MARCH 21, 2005SHAWNEE PLANNING COMMISSION MINUTESPAGE 13
The applicant has submitted the storm drainage improvement plans to the City for review and approval.
10.This development is subject to the provisions of SMC Chapter 12.24, which pertains to the construction and maintenance of on-site stormwater detention facilities.
On-site detention is mandatory because the entire residential development is larger than 20 acres. The applicant submitted a preliminary stormwater detention study with the original preliminary plat showing a conceptual facility plan for two basins, a drainage area map, and estimated storage volumes and allowable release rates based on the adequacy of the existing drainage system within 1,000 feet downstream of the development site. The facility on Tract ‘A’ was constructed with the first final plat. The second facility will be constructed on Tract ‘B’. The preliminary study was substantially complete and adequate for reviewing the preliminary plat although any design issues discovered during the review of the preliminary stormwater detention plan must be resolved prior to the approval of the final stormwater detention plan.
The detention facility required for this development will be designed in accordance with Division 4600, Storm Drainage, of the Shawnee Manual of Technical Specifications and Design Criteria. The required improvements are as follows:
A detention basin is required to have sufficient capacity to store the post-development runoff that exceeds the pre-development allowable release rate for a 1 percent (100-year return period) design storm.
The discharge from a detention facility will not exceed the maximum allowable release rate for the 20, 10, 4, and 1 percent (5, 10, 25 and 100-year return period) design storms.
The storm drainage system downstream of a detention facility is required to have sufficient capacity to convey the undetained peak discharge during the required design storm.
The applicant has submitted a final stormwater detention plans to the City for review and approval.
The licensed engineer responsible for the design of the detention facility must certify to the City that the facility was constructed in accordance with the approved plans. The certification must be submitted and approved prior to the issuance of any building permits for this development. A field survey of the facilities verifying as-built elevations and dimensions shall be completed and as-built drawings prepared showing both design values (crossed-out) and as-built values. The drawings shall be signed and sealed by the engineer, and include the following certification language: “I certify an as-built field survey has been completed and the stormwater detention facilities shown hereon have been constructed in accordance with the approved plans.” The as-built