Useful Tools for Predicting Erosion from Disturbed Rangelands: Disturbed WEPP for Rangelands The...
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Transcript of Useful Tools for Predicting Erosion from Disturbed Rangelands: Disturbed WEPP for Rangelands The...
Useful Tools for Predicting Erosion from Disturbed Rangelands: Disturbed WEPP for Rangelands
The Water Erosion Prediction Project in
the Forest Service
WEPP ...
Models soil erosion processes Was developed cooperatively with
– ARS– NRCS (SCS)– BLM– Forest Service– ....
WEPP ...
Is intended to replace the USLE– Which predicts Erosion Only
WEPP Predicts – Runoff– Erosion Rates– Sediment yield
WEPP Versions
Hillslope– Describes a single strip of hillslope
Watershed– Links hillslopes, channels,
and impoundments– Very difficult to run
WEPP Versions
Hillslope– Describes a single strip of hillslope
Watershed– Links hillslopes, channels,
and impoundments
– Very difficult to run
GIS Tool– GeoWEPP Prototype now available– Some enthusiasts are developing
custom methods
Hillslope– Describes a single strip of hillslope
Watershed– Links hillslopes, channels,
and impoundments
– Very difficult to run
GIS Tool– GeoWEPP Prototype now available
– Some enthusiasts are developing custom methods
FS WEPP Interfaces– For ease of use on the internet
– ARS has one too
WEPP Versions
WEPP Processes 2
Rainfall, infiltration, runoff, soil water Soil detachment, transport, deposition and
delivery
WEPP Processes 3
Rainfall, infiltration, runoff, soil water
Soil detachment, transport, deposition and delivery
Plant growth, evapotranspiration, and senescence
WEPP Processes 4
Rainfall, infiltration, runoff, soil water
Soil detachment, transport, deposition and delivery
Plant growth, evapotranspiration, and senescence
Residue accumulation and decay
WEPP Processes 5
Rainfall, infiltration, runoff, soil water
Soil detachment, transport, deposition and delivery
Plant growth, evapotranspiration, and senescence Residue accumulation and decay Soil consolidation
Erosion Processes 2
Interrill Erosion– Raindrop splash
– Shallow Overland Flow
Rill Erosion– Concentrated Channel Flow– Assumes about 1 m spacing
between rills» Varied for roads
Erosion Processes 3
Interrill Erosion– Raindrop splash
– Shallow Overland Flow
Rill Erosion– Concentrated Channel Flow
– Assumes about 1 m spacing between rills» Varied for roads
WEPP does NOT model gullying or landslides
GeoWEPP File Structure
ModelWEPP
DATADEM
DigitalRaster
InterfaceGeoWEP
P
Topographic AnalysisTOPAZ
GIS ArcView
ClimateCLIGEN
(& Prism)
Example WEPP Application
Fort Carson, Colorado Nearest Climate Station: Timpas, CO Typical Slope Length: 300 m (1000 ft) Steepness: 25% Soil: Loam Vegetation: Grass/Sage,
about 30% cover Observed erosion rates:
2.5 Mg/ha (1 t/acre)
Disturbed WEPP Performance
Predicted Vs. Observed Disturbed Rangeland Sediment Delivery
y = 0.9593x + 0.681
R2 = 0.7315
0123456
0 2 4 6Observed Sediment Delivery (Mg/ha)
Pre
dict
ed S
edim
ent
Del
iver
y (M
g/ha
)
Avg Erosion = 2.5 Mg/ha
ERMiT Template
OFE 1
OFE 2Top Slope
Average Slope
Toe Slope
OFE 3
P(Erosion) = f(P(Climate), P(Soil), P(Distribution))
For forest, chaparral, and rangeland fire applicationsPost processing for mitigation evaluation
GeoWEPP Template
Download (or obtain) a digital elevation model …
Select watershed outlet …– Up to 2 sq mi for watershed output (“Offsite”)– No area limit for hillside output (“Onsite”)
Select files developed in WEPP Windows Do not try ArcView Functions until all
GeoWEPP runs complete
Download GeoWEPP Topo Data
Digital Elevation Model Digital 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
Channel Input
Mg
OutputMg
2 91 171
3 45 51
4 16 18
Delivery Ratio 0.6
Avg Erosion 0.5 t/ha (0.2 t/a)
43
2
Conclusions
WEPP Technology shows considerable promise for natural resources to aid in site-specific and small watershed erosion analysis on rangelands