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<br />001497 <br /> <br />11 <br /> <br />an adequate source of irrigation water. In the design of water storage fa- <br />cilities, storage required would be governed by the expectancies of various <br />low flows. The economics of the design would be concerned with the proba- <br />bility of failure to supply the desired quantity of water. Again as in the op- <br />erational problem, the probabilities of various base flows rather than low <br />flows would be used if upstream developme nts withdrew direct runoff from <br />the streamflow. <br /> <br />Base-flow data are helpful in certain hydrologic investigations. They <br />provide an index for comparing ground-water characteristics of different <br />basins, for studying rainfall-runoff relations, and for studying the effect of <br />ground-water developme nt on the flow of streams. <br /> <br />Meaning of direct runoff. -- Flood flow, designated herein as direct run- <br />off, endures for a relatively short time and consists mainly of surface run- <br />off and a part of the interflow. It is the major portion of the total stream- <br />flow in Kansas and is conveniently determined as the remainder of the <br />total flow after the base flow has been separated on the hydrographs. <br /> <br />Uses of direct-runoff data.- -The most important use of direct-runoff <br />data is in estimating the probability of occurrence of some given flow. In <br />the following examples the probability of various rates of direct runoff <br />would be used in determining the economic feasibility of a project. Direct <br />runoff can be used or stored at or near its source and prevented from <br />reaching a stream without reducing the base flow of the stream. The ca- <br />pacity required to store this water would be governed by the expectancies <br />of given amounts of direct runoff. Proper conservation practices would <br />allow some of this direct runoff to be detained and used by crops. Direct <br />runoff is usually the source of supply for the small headwater farm ponds. <br />Where the low flow of a stream into a reservoir must be released to down- <br />stream water users by law, direct runoff is often the only source of supply <br />of water available for storage. <br />