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WSP11369
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Last modified
1/26/2010 3:17:10 PM
Creation date
10/12/2006 4:56:02 AM
Metadata
Fields
Template:
Water Supply Protection
File Number
8220.101.09
Description
Glen Canyon Dam/Lake Powell
State
AZ
Basin
Colorado Mainstem
Date
3/1/1996
Author
USDOI-BOR
Title
Transition Times
Water Supply Pro - Doc Type
Publication
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<br />';~",".'I <br />,:?""i, <br />'. <br /> <br />(Bt!lJCh/Habitat Building Test Flow continued from page 5) <br /> <br />Anticipated Results and Benefits o/the Test Flow <br /> <br />Detennining adverse or beneficial impacts to resources in Glen <br />and Grand Canyons requires value judgments. Because all <br />impacts of the test flow on downstream resources are consistent <br />with natuJal processes, they are considered to be beneficial to the <br />overa1l ecosystem. Some of the anticipated impacts of the test <br />flow are as follows: . <br /> <br />Grand Canyon <br /> <br />,<::?1I\ <br />;WW,~I <br /> <br />Glen Canyon <br /> <br />The impacts to resources in the Glen Canyon will be different <br />from those in the Grand Canyon since there is little sediment in <br />the river system above the Paria River. Glen Canyon contains <br />what may be the only natural marsh on the entire river system <br />between the dam and Diamond Creek. This area supports native <br />vegetation and a population of northern leopanl frogs. In addi- <br />tion, the narrow canyon combined with constan1ly clear, cold <br />water promotes a unique aquatic and ter- <br />restrial ecosystem Studies of the test <br />flow in the Glen Canyon will include: <br /> <br />This test of the beachlhabitat-building <br />flow will provide an evaluation of one <br />of the more important elements of the <br />fmal EIS preferred alternative. <br /> <br />Depositionofftom 1 to 3 feet of <br />sedimentation to sandbars throughout the <br />Grand Canyon (There may be net ero- <br />. . <br />SlOn at some sandbars, but most should <br />experience net deposition.) Sandbar <br />deposition would be beneficial to cultural resources by covering <br />and stabilizing some sites. <br /> <br />Sediment: Assess the impact of the <br />test flow to detennine where sediment in <br />the Glen Canyon reach redistributes. <br /> <br />Fish: Assess impacts to native fish and tront and to the <br />aquatic food base. <br /> <br />River-based recreation activities may be affected dur- <br />ing the test flow, specifically in faster moving water. <br /> <br />Although nonnative fish life cycles will be temporarily <br />disrupted, backwaters will be reformed and immediately avail- <br />able for use by native and nonnative fish after the test flow. <br />Researchers will study the relationships between flow duration <br />and magnitude and backwater rejuvenation <br /> <br />The test flow will likely result in a temponuy reduction <br />in the aquatic food base in the Lees Feny reach, with increased <br />drift downstream. Research data will be gathered on relation- <br />ships between short-term high flows and the aquatic food base. <br /> <br />It is likely that some trout eggs, flY, and young will be <br />lost downstream. This temponuy loss may be mitigated by <br />stocking. <br /> <br />Some riparian vegetation in the new high water zone <br />may be lost through scouring or burial by sediment transported <br />by the test flow. Both emeJgent marsh and woody vegetation <br />will recover quickly in the months following the test flow. <br /> <br />Wildlife use riparian vegetation as habitat, and some <br />habitat will be temporarily impacted during the test flow. <br />Patches of bare sand created by the test flow will add diversity <br />and heterogeneity to the new high water zone habitats. <br /> <br />The endangered Iwmpback chub and razorback sucker <br />will benefit from the test flow through the refonning of back- <br />water habitats. The endangered Kanab arnbersnail will likely <br />sustain short-term population and habitat impacts and is antici- <br />pated to have a full recovelY. <br /> <br />Marsblleopard frogs: Assess impacts to the stability <br />of the frog population. <br /> <br />Water quality and productivity: Assess the impacts <br />to water quality and the overall productivity of the aquatic food <br />base which provides nutrients not only for the Glen Canyon <br />Reach, but also for the downstream river system. <br /> <br />Cultural: Assess the effects of the test flow on the <br />Spencer steamboat as well as monitoring terraces which could <br />contain undiscovered cultural resource sites. <br /> <br />SUtIUIUlI")' <br /> <br />This test of the beacMlabitat.ouilding flow will provide an eval- <br />uation of one of the more important elements of the fmal EIS <br />preferred alternative. We will be able to validate many of the <br />theories and predictions made by the scientists in the GCES final <br />reports. This will be the Imgest controlled hydrologic experi- <br />ment ever made below Glen Canyon Dam and will provide valu- <br />able information for the Adaptive Management Program. <br /> <br />The test flow will not resolve all of the questions, but it will pro- <br />vide important information for decisionmakelll in the future. <br /> <br />11 <br />
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