International Dredging Review

International Dredging Review

Woodside Construction dredged 300000 cubic yards of material from the Rappahannock River (Virginia) River Mile 109 in preparation for demolition and removal of Embrey Dam. They used a 10-inch Ellicott 370 dredge for the job. The material is mostly sand and gravel which tested at safe or undetectable levels of contaminants.

The dam consists of an original wooden crib dam built in 1855 and a 1070-foot-long concrete dam 60 feet downstream. Built in 1910 by the Spotsylvania Power Company the concrete dam was designed for hydropower production. The project is no longer producing power and has become a liability to the community.

A 100-foot hole will be blown in the concrete dam by Army and Air Force Reserve units on February 23 causing a 10 to 15-foot high wall of water to rush through the opening. The river will rise several feet until the reservoir that extends a mile upstream has disappeared returning the river to its historic channel. Also included in the project are bank stabilization and riparian restoration behind the dam and preservation of the historic Rappahannock canal.

A solicitation has been announced by the Norfolk District with a response date of February 26 for complete removal of the dams and all debris. The project is expected to be complete by 2006.

Russell Smith and John Berlin co-owners of Woodside Construction started the company 10 years ago to do heavy construction jobs and usually have two to three jobs going at once. They purchased the Ellicott 370 in August 2001 and plan to add one more dredge to their fleet.

The company is headquartered in Dayton Maryland. Smith manages field operations for the company while Berlin is the estimator and office manager.

Smith said that they look for difficult challenging projects and the 170-foot elevation to the placement site filled this requirement. The highest either of his levermen had pushed was 58 feet.

Pumping distance was a maximum of 2200 feet dredge to booster and 1600 feet from booster to discharge. The booster pump is a GIW 10” x 12” pump with a 400 hp Cummins Diesel motor and Spicer transmission making the unit a direct drive system.

“The crew has never been able to dredge a project and then see what they dredged” said Smith. Their work will be revealed when the dam is breached. Their task was to remove the sedimentation in the reservoir created by the dams leaving only the original streambed to keep the material from washing downstream when the dams are breached. The sediment was mainly in the site of the natural riverbed on the deeper south side of the river and they are dredging a half mile section 700 feet wide. The 370 digs in a 220-foot arc removing the material in two passes.

Even though they have been running 24 hours a day six days a week they are about a month behind mostly due to additional sedimentation deposited by hurricane Isabel in September. There are four crew members per shift – a leverman booster operator disposal site operator and superintendent – with one extra person on the day crew for fueling and other tasks. Dredging is expected to be finished the first part of February.

Besides sediment removal Phase I includes building dikes in the containment area and building a haul road and staging areas to the river for the dredge and booster pump station.

The placement site is a nearby 48-acre quarry the City of Fredericksburg purchased from Rappahannock Quarry LLC an affiliate of the Silver Companies in September 2003. Purchase price was $2.575 million.

In November the Corps requested that Woodside create a 200-foot breach in the crib dam as a preliminary to breaching the concrete dam. This gravity mass dam is six feet wide 700 feet long created by eight-inch timbers to make a box then filled in with 18-inch rock and planked on the upriver side. The dam silted over completely when the concrete dam was built and nobody has seen it since then said Erik Nelson senior planner for the City of Fredericksburg.

Woodside used a clamshell mounted on a 65 by 40-foot sectional barge to remove the timbers in the crib dam. Smith said the wood appears to be hard cypress.

They were awarded Phase I of the high-profile dam removal project in April 2003 and began work in July. Interest in the project was so great that at least three articles about the dredging project had appeared in local newspapers by November.

Local groups led by Virginia Senator John Warner had been pushing for the dam removal for 10 years. The project was authorized in Section 590 of the Water Resources Development Act of 1999 and Warner added $2.5 million to the fiscal year 2002 budget for the project. Total cost will be about $20 million.

A major objection to the dam was that it prevented fish specifically American shad and striped bass from migrating to more than 170 miles of historic spawning habitat in the Rappahannock and its tributaries.

A report by Friends of the Rappahannock states that annual shad harvests in Virginia have declined from more than 11 million pounds a century ago to an average of 385000 pounds in recent years. Today the turn-of-the-century landings would be worth about $8.5 million. The 1992 harvest of shad from Chesapeake Bay had a dockside value of $42169.

The Virginia Department of Game and Inland Fish (DGIF) confirmed that blockages by dams are a key factor in this decline.

From March 1 through June 30 there will be no work in the area and archeologists will make photos and sketches of the crib dam before it is removed as part of the demolition contract. The wood which has been under water for more than 150 years will probably have no salvage value said Mark Mansfield chief of planning at the Norfolk District Corps of Engineers.

There is another dam in the area said Erik Nelson. In the 1770’s a dam was built to divert water to a canal on the south side of the river to an iron works that produced ammunition and equipment for the Continental Army during the Revolutionary War. This facility and the City of Fredericksburg were targets of a loyalist cavalry attack in 1781 from which Thomas Jefferson narrowly escaped. Archeologists will look for traces of this dam also.