Over many years, the York Creek Drainage basin had changing runoff characteristics due to development. In general, previous areas were declining in the watershed. While additional detention was provided in some cases, the peak flows downstream were apparently increasing causing an increase in the frequency of flooding.
Prein&Newhof studied this watershed starting in 1999, determining the most effective mitigation strategies and to reduce the flood frequency, particularly to industrial buildings on West River Drive and residential structures on 4 Mile Road. These areas were flooded frequently, and a combination of improvements were recommended including structure replacements, channel modifications, and addition of in-line and off-line detention.
One recommended improvement focused on providing floodplain storage in the 4 Mile Road area. Three residential structures were frequently flooded and the project was initiated with the knowledge that a FEMA Grant could potentially be obtained to acquire the homes. Once acquired, the structures could be demolished and removed and the site excavated to provide flood shelf storage. Instead of flooded homes, a new floodplain storage area would be provided. This would reduce peak flows downstream during larger flood events as well.
A detailed analysis was required using SWMM and HEC–RAS models to evaluate the impact the new flood storage would have on peak flows and flood levels downstream. Results indicated that the reduced frequency of flooding for the proposed detention was enough to obtain the FEMA Grant. Ultimately, the proposed project included acquisition and demolition of the residential structures, floodplain excavation, overflow structure construction, utility removal, and restoration. Some challenges surfaced during the projects, and resulting adjustments to the design allowed for adequate flood storage while also meeting Drain Commissioner standards.
Prein&Newhof obtained a FEMA grant on behalf of the Kent County Drain Commissioner to buy and clear houses from this flood-prone area, and converted the vacant land into a side-stream detention area. When flow in York Creek rises during an intense storm, it spills out of its banks–on purpose–and floods the side-stream detention area until flow in York Creek subsides. This has the effect of reducing the peak flow in York Creek, which reduces downstream flooding. Downstream property owners have confirmed the significant impact of the project.
Watch the video to see our design at work after an intense rainfall!