The ability of flowing water to erode its bed is assumed independent of the amount of material it carries and is only a function of the energy expended by the flow Deposition takes place at a rate equal to wCV where w is the width of flow m C is the sediment concentration in the flow kg m and V is the settling velocity of the particles ms 1 The concentration at transport capacity C7 represents the sediment concentration at which the LISEM MANUAL version 2 x January 2 2002 20 rate of erosion by the flow and accompanying rate of deposition are in balance In this condition the net rate of erosion is zero and Df equals the deposition rate wC 7V The equation for soil detachment by flow and deposition during flow expressed in terms of settling velocity and transport capacity then becomes D Y T C V w dx 2 30 in which D is Df or Dp in kg s Ts is the transport capacity of the flow kg m and Y is a dimensionless efficiency factor The latter is included to account for the fact that the detachment will be limited by the cohesion of the soil
47. f ponded area with water height Although not all the surfaces had a random roughness but showed also oriented roughness elements the RR appeared to be the best roughness index to explain the variance in the dataset Tortuosity based indeices performed less as did the Linden Van Dooren indices Kam oe dy 0 1 e a a E y aa a a 0 01 RR Mmm 2mm 10mm 30mm 25mm Figure 2 4 Ponded area shape factor a related to RR Jetten and de Roo 2001 fraction ponded area i 0 5 10 15 ZU water height mm Figure 2 5 Ponded area fraction increase with water height for different values of RR increase with 5 mm intervals LISEM MANUAL version 2 x January 2 2002 15 Based on the MDS value and the fraction of ponded area the runoff before the water level reaches the MDS height is calculated as follows It is assumed that the runoff starts if 10 of the surface is ponded so that the equation above for fpa reads 0 1 1 exp a h 2 20 which means that at h In 0 9 a runoff starts If this threshold for h called here Start Depressional Storage or SDS is larger than MDS 0 9 of MDS is taken Between this starting value SDS and the MDS value the runoff gradually increases in a non linear way to reflect the observation that the surface usually consists of degraded agrregates which release little runoff untill they are fully submerged After the water level has passed MDS the runoff height increases linearly with wat
48. ficult to verify and the data would have to be extrapolated from a few measurements to a large extent A different approach was chosen here first flow incision takes place in certain areas only derived from field observations and secondly when incision takes place the width of the gully is based on an empirical relationship with the discharge The amount of erosion is based on the more deterministic erosion and deposition equations in LISEM such as described in the LISEM BASIC section 6 1 1 Ephemeral gullies The following text is copied from the thesis A spatial and temporal analysis of the characteristics importance and prediction of ephemeral gully erosion by Jeroen Nachtergaele 2001 who cooperated in the MWISED project Problems related to the definition of ephemeral gullies are two fold 1 Traditionally ephemeral gullies have been defined in the way they differ from rills and classical gullies Such negative definition is rather vague and open to discussion since it states what an ephemeral gully is not instead of expressing the essential nature of this erosion feature 2 As it is often the case with newly defined concepts many synonyms or nearly synonyms have been used to describe this erosion feature In what follows it is attempted to define ephemeral gully erosion and its related erosion features in such a way that it is at least clear what within this study is understood by the term ephemeral gully erosion Rill erosion i
49. g that a distinct wetting front exist They produced a one dimensional infiltration equation used and adapted by many researchers Generally the equation has the following form d Si 2 9 leg ZS Kap 2 10 Q and in which the infiltration rate m s the accumulated infiltration over time m k the hydraulic conductivity in the wetted zone m s t time since the start of the infiltration and Q potential head parameter m Note that k is not necessarily the saturated hydraulic conductivity but less according to Li et al 1976 According to Fok and Hansen 1966 this parameter is defined as Q h h 0 0 2 11 in which h the average capillary suction head at the wetting front h the ponded head water level at the surface Ow the water content of the wetted zone may be smaller than the porosity and 6 the antecedent moisture content To get the infiltration rate at any time equation 2 has to be solved first for and inserted into equation 1 This is usually done by iteration Li et al 1976 show that it is possible to use an explicit approximation by developing a power series expansion of the logarithmic term in equation 2 First the parameters are rewritten in their non dimensional form Pete eae a 2 12 Q Q k By using these parameters the equations are now rewritten as x l Ltt v 2 13 and I ln 1 r t 2 14 Replacing the logarithmic term with a power series and dropping the higher order ter
50. ge of the runoff in a non linear way w a Q The parameters a and b are predefined for Belgium from laboratory and field observations For areas which exceeds the critical threshold value gully width is calculated according to the relation W Se with a and b as empirical constants W is the gully width in meters and Qpeak IS the peak discharge of the runoff in m s For the Belgium loess belt these relationships are found by KULEUVEN for different kind of gullies in field and in laboratories the best relation is 0 413 Note that the user can define the parameters a and b in the interface LISEM MANUAL version 2 x January 2 2002 31 Figure 6 5 Critical areas according to the 5 algorithms white The lines are the actual mapped gullies The gully width has to be initialized in order for the erosion to start A sensitivity analysis shows that this value is not very sensitive and an arbitrary value of 0 1 m is chosen The width of the gullies increases with increasing runoff discharge till the point of the maximum peak discharge Fig 6 At that point gully width is assumed to be constant LISEM MANUAL version 2 x January 2 2002 32 1500 g 3 1000 _ E A O S 500 1 0 0 0 100 200 300 400 time min discharge l s w 2 37Q 0 37 m gully width m Figure 6 6 Simulated gully width when the peak discharge is passing a pixel which exceeds the critical threshold
