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001543 All studies have shown that stock ponds effects On surface runoff are extremely variabLe from year to year, depending to a cons iderable extent upon the amount and character of the precipitation and the accom- panying runoff. Storage in stock water reservoirs is not necessarily a true measure of the depletion in runoff from the basin since there are compensating factors that operate in su ch a manner that as one type of los s increas es, another may decrease. In years'of high precipitation, with reservoirs filled near capacity, evaporation' will be, at a maximum. , Under these co,rlditions, downstream channel losses are likely to be at a minimum and a part of reservoir seepage may be recovered. In years' of low precipitation and runoff when reservoirs remain at low stage with small water su rface area, evaporat ion approaches a minimum but less seepage is recoverable. - ::'.'~,.:::-:~. .~ , . Since each factor varies so much from year to year, most analyses use either average values or assume a set of maximum and minimum con- ditions in order to determine upper and lower limits of effect. All rational analyses attempt to estimate or account for the two major types of reservoir depletion, evaporation and seepage. Water evaporated from the water surface repres entsa", complete los s charge- able to the reservoir, whereas seepage may be 'recovered in part. Seepage is generally considered as the residual after net evapor- ation and beneficial consumptive use are subtracted from the total measured depletion in the reservoir. Seepage losses should be divided into evapo- transpira.tion, ground water increment, and, return flow to the stream; however, this requires an accurate knowledge of ground-water movement which is often difficult or impossible to obtain. ;"'ff~\ ~~" ~~i :::~:f:;;~: ~.~:~::i:>\:. . :,';',' ., ::;::A<;;:::~ \::':'':',;.~:::.~ -"-..:-''',--" The many uncertainties which exist in our present state of know- ledge regarding the hydrologic factors but which have an influence on water yield, point up the need for continued research and cooperative action by local, State, and Federal interests. Only in this way can an acceptable evaluation of the impact of the future water developments on available water supplies be assured. Floods Because stock ponds are comparatively small in size and control onl y a small portion of any major drainage area, theeffectivenes s of stock ponds on the higher flood flows is generally negligible. However, under certa.in conditi0113, where stock pond density is high and storage volumes are comparatively large, a significant reduc- tion in local flood peaks and volumes can be achieved, particularly for .;'".. 53 I j, t "..I