Great Lakes Online Watershed Interface W. Elliot, Research Engineer USDA Forest Service Rocky Mountain Research Station, Moscow, ID March, 2016 Guidelines for using the Web WEPP Watershed Tool to Support Post Wildfire Mitigation and Forest Management Access the Tool [http://cals-wepponlinegis.ag.uidaho.edu/gl/] Developers: USDA Forest Service Rocky Mountain Research Station, Air Water and Aquatic Science Program Dept. of Biological and Agricultural Engineering, University of Idaho, Moscow Dept. of Biosystems Engineering, Washington State University, Pullman and Puyallup USDA ARS National Soil Erosion Research Laboratory, W. Lafayette, IN US Army Corps of Engineers, Chicago Office Databases Accessed by the Online Tool: a) Google Map: Physical, Streets, Hybrid and Satellite layers b) USGS 30-m DEM, Land Use and Topographic Digital Raster Graphic, and Soils Layers c) NRCS SSURGO soil database where available d) PRISM 800-m resolution monthly precipitation, and maximum and minimum temperatures Find Your Site 1. Click Enter Great :Lakes Site. 2. Select your units: SI English 3. Zoom in by centering the map on your location, and clicking the zoom scale on the upper left or the scroll wheel on your mouse, or Hold down the shift key and select the area of interest by dragging the curser over the area, or Type in the name of the nearest town and state (eg: South Lake Tahoe, CA) or the longitude and latitude (eg: -120.00, 39.00) and click Go 4. Once in the vicinity of the site (scale bar third from the top of the scale), click Build_Channel_Network. At the bottom of the network building screen, click View_Channel_Network. a. Make sure the entire channel network and the upland divide of the watershed(s) of interest are covered by the channel network. 5. Zoom in one more step on the zoom scale, (second from maximum) and drag the screen so that you can easily select the watershed outlet of interest. 6. Decide on the outlet point, NOT ON A CONFLUENCE. Click Set Outlet Point, close the irritating box by clicking the x in the corner, and click on the desired outlet point.
Great Lakes Watershed Interface Online GIS Tool User Guidelines p 2 7. Select Build Subcatchments. At the bottom of the building subcatchments screen, click View_Watershed_Subcatchments. Zoom in if you like by clicking the zoom scale or dragging over the subwatershed. 8. Select Review Watershed Summary: a. Note the area of the subwatershed; i. If running the Peak Flow Calculator or Wildcat5 for a peak flow analysis, note the area, flow length and average steepness. b. Note the USGS land use classes in the subwatershed; c. Note the soil series data layer for the subwatershed; d. Copy any summaries of interest and paste into a word processor file to start a log file; e. Close the Window. 9. Enlarge the map as much as possible, and capture the screen with Alt/Print Scn. Paste the screen capture into the log file. Crop it, expand it or shrink it to suit and save the file for future reference as a record of hillslope polygon numbers. 10. For forest management runs, click Set Soils Using USGS Land Cover Map or specify Single Land Use and select Mature Forest. a. Select the dominant soil texture b. Click Review Watershed. c. Click Close Window. 11. Select Setup WEPP Model and click Modify Climate for this Location. a. Compare the Original Climate and Elevation to the PRISM Climate and Elevation. i. If the PRISM climate is more appropriate, click Use PRISM Values ; ii. If desired: adjust the climate in the center (green background) section of the screen 1. Change monthly values for precipitation depth and number of wet days by entering a percent (plus or minus) change in the bottom box, or by changing individual monthly values. a. Generally, the percent change in the number of wet days is about half the percent change in precipitation b. By increasing the precipitation and not the wet days, and/or decreasing the number of wet days, the intensity of the climate, that is the depth of precipitation on a wet day is increased. 2. Change the maximum and minimum temperatures by month, or by entering the monthly change in degrees for every month in the bottom boxes. 3. Change the intensity of the storm on a given day by entering a positive percent in the box below the table. This will have the effect of increasing the intensity of the very large events, while slightly decreasing the intensity of the remaining events.
