INVESTIGATION AND PLANNING CONSIDERATIONS
Barriers within a catchment should be assessed and prioritised to focus resources on those that will maximise fish passage. Pethebridge et. al. (1998) provides a useful methodology for such studies.
Recent research conducted by NSW Fisheries on waterway crossings on four streams in northern NSW has found that the numbers and diversity of native fish species were generally greatest below the first culvert or causeway crossing of a stream, at the lower end of a catchment (NSW Fisheries in prep.). The numbers and diversity of native fish were progressively reduced at each consecutive culvert or causeway crossing. This research indicates that rehabilitation efforts should focus on those barriers located at the lowest end of the catchment.
All waterway crossings, even "fish friendly" crossings, have the potential to impact upon the natural passage of aquatic and terrestrial wildlife. Therefore, a primary objective of strategic planning should be to minimise the total number of crossings - further to this, the following principles should be considered:
Avoid crossing waterways at or near sharp bends, sections of unstable channel, or major "riffle" systems. Riffles are shallow areas where water flows swiftly over rocks, gravel or timber. They act as channel stabilisers and by altering their stability essential habitat pools may be lost or severe bed erosion can be initiated.
Avoid locating crossings over "meandering" waterways where such meandering is likely to continue in the future and cause damage to the structure, erosion of the waterway channel, or the future misalignment of the channel with the crossing.
Avoid works that may change the frequency or spacing of an existing pool – riffle system.
Avoid disturbances to sections of a waterway channel or its associated bank vegetation, particularly where such areas represent either a unique, endangered or highly valued section of the waterway.
Avoid the removal of essential shade trees especially on waterways that have already experienced a significant loss of the natural vegetation cover.
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A detailed site assessment should be used to determine whether fish and aquatic habitat are present, the preferred type of watercourse crossing and the presence of existing barriers to fish passage both upstream and downstream of the proposed crossing. If fish are not observed, the presence of fish may need to be confirmed by checking the scientific literature for records of fish species caught either within the site or catchment area and by talking to local residents and fishing clubs. In all cases, the local fisheries department/authority should be consulted to determine whether the crossing design requires consideration of fish passage.
Table 1 provides one way of assessing fish passage needs and waterway crossing preferences.
fish passage requirements for waterways crossings