A. Storm sewers constructed within the street will be sized by the developer’s engineer and will consider all potential runoff requirements within the site and upstream of the site. Whenever practical, the storm water system design shall conform to the Pierce County Stormwater Management and Site Development Manual.
1. The storm sewer will be sized for a 100-year design recurrence criteria for storm drainage facilities.
2. The minimum size of storm sewers is eight inches in diameter.
3. Spacing of catch basins along the street must conform to engineering published recommendations, which consider profile of the street and street width.
B. On-site detention may be required for new development where downstream deficiencies exist or are anticipated to exist in the next five years. Development that will be less than 5,000 square feet of impervious surface is exempt from detention requirements. The square footage considers the total development of the property including the future potential impervious surface. Recommended design recurrence criteria for a commercial or residential storm drainage detention facility is a 10-year interval.