Great Lakes Watershed Interface Online GIS Tool User Guidelines p 3 b. When complete, click Save and Use Updated Values and Close Window ; c. Select Use modified climate on main screen. 12. Proceed with one of the following recommended analysis methods, Wildfire Analysis or Cumulative Watershed Effects Wildfire Analysis Generally, the first step in carrying out a watershed analysis is to do a wildfire run. This helps to determine which parts of the watershed are the most susceptible to erosion, and may guide the managers in selecting management practices, like avoiding prescribed fire on the areas at greatest risk to erosion. 13. For the default soil: select High Severity [texture] if the soils tend to be water repellant after a fire, or Low Severity [texture] if the soils are unlikely to be water repellant. 14. For the default land use: select Low severity fire because the burn severity is generally low. You may wish to specify a specific ground cover after the fire, as described in Step 31. 15. Select Watershed and flowpaths and years to simulate 10; (2 years for workshop) 16. Specify a Soil Loss Tolerance Value of 0.1 t/ha/yr (may need to specify 1.0 t/ha/yr for a watershed with higher post fire erosion rates). 17. Select Use single land use for watershed selected above and select Use single soil for watershed selected above. 18. Click Run WEPP and wait for the run to finish, then click View Erosion Maps. Zoom in on map if necessary. 19. Click the + symbol at the upper right of the map, and toggle off and on the Flowpath soil button to get the legend for the soil loss by pixel. 20. Enlarge the map as much as possible, and capture the screen with Alt/Print Scn. Open up a word processer and paste the screen capture into it. Crop it, expand it or shrink it to suit and save if for future reference. 21. Use the map to a. Target postfire treatments b. Identify sites that may require special care during forest operations or management activities. 22. Select Watershed Only and run for 50 years (10 years for a workshop) 23. Click Run, and when the run is complete, click View Erosion Maps. 24. Click the + symbol on the right side of the map, deselect and reselect Representative Hillslope Soil Loss, and the legend for the map colors will appear
Great Lakes Watershed Interface Online GIS Tool User Guidelines p 4 Note the hillslopes which are the greatest sources of sediment. This map may serve as a guide for targeting post fire treatments. Capture the screen save the map and legend. 25. Click Summary of Simulation Results and note the sediment delivery rates from the various hillslopes. Select everything on the screen, copy it, and paste it into a word processor or spreadsheet. 26. Click WEPP Model Text Output, a. Near the end of the file, note the sources of sediment from each hillslope and channel, b. At the end of the file, note the summary details of the run, including: i. The average annual precipitation; ii. The surface and lateral runoff; iii. The sediment delivery ratio; and iv. The sediment enrichment ratio, a key term in estimating nutrient delivery. The summary output can be copied and pasted into a word processor and saved for future reference. 27. Select the Return Periods results. Scroll down to the sediment delivery table. Note: We have observed occasional gross over predictions for large events on larger watersheds. If runoff and sediment delivery are unreasonably large, try decreasing the size of the watershed for the analysis, and then combine the results of the smaller watersheds when the individual watershed analyses are complete. a. Scroll down to the Return Period of Sediment Yield. These values can be considered the Total Maximum Daily Load (TMDL), with probabilities assigned to the values. b. Scroll to Return Period of Peak Runoff. These values can be used to size a culvert following a fire at the watershed outlet. Copy these tables, paste into the Word document and save for future reference. 28. If you are going to be doing a cumulative watershed effects analysis: a. From the Summary of Simulation Results, copy the hillslope erosion rates (not channels) and save them in a spread sheet. b. Click Save Watershed Project and follow the instructions on the save screen.
Great Lakes Watershed Interface Online GIS Tool User Guidelines p 5 29. If the run is for a BAER analysis, it may be necessary to estimate the effectiveness of treatments with the ERMiT hillslope interface. To do this: a. Open the Slope Steepness Screen. Copy the values and Paste the values into a working spread sheet. From the working spreadsheet, copy the columns and paste into the appropriate columns in the ERMiT or Disturbed WEPP Batch Processing spreadsheet. Rearrange the values into the desired number designation, area, length and steepness columns. [A future release will be developed that does not require rearranging the columns.] b. If you had selected Determine Soils by Individual Grid Cells or Determine Land Use by Individual Grid Cells, you can view the dominant land cover and/or soil series for each hillslope in the Summary of Simulation Result screen. These columns can also be copied and pasted into the spreadsheet for preparing inputs for the ERMiT or Disturbed WEPP Batch Processer. 30. If the run is to support cumulative watershed effects analysis, continue with the next step before losing all the output data. If you have lost the data, you may have saved all the important information in the Word document that you used to log the results of each run. Cumulative Watershed Effects (CWE) There are two approaches to running a cumulative watershed effects analysis, either treating individual hillslope polygons, and noting runoff and sediment delivery from both the polygon and watershed, or treating the entire watershed, and then combining conditions of each hillslope that describe the scheduled treatment. With the second option, the focus is on the hillslopes and not the watershed. In both cases, the user may have to build some site-specific files to describe observed onsite ground cover values. The recommended vegetation and soil selections that describe each of the land use conditions are given in Table 1. If the suggested vegetation conditions are not in the database, or if local information is available about post treatment ground cover the the user will need to build a custom land use file using the following steps; 31. Select Edit Soil or Landuse Properties and select the desired vegetation shown in Table 1. a. Select Customize this Landuse i. Specify the desired cover as shown in Table 1 (or as observed in the field) Example: For thinning with a skidder Select Shrubs and specify cover as 92%. ii. Click Save and Close Window. b. Select Change properties of hillslope. i. Close irritating window and click any hillslope in the current watershed ii. At the bottom of the hillslope window, click Add New Landuse Type iii. Select the customized land use cover you have just specified above, and give it a name; Example: Select Shrubs_92+ and name the landuse class Skidding.
