Useful Tools for Predicting Erosion from Disturbed Rangelands: Disturbed WEPP for Rangelands The Water Erosion Prediction Project in the Forest Service

Objectives of Presentation n To present three interfaces for Predicting Water Erosion on Rangelands

WEPP... n

n n Models soil erosion processes

WEPP... n n Models soil erosion processes n Was developed cooperatively with –ARS –NRCS (SCS) –BLM –Forest Service –....

WEPP... n Is intended to replace the USLE –Which predicts Erosion Only

WEPP... n Is intended to replace the USLE –Which predicts Erosion Only n WEPP Predicts –Runoff –Erosion Rates –Sediment yield

WEPP Versions n Hillslope –Describes a single strip of hillslope

WEPP Versions n Hillslope –Describes a single strip of hillslope n Watershed –Links hillslopes, channels, and impoundments –Very difficult to run

WEPP Versions n Hillslope –Describes a single strip of hillslope n Watershed –Links hillslopes, channels, and impoundments –Very difficult to run n GIS Tool –GeoWEPP Prototype now available –Some enthusiasts are developing custom methods

n Hillslope –Describes a single strip of hillslope n Watershed –Links hillslopes, channels, and impoundments –Very difficult to run n GIS Tool –GeoWEPP Prototype now available –Some enthusiasts are developing custom methods n FS WEPP Interfaces –For ease of use on the internet –ARS has one too WEPP Versions

WEPP Processes 1 n Rainfall, infiltration, runoff, soil water

WEPP Processes 2 n Rainfall, infiltration, runoff, soil water n Soil detachment, transport, deposition and delivery

WEPP Processes 3 n Rainfall, infiltration, runoff, soil water n Soil detachment, transport, deposition and delivery n Plant growth, evapotranspiration, and senescence

WEPP Processes 4 n Rainfall, infiltration, runoff, soil water n Soil detachment, transport, deposition and delivery n Plant growth, evapotranspiration, and senescence n Residue accumulation and decay

WEPP Processes 5 n Rainfall, infiltration, runoff, soil water n Soil detachment, transport, deposition and delivery n Plant growth, evapotranspiration, and senescence n Residue accumulation and decay n Soil consolidation

Erosion Processes 1 n Interrill Erosion –Raindrop splash –Shallow Overland Flow

Erosion Processes 2 n Interrill Erosion –Raindrop splash –Shallow Overland Flow n Rill Erosion –Concentrated Channel Flow –Assumes about 1 m spacing between rills »Varied for roads

Erosion Processes 3 n Interrill Erosion –Raindrop splash –Shallow Overland Flow n Rill Erosion –Concentrated Channel Flow –Assumes about 1 m spacing between rills »Varied for roads n WEPP does NOT model gullying or landslides

Overland Flow Elements n Describe variation in soil and vegetation down a hillslope OFE 1 OFE 2 OFE 3

FSWEPP File Structure Model WEPP Interface FSWEPP Internet Climate CLIGEN & Prism User Web Browser

GeoWEPP File Structure Model WEPP DATA DEM Digital Raster Interface GeoWEPP Topographic Analysis TOPAZ GIS ArcView Climate CLIGEN (& Prism)

Limitations to WEPP n Scale may be too small –Users frequently want 10 sq mi + watersheds

Example WEPP Application n Fort Carson, Colorado n Nearest Climate Station: Timpas, CO n Typical Slope Length: 300 m (1000 ft) n Steepness: 25% n Soil: Loam n Vegetation: Grass/Sage, about 30% cover n Observed erosion rates: 2.5 Mg/ha (1 t/acre)

Disturbed WEPP Performance Avg Erosion = 2.5 Mg/ha

Disturbed WEPP Template OFE 1OFE 2 Slope 1 Slope 2 Slope 3 Slope 4 Treatment 1 Treatment 2

ERMiT Template OFE 1 OFE 2 Top Slope Average Slope Toe Slope OFE 3 P(Erosion) = f(P(Climate), P(Soil), P(Distribution)) For forest, chaparral, and rangeland fire applications Post processing for mitigation evaluation

GeoWEPP Template n Download (or obtain) a digital elevation model … n Select watershed outlet … –Up to 2 sq mi for watershed output (“Offsite”) –No area limit for hillside output (“Onsite”) n Select files developed in WEPP Windows n Do not try ArcView Functions until all GeoWEPP runs complete

Download GeoWEPP Topo Data Digital Elevation ModelDigital Raster Graphic From an NRCS Lighthouse Web Site

GeoWEPP defines channels and hillslopes Stream Network Using ARS TOPAZ Topographic Model Representative Hillslopes Area = 324 ha (800 acres)

GeoWEPP Calculates Hillside Erosion and Sediment Yield Hillside Erosion Using WEPP Watershed Version Sediment Yields from Hills

GeoWEPP Calculates Channel Sediment Routing ChannelInput Mg Output Mg Delivery Ratio0.6 Avg Erosion0.5 t/ha(0.2 t/a) 4 3 2

Conclusions n WEPP Technology shows considerable promise for natural resources to aid in site- specific and small watershed erosion analysis on rangelands

Questions & Comments?