A review of the impacts and effectiveness of different road crossing structures on local fish communities.
Environmental Considerations in Planning
Research Idea Scope
Cost benefit analysis of culvert and bridge maintenance often omit aspects of ecological integrity. Over the lifetime of a stream crossing, the structure type will impact biological communities such as fish assemblages differently. Structures create physical barriers that can impede the movement of sensitive and less mobile fish species. The goal of this study is to determine how four different stream crossing structures commonly used by the Arkansas Highway and Transportation Department (AHTD) affect fish passage under variable stream conditions. The study will survey fish communities above and below crossings, monitor movements, and weigh the financial costs and environmental benefits of open span bridges, reinforced concrete 4-sided box culverts, 3-sided “bottomless” box culverts, and corrugated metal culverts. The financial cost and benefits will be calculated by estimating materials and installation cost along with the life expectancy of structures, and costs for regular maintenance needed to keep each structure type operating properly. Environmental benefits will be measured by the frequency of fish movement both upstream and downstream of structures and compared with reference sites within the same watersheds. The AHTD is regularly replacing structurally and/or functionally deficient structures with new ones. Some of these changes include the replacement of one structure type with another. This provides AHTD with the unique opportunity to conduct a before and after study directly comparing the ability of fish to utilize different crossing structures on the same stream segments. Some of the changes include bridges being replaced with box culverts, culverts replaced with bridges, as well as, replacements involving a change in the size and number of culvert structures. The ability to select appropriate structures that minimize financial costs and maximize environmental gains could minimize the long term impacts to local biological communities.
Urgency and Payoff
This study has important environmental implications because of Arkansas’ diverse and highly endemic fish communities, as well as 14 threatened or endangered mussel species dependent on fish as hosts for dispersal. With the current state of the aging infrastructure it is time to start examining these impacts now. Results will provide a valuable tool for design engineers to utilize in both environmental and fiscal decision making processes. Appropriate design is crucial on a project specific basis to reducing unnecessary environmental impacts especially on threatened and endangered species.
Nathaniel Goddard Arkansas Highway and Transportation Department 501-569-2281 ext. 49