Great Lakes Watershed Interface Online GIS Tool User Guidelines p 6 Table 1. Suggested soil, vegetation and ground cover conditions needed for a cumulative watershed effects analysis. Land Use Soil (Texture as appropriate) Vegetation Cover % Forest Forest Mature Forest 100 Thinned with Forwarder Shrub Shrub 96 Thinned with skidder Shrub Shrub 92 Prescribed Fire Low Severity Prescribed Fire 85 Recover yr 1 Sod Grass Poor Grass 92 Recover yr 2 Tall Grass Good Grass 96 Recover yr 3 Shrub Shrub 98 iv. Click submit and refresh the screen, and the new Landuse Class can be selected for any hillslope polygon, or for the entire watershed. Once you have identified or specified the required land use files, you can either: A. manually change individual polygons to work your way through the treatment cycle for each selected polygon [Forest Thinning Rx Fire Recovery 1 Recovery 2 Recovery 3 Forest]; or B. Change entire watershed to each condition, save the Summary of Simulation Results for each condition, and then combine hillslope sediment yields in a spreadsheet as shown in the following steps: 32. On the WEPP part of the main screen, near the bottom, specify Use single landuse for watershed selected above and Use single soil for watershed - selected above. 33. For the Default soil, select Forest [Texture] and for the Default Land use, select Mature Forest. 34. Set soil loss tolerance to 0.1 and specify years of run to 50 years (10 years for a workshop). 35. When the run is complete: a. Open the Summary of Simulation Results, copy the output for the hillslopes only (no channels) and paste into a spreadsheet. 36. Select the soil and land use for the thinned condition (Table 1) and repeat from step 34. a. When pasting into the spreadsheet, make sure the hillslopes are aligned with the previous run after pasting in the results.
Great Lakes Watershed Interface Online GIS Tool User Guidelines p 7 b. Delete the redundant columns. 37. Follow the same steps for the prescribed fire and recovery conditions. Once all of the runs have been complete, the spread sheet can be used to develop possible treatment scenarios. The user may choose to thin or burn one, several, or many hillslopes in a given year. Runoff amounts from the treated hillslopes can be combined with runoff and sediment yield from the untreated hillslopes, and average runoff (or weighted average) and total sediment can be determined for any combination of conditions within the watershed. The results can be compared to the wildfire run done at the start of the analysis. If hillslopes are thinned and not burned the following year, then a young forest treatment will follow a thinning. If the hillslopes are burned in a given year, then Recovery year 1 from Table 1 will follow the next year, then recovery 2, then a young forest. In drier watersheds, recovery may be slower. Appendix A shows an example of the start of a cumulative watershed effects analyses. 38. You may wish to add in an estimate for sediment from roads using the WEPP:Road, WEPP:Road Batch or WEPP FuME interfaces (http://forest.moscowfsl.wsu.edu/fswepp/). 39. You may wish to use the Disturbed WEPP Batch processor for the CWE analysis. If so, copy the hillslope data and paste it into a spreadsheet. Then copy the desired columns from the spread sheet and paste into the Disturbed WEPP batch processer. Once in the batch processer, different treatments can be specified for each polygon as above, and a batch sheet set up for each year of analysis. Saving and Exporting the Results It is possible to export the main layers as a series of GIS layers and combine the results from several runs into a larger map using GIS tools. Once a run is complete, select Download Watershed Project, and a zip file will be created and saved. This file can be unzipped and it will contain all the layers needed in a GIS, and all the files needed to open and run the downloaded watershed in WEPP Windows. The watershed can be saved and reopened following the instructions on the Save Watershed Project screen. Additional Information A pink shading covering the entire map following a run means that something has gone wrong, and the user will likely have to start over again. If the project has been saved before the problem, it may be possible to load the last saved version of that project. If this does not work, the location of the watershed outlet (longitude and latitude) are noted in the information from the saved project. The interface is still under development. The predictions are generally reasonable. There are plans to develop methods to enhance this interface for wildfire, CWE and road network analysis if resources are available. Also methods to save output screens as pdfs are planned.
Great Lakes Watershed Interface Online GIS Tool User Guidelines p 8 Appendix A. Example of a cumulative watershed effects analysis