Project completed November, 2009
Location: Alton, NH
Owner: Town of Alton, NH
Engineer: CMA Engineers
The Project required the replacement of an existing undersized metal culvert. The river bottom in the area of the bridge is ledge with overlying cobbles, this limited the capabilities of the cofferdam. The project involved the use of cast in place footings, cast in place stub walls, and precast open bottom box culvert. Inside of the bridge the bottom was infilled with rounded rock. The project being on a dead end road with a large number of vacation homes required the work to take place outside of the summer months and while maintaining travel across the roadway.
With the undersized existing culvert a temporary fix was installed with 3 bypass culverts in the event that the main culvert was not capable of handling the water flow. During a high flow event even these culverts were unable to handle the volume of water. The area around the existing culvert is quite natural and this was desired to be maintained as much as possible.
: Insufficient existing culvert capacity to handle high flow events.
: Installation of a open bottom box culvert with round rock installed to mimic the existing stream channel.
Issue: Limit disturbance to as small of a footprint as possible.
Solution: Only trees and rocks that were absolutely necessary to remove were disturbed. Several trees were worked around to maintain the natural, aged look of the stream area.