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EIS Arapahoe & Roosevelt National Forest, Pawnee National Grassland
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EIS Arapahoe & Roosevelt National Forest, Pawnee National Grassland
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Last modified
1/26/2010 4:38:28 PM
Creation date
6/15/2009 11:45:54 AM
Metadata
Fields
Template:
Water Supply Protection
File Number
8461.250
Description
Water Issues
State
CO
Basin
South Platte
Water Division
1
Author
USDA, Forest Service, Rocky Mountain Region
Title
EIS Arapahoe & Roosevelt National Forest, Pawnee National Grassland
Water Supply Pro - Doc Type
EIS
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Area Cut - For UNIMPACTED. enter "zero". For IMPACTED, Enter 100 acres or whatever the <br />? area entered into AREA (above). Because the intent is to estimate the unit water yield per acre <br />harvested, it is important that the entire stand be harvested. Entering a value for AREA CUT that <br />is smaller than the stand AREA will reduce the predicted water yield proportionately. <br />BA in Cut - For UNIMPACTED, enter the same basal area as in BA. see above. For IM- <br />PACTED, enter zero. <br />Roughness Height - The model seems to be insensitive to this, if Wind Speed is set to zero as <br />suggested. Default value is set to 1, I suggest we leave it at that. <br />Windward Width - As discussed above, windward width of clearcut units affects snow <br />deposition and snow scour. If precipitation is adjusted as recommended above, windward width <br />should be set to zero to turn off the models adjustment of precipitation. If the adjustment is not <br />made, I suggest that we consult with our silviculturists on the average width or size of anticipated <br />clearcuts. For example, our silviculturists anticipate that in an attempt to more naturally emulate <br />tire patterns in lodgepole pine, clearcuts will be in large mosaics with unharvested patches. The <br />average size of the harvested patches within the mosaic will be 15-25 acres. For clearcuts used <br />to estimate the effects of partial cuts and group selections, I suggest using a width equal to five <br />tree heights. The WRENSS handbook indicates that this width maximizes deposition into <br />harvested a.reas and such an assumption seems to be consistent with the mare recent research on <br />the effects of partial cutting at the Fraser Experimental Forest. <br />Block Area - If, and only if, WINDWARD WIDTH is entered as zero, the program takes the <br />? value entered into BLOCK AREA, assumes a rectangular opening and calculates the length of <br />? one side. This value is automatically entered into WINDWARD WIDTH. <br />That ends input into the program. The result is a list of water yield increase values. Tliere <br />should be three values for every timber type-location-treatment combination modeled by FVS. <br />one for each aspect (North, South, and East-West). The three values can be reduced to one by <br />weighting them by the area occupied by a timber type on each aspect. The result is a mean <br />weighted water yield for clearcuts. Yields from shelterwood or other partial harvest treatments <br />can be calculated by determining the percentage basal area reduction for each step in the <br />shelterwood harvest (as compared to the basal area before the first treatment) and reducing the <br />water yield accordingly. Multiplying the unit water yield increase by the average annual acres <br />harvested for each decade praduces an average annual water yield increase for each decade. <br />Summing water yield increase for each timber type-location-treatment produces a total average <br />annual water yield increase for the decade. <br />To account for water yield recovery, I suggest that we use the linear 80 year recovery curve <br />suggested by Troendle and King (1985), reduce the initial water yield for each decade for <br />subsequent decades and sum the results. <br />8
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