Glenmere Lake Dam, a large, high hazard dam, impounds a water supply reservoir with a surface area of 328 acres and drainage area of 2.4 square miles. The dam is approximately 600-feet long and consists primarily of an earth embankment with a maximum height of 24 feet, partly supported by masonry stone and reinforced concrete walls. The crest of the dam serves as a two lane paved County roadway. Glenmere Lake also provides habitat for the largest known population of the endangered, Northern Cricket Frog (Acris crepitans) in New York State.
Tectonic prepared an Engineering Assessment and Emergency Action Plan for the dam that included the following:
- Hydrologic and hydraulic analyses
- Dam breach analyses
- Inundation mapping and hazard class evaluation
- Incremental damage assessments
- Spillway capacity evaluation
- Subsurface investigation
- Stability and seepage analyses
- Topographic and bathymetric surveys
As a result of the Engineering Assessment, the spillway capacity and dam stability were found to be deficient. Tectonic performed additional studies including an evaluation of raising the dam embankment and enlarging the spillway to increase storage and spillway capacity to prevent overtopping.
Tectonic prepared permit application documents, design plans, cost estimates and construction documents to complete the necessary improvements and modifications that include modifying the alignment of the dam to reduce the length of the dam by more than 50 percent, installing a toe drain to control seepage, and replacing the existing spillway and spillway conveyance conduit.
The relocation and shortening of the dam were a unique approach that eliminated the need for costly environmental remediation, reduced impacts to the Northern Cricket Frog population and allowed construction to proceed without lowering the reservoir which would have drastically impacted the water supply and endangered species.
Construction is currently underway and Tectonic is providing resident engineering inspection and material testing services and also monitoring of the Northern Cricket Frog as required by the NYSDEC.