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• Board Meeting Date: 7/11/2007
• Description: ISF Section - Willow Creek and Beaver Creek New Appropriations in Moffat County
• Board Meetings - Doc Type: Memo

based on Manning's Equation (240% and 40% of Q), the summer flow recommendation based
on meeting 3 of 3 hydraulic criteria and the winter t10w recommendation based upon 2 of 3
hydraulic criteria.

Table 1: Data

Party Date Q 250%-40% Summer (3/3) Winter (2/3)
BLM 09/04/2003 1.08 0.4-2.7 1.9 0.9
BLM 09/04/2003 1.69 0.7 - 4.2 1.7 1.3

BLM = Bureau of Land Management DOW = Division of Wildlife
(1) Predicted flow outside of the accuracy range of Manning's Equation. 0 = Criteria never met in R2PRUDEN Staging Table.
* Estimated Flow based on a calculated DX4 value of 0.55.

Biologic Flow Recommendation
The summer flow recommendation, which met 3 of 3 criteria and is within the accuracy range of
the R2CROSS model is 1.8 cfs. The winter t10w recommendation, which met 2 of 3 criteria and
is within the accuracy range of the R2CROSS model range is 1.1 cfs. These recommendations
were derived by averaging the results of the two cross sections.

Hydrologic Data
After receiving the cooperating agency's biologic recommendation, the CWCB staff conducted
an evaluation of the stream hydrology to determine if water was physically available for an
instream t10w appropriation. Because there are no existing stream gages on Beaver Creek or
similar watersheds in the region, the next best approach is to use a regional equation that
estimates annual t10w characteristics. The USGS has developed regional equations (Estimation
of Natural Streamflow Characteristics in Western Colorado, Water Resources Investigations
Report 85-4086, 1985) that apply to Beaver Creek based on basin drainage area, mean annual
precipitation, mean basin elevation, and mean basin slope. The total drainage area of Beaver
Creek is approximately 44.17 square miles. Figure 4 depicts the numerous water rights located
downstream from the proposed segment. The mean monthly diversions for these water rights
were added and used as a check against the synthetic hydrology. This information is located in
the water availability portion of the appendix.

For this reach, the synthetic hydrograph shows that the summer t10w recommendation of 1.8 cfs
is available only from April 1 to August 31, and the winter flow recommendation of 1.1 cfs is
available from September 1 to March 31. Table 2 below displays the estimated average monthly
stream flow in Beaver Creek.

Table 2: Estimated Stream Flmv in Beaver Creek

cfs Jan Feb J\;lar Apr May Jun Jul Aue Sep Oct Nov Dec
2.25 2.67 5.73 6.78 10.62 19.65 4.25 2.31 1.99 2.91 2.67 2.4