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1 W. Elliot, PE, PhD USDA Forest Service, Rocky Mountain Research Station Moscow, Idaho Version: April, 2017 WEPP PEP The Water Erosion Prediction Project (WEPP) Post Fire Erosion Predictor (PEP) is an online GIS interface intended to support watershed managers after wildfire to evaluate the risks of upland erosion, sediment delivery and flood flows from small watersheds. It is available to any user with internet access at: The interface is limited to predicting erosion from wildfires that occur within the lower 48 states of the U.S. The WEPP PEP interface is best suited to subwatersheds under 1,000 acres (400 ha). Maps of runs from these subwatersheds can be downloaded and merged with ArcMap. Output data tables can be copied and pasted into Word or Excel documents for report preparation and summarizing. The steps for using the model to predict erosion and peak flows following a wildfire, evaluate the effectiveness of mulching on sediment delivery and peak flows, an estimate the prefire erosion rate are presented below. Defining a Post Wildfire WEPP Watershed Run 1) Open up blank word processor for a log file and spread sheet document for processing outputs a. Enter a title and date on both documents 2) Go to WEPP PEP: 3) Click Enter WEPP PEP 4) Select Fire to model a. If the fire to be modeled is not in the list, click upload your own map at the top of the page and follow the instructions that are given. 5) Select Units ( SI or English) 6) Zoom into Level 9 7) Confirm MSCL and CSA a. For watersheds greater than 1000 acres (400 ha), users may want to increase Critical Source area proportionately, like CSA = 20 acres if a watershed of 2000 acres is desired (more information in the Troubleshooting Section). Note: with larger areas, upland erosion processes are less important than channel processes. At this time, there have been some problems with the interface over predicting channel erosion, so use caution if channel sediment delivery greatly exceeds upland erosion. Channel deposition is frequently observed on most channel reaches following a wildfire. 8) Copy Map Extent and Zoom Level and paste into Log File 9) Click Build Channel Network 10) Click View Channel Network

Steps to Run WEPP Post Fire Erosion Predictor (WEPP PEP) p. 2 Figure 1. Watershed Delineated within the 2013 Kelly Fire on the Sawtooth National Forest. 11) Click Burn Severity Classifier a.

2 Steps to Run WEPP Post Fire Erosion Predictor (WEPP PEP) p. 2 Figure 1. Watershed Delineated within the 2013 Kelly Fire on the Sawtooth National Forest. 11) Click Burn Severity Classifier a. Select Texture b. Edit Ground Cover amounts Note: Ground cover is a more important variable than soil texture. Post fire monitoring teams should measure both ground cover and soil water repellency for different fire severities (Parsons et al., 2010). c. Specify if High Severity is Water Repellant or not d. Click Submit e. Click Yes to close tab 12) Define outlet point by clicking either User Cursor or Enter Coordinates a. Outlet CANNOT at a confluence b. A road/stream crossing is common location for an outlet c. If redoing a previous watershed, Click Enter Coordinates 13) Click Build Subcatchments 14) Click View Watershed Subcatchments (Figure 1) 15) Click Alt/Print Screen and paste into the Word document log 16) Click Review Watershed Characteristics a. Copy Watershed Summary Table within the borders at the top of the screen (Figure 2) and paste into the Log Note the watershed area, and latitude and longitude of the outlet. b. Scroll to the bottom of the Page, copy the Soils Summary Table and Paste into the Log Note the distribution of burn severities within the watershed c. Click Close Window

3 Steps to Run WEPP Post Fire Erosion Predictor (WEPP PEP) p. 3 Figure 2. Summary Table at the top of the Watershed Summary screen 17) Click Set Up WEPP Model 18) Click Modify Climate for this location a. Click Use PRISM Values if necessary, and it usually is necessary. b. Calculate the percent change in annual precipitation from the nearest climate station to the PRISM value c. Divide that percent change in rainfall amount by two, and enter the value in the blank box at the bottom of the Number of Wet Days column. In other words, if precipitation is 50 percent greater for the PRISM grid than the nearby weather station, then the number of wet days needs to be increased by 50/2 = 25 percent. d. Click in any other box for the screen to accept the change. Note the change in wet days compared to the original nearby station value. e. Click Save and Use Updated Values f. Click Close Window 19) Check Use modified climate Flowpath analysis to determine pixels with the greatest erosion rates 20) For Simulation Type, select Watersheds and Flowpaths 21) Specify years to simulate as 1 or 2 22) Set T value to 1 23) Click Run WEPP Simulation 24) When the run screen reports WEPP Runs are Done, click View Erosion Maps a. If the map is all green, click Reclassify Output Maps and decrease the T value to see if it is possible to see a greater differentiation of erosion rates

