1710 W MARINE VIEW DR 2024-01-03

Table 3: Peak Discharge Summary Return Period 2-year 10-year 25-year 100-year Rational Method Pre -Developed Peak Discharge (cfs) NA NA 2.66 3.04 Post Developed Peak Discharge (cfs) NA NA 2.21 2.82 MGS Flood Pre -Developed Peak Discharge (cfs) 0.306 0.479 0.578 5. PERMANENT STORMWATER CONTROL PLAN Post Developed Peak Discharge (cfs) 0.293 0.387 0.553 0.839 The existing stormwater system serves the project site as well as the South Marina Parking lots and the Lombardi's Parking lot. Refer to the Appendix C for a visual depiction of the conveyance system. This conveyance system will be modified at the project site. The conveyance system will be analyzed as two systems. The first system, A, is part of the proposed site improvements and collects the stormwater for the project area. System A flows through a treatment vault on -site before discharging into system B. The second system, B, collects runoff from the Port of Everett South Marina Parking Lot and other areas upstream of the project limits. System B consists of existing pipes and catch basins as well as a new conveyance through the project site. The area contains multiple drainage sub -basins that collect in individual inlets that make up the site's existing Port -owned conveyance system.. Drainage is routed to two outfalls north of the site. Outfall 1 is a 30" diameter pipe and located south of Lombardi's restaurant approximately 160' north of the site. Outfall 2 is a 36" diameter pipe located approximately 400' north of the site at Guest Dock 2 in the Port of Everett Marina. The PGL site contains multiple drainage subbasins: BO consists of all areas that drain to existing inlets and system B, while Al-A7 drain to new inlets on the PGL site. Roof drains connect to system A at CB 10. Runoff from basins Al-A7 and the roofs are treated in a single treatment vault on -site. All runoff is combined at the north end of the site and connected to the Port -owned conveyance system and outfalls north of the site. See Appendix C for drainage plan of the site. 6. OFFSITE ANALYSIS The proposed project stormwater drainage system will connect to the existing south marina stormwater drainage system. As such, the effects of the proposed development on the existing system need to be analyzed. Additionally, the existing system needs to be analyzed to determine its effects on the proposed design. A portion of the existing system will be replaced within the project, therefore and analysis of the system upstream of this replacement is required. 6.1. UPSTREAM ANALYSIS The existing conveyance collects runoff from the Port of Everett South Marina parking lot and connects through the project limits to the marina outfalls. The existing conveyance pipe is located within the proposed building footprint. The storm system will be rerouted using new storm drains and manholes around the building and will reconnect to the existing conveyance on the northside of the site. The new P I nN, F71)