Needed Improvements to a 1,200 Foot Water Supply Dam
Tighe & Bond completed both a regulatory inspection and alternatives analysis with repair options for the deficiencies observed during the inspections on both the dam and dike. The inspection noted several issues with the dam, which included: deteriorated spillway and training walls, steep slopes, uneven crest, and a low-level outlet that required improvements. Deficiencies at the dike included deteriorated and missing mortar in the stone masonry face, telephone poles in the downstream slope, uneven grading, and woody vegetation.
In addition to the visual inspection, a subsurface exploration program with test borings was completed to determine the material makeup of the dam and dike with the installation of groundwater monitoring wells to determine the phreatic surface within the structures. The data collected was then used for the seepage and stability analysis. A hydrologic and hydraulic evaluation was also performed to determine the spillway design requirements. Tighe & Bond then prepared an alternatives analysis to address the deficiencies identified in the visual inspection, seepage and stability analysis, and hydraulic and hydrologic evaluations, complete with opinions of probable cost.
Tighe & Bond provided design, permitting and construction phase services for improvements to both the dam and dike. The improvements included reconstruction of the spillway weir and training walls with cast-in-place concrete and repointing the upstream stone masonry face of the dike. In addition, there was the construction of a concrete gatehouse on the upstream end of the low-level outlet with a pedestrian bridge for access, riprap slope protection/flattening along the upstream slope of the dam, flattening approximately half of the downstream slope of the dam, and installing a toe drain and overtopping protection along the entire downstream slope of both the dam and dike.