Re: Flooding Issues Analysis and Suggested Solution

Eric,

At your request, I visited the subject property on Ploof Road to perform an engineering analysis of the area in order to determine the cause and possible solutions to the recent flooding. As part of the study, I walked the complete area, including surrounding properties, to determine the sources and volume of water impacting the site. I also performed general calculations regarding the flow of water around the property, including both incoming and outgoing flow rates.

I have included marked-up maps showing the property and the general vicinity, including existing retention ponds, drainage ditches, and culverts. It should be noted that the surrounding properties to 9550 Ploof Road have been significantly developed between 2014 and 2024. Although these properties include retention ponds intended to slow water flow, the outflow from all ponds aggregates at a common location where a small culvert pipe passes under Ploof Road. The cross-sectional area of this pipe is approximately 7 square feet.

During a significant rainfall event, based on my calculations, it is evident that a bottleneck exists in the outflow from the property as water passes through this undersized culvert beneath the roadway, as shown on the marked-up map. This bottleneck causes water to back up and pond on the north side of the roadway until the roadway becomes covered. The issue is further exacerbated by a likely undersized retention pond on the adjacent property to 9550 Ploof Road, located to the northeast, as shown in the accompanying marked-up photographs.

Based on this study, it is my recommendation that the culvert under Ploof Road (at the marked location) be increased in size to allow improved flow from the north side of the road to the south side. To fully eliminate the bottleneck, a bridge, culvert, or series of smaller culvert pipes providing a total clear cross-sectional area of approximately 100 square feet is required.

Please feel free to contact me if you have any questions, comments, or concerns.