Simulation of the effects of management alternatives on the stream-aquifer system, South Fork Solomon River Valley between Webster Reservoir and Waconda Lake, north-central Kansas

With extensive irrigation use of both surface water and groundwater in the South Fork Solomon River valley shortages of these water supplies have been created. A two-dimensional digital model of transient groundwater flow was applied to investigate the potential effects on the stream aquifer system of seven management alternatives. These alternatives included proposals to conserve surface water supplies by lining the Osborne Irrigation Canal with clay, replacing the lateral canals with pipe, removing phreatophytes, decreasing surface water use by 75%, 50%, or 25% and replacing it with groundwater sources, and continuing 1978 groundwater use and 1970-78 average surface water use until the end of the 20th century. Results were assessed by comparison of drawdowns of hydraulic head in the alluvial aquifer and base flow for each simulation. As listed in order of the smallest to the greatest potential effects on the system relative to drawdown and base flow the alternatives are: (1) removal of one-half of the phreatophytes; (2) continuation of 1978 groundwater withdrawals and average 1970-78 surface water supply; (3) replacement of the lateral canals with pipe; (4) lining the Osborne Irrigation Canal with clay; (5) decrease of surface water use by 25% and replacement of it with groundwater; (6) decrease of surface water use by 50% and replacement of it with groundwater; and (7) decrease of surface water use by 75% and replacement of it with groundwater. The removal of one-half of the phreatophytes would result in a decrease in average drawdown in the alluvial aquifer to about 1.74 ft and an increase in base flow of the Solomon River to about 12.3 cu ft/sec. The decrease of surface water supply by 75 % and a corresponding increase in groundwater withdrawal would result in an increase in drawdown in the aquifer to about 2.5 ft and a decrease in base flow to about 6.8 cu ft/sec. (Lantz-PTT)