4 Steps to Run WEPP Post Fire Erosion Predictor (WEPP PEP) p. 4 Figure 3. Example of a Flowpath Run for a single year. Increasing the number of years would increase run time, but likely result in more pixels with elevated erosion rates. b. If the map is all red, click Reclassify Output Maps and increase the T value to see if it is possible to see a greater differentiation of erosion rates 25) The map shows the distribution of erosion by pixel (Figure 3). Those pixels with the greatest erosion rates may be areas worth considering for treatment to reduce hillslope erosion. 26) Click Alt/Print Screen, and paste the map into the log file Watershed analysis to determine hillslopes delivering the most sediment, and peak runoff rates 27) For Simulation Type, select Watershed Only 28) Specify Years to Simulate 20 a. Years to simulate can be increased to obtain greater return period predictions 29) Specify Soil Loss Tolerance (T Value) as 1 (ton/ac/yr) 30) Click Run WEPP Simulation 31) When the run screen reports WEPP Runs are Done, click View Erosion Maps (Figure 4) a. If the map is all green, click Reclassify Output Maps and decrease the T value to see if it is possible to see a greater differentiation of erosion rates. b. If the map is all red, click Reclassify Output Maps and increase the T value to see if it is possible to see a greater differentiation of erosion rates. 32) The map shows sediment delivery by hillslope polygon, and which hillslopes may be worth treating to reduce sediment delivery from the watershed 33) Click Alt/Print Screen, and paste the map into the log file 34) Click Summarize Simulation Results (Figure 5) a. Copy the summary above the table of hillslopes, and paste into the log file

5 Steps to Run WEPP Post Fire Erosion Predictor (WEPP PEP) p. 5 Figure 4. Example of a 20-year Watershed Run b. Copy the table of hillslope erosion rates and paste into a spread sheet c. Note the channel erosion by segment. Channel erosion rates may be over predicted at this time, but work is ongoing to improve channel processes d. Click Close Window 35) Click Return Periods (Figure 6) a. Note the Return Period of PRECIPITATION in Event by Event Output and compare to local return period values for precipitation. i. Note the peak flows and sediment delivery amounts associated with these storms b. Scroll down to the Return Period of PEAK RUNOFF in Event by Event Output c. Copy the table and paste it into the log file i. Note whether big events are from rainfall or snowmelt ii. Scroll to the bottom of the screen and click Close Window 36) Click Download Input for ERMiT and Disturbed WEPP a. Open the file and Save As the desired file name in the desired directory b. The csv file can now be used by the ERMiT Batch or Disturbed WEPP Batch spreadsheet i. At this time, the ERMiT batch may not like to process Unburned polygons, 37) If you want to merge this analysis with other runs using ArcMap, click Download Watershed Project and follow the onscreen instructions. 38) If you want to come back to this watershed in the future, click Save Watershed Project, and follow the onscreen instructions.

Steps to Run WEPP Post Fire Erosion Predictor (WEPP PEP) p. 6 Figure 5. Average annual erosion values and part of the watershed summary by hillslope in the Summary of Simulation Results page.

