Hydraulic Modeling · Drainage Design · Detention Design · Channel Design · Water Quality

JR Engineering provided comprehensive drainage planning and design services for Reunion Village 9, an approximately 800-acre planned development in Commerce City that includes the Ragweed Draw major drainageway. The project required JR to take the Ragweed Draw basin from watershed-level planning through development-wide preliminary design and ultimately into final design and construction documents for a naturalized channel system with online water quality and detention. Beginning with a master hydrology analysis of the Ragweed Draw watershed and continuing through the Preliminary Drainage Report and Phase 1 Final Drainage Report, JR developed a coordinated drainage strategy addressing hydrology, stormwater conveyance, flood control, water quality, detention, channel improvements, and downstream infrastructure capacity. The work established the full-buildout drainage framework that could be carried forward into successive development phases and then providing the detailed engineering necessary to construct the initial District infrastructure and Ragweed Draw channel improvements.

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Watershed Planning & Hydrologic Modeling

A primary challenge was developing a reliable hydrologic and hydraulic basis from a collection of previous studies, evolving development planning, and existing infrastructure that did not always align.  JR evaluated previous outfall planning studies, FEMA-related information, existing drainage reports, current survey, and the latest development layouts to reconcile basin boundaries and drainage patterns throughout the watershed.  The analysis identified areas where previous basin delineations no longer reflected existing development and where land-use, imperviousness, and drainage assumptions required updating.  These efforts produced an updated hydrology model (Colorado Urban Hydrograph Procedure with EPA-SWMM) model of the entire Ragweed Draw watershed that incorporated both onsite and offsite tributary areas and provided a comprehensive basis for evaluating alternatives and establishing the ultimate drainage strategy.

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Drainage, Detention & Flood Control Strategy

JR then translated the watershed-level analysis into an overall drainage concept for the Village 9 development, a naturalized channel design based on full build-out hydrology with online full-spectrum detention facilities along Ragweed Draw, additional interim phased detention and water-quality facilities, storm sewer infrastructure, and roadway drainage. A particularly innovative component was the voluntary over-detention strategy in Village 9, which was used to reduce the 100-year peak discharge leaving the development at E 104th Avenue to 50 percent of historic levels.  This provided a benefit to downstream properties and existing undersized infrastructure, and enabled future downstream improvements to be based on a lower-than-historic flow rate.  JR evaluated the timing and interaction of multiple detention facilities throughout the Ragweed Draw watershed rather than treating each development parcel independently, allowing the District to establish a unified drainage system that could accommodate future filings while maintaining the required downstream discharge limits.

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Final Design & Channel Improvements

Building on the master planning and preliminary design, JR completed final drainage design for Phase 1, including approximately 201 acres of Phase 1 District infrastructure, roadway drainage, storm sewer, detention and water-quality facilities, and restoration and enhancement of the Ragweed Draw channel. The final design carried ultimate buildout hydrology into the Phase 1 facilities so that infrastructure constructed today would function at full build-out.  JR designed the Ragweed Draw channel using a naturalized approach consistent with current Mile High Flood District principles, with full-spectrum and interim detention facilities, roadside and offsite swales, and coordinated drainage improvements with existing and future utility corridors and development grading. The result was a complete progression from watershed master-planning and alternatives analysis to preliminary development planning, final hydrologic and hydraulic engineering, and construction plans.  JR Engineering provided construction management.