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APPLYING WEPP-Mine TO WESTERN ALKALINE SURFACE COAL MINES

J.Q. Wu, S. Dun, W.J. Elliot, H. Rhee J.R. Frankenberger, D.C. Flanagan P.W. Conrad, R.L. McNearny. APPLYING WEPP-Mine TO WESTERN ALKALINE SURFACE COAL MINES. Introduction.

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APPLYING WEPP-Mine TO WESTERN ALKALINE SURFACE COAL MINES

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  1. J.Q. Wu, S. Dun, W.J. Elliot, H. Rhee J.R. Frankenberger, D.C. Flanagan P.W. Conrad, R.L. McNearny APPLYING WEPP-Mine TO WESTERN ALKALINE SURFACE COAL MINES

  2. Introduction • A crucial component of planning surface mining operations as regulated by the National Pollutant Discharge Elimination System (NPDES) is to estimate potential environmental impacts during and after mining operations • Reliable watershed hydrology and erosion models are effective and efficient tools for evaluating postmining site-specific sediment control and reclamation plans for the NPDES

  3. Objectives • The objectives of this workshop are • To introduce the newly developed WEPP-Mine, an online GIS interface for the USDA’s WEPP model, as a management tool for western alkaline surface mines • To apply WEPP-Mine, in a case application, to evaluate pre- and postmining watershed hydrological and erosion processes and impacts of BMPs at the Big Sky Mine, eastern Montana, USA • To obtain feedback from and exchange with stakeholders (state regulatory personnel, researchers, private consultants) and other workshop attendees to further refine WEPP-Mine

  4. WEPP • WEPP (Water Erosion Prediction Project) was initiated in 1985 as a new‐generation water erosion prediction technology for use by federal action agencies involved in soil and water conservation and environmental planning and assessment • WEPP was developed by the USDA‐ARS with user requirements collected from the Bureau of Land Management (BLM), Forest Service (FS), and Soil Conservation Service (SCS) • The WEPP model is a result of a large team efforts involving many scientists and experts

  5. WEPP cont’d • WEPP was intended to replace empirically-based erosion prediction technologies (e.g., USLE) for assessing the soil erosion impact of diverse land uses ranging from cotton fields to mountain forests • It simulates many of the physical processes important in water erosion, including infiltration, runoff, ET, percolation, subsurface lateral flow, raindrop and flow detachment, sediment transport, deposition, plant growth, residue decomposition, and changes in soil properties

  6. WEPP cont’d • The WEPP model can be used for common hillslope applications or on watersheds • In addition to WEPP core codes, the current version includes a parameter database and various interfaces, including a GIS and web‐based interfaces • WEPP technologies have been successfully used in the evaluation of important natural resources issues throughout the US and in many other countries

  7. WEPP Watershed • WEPP discretizes a watershed into hillslopes, channel segments, and impoundments • An impoundment can be on the channel network or at the foot of a hillslope

  8. WEPP Inputs • Climate • Observed daily values of precipitation (amount, duration, relative time to peak, relative peak intensity), temperatures (max, min), solar radiation, and wind (direction, speed) • Generated with CLIGEN, an auxiliary stochastic climate generator • Topography • Slope orientation, slope length, and slope steepness at points along the slope profile

  9. WEPP Inputs cont’d • Soil • Surface soil hydraulic properties, erosion parameters, and texture data for the soil profile • Soil properties of multiple layers to a maximum depth of 1.8 m can be input • Land management • Information and parameters for plant growth, tillage, plant and residue management, initial conditions, contouring, subsurface drainage, and crop rotation

  10. WEPP Outputs • Event-by-event summary of runoff and soil erosion • Graphical output for soil detachment and sedimentation along a slope profile • Daily water balance • Plant growth and residue decomposition • Snow accumulation and snowmelt and soil frost and thaw • Dynamic change of soil properties • Sediment yield • Return-period analysis

  11. WEPP Impoundments • WEPP simulates foothill small ponds behind • Filter fence • Straw bales • WEPP also simulates sediment ponds with hydraulic structures • Drop spillway • Perforated riser • Culvert • Emergency spillway • Rock-fill check dam

  12. Drop Spillway

  13. Perforated Riser

  14. Culvert

  15. Emergency Spillway

  16. Rock-fill Check Dam

  17. Filter Fence

  18. WEPP Application to Mining Areas • To simulate the effect of mining operations on soil erosion and to evaluate sediment control BMPs, typical WEPP applications to mining areas may involve the assessment of • Premining condition as a baseline against which other scenarios can be compared • Postmining with revegetation • Postmining with revegetation and a sediment pond • Postmining with revegetation and a silt fence

  19. WEPP-Mine • WEPP-Mine was developed based on the USDA’s online GIS interface for the WEPP model • It provides functions specifically for applications to mining areas • Using user-specified DEMs • Using reclamation maps • Simulating watershed-specific sediment ponds • It can be accessed using a web browser at http://wepponlinegis.bsyse.wsu.edu/osm

  20. WEPP-Mine Inputs • USGS 30-m DEM • USGS 2006 National Land Cover • NRCS SSURGO soil data • Spatial data automatically retrieved from the online servers by default • Soil and landuse can also be customized within the WEPP-Mine interface • Special permission is required for uploading user-specified DEMs and reclamation maps

