BOARD01130

• Board Meeting Date: 1/26/2000
• Description: ISF Section - Instream Flow Appropriations - Water Division 5
• Board Meetings - Doc Type: Memo

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measured discharge at the time of the survey eQ), the accuracy range of predicted flows based on
Manning's Equation e240% and 40% of Q), the summer flow recommendation based upon
meeting 3 of 3 hydraulic criteria and the winter flow recommendation based upon 2 of 3
hydraulic criteria.

Table 1: Data

Party Date Q 250%-40% Summer (3/3) Winter (2/3)
BLM 7/8/98 4.32 10.8 - 1.7 5.0 Lit)

BLM = Bureau of Land Management (I) Predicted flow outside of the accuracy range of Manning's Equation.
? = Criteria never met in R2CROSS Staging Table.

Biologic Flow Recommendations
The BLM recommended a 5.0, 2.3 and 1.3 cfs summer flow and a 0.8 cfs winter flow based on
their July 8'\ 1998, data collection effort and their water availability analysis. CWCB staff has
reviewed the data collected by the BLM. The summer flow recommendation, which meets 3 of 3
criteria and is within the accuracy range of the R2CROSS model. is 5.0 cfs. The winter flow
recommendation, which meets 2 of 3 criteria but falls outside of the accuracy of the R2Cross
model, is 1.2 cfs. CWCB staff believes recommendations that fall outside of the accuracy of the
model, below 40% of the measured discharge, may underestimate the required winter flow. To
determine the winter flow recommendation, staff looked at valid winter flow recommendations
for the stream segment located above First Anvil Creek e2.1 cfs). After consulting with the
Colorado Division of Wildlife, staff believes 2.1 cfs will be sufficient to protect the natural
environment to a reasonable degree.

Hydrologic Data

After receiving the cooperating agencies' biologic recommendation, the CWCB staff conducted
an evaluation of the stream hydrology to determine if water was physically available for an
instream flow appropriation. The hydrograph was derived from data collected by the USGS
stream gage for East Fork Parachute Creek near Anvil Points eID #09092960), which has a
drainage area of 14.5 square miles esee Gage Summary in Appendix C). The period of record for
this gage is 1976 to 1983, the period of record used by staff in their analysis was 1976-1983, or
seven years of record. The estimated drainage area of East Fork Parachute Creek upstream and
including First Anvil Creek is approximately 14.7 square miles. The drainage area upstream of
Bull Gulch is 19.4 square miles. Tables 2 and 3 below display the estimated flow of East Fork
Parachute Creek at the confluence with and First Anvil Creek and Bull Gulch, in terms of a
percentage of exceedence. The orange shading highlights how often the summer flow has been
available and the blue shading highlights how often the winter flow recommendations have been
available.

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Table 2: East Fork Parachute Creek downstream of First Anvil Creek
n nu Fe Mrh Aril M una Jul

A tStmr t rNvemberD mr

1 % 1.13 2.70 7. 21.60 ,36 1. 1, 1.
20% 0,74 0.91 2.00 18,00 95.00 21,00 4.60 2.30 1.40 1.20 1.10 0,91
50% 0,62 0.70 1.00 5.90 39,50 7. 2.60 1.50 1.00 0,98 0.92 0.64
% 0 0,36 1.00 ,17 O. .1 O. O.
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