51. ge of this approach is that the code is very compact and that several developers can work with the code at the same time without the need of knowing a higher programming language such as C or Pascal LISEM MANUAL version 2 x January 2 2002 34 Note that for processes where iteration is required Such as the kinematic wave and Richard s type infiltration special functions are developed The advantage for the user lies in the fact that the output maps of runoff and erosion deposition can be viewed directly with PCRaster without the need of conversions PCRaster can also be used to vcreate input maps using separate statements for each map examples of which are given in the input maps section These commands have the general syntax percalc options out map in map where a large number of opertaions are available for the in map Note that PCRaster is very strict on the variable types which have to be specified explicitely if the type type of resulting map is ambiguous The types are boolean 0 1 directional 0 360 Idd network direction 1 9 nominal class integer ordinal class integer scalar real value Alternatively all input maps can be created in one operation with the script that can be found on the LISEM website The script is run with the command percalc f lLisemmaps mod which produces the LISEM input maps based on 4 basic catchment maps NOTE PCRaster has no capabilities of digitizing maps It can howe
52. ght away with the input screen and starts executing the runfiles in the list e dump the active visible screen to a printer e g the simulation screen e dump the active screen to a GIF file e resize the screen so that it is entirely visible 800x600 pixels gt UAD e the icons DUR SH the run buttons o the arrow executes the run file list the pause icon pauses the run and it can be resumed with the arrow the cross halts the current run and starts the next the last symbols halts all runs O O O On the top of the screen a number of tabs are visible eee eee 1 Start general directories and options 2 Basic Maps input map names o Swatre infiltration options 3 Simulation water balance totals hydrograph and sedigraph 4 Output maps output timeseries 8 2 Start tab Input directories Names of workspace input directories and rainfall file Clicking on the icons brings up a directory tree to change the dir or it can be types Clicking on the text page icon brings up a window with the rainfall file for inspection not edit Output directories Specification of the output directories and file names The result directory is made automatically if it doesn t exist Limit the number of runoff map characters the runoff maps are stored as tryO0010 500 tryO0010 750 etc with simulation time minutes before the dot and fractions of minutes as extension Selecting the PCRaster timeseries option creates sequential map nam
53. h a D50 150 all sediment will deposit even if the sediment in flow has a D50 that is less To avoid these kind of effects use a homogeneous D50 map or better use the version LISEM MULTICLASS SEDIMENT 7 2 6 Channels Channels in LISEM are meant to be man made ditches with a width much smaller than the grid cell typically a ditch of less than 1 5 m wide in a grid cell of 10x10 m The channel network MUST be a continuous network connected to the outlet Water that enters the channel in LISEM does not come out again the channels do not overflow and if the channels are not connected to the outlet they are effectively sinks LISEM does a separate kinematic wave for the channel LISEM MANUAL version 2 x January 2 2002 44 Simulations can also be done considering a concentrated flow line such as a thalweg to be a channel The PCRaster operation accuflux can be used to determine a channel based on the Idd percalc chanmask map scalar if accuflux ldd cellarea 1t 10000 1 This command creates a mask of a channel having value 1 as the channel and MV outside based on the contributing area all cells that have 10000 m2 of drainage area upstream are considered a channel The mask itself is not used in LISEM but it can be used to create the channel input maps CAUTION The channel form hydraulic radius and resistance Manning s n determine to a large extent the shape of the hydrograph Channels are considered impermeable LDDCH
54. he 4 large values are thresholds to remove the pits and create a continuous LDD It is also ppossible to generate a valid LDD map based on the tillage direction A PCRaster macro has been constructed by Takken et al 2000 that combines major topographic concenration lines with tillage direction per field including headlands and dead furrows NOTE errors with LISEM related to the kinematic wave where MVs are reported missing values are often because the LDD does not have the same dimensions as the other maps LISEM MANUAL version 2 x January 2 2002 36 AREA all maps are checked against this map for the number and location of non missing value cells If maps do not have the same size and number of valid cells an error occurs percalc area map catchment ldd map pit ldd map GRAD this is the gradient in the direction of the LDD PLEASE NOTE this must be the SINE of the slope not the tangent Because the slope can occur in the denominator of various algorithms it cannot be O zero Use the slope command to create the slope from the DEM percalc grad map slope dem map or make a gradient map with the tangent of the slope in the direction of the flow it has to be covered with the slope derived from the DEM to account for edge cells percalc grad map dem map upstream ldd map dem map downstreamdist ldd map percalc grad map cover grad map slope dem map convert this map to a sine and make sure it is larger
55. he rainfall is added to the current water height in each cell However the slope angle is taken into consideration the rain falls on a horizontally projected surface while the actual terrain has a slope Thus the rain is spread out over a larger area and the resulting water height is lower h h P cos a 2 1 Where P is the rainfall depth in that timestep mm and a is the slope angle The assumption here is that the slope is in one direction only and the cell has a surface of DX DX cos a 2 2 Interception Interception by crops and vegetation is simulated by regarding the canopy as a simple storage as a simple storage The cumulative interception during an event is calculated as Aston 1979 Ka p ECO S Ce Omax l e Sam 12 2 where S is the cumulative interception mm Pcum is the cumulative rainfall mm k is a correction factor for vegetation density equals 0 046 LA en determines the rate with which Smax is reached c is the fraction of vegetation cover and Smax is the canopy storage capacity mm estimated from the LAI mim by Von Hoyningen Huene 1981 Smax 0 935 0 498 LAT 0 00575 LAT 2 3 Note that the LAI represents the average leaf area of the fraction of the gridcell that is under vegetation For example a gridcell with a single tree has a LAI of e g 6 m m while the cover fraction c of the gridcell takes care of the fact that most of the cell is bare 2 3 Infiltration Infiltration can be
56. his seems somewhat superfluous but the gridcell size in LISEM is user defined and so the option is available The following surface types can be defined normal soil surface tilled crusted compacted road impermeable grasstrips Two maps with information are needed to do this 1 For each surface type a map is needed that defines the fraction of a cell with that surface type For instance where the crust fraction map has values gt 0 LISEM assumes that it has to calculate a separate infiltration for the crusted surface fraction of the gridcell 2 In order to do this LISEM needs a map for the saturated hydraulic conductivity of the crust note that these names are optional Note that the SWATRE infiltration module has a different data structure so the infiltration of different surface types is not done by a Ksat map but by specific soil physics tables AU other parameters are assumed identical to the normal surface to avoid too many maps the infiltration of e g a crust is not at all modelled in a physically based way and the separate ksat should be seen as a calibration variable These surface types can be switched on and off in the interface without the need to change the maps In this way scenarios can be modelled that simulate e g the effect of severe crusting or compaction The resulting water height at the surface is calculated as a weighted average of the normal infiltration and the infiltration of the area with a differe
