BOARD02010

• Board Meeting Date: 9/24/2001
• Description: Snowmass Water and Sanitation District 404 Permit
• Board Meetings - Doc Type: Memo

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Another interesting observation by Nehring was the need to omit the data from 1983 for
the Arkansas River in southeastern Colorado. Nehring (1993) states" In April 1983, while
brown trout sac fry were immobile in the interstitial spaces in the gravel, flows were reduced
66% below the October 1982 spawning flows, probably resulting in the failure ofthe 1983 age
class, This was justification for omitting the 1983 data pair."

Chadwick's assumptions in_his 1998 report on the minimal effects ofa I to 3 day low
flow of 4 cfs are supported by the natural conditions in Snowmass Creek. Occasionally, ice
dams occur that create instantaneous low flow events approaching 4 cfs that last for only a short
period. The effects on populations are within the realm of natural population cycles. At
durations of a 4 cfs flow from 3-30 days, Chadwick reports the impacts would be more severe
but using his 20% loss of habitat, he states effect would not eliminate brown trout from
Snowmass Creek. The evaluation of a 4 cfs flow for 3-30 days does not mimic natural
conditions as ice dams do not persist that long. There is little evidence to support the
assumptions that a 4 cfs flow for more then 1 to 3 days would have minimal impacts on the trout
populations of Snowmass Creek.

b) Habitat Evaluation Reports:

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i) Don Chapman Consultants, Inc. prepared a 1996 report for the Caucus entitled
"Winter Ecology of Trout: Implications for Snowmass Creek." Chapman discussed the winter
ecology of trout, the effects of stream ice on trout winter habitat, the effects of reduced flows on
winter habitat, the ability of flow simulation models to predict impacts in ice-covered streams,
and recommendations for Snowmass Creek. Of note in this report, Chapman also challenges the
Chadwick high flow bottleneck theory and notes that Snowmass Creek has abundant side-
channel and beaver pond wetlands to provide juvenile and YOY habitat. Chapman reports on the
loss of habitat due to anchor ice and the increased likelihood of anchor ice with reduced stream
flows. This report also discussed several earlier reports on the effects of reduced winter flows on
trout populations including several reports on streams similar to Snowmass Creek. Chapman
also evaluates the various low flow recommendations of others that are primarily based on the
hydro graph for the stream in question. For Snowmass Creek, he recommends the Mundie Rule
that only allows reductions of25 to 30% of the mean monthly flows and no reductions during
periods of very low flows. In addition to the discussion of winter habitat requirements, this
report provides valuable information since it lists at least 7 published studies that document the
negative impacts to trout populations from winter stream depletions,

ii) The Permittee provided a report by C.F. Leaf entitled "Ice Formation and Winter
Flow Regime in Snowmass Creek." In this report, Leaf (1998) used the hydro graphs and
temperature measurements by Walsh and Walsh (1995) to perform a series of energy balance
analyses for different flow regimes. His fairly complex calculations demonstrate that the
relatively minor increase in ice formation would not affect average velocities and the hydraulics
of flow during the winter as compared to winter flows without ice formation.

iii) The Walsh and Walsh (1995) report provides empirical data on the effects of a
decreasing winter flow regime on trout redds in Snowmass Creek. A trout redd is the nest that
e trout use to both reproduce and incubate the young, Trout select redd locations based on depth,

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