Tata & Howard has prepared numerous dam emergency action plans (EAPs) for Connecticut dams in accordance with CT DEEP regulations. Between 2015 and 2017, we have completed 52 EAPs for significant and high hazard dams throughout Connecticut. Our clients have included municipalities, private dam owners, and the CT DEEP. The EAPs include the following:
Preparation of an inundation map and flood inundation summary table for the EAP based on the dam failure analysis. The inundation maps include the limits of potential flooding (LoPF), selected cross sections, estimated time to peak stage, and the water depth at selected locations within the LoPF. For dams with no dam failure analysis, Tata & Howard prepared inundation maps for a hypothetical dam failure using hydrologic routing techniques.
Preparation of a list of roads and addresses at risk and subject to flooding based on the inundation map.
Preparation of dam monitoring procedures including identifying the persons responsible as well as procedures for monitoring the dam during periods of heavy rain and runoff, or when conditions develop that warrant closer monitoring, such as increased or new seepage, cracking, settlement or sabotage. The EAP provides dam specific information to assist the dam owner or operator in determining the appropriate emergency level for the event.Preparation of a formal warning notification procedure to alert the local authority responsible for acting on a warning or determining whether to evacuate residents and businesses within the inundation area after an unusual or emergency event is detected or reported at the dam.
Preparation of notification flow charts with emergency contact information of federal, state, and local agencies that are responsible for providing emergency services. The flow charts depict the order and circumstance under which the contacts should be notified. The EAPs also include a list of other emergency services contacts, such as the National Weather Service and local media, as well as the addresses of the local emergency operations center (LEOC) and shelters available to residents during an emergency per CT DEEP requirements.
Preparation of a termination procedure for ending monitoring and response activities once the emergency is over.
Preparation of criteria to review and update the EAP at least once every two years, or more frequently as necessary to reflect significant changes to the dam structure or downstream area, including verification of contacts in the emergency notification charts. The criteria also include guidance for the dam owner to conduct an exercise or test of the EAP concurrent with the review.
Preparation of aerial, location, and watershed maps for the dam.
The Means Brook Reservoir Dam is a concrete gravity dam that was constructed on rock in 1916 in Shelton, Connecticut. The aging dam required repairs in to improve reliability and safety, modernization and rehabilitation of the gate chambers, and replacement of the deteriorated upstream and downstream faces of the dam and the crest, which were severely spalled and delaminated. Hydraulic, hydrologic, and structural studies had indicated that the dam would be overtopped by about 3.9 feet by the Probable Maximum Flood, and that the dam did not have sufficient stability factors of safety for this extreme loading condition. The dam reportedly overtopped by about four inches during the 1955 flood. In 1977, modifications were made to the dam including extension of the spillway to its current length of 100 feet, and construction of a 2.1-foot high concrete parapet wall along the upstream crest of the dam.
Tata & Howard provided design and construction administration for the rehabilitation of the dam that included the following:
Concrete repairs to the crest and both faces of the dam:
Deteriorated and delaminated shotcrete and concrete removed to sound concrete;
Anchor dowels and reinforcing installed, and new concrete surfaces poured;
Upstream face was resurfaced to a depth of about six feet below spillway, and the downstream face to two feet below grade;
New concrete surface designed with a nominal thickness of 12 inches on the downstream face and six inches on the upstream face.
Installation of rock anchors post-tensioned in holes drilled through the dam into the rock foundation to improve stability and provide adequate factors of safety for overtopping by the Probable Maximum Flood.
Removal and replacement of one section of the spillway training wall, and removal and resurfacing of concrete on remaining walls.
Repairs and improvements to the gatehouse and chambers:
Reshingling of gatehouse roof;
New steel plate exterior door for additional security;
Blocking up the existing windows;
Replacement of antiquated electrical system;
Replacement of both of the inoperable sluice gates and their appurtenances in the upstream gate chamber;
Replacement of the former vertical brass ladders in the intake gate chambers with new fiberglass ladders, including a base for fall protection and retrieval system;
Replacement of wooden stairs in the lower gatehouse with new aluminum ships ladder;
Replacement of the pneumatically operated butterfly valve on the 30-inch service main in the basement of the lower gatehouse with an electrically operated butterfly valve that can be remotely controlled;
Installation of an extension stem and electric operator;
Replacement of the 8-inch chamber drain and 10-inch auxiliary outlet gate valves;
Replacement of wooden hatches over floor openings within the gatehouse with aluminum grating with cover plates;
Installation of chain link fence along portions of the spillway training wall for safety; and at both ends of the dam for security;
Installation of galvanized steel pipe railings along the upstream and downstream crest of the dam for safety; steel pipe rails were chosen for the dam crest instead of chain link fence because the dam crest is subject to overtopping.
The project received a 2017 Excellence in Engineering Merit Award from the American Council of Engineering Companies, Connecticut. Read more here.
Milford Water Company retained Tata & Howard to perform a visual inspection and prepare a report of conditions for Echo Lake Dam and appurtenant structures. Echo Lake Dam is located at the head of the Charles River in Hopkinton, Massachusetts, and serves to impound water to create Echo Lake, a public water supply reservoir for the Town of Milford, operated by the Milford Water Company.
