RMV Rienda Flood Detention and Water Quality Basins WQMP and Design

Rancho Mission Viejo, CA

PACE designed a system of flood and water quality basins located along the southern boundary of Rienda, just north of San Juan Creek, to manage runoff flows from the 1,300-acre tributary watershed. A total of three diversion structures within the storm drain system are designed to divert the required design capture volume to the nearly 80 acre-feet water quality basins for treatment and infiltration. Flows in excess of the required design capture volume are routed to the flood detention basin for storage and peak attenuation prior to being discharged to San Juan Creek. The water quality basins comprise a unique stormwater management system, including advanced pretreatment facilities to protect the infiltration potential of the infiltration basin. The infiltration basin provides both stormwater infiltration and groundwater recharge using recycled wastewater and represents a first-of-its-kind integrated water management facility for southern California. PACE has prepared conceptual and Rough Grade WQMPs for the development that describe the design and performance of the water quality basins and has secured Orange County approval of preliminary designs of the basins. The proposed flood detention basin is designed to discharge within 72 hours, per County requirements, all while providing roughly 170 acre-feet of storage volume. Analysis demonstrated the water quality and flood detention basins are outside the jurisdiction of the Division of Safety of Dams (DSOD), and coordination took place with the DSOD to achieve their concurrence. A revised CLOMR was updated to include the revised flood limits associated with these floodplain improvements, and a LOMR will be processed upon completion of construction of these facilities.

Key Features:

• Water quality basin planning and design in compliance with County requirements
• Conceptual and rough grade WQMPs approved by County
• Hydraulic and scour analysis
• Basin revetment for scour protection
• Grading, sizing, and layout of basin configuration and alternatives