Water Erosion Research at Washington State University

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Water Erosion Researchat Washington State
University

• Joan Wu, Markus Flury, Shuhui Dun, Cory Greer,
  Prabhakar Singh
• Washington State University, Pullman, WA
• Don McCool
• USDA ARS PWA, Pullman, WA
• Bill Elliot
• USDA FS RMRS, Moscow, ID
• Dennis Flanagan
• USDA ARS NSERL, West Lafayette, IN

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Major Funding Sources

• In-house funding from various collaborating
  research institutes
• US Forest Service Rocky Mountain Research Station
• Inland Northwest Research Alliance
• USDA National Research Initiatives Programs
• US Geological Survey/State of Washington Water
  Research Center

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The Needs

• Protecting and improving water quality in
  agricultural watersheds are major goals of the
  USDA NWQ and NRI Programs
• For many watersheds, sediment is the greatest
  pollutant
• In watershed assessment, it is crucial to
  understand sedimentation processes and their
  impacts on water quality
• To successfully implement erosion control
  practices, it is necessary to determine the
  spatio-temporal distribution of sediment sources
  and potential long-term effectiveness of sediment
  reduction by these practices

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• Surface runoff and erosion from undisturbed
  forests are negligible
• Stream formed due to subsurface flow has low
  sediment

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• Both surface runoff and erosion can increase
  dramatically due to disturbances
• Models are needed as a tool for forest resource
  management

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The WEPP Model

• WEPP Water Erosion Prediction Project
• a process-based erosion prediction model
  developed by the USDA ARS to replace the
  functional model USLE
• built on fundamentals of hydrology, plant
  science, hydraulics, and erosion mechanics
• WEPP uses observed or stochastically-generated
  climate inputs to predict spatial and temporal
  distributions of soil detachment and deposition
  on an event or continuous basis, along a
  hillslope or across a watershed
• Equipped with a geospatial processing interface,
  WEPP is a promising tool in watershed assessment
  and management

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The WEPP Model contd

• WEPP Windows Interface
• WEPP Internet Interface
• GeoWEPP

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Long-term Research Efforts

• Goal
• Continuously develop, refine and apply the WEPP
  model for watershed assessment and restoration
  under different land-use, climatic and hydrologic
  conditions
• Objectives
• Improve the subsurface hydrology routines so that
  WEPP can be used under both infiltration-excess
  and saturation-excess runoff conditions in crop-,
  range- and forestlands
• Improve the winter hydrology and erosion routines
  through combined experimentation and modeling so
  that WEPP can be used for quantifying water
  erosion in the US PNW and other cold regions
  where winter hydrology is important
• Continually test the suitability of WEPP using
  data available from different localities within
  and outside the US

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Progresses Made

• Numerous modifications to WEPP have been made to
• Correct the hydraulic structure routines
• Improve the water balance algorithms
• Incorporate the Penman-Monteith ET method (UN FAO
  standard)
• Improve the subsurface runoff routines
• Expand and improve winter hydrology routines to
  better simulate
• Freeze-thaw processes
• Snow redistribution processes
• WEPP new releases accessible at NSERLs website
  http//topsoil.nserl.purdue.edu/nserlweb/index.htm
  l

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Ongoing Studies
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Palouse Conservation Field Station (PCFS),
Pullman, WA

• Laboratory and field experimentation on runoff
  and erosion as affected by freezing and thawing
  of soils

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Tilting flume at PCFS
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Experimental plots at PCFS
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WEPP Applications at UB, Italy

• Experimental Watershed, University of Bologna,
  Italy (Drs. Paola Rossi Pisa and Marco Bittelli)
• Joint MS program providing source of students
• State-of-the-science research facility

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DEM Effects on WEPPErosion Modeling

• Paradise Creek Watershed, ID (Dr. Jane Zhang)

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WEPP Applicationsfor Watershed Erosion Modeling

