Ground-water resources of Hamilton County, Nebraska, with a section on the chemical quality of the water

Abstract

Hamilton County includes an area of about 538 square miles and in 1960 had a population of 8,665. The general physiography of the county is that of an almost level eastward-sloping depositional plain, the original surface of which has been slightly modified by stream erosion and wind action. The West Fork of the Big Blue River is the only perennial stream in the county. Ephemeral streams, which flow only during and after heavy rains, are the Big Blue River, Lincoln Creek, and Beaver Creek. The Platte River, which forms the northwest boundary of the county, flows during the winter months but usually is dry during the summer. The climate is subhumid, the normal annual precipitation being about 24 inches. Agriculture is the principal industry in the county; corn is the most important crop. More than 113,000 acres was irrigated with water pumped from 1,196 wells in 1957. Hamilton County is in the southeastern part of the loess-plains region of Nebraska, just west of the glaciated region. Sand and gravel, and associated silt and clay deposits of Quaternary age, mantle the area. The parts of these deposits that are below the water table are saturated and yield large quantities of water to wells. The deposits of Quaternary age rest on an eroded bedrock surface of rocks of Cretaceous age, except in one small area in the southwestern part of the county where they rest on a remnant of deposits of Tertiary age. The deposits of Tertiary age are partly consolidated fine-textured sand, silt, and clay. These deposits are saturated and may yield water to some wells. The rocks of Cretaceous age have little significance as potential source of ground water in Hamilton County. The water that is available to wells in the county is derived principally from precipitation; the recharge through the soil is believed to average about 40,000 acre-feet per year. Some recharge is also obtained from the Platte River when it is in flood stage, but the amount thus received is relatively small compared to that received from precipitation. The use of ground water for irrigation has increased greatly since 1952, and analyses of the hydrologic data indicate that the groundwater discharge exceeds the recharge. The natural recharge is about equal to the amount of water required to irrigate one-ninth of the land. Development in 1957 had reached the point where almost one-third of the land in the county was being irrigated with ground water. N-l N-2 CONTRIBUTIONS TO THE HYDROLOGY OF THE UNITED STATES The ground water is generally of relatively low mineralization and in most of the county is of the calcium bicarbonate type. Near the north and west borders of the county, the relatively high mineralization and high concentrations of sulfate in the ground water probably are due in part to recharge from the Platte River. The continued lowering of the water table may cause the more mineralized water in the western part of the county to move into the areas where the water is now the least mineralized. The water is suitable for irrigation, domestic, and many in...