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Estimating Additional Water Yield From Changes in Management of National Forests in the North Platte Basin
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Estimating Additional Water Yield From Changes in Management of National Forests in the North Platte Basin
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Last modified
3/29/2013 2:57:42 PM
Creation date
3/6/2013 10:50:04 AM
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Water Supply Protection
Description
An Independent Report Prepared for the Platte River EIS Office U.S. Department of the Interior Related to Platte River Endangered Species Partnership (aka Platte River Recovery Implementation Program or PRRIP),
State
CO
NE
WY
Basin
North Platte
Water Division
6
Date
5/12/2000
Author
Charles A. Troendle, Matcom Corporation & James M. Nankervis, Blue Mountain Consultants
Title
Estimating Additional Water Yield from Changes in Management of Ntional Forests in the North Platte Bains, Final Report
Water Supply Pro - Doc Type
Report/Study
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t <br />1 <br />1 <br />In addition, the effect of forest density changes on summer <br />evapotranspiration has also been better defined than in earlier models <br />(Troendle 1987; Kaufmann et al. 1987). Partial cutting or thinning can <br />result in reduced transpiration in the summer; however, the efficiency in <br />delivering an increase in flow to the stream channel is a function of seasonal <br />precipitation. In average or wet years, reduced basal area resulted in less <br />soil water depletion and an increase in water available for stream flow; <br />however, in below average precipitation years, the residual vegetation used <br />the available water. In all cases, water use per unit of residual basal area or <br />leaf area index increased dramatically; as a result, total water use by the <br />remaining vegetation increased. Observations at the plot level support and <br />help interpret the responses observed in the watershed experiments. <br />Since the early 1980's, process studies have documented much more about <br />the interaction between forest canopy and snow pack accumulation. Small <br />patch clear -cuts are no longer considered the only long -term harvesting <br />practice for water yield augmentation. This improved understanding has <br />been incorporated in a revision of the sub alpine water balance model <br />WATBAL so that we may now simulate evapotranspiration changes, <br />summer and winter, and project water yields as a function of any forested <br />condition or silvicultural activity. Input data for the revised WATBAL <br />model include slope, elevation, aspect, average precipitation, and basal area <br />by species for the forested area being modeled (Shepperd, et al. 1991 and <br />Troendle 1991). <br />As Leaf (1999) noted, the technology does exist to increase water yield <br />through timber harvest and as he infers, the corollary exists that increasing <br />forest density to the level of complete hydrologic utilization for the site will <br />result in flow reduction (Troendle and Leaf 1980). Shepperd et al. (1991) <br />simulated that in a "no harvest" alternative of mature stands of either <br />lodgepole pine or spruce -fir that represented stands already at complete <br />hydrologic utilization, long -term water yield projections were largely <br />unaltered because forest succession caused species composition and <br />structure to change with minimal change in either stand density or water <br />yield. Assuming the acreage of the landscape that is in forest is not altered, <br />one would not expect to observe changes in flow at the streamgage as a <br />result of already mature forest stands succeeding to their climax state <br />(Shepperd et al. 1991). <br />13 <br />
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