7007 SEAWAY BLVD 2018-01-02 MF Import

..�-, � I1.0 Project Overview The goal of the project is to develop a wetland sanctuary with public access specifically including constructed wetland improvements, trail system, parking azea and amphitheater. Figure 1 is a Ivicinity map shnwing the lceation of the site. 2.0 Prelimioary Conditions Summary Natural drainage at the sile generally slopes to the aoriheast and into Narbeck Creek. Nazbeck Creek tlows through the property in a northerly direcuon. Runoff generated to the west of the site on Seaway Blvd. and west of Seaway Blvd. is collected in a drainage system in Seaway Blvd. Information on drainage systems i� the project area was obtained Crom the City of Everett. Site development will not change the on-or ofl=site drainage pattems at the site. Figure 2 shows a City Iof Everett map with a description of the Narbeck Creck Basin. 3.0 Off-site Analysis I �� The Cit of Everett has determined that the downstream drainage system capacity.issuitahle for the ° nroposeA system. The outlet forthe majority ofthe impervious surfaces will discharge to the on-site I ' , wetland and then continue to drain to th�north off the site to Narbeck Creek. A small portion ofthe �� , road (0.12 acres) will discharge into the City drainage system along Seaway Blvd. That system dischazges to Powder Mill Gulch Creek a distance oCaSout one-halfmile west ofthe site. I �f 4.0 Analysis and De�ign of ReGnired Erosion and Sedimeet Control BMP's I See Appendix A for the"Temporary Erosion and Sedimentation Control Strategy"prepared by the Vl�atershed Company for narrative description of the erosion and sedimentation control BMPs chosen. Also,in Appendix A,see attached reduced copy ofthe drawings 3 through 6 for the Erosion Iand Sedirtientation Control Plan. 5.0 Analysis and Design of Required Runoff Control BMP's IThe site mainly consists of the wetlands arca,however a portion of the site contains an impervious driveway and parking lot. These impervious azeas aze drained towards bvo separate facilities. The I majority of the road and parking lot runoff is captured by storm drains and conveyed to a wet detention pond in the northwest corner of the site. The pond outfall discharges to the wedand azea. I A small portion of the driveway, at the site entrance, drains back towards Seaway Blvd. into two catch basins. Thc runoff is then convcyed to a wet detention vault. The outfall to the vault Idischarges to the drainage system along Seaway Blvd. Both systems provide treatment and detention to stream bank erosion control standazds. The amount of dead storage in each system is equal to lhe G-month, 24-hour event. The runoff is controlled to detain the post developed 2-year peak discharge to 50%of the pre-developed Z-year peak discharge and match the 10-ycar and 100-year post developed peak discharges to the same pre-developed peak Idischarges. The SBUH model was used in the hydrologic calculations. i � June 29, 1998 Narbeck Wetland Sanctuary Page 1 ' Stormwater Site Plan