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Last modified
1/26/2010 12:34:04 PM
Creation date
10/11/2006 10:52:51 PM
Metadata
Fields
Template:
Water Supply Protection
File Number
8200.700
Description
Colorado River Basin - General Publications
State
CO
Basin
Colorado Mainstem
Water Division
5
Date
11/1/1979
Author
US Forest Service
Title
Managing Vegetation to Increase Flow in the Colorado River Basin - US Forest Service
Water Supply Pro - Doc Type
Report/Study
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<br />000718 <br /> <br />areas are not likely to be the source of large <br />amounts of additional water because the area is <br />small and values are high for other uses that. for the <br />most part, are not compatible with treatment prac- <br />tices required to accentuate water yield. Although <br />big sagebrush and pinyon-juniper are extensive <br />types, neither shows promise for improving water <br />yield, except on the most favorable sites. While the <br />potenlial appears greater in the alpine and moun- <br />tain grasslands, the increases (tables 1 and 2) must <br />be considered tentative, since they are based on <br />increased catch of snow by snow fences on ex- <br />perimental sites. It has not been tried within an <br />actual watershed. <br />Where clearcutting and type conversion are not <br />acceptable, water yield response will be less than <br />full potential, depending on the amount and <br />methods of vegetation reduction. The potential in- <br />creases for the mixed conifer, ponderosa pine, <br />aspen, and chaparral vegetation types were ad- <br />justed for multiple use and other considerations <br />(tables 1 and 2 and parentheses in table 3). The <br />potential increases were reduced by one-half or <br />more in all the commercial forest types, except the <br />subalpine forests, where patch cutting, which <br />tends to be most water productive, was also con- <br />sidered to be acceptable from a multiple use <br />standpoint. Where patch cutting is not acceptable <br />in subalpine forests, and other silvicultural sys- <br />tems, such as individual tree selection. group <br />selection, or shelterwood methods, are used, the <br />potential for increasing water yield may be less <br />than one-half that expected from patch cutting <br />(Leaf 1975). <br />Adjustments for mixed conifer forests reduced <br />the potential increases from a depth of 3 to 4 inches <br />to a depth of 1 to 2 inches over the area being <br />managed. based on an assumed management <br />strategy of periodic patch cutting to maintain <br />about one-third of the area in small openings. In <br />ponderosa pine, clearing away dense stands of <br />trees can increase water yield by 1 to 3 inches over <br />the areas cleared. However, management practices <br /> <br />designed to provide an acceptable mix of forest <br />products and other resources are expected to pro- <br />duce, on the average, only about 0.1 to 1 inch of <br />additional water per year. The adjustments for <br />aspen from 3 to 5 inches down to 0.3 to 1 inch <br />reflects a somewhat arbitrary choice of clearcutting <br />options, one at rotation age of 80 years for wood <br />products (0.3 inch average annual increase for 80 <br />years on the area actually clearcut) and the other at <br />rotation age of 25 years to favor wildlife (1.0 inch <br />average annual increase for 25 years on the clearcut <br />portions). The adjustment in the potential increase <br />for chaparral vegetation from 1 to 5 inches to an <br />average of 2.4 inches for areas actually converted <br />reflects lower onsite efficiency expected from a <br />mosaic pattern of treated and untreated areas, and <br />an estimate of offsite losses in transit to points of <br />use downstream. <br />Water yield potentials for selected vegetation <br />types are compared in table 3 with two previous <br />evaluations in 1960 and 1974. The 1960 Senate <br />Select Committee estimates pertain to the South- <br />west generally and the 1974 Ffolliott-Thorud esti- <br />mates to the State of Arizona only. Current un- <br />adjusted estimates compare fairly well with the <br />Senate Committee estimates in the subalpine, <br />mixed conifer, aspen, and pinyon-juniper types, <br />but are considerably higher in ponderosa pine and <br />chaparraL However, the Senate Committee value <br />of 0.5 inch of increased water yield for the pon- <br />derosa pine agrees with the current adjusted esti- <br />mate of 0.1 to 1.0 inch. The higher projection for <br />the chaparral in the current evaluation can be attri- <br />buted to the favorable outcome of several brush <br />conversion studies of the Arizona Watershed Pro- <br />gram' conducted after the Senate Committee re- <br />port in 1960. Similar tests in the pinyon-juniper <br />vegetation failed to strengthen early projections for <br />low increases from type conversion in this exten- <br />sive cover type. <br /> <br />6A cooperative research effon by federal, state. and water user <br />interests was started In the 1950's to Investigate the feasibility of <br />increaSing water yield in Arizona by manipulation of vegetation. <br /> <br />Table 3.-Comparison of current evaluation of potential increases (inches) with other estimates <br /> <br />Current <br />evaluation <br /> <br />u.s. Senate <br />1960 <br /> <br />Flollio<< & Thorud 1974 <br />{Arizona only} <br />Low High <br />option option <br /> <br />Subalpine <br />Mixed coniler <br />Chaparral <br />Ponderosa pine <br />Aspen <br />Pinyon-juniper <br /> <br />1 - 3 <br />'3 - 4 (1 - 2) <br />1 - 5 (2.4) <br />1 - 3 (0.1 - 1) <br />3 - 5 (.3 - 1) <br />0.0.5 <br /> <br />3.0 <br />4.5 <br />0.5 <br />.5 <br />3.0 <br />.25 <br /> <br />1.2 6.0 <br />1.2 2.4 <br />1 2 2.4 <br />included With mixed conifer <br />negligible <br /> <br />'Figures in parentheses are adjusted to reflect multiple use or other consideratIons. <br /> <br />21 <br />
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