Laserfiche WebLink
Common Features and Objectives for All Action Alternatives <br />Annual Pulse Flows <br />In addition to recommending species flows for each period of the year, the Service recommends that pulse <br />flows occur annually during natural periods for high runof£ February to mid-March and May through <br />June. These "annual pulse flows" would be in the range of 2,000 to 3,600 cfs for 7 to 30 days, and the <br />10-year running average of the 30-consecutive-day flow would be 3,400 cfs in May through June. <br />Table 3-5 shows the specific frequency and magnitude of flows targets for annual pulse flows. <br />Table 3-5.-Annual Pulse Flow Targets at Grand Island (cfs) <br />Exceedance Probability <br />(Recurrence Interval) Recommended Flow in cfs Notes <br />75 percent (3 of 4 years) 3,100 to 3,600 (February - March) 30-day duration for February - March <br /> 3,000 (May - June) 7- to 30-day duration for May - June <br /> 3,400 (May - June) 10-year running mean of 30-consecutive-day exceedance <br />100 percent (all years) 2,000 to 2,500 (February - March) 30-day duration for February - March <br />Together, the species flows and annual pulse flows described above constitute "Program target flows". <br />These will be used by the Program as the initial benchmarks for measuring Program flow improvements, <br />but this does not preclude the potential importance of other (higher) flows for habitat recovery, as <br />described below. <br />Peak Flows <br />The Service also recommends that flows in excess of the annual pulse flows described above occur in the <br />Platte River on a periodic basis (Bowman and Carlson, 1994). These "peak flow" recommendations are <br />summarized in table 3-6. <br />Table 3-6.-Peak Flow Targets at Grand Island (cfs) <br />Exceedance probability Recommended flow in cfs Notes <br />(recurrence interval) <br />20 percent (1 in 5 years) 16,000 (February - June) 5-day duration <br /> At least 50 percent of these flows should occur between May 20 <br /> to June 20 <br /> May - June preferred for habitat benefits <br /> February - June OK for channel maintenance <br />40 percent (2 in 5 years) 12,000 (February - June) 5-day duration <br />] 0-year running average 8,300 to 10,800 <br />of 5-consecutive-day (February - June) <br />exceedance