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O ~ 1 I" I u.l '" (, 2. ., in locating such a boundary lies in the fact that our data are vitiated by pumping. The idea seems not to hold with the water-table fluctuations in wells on the Arkansas River bottoms between Pueblo and Nepesta. Perhaps the reason for this can be accounted for but at present it is obscure. ., The water table in areas where replenishment occurs from natural sources and is uncertain, the usual condition is that of over- draught for considerable periods of time. In this type of situation, hydrographs usually show a water table higher in spring than in fall. This is easily accounted for. Observation wells are usually pumped wells and during the pumping season they develop cones of depression around them. Readjustment occurs for sometime after the pumping season resulting in a local recovery during the winter. With over- draught occurring, each successive spring measurement will show a lower water table. THE SOUTH PLATTE RIVER SYSTEM Areas in Classification 1. I . I From Waterton to Julesburg, the South Platte is underlain with sands and gravels from which. ground water can be extracted easily and cheaply. It is now highly developed particularly below Denver. The valley which it occupies is reasonably well defined for most of its length. Generally the lands of the valley are composed of two levels; a low- lying or what might be normally defined as a flood plain and a some- what higher terrace. Pumping plants are to be found on both levels. The total valley width. seldom exceeds 4 miles. Tentatively I would place all of most of th.ese lands in Classification 1. Sands and gravels also underlie the valleys of the Cache La Poudre, Thompson, St. Vrain. Boulder Creek, Clear Creek, Bear Creek, and Cherry Creek. All these streams carry appropriated water and in some of the valleys, irrigation wells are quite numerous. I would place rno st but not all such wells in Classification 1. " Since the above areas in which ground-water use is occurring are also covered by surface water irrigation systems, replenishment has been adequate. Only for periods of short duration - a few years - has there been a serious lowering of the water table. These have occurred during drought periods and subsequent recovery has been complete. Not only has the replacement of lost storage been taken from stream flow but also a very large part of the water that was currently pumped from the wells. Herein lies the conflict of interests between surface and ground-water users. .' - 2 -