The dam measures approximately 198 feet in length with a structural height of 41 feet and a hydraulic height of 30 feet from the 24-inch outlet pipe to spillway crest. The dam was built in 1898, raised 10 feet with stone masonry in 1901, and raised 2.5 feet with stop planks in 1987. The dam is classified as large and high hazard potential.
The Phase I Inspection / Evaluation Report was performed in accordance with MGL Chapter 253, Sections 44-50 of the Massachusetts General Laws. The purpose of the investigation was to inspect and evaluate the present condition of the dam and appurtenant structures to provide information that will assist in both prioritizing dam repair needs and planning/conducting maintenance and operation.
The investigation was divided into four parts: 1) obtain and review available reports, investigations, and data previously submitted to the owner pertaining to the dam and appurtenant structures; 2) perform a visual inspection of the site; 3) evaluate the status of an emergency action plan for the site and; 4) prepare and submit a final report presenting the evaluation of the structure, including recommendations and remedial actions, and opinion of probable costs.
Baldwins Pond Dam is a stone masonry and earthen embankment dam located on Harbor Brook just upstream of Westfield Road. The dam has a length of about 200 feet and a maximum height of about 17 feet. A concrete gate chamber at the right (looking downstream) end of the spillway provides controls for the 30-inch low level outlet, which discharges through the right training wall. Access to the operator is provided through a hatch in the top of the chamber. The spillway has an overflow length of 85 feet and a stepped concrete apron at the downstream toe. The upstream embankment slope and the area downstream of the apron are protected with riprap. Baldwins Pond has a surface area of 6 acres and a tributary watershed of 8.34 square miles.
The dam was rehabilitated in 1998, designed by Tata & Howard’s Waterbury, CT office.
Tata & Howard’s Waterbury, CT office completed forty (40) dam inspections and reports for the Department of Energy and Environmental Protection (DEEP) for dams located in the Western District of Connecticut, including fifteen flood control dams. The dams were rated from a hazard classification of ‘C’ to ‘BB’, and were located in urban environments, suburban locations, and rural settings. The construction of the dams varied from earthen embankments to mortared stone masonry to concrete to roller compacted concrete. The spillways varied as well, including ogee spillways, broad crested weirs, intake risers, and a drop inlet structure.
Each report included a description of the dam, inspection checklists, photographs, a sketch of the dam identifying the major features and showing the photo locations, an aerial photograph and location plan, and recommendations for improvements.
T&H staff also provided the DEEP with a cost estimate for the recommended repairs and maintenance at the 23 non-flood control dams, including contingencies for engineering services, permitting, and construction administration support services.
The Fosters Pond Dam reconstruction project presented several challenges. The existing spillway was inadequate to discharge the 100-year spillway design flood, and the existing dam was in extremely poor condition. The embankments lacked erosion protection and were very steep, the crest was narrow, and the outlet had fallen into disrepair, rendering it inoperable. Therefore, it was imperative that the reconstruction design of Fosters Pond Dam be designed to improve both safety and reliability, provide a functional and operable outlet, and provide ease of maintenance.
The reconstruction included the construction of new and higher reinforced concrete spillway training walls, upstream riprap erosion protection, a new reinforced concrete gate structure with 24″ inlet and outlet pipes and sluice gate, widened embankment crests to 12′, flattened slopes for ease of maintenance, and a gravel road to allow access to the embankment and gate structure. Riprap erosion protection is now provided on the upstream slopes as well as in the discharge channel. Because of these improvements, the dam can safely pass the 100-year spillway design flood with over a foot of freeboard. The length and level of the spillway weir remains unchanged.
Saugatuck Dam is a concrete water supply dam in Weston, CT built in 1940, now owned by Aquarion Water Company. The majority of this project included repairs and modification to the gatehouse and gate chambers at the dam. Repairs included rebuilding the gatehouse walls, cleaning and painting the intake and outlet valves, and removing and replacing the stems and valve operators. Modifications included installing platforms made of steel beams and fiberglass in the gate chambers to provide safer access the valves in the chambers, and the interconnection of the 36” supply main and the 48” diversion main at the toe of the dam to provide greater flexibility for releasing water from the reservoir.
THE CHALLENGE: The existing spillway is inadequate to discharge the 100-year spillway design flood, and the existing, aging dam is in very poor condition. The embankments are steep and lack erosion protection, the crest is narrow, and the outlet is in disrepair and inoperable. The reconstruction of Fosters Pond Dam needs to be designed to improve the safety and reliability of the structure, provide an operable outlet, and make the structure easier to maintain.
THE SOLUTION: The reconstruction includes constructing new, higher reinforced concrete spillway training walls, providing upstream riprap erosion protection, constructing a new reinforced concrete gate structure with 24-inch inlet and outlet pipes and sluice gate, widening the embankment crests to 12 feet, flattening the slopes for ease of maintenance, and providing a gravel road to allow access to the left (looking downstream) embankment and gate structure. Riprap erosion protection will be provided on the upstream slopes and in the discharge channel. With these improvements, the dam will be able to safely pass the 100-year spillway design flood with 1.1 feet of freeboard. The level and length of the spillway weir will remain unchanged.
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