Ground Water and River Flow Analysis

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ill] The Central Platte River has a strong connection to the High Plains Aquifer System (the surface soils and the underlying Ogallala formation) (figure 4). Therefore, water movement between the river and the aquifer system is relatively unrestricted, responding primarily to changes in gradient as the water seeks its lowest level. Recent alluvial deposits Platte River Figure 4 CLIMATE High Plains Aquifer The climate dictates the amount of precipitation available for infiltration and the intensity of precipitation events. Higher intensity rainfall produces more runoff while gentler rains tend to produce more infiltration. Central Nebraska usually gets high intensity events (e.g., cloudbursts) in the late spring and summer and longer duration, gentler rains during cooler periods. In general, water table elevations rise in years with above normal rainfall and fall in years with below normal rainfall. ZZIUSGS science far a dwi9�9 warty Precipitation has been well above normal since 1980, which contributes to water tables that are currently higher than they have been since the 1950s and are generally rising. In the past 20 years, precipitation in the Central Platte Valley has been well above average. Precipitation during the early part of the twentieth century was well above normal. Beginning in the 1930s, it dropped below normal and did not return to above normal until the early 1980s. Since then it has been above normal except for a short period in the early 1990s. Figure 5 PRECIP compares annual precipitation at Grand Island with the one hundred year average precipitation from 1900 to 1999. Ground Water and River Flow Analyses 1 1