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<br />The USGS studied this recharge experiment using a digital groundwater <br /> <br /> <br />model (6). In the model study cyclic operation of the pumped well and the <br /> <br /> <br />recharge pit were simulated. The well was pumped for four months and turned <br /> <br /> <br />off. Similarly the recharge operations were conducted for the same four <br /> <br /> <br />months and then stopped. The concept was that the pumped well, which was <br /> <br /> <br />closer to the river, would deplete stream flow in the South Platte River <br /> <br /> <br />sooner than the return flow to the river from the recharge operations would <br /> <br /> <br />occur. Conversely, the return flow to the South Platte River from the <br /> <br /> <br />recharge operations, which were located farther from the river, would be <br /> <br /> <br />delayed and would occur after the depletion of the stream flow caused by the <br /> <br /> <br />pumped well. With the proper configuration of the pumped well and recharge <br /> <br /> <br />pit, located at the proper distances from the river, it was conceivable that <br /> <br /> <br />the pumping and recharge operations could be timed so that the depletion <br /> <br /> <br />caused by the pumped well would occur during the non irrigation season and <br /> <br /> <br />the return flow to the river would be delayed to occur during the irrigation <br /> <br /> <br />season. It was found that for the case studied it took seven years to reach <br /> <br /> <br />dynamic equilibrium between the rate of stream depletion in the South Platte <br /> <br /> <br />River caused by the pumping well and the rate of stream accretion due to the <br /> <br /> <br />recharge operations. The model showed that for equilibrium conditions a <br /> <br /> <br />depletion for six months and an accretion for six months would occur. The <br /> <br /> <br />study recommended for augmentation purposes that the pumpage should occur <br /> <br /> <br />during the months of November through February, so that the resulting stream <br /> <br /> <br />depletions would occur from January through June, in order to avoid <br /> <br /> <br />depletion during the critical low-flow months of July and August. However, <br /> <br /> <br />during the first three years of operation (during the transient simulation <br /> <br /> <br />period), depletion of stream flow caused by the pumped well was greater than <br /> <br /> <br />return flow from the recharge operations over the entire year with the <br /> <br /> <br />result of net depletion of stream flow occurring even during the irrigation <br /> <br />10 <br />