6 Steps to Run WEPP Post Fire Erosion Predictor (WEPP PEP) p. 6 Figure 5. Average annual erosion values and part of the watershed summary by hillslope in the Summary of Simulation Results page. Modeling the benefits of mulching 39) Close the Browser, and restart the analysis by going to the WEPP PEP site and selecting the desired fire. 40) When the window for the desired fire is open, copy the Map Extent Coordinates from you log file and paste them into the entry window at the top of the screen to the left of the Example: Pullman, WA example, and click Go 41) Click the zoom scale on the left side of the screen, NOT THE MAP, until the desired Zoom Level is noted. a. Re enter the Map Extent Coordinates and click Go to be sure you are where you want to be. 42) Click Build Channel Network and then View Channel Network 43) Confirm Use Burn Map is selected 44) Click Enter Coordinates to specify the same watershed outlet as used for the first run a. Copy the watershed outlet coordinates from the Watershed Summary saved from the first run, paste into the input screen and click OK. 45) Click Build Subcatchments and View Subcatchments 46) Click Burn Severity Classifier a. Under high severity fire, change cover to 70 percent to show the benefits of applying 1 ton/acre of mulch

Steps to Run WEPP Post Fire Erosion Predictor (WEPP PEP) p. 7 Figure 6. Tables summarizing Return Periods for daily precipitations, daily runoffs, and peak runoff rates. i.

7 Steps to Run WEPP Post Fire Erosion Predictor (WEPP PEP) p. 7 Figure 6. Tables summarizing Return Periods for daily precipitations, daily runoffs, and peak runoff rates. i. Cover can be increased on other severities if desired as well. The user must estimate the cover following treatment. b. If the soil is water repellant, select Is and click Submit c. Click Yes to close tab 47) Click Review Watershed Summary a. Confirm that the watershed has the same area and the same number of hillslopes and the same distribution of burn severity as the untreated run data you have saved in your log b. At the bottom of the summary, click Close Window 48) Modify the climate as described in Steps 17) and 18) 49) Select Watershed Only, 20 years to Simulate and a T value of 1 ton/ac/yr 50) Click Run WEPP Simulation 51) When the run screen reports WEPP Runs are Done, click View Erosion Maps a. If the map is all green, click Reclassify Output Maps and decrease the T value to see if it is possible to see a greater differentiation of erosion rates b. If the map is all red, click Reclassify Output Maps and increase the T value to see if it is possible to see a greater differentiation of erosion rates 52) Click Alt/Print Screen, and paste the map into the log file

Steps to Run WEPP Post Fire Erosion Predictor (WEPP PEP) p. 8 Figure 7. When the No Burn Map option is selected, the screen does not display the burn severity map layer.

8 Steps to Run WEPP Post Fire Erosion Predictor (WEPP PEP) p. 8 Figure 7. When the No Burn Map option is selected, the screen does not display the burn severity map layer. 53) Click Summarize Simulation Results a. Copy the header information and paste into the log file b. Copy the table of Erosion by hillslope and paste into the spreadsheet i. In the spreadsheet, highlight the high severity hillslopes to see the effects of mulching. ii. Carry out other spreadsheet summary analyses to suit, like benefits of mulch, overall change in hillslope sediment delivery, sediment reduction on high severity hillslopes, etc. iii. Managers may wish to focus benefits on selected hillslopes only. iv. Scroll down and click Close Window 54) Click Return Periods a. Scroll down to the Return Period of PEAK RUNOFF in Event by Event Output b. Copy the table and paste it into the log file c. Compare the peak flows following mulching to the untreated peak flows. Unburned Erosion and Peak Flow Rates 55) Exit WEPP PEP, close the browser and start over, using the same Extent and Zoom Level 56) Build the Channel Network 57) Select the No Burn Map (Figure 7)

9 Steps to Run WEPP Post Fire Erosion Predictor (WEPP PEP) p. 9 58) Enter the Coordinates for the watershed outlet. 59) Follow steps 44 to 54. Synthesizing the results 60) If every run was exported, combine all maps in a GIS 61) Use spreadsheet of hillslope results to show effects of mulching 62) Use peak flow results to show need for culvert evaluation If you want more information about a watershed run. Click Detailed Simulation Results and note: 1) Watershed Structure showing which hillslopes and channels feed into each channel segment 2) Annual summaries for a. Runoff volume for each hillslope b. Subrunoff or lateral flow volume from each hillslope c. Soil loss or upland erosion on each hillslope d. Deposition, if any, on each hillslope e. Sediment delivery from each hillslope f. Water discharge from each channel segment g. Sediment delivery from each channel segment h. Flow into each channel from hillslopes and upstream channels i. Subsurface flow from the upstream channels j. Summary of delivery from channel outlet i. Note the soil loss from the hillslopes compared to the soil loss from the channels k. Particle size distribution of sediment leaving watershed l. Primary particles in sediment leaving watershed m. Specific surface, and enrichment ratio i. To get delivery of a pollutant, multiply the concentration of the pollutant on the landscape times the sediment delivery amount times the enrichment ratio. For example, if the Phosphorus concentration is 1200 mg/kg on the landscape, the sediment delivery ratio is 2, and the sediment delivered from the hills is 1 Mg/ha, then the P delivered is 1 Mg/ha x 1000 kg/mg x 1.2 g P/kg P soil x 2 => 2.4 kg/ha (2.5 lbs/acre) 3) Average annual summaries of the above information Trouble Shooting If you are trying to build a subwatershed, and is taking more than a minute or two: You probably failed to ensure all of the headwaters were on the screen when you clicked Build Subwatersheds. 1) Click the browser s back arrow key, 2) Zoom out to level 9 3) Make sure the headwaters of your watershed are on the screen 4) Click Build Channel Network

