WSP04556

• File Number: 8449.900
• Description: Bear Creek
• State: CO
• Basin: South Platte
• Date: 12/1/1991
• Author: Leonard Rice
• Title: Change of Pioneer Union and Hodgson Ditch Water Rights for Use at Fox Hollow Golf Course Cae 90CW185 - Supplemental Engineering Report
• Water Supply Pro - Doc Type: Publication

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Appendix B
Derivation of Relationships Suggested for Use
To Determine Return Flow Obligations for Case No. 90CW185

Applicants engineers have performed analyses of historic use
associated with 14.569 shares of Pioneer Union Ditch and 32.5
shares of Hodgson Ditch. This analyses, described in the text of
this report, has provided an information base from which to better
understand the historic depletions and return flows associated with
the subject water rights.

In developing proposed terms and conditions for Case No. 90CW185,
it was important to characterize the return flows obligations in a
manner that can be effectively administered. It is desirable to
characterize historic returns by relation to some historic event
that is expected to be replicated in the future. We have
characterized the historic return flow obligation in terms of the
historic diversions. Expressing the return flow obligation as a
percent of diversions creates a reasonable and administrable means
of determining future return flow obligations.

To determine the percentage of a diversion made during an
irrigation month that is owed back to the stream system as return
flow, we have plotted on Figures B-1 through B-7 the estimated
monthly historic return flow obligation against the monthly
historic diversions associated with the subject water rights.
These graphs also show the percentage line suggested for use in the
terms and conditions that was developed by taking the estimated
historic return flow obligations as a percent of historic
diversions. Often data points at low diversion rates were excluded
from this calculation but used to calculate a minimum return flow
volume that would be owed regardless of diversion amount. The
return flow obligations expressed as a percentage of diversions,
subject to a minimum amount, are shown below.

Return Flow Obligations Expressed
as Percentage of Diversions made during that Month

Apr May Jun

% of Diversions 36% 35' 32%

Minimum 8 6 12
obligation (af)

Jul

Aug
47%
21

Sep
60%
21

90%
o

Oct

35%
21

The total return flow obligations during November through March
each year will equal 68 af. This amount will be delivered to the
stream system at times and amounts as reasonably directed by the
Division Engineer or his staff based on the location of the calling
water right. This relationship compared to the data points is
shown in Table B-8.

B-1

~ Leonard Rice Consulting Water Engineers. Inc.