1300 100TH PL SE CITY KIDS DAY CARE 2025-05-02

The off-site street runoff will be collected into a catch basin and pipe storm sewer system. The system runs parallel along 100th Place SE and daylights into the drainage ditch. The on-site runoff will be detained in an underground detention pipe before discharging off site into the new storm system along the 100th Place SE. The detention system was si to detain the stormwater runoff from the new impervious area of 6,500 square feet. For simplifying the drainage system,runcff from an equivalent existing paved area was collected into the detention system to substitute the 1,600 square foot sidewalks along 100th Place SE(see Appendix B). . . Detention Pipe Design Criteria The following stormwater detention design criteria will apply to this project: • Limit peak flows of the 2-year developed 24-hour design storm to 50 percent of the release rate of the 2-year existing 24-hour design storm. • Limit peak flows of the 10-year developed 24-hour design storm to the release rate of the 10-year existing 24-hour design storm. • Limit peak flows of the 100-year developed 24-hour design storm to the release rate of 1 the 1011-year existing 24-hour design storm. As outlined in the City of Everett Stormwater Management Manual,to account for back-to-back storm events and drainage modeling inaccuracies,the calculated detention volume was increased by a factor of 30 percent(see Appendix C). •. Summary . _. The following table of rainfall depths is for the 2-year, 10-year,and 100-year,24-hour design storms in the City of Everett based on Table 1-5.4 in the City of Everett Stormwater Management Manual: Design Storm Rainfall Depth(inchesi 2-year,24-hour 1.55 10-year,24-hour 2.25 100-year,24-hour 3.25 le Enter Csontry Etirptirs Nevieisor 20*1 Hydramiks Repot -2- Reid"9itlt16eton