NonBasicSpecificComments04

• Title: Comments 4
• Date: 10/23/2003
• SWSI - Doc Type: Comments

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Rick Brown (eWeR); Kelly DiNatale (CDM)
Tom Iseman, The Nature Conservancy
Robert Weaver and J obn Gerstle
Statewide Water Supply Initiative - Environmental Demand
October 23, 2003

The Nature Conservancy is pleased to work with the Colorado Water Conservation Board and
Camp Dresser & McKee to develop approaches to characterize 'enviromnental' or tin-stream'
water demands in the State of Colorado. This briefmemo addresses three key issues: 1) the
composition of enviromnental demand; 2) an approach to characterizing environmental
demand; 3) a proposal for characterizing enviromnental demand tlrrough SWSI.

Environmental Demand:
We believe that the Colorado Water Conservation Boardts Instream Flow Program is the
appropriate place to begin in considering enviromnental deJ?1and. Since 1973, the CWCB has
managed a successful program to protect, "minimum stream flows...to preserve the natural
environment to a reasonable degree (CRS 37-92-102(3)). n The CWCB has employed a
consistent methodology (R2CROSS) to identify minimum flow thresholds and has appropriated
instream flow water rights on thousands of miles of streams. The CWCB has also identified
'water short' or ftruncated' stream segments that highlight streams where the minimum flows are
not being met. This information will provide a solid foundation for the characterization of one
important dimension of environmental demand+

However, we believe that the Statewide Water Supply Initiative should go beyond minimum
stream flow in characterizing environmental demand. Our water-dependent natural enviromnent,
including diverse aquatic communities and verdant riparian forests, demands more than a year-
round minimwn flow (Instream Flow Council 2003). The ecological integrity of freshwater
ecosystems is strongly dependent on a range of naturally variable flow conditions, including a
combination of seasonal high flows, intermittent flood pulses, and stable base flows (poff et al.
1997, BUIll1 and Arthington 2002, Baron et al. 2003). These variable flows serve a variety of
critical enviromnental functions, including providing biological cues, regenerating floodplain
riparian areas, and performing charmel maintenance. Several10caI cases illustrate progress
towards protection of these elements of environmental demand, including flow recommendations
for the endangered fish recovery program, the Upper Colorado River Study (UPCO), and the
State's inclusion of seasonal variability in recent instream filings (e.g. San Miguel River). The
Statewide Water Supply Initiative should adopt this more comprehensive approach in its
characterization of enviromnental demand for water1.

Characterizing Environmental Demand:
The Nature Conservancy reconnnends a two-step approach to characterizing enviromnental
demand for water: 1) identify and locate critical water-dependent species and natural systems;
and 2) assess the environmental demands (or ecological flow needs) of those systems~

1 Particularly as the State Legislature recently granted the CWCB authority to secure instream flows that improve the
natural environment (SB 156).