57. hoauez Dr a smu suspended sediment lux class 5 mul C datekchinaves Omi m mE suspended sediment flux class 6 mul C datehchina ves Omi z RM T sequential naming for PCRaster display 1 999 l Runot maps in unit discharge lisim LISEM MANUAL version 2 x January 2 2002 54 9 LISEM OUTPUT LISEM generates a wide variety of outputs that enables the user to evaluate any erosion scenario in detail Not only total values of the water balance variables and of erosion deposition and soil loss from the catchment are given also so called timeseries can be generated which are a series of output maps at regular intervals or at times chosen by the user These timeseries can be shown in the display 2D or aguila 3D program of PCRaster as a sequence of images giving the impression of a film of the variable 9 1 Main output screen and totals The picture below shows the output screen with total values of all water balance variables as well as erosion depostition and soil loss The hydrograph sedigraph and sediment concentration as shown as graphs Time Active run file C data limb TESTDATA Ptap run 42 790 Catehmentsize ha 10 000 gideeli m E ae a E Start ime pain 180 O00 Erd lime min Hydrograph Sediment main o utlet a ooo besten rec EE BESCH j 1 800 L e 00 5 400 F 35 05 Disch Raintall et 1 600 e SO g i r 1 d Ee i Z CH 0394 Irtenseption trenf 1
58. indows version 7 0 uput data names and EE Work directory CcAdatale data chinas Bec Result directory C data chinatres Ort Map directory E data erina imz El Erosion map 2 ob hain outlet otes Deposition map 6p op Sub catch 1 Jo Ce lel jel Totals fence Sub catch 2 OU AC Simulation times Geen Ee Rainfall file GER Begin time min End time nie 93 Surface ypa ___ _ IT Include Compacted oreas Timestep sec Mo Infiltration Model options 2 Bee I Include Crusis l Runot oni no erosion l Include Grass Strips C Simulate main channels Green amp Ampt 1 layer SE EE J E Simulate Chenrellmtilination C Green amp Ampt 2 layer additional options A SEET S E l subsoil impeneable Splash delive a Lad erate 100 S SE A4 PEE SE GE y an EE Cdatal china inean un ia Clear list Acitive run file 1Orew na EI LISEM MANUAL version 2 x January 2 2002 49 8 1 Speed buttons amp Tabs The icons on top of the interface are load a run file save a run file save a run file under a different name save the directory name of the workspace in the lisemwin ini file NOTE that the lisemwin ini file also contains the LISEM Type 0 Basic 1 Wheeltracks etc and the names upto 4 runfiles full path names needed If the variable LisemType 1 LISEM starts with the opening screen top picture else it starts strai
59. inithead headout C data china 10m2 headout map Channelinfil chanksat C data china 10m2 chanksat map chanstor C data china 10m2 chanstor map Channels lddchan C data china 10m2 lddchan map chanwidth C data china 10m2 chanwidt map chanside C data china 10m2 chanside map changrad C data china 10m2 changrad map chanman C data china 10m2 chanman map chancoh C data china 10m2 chancoh map Wheeltrack lddwheel C data china 10m2 1lddwheel map wheelnbr C data china 10m2 wheelnbr map wheelwidth C data china 10m2 wheelwid map wheeldepth C data china 10m2 wheeldep map wheelgradient C data china 10m2 wheelgrd map wheelman C data china 10m2 wheelman map wheelcohesion C data china 10m2 wheelcoh map ksatwt C data china 10m2 ksatwt map Texture fractionmu0 C data china 10m2 mu0 map fractionmul C data china 10m2 mu0 map fractionmu2 C data china 10m2 mu0 map 62 LISEM MANUAL version 2 x January 2 2002 63 fractionmu3 C data china 10m2 mu0 map fractionmu4 C data china 10m2 mu0 map fractionmu5 C data china 10m2 mu0 map NutsP peont C data china 10m2 pcont map psolute C data china 10m2 psolut map pefficiency C data china 10m2 peff map psorp C data china 10m2 Psorp map peonv C data china 10m2 Pconv map NutsNO3 no3cont C data china 10m2 NO3cont map no3solute C data china 10m2 NO3solut map no3efficiency C data china 10m2 NO3eff map no3sorp C data china 10m2 NO3sorp map
60. ity of overland flow Int Assoc Hydrol Sci Pub 189 45 63 Hoyningen Huene J von 1981 Die Interzeption des Niederschlags in landwirtschaftlichen Pflanzenbestanden Arbeitsbericht Deutscher Verband fur Wasserwirtschaft und Kulturbau DVWkK Braunschweig 63p Jetten V De Roo A and Favis Mortlock DT 1999 Evaluation of field scale and catchment scale soil erosion models in Modelling of Soil Erosion by Water on a Catchment Scale APJ de Roo ed GCTE Focus 3 workshop 14 18 April 1997 Utrecht University CATENA Special Issue Jetten VG De Roo APJ and Guerif J 1998 Sensitivity of the LISEM model to parameters related to agriculture in Global Change Modelling Soil Erosion by Water J Boardman ed NATO ASI series Jetten VG Boiffin J and De Roo APJ 1996 Defining Monitoring strategies for runoff and erosion studies in agricultural catchments a simulation approach Eur J Soil Sci 47 579 592 Kamphorst E Jetten VG Guerif J Pitkanen J lversen B Douglas J and Paz Gonzales A 2000 Predicting depressional storage from soil surface roughness Soil Sci Soc Am J 64 1749 1758 Li R Stevens MA and Simons DB 1976 Solutions to the Green and Ampt infilttration equation J Irrig Drain Div 2 239 248 LISEM 2000 Limburg Soil Erosion Model Faculty Geogr Sci Utrecht University The Netherlands http www geog uu ni lisem Ludwig B Boiffin J Chadoeuf J and Auzet AV 1995 Hydrological struc
61. ll width The width is ussually a field measured value width percalc chanwidt map if chanmask map ne 0 width CHANSIDE tangent of the angle between the channel side and the vertical 0 is a rectangular channel 1 is a side angle of 45 degrees 10 is a very wide channel 84 degrees Note that the width of the top of the water level depends on this side angle if the water rises the stream becomes wider but it cannot become wider than the gridcell percalc chanside map if chanmask map ne 0 0 7 3 Additional maps needed for EUROWISE All input and output maps in LISEM are in the format of the PCRaster GIS This raster GIS is produced by PCRaster environmental software and can be obtained through their website where you will find a complete list of functions and examples In order to run EUROWISE LISEM GULLIES a few additional maps are needed on top of the regular maps needed with the LISEM BASIC version Note that the names are not compulsory but default in the current version They can be changed individually in the interface EUROWISE needs a Digital Elevation model for the critical area assessment and a few additional maps that define the structure of the layers to be eroded DEM Digital elevation model used to delimit the critical areas according to the algorithm chosen in the interface by the user The analysis is done inside EUROWISE GULWIDTH initial width of the gully for those areas where incision takes
