10602 16TH AVE SE 2025-07-28 - Laserfiche WebLink

Sum of all areas in ac above slightly exceeds total area of disturbance due to rounding errors. However, the sum of the sf areas matches the total site area of 135,609 sf or 3.11 acres. The new impervious surfaces for this parcel will be mitigated using on-site stormwater management BMPs including perk filters, detention vault and soil management. A. UPSTREAM ANALYSIS During the site visit it was observed that due to the site grades and surrounding development/improvements the only area potentially contributing runoff to the short plat is from the landscaping along a portion of the southern property line. This runoff enters the site and sheet flows to the east. It was clear that all off-site flows will be allowed to enter this site and the proposed development will not create any impediments or cause any of the flows to back-up onto the off-site areas. Based on the location of the proposed improvements the existing runoff from the upstream area will continue to flow unaffected through this site after the project has been constructed. B. DOWNSTREAM ANALYSIS Runoff from the proposed disturbance area of the site sheet flows to the west or east. To the west the runoff is collected in one of two wetlands on-site that drain to the north or south. The SW basin on this site drains to the southern wetland that then drains south and is collected by an 8" culvert and then the flows pass through the existing project to the south and discharge into the 16th Ave SE R.O.W conveyance system. The 16th Ave SE system flows north and into an open detention/wet pond east of the roadway and north of 107th PI SE. The detention wet pond is the point of confluence for all the on-site basins associated with this project. The NW basin drains into the existing northern wetland west of the proposed improvements. This wetland drains north and into an open detention/wet pond and then east, via 12" pipes beneath the 16t"Ave SE cul-de-sac to a low area east of the R.O.W. This low area drains south and is collected by the detention/wet pond noted above. The east basin drains east and is collected by the conveyance system within the 16th Ave SE R.O.W. This conveyance system turns east in a CB located at the SE corner of this project. The flows then enter the detention wet pond east of the R.O.W. The wet pond discharges to the south via a 15" pipe system and the flows enter another pond to the south of the 107t" PI SE roadway. This pond drains to the south and is collected by a piped conveyance system that drains south and east and eventually into Silver Lake. During the site visit there were no signs of capacity or erosion issues in the downstream area. 4. SWPPP NARRATIVE The intent of this section is to provide the information necessary to support the engineering plans in order to implement a design that will; reduce, eliminate or prevent the discharge of stormwater pollutants, meet or exceed the water quality and sediment management standards for the City and State, and prevent adverse impacts to the Northlake Court Townhomes 13-0609 May,2014 Page 7