Laserfiche WebLink
<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 - <br />