Strategies for Impediment Rehabilitation to Create Fish Passage Opportunities in the Rappahannock River Basin

About the report:

Areas where anthropogenic development coincides with aquatic systems often impede the flow of organisms and nutrients in either an upstream, downstream, or bidirectional path. These impediments are especially outstanding in the tidal and nontidal freshwater areas of Virginia where diadromous fishes are hindered from moving upstream onto spawning grounds and the upstream ecosystems lose out on the contribution of marine derived nutrients. Recent removals of major impediments such as Embry Dam Fredericksburg, Virginia, opens large expanses of previously blocked spawning habitat for recreationally and commercially important diadromous species. Many smaller river systems require different methods of impediment rehabilitation and various fish passage systems are being used throughout the country to assist in the reconnection of previously impeded stream segments. The primary intent of this research was to assess different fish passage systems as they relate to impediments created by road culverts and to design and install systems in Virginia. Road culverts are common throughout the state and represent one of the important types of potential barriers to upstream migration. We examined the available literature (mostly from Pacific Northwest river systems), explored extant impediment databases (created by VDGIF and VCU) for the Rappahannock River drainage, monitored the effectiveness of the two major fish passage types being used in Maryland (pool-weir designs and Alaskan steep pass design), consulted state and federal officials, chose sites for Virginia stream implementation of fish passage and had fabricated the appropriate passage structures. It was concluded that site selections can be prioritized, if fish passage is a primary concern, by use of databases that describe anadromous fish use in the appropriate watershed. Models of spawning and nursery habitat preferences help in site selection by allowing quantification of habitat to be opened by the installation of fish passage. Detailed design of the passage structure(s) must be made on a site-by-site basis. To date, there are insufficient data to state firmly whether a steep pass design is better or worse that a pool-weir as both designs work under variable conditions. Considerations in passage design include the type, size, and height of the current impediment, future maintenance requirements, and potential use by the various species of concern and funding available for the system development, placement, and maintenance.

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