One simple way to improve the ecological function of a waterway is to remove the man-made structures that impede its functions. These structures often consist of old dams that no longer serve their purpose, and culverts that are undersized, poorly designed, and/or malfunctioning.
Dams, current and past
Over the centuries, the Neponset River and its streams have been modified to suit various human activities and we experience the legacy of these modifications today.
For instance, the remains of old dams on the river – as well as artificial widening of the river channel – continue to make waterway travel challenging for both wildlife (e.g., fish) and humans (e.g., paddling a boat) more difficult, especially during times of low flow. The site of the collapsed “rubble dam,” about 200 yards downstream of the Truman Parkway canoe launch, is one such challenging site.
At the Watershed Association’s urging, there is an ongoing effort to get herring and shad (and recreating humans) past the Baker and Tileston and Hollingsworth Dams, especially by modifying or removing the dams.
If the dams are removed or modified sufficiently, and the channel partially restored to a more natural shape, paddling through this stretch of the river will become much safer, easier, and less susceptible to low flows.
At other points in the river, there are small, vegetated islands – another legacy of old dams. For example, downstream from Ryan Playground in Mattapan, the river enters a stretch of braided or “anabranch” channel where it splits into numerous small threads that weave their way through tiny islands covered primarily with Reed canarygrass. This area is sometimes referred to as the “wild rice islands,” although no wild rice has been observed here.
Before 1955, this area would have been underwater, part of the mill pond created by the Jenkins Dam, which sat just upstream of the modern day shopping plaza on River Street near Central Avenue. The Jenkins Dam collapsed in 1955’s Hurricane Diane and ultimately was removed by the state. The small islands and braided channel were formed as the river carved a new route for itself through the thick deposits of silt that had accumulated behind the Jenkins Dam.
The Lower Neponset River restoration project presents a unique opportunity to continue the revitalization of neighborhoods along the river by making the Neponset cleaner, more accessible, and closer to its natural condition.
In August 2017, the middle dam in a series of three was significantly altered to ensure the survival of a small breeding population of brook trout that inhabits the headwaters of Pine Tree Brook.
In the fall of 2015, a small group of volunteers removed two boulder dams from the brook and helped restore the brook trout habitat for which Traphole Brook is famous.
Changes in the Neponset River over the last 30 years have dramatically increased the river’s importance as an aesthetically pleasing backdrop that people can enjoy as they go about their daily business.
Dam removal would greatly expand fishing opportunities. Boating which is currently blocked by the dams would be safer and considerably more enjoyable, and the safety of those recreating along the banks of the river would be enhanced.
When we remove a dam or poorly functioning culvert from a stream or river, we benefit the waterway in number of ways. We restore opportunities for fish and other aquatic wildlife to travel longer stream lengths, accessing more habitat, mates, and shelter, and potentially even passing between streams, the river, and the ocean. We also improve water quality—reducing pollutant levels, cooling water temperatures, and increasing dissolved oxygen levels.
Better water quality means that the waterway can support more species of fish and other aquatic wildlife. We also restore natural stream processes, like the distribution of sediments and nutrients along streambeds, which contributes to the waterway’s ability to support more species, returning a greater degree of aquatic biodiversity. And, we reduce the risk of flooding, injury, and property damage.
Removing barriers to migration
When we remove dams from streams and rivers that are key for fish spawning migrations, we enable groups of fish species to migrate along the waterways.
Of the methods available for restoring fish passage, dam removal provides the most overall ecological benefits – restoring river hydrology, connectivity, water quality, recreation, ecology, and fish passage for a variety of fish species. In comparison, installation of a fish ladder at an existent dam only potentially provides access for a few species.
Because of the Neponset Watershed’s lengthy history of industrial development, Neponset dam removal projects can be complicated by potential pollutants in river-bottom sediments, which may require removal, treatment and proper disposal.
Note that when a dam cannot be removed – potentially because its uses are important, the dam-owner is not interested in removing the dam, or the community is not interested – some degree of fish passage may be restored by installing fishways, including: upstream and downstream fish ladders, fish lifts (elevators), or nature-like fishways.
Nature-like fishways pass more types of fish than fish ladders, and include rock ramps and by-pass channels. The fishways mimic natural river morphology. In Massachusetts, the most typical fishways are weir pools and notched weir pools, as well as Denil ladders, stream baffles, Alaskan steep pass, combination designs, vertical slot and fish lifts. For migratory fish, the Denil-type, Alaskan steep pass fishways are the most effective. However, some migratory fish such as smelt, striped bass, and sturgeon do not climb fish ladders. A significant proportion of Massachusetts fishways need repair or re-design. A 2001-2002 study by the MA Division of Marine Fisheries assessed waterway blockages, fishways, and anadromous fish in coastal MA waterways. Data from this study are key to future restoration efforts, suggesting sites for construction of new fishways, removal of blockages, waterway restoration, etc.
More aquatic habitat restoration options
Besides removing waterway obstructions to restore ecological functions along a waterway, we can:
- Restore river contours and riparian habitats and buffers
- Reduce water pollution
- Reduce water withdrawals and increase groundwater recharge, to improve water flow in waterbodies
- Remove waterway blockages to restore waterway connectivity and water flow
- Restore spawning habitat substrate and water quality
- Restore riparian buffers
Is there an opportunity for aquatic ecological restoration on your property? Contact Executive Director, Ian Cooke at 781-575-0354 x305 or firstname.lastname@example.org.