62. ltan model empirical sub model is based on a storage concept The main advantage of the model is the capability of recovery in soil infiltration capacity during periods of light or zero rainfall The infiltration rate is expressed in terms of cumulative infiltration initial soil water content and other soil variables P forceas STORE TP DF with f infiltration rate mm h FC infiltration rate at steady state mm h A the maximum possible increase in infiltration rate over the steady state rate FC mm h S storage potential of the soil mm above the impeding strata total porosity TP minus the antecedent soil water ASM S 1 ASM TP DF DF the effective depth to the impeding strata control zone depth mm TP total porosity volume ASM antecedent soil moisture saturation DR cumulative drainage mm F cumulative infiltration mm P dimensionless coefficient relating the rate of decrease in infiltration rate with increasing soil moisture content LISEM MANUAL version 2 x January 2 2002 10 Huggins and Monke 1968 introduced an expansion of the model assuming a relationship between percolation or drainage and soil water content Using both equations the recovery of infiltration rate as the result of a temporary interruption in rainfall can be predicted They assume drainage when soil moisture content in the control zone exceeds field capacity ar Bot Siac ioe 2 7
63. m there 3 This zone is accumulated along the network to give a continuous area 4 A critical threshold slope angle is applied when necessary depending on the area 5 Isolated critical pixels are removed 6 Isolated non critical pixels are classified as critical if the pixels upstream and downstream are also critical repair holes in the critical zone EE OL Fi Tree HHH Critical area analysis HHH binding INPUT MAPS Dem dem map Feritl fcritl map PCrit2 Crit2 map Reg fcrit3 map Ferit4 fcrit4 map Porits crits map initial SURFACE TOPOLOGY create ldd LISEM MANUAL version 2 x January 2 2002 30 report Ldd lddcreate Dem 1E25 1E25 1E25 1E25 create upstream area and slope map Upstream accuf lux Ldd cellarea Slope max slope Dem 0 001 B celllength COMPUTE CRITICAL THRESHOLDS critical threshold according to Vandaele 1996 report Feritl if Slope Upstream B 0 4 gt 0 5 and Slope gt 0 04 0 nominal 10 critical threshold according to Moore et al 1988 report Ferit2 if Slope Upstream B gt 18 and ln Upstream B Slope gt 6 8 0 nominal 10 critical threshold according to Vandaele et al 1996 report Ferit3 if Slope gt 0 025 Upstream 10000 0 4 0 nominal 10 Critical threshold according to Desmet and Govers report Ferit4 if Slope Upstream B 0 4 gt 0 72 0 nominal 10 critical threshold according t
64. ms yields a quadratic function that can be solved simply by retaining the positive root L Lat t t 8 2 15 which can be rewritten in the dimensional form as dI L 21 kdt 4 21 kdt 8kdt Q D 2 16 This is the relation used in LISEM whereby dl gt 0 if the solution is negative it has no meaning The Green and Ampt model is very sensitive to the choice of Ksat and initial moisture content The initial assumption that the wetting front moves down as a wet body parallel to the surface with a speed dictated by the Ksat is not correct Many researchers therefore suggested field variables a field porosity or a field Ksat or a suction at the wetting front that is not the matrix potential at a given time but a more soil property NOTE This means that in practice the Green and Ampt solution needs calibration either by decreasing the Ksat values or the storage capacity of the soil LISEM MANUAL version 2 x January 2 2002 12 2 3 4 Morel Seytoux and Verdin not implemented yet 2 3 5 Subtraction of Ksat The saturated hydraulic conductivity is subtracted from the net rainfall simulating instant saturation in a simple way This option can be used for testing and quick and dirty estimates 2 4 Surface definition on a sub gridcell level LISEM enables the simulation of several types of soil surfaces in a grid cell These represent different soil structures For small sized gridcells lt 100m2 t
65. n Synonyms used to describe erosion due to ephemeral gullies are concentrated flow erosion Foster 1986 Auzet et al 1995 talweg erosion Papy and Souchere 1993 thalweg gullies De Ploey 1990 megarills Foster 1986 rills in valley floors Evans and Cook 1987 valley bottom rills Boardman 1992 With respect to the differences between rill ephemeral gully and classical gully erosion it is clear that ephemeral gullies and classical gullies can be discerned based on their persistence In contrast to the permanency of classical gullies ephemeral gullies are short lived Definitions of ephemeral and classical gullies often refer to the means by which these gullies are resp are not obliterated i c normal tillage operations Defining the exact operation or equipment however is less relevant since this is variable in both space and time Relevant is the fact that once formed a classical gully evolves by erosion of the gully floor head cut migration and erosion of the gully walls which implies a combination of processes e g water erosion and mass movement As ephemeral gullies form are disguised and potentially form again on the same spot their evolution requires mainly a repetition of the incision process while the relative importance of head cut migration and erosion of the gully walls is less significant Differences between rills and ephemeral gullies are not always very clear Foster 1986 gives two firm argumen
66. ns a complete list of maps abd their paths so it is easier to adapt an existing run file of a different project than clicking on each map name in turn Clicking on a name opens a directory window and the name field can be linked to a specific map There are no compulsory names in LISEM but a series of default names are used that date from LISEM versions that did not have this name LISEM MANUAL version 2 x January 2 2002 52 selection feature Thus old databases can still be used The restore names button will replace all mapnames with their defaults and will fill up empty places ne Lisem for Windows verston 20 Bem IT CO Start Basic maps Simulation Output maps Catchment amp Lond use Sod euface Infiltration Channels Generel catchment mapes n area mark boundary check for al othe maps Slope graderit in direction of Hos Local Quan Drechon overland few direction 1 outlet map Map catchment quilet comespondng to LOD map Raingauge 2one ID numbers aoa Tae ace cover Du Vege ator arid ie Lea aea pdez ol the plart cove m a gildor OREA ch map Plart height im E Ed Goart map Whidlh of impermeable roads rn Look mi Sy china ke r SE SC senn map Width of grace ships im PS am Ez MADEIRE ee con resin i Hanning Grass orassman map maninge n of grass strips E 20102 rutin Se G nn Ges E charenszk map 9 Sen Eeim E Sm E tes20m I drg resim File n
