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• 5 <br />II. ADJUSTMEt7T OF PRELIMINARY DATA FOR MULTSED CALIBRATION <br />The MULTSED model was used to analyze two conditions, premining or present <br />mining and post mining. The premining and present-mining cronditions are assumed <br />the same due to a large amount of previous mining activity in the study area. <br />This condition represents the existing site conditions and is referred to as the <br />present-mining condition throughout the report. The post-mining conditions rep- <br />resent complete reclamation and revegetation of the study area. <br />Adjustment of the preliminary data as presented in the Preliminary Data <br />Base Report vas necessary in order to calibrate the MULTSED model. The changes <br />were made to bring the peak discharges and runoff volumes of each watershed <br />within a range that was estimated by regression equations. Comparison of the <br />L MULTSED results and the estimates using regression equations are presented in <br />section 5.1. <br />f" <br />2.1 Rainfall <br />In the Preliminary Data Base Report, a bell-shaped hyetograph was developed <br />for the design storm which has a duration of 24 hours. The rainfall intensities <br />are small at the start and end of the design storm. Based on the characteristics <br />of the watersheds, these small intensities do not produce significant runoff. <br />For use in the MULTSED physical process model, the rainfall hyetograph was short- <br />ened by leaving out small rainfall intensities at the start and end of the design <br />storm which were less than 0.08 inches per hour. For the 10-year design storm, <br />the hyetograph ras input starting at the eighth hour and ending rith the four- <br />teenth hour for a total duration of seven hours. Also, the entire 24-hour <br />hyetograph was input for the Newlin Creek ratershed. This ratershed has the <br />largest drainage area which comprises approximately 12.2 square miles. The dif- <br />ference in results using the seven-hour and 24-hour hyetograph vas small with <br />the difference in peak discharges and runoff volume being less than four portent. <br />The Magpie Creek and Tipple Area watersheds have smaller contributing drainage <br />areas and the differences in runoff volume and peak discharge would be even <br />less. For use in the MULTSED physical process model, the hyetograph with the <br />shorter duration was used. The advantage of doing this is savings in both time <br />• and money by requiring less computer time and storage. <br />The 25-year and 100-year hyetographs were also shortened. The full 24-hour <br />~- hyetograph was not input for these design storms and the rainfall intensities <br />' less than 0.08 inches per hour at the start and end of the design storm were <br />