5406 S 1ST AVE 2021-02-25 - Laserfiche WebLink

• B. DOWNSTREAM ANALYSIS • Runoff from the proposed disturbance area of the existing site appears to sheet flow to the east over pervious surfaces toward the eastern property line. Runoff appears to leave the site over the eastern property line and drains to the right-of-way of S. 1st Ave. There wasn't a-distinct .drainage _ditch, .however runoff appeared to drain within a vegetated, grassy shoulder on the west side of S. 1st Ave to the south or onto the roadway to the south. There was a catch basin found approximately 80 feet to the south of the project site within the right-of-way. This catch basin directed runoff south to another catch basin found at the corner of Lenora St and S. 1st Ave. Runoff appears to drain through a series of catch basins and pipes passing beneath S. 1st Ave and draining to the east, then passing beneath Lenora St to the south. Runoff then dispersed into a vegetated ditch along the southwest side of the railroad tracks. Due to safety, the remainder of the downstream was not followed on foot. However, it appeared runoff continued within this large ditch to the south. Based on contours and grade of the land, runoff appeared to continue within this wide ditch to the south and eventually drain north to the Snohomish River. Based on the fact that all of the new plus replaced impervious surfaces will be infiltrated either on or off-site, developed flows are expected to match or be less than the existing conditions. During the site visit and review of the downstream system, no portion of the system appeared to be inadequate. • • Zillah Lot 2 SFR 18-0605 Aug.2019 Page 6