67. nt soil structure based of the fraction in the gridcell Therefore the infiltration is averaged for each timestep 2 5 Storage in micro depressions The surface storage is not treated as a sharp threshold runoff takes place before the water level reaches some threshold value of average surface storage This is done because runoff at a micro scale is a spatial process of ponds that fill up and overflow into each other The LISEM MANUAL version 2 x January 2 2002 13 gridcell in LISEM represents an area of for instance 10x10 m and before the average storage of this surface is filled the water at the edges of this area is moving downstream The average depression storage can be measured at a given scale The start value is more difficult and in LISEM a pragmatic approach is taken based on the fraction of the surface that is ponded Surface storage is calculated using the Maximum Depression Storage MDS This is the threshold value of a given area above which surface micro depressions overflow all depressions are connected to each other and to an point outside the reference area so that in principle each additional drop of water will flow outside the reference area The MDS is determined by Kamphorst et al 2000 from 221 digital elevation models of various types of micro relief in a wide variety of agricultural circumstances and soil types The analysis is based on DEMs of roughly Jm Figure 1 shows the relation between the MDS and Random
68. o Vandaele et al 1997 Portugal report Ferit5 if Slope Upstream B gt 40 and ln Upstream B Slope gt 9 8 0 nominal 10 An example critical areas for the Kinderveld test site BE Figure 5 shows 6 images of the Kinderveld test area near Leuven BE where gullies where monitored in the MWISED project see introduction The test site has a size of 13 7 ha and a grid cell size of 5x5 m The measured gullies are shown as a black line while the white areas are the 5 critical areas susceptible to gully erosion It can be seen that all critical areas include the gullies except for algorithm 5 which begins too far downslope Also the figure shows that the algorithms 1 and 3 produce too large areas while 2 and 4 are closer to reality Since the main overland flow process is Hortonian overland flow criteria 4 seems the to give the best result 6 2 3 Ephemeral gully formation The section above results in a water flux and sediment flux on the surface that is distributed using the kinematic wave principle The sediment is a result of erosion which may or may not cause gully formation depending on the location in the field As is explained above the gullying is assumed to take place ONLY in the critical areas The following approach is taken to simulate the incision processes Gully width The gully formation i e the deepening of the critical area is not necessarily over the whole grid cell width the gully width depends on the peak dischar
69. outmul C data china res10m1 smul outmu2 C data china res10m1 smu2 outmu3 C data china res10m1 smu3 outmu4 C data china res10m1 smu4 outmu5 C data china res10m1 smu5 outmu6 C data china res10m1 smu6
70. phemeral gullies in the Belgian loessbelt and the Spanish Guadelantine area often occur on the same locations These zones of likely incision termed critical areas here can be derived from an analysis of the area contributing runoff A to a given location and the local slope of that location S Different types of critical thresholds for the Belgian loess belt are found in the literature For the EUROWISE model four empirical critical threshold values are evaluated e Critical threshold value according to Vandaele 1996 SA S05 6 1 e Critical threshold value according to Moore et al 1988 d gt 6 6 o A gt 18 and A 6 2 e Critical threshold value according to Vandaele et al 1996 o gt 0 025 A 10000 6 3 e Critical threshold value according to Desmet and Govers 1997 S A gt 0 72 6 4 The critical threshold values are area specific The equation of Moore et al 1988 is a more uniform relationship whereby A S gt 18 is related to the erosive power concentrated Hortonian overland flow while the relation n A S gt 6 8 is assumed to be a measure of soil saturation and therefore is more related to the process of saturated overland flow According to Poesen et al 1997 gully development in the Belgian loess belt is essentially caused by concentrated Hortonian overland flow Therefore Moore s equation was considered at first less appropriate for the area LISEM MANUAL version 2 x January 2 2002 28
71. place in practice this is the critical area This parameter is maybe not necessary and will disappear in the future based on a sensitivity analysis of various areas LISEM MANUAL version 2 x January 2 2002 46 GULLYMAN resistance to flow at the bottom of the gully based on Manning s n This wilol be purely based on assumptions but a value is needed like the channel maps in the lisem basic version BULKDENS this map can be made by interpolation of measured values or by reclassifying a soil or land use map The classification can be done with a lookup table as is explained in the LISEM BASIC input map section soil surface maps percalc bulkdens map lookupscalar unit soil tbl 1 where soil tbl is a text file containing bulk density values of each map unit NOTE that the gauges must be situated inside the Idd map area otherwise it will not be included in the spread operation GULDEPTH the depth to a second layer with a higher bulk density and cohesion Although in reality there can be a gradual increase in bulk density EUROWISE assumes an abrupt change to simulate the situation of a loose seedbed on a more compact sub soil This map determines to a large extent whether the widening of the gully The depth can be assumed constant percalc guldepth map scalar if unit map eg 1 8 12 gives a map with a depth of 8 cm for unit 1 and 12 cm for all other units Also a random change noise around a mean value could be assumed per
72. posit further downstream Below an example is shown of these output maps left is erosion mostly in the thalweg right is deposition on the slopes LISEM MANUAL version 2 x January 2 2002 56 9 4 Timeseries The following timeseries output maps can always be generated runoff as discharge in l s or unit discharge l s m water height at the surface mm runoff height mm concentration of suspended sediment g l erosion ton ha deposition ton ha LISEM Wheeltracks has the same output map options except that the discharge and runoff water height will include the flow in the wheeltracks LISEM Multiclass has as additional output the timeseries of suspended sediment concentration of all 6 classes LISEM Nutrients has as additional output the timeseries of the NO3 NH4 and P losses in solution suspension and infiltration as well as the suspended clay concentration LISEM Gullies has as additional output the timeseries of the gully with depth and volume LISEM MANUAL version 2 x January 2 2002 Of 10 REFERENCES note these references are copied from LISEM literature and not checked yet Aston AR 1979 Rainfall interception by eight small trees J Hydrol 42 383 396 Auzet AV Boiffin J and Ludwig B 1995 Concentrated flow erosion in cultivated catchments influence of soil surface state Eath Planet Sci Lett 20 759 767 Beasley DB and Huggins LF 1982 ANSWERS Users Manual U S Environmen
