Platte River Wetland Hydrology Study

Home Browse Search

to the Platte River. The Elm Creek transect was almost perpendicular to the River, however, and there was a steep gradient toward the River from the south and a moderate gradient toward the River from the north. Groundwater contours at each site showed a predominant gradient down - valley, but precipitation directed this gradient toward the River at each site and evapotranspiration apparently directed this gradient toward the center of the island at Crane Meadows. The depth -to- groundwater maps showed that Elm Creek had the deepest groundwater levels, Rowe Sanctuary had intermediate groundwater levels, and Crane Meadows had the highest groundwater levels. Up to 77 % of the representative area at Crane Meadows had groundwater levels e me Ian s nn evel. The effective rooting depth for plants located in the wettest areas of Crane Meadows was a out 3 ft below the surface, and 5 to 6 ft below the surface for the drier areas. Groundwater withdrawals for adjacent irrigation had little or no direct affect on the groundwater levels at the three study sites. This was probably because most irrigation wells were at least a half mile from the nearest groundwater -level recorder. River stage, precipitation, and evapotranspiration were nearly always highly correlated with the groundwater level, with river stage usually the most highly correlated. The conclusions from this study are: 1. River stage is most often the dominant influence on the groundwater level. 2. Precipitation is usually the next most dominant influence on groundwater levels. 3. Evapotranspiration from the water table does not become important until May, and is usually insignificant again by late September. 4. Groundwater withdrawals for adjacent irrigation has little or no direct affect on the groundwater levels at the three study sites.- The cumulative effect on the study-site roundwater fT�*r+ �rnundwgtrr ew withdr xlver ev was not evaluated_ hnwevPr 5. Plants in the wettest areas of Crane Meadows appear able to remove water directly from the water table up to about 3 ft below the surface. The water table seldom drops below 3 ft in these areas. Plants in the drier areas of Crane Meadows appear able to remove water directly from the water table up to 5 -6 ft below the surface. The water table in these drier areas seldom drops below this limit. 6. Crane Meadows has more area with shallower groundwater levels than either Rowe Sanctuary or Elm Creek. 7. Median groundwater levels typically peak by March and then gradually declined through September. Recharge begins in October and varies between a gradual recharge over the winter at the drier sites, to a relatively rapid recharge at the wetter sites following plant senescence. 8. The groundwater gradient is primarily down - valley at each site. Large precipitation events, however, direct this gradient toward the River at each site and evapotranspiration apparently directs this gradient toward the center of the island at Crane Meadows during the summer. iii