Useful Tools for Predicting Erosion from Disturbed Rangelands: Disturbed WEPP for Rangelands

The Water Erosion Prediction Project in

the Forest Service

Objectives of Presentation

To present three interfaces for Predicting Water Erosion on Rangelands

WEPP ...

WEPP ...

Models soil erosion processes

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 ...

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

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 1

Rainfall, infiltration, runoff, soil water

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 1

Interrill Erosion– Raindrop splash– Shallow Overland Flow

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

Overland Flow Elements

Describe variation in soil and vegetation down a hillslope

OFE 1OFE 2

OFE 3

FSWEPP File Structure

ModelWEPP

InterfaceFSWEPPInternet

ClimateCLIGEN& Prism

UserWeb

Browser

GeoWEPP File Structure

ModelWEPP

DATADEM

DigitalRaster

InterfaceGeoWEP

P

Topographic AnalysisTOPAZ

GIS ArcView

ClimateCLIGEN

(& Prism)

Limitations to WEPP

Scale may be too small– Users frequently want 10 sq mi + watersheds

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

Disturbed WEPP Template

OFE 1 OFE 2

Slope 1

Slope 2

Slope 3Slope 4

Treatment 1

Treatment 2

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

Questions & Comments?