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Roadway Drainage Modifications

ALTON, NH – The floods of 1990, January 1996 and October 1996 have repeatedly eroded the road and ditches in the southern section of the Town of Alton in Belknap County.

The Mitigation Project replaced six undersized culverts and installed riprap along the ditch line. Increased culvert sizes improved the discharge rate, preventing washouts.

The Town of Alton considers this project a success. June 1998 rains flooded and eroded many other roads in Alton. However, the June rains did not impact the project area, minimizing traffic disruption and municipal costs.

At least $15,000 in damages were avoided in June 1998. Some lessons learned include the need to use pre-cast concrete headers instead of masonry headers. Pre-cast concrete better survives the frost heaves. Also, larger rocks and gravel in ditches are better left exposed. The loam sometimes picks up and clogs the drains and culverts.

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