Those Dammed Lakes - Hydro-Environmental Analysis: Freshwater Environments - page 315

Dam removal is a major engineering activity and there are a variety of potential impacts to con-
sider if a dam is to be removed, including (Conyngham et al. 2006):

• Release of excessive sediments: reservoirs store large quantities of sediments, which may

be released or must be removed as part of dam removal projects.

• Release of toxic sediments: sediments deposited behind dams may be contaminated and

may require remediation prior to or following removal.

• Release of nutrients: sediments also store nutrients, which may be released following dam

removal causing downstream increases in aquatic plants, such as algae.

• Undesirable vegetation response: plant growth downstream may be adversely impacted.

• Physical instability and bank erosion: as discussed for rivers and streams, taking a system

out of sediment equilibrium may cause channel degradation, such as bank collapse, chan-
nel incision, and other impacts.

• Risk of downstream ice damming: dam removals in ice-prone rivers have been observed

to cause an increased risk of ice jamming and damming (USACE 2001; White and Moore
2002, cited by Conyngham et al. 2006).

• Mobility of invasive organisms: some dams act as barriers to invasive species (such as the

sea lamprey) or to separate introduced and native species; thus, the removal of that barrier
may negatively impact the river or stream.

A variety of legal and regulatory issues are associated with dam removal. For example, fed-
eral, state, and local permits are required for dam removal. However, the laws and regulations on
which these permits are based are often designed for public safety and environmental protection,
rather than restoration, which may complicate the dam removal process. Bowman (2002) provides
a review of the laws and regulations impacting dam removal. Dam removal as a restoration process
will be discussed in greater detail in Chapter 18 on restoration and management.

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Bowman, M.B. 2002. Legal perspectives on dam removal. BioScience 52 (8), 739-747.
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