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<br />USE OF THE STUDY
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<br />"..
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<br />The infonnation derived from this study can be used by
<br />city, county, state and federal planners and specialists as a
<br />source of infonnation, guide for general planning, and for
<br />the preparation of an emergency watershed protection plan.
<br />This report, and the GIS database developed with it, has
<br />reliable infonnation including rangeland sediment yield,
<br />slope, vegetation, watershed acreage, and slope failure areas.
<br />All of this infonnation can be quickly accessed in an
<br />emergency post-fire situation.
<br />Data developed from this study was incorporated into a
<br />GIS for analysis. The GIS database will allow the USer to
<br />estimate sediment yield from a burned area by digitizing the
<br />burn area and assigning burn intensities. The burn intensity
<br />assigned to a burn area will dictate which sediment yield rate
<br />the model uses to generate the total post-fire, upland
<br />sediment yield. The software reports the sediment yield
<br />from the watersheds within a burned area. This data can be
<br />generated as soon as a fire is declared "contained" instead of
<br />waiting days until the fire is declared "out". The potential
<br />sedimenl yield is used to determine the need for emergency
<br />protection of life and property.
<br />Containment of a fire verifies a burn boundary. With
<br />the sediment yield potentials for each soil and each
<br />watershed already in a database, work with the GIS and the
<br />sediment yield model can start. Before this database was
<br />developed for Davis and Weber Counties, a team would have
<br />been assembled to evaluate the burn area and make
<br />recommendations for mitigation which could take two to
<br />four days.
<br />The database developed with this study can be copied to
<br />a single 8.millimeter data cartridge. The GIS software,
<br />knowledge of the software, data storage requirements and a
<br />graphics monitor will be needed to access and display the
<br />data.
<br />The United States Department of Agriculture, Natural
<br />Resources Conservalion Service (NRCS-fonnerly the Soil
<br />Conservation Service) can provide technical and fmancial
<br />assistance to land managers under the authority of the
<br />Emergency Watershed Protection Program (EWP) when
<br />there are hazards to life and property resulling from a sudden
<br />impainnent of a watershed. Only public entities with
<br />authority to obtain easements may apply for assistance under
<br />the EWP,
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<br />GEOGRAPHIC INFORMATION SYSTEM
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<br />A Geographic Infonnation System (GIS) is a
<br />computerized system for inputing, managing, manipulating,
<br />analyzing and displaying spatially referenced data. GIS
<br />technology is used to measure, overlay, compare, and
<br />analyze geographic data such as vegetation, soils, streams,
<br />roads, land use, land ownership and, slope (Figure 2).
<br />The GIS software ARCIINFO version 6.0, developed by
<br />Environmental Systems Research Institute (ESRI) Redlands,
<br />California, was used to develop the database for this study.
<br />The GIS software can produce graphics on the screen or
<br />on paper that illustrate the results of analyses to the people
<br />who make decisions about emergency mitigation. Maps and
<br />other graphics can be generated allowing officials to
<br />visualize and understand the results of an evaluation or
<br />simulations of potential events.
<br />This technology is evolving rapidly and becoming more
<br />user-friendly with a variety of ready- to-use digital
<br />geographic data available from government agencies,
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<br />
<br />Figure 2. The GIS software can create a map illustrating
<br />such themes as soils, sediment yield, vegetation, slope. roads,
<br />streams, boundaries, and their related tabular data,
<br />
<br />The GIS work for this study involved an arrangement
<br />between the USDA-Natural Resources Conservation Service,
<br />Salt Lake City and the Region IV USDA-Forest Service GIS
<br />office located in Ogden, Utab. This arrangement facilitated
<br />the sharing of data, hardware, software, expertise and work
<br />space with NRCS project personnel at the regional Forest
<br />Service office in Ogden, Utab.
<br />The data and illustrations developed for GIS analysis
<br />can be used in future studies of natural resources or hazard
<br />assessments for proposed developments along the urban-
<br />wildland interface. The database can also be used for
<br />comparison to other methods used for modeling sediment
<br />yield in this type of terrain such as the Revised Universal
<br />Soil Loss Equation (RUSLE, 1993).
<br />The GIS database can help estimate surface water runoff
<br />along the Wasatch Range in Davis and Weber counties,
<br />Techniques for estimating surface water runoff in Davis
<br />County were developed as a result of the Davis County
<br />Foothill Development Study (1980). The data contained
<br />within the GIS database helps to detennine "Losses" in the
<br />general water balance equation: Precipitation = Runoff +
<br />Losses. The GIS database provides infonnation on
<br />watershed physiography, soil, and vegetation, which is
<br />needed to determine the "losses" part of the equation (Jaynes,
<br />1980).
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<br />PRESENT-CONDITION
<br />SEDIMENT YIELD MODEL
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<br />The present-condition sediment yield was modeled to
<br />establish a baseline condition from which to develop a low-
<br />intensity burn and high- intensity burn sediment yield rate.
<br />Most of the area in the study rated as either Low (< 0.6
<br />tons/acre, < 0.49 cubic yards/acre) or Moderate (0.6 to 1.49
<br />tons/acre, 0.49 to 1.2 cubic yards/acre). The southern section
<br />of the study area contains relatively less consolidated
<br />Tertiary Conglomerate and contains a large area in the
<br />Moderate sediment yield category. The rating classifications
<br />are taken from the PSIAC sediment yield procedure (Present-
<br />Condition Sedimenl Yield Rating. Map-I). Appendix A lists
<br />the present-condition sediment yield rates for each watershed
<br />in the study.
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