Culvert design is extremely important because fish passage in rivers, creeks and other waterways are essential for reproduction and survival of many fish species. If poor designs of culverts are installed, upstream fish migration can be impeded. Many culverts have been designed especially for fish migration and passage. Culverts have many impacts to stream system even when fish passage is successful including; channel disruption during construction, hydraulic effects up and downstream, increased or decreased flow rates or many other impacts. When stream crossings are necessary three possibilities are considered, a bridge, a culvert, or an environmentally conscious culvert. When considering fish migration, a bridge is most effective although for financial reasons rarely a feasible option. An environmentally conscious culvert is the only other option, which at a reasonable price will successfully allow fish migration and will have minimum disturbance to the stream.
Many different culvert options are available for stream crossings comprising of a no slope design, a hydraulic design, or a stream simulation design. When considering any one of these designs many concerns need to be addressed including; direct habitat loss, water quality, upstream and downstream channel impacts, ecological connectivity, construction impacts, and possible failure. Direct habitat loss can occur if the culvert is installed in current fish spawns, growth areas, feeding areas, or migration areas. Water quality is effected during construction of the culvert as dirt particles or other foreign material enters the stream. Upstream and downstream channels are affected if flow rates are changed by water depth or channel depth and can further effect stream qualities. Ecological connectivity encompasses many factors surrounding the impact of culverts on the streams ecosystem. The movement of the streams ecosystem between upstream and downstream is considered one of the most important factors as the health of fish and other life rely on its ecosystem.
Fish passage can be obtained through no slope culverts if properly designed. No slope design incorporates a culvert in which allows a stream bed to be formed for natural movement as well as a flat gradient. This type of culvert is normally used when little to no disruption can occur to stream as well as simple installations. This type of installation should not be used if the culvert is too long or if the upstream countersink is too high compared to downstream.
A hydraulic design option can be used to situations when culvert design need retrofitting for target species to pass. A hydraulic system has many limitations, as it is more costly and less reliable for steep channels, and does not account for the stream system but rather one target species. Hydraulic culvert systems are designed based on hydrology, species requirements, and water velocity and depth. This design produces the target species ideal stream conditions during...