WSP11259

• File Number: 8441
• Description: Colorado - Big Thompson - Green Mountain
• State: CO
• Basin: South Platte
• Date: 3/12/1985
• Author: CRWCD by West. Eng.
• Title: Green Mountain Reservoir Water Sales Impact on Flows in Gore Creek
• Water Supply Pro - Doc Type: Publication

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are expected to be confined to a point just upstream of the confluence with Red

Sandstone Creek. Since no specific municipal diversion point is mentioned in

the VVCWD application, it was necessary to apportion the total municipal demand

over the possible diversion points as reflected in the water rights mentioned

in the VVCWD application. Total demand was apportioned according to the

percent of decreed diversions possible in each reach. Table 3 illustrates the

percent of total diversion possible in each study reach. Demand in terms of

diversion requirement was then found by applying the percent of total

diversions possible within each sub-reach (in Table 3) to the expected total

demand in Table 2. Table 4 shows the amount of future municipal and snowmaking

diversions expected from VVCWD future water use patterns.

Depletion Analysis

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Flow on Gore Creek was analyzed to determine potential depletions by

assembling the previously derived data into a simulated-streamflow operation

study. Items used in the simulation included historic discharge data,

calculated tributary inflow, stream losses, VVCWD diversions, and return flow.

The basic approach used was to evaluate streamflow at the five critical points

previously identified on Gore Creek under two conditions: (1) without any

additional diversions for municipal and snowmaking uses, assuming that any

future development would require conversion of water rights from other uses or

construction of water storage facilities in the Gore Creek drainage, and (2)

with full usage of water from Green Mountain Reservoir as replacement for

future additional municipal and snowmaking diversions from Gore Creek and its

tributaries.

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Streamflow without water sales was found for each particular reach by

summing upstream inflow and subtracting stream loss. Upstream inflow was found

by summing gage records (where available) with estimated tributary inflow.

Streamflow with the proposed water sales was found by subtracting any VVCIo.'D

diversions from the inflow into the reach, then adding any VVCWD return flows

that occur. Appendix B and Appendix C provide a detailed description of the

simulated operation and the data used in it. To more adequately analyze dry

year conditions, the period of study wa" lengthened beyond water year 1977 to

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