2600 FEDERAL AVE 2021 PORT OF EVERETT 2025-09-29

Iq:I Consulting Engineers Page 13 of 13 Basin A: Conveyance Based on model results, the max flow through the 18 inch storm pipe (2.51 cfs) is well within the design capacity of the 18 inch storm line(13.10 cfs)and has adequate capacity to convey the 25-year storm event. Backwater Based on model results,there is no overtopping at the 100-year event with a fixed tidal elevation of 11.06. The max Hydraulic Grade Line (HGL) in the system is 11.73 at the lowest structure in the system. The freeboard in the lowest manhole is approximately 3.27 feet. An in-line check valve is proposed at the structure just downstream of the high flow bypass structure to reduce the risk of tidal water backing up into the system.See Appendix F for profiles that show Max HGL in the system and model output. Basin M: Conveyance Based on model results, the max flow through the 36 inch storm pipe (26.16 cfs) is well within the design capacity of the 36 inch storm line(51.88 cfs)and has adequate capacity to convey the 25-year storm event. Backwater Based on model results,there is no overtopping at the 100-year event with a fixed tidal elevation of 11.06. The max HGL in the system is 12.52 at the lowest structure in the system. The freeboard in the lowest manhole is approximately 2.50 feet. An in-line check valve is proposed at the structure just downstream of the high flow bypass structure to reduce the risk of tidal water backing up into the system. See Appendix F for profiles that show Max HGL in the system and model output. 5.9 Downstream Drainage System Basin A and M discharge to Port Gardner Bay through new Outfalls A and M. Port Gardner Bay is tidally influenced and is considered a non-sensitive receiving waterbody. Outfall A and M will discharge to newly constructed riprap energy dissipators on the riprap armored shoreline.