WSP07311 - Laserfiche WebLink

Home Browse Search

<::) o I) ,;.. <.n c;p F. c. Category: Duration: Flow> 5,000 cfs during runoff period 21 days, natural variability maintained by meeting the conditions in Table 9-1. 50% on average. Minimum frequency for other durations listed in Table 9-1. Maximum period without meeting the specified conditions - 6 years. Frequency: Purpose: Flows of 5,000 cfs or greater for 21 days are necessary to clean backwaters and maintain low velocity habitat in secondary channels in Reach 3, thereby maximizing nursery habitat for the system. D. Category: Duration: Flow >2,500 cfs during runoff period 10 days, natural variability maintained by meeting the conditions in Table 9-1. Frequency: 80% on average, Minimum frequency for other durations listed in Table 9-1. Maximum period without meeting the specified conditions - 2 years. Purpose: Flows above 2,500 cfs cause cobble movement in higher gradient areas on spawning bars. Flows above 2,500 cfs for 10 days provide sufficient movement to produce clean cobble for spawning. Further these conditions provide sufficient peak flow to trigger spawning in Colorado Squawfish. E. Category: Peak timing similar to historic conditions, including variability Timing: Mean peak with re-operation to be within 5 days," of mean for historic period Variability: Standard deviation of date of peak to be 14-25 days Purpose: Maintaining similar peak timing will provide hydro graph ascending and descending limbs similar to historic conditions which is thought to be important for spawning of the endangered fish. Category: Target Base Flow (mean weekly non-spring runoff flow) Level: (~~OO~f~t Farmington to Lake Powell with 250 cfs minimum from - avaJo dam Purpose: Maintaining low, stable base flows enhances nursery habitat conditions. Flows between 500 and 1000 cfs optimize backwater habitat. Selecting flows at the low end of the range provides more water availability for spring releases and provides capacity for storm flows to increase flows and still maintain optimum backwater area. This level balances provision of near-maximum low velocity habitat and near-optimum flows in secondaries while allowing water to be available for maintaining required frequency, magnitude and duration of peak flows.