Laserfiche WebLink
<br />CASE STUDY <br /> <br />The second part of this study was aimed at evaluating the second major <br />component of the CUHP program. While CUHP is most often employed using <br />the 1-hour rainfall method, it has the capacity to do the same evaluations using a <br />detailed storm hyetograph. Since this method is less often used in practice the <br />results are not as meaningful per se, however, the implications in concert with <br />the results of the CUHP calibration are very meaningful. The basic algorithms <br />and mathematical engine is the same in CUHP whether a 1-hour rainfall is used <br />or a detailed hyetograph is used. Therefore, in theory, the storm hydrograph <br />produced using the 'calibrated' parameters and an actual storm hyetograph <br />should be very close to observed conditions. Therefore, this study was <br />considered to be an independent verification of the calibration. <br />There are six rainfall gages either within or in close proximity to the <br />Harvard Gulch drainage basin (see map 1). The continuous rainfall gages record <br />precipitation in five-minute intervals to the nearest one hundredth of an inch (0.01 <br />inches). Stream flow data was determined using a USGS stage-discharge gage <br />located on Harvard Gulch at Harvard Park (USGS gaging station 06711575). <br /> <br />AUGUST 14, 1980 <br /> <br />The selection of an appropriate rainstorm event was based on two factors. <br />The first criterion required that the precipitation be of sufficient magnitude and <br />duration. The target was to meet at least the UDFCD 2-year precipitation, <br />preferably over a period of about one-hour. The second criterion required the <br />precipitation event to have registered on all six rain gages, therefore <br />encompassing the entire drainage basin. These criteria proved more challenging <br />than expected. The storm of August 14th, 1980 was the only rainstorm that had <br />data available for all six rain gages and the continuous stage-discharge gage <br />approaching the 2-year precipitation event. <br />The Harvard Gulch drainage basin was spatially subdivided into zones of <br />influence by the individual rain gages using the Thiesen Polygon method (see <br />map 2). The area percent of each polygon was multiplied by the 5-minute <br />precipitation depth at each time interval and summed across all six gaging <br />stations. The resulting rainfall profile became the hyetograph for the entire basin <br />(see graph 7). The hyetograph was then entered into the CUHP program along <br />with the calibrated basin parameters. The resulting storm hydrograph (graph 8) <br />was generated and plotted against the observed runoff for the storm event. <br />As you can see, the predicted hydrograph is very similar to the actual <br />obserVed flow profile with similar peak flow but attenuated peak shape. Much of <br />the attention in this investigation has been devoted to peak flow. However, storm <br />runoff volume is also of interest. The actual storm hydrograph and the predicted <br />storm hydrograph were plotted using incremental volume calculations (graph 9). <br /> <br />Application and Evaluation of CUHP <br /> <br />Page 19 of 52 <br />