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Reunion T-88 Watershed Hydrologic Analysis

T-88 Watershed Reunion Master Drainage Plan Commerce City, CO


JR Engineering prepared hydrologic and hydraulic modeling, to support construction plans and specifications for the Reunion T-88 Regional Water Quality and Detention Pond located in Commerce City.  The project involved the conversion of an existing retention pond to detention and water quality meeting current City and UDFCD criteria, which required a thorough analysis of the 700-acre basin’s developed conditions hydrology.

In 2015, the City of Commerce City began addressing the T-88 Basin stormwater outfall to Third Creek as part of the Tower Road expansion project.  The conversion of Reunion’s existing retention pond became necessary as part of a public/private partnership and these improvements allow additional development in the watershed.  Several alternatives were prepared and cost/benefits were compared so that the City and Reunion could select an alternative.  UDFCD was consulted for the alternatives evaluation

JR Engineering prepared an overall CUHP 2.0 model and EPA SWMM model for the ultimate T-88 Basin system using NOAA Atlas 14 point precipitation based on existing and planned development, future offline water quality/detention facilities, and routing of flows through conveyance infrastructure to determine an inflow hydrograph to the proposed T-88 Regional Pond.  This hydrology model was integrated into the storm conveyance infrastructure hydraulic model being worked on by the City’s consultant.  JR Engineering prepared an overall T-88 Basin hydrology report which allocated water quality and detention needs basin-wide based on planned land use by multiple developers.

The T-88 Pond was then designed using the UD-Detention design aid with the SWMM inflows, and over-detention was provided in the T-88 Regional Pond to utilize existing downstream culverts which were undersized for the T-88 Basin’s future conditions developed discharges.

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