Monitoring Stream and Watershed Restoration

Chapter 10: Evaluating Fish Response to Culvert Replacement and Other Methods for Reconnecting Isolated Aquatic Habitats

George Pess, Sarah Morley, and Philip Roni


The reconnection of isolated aquatic habitats is a common goal of many watershed restoration efforts. Previous chapters have discussed road improvements, floodplain restoration, estuarine restoration, improvements of instream habitats, and other types of restoration that include removal of artificial barriers to fish migration. For example, many road rehabilitation projects include removal or replacement of culverts that are impassable to fish. Instream and riparian projects often are completed alongside culvert removal projects. Estuarine and floodplain projects often include removal of levees or water control structures that impede fish access to important off-channel habitats. In this chapter, we discuss how to monitor and evaluate fish response to reconnection of isolated habitats or to the removal of artificial migration barriers. We provide an overview of the problem, discuss how methods and designs for monitoring fish response to removal of migration barriers might differ from types of restoration previously discussed, and provide examples and recommendations of what and how to monitor. We only briefly discuss physical monitoring, because it has been covered in detail in previous chapters. Hydraulic evaluations of different types of culverts and stream crossing are covered in texts and agency documents on engineering and fish passage design (e.g., Clay 1995; ODFW 2001; WDFW 2003).

Fish passage through culverts, tide gates, and other artificial barriers in streams and estuaries is critical to maintaining connectivity among habitats (Roni et al. 2002). Roads, culverts, levees, pipeline crossings, and other man-made stream crossing structures can block access for migratory fishes and other aquatic fauna, and can biologically disconnect large amounts of aquatic habitat from the river system. Such structures also can compromise delivery of materials, including sediment, wood, organics, and marine-derived nutrients, or, in the case of estuarine and off-channel habitats, the influx of water and nutrients.