Maryland dam faces sedimentation threat

In September 2011, Tropical Storm Lee caused flooding in the mid-Atlantic region.  The Susquehanna River rose far above its banks, causing disruptive floods in Pennsylvania and Maryland.  Near the river’s mouth into Chesapeake Bay, massive flooding threatened to breach the 572-megawatt Conowingo Dam.

With its flood gates wide open, the dam survived the flooding.  At peak flows, about 7 million gallons flowed through the dam every minute.  That water transported millions of tons of sediment from the Susquehanna watershed out into the bay, along with large amounts of trash and debris.

The impacts of the flood are still being assessed.  Under typical operations, the dam builds up about 2 million tons of sediment every year, or about two-thirds of the Susquehanna River's total sediment burden.  (Compare the dams currently being removed from the Elwha River in Washington, which had trapped an estimated 24 million cubic yards of sediment.)  Overall, four dams on the Susquehanna might hold up to 280 million tons of sediment.

While Lee removed several years' worth of sediment from the Conowingo Dam, more sediment builds up every year.  The Army Corps is concerned that the Susquehanna River dams have nearly reached their full capacity to hold sediment, and is launching a project to study what could be done, such as sediment dredging or remediation.

June 7, 2011 - Washington dam removal in process

While state and federal governments pursue policies supporting the development of new renewable energy resources, existing hydroelectric dams are being removed.  Last year, I noted the plan to remove the Elwha and Glines Canyon Dams on the Elwha River on Washington's Olympic Peninsula.  That plan is moving forward; last week, after 99 years of producing renewable power, the dams' electricity-generating turbines have now been turned off.

The Elwha River restoration project will be the largest dam removal in U.S. history.  All told, the dam removal project is projected to cost $324.7 million.

The Elwha project is made more interesting by its factual context, including land conservation, fish impacts, and sedimentation.  Much of the river's 45-mile course runs through Olympic National Park, making power generation a use some feel is incongruous with the watershed's protected status.

The Elwha River was formerly home to impressive runs of anadromous fish, including salmon, which have been an important part of local native Americans' culture.  In 1910, the river produced approximately 390,000 wild salmon and sea-run trout, but that number dropped more than 99% to only about 3,000 wild native salmonids in 2005.  The dams are believed to have played a part in this decimation of that fish stock.

Thanks to the glacier-fed nature of the watershed, massive amounts of sediment have built up behind the dams -- perhaps as much as 24 million cubic yards, or enough sediment to cover almost 15,000 acres one foot deep.

Dam demolition and removal itself is scheduled to begin September 17, 2011. 

September 3, 2010 - Elwha dam removal; Northwest Passage

Hydroelectricity: I'm continuing to follow the removal of two dams on the Elwha River in Washington.

Here is a map I created showing the two dam sites.

Here is the Bureau of Reclamation's information on sedimentation behind the Elwha River dams: nearly 18 million cubic yards of sediment behind Glines Canyon Dam and Elwha Dam.  The Bureau gives this history:

Private companies constructed two large dams on the Elwha River during the early 1900’s. Elwha Dam, constructed during the period 1910-13, is a 105-foot high concrete gravity dam that forms Lake Aldwell 8 miles upstream from the river's mouth. Glines Canyon Dam, built in 1927, is a 210-foot high concrete arch dam that forms Lake Mills 13 miles upstream from the river's mouth. When the dams were first built, they were significant producers of electricity on the Olympic Peninsula. Today, the dams are operated in a run-of-the river mode and generate about 40 percent of the electricity needs for the Diashowa America paper mill in Port Angeles, Washington.

The Bureau also has interesting information on erosion after drawdown.  As we've seen before, drawdown can be done to minimize harms but can also cause serious problems if the newly exposed slopes of the impoundment or riverbank are unstable.




Meanwhile, in Maine, a graphic example of how business climate can make a difference: an entire lumber mill, closed for the past four years, is up for sale and might be moved piece by piece to Siberia.  People often talk about how jobs move overseas; here, not only the (already lost) jobs but the workplace may move.
The situation on the Sebasticook River continues to brew after the Fort Halifax dam removal; now, town officials are considering a renewed investigation into erosion of the riverbanks after drawdown and dam breach.

An interesting bit of fisheries news: Native Americans from the Passamaquoddy Tribe continue to fish federal waters, despite being cited for lack of permits and certain mandatory safety gear during a scallop fishing trip off Nantucket.  The natives point to their indigenous fishing rights.

Arctic news: I have a special interest in the Canadian Arctic, including the fabled Northwest Passage.  Today comes news that a fuel tanker has run aground along that shipping route on a sandbar near Gjoa Haven.

August 31, 2010 - dam removal; biodiesel

Seen on the road: this soda distribution truck is "powered by BIODIESEL".

I'm following the dam removal projects on the Elwha River on the Olympics Peninsula in Washington.  One component of the $351 million river restoration project is the removal of two dams for about $40 million to $60 million: Elwha Dam (108' tall) and Glines Canyon Dam (210' tall).  Glines Canyon Dam is located within the boundaries of Olympic National Park.  This will be the nation's largest dam removal project to date.

Here's the National Park Service's website about the Elwha River Restoration project.


Dam removal is a hot topic.  Arguments in favor of dam removal typically include safety, fish passage, and water quality problems caused by some dams.  On the other side, arguments for keeping dams in place include mandates to generate local renewable power and flood control.