Physical History of the Platte River in Nebraska

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2.1.3 Trans -basin Diversions The availability of water from the lesser developed portions of neighboring watersheds (primarily the Colorado River Basin) coupled with the increasing demand for water in the Platte River Basin led to the concept of diverting water from one basin to the other, hence the term trans -basin diversion. To obtain more water, trans -basin diversion projects were constructed beginning in the 1890's to deliver water primarily from the Colorado River watershed to South Platte River basin irrigators. Figure 2.8 shows that water began to be transferred into the South Platte River Basin before 1900. The volumes of water transferred rose on a relatively steady trend until about 1950 when the Colorado Big Thompson Project came on line, dramatically increasing trans -basin inflow into the South Platte Basin. This imported water increases the water supply to the Platte River Basin, a portion of which reaches the Platte River after having been used and reused and eventually joining the river as return flow. 2.1.4 Groundwater Development In addition to the development of surface water, farmers began to look to groundwater for irrigation in a significant way in the early 1900's. The Missouri River Basin Commission (1976) stated that, Significant use of ground water as a source of irrigation supply began about 1926 and has developed rather rapidly in the last 40 years. Development has been extensive in both valley and upland areas, particularly in the eastern two- thirds of the basin. In 1970 about 60 percent of the total irrigated acreage in the basin was from ground water, accomplished almost entirely by private individuals. Figure 2.9 shows the growth of registered irrigation wells from 1930 to 1975, when it was reported by the Missouri River Basin Commission (1976) that there were almost 24,000 wells in 1973. 2.1.5 Summary of Current Water Resources Development Conditions Water resources development occurred in four basic stages as discussed by Eschner et al. (1983). The first stage was characterized by the construction of small, crude irrigation ditches to provide water to small parcels of land on the floodplain. The second stage expanded construction of larger and more sophisticated canal systems to extend irrigation to benches above the valley floor. During this period, over- appropriation occurred such that canals with later water rights could not always be filled. The third stage reflected this fact by constructing reservoirs to store water during the peak flow period of snowmelt runoff. During this stage, summer flows generally remained over - appropriated since many new canals were constructed. The fourth stage is represented by continued reservoir construction, but at a slower pace. The stored water was used to fulfill existing water rights. Groundwater withdrawals provided water to meet new demands for irrigation. The Platte River Basin, under current conditions, is one of the most intensively managed river systems in the United States. Because of the great importance of water to those who 14