By Jim Hegarty, PE
It’s been five years since P&N designed a new culvert on Two Mile Road where it crosses over Big Creek in the Village of Morley. I stopped by recently to see how some of its design features are working.
Morley was delighted with the project because they received a grant from MEDC that made the project possible. The previous bridge structure was too small for the creek, and it had deteriorated to the point that weight limits prohibited school buses and emergency vehicles from crossing it.
P&N’s design incorporated five environmentally-friendly features into the project to improve the health of Big Creek and its habitat.
- The new bridge actually is a concrete box culvert, buried two feet below the stream bottom, allowing a ‘natural’ sand and gravel base to form through the culvert.
- The culvert’s opening area is much larger than the bridge it replaced. When heavy rains come, the water under the bridge moves much more slowly than previously, stopping the serious erosion issues on the bank directly opposite the bridge.
- To stabilize the steep stream bank across from the culvert’s outlet, P&N designed root wads to slow water at the bank’s toe and to stop it from further sloughing into the creek.
- P&N designed a rock weir across Big Creek just downstream of the culvert’s outlet to slow the stream’s velocity at the steep bank and to allow gravel and sand to settle to the culvert’s bottom.
- Finally, we used a natural, vegetated Delta-Lok retaining wall (a system that uses plant shoots inserted into a soil-filled canvas bag) at each end of the culvert to stabilize the bank and prevent erosion.
The good news: all five of these features are working as designed!