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<br />2 <br /> <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />measured in streamflow. This effort would require a reconnaissance of the mid- to <br />upper reaches of numerous small streams draining the basin to locate suitable sites for <br />monitoring. The distribution of streamflow along a reach of a stream would be measured <br />repeatedly over a period of years or seasons as water levels rise or decline in the bedrock <br />aquifer. Changes in the distribution of streamflow could indicate changes in the rate and <br />distribution of bedrock discharge to the streams. Such measurements of the effects of water <br />levels on streamflow could be a direct confirmation of model results. Annual stream gain-loss <br />measurements at perhaps five sites and monthly water-level measurements in nearby bedrock <br />wells might require $10,000 per year during a multi-year monitoring program. <br /> <br />3. The model calculates ground-water discharge to stream valleys but these numbers may not <br />be representative of actual streamflow in many valleys because of other factors not included in <br />the model such as underflow in aluvium, stream diversions, pumping from alluvial aquifers, and <br />return flows from sewage treatment plants. These other factors could be much larger than the <br />changes in bedrock discharge to the valley and could obscure the bedrock affects. A <br />modification could be made to the Denver Basin model to allow it to make calculations of <br />streamflow and streamflow depletions that are more representative of actual streamflow. A <br />more realistic calculation of streamflow depletion is needed to give the public, lawmakers, and <br />water-law administrators a better understanding of what is happening, and potentially could <br />happen, to streamflow in areas undergoing water-level decline in the underlying bedrock <br />aquifers. <br /> <br />One method to meet this goal involves constructing a post-processor computer program that <br />could be linked to the discharge-to-stream-valley output from the existing Denver Basin <br />model. The post-processor would incorporate all the diversions, pumping, and return flows <br />that affect streamflow in the various reaches of each valley and produce a calculated <br />streamflow at various points in the valleys. Model simulations of effects of future bedrock <br />pumping could then be run through the post-processor program to also simulate the pumping <br />effects on future streamflow and streamflow depletions. These streamflow simulations could <br />then be more easily compared to actual measured baseflow in streams as an additional <br />verification of the model. Development costs for the post-processor program may require <br />$50,000 for a 1-year effort. <br /> <br />4. The rate at which ground water is being withdrawn from the bedrock aquifers is another vital <br />component in the Denver Basin model, and the model response is sensitive to this rate of <br />withdrawal. Efforts to better measure bedrock pumping will enable better calibration of the <br />model and more realistic simulations of future water-level changes. <br /> <br />Much of the pumping data needed to make better withdrawal estimates already is being <br />collected by the larger water purveyors in the Basin. What remains to be done is to collect the <br />pumping records, interpret the data to determine pumping from each bedrock aquifer, and <br />publish the data perhaps as part of the Division of Water Resources' annual Denver Basin <br />water level report. Pumping by numerous small capacity water purveyors and individual well <br />owners generally is not metered, and some staff time would be needed to estimate and verify <br />(with field checking) these rates of withdrawal. Accomplishment of this task may require <br />increased funding to support additional staff within the Division of Water Resources. <br />