BOARD00820

• Board Meeting Date: 7/26/2006
• Description: ISF Section - Pine River Proposed Water Donation - La Plata County
• Board Meetings - Doc Type: Memo

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186 cfs. The win1er flow recommendations, which meet 2 of3 cri1eria and were within the accuracy range
of the R2CROSS model, range from 161 cfs to lIS cfs (see Table 2 below).

Tb

a Ie 2: Fool BriMe Site:
Date XS# 0 ~O--;an"~ 3/3 2/3
4/8/04 I 124,9 312-50 222 ---
4/8/04 2 131.3 336-54 200 115
4/8/04 3 122.6 306-49 \86 ---
4/8/04 4 136.7 340-54 260 161
Averaoe 217 \38

Averaging the four summer flow recommendations within range, results in a 217 cfs recommendation.
Averaging the two winter flow recommenda1ions within range, results in a 138 cfs recommendation.

ISF Recommendation to Preserve the Natural Environment to a Reasonable Degree
To summarize the data listed above, the CDOW collected stream cross section data at 11 different locations
within the proposed instream flow reach of the Pine River. The average width of the stream channel
increased from approximately 70 feet to approximately 110 feet from the upper third of the stream reach,
CWR data collection site, to the lower third of the proposed stream reach, FB data collection site. The
CDOW believes the two different data collection sites represent the different and distinct types of natural
environments found wi1hin this reach of the Pine River (i.e. narrow confined reach to wide unconfined
reach). The summer flow recommendations, which meet 3 oD criteria and were within the accuracy range
ofthe R2CROSS model, range from 260 cfs to 72 cfs. The winter flow recommendations, which meet 2 of
3 criteria and were within the accuracy range of the R2CROSS model, range from 161 cfs to 30 cfs.
Averaging the II summer flow recommendations within range, results in a 136 cfs recommendation.
Averaging the seven winter flow recommendations within range, results in a 75 cfs recommendation.

ISF Recommendations to Imnrove tbe Natural Environment.
The CDOW used the Tennant Method (a.k.a. Montana Method) in conjunction with the stream cross section
data collected in April and July of 2004, to determine 1he proposed flows for improving the natural
environment. CDOW analyzed the data recorded by the stream gage "Los Pinos River near Bayfield - ID
Number 09353500", period of record of 1927 - 1986, to determine the average annual flow (see attached
gage and cross section data).

Based on 1his analysis the CDOW recommends:

. Flows between 360 - 217 cubic feet per second are recommended for 1he May I through May 31
time period. The CDOW believes flow amounts in this range would improve 1he natural
environment 10 a reasonable degree by providing optimum to outstanding habitat;

. Flows up to 720 cubic feet per second are recommended for June I through June 14 time period.
The CDOW believes flows up 10720 cfs would improve the na1ural environment to a reasonable
degree by providing flushing flows;

. Flows be1ween 360 - 217 cubic feet per second are recommended for Junel5 through October 14
time period. The CDOW believes flow amounts in this range would improve the natural
environment to a reasonable degree by providing op1imum to outs1anding habitat;

. Flows between 140 - 75 cubic feet per second are recommended for Oc10ber IS 1hrough April 30
lime period, The CDOW believes flow amoun1s in this range would improve 1he natural
environment 10 a reasonable degree by providing ou1standing habitat.