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not require the user to have much knowledge of the theory of its use. In other words, the computer program becomes the notorious 'black box'. Data is fed into the 'black box' and results come out of the 'black box'. With no further knowledge, the results are assumed to be correct, and it is well stated that "... a little knowledge is a very dangerous thing". As with most computer models, CUHP was designed to accomplish multiple tasks under various conditions. Effective use results from a full understanding of both functionality and intent of the program. This investigation looks at what makes CUHP an accurate forecasting model. . Two different objectives were outlined for this investigation. The first entailed calibrating CUHP for an urban drainage basin with known hydrologic data. The important factor in calibrating the storm hydrographs is matching peak flow. Frequency analyses were performed using historical data for the drainage basin and compared with CUHP predicted peak flow for different return periods. The computer model was then calibrated for best performance. The second objective was to use storm hyetograph data from an actual storm in the drainage basin and evaluate how well CUHP modeled the event using the calibrated parameters from the frequency analysis. WHAT IS CUHP The Colorado Urban Hydrograph Procedure (CUHP) is a rainfall-runoff model that generates unit hydrographs, storm hydrographs, hyetographs, peak flow, and runoff volume data for drainage basins under known rainfall conditions. There are two methods for entering precipitation data into the model, using 1- hour rainfall depths or using a detailed storm hyetograph. CUHP has the capacity to accept up to 18 standard variables that effect the outcome of the results. They are summarized in table 1. In addition to the 18 standard variables, eight additional variables are available to define the shape of the resulting hydrograph. These "shaping factors", which are described in Table 2, are generally only used when a unit hydrograph for a catchment is pre-defined. Once the catchment parameters have been defined, CUHP calculates the excess rainfall by subtracting infiltration losses (either constant or by using Horton's equation), depression storage, and water quality capture volume ('NQCV). A unit hydrograph column matrix is then constructed which is then cross-multiplied by the storm excess rainfall. Four equations are used in determining the shape of the unit hydrograph. The equations describe time from midpoint of unit ranfall to peak (tp), time from beginning of unit rainfall to peak (Tp), peak rate of runoff (qp), and peak flow ofthe unit hydrograph (Qp). These . equations and parameters are outlined by the Urban Drainage and Flood Control District Manual. Application and Evaluation of CUHP Page 3 of 52