73. r 01000 THETAS1 Saturated volumetric soil moisture content scalar l 0 4 THETAI1 Initial volumetric soil moisture content scalar E 0 1 Pai Soil water tension at the wetting front scalar em 0 1000 SOILDEP4 Soil depth scalar Imm 0 1000 G amp A1 Additional surfaces In addition separate ksat maps have to be defined for crusted soils wheel tracks or grass strips These maps are required when any or all of the extra options in the infiltration options menu are checked Map name Contents Type Unit Range KSATWT wheeltrack Ksat used with infiltration option eee E JA include wheel tracks S grass strip Ksat used with infiltration option DCH SO TE EM EE include grass strips KSATGRA KSATCRST crust Ksat used with infiltration option ae manr lo100G include crusts NOTE in addition the user has to define the maps WHEELWID MAP GRASSWID MAP and or CRUSTFRC MAP These options are only used for the first layer of the Green and Ampt module If a 2 layer Green and Ampt is used the second layer will be identical for all option G amp A2 Two layer Green amp Ampt Requires all maps of Green and Ampt 1 layer plus an identical set for 2nd layer The depth of the second layer soildep2 is only of consequence when the impermeable sub soil option is checked see remark above Map name Contents Type Unit Range KSAT2 see KSAT1 aaler Imm hr see KSAT1 ITHETAS2 see THETAS1 scalar se
74. r more freedom and it is much clearer what happens in the simulation however this also means that the user knows what he she is doing Basic processes incorporated in the model are rainfall interception surface storage in micro depressions infiltration vertical movement of water in the soil overland flow channel flow in man made ditches detachment by rainfall and throughfall transport capacity and detachment by overland flow Also the influence of compaction e g by tractor wheelings small paved roads smaller than the pixel size and surface sealing on the hydrological and soil erosion processes is taken into account The processes are described in detail in the theory section The latest developments include the modelling of wheel tracks as small channels multiple sediment classes for erosion and deposition the loss of P NO3 and NH4 in solution and in suspension the incision and formation of gullies Although not directly visible to the user the model is one of the first examples of a physically based model that is completely integrated in a raster Geographical Information System PCRaster van Deursen amp Wesseling 1992 The source code is a mix of C code GIS operations mathematical operations and hydrological functions kinematic wave Richards equation No conversions are necessary between PCRaster and the model All input and output maps are raster maps that can be easily displayed and treated with the PCRa
75. runoff b Additional micro relief storage accompanied by runoff c Runoff only with the micro relief storage To determine the transition from stage a to stage b the data of Onstad 1984 were re analyzed From this analysis the following equation was developed simulating the starting point of runoff RET start Im cm RET start 0 0527 RET max RR 0 0049S Thus during stage 1 all excess rainfall becomes depression storage Then from point RET starr tO point RET max both overland flow and further depressional storage occur based on a linear filling of the depressions until RET max After RET max all excess rainfall becomes runoff Thus using these relationships the actual storage in depressions RET in cm can be calculated Also using the same input data the maximum fraction of the surface covered with water FWA max can be calculated Onstad 1984 FWAwax 0 152RR 0 008RR 0 008RRS The actual fraction of the surface covered with water FWA is calculated using a relationship based on the work of Moore amp Larson 1979 and Onstad 1984 FWA FWAwax RET RET max S Ponded area is calculated according to the following equation FWA 1 exp a WH RETrain FWAmax where a is a calibration factor currently at 5 and WH is the water height of the water layer at the surface version 1 53 and earlier In earlier versions the FWA was defined as a linear increase based on the stages 1 2 and 3 described abo
76. s defined as erosion in numerous small channels that are uniformly distributed across the slope and that can be obliterated by tillage Hutchinson and Pritchard 1976 According to the Soil Science Society of America 1997 rill erosion is characterized by numerous and randomly occurring small channels of only several centimetres in depth Rills form on sloping fields mainly on cultivated soils Rills can follow tillage marks or they may develop much like a drainage network of rivers in a large basin Foster 1986 Classical gully erosion is defined as erosion in channels that are too deep to cross with farm equipment Hutchinson and Pritchard 1976 According to the USDA Soil Conservation Service 1966 classical gullies are channels formed by concentrated flow of water removing upland soil and parent material and of a size to large to be obliterated by normal tillage operations Bank gullies form where a concentrated flow zone a rill or an ephemeral gully crosses and erodes an earth bank e g a terrace a river bank Poesen 1993 Poesen and Hooke 1997 Bank gullies may develop upslope by head cut migration LISEM MANUAL version 2 x January 2 2002 24 Ephemeral gully erosion was first comprehensively discussed by Foster 1986 The introduction of ephemeral gullies as a separate erosion class resulted from the fact that in the 1980 s soil conservationists in the US became progressively aware that if only rills and classical gullies ar
77. s n map while the strip itself is specified here Surface types Activating this option will enable the user to define surface types that occupy only a fraction of the pixel This influences infiltration and in the case of grass strips also the flow resistance At least two additional maps are needed one that defines for each cell the fraction of the cell containing this type e g crustfrc map contains values 0 1 and other maps that define the infiltration characteristics e g Ksatcrst map tell LISEM how much the ksat is for the crusted fraction of a cell When the SWATRE infiltration model is chosen the structure is different Infiltration Clicking on an infiltration model will activate certain map input options Additional choices for infiltration are e subsoil impermeable the layer below the last layer depends on the infiltration method infiltration zone is assumed impermeable Thus the soil will gradually fill up This has not been tested for the Holtan equation otion 3 e callibration Ksat the Ksat value in the soil physics tables see SWATRE or in the ksat maps other infiltration methods is multiplied by this factor Ks new Ks_table factor 100 8 3 Basic maps LISEM Basic needs a series of input maps organized as described in the input maps section Catchment amp Land use Soil suface Infiltration Channels Catchment and land use etc In these windows the maps can be selected The run file contai
78. ster software LISEM MANUAL version 2 x January 2 2002 6 2 LISEM BASIC THEORETICAL FRAMEWORK For each gridcell rainfall and interception by plants are calculated after which infiltration and surface storage are subtracted to give net runoff Subsequently splash en flow erosion and deposition are calculated using the stream power principle and the water and sediment are routed to the outlet with a kinematic wave procedure Special cases can be defined for roads and compacted areas and man made channels can be taken into consideration Figure 2 1 Flow chart of LISEM BASIC tari cell H N ei f fraction Zi surface type K h theta L wen mm mm mm mn mm mm mm mm mm mm mm mm mm mm mm mm mm mm mm mm mm mm mm mm mm mm wm mm mn ds en mm ms interrillt rill D slope OGY ME e Channel suspendec oe Ger fi SeqCIMeENT downslope Fi channel shape Qe Channel CH Cohesion O50 LISEM MANUAL version 2 x January 2 2002 T 2 1 Rainfall LISEM uses rainfall intensities per time interval so called break point data These are stored in an ASCII file Data from multiple raingauges can be entered in an ASCII input data file with columns for each rainfall gauge A map with areas having the raingauge ID number determines the spatial distributed rainfall input This map can be based for example on Thiessen polygons or on a geomorphological analysis assigning valleys to raingauges T
