8th Street Bridge Replacement
The East 8th Street Bridge crosses Dry Creek and was determined to be structurally deficient and was the driver behind this project. Matrix Design Group, Inc. was selected by the City to design a new bridge across Dry Creek and design roadway and stormwater improvements for East 8th Street between Utica Avenue to Amarillo Avenue.
The Matrix hydraulics team worked with the City to design a bridge that had minimal impact on the 100-yr water surface elevation to avoid the requirement for a floodplain development permit and Letter of Map Amendment (LOMR). Matrix developed a hydraulic model using HEC-RAS to calculate water surface elevations and evaluate scour conditions for the proposed bridge.
Currently there is no stormwater conveyance infrastructure along this section of East 8th Street except for two roadside swales that parallel the road. Flooding has been documented and there is notable bank erosion where the two swales discharge into Dry Creek. Matrix developed a unique stormwater conveyance solution that incorporated an underground storm system while also utilizing the full benefit of the existing roadside swales for water quality and flood conveyance. The inlets to the storm system were sized to be overtopped in larger flood events and redirect flood flows into the roadside swales. Curb cuts were also designed throughout the corridor at locations where inlets were not recommended to direct flows generated from the road surface into the roadside swales. Preserving and utilizing the roadside swales allowed for stormwater quality treatment for a full range of flows and also reduced the required size of the storm system which ultimately resulted in a construction cost savings. This stormwater solution successfully provided flood conveyance for all of the contributing drainage area to this project which is very rare in an urbanized area where no stormwater infrastructure previously existed.