10 Steps to Run WEPP Post Fire Erosion Predictor (WEPP PEP) p. 10 5) Make sure once the channel network is complete, that the crests of all of the ridges for your desired watershed are within the channel network that has been generated. If you get the Pink Screen of Death. This sometimes happens if you have opened up additional live screens to WEPP PEP or the WEPP GL online watershed interface. The server gets confused and has a meltdown! 1) Try clicking the browsers back arrow button once or twice to see if you can get to a screen just before the pink. 2) At the bottom of the screen, click Save Watershed Project, and follow the instructions for saving. 3) Completely close the Browser. 4) Restart WEPP PEP, select your desired fire, and on the opening window, Click Projects at the top of the screen to reload your project. 5) From the reloaded project, resume following the steps to take you from where you are to where you want to go. There may be other reasons for the pink screen appearing, but we are not sure of all the reasons behind this problem, yet If you are doing a run and it takes more than about 5 minutes to complete. 1) The watershed may be too big a. Click the browsers back arrow to get to a previous screen if possible. b. Select a smaller watershed c. To model the larger watershed, before step 7 on page 1 ( 7) Confirm MSCL and CSA), increase the Minimum Channel Length to about 200 ft for every 1000 acres (60 m for every 400 ha), and the critical source area (CSA) to be about 1 percent of the watershed area i. Erosion predictions will be less accurate, but areas of high erosion risk will still be apparent. ii. Do not try a flow path analysis on watersheds greater than 1,000 acres (400 ha) unless you are very patient. iii. Be wary of channel sediment delivery as the interface may be over predicting channel erosion. 2) Too many users are accessing the server at the same time a. If users are nearby, try and coordinate runs. b. If other users are unknown, try again at another time 3) There may be a problem with the GIS data. a. Try running a small hillslope nearby to see if that works i. If the nearby watershed runs, then there may be missing data b. If the nearby watershed does not run i. Try running a smaller watershed that is not nearby. ii. There may be a problem with one of the GIS layers. 1. See if you can get another fire to run for a small watershed to confirm that the server is working.

11 Steps to Run WEPP Post Fire Erosion Predictor (WEPP PEP) p. 11 References c. The watershed may span a UTM Zone boundary i. Try running subwatersheds that to not cross the UTM boundary Dun, S., J.Q. Wu, W.J. Elliot, J.R. Frankenberger, D.C. Flanagan and D.K. McCool Applying online WEPP to assess forest watershed hydrology. Trans ASABE. 56(2): Elliot, W. J Erosion processes and prediction with WEPP technology in forests in the Northwestern U.S. Trans ASABE. 56(2): Flanagan, D.C., J.R. Frankenberger, T.A. Cochrane, C.S. Renschler, W.J. Elliot Geospatial applications of the water erosion prediction project (WEPP) model. Transactions of the ASABE 56(2): Parsons, A., P.R. Robichaud, S.A. Lewis, C. Napper and J.T. Clark Field guide for mapping post-fire soil burn severity, General Technical Report RMRS-GTR-243. Fort Collins, CO: Rocky Mountain Research Station. 49 p.

Great Lakes Online Watershed Interface W. Elliot, Research Engineer USDA Forest Service Rocky Mountain Research Station, Moscow, ID March, 2016

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