Grange Hall Creek in Thornton, Colorado, had become so incised that six sanitary sewer crossings were exposed. One of the crossings, encased in concrete, was even suspended above the channel bottom. To repair the creek, the Urban Drainage and Flood Control District (UDFCD) and the City of Thornton undertook channel improvements along approximately 5,000 linear feet.
Proposed channel improvements included the following:
Olsson prepared the construction plan set and assembled it in a manner that best accommodated the construction budget. Part of the project was constructed by one of the UDFCD maintenance contractors. The remainder of the channel improvements was publicly bid.
Through hydraulic modeling of the project’s reach and improvements, Olsson found indications that small increases in the base flood elevations would result as part of the project’s improvements. To accommodate this, Olsson prepared a conditional letter of map revision (CLOMR) and a letter of map revision (LOMR) for FEMA. A roadway improvement project on 104th Avenue was also included in the CLOMR and LOMR submittal.
In addition, Olsson provided construction phase services and coordinated with ERO Resources to obtain an individual permit from the U.S. Army Corps of Engineers for the project.