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Vi <br />• Infiltration in the Platte River Valley is high and the storage capacity is about 15 to <br />20 percent. One inch of rainfall that reaches the water table raises the water table 5 <br />to 6 inches. <br />• Ground water levels in the Central Platte Valley outside the flood plain are typically <br />higher than the river elevation. Therefore, water movement is toward the river. <br />Currently, the one exception is in the Upper Big Blue and Little Blue River drainage <br />where the natural gradient is away from the Platte River to the southeast. <br />• Within the primary flood plain, the ground surface is typically 1 to 3 feet above the <br />river water level. In such conditions, evaporation and plant usage work to lower the <br />water table to roughly the same elevation as the river. When this condition develops, <br />ground water movement tends to be down the valley parallel to the river. <br />• From 1980 through 1999, total precipitation at 11 stations in the Central Plaate <br />Valley averaged 42 inches greater than normal. The smallest excess precipitation for <br />the period was 20 inches at Paxton, and the largest excess precipitation for the period <br />was 67 inches at Loup City. Several of the stations have received 10 percent or more <br />above normal for the past 19 years. <br />PROGRAM FLOWS <br />During the first increment of the Proposed Program (10 to 13 years), the Program will <br />seek to provide improved flows in the Central Platte River for endangered species. Two <br />proposed types of Program water releases were analyzed: <br />• Pulse flows of 6,000 to 10,000 cubic feet per second would raise the river level at <br />most 10 to 12 inches (but not above full bank capacity) for 3 days. Under this <br />regime, ground water levels would raise 1' /2 inches 500 feet from the river and 1/2 <br />inch 2,000 feet from the river for a short time. Ground water levels would not be <br />affected more than 3,500 feet from the river. <br />Base flow augmentation would add 500 and 1000 cfs to existing flows. These <br />increases would be provided several times during the average year to meet various <br />species' needs. Flows would raise the river by about 5 inches. If this continued for <br />30 days, ground water levels would raise by 3 inches 500 feet from the river and 1 <br />inch 2,000 feet from the river. Ground water levels would not be affected more than <br />3,000 feet from the river. <br />Executive Summary <br />1 <br />