2020 112TH ST SW MAPLEWOOD COURT SITE DEVELOPMENT 2016-01-01 MF Import

Maplewood Cnurt. _ ___ _ _ _ _ ._ _ 07-a502 INTRODUCTION The Maplewood Court project ccnsists of 19 residentiai attached condominium unds contained in three buildings. The pro)ect site is located at 2020 112th Street SE, on the south side of the road, approximately 5Q0 feet east of Airport Way. Stortnwater runoff in the development will be collected in a series of yard drains and catch basins connected to storm drain pipe 3ystem for conveyance to an existing detention vault in the southwest comer of lhe project site. This supplementary drainage repoR has been prepared to update the design calculations for the existing detention vault. The original drainage calculations were prepared by 2erg Engineering in October 2003. The report was prepared to address the feasibility of future commercial use of lhe 1.11 acre project site. The calculations for the vault and wet pond were oased on an assumed impervious area of 37,438 square feet. The report presented the design for a 30' x 85' detention vault. In accordance with City Code, water quality was provided in dead storage in the vault and in a small wet pond at the vault oullet. The vault was constructed and the 1.11 acre site was graded in accordance this approved design. The proposed condominium is located on the same 1.11 acre project ake. The development will create 18,435 square feet of impervious area. Since this amount of impervious area is far below the area the vault was designed for, the vault and wet cell have more than adequate capacity lor the proposed development. The vault was originally designed to release flows at one-half lhe pre-developed rate for tha 2- year storm and at the pre-developed rates for the 10 and 100-year storms. The release r&tes for the tacility were reduced to reflecl a second growth forested condition io meet City Code. The "Waterworks" program with the Santa Barbara Unil Hydrograph (SBUH) method and Type 1A rafnfall distributfon was used in the desfgn of the proposed taGl'�ty. In order to assess the impact of the Maplewood Court residential project, the existing vault was evaluated using design flows from the development. As shown In ti�e attached summary oi results, the existing vault design meets the design standard for the 2-year storm; and provides a more than adequate redudion in peak flows for the 10 and 100-year storms. This report also conlains a backwater analysie for the proposed stortn drain pipe system that connects to the existing vault. The analysis shows that water surfece elevation in the existing vault will not have any impact of the storm drain system. fR0[�P FOUR, lnc. I6030 Jaanlla-Il iadlm•llfe N aP .ti'F. Rorhe(l, 1i:� 9R01 /