Laserfiche WebLink
<br />\) ff2 ;) 8 3 <br /> <br />THE STATE OF NATURAL AND CULTURAL RESOURCES <br />IN THE COLORADO RIVER ECOSYSTEM' <br /> <br />ABSTRACT <br /> <br />-;- <br /> <br />The status of physical, natural and cultural resources of the Colorado River affected by <br />Glen Canyon Dam are summarized to provide relevant information to stakeholders and the <br />newly formed Adaptive Management Work Group (AMWG). In addition, this 1997 (Fiscal <br />Yead998) State of Natural and Cultural Resources in the Colorado River Ecosystem report <br />derives most of its understanding of riverine resource status from analyses of data collected <br />prior to, during and after the 1996 Bureau of Reclamation (Reclamation) BeachlHabitat- <br />Building Flow experiment, hereafter referred to as the "1996 Test Flow" <br /> <br />.E <br /> <br />Physical resources and processes are related to mainstream and tributary flow and <br />sediment interactions from the 1996 Test Flow mobilized sediments, rejuvenated numerous <br />sand. bars, including 50% to 84% of river camping beaches, and deposited protective <br />sediments in arroyos having cultural sites. However, bar-building did not exceed that <br />observed from the 1983-1984 high flows. <br /> <br />. <br /> <br />~. Substantial erosion occurred during the high sustained flows oflate 1996 and 1997, <br />after:the 1996 Test Flow. During the 1996 Test Flow, bar building was rapid in eddies <br />downstream of the Little Colorado River (LCR), and secondary recirculation was ideritified as <br />an important sediment redistribution process. The 1996 Test Flow reworked new debris <br />flows at tributary mouths, reshaping some Grand Canyon rapids. Sediment storage on the bed <br />of the Colorado River was reduced until mid-summer 1997, when monsoon flooding in the <br />Paria River contributed substantial new fine sediments. One hypothesis from this above. <br />information is that more frequent. short-duration high flows may help conserve sediment in <br />this system. <br /> <br />Changes in water flows affect aquatic biological resources including the aquatic <br />foodbase and fisheries. High flows in 1996-1997 resulted in extensive colonization of the <br />8,000 cfs to 20,000 cfs zone by benthic macrophytes and invertebrates, which comprise the <br />aquatic foodbase. The 1996 Test Flow reduced this foodbase briefly, but it recovered quickly <br />and minimal impacts were reported on the fisheries. The 8,000 cfs constant flow of August <br />30 through September I, 1997 desiccated exposed macrophyte beds, but also created minimal <br />impact on the fisheries. <br /> <br />Reproduction of endangered humpback chub in Grand Canyon is almost entirely <br />restricted to the lower Little Colorado River, and the population may be declining (Douglas <br /> <br />'For the purpose of this document. the Colorado River ecosystem is defined as the Colorado River <br />mainstem corridor and associated ripanan and terrace zones primarily from the forebay of Glen Canyon Dam <br />to the western boundary of Grand Canyon National Park. a distance of approximately 293 river nules. <br /> <br />Final Draft - 12/12/97 - For AMWG Review <br />