Ground Water and River Flow Analysis

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20 , • Predictability diminishes rapidly further away from the river on average: 78 percent at 700 feet, 38 percent at 1,000 feet, and 16 percent beyond 10,000 feet. • In the Elm Creek transect, the groundwater mound under the Central Nebraska Public Power and Irrigation District apparently exerts more control over groundwater , movement and elevation than the Platte River. Ground water levels within a few hundred feet of the river are influenced by river elevation changes. Ground water levels more than 1,000 feet from the river appear to be more closely related to precipitation. RESULTS OF CURRENT YEAR MONITORING As of July 5, 2000, the current year monitoring program has produced results that are consistent with those of the 1999 monitoring. River levels in March and April were very similar for the two years. May 1999 saw higher river elevations, but they subsided by the end of the month to levels comparable to 2000 flows. However, beginning in mid June 2000, river flows began to decline to more normal summertime flows of less than 1,000 cfs. These low flows never occurred in 1999. Precipitation beginning in mid April 1999 was fairly significant, whereas the 2000 precipitation was minimal up to mid June, except for two moderate events of less than 1 inch at each transect. Larger rains ranging from 1 to 6 inches fell on June 12 at the Minden transect, on June 19 to Elm Creek and Minden transects, and on July 3 and 4 to all the transects. No rains greater than 2 inches were measured at any of the locations in 1999. The significant differences between the years in river level and precipitation patterns provide an opportunity to study the interrelationships among river level, precipitation patterns, and ground water levels under distinctly different circumstances for the 2 years. In 2000, the wells that are within 200 feet of the river bank track the river very closely, as would be expected. Wells farther from the river appear to be more independent of the M river. For instance, the river at the Elm Creek transects underwent a series of 6 -inch fluctuations, each about 1 week duration, during March. At the same time, the water surface in well 8- 19 -3ABB (1 /z miles from the river) averaged 2 feet higher than the river I and rose about 1 -inch on a straight line. Several wells in the Alda and Minden transects were monitored in both years (figure 8). Several precipitation events in 1999 appeared to produce rises in the water surface in the wells. In the absence of precipitation in 2000, the wells do not display such rises. For Ground Water and River Flow Analyses 1