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<br />,.. '1' <br />1., oJ .... \J ... <br /> <br />17 <br /> <br />STORAGE REQUIREMENTS AT STREAMFLOW STATIONS <br /> <br />Prior discussion has been concerned with the natural minimum flow of the <br />streams. With knowledge of these characteristics it is now possible to deter- <br />mine the streamflow that may be attained by storing water during periods of <br />plenty and releasing water during periods of drought. The storage capacity <br />must be large enough to maintain a usable amount of outflow throughout drought <br />periods but not be so large as to entail unnecessaryconstruction costs and ex- <br />cessive evaporation losses, To obtain an optimum balance between costs and <br />benefits requires knowledge of the amount of sustained flow that can be released <br />from specific amounts of reservoir capacity with a specified chance of fulfill- <br />ment, This section of the report gives such information on the magnitude and <br />frequency of storage requirements at each of 113 gaging stations in Kansas <br />and vicinity and compares the requirements wi th those for a major drought. <br />Also included are approximate values of storage-required frequency for 29 <br />short-term and partial-record stations. Only gross outflow rates are defined. <br />Users must evaluate the specific evaporative and seepage losses at a pro- <br />posed reservoir. It should be noted that evaporation losses increase as res- <br />ervoir surface area increases and a point may be reached where addingcapa- <br />city to a reservoir would not increase its ability to maintain desired outflow <br />during drought periods, particularly as the increase in size of reservoir is <br />usually accompanied by an increase in the length of time the water must be <br />held in storage. <br /> <br />Sto rage Requireme nt s for Drough t of 1952 - 57 <br /> <br />As early as 1883, Rippl, a British engineer, suggested that storage re- <br />quirements for water supply could be investigated by a mass curve of accu- <br />mulated successive volumes of streamflow, A mass curve of actual runoff is <br />still cons idered an approp riate device to show the storage requirements in a <br />critical period, (Johnstone and Cross, 1949, p. 93-95), (Mitchell, 1950, p. 27- <br />34). In Kansas the drought of 1952-57 was particularly critical and caused the <br />lowest sustained drought flows of record at more than two-thirds of the long- <br />term gaging stations. Accordingly, storage requirements for 1952-57 have <br />been computed by the mass-curve method at most stations analyzed in this re- <br />port to provide a comparison with the storage requirements developed on a <br />frequency basis, <br /> <br />Figure 3 illustrates mass-curve analyses for station No, 66, Delaware <br />River at Valley Falls. The mass curve is shown as a heavy line that depicts <br />monthly accumulations of observed streamflow plotted against time. The curve <br />rises slowly when the flow is small and rises rapidly when the flow is large. <br />Thus the slope of the mass curve is a measure of the rate of flow of the stream, <br />whichis the inflow to a possible reservoi r if located at that site. Similarly, the <br />slope of any straight line on the diagram represents a rate of streamflow which <br />may be considered as a selected draft or rate of gross outflow from a reser- <br />