Ground Water and River Flow Analysis

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6 TOPOGRAPHY Aquifer recharge from precipitation in central Nebraska is relatively high due to the generally flat terrain and the sandy soil textures. The three possible outlets for ground water are rivers, pumping, and consumptive use by plants. The top of the water table depends on the elevation where ground water comes to the surface (for example at natural streams, springs, man -made drains, or pumps). Groundwater surfaces can never be lower than these discharge points. Topography also affects how much of the precipitation seeps into the ground, thus increasing the volume of ground water. On steep slopes, a large portion of rainfall runs off as surface water. In flat to gently rolling land, less water runs off and more soaks into the soil. Water that soaks in replenishes soil moisture in the root zone for plants to use, or it moves all the way to the water table and becomes part of the ground water, thus raising the elevation of the water table. The Platte River Valley is characterized by flat to gently rolling topography and high infiltration rates. Through much of the valley, the primary flood plain lies 1 to 3 feet above the water surface of the river and is flat for several Within the primary flood plain, the ground surface is typically 1 to 3 feet above the river water level. In such conditions, evaporation and plant usage work to lower the water table so ground water movement tends to be down the valley parallel to the river. Local conditions change with day -to -day weather patterns, but return to normal just as quickly. hundred feet away from the river. Therefore, a large portion of rainfall does not run off but infiltrates the soil and moves beyond the root zone to eventually become ground water. The Platte River channel is the lowest point in the Central Platte Valley. Because ground water moves to the lowest point, it generally moves toward the Platte River. GEOLOGY AND SOILS The surface soil texture controls how fast water can infiltrate the soil to become ground water. In the study area, soils generally are sandy, light textured, and highly permeable. Infiltration in the Platte River Valley is high and the storage capacity is about 15 to 20 percent. One inch of rainfall that reaches the water table raises the water table 5 to 6 inches. Ground Water and River Flow Analyses The aquifer is highly permeable and there is no barrier between the aquifer and the river. J t i I