Can rivers be restored through dam removal?
Although most rivers cannot be completely restored to historic conditions – simply because of the amount of development that has occurred on and along them – dam removal can often recreate conditions that move the river towards those historic conditions. For example, migratory fish are returning to the Musconetcong, Millstone, and Paulins Kill after dam removals on those rivers.
Nationally, fish are returning to historic stretches of river that had been previously obstructed on Butte Creek in California, the Souadabscook River in Maine, and the Clearwater River in Idaho, as a result of dam removals. (AR)
Will the removal of a dam matter if other dams in the system are not removed?
Some rivers are so heavily developed and dammed that removal of one dam on that river will only return flows to a small portion of the river. Generally, dams that have been targeted for removal are strategically located – removal will open up a section of the river critical to fish and wildlife and/or recreation. In some cases, this additional section of river is enough to sustain crucial populations of endangered or threatened species of fish, mollusks, and other wildlife. (AR)
How does dam removal affect fish?
Dam removal benefits fish in many ways, including: (1) removing obstructions to upstream and downstream migration; (2) restoring natural riverine habitat; (3) restoring natural seasonal flow variations; (4) eliminating siltation of spawning and feeding habitat above the dam; (5) allowing debris, small rocks and nutrients to pass below the dam, creating healthy habitat; (6) eliminating unnatural temperature variations below the dam; and (7) removing turbines that kill fish. (AR)
How will the dam’s removal affect fish and wildlife habitats in the area?
Dams alter the natural physical, biological and chemical functions of rivers. And, since healthy rivers are considered the lifeblood of healthy habitats, dams can result in unsustainable and degraded conditions for a variety of aquatic and terrestrial species. The habitats that have been created solely because of the dam’s presence will change if the dam is removed. For instance, a deep water marsh may be restored to a shallow marsh or a wet meadow. NJ Fish and Wildlife and other natural resources agencies can help provide site-specific information and predicted changes. (NHDES)
How will fishing opportunities change if the dam is removed?
Dam removal improves the health of the river and aquatic habitat, typically to such an extent that anglers can look forward to increased numbers of fish and more places to fish for them. In some cases, removing a dam will change the type of fishery. For instance, a warm water fishery may be restored to a cool or coldwater fishery. In many cases, free-flowing rivers allow a wider variety of warm, cool and coldwater species to seasonally occupy portions of the same river, providing greater fishing variety. Anglers often like to fish right below dams, and some may oppose removal because they feel they’ll lose a good fishing spot. But it’s important to realize that the fish aren’t necessarily there because it’s good habitat, they’re often there because they’re prevented from moving further upstream. (NHDES)
What will the restored river look like?
Generally, the easiest way to predict how a river would look if a dam were removed is to look at the river upstream of the impoundment and downstream of the dam. Unless there is a significant geologic feature (e.g., a waterfall) in the impounded stretch of the river, it is unlikely that the restored river will be significantly different than what is seen in free-flowing parts of the river. Bear in mind that some dams are built to artificially raise the water level of a natural lake or pond. If that is the case, the extent of the pond post-dam removal can be predicted through modeling and/or sounding surveys. (NHDES)
What will the newly exposed pond bottom look like?
Land will be exposed when an impoundment is drawn down during dam removal. The amount of land that will be exposed depends upon the site conditions. If nearby sections of the free-flowing river have rocky banks, chances are that the restored section will too. If nearby sections of the river are vegetated, chances are that newly exposed lands will re-vegetate within a matter of weeks during growing seasons, thanks to the many seeds that have accumulated in the sediment over the years. Depending on the time of year and make-up of the sediment that is exposed, there may be an odor of decomposition for a short period of time (typically ranging from a few days to a few weeks). However, once this “new” land is exposed to sunlight and oxygen, plants grow very quickly, drying up the water-logged sediment in the process. Of course, if the exposed land is subject to tidal action or other significant water level fluctuations, this area may not revegetate as much or as quickly. (NHDES)
How quickly do rivers recover after dam removal?
Rivers are very dynamic and resilient systems. Experience has shown that natural river systems can be restored relatively rapidly after dam removal. For example, spawning fish returned to the Musconetcong, Millstone, and Paulins Kill Rivers only months after dam removal projects there. (AR)