Capital Hill PUD, Tentative (14-020) <br />March 3, 2017 <br />By having all the storage facilities fall within the footprint of the roadway, or just outside the roadway, the <br />stormwater improvements are far less likely to encroach on the existing vegetation. The existing condition <br />draining to discharge location 2 was assumed to be a 38-foot-wide section of sheet flow draining from the top of <br />the hill, located about 380 feet away. The basin area of roughly 14,900 square feet created a peak discharge rate <br />during the 10-year design storm of 0.16 cubic feet per second (cfs). With the current layout proposed for the <br />private roadway, the basin area directing runoff to the 38' level spreader increases dramatically (3x) up to <br />45,520 square feet. It is for that reason that several tanks were selected, and multiple level spreaders are <br />proposed. By matching the peak discharge rate of 0.16 cfs / 38 linear feet of level spreader, the post developed <br />improvements match the pre-developed discharge rates and runoff conditions. <br />The discharge to location 3 under the post developed condition shows a peak discharge rate of 0.11 cfs, where <br />the existing condition was 0.10 cfs. This difference in peak discharge rate is minimal, and the discharge will be <br />into a bubler that will runoff onto pervious pavement. The water will essentially flow into the ground and along <br />the top layer of gravel as it does today. For that reason, no additional detention or flow control was designed for <br />this discharge location. <br />For additional information on the facility details, or the HydroCAD analysis, please see Appendices A & C. <br />4.0 CONCLUSION <br />The stormwater system for the Capital Hill PUD has been designed in accordance with the city of Eugene <br />Stormwater Management Manual for Water Quality & Flow Control requirements. <br />Branch Engineering, Inc. <br />5 <br />