Stream: Cochetopa Creek ‎(Lower Segement)‎ Executive Summary

• Description: Stream: Cochetopa Creek ‎(Lower Segement)‎ Executive Summary
• State: CO
• Water Division: 4
• Title: Stream: Cochetopa Creek ‎(Lower Segement)‎ Executive Summary
• Water Supply Pro - Doc Type: Report/Study

biologic instream flow recommendations. The CDOW has determined that maintaining these
three hydraulic parameters at adequate levels across riffle habitat types, aquatic habitat in pools
and runs will also be maintained for most life stages of fish and aquatic invertebrates (Nehring
1979; Espegren 1996).
For this segment of stream, two data sets were collected with the results shown in Table 1 below.
Table 1 shows who collected the data (Parry), the date the data was collected (Date), the
measured discharge at the time of the survey (Q), the accuracy range of the predicted flows
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 flow recommendation based upon 2 of 3
hydraulic criteria. It is believed that recommendations that fall outside of the accuracy range of
the model, over 250% of the measured discharge or under 40% of the measured discharge may
not give an accurate estimate of the necessary instream flow required.
Table 1: Data
Party
Date
Q
250 % 40%
Summer 3/3
Winter 2/3
BLM
10/07/2008
31.70
79.2-12.7
14.68
Out of Range
BLM
10/07/2008
24.48
61.2-9.8
16.06
Out of Range
The summer flow recommendation, which meets 3 of 3 criteria and is within the accuracy range
of the R2CROSS model, is 15.3 cfs. The recommended flow of 6.8 cfs, when added to the
existing ISF flow of 8.5 cfs equals 15.3cfs. The summer flow recommendation was derived by
averaging the results of the data sets.
Hydrologic Data and Analysis
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 flow appropriation. This evaluation was done through a computation that is, in essence,
a "water balance ". In concept a "water balance" computation can be viewed as an accounting
exercise. When done in its most rigorous form, the water balance parses precipitation into all the
avenues water pursues after it is deposited as rain, snow, or ice. In other words, given a specified
amount of water deposition (input), the balance tries to account for all water depletions (losses)
until a selected end point is reached. Water losses include depletions due to evaporation and
transpiration, deliveries into ground water storage, temporary surface storage, incorporations into
plant and animal tissue and so forth. These losses are individually or collectively subtracted
from the input to reveal the net amount of stream runoff as represented by the discharge
measured by stream gages. Of course, the measured stream flow need not be the end point of
interest; indeed, when looking at issues of water use to extinction stream flow measurements
may only describe intermediate steps in the complex accounting process that is a water balance
carried out to a net value of zero.
In its analysis, CWCB staff has attempted to use this idea of balancing inputs and losses to
determine if water is available for the recommended Instream Flow Appropriation. Of course,
this analysis must be a practical exercise rather than a lengthy, and costly, scientific
investigation. As a result, staff has simplified the process by lumping together some variables
and employing certain rational and scientifically supportable assumptions. The process may be
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