79. t file PROFILE INP In this file the number of nodes are given for the solution of the Richards equation using a finite difference approximation and their depths These are independent of the actual soil horizons NOTE that the node depths are used in LISEM as boundaries between simulation layers not centres Below the nodes the soil profiles are given see syntax below with pointers to the names of the tables describing the soil physical relations pF curve and hydraulic conductivity curve of a particular soil type NOTE that in this file ALL information is stored including that of the units for crusts wheel tracks and grass Strips So if these features are simulated the file PROFILE INP has to be adjusted to reflect their presence LISEM MANUAL version 2 x January 2 2002 40 The file PROFILE INP has the following layout e ee ee ee ee e e Reain of file zess e 14 number of soil lavers 2 5 1 denth of hoiundarv between first and second laver cm 5 2 denth of baundarv between second and third laver 10 3 etc 20 25 30 40 50 60 70 80 90 100 14 denth of final soil laver cm 1 descrintion of man unit 1 Used in Swatre if ASCRP TRT 15 SUR REST TRT the name of the soil nhvsics table to he used the denth down to which the above table is used cm use this table for denth 15 30 30 C AT TRT 100 2 descrintion of man unit 2 Used in Swatre if ASCRP A TBL etc 15 STIR REST TRT
80. tal Protection Agency Region V Chicago Illinois Purdue University West Lafayette Indiana 54p Belmans C Wesseling JG and Feddes RA 1983 Simulation model of the water balance of a cropped soil SWATRE J Hydrol 63 271 286 Beven KJ and AM Binley 1992 The future of distributed models model calibration and uncertainty prediction Hydrol Proc 6 279 298 Boardman J and _ Favis Mortlock DT 1998 Modelling Soil Erosion by Water Springer Verlag NATO ASI Series l 55 Berlin Boardman J Ligneau L De Roo APJ and Vandaele K 1994 Flooding of property by runoff from agricultural land in northwestern Europe Geomorph 10 183 196 Chow VT Maidment DR and Mays LW 1988 Applied Hydrology McGraw Hill 572p De Roo APJ Offermans RJE and Cremers NHDT 1996b LISEM a single event physically based hydrologic and soil erosion model for drainage basins Il Sensitivity analysis validation and application Hydrol Proc 10 1118 1127 De Roo APJ Wesseling CG and Ritsema CJ 1996a LISEM a single event physically based hydrologic and soil erosion model for drainage basins Theory input and output Hydrol Proc 10 1107 1117 Favis Mortlock DT 1998 Validation of field scale soil erosion models using common datasets in Modelling Soil Erosion by Water J Boardman and DT Favis Mortlock eds Springer Verlag NATO ASI Series I 55 89 128 Govers G 1990 Empirical relationships on the transporting capac
81. ted as e Ds Df Dp 2 26 2 6 1 Splash detachment Splash detachment Ds g s is simulated as a function of soil aggregate stability rainfall kinetic energy and the depth of the surface water layer The kinetic energy can arise from both direct throughfall and drainage from leaves Using splash tests the following general equation has been derived unpublished data Ds 2 82 As Ke exp 1 48 h 2 96 P A 2 27 in which Ds is splash detachment g s As is the aggregate stability median number of drops to decrease the aggregate by 50 Ke is rainfall or throughfall kinetic energy J m h is the depth of the surface water layer mm P is the amount of rainfall or throughfall under the plant canopy in the timestep mm A is the surface over which the splash takes place m In LISEM splash detachment is calculated as the sum of all splash under and beside plants throughfall and rainfall and on ponded and dry areas DS_Tpondea A fpa 1 cover A and Ke is Ke 2 28 Ds_toondead A fpa cover A and Ke is Ke DS ro A 1 fpa 1 cover A and Ke is Ke DS Lo A 1 fpa cover A and Ke is Ke The kinetic energy of free rainfall and throughfall from the plant canopy as respectively Ke 8 95 8 44 log 1 2 29 Ke 15 8 saqrt h 5 87 where is the rainfall intensity mm h and h is the height of the plants m In equations 8a to 8d fis the splash delivery fraction a user defined fraction that determin
82. than 0 percalc grad map sin atan max 0 001 grad map ID this map can be made in various ways using Tiessen Polygons or zones based on relief The numbers in this map must correspond to the number of rain gauges in the rainfall file An example is to create a map according to Thiessen polygons from a map with pxiels that have the numbers of the rain gauges percalc id map nominal spreadzone gauge map 0 1 Alternatively the relief can be taken more into account by taking the slope as a weighing factor percalc id map nominal spreadzone gauge map 0 grad map or by using the mean elevation line between two gauges as a separation line gauges have id numbers 1 2 and 3 here dem is a map percalc al percalc a2 percale a3 maptotal if pl eq 1 dem 0 maptotal if p2 eq 2 dem 0 maptotal if p3 eq 3 dem 0 percalc a4 al a2 2 porcalo as a2 a3 2 percalc id 3 LE ap nominal if dem lt a4 1 if dem lt a5 and dem ge a4 2 3 NOTE that the gauges must be situated inside the Idd map area otherwise it will not be included in the spread operation OUTLET a map with values 0 background and 1 which is the main outlet On this cells a hydrograph and sedigraph are stored as ASCII files Two additional cells can be given numbers 2 and 3 compulsory to store hydrographs and sedigraphs for additional locations e g sub catchments The main outlet is found by pcrcalc outlet map pit Idd map LISE
83. ts to distinguish rills from gullies 1 Flow in rills is usually classified as a part of overland flow that is assumed to occur uniformly across a slope even though it is concentrated in rills In contrast flow in ephemeral gullies is clearly channelized Also erosion due to rills will affect the entire slope while erosion due to ephemeral gullies is much more confined However net erosion due to rills ephemeral gullies should be assessed by taking into account the combined effect of water erosion formation and tillage erosion removal 2 Subsequent ephemeral gullies will occur in the same spot while the position of rills is variable from time to time since it is strongly influenced by micro topography e g tillage marks In addition to the arguments of Foster 1986 it can be remarked that rills and gullies also differ in the way they contribute to the drainage pattern of a watershed While rills are usually limited by field borders ephemeral gullies often extend over multiple fields In terms of erosion this implies that rills normally only redistribute soil within one field whereas ephemeral gullies transport soil material to completely different parts of the watershed The difference between rills and ephemeral gullies with respect to LISEM MANUAL version 2 x January 2 2002 25 the way they affect a watershed s hydrology is also clearly illustrated by Steegen et al 2000 They showed that there exists a positive relation between
