IDENTIFICATION OF RECHARGE AREAS FOR IRRIGATION WATER IN CARBONATE TERRANES

The annual discharge of the Cub River, an important tributary of the B ear River, exceeds the total annual precipitation within its drainage basin. Because a thick sequence of carbonate rocks comprises the north ern Bear River Range, it is obvious that groundwater inflow from one o r more areas outside the Cub River drainage basin must be the source o f the excess flow. Although this investigation is concerned with a loc al or regional problem, the techniques employed are suitable for simil ar problems in other areas of the United States which are underlain by carbonate rocks. The results of this investigation demonstrate that W illow Spring is the source of the excess flow for the Cub River. A hyd rograph analysis performed for the Cub indicates that approximately 57 % of the total flow during the period from May 29, 1991, to February 5 , 1992, was contributed by groundwater flow, and that Willow Spring co ntributed roughly 78% of the groundwater flow. The upper Cub River is located in Idaho, but as much as 45% of its water may come from ground water that is recharged in drainage basins whose streams flow into Uta h. Thus, irrigators in Idaho may be using water that originates in dra inage basins whose streams flow into Utah, unbeknownst to them or thei r counterparts south of the state line.