Issues
Dams & Culverts and Their Effects on our Watershed
Click here to download the IRWA Fact Sheet on Dams & Culverts (PDF, 793kb).
| There are more than 70 dams and 500 road-stream crossings in the Ipswich River watershed. These dams, as well as the culverts and bridges that are located where roads and streams intersect, can have major effects on our streams and rivers. |
| Many dams in the Ipswich River watershed were built in the 1800s to power industrial mills, but no longer serve this purpose. Some create recreational or scenic ponds, while others are crumbling or neglected. |
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Dams and Culverts in the Ipswich River Watershed
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Numerous road-stream crossings are poorly designed or not well-maintained. These structures are found throughout the watershed, and addressing them represents one of the best opportunities we have to restore the Ipswich River to health.
We are working with communities to evaluate impacts and restoration potential at dams and culverts throughout the watershed.
Effects of Dams on Fisheries and Aquatic Species
- Dams and poorly designed culverts reduce the quality of river habitat. Impoundments (the ponds that form upstream of dams or undersized culverts) reduce the amount of natural river habitat available for native fish. Many dams in the Ipswich River watershed are built over rare riffles (light rapids where water flows over a shallow section of a river) that once provided excellent habitat for fish and other aquatic species. A study of the impact of dams and low-flow conditions on macroinvertebrates (bottom-dwelling organisms like some types of worms and insects) in Fish Brook in Boxford indicated that macroinvertebrate communities were degraded at both dam and low-flow sites, suggesting that these structures affect habitat quality.
- Dams and hydrologic alterations have changed the type of fish living in the Ipswich River. Fish that evolved in a free-flowing river generally cannot survive in impoundments due to differences in temperature, dissolved oxygen and other factors. Surveys show that the Ipswich River fish community is dominated by pond fish and generalist species such as pickerel, eel, and sunfish. Fluvial fish that should predominate in a healthy river, such as fallfish, common shiner, and dace, are absent or poorly represented. See our Fisheries Resources page for studies and more information.
- Dams and some culverts act as barriers to the movement of fish. Migratory fish such as river herring, rainbow smelt, and American shad must travel up rivers from the ocean in order to reach their native spawning grounds. These important species have been observed at the Ipswich Mills Dam (see our Herring Count Reports), indicating that they are ready to use the valuable habitat found in the Ipswich River. Unfortunately, poorly designed culverts and dams without well-designed fish passage structures can prevent these and other species from accessing crucial habitat.
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Effects of Dams on Communities
- Dams both enhance and limit recreational opportunities on the Ipswich River. Many dams in the Ipswich River watershed create ponds used for fishing, swimming, or boating. During dry periods, the ponds created by dam impoundments allow for boating and swimming, even when other sections of the river may be too low. However, dams on the mainstem of the Ipswich River also impede boating access in certain areas. For example, in order to canoe or kayak down the Ipswich River, boaters must portage around three significant dams. Fishing for brook trout is limited because they need the flowing riffle habitats that are flooded by dams.
- Dams may be highly valued by local communities. Many dams have significant historic or scenic value. In some cases, the dam and its impoundment serve as a focal point for houses, buildings, and other infrastructure built nearby. When evaluating the future of a dam and impoundment, it is important in all cases to consider the historic and scenic value of a dam to neighbors, as well as the value of a free-flowing and healthy river to the entire community.
- Dams and culverts can present a danger to public safety if they are not maintained regularly. Over time, the structural integrity of dams diminishes and periodic maintenance is required. Many of our dams have fallen into disrepair over time, and in some cases present a danger to people who might play, swim, or boat on or around these unsound structures. Some undersized or poorly maintained culverts may contribute to localized flooding.
- Dams can have high maintenance and liability costs. In Massachusetts, dam owners are liable for dam failures or safety dangers. Dam insurance premiums can be expensive. For many dams, it makes sense to compare the costs of safely maintaining and holding liability over a dam with removal of the structure entirely.
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What can we do?
The negative effects of dams and culverts on the river system can be mitigated through careful management of these structures. In some cases, fish passage at a dam can be greatly improved by the installation of a fish ladder or bypass channel. In other cases, it makes more sense to remove a dam or replace a culvert so that both people and aquatic species can benefit from a free-flowing system. Consideration of the full spectrum of costs and benefits (to the ecosystem, to the community, to the dam owners, to those who use the river) can help us determine the appropriate course of action. In cases where the effect of the dam on the river or community is unknown, feasibility studies of various management options can provide valuable information to inform decision-making.
For more information:
Dams and Dam Removal
Culverts
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