Fish passage design at road culverts: A design manual for fish passage at road crossings
fish passage, design, culverts, manual, migration, salmonids, engineering, hydrology, fishways, design of fishways, channel, habitat, structures, guidance
This manual is for the design of permanent new, retrofit, or replacement road crossingculverts that will not block the migration of salmonids. The manual is intended for use bydesigners of culverts including private landowners and engineers. The level of expertisenecessary to use this manual varies depending on site conditions and the design option selected.For all but the no-slope design option (described below), it is assumed that the designer has abasic background of hydraulic engineering, hydrology, and soils/structural engineering toaccomplish an appropriate design. Formal fishways may be required at some culvert sites to provide passage. The design of fishways is beyond the scope of this manual though there is abrief description of some basic design concepts included here. A fish passage engineer should beconsulted for additional assistance for the design of fishways. The organization of the manualfollows the logical steps expected in a prudent culvert design. A data form is provided in AppendixF describing the data needed for the design and for those evaluating the design. For explanationsand definitions of terms describing the channel, hydrology and data requirements see theExplanation of Data also in Appendix F. Several case studies showing various culvert designoptions are described in Appendix G. The manual is based on the premise that a culvert is thedesired road crossing option at a site. That does not mean that for fish traffic, fish passage orother ecological functions, a culvert is the actually best solution or even permitted. Though thismanual focuses on fish passage, there are other habitat and ecological considerations that arefactors in the siting and design of road crossing structures. Those considerations are outlined inthe section Other Passage and Habitat Considerations. This manual does not provide guidanceabout the inventory of culverts or the prioritization of culvert barrier remedies. That information isincluded in Fish Passage Barrier Assessment and Prioritization Manual, 1998 by WDFW.