Form and Function

Rivers and streams are dynamic and their changing nature needs to be accommodated in planning, expanding or operating transportation infrastructure where roads and other linear infrastructure cross water or occur in a floodplain. This is necessary not only to minimise direct ecological effects to habitat, fish and other aquatic species but also to help reduce the potential damage to infrastructure from flooding, erosion and channel movement. Damage to infrastructure can often lead to additional environmental impacts. 1 Streams need special consideration when planning roads. 2 Protect natural stream processes: avoid constricting natural stream channels. 3 Roads often interfere with natural stream processes, impacting aquatic species. 4 Roads along shorelines: avoid simplifying stream channels and use dynamic natural systems as the model. 5 Reduce impacts at stream crossings by using designs that simulate natural channel conditions. Fish and aquatic organisms, such as amphibians, reptiles and invertebrate species can be directly affected by roads, especially at water crossings. If these are not designed correctly, crossings result in the direct loss of natural habitat and can become barriers to movement caused by high velocity, inadequate water depth or excessive drops, especially at the outfall. To help minimise these problems, it is best to accommodate the natural conditions of streams, allow for a wide range of natural stream flow channels, avoid constricting flows and avoid reducing channel and shoreline complexity.