Model Integration - How WEPP inputs are calculated from GIS data. ( ArcGIS,TOPAZ, Topwepp)

Model Integration - How WEPP inputs are calculated from GIS data. ( ArcGIS,TOPAZ, Topwepp)

ArcGIS 9.1-9.3 Allows user to locate area of interest, assemble grids, visualize outputs. TOPAZ Performs DEM analysis, watershed delineation, subcatchments, flow direction, channel network. Topwepp Builds WEPP inputs from grids, runs WEPP model, produces output maps.

WEPP background GIS implementation ArcGIS 9.1-9.3,TOPAZ, Topwepp Limitations Future work areas

Hill 1 Hill 2 OFE 1 OFE 2 Hill 3 Hill 4 Hillslopes Overland flow elements OFE s Channels / Impoundments Watershed structure Soils Management Climate Channel Hill 5 Impoundment Watershed outlet

User manually assembles hillslopes, channels to form watershed. Representative hillslopes for sub-catchments. Time consuming for all but simple structures. Discrepancy between users using different slope representations.

Derive WEPP slope profiles from DEM and TOPAZ output grids. Use soil and land use maps to help determine WEPP soil and management inputs. Provide for watershed (representative hillslope) WEPP simulations and also detail flowpath simulations.

Uses a representative hillslope for each subcatchment and channel. Runs WEPP watershed simulation with channel routing. Each subcatchment is assigned a single value for soil loss which is the average over the representative profile. Same simulation as Windows interface watershed.

Runs WEPP for each flowpath. Usually several hundred WEPP runs. Soil loss values are weighted where flowpaths merge. Soil loss values are displayed along the cells of the profile. More detailed results than hillslope approach No channel routing.

ArcGIS DEM, CSA, MCL TOPAZ model Subcatchments, boundary, channel network grids Topwepp Soil, management grids + legends Soil loss grids, reports Flowvectors, flowpath, slope grids WEPP Slope, management, soil files, projects, structures Plot Output, main text outputs WEPP model

Jurgen Garbrecht USDA-ARS Grazinglands research laboratory Lawrence W. Martz Dept. of Geography, Univ. of Saskatchewan http://www.ars.usda.gov/main/docs.htm?docid=21167 Digital landscape analysis tool (using grid based DEM s) delineate watersheds subcatchment areas channel network structure

TOPAZ Delineated Subcatchments

Tools: ArcGIS 9.1-9.3 TOPAZ Delineate from: outlet point DEM area outlet

Minimum Channel Length Critical Source Area Flow direction Flow accumulation number of upstream cells contributing to form channel TOPAZ output

Set of Rules: number size (area, cell size, etc.) channel / hillslopes TOPAZ Output Grid

NETFUL channel network BOUND watershed boundary SUBWTA - identifies indices for subcatchments and channels. FVSLOP slope at each cell FLOPAT defines flowpath start and end points. FLOVEC drainage direction at each cell

Uses TOPAZ output files Soils and management grids from ArcView Calculates profiles for watershed and flowpath simulations Uses dominant management and soil for each flowpath or hillsllope. Runs WEPP, merges outputs into grids that ArcView reads.

WEPP channels WEPP hillslopes

Flowpaths Watershed (grid based DEM) Flowpath outlet Slope Profile of flowpath for WEPP run

z Determined using all flowpaths in a subcatchment. l

p = 1 2 3 4 m E i m p 1 z m p 1 p, i * k p k p L 3 2 1 E i = weighted slope value for all flowpaths at a distance i from channel Z p,i = slope of flowpath p at distance i from channel k p = weighing factor (a*l)

Hillslope methods Method #1: Match channel length to adjacent hillslope width and use A=W*L to obtain length of hillslope. Method #2: Calculate a representative slope profile length. Used for top hillslopes. Method #1 Method #2 Method #1 L L W

hillslope Discharge weighted mean length of all flowpaths within irregular overland area. L n l i i 1 n i 1 * a a i i l flow path length a upstream drainage area W = A / L

Raster based watershed Interactions. Weighting. No channel routing. Numerous WEPP runs. (One for each flowpath)).

WEPP output plot file is used to get soil loss values down the profile. These values are interpolated to fit along the flowpath grid cells. When only one flowpath occupies a cell the soil loss value at that point is used. Where flowpaths merge the soil loss values from all flowpaths at that cell are weighted based on cumulative length from channel and area of contributing flowpath from the channel to that cell.

TOPAZ output grids for slope, subcatchment indices (hillslopes and channels), flow vectors, flowpath positions. Soils map layer Management map layer

Management Soils Subcatchment areas HILLSLOPES (single OFE)

Soil and management types are associated with actual WEPP inputs as part of topwepp program. User sets up what associations are used. The dominant soil or management for each subcatchment is used in hillslope simulation. (single OFE) Flowpath simulations can have multiple landuses and/or soils.

Current version uses single OFEs (dominant soil and management) for representative hillslope. One climate dataset per watershed Does not account for impoundments DEM, soils, management data availability Resolution of data watershed boundary subcatchment areas / hillslopes profile creation User editable only at the level of subcatchments