- Executed bathymetric and topographic survey, field geomorphological, natural habitat, and sediment quality field investigations.
- Performed hydrologic and hydraulic analysis and fish passage evaluation.
- Developed 65-percent level conceptual drawings and construction cost estimates.
- Developed photo-renderings of the post-breach condition.
Challenge
Starr Mill Pond Dam is a 15-foot-high, 85-foot-long stone masonry dam located on the Coginchaug River in the City of Middletown, Connecticut. Originally constructed to power an adjacent mill in the early 1800s, the dam is listed in the National Register of Historic Places and is now privately owned. The dam no longer provides power to the mill and presents a barrier to fish passage. However, the Coginchaug River is a high-quality river targeted by The Nature Conservancy for floodplain and diadromous fish passage restoration.
Solution
Based on our extensive experience with similar dam removal projects, The Nature Conservancy contracted GZA in 2018 to develop a conceptual design for dam removal. GZA performed a series of field investigations including bathymetric study, topographic survey, and wetland, fisheries, and fluvial geomorphology condition assessment. We also developed hydrologic and hydraulic modeling to support both our fish passage evaluation and our design of the conceptual dam breach channel. Our sediment management evaluation included both sediment quality sampling to screen for potential contaminants and development of sediment management alternatives and on-site re-use options for the post-dam condition. These studies informed our 65-percent conceptual plans, renderings of a post-breach condition, and an opinion of probable construction costs for the removal of the dam.
Benefit
The removal of the dam would address the observed deteriorated condition of the dam, reduce liability for the dam owner, and provide environmental benefits by restoring the impoundment areas to a natural wetland and a free-flowing stream system. While The Nature Conservancy is providing coordination with the private dam owners, GZA’s evaluation of the impact of the removal of the dam provides important information regarding the benefits of stream restoration. GZA’s proposed plan includes proactive measures that could be taken to improve the resource areas of the Coginchaug River. The aim of the proposed design optimized the benefits of the project, while minimizing the impacts.