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area that is difficult to farm, (2) a field area of perceived high percolation rates, (3) an <br /> area that is not presently farmed, for whatever reasons, such as a center pivot corner, <br /> (4) a recharge structure close to an existing Union Ditch headgate or an existing Union <br /> Ditch lateral, and (5) the proximity of the site to the river. Presumably, property owned by <br /> Union Ditch shareholders is preferred over land owned by non Union Ditch shareholders. <br /> It is important to note that pond sites have been identified based on easily observable, <br /> surface conditions. It is possible that a recharge structure could cause adjacent ground <br /> to become saturated and water logged. It would be desirable to reduce the risk of such <br /> by picking sites where negative impacts of the recharge structure can be minimized. <br /> Water Availability for Recharge <br /> The Union Ditch intends to divert water from the South Platte River for recharge <br /> purposes when there is a free river condition. When there is a free river, Union's junior <br /> water right decree (pending) will be in priority and may be diverted. Recent drought <br /> conditions in the region have produced a situation where there has been a call on the <br /> river even during the winter months and during high runoff periods. According to the <br /> local Water Commissioner, Bob Stahl, prior to the drought there was typically a free river <br /> situation during the winter months, during peak spring runoff periods, and during large <br /> storm events. In the event that normal water conditions return, Bob Stahl believes there <br /> will be ample opportunities for the Union Ditch to divert water under their junior decree <br /> for recharge purposes. However, it is not possible to accurately predict when and how <br /> much water will be available through the junior water right in the future. <br /> Evaluation of Proposed Recharge Structures <br /> The proposed recharge structures were evaluated for purposes of identifying priority <br /> recharge ponds and to gain a better understanding of how a recharge project would <br /> operate in the vicinity of the Union Ditch. In theory, the selection of priority pond sites for <br /> a recharge project should depend on the goals of the project (e.g. when timed accretions <br /> are desired in the river) as well as the characteristics of each recharge structure, namely <br /> the stream depletion factor. In actual practice, the selection of the site may have more to <br /> do with the overall feasibility of developing the site at a given location. <br /> The stream depletion factor method (SDF) is a method that can be used to estimate the <br /> impact of recharge on the flow in the South Platte River. Stream depletion factors, <br /> expressed in units of days, are used to determine the lag time from when irrigation well <br /> water is pumped from or when water is recharged to an alluvial unconfined aquifer and <br /> when a depletion or accretion happens in the river (Garcia et al., 2001)1. Tables 1 and 2 <br /> include the SDF values for the proposed recharge ponds and for various canal reaches <br /> along the Union Ditch, respectively. The SDF View Model (IDS, 2000) is a commonly <br /> used computer model designed to estimate stream accretion from recharge or stream <br /> depletion from well pumping. <br /> Figure 2 illustrates stream accretion patterns for a single recharge event in year one for <br /> various SDF values. Recharge ponds with higher SDF values or that are further from the <br /> 1 Stream depletion factors were developed to estimate stream depletion from well pumping,but can also be used to <br /> estimate stream accretion from recharge. <br /> Aqua Engineering, Inc. Recharge Project Potential <br /> February 17, 2004 - 5- <br />