BOARD00970

• Board Meeting Date: 7/22/1993
• Description: Agenda or Table of Contents, Minutes, Memos. Partial.
• Board Meetings - Doc Type: Meeting

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QUANTIFICATION SUPPLEMENT - UTILE DRY CREEK
July 1, 1993
PAGE 3

Division to a number of cubic feet per second needed to preserve the natural environment
and instream values of little Dry Creek?" We all know that R2CROSS has a set of
hydraulic criteria, a "recipe" for developing instream flow recommendations for salmonids.
With IFIM there is no such "recipe" for selecting a flow value that will protect the fish
species or life stage of interest. The real utility of IFIM is to answer the question, ''How
does habitat change when the flow regime changes?" One can use IFIM output to select
flow scenarios which will maintain a certain level of habitat but there is not a "recipe" - the
method requires experience and professional judgement. The following section will discuss
in more detail the steps utilized by the Division of Wildlife in the flow quantification for
Little Dry Creek.

DETAILED RATIONALE FOR FLOW RECOMMENDATION

This section will refer to several values in the Division's April 5, 1993 report. All of
the values discussed below come from Table 1 and Table 2. In addition, some. of the
. following discussion will refer to the curves in Figure 5 and Figure 6.

One important concept that is the initial basis for the rationale utilized in the flow
recommendation warrants repeating. The three species of fish that are found in Little Dry
Creek are all quite common in Colorado streams; none of them are either state or federally
listed as threatened or endangered, none are candidates for such listing, and none are
designated as species of special concern. It is therefore the position of the Division of
Wildlife that a fairly conservative approach to flow protection is appropriate. In other
words, the following flow recommendations should be adequate to MAINTAIN the existing
fish populations and to preserve their ability to reproduce and thrive in Little Dry Creek.

The flow recommendation development occurred as follows. Looking at Figure 5 and
Figure 6 of the April, 1993 report, the starting point for flow quantification was selected as
the most positive inflection point on the adult curves.! This, once again is a conservative
approach to flow protection; a more aggressive approach might be used for a listed species
where the least positive inflection point might be the starting point (i.e. where the slope of
the curve approaches zero).

In Figure 5 the key inflection is at 3.2 cfs, 3.2 cfs and I cfs for creek chub adults,
fathead minnow adults, and white sucker adults, respectively. The habitat (expressed in
square feet of WUA) maintained at that flow is 3340, 3313, and 1478 square feet,

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IThe use of inflection points on a flow vs. habitat curve is
an accepted method of analysis.