SD18 - Technical Alternatives Analysis to Provide Fish Passage at Embrey Dam


Executive Summary:
Embrey Dam is a 22' high concrete structure located just east of the Interstate 95 crossing of the Rappahannock River. The dam currently blocks anadromous fish from migrating upstream to more than 70 miles of the upper sections of the river. Virginia Senate Joint Resolution No. 296 was approved in early 1997 requesting the Virginia Department of Game and Inland Fisheries to conduct a study on the recommended methods of providing fish passage at Embrey Dam.

As a part of the study undertaken by the Virginia Department of Game and Inland Fisheries, TIMMONS, Inc. has been contracted to evaluate the technical feasibility of three previously identified alternatives for providing fish passage. The technical alternatives considered include: constructing a vertical slot fishway, breaching a portion of the dam, and removing the entire dam. To fully evaluate these options for providing fish passage, a "decision matrix" strategy was developed dividing the critical issues into technical, regulatory, and "local" categories. Issues that could be assigned specific capital and/or maintenance costs were included within a "technical decision matrix" to develop the recommendations outlined within this study. Local issues that resulted from various meetings held with federal, state, and local agencies provided input to create a "local decision matrix" of issues that have been identified for further study.

The partial and complete dam removal alternatives require that the sediment that has accumulated behind the dam be addressed. Options to address the sediment issue include full removal/hauling of the sediment off-site, and various combinations of removal, release, and stabilization of the sediment in place. The most expensive option is full removal and the least expensive option is a full release. This following financial analysis utilizes a conservative cost estimate of $4.24 million for full sediment removal to independently evaluate the three alternatives for providing fish passage.

The results of the technical decision matrix include the following:

Fish Passage Option 1 Gravity Dam
50-year Present Worth: $10,200,000

Complete Dam Removal
50-year Present Worth: $7,450,000

Partial Dam Removal
50-year Present Worth: $7,400,000

The 50-year present worth analysis shows that either complete or partial dam removal is significantly less expensive than the most cost effective option of constructing a fish passage. The present worth of the two alternatives for dam removal is within two percent of each other. This study therefore recommends that the alternatives for either total or partial dam removal be progressed further through the regulatory process to effectively accomplish the goal of providing fish passage at Embrey Dam.