OLR Research Report

October 4, 2010




By: Kevin E. McCarthy, Principal Analyst

You asked for a discussion of the arguments for and against hydropower.


This report focuses on small-scale hydropower, as there is little large- scale hydropower in Connecticut. The U.S. Department of Energy (DOE) considers a hydropower facility to be large if it can generate more than 30 megawatts (a megawatt of capacity can serve 750 to 1,000 homes). According to the Connecticut Siting Council, there are 10 hydropower facilities in the state, with generating capacities ranging from 70 kilowatts (Bantam 1) to 41.5 megawatts (Shepaug 1). A 1995 DOE study (http://hydropower.id.doe.gov/resourceassessment/pdfs/states/ct.pdf) identified and assessed 68 hydropower sites in the state. It found they have potential capacities ranging from 6.5 kilowatts to 10 megawatts. Most of the sites have capacities under 1 megawatt. In contrast, Hoover Dam has a capacity of 2,080 megawatts and the hydropower facilities on the American side of Niagara Falls have a combined capacity of 2,515 megawatts.

There are several types of hydroelectric facilities. The most common type is an impoundment facility. These facilities, most of which are large, use dams to store river water in a reservoir. Water released from the reservoir flows through a turbine, spinning it, which in turn powers a generator to produce electricity. A run-of-river facility channels a portion of a river through a canal or penstock and may not require the use of a dam. A pumped storage facility stores energy by pumping water from a lower reservoir to an upper reservoir during periods when the cost of generating electricity is low. During periods of high electrical demand, the water is released back to the lower reservoir to generate electricity.

Arguments in Favor

There are economic and environmental arguments for hydropower. Generally, hydropower facilities have high capital costs but very low operating costs. Over their lifetime, the total cost of producing power at a hydroelectric facility is typically less than that for a fossil fuel or nuclear plant. Hydropower facilities are dispatchable, i.e., their owners can, within limits, increase or decrease power production to reflect changes in electric demand.

Hydropower is a renewable resource, relying on the natural cycle in which water falls as precipitation, flows in rivers to lakes and oceans, and evaporates from these water bodies back into the atmosphere. Hydropower facilities produce no air pollution. They emit no carbon dioxide, and their “cradle to grave” greenhouse gas emissions are less than most other types of generation (this approach measures emissions associated with facility construction and operation, as well as direct emissions).

Impoundment facilities typically offer a variety of recreational opportunities, notably fishing, swimming, and boating. The Federal Energy Regulatory Commission, which regulates hydropower, generally requires these facilities to provide public access to the reservoir to allow the public to take advantage of these opportunities.

Argument Against

The primary arguments against hydropower are environmental. Impoundment and pumped storage facilities can cause serious environmental harm to surrounding areas. They can alter the amount and quality (e.g., oxygen level) of water flowing downstream, which affects plant life as well as both aquatic and land-based animal species. Turbines kill fish in the river, although this impact can be mitigated through the use of fish ladders and similar structures. Dams block migratory routes, particularly for anadromous fish such as salmon that live in the ocean but come up rivers to spawn. The creation of new dams can destroy the habitat of species, including forests. The destruction of forests produces methane, a potent greenhouse gas. Dams also reduce sediment and nutriment flow downstream and reduce the temperature of the water.

In addition to these environmental impacts, impoundment facilities can reduce the aesthetic value of streams, particularly wild rivers. As a result of environmental and aesthetic concerns, a number of dams in New England have been removed in recent years, including dams on the Kennebec River in Maine and the Pawcatuck River in Rhode Island. In contrast, run of river facilities have a smaller environmental impact, and produce relatively little change in the stream channel and flow.