• Reeder Experimental Watershed at the USDA ARS
  CPCRC, Pendleton, OR (Dr. John Williams)
• Paradise Creek Watershed, ID (Drs. Jan Boll and
  Erin Brooks)
• Mica Creek Watershed, ID (Dr. Tim Link)

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Long-term Research Efforts

• Goal
• Continuously develop, refine and apply the WEPP
  model for watershed assessment and restoration
  under different land-use, climatic and hydrologic
  conditions
• Objectives
• Improve the subsurface hydrology routines so that
  WEPP can be used under both infiltration-excess
  and saturation-excess runoff conditions in crop-,
  range- and forestlands
• Improve the winter hydrology and erosion routines
  through combined experimentation and modeling so
  that WEPP can be used for quantifying water
  erosion in the US PNW and other cold regions
  where winter hydrology is important
• Continually test the suitability of WEPP using
  data available from different localities within
  and outside the US

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Comparison of Processes
Earlier versions of WEPP typically
overestimated Dp
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Redistributionof Infiltration Water in WEPP
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Code Modification

• Provide options for different applications
• a flag added to the soil input file
• User-specified vertical hydraulic conductivity K
  for the added restrictive layer
• e.g., 0.005 mm/hr
• User-specified anisotropy ratio for soil
  saturated hydraulic conductivity
• horizontal Kh ? vertical Kv, e.g., Kh/Kv 25

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Code Modification contd

• Subroutines modified to properly write the pass
  files
• WEPPs approach to passing outputs
• Subsurface flow not passed previously
• Simplified hillslope-channel relation
• All subsurface runoff from hillslopes assumed to
  enter the channel
• Flow added and sediment neglected

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A Case ApplicationModeling Forest Runoff and
Erosion
Dun, S., J.Q. Wu, W.J Elliot, P.R. Robichaud,
D.C. Flanagan, J.R. Frankenberger, R.E. Brown,
A.C. Xu, 2007. J. Hydrol (in review)
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Study Site Hermada Watershed
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Physical Setting

• Located in the Boise National Forest, SE Lowman,
  ID
• Instrumented during 1995-2000 to collect whether,
  runoff, and erosion data
• 5-yr observed data showing an average annual
  precipitation of 954 mm, among which nearly 30
  was runoff

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Re-processed Precipitation
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Watershed Discretization
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Model Inputs

• Topography
• Derived from 30-m DEMs using GeoWEPP
• 10-ha in area, 3 hillslopes and 1 channel
• 40-60 slope
• Soil
• ? Typic Cryumbrept loamy sand 500 mm in depth
• underlying weathered granite
• Management
• 1992 cable-yarding harvest
• 1995 prescribed fire
• West and North slopes with low-severity burn
• South slope and channel unburned
• Climate
• 11/1995-09/2000 observed data

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Results
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Living Biomass and Ground Cover(WEPP v2004.7)
(a) and (b) unburned S slope (c) and (d)
burned W slope
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Living Biomass and Ground Cover(WEPP v2006.5)
(a) and (b) unburned S slope (c) and (d)
burned W slope
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Runoff and Erosion Obs. vs Pre.(WEPP v2004.7)
Observation Period 11/3/1995-9/30/2000
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Runoff and Erosion Obs. vs Pre.(WEPP v2006.5)
Observation Period 11/3/1995-9/30/2000
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Summary

• Numerous modifications have been incorporated
  into WEPP v2006.5
• Specifically, changes were made in the approach
  to, and algorithms for modeling deep percolation
  of soil water and subsurface lateral flow
• The refined model has the ability to more
  properly partition infiltration water between
  deep percolation and subsurface lateral flow
• For the Hermada forest watershed
• Vegetation growth and ground cover were described
  realistically
• WEPP-simulated annual watershed discharge was
  compatible with field observation and predicted
  annual sediment yield was not significantly
  different from the observed
• Nash-Sutcliffe model efficiency coefficient for
  daily runoff of -0.77 suggests further
  improvement on winter routines are needed

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Thank You!
Questions?