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<br />OOO~1l1 <br /> <br />was dominated by a major drought, and extensive water development <br />had already occurred throughout the basin.* Despite the drought <br />and water developments, two vestigial flow pulses are prominently <br />displayed in the hydrograph of the Duncan gage. In general, the <br />first pulse began in February and peaked in early March. The <br />second pulse began in May and peaked in late May and early June. <br />This pattern is typical of many rivers in the northern Great <br />Plains with headwaters in the Rocky Mountains. The respective <br />pulses are attributable to spring rain and snowmelt on the plains <br />and on mountain snowmelt, respectively. <br /> <br />In addition to wet meadow maintenance, other ecological functions <br />associated with flow pulses include channel maintenance, <br />importation of allochthonous nutrients, inorganic, and organic <br />material, maintenance of riparian woody habitats, and cues for <br />spawning and migration of riverine fish species (Crance 1988, <br />Junk el al. 1989). <br /> <br />Regardless of protection provided by this possible approach to <br />management, these flow pulses will not protect all existing <br />values provided by the meadows. For example, October and <br />November 1987 flows up to 2300 cfs contributed to inundation of <br />sloughs in the Crane Meadows near Grand Island for an extended <br />period of time and scores of thousands of ducks used the area. <br />Such events would not be protected by simply protecting spring <br />flow pulses alone. <br /> <br />Recommended Targets: <br /> <br />Target spring flow pulses to resemble the pattern and level of <br />natural, pre-development hydrograph are recommended. Gaging data <br />from Duncan, 1929-1938, are a possible model for adjusting the <br />flow pattern (Appendix C). The level of the spring flow pulse <br />targets should vary year by year and be determined according to <br />the projected annual basin run-off. The extremely high discharge <br /> <br />. <br />Eschner et al. (1983) reported that most of the natural flow <br />diversions in the basin were in place by 1930. Based on records <br />of ap~ropriations to new canals or additional appropriations to <br />exist1ng canals, Eschner et al. (1983) estimated about 6940 <br />canals were either constructed or enlarged on the North Platte, <br />South Platte, and Platte River (above the Loup) drainages from <br />1851 to 1930. Overappropriation of summer flows on the South <br />Platte Basin had occurred by the late 1800's and <br />overappropriation of summer flows in most of the North Platte <br />Basin had occurred by 1915 (Eschner et al. 1983). Eschner et al. <br />(1983) also reported that 704 wells were constructed in the <br />Platte River valley in Nebraska between 1911 and 1930. In <br />addition, about 30% of the current usable reservoir storage <br />capacity in the basin was developed by 1930 (Eschner et al. <br />1983) . <br /> <br />14 <br />