Granby Ditch Channel Improvements | The Citadel on Colfax

The Granby Ditch is an unimproved historic overflow from the Highline Canal which was transformed into a major drainageway as Aurora developed around it. To better accommodate the development and to improve the ditch to a stable defined drainageway the Granby ditch was realigned through the site.

The Granby Ditch is a non-jurisdictional Waters of the United States major drainageway for the City of Aurora. A Conditional Letter of Map Revision (CLOMR) had previously been completed on the Granby Ditch, but the planned project around the ditch had changed significantly from what was approved with the initial CLOMR. Galloway worked with the City and the Mile High Flood District (MHFD, formerly UDFCD) to redesign and remodel the channel ultimately proving that the revised plan and channel designs were in conformance with the previously approved CLOMR, allowing the project to move forward without needing to resubmit a new CLOMR.

The channel design includes a twin box culvert to provide a roadway crossing, a grouted boulder drop structure, bank stabilization, and analysis of split flow due to the undersized storm sewer system in Colfax. Galloway also provided design for two on-site detention and water quality ponds using the Excess Urban Runoff Volume method (Full Spectrum) in conformance with the City of Aurora storm drainage standards. In addition to designing the stormwater system, Galloway provided engineering services to widen Colfax Avenue (SH-40) for 0.27 miles and restripe Sable Boulevard to allow for a new left turn movement. The five interior roadways were designed to adhere to City of Aurora standards, and on-street parking with larger hardscape and amenity areas were provided to provide an urban feel to the central park area of the site. Galloway also provided a design to relocate a 15-inch sewer main through the site and provided better maintenance access to the sewer’s mainline.

Although a part of a larger private project, the Granby Ditch facility is owned and maintained by the City of Aurora and is Urban Drainage maintenance eligible. The City of Aurora was integral in the scope and design of this realignment. The project also installed storm sewer inlets and pipe within the roadways. Upon completion the storm sewer will be owned and maintained by the City of Aurora.