Not Stepping in the Same River Twice:

Making Strides in Ecological Restoration through Dam Removal

David Morgan

Widespread dam removal would have been unthinkable in the mid-20th century, when government-
sponsored dam construction was at a fever
pitch. Six thousand new large federal projects
diverted, restrained, and impounded rivers
across America between 1930 and 1970. These
dams carried the banner for a modern vision of
society using technology to harness and exploit
natural processes. They fed agricultural
production, encouraged development in arid
climates, and powered wartime industries.

Meanwhile, more widespread smaller dams
steadily stopped up water flows on private
property. As many as 2.5 million dams are stiil
in place, though perhaps not for long. The dams
are old, many nearing or beyond their usable
life, and the cost of maintaining or replacing
them often outweighs their benefit. Safety
standards, too, dictate that the failing infrastructure has to go, and there is a growing awareness of the
ecological benefits of dam removal. The U.S. Geological Survey reports that dam removal has outpaced
dam construction in every decade since the mid-1970s In essence, dams have become obstacles
signaling where river restoration should go next. The challenges, lessons, and opportunities afforded by
dam removal offer promising insights and best practices for aspiring restoration projects. This article
looks at each of these in turn, focusing on the gamut of dam removal considerations, the availability of
data tracking dam removal results, and the many opportunities that dam removal opens for restoration
practice.

Scientists are increasingly called upon to evaluate the impacts of dams and their potential removal.
Several landmark studies in recent decades have indexed the adverse biological, chemical, and physical
effects dams have on rivers and watersheds. One of the most commonly cited effects is the limits dams
place on fish passage. Dams block rivers and constrain migration patterns. Even when dams are
passable, the river's flow can be altered from the seasonal variations fish and other species depend
upon for timing their growth and reproduction cycles. There are also upstream and downstream habitat
effects. Sediments, logs, rocks, and other important features of a river get caught behind the dam,
smothering the impounded area and depriving the rest of the river of material it needs to maintain its
ecological integrity. Water quality can also decrease in a dammed river, due to abnormal fluctuations in
temperature, nutrient and oxygen levels.

While these effects are understood in general terms, each dam removal project is different. The
challenges associated with each project need to be identified on a case-by-case basis, guided by
restoration objectives. Rivers are complex systems and exhibit considerable variation in the sequence,
timing, extent, and magnitude of their response to changes affecting them. Dam removal, fortunately, is

Dammed cranberry bog restoration in process in the Childs
River. This SNEP-funded project aims to restore this bog to its
natural state as a wetland. Click the photo for more
information. Photo credit: Carriage Shop RD Pond Stream
Diversion, courtesy of Dennis Martin

-------
a relatively controllable change to a river system, so scientists have been able to test and refine their
understanding of what is possible in terms of restoration. Accounting for factors like the size of the dam,
the kind of stress it has imposed on the river, and how it operates can help inform predictions about
restoration outcomes. Ecological context matters, too. The amount of valuable habitat that already
exists up or downstream from the dam will affect how plant and animal species respond to the change,
as will the kind of habitats that are reconnected and where they are located in the river. How closely the
dam is located to other development, how intense that development is, and the effects of its removal
on health, safety, and the economy are all related social concerns.

The Massachusetts Division of Ecological Restoration (DER) evaluates projects on these terms using its
Restoration Potential Model Tool. The tool tracks the characteristics of all 3,000+ dams in the
Commonwealth. It models how effective a dam removal can be in terms of providing ecological benefits.
DER has also made some of its dam removal data available for download, including the economic,
safety, and environmental monitoring findings. The practice of post-removal evaluation is still limited
but is on the rise as dam removal increases in popularity. The U.S. Geological Survey, working with the
nonprofit American Rivers, now tracks scientific studies on the outcomes of dam removal and visualizes
the data in the Dam Removal Information Portal (DRIP). The portal not only tracks and maps projects, it
links users to the associated studies for further details. DRIP reports the salient characteristics that get
weighed early in removal decisions, including essential details about the dam. The cataloged reports
include studies of tradeoffs, whether social, economic, or with respect to impact on other infrastructure.
Physical and biological outcomes are also commonly reported. DRIP is not comprehensive—not all dams
are tracked, and not all studies are included—but it is as close to a one-stop-shop for dam removal
information as has been achieved to date.

Dam removal also provides many opportunities that do not get indexed in databases but relate to other
social and ecological trends. Increased demand for renewable energy sources, for example, puts the
transition from fossil fuels in conflict with the prospect of removing hydropower producing dams. It is
not uncommon for such facilities to operate as "peaker" plants, which come online at times of peak
energy demand and can be highly disruptive to river flows. To minimize the harms from such plants,
criteria have been developed for certifying projects as low-impact, and changes to how the dams
operate can be negotiated when owners must renew their licenses, as has been done recently for dams
in the Connecticut River. Where ponding behind a dam is desirable, Beaver Dam Analogs have been
employed to mimic the kind put in place by beavers themselves. This ecological alternative provides
numerous benefits, including naturalistic flow regulation, fish passage, and habitat creation. These
analogs can even be designed in a way that beavers will maintain them on their own.

The work ahead is significant. Dam removals still number in the low thousands nationally, but the trend
favors retiring old, potentially unsafe infrastructure in favor of more ecological alternatives. In fact,

SNEP has supported similar efforts such as those in the Childs River restoration project. Further studies
are needed to gain a holistic understanding of dam removal's potential, both at the site level and at
scale. The steady shift away from damming contrasts with the 20th-century notion that society benefits
from controlling rivers. Perhaps it also promises a 21st-century vision of restoring the capacities of rivers,
the diverse benefits of which we can all enjoy.

-------