Ground Water and River Flow Analysis

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Considering all these factors is essential in understanding the rise and fall of the local water table: 1. Topography 2. Geology 3. Climate 4. Crop consumption 5. Irrigation 6. Urbanization 7. Ditches and drains 8. Local river levels river, and the flood plain varies in width from a few feet to as much as 2 miles on either side of the river. Any significant precipitation event causes the water table to rise to levels that are harmful to low lying agricultural lands as well as basements. Because the water table slopes toward the river, topographic lows farther from the river also experience normal water table depths in the 5 to 10 foot range or shallower. Ground water levels in topographical lows in the May 25 -27, 1999, snapshot were within 5 feet of ground surface at points nearly 10 miles from the Platte River. As figure 3 Section B -B' shows, the ground water elevation is close to the surface, particularly from the Platte River to beyond the Wood River. The right hand side of the graph shows the lower ground water levels on the south side of the Platte River. (See appendix D for more detailed maps of the gaining and losing reaches of the Platte River). GROUND WATER INFLUENCES IN THE PLATTE koVER V ALLEY Simply put, the local depth to ground water depends upon how much water is brought into an area, both above ground and underground, and how fast that water is drained from or pumped out of the ground. Natural conditions (e.g., topography, geology, climate, and crop consumption) determine the location of the water table. Human activities (e.g., pumping for irrigation or municipal /industrial uses, urbanization and paving, water management facilities such as flood control channels and irrigation canals, and lawn watering) modify these natural factors. Along the Platte River in Central Nebraska, records show that the water table within a few hundred feet of the river is usually 1 foot or more higher than the river. At distances of several thousand feet from the river, the water table is nearly always several feet higher than the river. The exceptions that do occur are invariably related to geology and irrigation withdrawals, such as in the head waters of the Little Blue River east of Gibbon where.the ground water levels are naturally lower, establishing a ground water gradient away from the river. 5 Ground Water and River Flow Analyses