Overview
The City of Norfolk was interested in expanding recent watershed modeling efforts to create a stormwater master plan for the Ohio Creek watershed. The purpose of the Plan is to build upon the recently completed GIS-based watershed model with updated field collected data and to make recommendations for stormwater management improvement strategies throughout the watershed. The field inventory for this master plan was completed in late February 2011.
Additionally, the City of Norfolk was interested in creating additional culvert capacity to Ohio Creek as it flows from the north side of Interstate 264 and under the Interstate. There is currently an 8’ by 6’ box culvert at this location which has been a chronic choke point in the City’s stormwater conveyance system. The situation was exacerbated by the development of the Norfolk Light Rail Transit Vehicle Storage and Maintenance Facility (VSMF), which is located immediately adjacent to and upstream of Interstate 264 on a 9.80 acre site.
The development of this site immediately upstream of the Interstate 264 crossing has assisted in identifying the drainage discharge relief issues. One method of providing additional drainage relief investigated was to directional bore an additional culvert (or culverts) under Interstate 264. This required significant coordination and approval from VDOT. It was determined that VDOT would require a thorough review of alternatives before permitting the directional bore option. VDOT was concerned that the directional bore alternative could seize during construction and ultimately result in a temporary closure of the Interstate to open cut and correct the situation.
Timmons Group provided a Feasibility and Alternatives Analysis to evaluate the feasibility and risks associated with potential solutions to the drainage problem and identify the most feasible solutions to proceed with detailed investigation. Options could include: upstream detention; diversion; infiltration and attenuation from low impact development (LID) retrofits and a stormwater pumping station. The options were evaluated by a team of City, Timmons Group and VDOT staff.
Timmons Group evaluated the Ohio Creek watershed to mitigate existing flooding and to elevate potential flooding to the Light Rail VSMF. The evaluation examined the impacts of the existing tide gates in Ohio Creek as well as three other locations and evaluated impacts to the drainage associated with the Norfolk Light Rail Transit VSMF. An Alternatives Analysis was prepared to identify and evaluate tide gate options to minimize tidal impacts to the drainage system. The study determined the pollutant removal requirement mandated by the City and State and identified and evaluated water quality retrofit alternatives at the Norfolk Light Rail Transit VSMF.
