5901 23RD DR W SEAWAY CORP 3C 2025-07-29

I Ipond is designed with 4' of live storage, resulting in an available volume of 127,080 cf(2.92 ac- ft). Live storage will be provided between elevations 507 and 511.1, with 1' of freeboard I provided to elevation 512.1. Dead storage for runoff control treatment will be provided beneath the live storage. The surface pond is greater than 30 feet wide at the top, therefore an access road will be provided to the bottom chamber. A 6' high fence will be constructed around the I pond with an access gate on the east edge of the pond. Figure 6 shows three section views of the pond. Volume Correction Factor IDeveloped conditions will increase the impervious cover of the site to 90%. From Figure 1-3.1, this results in a 0.46 correction factor, which means oversizing the pond by 46%. The pond size input into WaterWorks reflects the correction factor of 1.46. Multiple Orifice Control Structure I A Type 11-72 Catch basin with a combination of restrictors will be located in the southwest corner of the pond. One restrictor will release to Powder Mill Gulch at 74% of the allowable release rate and the second restrictor will release at 26% of the allowable release rate to the I existing 18" stub in the northwest corner of the site. The restrictors are designed to control release from the pond to match existing runoff rates for the 2, 10 and 100-year storms. Figure 7 shows a detail of the two multiple orifice restrictors. IFrom Appendix A, the peak developed flow for the 100-year storm is 10.6 cfs. Overflow conditions would create a flow of 5.3 cfs then since there are two stand pipes providing I release. From Figure 1-5.16, a flow of 5.3 cfs in a 12" diameter riser results in a head of 1.8 feet. IB. Treatment Using the developed site conditions as described above, the required permanent pool I volume based on the 6-month, 24-hour storm is 49,581 cf. The proposed wetpond is 480' long at the surface, has 31 side slopes and provides a total of 65,490-cf storage in both cells. The wetpond is divided into two cells, an open water cell and a wetland I treatment cell. The open water cell of the proposed wetpond is 3' deep, and will provide approximately 67% of the total permanent pool volume. The wetland treatment cell is 2.5' deep and will provide approximately 33% of the total permanent pool volume. The Ifollowing table shows the permanent pool area by elevation. Stacie Area (sf) Volume (cf) Volume (acft) 504.0 10,550 0.00 0.0000 I 504.5 15,032 6,395.50 0.1468 505.0 16,639 14,313.25 0.3286 505.5 18,275 23,041.75 0.5290 I 506.0 19,942 32,596.00 0.7483 506.5 21,637 42,990.75 0.9869 507.0 23,362 65,490.25 1.5034 I 1 4 I