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Navajo Reservoir Operations Vol. II
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Navajo Reservoir Operations Vol. II
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Last modified
1/26/2010 12:33:38 PM
Creation date
10/11/2006 10:46:49 PM
Metadata
Fields
Template:
Water Supply Protection
File Number
8220.105.I
Description
Colorado River-Water Projects-Navajo-Environmental Studies
State
CO
Basin
Colorado Mainstem
Water Division
5
Date
9/1/2002
Author
BOR
Title
Navajo Dam EIS-Draft EIS-Navajo Reservoir Operations-Volume II
Water Supply Pro - Doc Type
EIS
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<br /> <br />II <br />. <br />. <br />.. <br />. <br />. <br />. <br />. <br />. <br />r, <br />, j <br />, .. <br />I. <br /> <br /> <br />[J <br />LI <br />. <br />II <br />.. <br />.. <br /> <br />The model was completed with input from the Bureau of Reclamation, Bureau ofIndian Affairs, and <br />the states of New Mexico and Colorado. <br /> <br />Mimicry of the natural hydrograph is the foundation of the flow recommendation process for the San <br />Juan River. The flow recommendations require mimicry of statistical parameters of flow based on <br />flow/geomorphologylhabitat linkages and the statistical variability of the pre-dam hydrology rather <br />than mimicry of each annual hydrograph. Therefore, the resulting flows will not mimic a natural <br />hydrograph in all years, but will mimic the variation and dynamic nature of the 65-year record of the <br />San Juan River. <br /> <br />The hydrograph recommendations are designed to meet the conditions required to develop and <br />maintain habitat for Colorado pikeminnow and razorback sucker and provide the necessary <br />hydrologic conditions for the various life stages of the endangered and other native fishes. The <br />conditions are listed in terms of flow magnitude, duration, and frequency during the spring runoff <br />period. Duration is determined as the number of days that the specified flow magnitude is equaled <br />or exceeded during the spring runoff period of March I to July 31. Frequency is the average <br />recurrence of the conditions specified (magnitude and duration), expressed as a percent of the 65 <br />years of record analyzed (1929 to 1993). The underlying assumption in the flow conditions is that, <br />over a long period of time, history will repeat itself: if the conditions were met during the past 65 <br />years, they will also be met in the future. To the extent that the water supply is different in the future. <br />then the natural condition would also be altered and the conditions of mimicry would be maintained, <br />although the exact flow recommendation statistics may not be met. <br /> <br />. <br /> <br />To allow for gage and modeling error and the difference between the flows at the historical gage at <br />Bluff, Utah, and the Four Comers gage, maximum allowable durations are computed for 97% of the <br />target flow rate. In most cases, the primary recommendation is for a specified flow rate (Le.. 10,000 <br />cubic feet per second (cfs)) of a minimum duration (i.e., 5 days) for a specific frequency of <br />occurrence (i.e., 20% of the years). In addition to the primary recommendation, variability in <br />duration is desirable to mimic a natural hydrograph. Therefore, a frequency table for a range of <br />durations for each flow rate is recommended. A maximum duration between occurrences is also <br />specified to avoid long periods when conditions are not met, since such long periods could be <br />detrimental to the recovery of the species. The maximum period without reaching a specified <br />condition was determined as twice the average required interval (except for the 80% recurrence of <br />the 2,500 cfs condition, where 2 years is used). For example, if the average interval is I year in 3, <br />then the maximum period between meeting conditions would be 6 years. The maximum periods <br />were based on the collective judgemerii of Biology Committee members after review of historical <br />pre-dam statistics. Following are the co'nditions specified: <br /> <br />. <br /> <br />A. <br /> <br />Category: <br /> <br />Flows> 10,000 cfs during runoff period (March I to July 3 I). <br /> <br />Duration: <br /> <br />A minimum of 5 days between March 1 and July 31. <br /> <br />SJRIP Biology Committee <br />May 1999 <br /> <br />8-5 <br /> <br />Executive Summary <br />Row Report <br /> <br />" <br /> <br />. <br />
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