1903 HOLLOW DALE PL 2018-01-02 MF Import

Swamp Creek meanders souther!y and enters a 16" CMP through a trash rack within 112th St. sW, where they are then conveyed to the east within the street drainage pipes. Within200' the storm outlets into a biofiltration swale and then into Swamp Creek. The confluence is then received into a 48" CP and passed beneath the roadway to the south. Fasto� rly DrainAg Course: Approximately 50' east of the southeasterly property corner the Hollow Dale Road ditch opens into a main tributary to Swamp Creek and crosses beneath the road via 24" RCP. Within 200' the Westerly drainage described previously combines with this main tributary. This completed the downstream analysis. The downstream drainage corridor from the site to the west has experienced flooding hazard near 1919 Hollow Dale Road and within the wetland area adjacent. to their southerly boundary. 40 aF A 100 year storm detention is offered with this design rather than the 10 ye required under Title 24 Drainage to allow additional detention. This J 1e5J�r'or �o f(nQ conservative given the small developed stormwater flows. n�et;t fl drgir 11 oth drainage 1 kj( 1 have reduced p'd ; the City of AAeI s ism only The preliminary design had called for a diversion to the east sin ways combined within a few hundred feet to the south. This of standing water due.to poor gradients, siitati--an I, t Everett --Mitt not allow runoff diversions nor variances, therefore Ar nave corridor that can be used. No oo er f{au tflg, erosion, conveyance restrictions were observed other than those described. • . I •P.1 (Refer to attached data sheets) Two soil logs were dug on 1111197 after a record snow and rainfall. The water table was observed at 16" - 26" below the ground surface. A percolation test was also conducted to 1�. ess the permeability of the soil. The average for the two holes was approximately 8 minutes/inch. Although requested by the county, this soil percolation information is not pertinent with respect to the pond design. The water table elevation in the vicinity of the pond is the more valuable; however, that will also be lower after access drive and roof drain tightline installation. In addition the existing ditch and onsite wetland will be reconstructed to allow less surface water to pond near the detention area. ' ut KrIVIt I-ERC0496033 1120196 ORP 4/0V