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, APPLICATION AND EVALUATION OF THE COLORADO URBAN HYDROGRAPH PROCEDURE By Bruce Anderson INTRODUCTION The ability to accurately forecast hydrologic conditions during a major storm event has always been an important goal of water resource engineers across the globe. As urban centers grow and cities develop it has become clear that city planners must contend with the increasing complexity of storm water management. Because of quick growth in previously undeveloped suburban areas it is no longer sufficient to analyze current and historical data. Hydrologists must now predict future growth to anticipate needs beyond the present. Engineers rely on mathematical models to predict storm water profiles. These predictions are used to design structures, roads, retention and detention facilities, and flood control systElms. Substantial loss of property can result from underestimation and costly construction can result from overestimation. Therefore it is of great importance for city planners and construction contractors to have accurate forecasting models. Colorado, in an effort to standardize the prediction models within the state, developed the Colorado Urban Hydrograph Procedure (CUHP). The procedure was later developed into a computer program (CUHPF/PC) for ease of use. There are a variety of hydrologic models available. Most of these models have been developed by, or in partnership with, government agencies. The Soil Conservation Service (SCS), the Environmental Protection Agency (EPA), the U.S Army Corp of Engineers, and the United States Geological Survey (USGS) have all developed models. Local municipalities frequently look to these federal agencies for guidance since it is these same agencies that are critical when flood control measures prove to be inadequate. It is beyond the scope of this report to examine the comparative accuracy of all the available models. Zamello reported such an effort of nine runoff models published in 1998, which proved to be inconclusive. What is conclusive, . . however, is that the State of Colorado in conjunction with the Urban Drainage and Flood Control District (UDFCD) and the Denver Regional Council of . Governments has determined that the CUHP method is valid for the state. Since this procedure is established practice it is important to understand when the model is most accurate and what information best establishes that accuracy. PURPOSE ., As stated previously, it is not the intent of this investigation to determine the appropriateness of the CUHP model, but to determine the best way to use it accurately. Computerized rainfall-runoff models are a double-edged sword. While they provide a user-friendly interface that quickly provides results, they do Application and Evaluation of CUHP Page 2 of 52 .,t