Small hydraulic structures, big environmental problems: is it possible to mitigate the negative impacts of culverts on stream biota?

Abstract

The present study is a broad and critical review of the transdisciplinary literature on the construction of culverts and their impacts on stream hydrology and geomorphology as well as on stream habitats and biota. For engineers, a culvert is a structure, usually of the tunnel type, that transfers a stream or open drain under a road, railway line or other obstacle from one side to the other. In fact, culverts are complex hydraulic structures whose impacts on stream ecosystems must be evaluated and understood before they are designed. The objective of this paper is to analyse and discuss recent knowledge about culvert functioning in terms of their negative effects on the passage of freshwater biota, particularly fish, and on entire stream ecosystems. We present the results of many studies showing that improperly designed culverts are barriers for migrating animals and usually have serious ecological consequences (mainly fish life history disturbances). We also pay attention to different culvert modification methods that increase their passability for organisms and mitigate culvert impacts on the surrounding environment. The other purpose of this review is therefore to emphasize that the integration of the knowledge and professional experience of biologists and ecologists with those of river managers, river engineers, hydraulic engineers, hydrologists and geomorphologists is necessary to design culverts that preserve the natural properties of streams.