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U'" rJ, U ~ l: ' KANSAS STREAMFLOW CHARACTERISTICS PART 2 LOW-FLOW FREQUENCY by L. W. Furness ABSTRACT Low-flow frequency curves have been developed from records of daily streamflow at 115 gaging stations in Kansas and adjoining areas. These curves show how frequently on the average a stream may fail to provide var- ious average rates of flow under natural conditions and in some instances under regulated conditions. Eight separate frequency curves for each sta- tion evaluate the minimum average flow expected in periods of 1, 7, 15, 30, 60, 120, 183 days and 12 months, respectively. By correlation with selected long-term records, the low-flow data observed at individual sites have been extended in time to reflect the 37-year period 1920-56, and have been ex- panded areally to reflect regional rather than local experience, Low flows in Kansas streams tend to decrease progressively to the west with such exceptions as lower amounts in the Marais des Cygnes basin and higher amounts in parts of south central Kansas, Maps compare the varia- tions of minimum flow in Kansas for equal sized basins. For example, the 7-day average discharge reaches zero every other year on most streams in the western half of Kansas andin parts of the Marais des Cygnes and Neosho basins, On a square mile basis, minimum 7-day flow is more sustained in the South Fork Ninnescah River basin than elsewh ere in Kansas and amounts to 0,061 cubic feet per second per square mile for a standard area of 500 square miles. Procedures are outlined for estimating low-flow frequency curves on streams in Kansas of more than 100 square miles drainage area where no gaging stations have been operated, At low flow, the estimates are based on discharge measurements made at base flow, At higher flows where base- flow measurements are seldom obtainable, maps of the geographic variations provide valuable information, The low-flow frequency curves developed herein, which are based on un- regulated flow, can be used in the study of future water developments. The recent accelerated expansion of water uses makes it essential that natural stream behavior be defined while natural conditions still prevail. 1.