Saturday, 15 July 2006

Validation and Implementation of a Geospatial Soil Erosion Model for Forest and Rangeland Management.

Chris Renschler, National Center for Geographic Information and Analysis (NCGIA), University at Buffalo, 105 Wilkeson Quad, Buffalo, NY 14261-0023, William J. Elliot, USDA-Forest Service, Rocky Mt. Research Station, Moscow, ID 83843, Jerry Ritchie, ARS-BARC-HRSL, 10300 Baltimore Ave, Beltsville, MD 20705, and Mary H. Nichols, USDA Agricultural Research Service, Southwest Watershed Research Station, 2000 East Allen Road, Tucson, AZ 85719.

Currently available spatially distributed soil erosion models linked to Geographic Information Systems (GIS) have limitations in accurately representing environmental properties and processes at various spatial and temporal scales. A new model approach developed for the Geospatial Interface for the Water Erosion Prediction Project (GeoWEPP) enables soil and water conservationists to take into account detailed topographic, soils, and land use pattern to derive soil redistribution patterns at various spatial and temporal scales. A new raster-based modelling approach simulates the sediment budget along representative hillslopes of contributing areas to single channel cells rather than only those to channel segments. Forest and rangeland validation studies have shown that the combination of different representations of hillslopes, the hillslope-channel interface, and the channels allows land managers to assess on- and off site impacts of various land use scenarios. In the case of the nested Lucky Hills watersheds - a rangeland ecosystem study site near Tombstone, Arizona detailed climate, runoff and sediment time series were used to parameterize and validate the models performance. While event-based discharge and sediment measurements at the nested watershed outlets were used to validate short-term performance, distributed 137Cs samples were used to assess the long-term soil redistribution pattern over a 50-year time period. Over longer time periods, fluvial processes remove 137Cs-bounded soil particles from the upper hillslopes to lower hillslope parts within a watershed. By measuring the amount of 137Cs-bounded material at a site, the amount of erosion and deposit over time can be calculated (see model results in upper left corner of the figure). In another validation study GeoWEPP was used to predict post-fire soil erosion from hillslope plots and small watersheds collected after the 2000 Bitterroot Valley Fires in western Montana. A series of silt fences were used to measure erosion on four stands of mixed ponderosa pine and Douglas fir on steep slopes (> 40 percent) and small watersheds for evaluating mitigated and non-mitigated effects. Rainfall intensity was the most significant factor for explaining postfire erosion rate variability. GeoWEPP was able to assess the event-based plot measurements and predict short-term soil erosion at the small watershed scale. Both studies are among several validation studies to design and implement the GeoWEPP modelling platform to assist wildland managers to design best management practices and rehabilitation strategies for a variety of scenarios at the hillslope and watershed scales. As seen in the figure, GeoWEPP is used by Burned Area Emergency Response (BAER) team members to assess the post-fire mitigation measures after fires as well as for fuel reduction measures to mitigate the impact of large-scale high intensity fires and their consequences. The experience of coordinating this effort lead to a scaling theory indicating that any soil scientist or field personnel gathering relevant environmental data, any GIScientists processing this data for GIS databases, any environmental modeller, and any decision maker has to be involved in model development and its implementation process. Only the effectively communication among the disciplines involved allow to understand the importance of aggregating and disaggregating information to produce useful simulation results to support successful land management.

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