Wason Pond Dam Reconstruction

Chester, New Hampshire

The Town of Chester acquired Wason Pond to preserve the area for public recreational use. DuBois & King conducted an engineering evaluation to assess the condition of the dam and identify short-term repairs and long-term improvements. The primary concerns with the dam was inadequate hydraulic capacity, structural stability, and seepage. This effort led to a full rehabilitation of the dam.

The dam is an earthen embankment with a concrete overflow spillway located near the left abutment. The dam is approximately 165 ft long and 15.5 ft high. Dry laid-up stonewalls form the downstream face of the spillway and adjacent walls. The spillway consisted of a concrete slab set on top of laid-up stones and had a clear width of approximately 18 ft at the upstream crest. Removable flashboards were located along the upstream edge of the spillway crest. The drainage area into the pond is approximately 1,633 acres (2.55 square miles).

The required capacity of the spillway was greater than what the site would accommodate. Due to the confines of the site, the spillway was designed as a two-cycle labyrinth weir to achieve the hydraulic capacity. The rehabilitation included concrete training walls, a seepage cut-off wall, and installation of a mineral toe drain filter for seepage control.

To meet schedule objectives, the project was developed to utilize winter construction. The dam accommodated a new pedestrian crossing, linking hiking trails and improving recreational opportunities of the area. D&K’s services included:

Coordination with NHDES Dam Bureau
Engineering safety inspection
Identification of deficiencies
Structural assessment and design
Hydrologic and hydraulic analysis and design
Geotechnical assessment and design
Evaluation of repair alternatives
Cost analysis
Preparation of an engineering report
Bid phase services
Construction engineering and oversight