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<br />Statement of Work J;;:-+ {'o/ Y~':'-I' use..
<br />Estimating Water Yield from Changes in Management of ;reFa-r/,,{ ~ fL
<br />National Forests in Colorado ~r6- f/'t>>/ J. . 0 r
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<br />. Background ./l, II. T-h'~ ""do S j
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<br />The purpose of this proposed study is to provide a reconnaissance-level analysis assessing the 8 Oa rd III tf.
<br />current status of stream flow originating on U S Forest Service lands in Colorado and evaluating I? Jt.
<br />the impacts that past and future forest management practices have had or will have on that stream Do- 0
<br />flow regime.
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<br />A similar analysis has been completed for the National Forest Lands in the North Platte River
<br />Basin. This proposal addresses the implementation of a similar analysis for the remaining
<br />Colorado River Basins. The major Rivers include the Arkansas, the Rio Grand, and the Colorado
<br />River. The Colorado River includes the Gunnison, San Juan, Animas, Dolores, San Miguel,
<br />Yampa, and White Rivers.
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<br />There are two components to the analysis proposed for each river basin. First, using data
<br />obtained from each of the U.S.D.A. National Forests involved, an evaluation will be made on the
<br />current status of the forested lands administered by the U.S. Forest Service. Each identifiable
<br />unit of land, or polygon, will be characterized by it's cover type (forest, grass, shrub, water, bare,
<br />etc), stand class/age (non-stocked, seedling, sapling, pole, saw timber), management class
<br />(wilderness, suitable for timber harvest, not suitable for timber harvest, tentatively suitable for
<br />timber harvest), aspect, and elevation. Once characterized, similar stands (polygons) can be
<br />aggregated and the water yield can be simulated. Simulations will be done at the level of the
<br />forest and aggregated to the level of the river basins identified above. This analysis will represent
<br />the baseline water yield characterization that will be carried into the future or regressed in time to
<br />reflect historical conditions.
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<br />The historical impact of forest management practices on water yield will be evaluated in the
<br />following manner. Based on Forest Service survey data, a relationship between stand age and
<br />stand class will be developed. The current age of all stands will be discounted in 20-year
<br />increments and at each 20-year increment; a new stand classification will be assigned the stand,
<br />if appropriate. For example, stands that are currently "saw timber" may retain the saw timber
<br />classification for a few 20-year increments and then recede to a pole or sapling designation
<br />depending on current age. Stands currently designated with as non-stocked or seedling status
<br />would most likely recede to saw timber and then pole status. For each 20-year increment, a
<br />different description of the forest will be derived. Theoretically, that description will represent
<br />what the current forest should have looked like 20, 40, or 100 years ago. The water yield will be
<br />simulated for each of the time periods to assess the long-term effect of forest change on water
<br />yield.
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<br />Future impacts can be assessed by defining the recent level of Forest Service activity and
<br />simulating the impact that maintaining that level of activity will have on future water yields. In
<br />addition, scenarios can be simulated that evaluate the effect alternative management regimes as
<br />well as natural impacts do to insects, fire, blow down, etc.
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