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<br />Mlj4S <br /> <br />. <br /> <br />. <br /> <br />Aauatic Ori!anisms <br /> <br />Aquatic invertebrates provide the forage base for fish and other wildlife. These (hyporheic) <br />organisms occupy, at least for some fraction of their lifespan, interstitial habitats within the <br />substratum of the river bottom. The volume of saturated substratum is largely a function <br />of channel shape, volume and size distribution of substrate, and the stage-discharge <br />relationship in the channel. As shallow ground water levels are lowered by reduced <br />discharges, the quantity and quality of habitat required by these organisms is impaired. The <br />NPS contracted with scientists from the University of Montana and CSU to verify the <br />existence of these organisms in Black Canyon of the Gunnison National Monument (BLCA) , <br />define their role and importance in the lotic food web of the Gunnison River, and to <br />identify the stream flows necessary to maintain the physical and ecological character of the <br />hyporheic community. Draft report was prepared in 1991. <br /> <br />Visitor Access <br /> <br />The inner canyon of Black Canyon has been, and continues to be, generally inaccessible. <br />Foot travel along the canyon floor is restricted by geologic formations (e.g., cliffs) and to <br />varying degrees by extremely swift, dangerous stream currents and rapids. Only at very low <br />flows is the stream relatively shallow and of sufficiently low velocity to allow the average <br />visitor to wade across the river and navigate steep slopes and cliff faces which extend to the <br />waters edge. Studies conducted by the NPS have shown that increased accessibility up and <br />down the canyon floor will occur at stream flows of approximately 600 cfs and below. Low <br />flows (i.e., < 500-6OOcfs) , especially during the summer season (Memorial Day to Labor Day <br />has historically been the period of peak visitation) may lead to overcrowding, overuse, and <br />unacceptable resource damage within the inner canyon. <br />