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Section E.2 <br />Final <br />TO: File <br />FROM: David M. Frick, Ayres Associates <br />SUBJECT: Task Memorandum 10.2 -Evaluate Extension of Historical Data <br />Introduction <br />The feasibility of developing a longer period of record and possibly generating stochastic data for the <br />CRDSS Water Resources Planning Model is being investigated by the State of Colorado, assisted by <br />Boyle Engineering Corporation and Ayres Associates. This memo presents results and ideas arising <br />from this investigation, as well as conclusions and recommendations. The objective of this task was as <br />follows: <br />Investigate options and develop an approach for extending the period of record within <br />the CRDSS database to enhance the Water Resources Planning models. <br />Approach <br />The investigation has been divided into several subtasks including data extension feasibility, evaluation <br />of historical data extension, evaluation of stochastic data development, and review of other data <br />extension techniques. This memo covers the evaluation of historical data extension, which consists of <br />two major components: naturalizing flows, and then filling or extending the data. The evaluation was <br />accomplished by: (1) investigating the availability of historical data; (2) evaluating methods for <br />estimating diversion data necessary in computing natural flows; (3) evaluating methods for estimating <br />depletions to aid in calculating return flows; and (4) investigating regression models for the extension of <br />hydrologic data. <br />Overview of the CRDSS Planning Model <br />StateMod is a model that takes into account various factors in order to determine natural streamflows for <br />a particular basin. If diversion records are available, the natural flow at a gaged site is computed in <br />StateMod using Equation 1 for a given time period, t: <br />N~=Gt+Dt-Rt+OSt-It+Et (1) <br />Where: <br />Nt is the computed natural flow at a site in the basin; <br />Gt is the gaged flow at that location; <br />D~ is the sum of the diversions in the basin above the site; <br />Appendix E E-14 <br />