  21. WEPP-Mine Inputs cont’d • CLIGEN-generated climate based on long-term monthly statistics is currently used (the use of observed climatic data will be implemented) • The CLIGEN database includes more than 2,600 weather stations across the US • Weather statistics of the station closest to the watershed outlet is used by default • PRISM 800-m gridded monthly averages is applied to the monthly statistics to account for location and elevation differences from the CLIGEN station

  22. WEPP-Mine Outputs • Channel network • Subcatchments • Watershed summary • Average annual values of the simulation results • Return-period and frequency analysis • Flowpath soil loss map • Representative hillslope runoff map • Representative hillslope soil detachment map • Representative hillslope soil loss map

  23. WEPP-Mine Output cont’d

  24. General Steps for WEPP-Mine Applications • Select area of interest • Generate channel network • Select watershed outlet and discretize watershed and subwatersheds • View watershed summary • Customize watershed inputs • Run WEPP • Analyze WEPP simulation results

  25. Computer Requirement • A computer connected to internet • A web browser • Following instructions on the web page (select and click buttons)

  26. Premining Simulation • WEPP simulation for the premining conditions can be accomplished by following the general steps for WEPP-Mine application without customizing watershed inputs

  27. Premining Simulationcont’d

  28. Postmining Simulation • User-specified DEM is used for topographical inputs for postmining conditions • A reclamation map can be uploaded for postmining soils and land managements • Soils at the disturbed mining areas are composed of mine spoils and a 0.6-m top soil layer if top soil is applied during reclamation • Postmining top soil is a mixture of the onsite soil described in the SSURGO database • Surface soil hydraulic and erosion parameters were adjusted according to reclamation stages

  29. Postmining Soil and Landuse

  30. User-Specified Maps • The required format includes • Raster map in ASCII • 30-m resolution • UTM projection • 0 for “no data” • The corresponding projection file for the map needs to be loaded • The IP address of a user is verified for uploading files to the WEPP-Mine server

  31. User-Specified DEM

  32. Reclamation Map

  33. Sediment Pond • After a watershed is discretized, one can specify sediment ponds • Impoundment inputs include dimensions of the pond and related hydraulic structure parameters • Default pond dimensions (stage-area-length relationship) are determined based on horizontal areas encircled by two half ellipses separated by the widest line of the area • Inputs for chosen hydraulic structures of a pond are shown after clicking the “Set Structure Parameters” button • User inputs override the default values

  34. Sediment Pond cont’d

  35. Sediment Pond cont’d

  36. Case Application

  37. Study Site • WEPP-Mine was applied to Watershed III in Area A, Big Sky Mine, a major surface coal mine in southeast Montana

  38. Big Sky Mine Area A • Mining completed in 1989 • Major reclamation activities (regrading, topsoil replacement, and revegetation) completed in 1992 • Since 1984, many watersheds in the Big Sky Mine have been monitored for channel flow and water quality

  39. Field Observations

  40. WEPP Simulations • Four WEPP runs were made to examine model performance in simulating the effect of three sediment control BMPs • Premining (natural) condition • Postmining with revegetation • Postmining with revegetation and a sediment pond • Postmining with revegetation and a silt fence

  41. Inputs for Premining • Oldest DEM available for the study area • NRCS SSURGO soil data • USGS National Land Cover dataset for landuse and management • Soil and management data acquired using the online WEPP GIS interface

  42. Postmining with Revegetation • Topographic map taken from the “Big Sky Mine 2008 Annual Report” • Soil and management data for the disturbed areas from the reclamation and bond status report • Soil and management data prepared based on field observations

  43. Watershed Delineation: Premining and Postmining • Topographic, soil, landuse, and management conditions vary from the mining to postmining period and differ from the natural, premining conditions

  44. Sediment Pond • A sediment pond set near the outlet of the watershed • Volume 60,000 m3 • One culvert 2.4 m above bottom • Culvert i.d. 18 cm

  45. Silt Fence • A silt fence set on the toe of a hillslope near the watershed outlet • Fence height 1m Curtsey: USDA Forest ServiceRocky Mountain Research StationForestry Sciences Laboratory, Moscow, ID

  46. Return-period Analysis • 25-yr WEPP simulations were carried out using observed precipitation and temperature for 1984–2009 from Colstrip climate station (5 mi northwest of the site) and other required climate data generated using CLIGEN • Return-period analyses were performed on field observations and WEPP simulations • Runoff and sediment yields of WEPP-simulated events with a return period of 2, 5, 10, or 20 yr were compared with field observations

  47. Return-period Analysis • Return periods were estimated using Chow’s frequency factor method and Gumbel’s distribution with an annual maxima series following Patra (2000) T: the specified return period XT: the estimated value for a return period T Xm and sx: the mean and standard deviation of the annual maxima of the events

  48. Results

  49. Resultscont’d

  50. Resultscont’d • WEPP overestimated observed runoff and sediment yield • However, WEPP simulation results showed the effectiveness of the sediment control practices • A silt fence near the watershed outlet would help to reduce sediment yield slightly from the postminingrevegetation condition • WEPP simulations indicated a sediment pond to be more effective, with a reduction of sediment yield of 50%

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