Laserfiche WebLink
<br />III- 2 <br /> <br /> <br /> TABLE I <br /> DESIG N RAINFALL <br /> Boulde r County T IS R70W <br />Duration Rainfall (Inche s) <br />(Hours) 5 year s 25 years 100 years <br />I 1. 43 2.03 2.50 <br />2 1. 65 2.32 2.85 <br />3 1. 80 2. 51 3.08 <br />4 1. 91 2.65 3.26 <br />5 2.00 2.77 3.41 <br />6 2.07 2.86 3.52 <br /> <br />The procedures from the Urban Storm Drainage Criteria Manual <br />were used in developing runoff patterns. Initially, the Colorado Url:a n <br />Hydrograph Procedure (CUHP) was utilized to develop peak flows. How- <br />ever, the CUHP is designed primarily for urbanized drainage basins and <br />the resulting hydrographs were not representative of a large undeveloped <br />mountain basin. The CUHP method resulted in high peak flows and it <br />became apparent that this procedure would not be suitable for the South <br />Boulder Creek Study Area. Therefore, a more rigorous approach <br />utilizing a synthetic unit hydrograph calibrated to the basin was required. <br /> <br />The presence of Gross Reservoir limits the usefulness of previous <br />stream gaging records and the information available concerning the effect <br />of historical storms. The storm of 1969 provided a limited opportunity <br />to calibrate a synthetic unit hydrograph. To supplement this historical <br />information on the creek, the basin and stream flow characteristics of <br />several nearby systems were compared to determine the reasonableness <br />of the assumptions made with the use of the 1969 storm. Unit peak flows <br />we re calculated us ing the equation: Qp = 640 Cp <br />tp <br />Qp = Peak rate of runoff in cfs per square mile. <br /> <br />Cp = A coefficient related to the peak rate of runoff. <br /> <br />~ = Time to peak of hydrograph in hours. <br />