<br />Biological and Field Survey Data
<br />
<br />The NPS has conducted scientific studies and analysis as reported in the May 9th 2003 letter from
<br />the DI to Greg Walcher, Executive Director, Colorado Department of Natural Resources, These
<br />studies indicate the Black Canyon and Gunnison Gorge are matchless environments, which have
<br />created a diverse group of isolated biological communities that provide unique opportunities for
<br />scientific study, This segment of river also contains one of the finest trout fisheries in the world
<br />and has been designated by the Colorado Division of Wildlife as Gold Medal and Wild Trout
<br />Water (see "Scientific Basis for the Requested Appropriation to Protect the Natural Environment
<br />of the Black Canyon of the Gunnison National Park to a Reasonable Degree" in Appendix A-
<br />Attachment B),
<br />
<br />Instream Flow Recommendation
<br />
<br />This initial recommendation is designed to address the unique requirements of the river segment
<br />without regard to water availability,
<br />
<br />For this segment of river, the NPS collected data on Sediment, Aquatic Invertebrates, Fish and
<br />Streamside Vegetation (see Streamflows Necessary to Protect the Natural Environment _
<br />Appendix A - Attachment B), These NPS studies conclude:
<br />
<br />· Sediment - "To protect critical biological habitats and the spectacular gorge, sediment
<br />transport capacities and main stem channel proportions must be maintained. Peakflows
<br />are necessary to scour the riverbed and rework debris flows and other coarse-grained
<br />deposits within the main stem channel, Peaks between 2,500 cft and 10,000 cft
<br />effictively mobilize gravels and cobbles within the low flow channel, adjacent low flow
<br />banks, and overflow channels, However, flows in excess of 10,000 cft are needed in
<br />some years to mobilize materials on lateral gravel bars and debris flow deposits,";
<br />· Aquatic Invertebrates - "To protect aquatic invertebrates populations and habitats in
<br />the main stem channel and adjacent alluvial deposits requires peak flows to redistribute
<br />sediment, and circulate water, oxygen, and nutrients through the channel alluvium,
<br />Peaks between 2,500 cft and 10,000 cft effictivelymobilize gravels and cobbles within
<br />the low flow channel, adjacent low flow banks, and overflow channels; thus serving to
<br />scour attached algae, flush entrained organic matter, re-oxygenate channel alluvium,
<br />and wet aquatic habitats within the active channel, Flows in excess of 1 0, 000 cft, which
<br />move gravels and cobbles on lateral gravel bars, are needed to rejuvenate and create
<br />new aquatic insect habitat, Appropriate ramping rates associated with the peak must
<br />allow ample time and opportunity for hyporheic and other aquatic insects to respond to
<br />changingflow conditions.., ";
<br />· Fish - "To enhance native fish species, while at the same time assuring the continued
<br />presence of a self-sustaining exotic sport fishery, requires base flows; annual peak and
<br />shoulder flows with appropriate timing, magnitude, and duration: and occasional large
<br />peaks to create new biotic habitats.., Appropriately timed annual peaks between 2,500
<br />cft and 10,000 cft remove fine sediment, accumulated organic debris, and algae from
<br />the active channel without disrupting species lift cycles, Rare, large peaks greater than
<br />10,000 cft redistribute inorganic substrate and create new biotic habitats, ";
<br />· Streamside Vegetation - "To prevent the permanent establishment of woody riparian
<br />vegetation and to limit the encroachment of herbaceous vegetation on depositional
<br />features located between the current active channel and the canyon walls requires peak
<br />flows if sufficient magnitude to mobilize rooted substrates ,.. Rare large peaks (greater
<br />than 10,000 cft) preclude permanent encroachment of large woody vegetation on
<br />
<br />- 3 -
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