A Post Processing Tool to Assess Sediment and Nutrient Source Allocations from SWAT Simulations Michael Van Liew William Puknat Montana Department of Environmental Quality Helena, Montana, USA
PROBLEM: Development of Pollutant Load Allocations with SWAT Multiple simulations with SWAT required from a baseline period Retrieval of output files associated with non-point, point, and bank constituent sources Labor intensive post processing of retrieved data is required to compute average monthly or seasonal source allocations
SOLUTION: Creation of a set of programs to extract data from SWAT output and perform the necessary computations to develop average and monthly pollutant load allocations mixed crops 31% bank erosion 22% point sources 9% range forest 7% grass 31%
Major Assumption in Developing the Post Processing Tool The relative proportions of water quality constituents simulated from the landscape for each land cover and management type are assumed to be the same as those present in the most downstream reach of a delineated watershed
Procedure Output the reach and hru files from SWAT for a baseline condition that represents existing water quality conditions in an impaired stream system Rerun SWAT without simulating the effect of bank erosion and retrieve that reach file Rerun SWAT again without simulating the effect of point sources and retrieve this third reach file
Post Processing Tool (1) SWAT- HARD - reads the three output.rch files and retrieves sediment and constituents for nitrogen and phosphorus from the most downstream reach in the watershed - reads the output.hru file and retrieves sediment and nutrient constituents for each land cover type
Column Extraction
Column Extraction
Output HRU Text File
Output RCH Text File (x3)
Post Processing Tool (2) SWAT PoP - a Microsoft Excel program with of VBA code to automate all calculations - reads text files created by SWATHARD - sorts files by land cover type, month, and watershed area - tabulates sediment, total N, and total P by bank, point, and non-point sources
1 3 2 Sort and Sum Constituents
Sum Land Cover Elements
Compute Averages
Application of Tool: The Bitterroot Watershed 7300 sq km drainage in Western Montana Numerous tributaries impaired for either sediment, N or P Four Waste Water Treatment Plants SWAT project consists of 85 subbasins and 1808 HRUs Watershed delineated with 15 land cover and 38 soil types Model simulations run for 11 year period of record from 1993 to 2003
Lolo Gage earlier record Florence Gage Missoula Airport Missoula Gage Location of Climate Stations Streamgages Stevensville Blodgett Gage earlier record Hamilton Twelve Mi. Cr Daly Cr Skalkaho Gage Darby Darby Gage East Fork Gage Laird Gage Nez Perce Camp Saddle Mt. Sula 33 Subbasin Number Climate Station Stream Gage
Seven Subbasin Groupings used for Calibrating Parameters that govern the Hydrologic Response on the Bitterroot Watershed
Modeled Sources of Sediment Yield for the Bitterroot River at Missoula based on an 11 year average 50.0% 45.0% 44.2% 40.0% 35.0% 30.0% 25.0% 22.7% 20.0% 15.0% 10.0% 16.2% 11.3% 5.0% 0.0% Bank erosion Range grass Range brush Forest Mixed crops 3.4% 0.9% 0.8% 0.2% 0.1% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% Hobby livestock Pasture Point sources Med urban dev Alfalfa Forest harvest Low urban dev Hobby lawn Wetlands Septic systems Barren/Ice Unpaved roads
Modeled Sources of Total Nitrogen Yield for the Bitterroot River at Missoula based on an 11 year average 25.0% 21.1%21.0% 20.0% 18.1% 15.0% 10.0% 10.1% 7.7% 6.1% 5.0% 4.2% 3.2% 3.1% 2.8% 2.2% 0.0% 0.3% 0.1% 0.1% 0.0% 0.0% 0.0% Bank erosion Pasture Mixed crops Forest Septic systems Range grass Alfalfa Point sources Hobby lawn Range brush Hobby livestock Med urban dev Low urban dev Forest harvest Wetlands Barren/Ice Unpaved roads
Modeled Sources of Total Phosphorus Yield for the Bitterroot River at Missoula based on an 11 year average 35.0% 30.0% 29.6% 25.0% 20.0% 19.8% 15.0% 10.0% 14.6% 11.6% 10.3% 7.1% 5.0% 0.0% 2.5% 1.8% 1.6% 0.7% 0.1% 0.1% 0.1% 0.1% 0.0% 0.0% 0.0% Bank erosion Mixed crops Range grass Range brush Forest Point sources Pasture Alfalfa Hobby livestock Med urban dev Low urban dev Septic systems Hobby lawn Forest harvest Wetlands Barren/Ice Unpaved roads
Modeled Monthly Sources of Sediment Yield for the Bitterroot River at Missoula 100.0% 90.0% 80.0% Point Source Bank Erosion Non Point Source 70.0% 60.0% 50.0% 40.0% 30.0% 20.0% 10.0% 0.0% jan feb mar apr may jun jul aug sep oct nov dec
Modeled Monthly Sources of Total Nitrogen Yield for the Bitterroot River at Missoula 100.0% 90.0% 80.0% Point Source Bank Erosion Non Point Source 70.0% 60.0% 50.0% 40.0% 30.0% 20.0% 10.0% 0.0% jan feb mar apr may jun jul aug sep oct nov dec
Modeled Monthly Sources of Total Phosphorus Yield for the Bitterroot River at Missoula 100.0% 90.0% 80.0% Point Source Bank Erosion Non Point Source 70.0% 60.0% 50.0% 40.0% 30.0% 20.0% 10.0% 0.0% jan feb mar apr may jun jul aug sep oct nov dec
Conclusions A post processing tool has been developed by Montana DEQ to facilitate the computation of sediment and nutrient load allocations simulated by SWAT for 303d listed streams The tool computes average monthly or seasonal allocations associated with bank erosion, point sources, and non-point sources This newly developed tool has been shown to substantially reduce the time required to develop pollutant load allocations for specific stream systems within large, complex watersheds
Future Development Combine into one VB.NET application using a SQL Server back-end Provide users with a variety of output formats
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