Dam removal is not new, says Michael Murphy from Epro Engineering and Environmental Consulting in the US. And it didn’t start with the Edwards dam in Maine.

Formerly sited on the Kennebec river, Edwards has become synonymous with dam removal in the US. The Federal Energy Regulatory Commission’s (FERC’s) unprecedented action to order removal of the dam in 1997 – fish passages required for licence renewal rendered the hydro power project uneconomical – caused controversy all round.

A settlement in May 1998 transferred ownership of the dam to the City of Maine for the purpose of removal. Edwards dam was breached on 1 July 1999 and was completed by October of the same year.

Reflecting on the case, and voicing his own opinions, Lee Emery from FERC says that the Edwards removal was a multi-million dollar disaster. While Walter C Ferguson, also from FERC, comments: ‘Edwards proved to be a gold medalist in legal gymnastics.’

‘NGOs are now, somewhat mistakenly, using Edwards dam as a poster child in their national dam removal campaign,’ says Richard Donnelly from Acres International in Canada. How-ever, many hydro industry members believe the only lesson to learn from Edwards is how not to remove a dam.

Reasons for removal

But why are dams removed in the first place? Martin McCann is from the National Performance of Dams Programme at Stanford University and is co-ordinating a national effort to retrieve, archive and disseminate information on the performance of dams and their removal. ‘It’s difficult to develop a true picture of dam removal,’ he says. ‘Data is not systematically gathered and reasons for removal have only been cited in 42% of cases.’

McCann describes dam removal as a web of interacting factors which are often hard to unravel. Although it can be difficult to pinpoint a single item, the following factors more often than not come into play:

• Dam safety – this can be costly both from an economic and social perspective.

• Economics – the cost of renovating the dam outweighs future benefits.

• Environmental concerns.

• Lack of significant benefits – the dam is no longer needed and has quite simply outlived its purpose.

Donnelly has been researching documented case studies of dam removal in North America. His investigations have shown that the reasons for removal in 22 examples were as follows:

• Dam safety = 54%.

• Dam safety/spill capacity = 23%.

• Fisheries = 14%.

• Reservoir siltation = 9%.

Despite the fact that dam removal has been an ongoing activity throughout the twentieth century, with the first documented case in 1912, more and more dams are continuing to be removed. McCann says that since 1900, 587 identified dam removals have taken place in the US. Of these, 428 dams were more than 2m in height or 30m long. Very few removals actually took place during the early part of the 1900s, but since 1980 350 have occurred, with 140 taking place from 1995-2000.

In almost 95% of cases, the removed structures do not meet the icold criteria for large dams (>15m). ‘Over the years the average size of the dam has stayed the same,’ McCann explains, ‘but since 1980 there has been an increase in the maximum height of those removed.’

Age, safety and the environment have all played influential roles in dam removal over the past 30 years. Changing perceptions have led to a reassessment of solutions to problems, with dam removal being viewed as a viable alternative.

Emery is keen to point out that the removal of FERC-licensed hydro power projects is a rare event. ‘This is the exception and not the rule,’ he says. ‘It has been that way in the past and is likely to be so in the future.’ As of 14 February 2001, 11 dam removals had occurred out of 1009 FERC licensed projects and 597 exemptions. Emery added that in the next 5-25 years only two such projects have been ‘tentatively scheduled’ for possible removal, although several other dam removal actions are currently being considered.

Dam removal is an expensive proposition, especially when borne by the licensee, and a lack of adequate research and engineering analysis prior to removal can be costly. For example, before removal, reservoir sediments need to be tested for toxic pollutants; the volume of sediments usually present upstream of the dam needs to be determined, as well as potential impacts of their release on downstream users; while potential hazards and blockages in the reservoir which could become exposed after dam removal need to be investigated.

With the estimated cost of removal ranging from US$25,000 to US$2M, millions of dollars can also be spent in the aftermath of the removal – clean up operations downstream can be expensive. Donnelly’s research breaks down decommissioning costs into three categories: infrastructure removal costs (30%);

environmental engineering (22%); and sediment management (48%). The increasing trend to remove dams in the US, for whatever reason, has not made this an easier process. Experience has proved that dam removal is neither simple nor totally beneficial to the riverine environment. Edwards dam on the Kennebec river was only one example which showed that sediment management can be a monumental problem – over 470,000m3 was dredged from the river after removal. And the value of pre-removal studies can not be over emphasised.

Soundbite opportunity

McCann also points out that the removal option has many sides. Dam removal is either considered and implemented when the dam cannot meet reasonable economic, environmental, use and safety criteria; considered and rejected when the latter is not so; or never considered because the project’s benefits are too significant, such as providing lifeline services and flood protection etc. This does then raise questions about the four Snake river dams in the Columbia river basin. Targeted for removal as they form part of salmon’s migratory corridor, these dams also provide significant power, irrigation and transportation benefits for the local vicinity. But as recent research has shown, environmental problems, such as reversing the decline in salmon, run a lot deeper than simply removing dams.

According to McCann, although current data suggests that removal is not an option that is considered or even exercised very often, the subject has become a ‘soundbite opportunity’. He adds that while removal cases are given great publicity, too little is known about non-removal – when dam removal was considered and not exercised. If more information was gathered on this it may help to balance, and provide a greater insight, into the dam removal debate.