84. ture and erosion damage caused by concentrated flow in cultivated catchment Catena 25 227 252 Merriam RA 1960 A note on the interception loss equation J Geophys Res 65 3850 3851 Moore ID and Foster GR 1990 Hydraulics and overland flow in Process Studies in Hillslope Hydrology MG Anderson and TP Burt eds John Wiley 215 254 Morgan RPC Quinton JN Smith RE Govers G Poesen JWA Auerswald K Chisci G Torri D Styczen ME and Folly AV 1998 The European Soil Erosion Model EUROSEM Documentation and User Guide Silsoe College Cranfield University Nearing MA 2000 Evaluating soil erosion models using measured plot data Accounting for variability in the data Earth Surf Prop Landf accepted Onstad CA 1984 Depressional storage on tilled soil surfaces Trans Am Soc Agric Eng 27 729 732 Rauws G and Govers G 1988 Hydraulic and soil mechanical aspects of rill generation on agricultural soils J Soil Sci 39 111 124 LISEM MANUAL version 2 x January 2 2002 58 Risse LM Nearing MA and Laflen JM 1991 Assessment of error in the Universal Soil Loss Equation using natural runoff plot data Am Soc Agric Eng Paper 91 2558 Am Soc Agric Eng Winter Meeting Chicago IL Dec 17 20 Takken Jetten VG Govers G Nachtergaele J and Steegen A 2001 The effect of tillage induced roughness on runoff and erosion patterns Geomorph 37 in press Takken 2000 Effects of
85. type An average water height is than calculated for each gridcell resulting in an average hydraulic radius with which the velocity is calculated The field surface has a certain roughness and therefore only a part of the water will move field wheel road track dry ponded bn CERN A tlowwidth Gridcell DX Water height Figure 2 7 Calculation of average water height and flowwidth The velocity V m s is calculated with Manning s formula V R sqrt S n 2 22 In which R hydraulic radius m calculated with the flowwidth and average water height see figure 5 S sine of the slope fraction n Manning s n dimensionless The discharge Q m s per cell is then calculated with Chow et al 88 A adr 2 23 LISEM MANUAL version 2 x January 2 2002 18 In which a Wie Sat 2 24 b 0 6 A wet cross section m There is evidence that alpha is constant for small rills and independent of slope and resistance Govers 1997 because the flow will find a new equilibrium and uses its energy to form new rill dimensions while the velocity does not change Research is currently being done to see if this should be incorporated in LISEM For the distributed overland and channel flow routing a four point finite difference solution of the kinematic wave is used together with Manning s equation Procedures of the numerical solution can be found in Chow et al 1988 and Moore amp Foster 1
86. ulation times Begin time 1 End time 99 Timestep 5 General options No Erosion simulation 0 Include main channels 0 Channel Infiltration 0 Additional options Grassstrip Mannings n 0 3 Splash Delivery Ratio 0 1 Infiltration Method 3 Include wheeltracks 0 Include grass strips 0 Include crusts 0 Ksat calibration 100 Impermeable sublayer 0 SWATRE internal minimum timestep Matric head files 0 Geometric mean Ksat 0 LISEM MANUAL version 2 x January 2 2002 Output Runoff maps in 1 s m 0 Timeseries as PCRaster 0 Regular runoff output 1 Output interval 4 User defined output 0 Output times CheckOutputMaps 1 1 0 0 0 0 CheckOutputMapsNUT 0 1 0 1 0 0 0 0 0 CheckOutputMapsMC 0 1 1 1 0 0 0 0 0 CheckOutputMapsGUL 1 1 0 0 0 0 Texture classes ClassMu 2 16 32 53 75 105 TCCal map names Catchment area C data china 10m2 area map grad C data china 10m2 grad map ldd C data china 10m2 ldd map outlet C data china 10m2 outlet map TD C data china 10m2 id map Landuse cover C data china 10m2 per map lai C data china 10m2 lai map ch C data china 10m2 ch map road C data china 10m2 roadwidt map grasstrip C data china 10m2 grasswid map Erosion coh C data china 10m2 coh map cohadd C data china 10m2 cohadd map aggrstab C data china 10m2 aggrstab map d50 C data china 10m2 d50 map Surface rr C data china 10m2 rr map manning C data china 10m2 n map crustfirc C dat
87. ve However the increase was defined in such a way that abrupt changes inj fraction of ponded area were calculated with only a small increase in water height Therefore the linear equations were replaced with the single exponential equation above LISEM MANUAL version 2 x January 2 2002 17 Also in earlier versions a part of the depressions was not included in the FWA because they were thought to be isolated The effects of this was hardly noticeable and the fraction of depressions isolated was based on observations rather than a spatial analysis Thus this variable became just an extra parameter to calibrate and it was removed from the source code in order to simplify depression storaage The fraction of isolated depressions FWA so was calculated as follows Based on the findings of Linden et al 1988 some depressions are temporarily isolated and do not contribute to overland flow From their data it was determined that if the storage RET was less than 75 of the RETMAX 20 of the depressions are isolated If RET is between 75 and 100 of RETMAX then the following equation was derived FWA so 0 20 FWA 1 4 RET RET max 0 75 2 5 2 Overland flow and channel flow A gridcell can have more than one type of surface e g a road smaller than DX is impermeable a wheeltrack is compacted and a field surface may be ponded or not The infiltration characteristics vary according to the surface and the infiltration is calculated for each
88. ver import maps from IDRISI and ARC INFO basic Arc grid format Also PCRaster has extensive capabilities of geostatistical interpolation 7 2 The input maps All input and output maps in LISEM are in the format of the PCRaster GIS This raster GIS is produced by PCRaster environmental software and can be obtained through their website where you will find a complete list of functions and examples LISEM needs a minimum of 24 maps depending on the input options selected in the interface e g enabling the simulation of ditches requires additional maps and some infiltration option require more maps than others If needed all maps can be derived from 4 base maps digital elevation model land use soil type and impermeable areas such as tarred roads this is needed because the road can be narrower than the gridcell size and LISEM needs to know what type of soil or land use exists adjacent to the road All input data can be derived form these four base maps but off course other sources can be used to make the input maps geostatistical interpolation remote sensing etc LISEM MANUAL version 2 x January 2 2002 35 The spatial input data for LISEM can be structured as follows Catchment maps Vegetation maps Soil surface maps Infiltration related maps Erosion deposition related maps Channels oe e In this part all input maps are listed with the PCRaster commands to make them Since PCRaster is also capable of running ma

Limburg Soil Erosion Model USER MANUAL

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