the passage of small fish, specifies water velocities below 0.15 m/s and zero headloss under most operating conditions (Mallen-Cooper 2001). The impacts that culverts may have on fish passage is outlined in 1, noting that these impacts vary across culvert zones (Kapitzke 2010; see Figure 2.2). Table 2.1: Barrier effects of culverts. Barrier effect Impact on fish passage Culvert velocities pose a barrier to fish passage when the distance High velocity due to: between rest points is greater than the maximum distance fish can steep gradient culverts swim at burst speeds. uniform channel with lack of roughness constriction of waterway at the culvert Shallow water can inhibit fish swimming effectively, particularly Shallow depth due to: larger species. Fish may become injured, especially in high flow gradient culverts conditions. wide culvert bases that disperse flow Lack of resting place or shelter due to: Lack of resting places pose a barrier to upstream fish passage if the length between shelter areas is greater than the maximum simplified channel form distance fish can swim between resting. lack of substrate complexity Excess turbulence due to: Turbulence levels may exceed tolerance of particular fish and therefore present a barrier to upstream movement. Fish lose ability steep gradient culverts to navigate through the culvert and they are unable to recognise constriction of water at culvert inlet primary flow direction. upstream build up low tailwater levels Excessive head loss due to: Many Australian native fishes have little capacity to jump and are sudden change in bed profile therefore unable to negotiate small water surface drops. Low levels of light due to: Many Australian native fishes have a tendency to avoid dark areas long, narrow culverts and may not enter culverts with reduced light levels relative to the stream outside of the culvert. Figure 2.2: The impacts of culverts across culvert zones (from Kapitzke 2010). 6 Guidelines for fish passage at small structures
the passage of small fish, specifies water velocities below 0.15 m/s and zero headloss under most operating conditions (Mallen-Cooper 2001). The impacts that culverts may have on fish passage is outlined in 1, noting that these impacts vary across culvert zones (Kapitzke 2010; see Figure 2.2). Table 2.1: Barrier effects of culverts. Barrier effect Impact on fish passage High velocity due to: steep gradient culverts uniform channel with lack of roughness constriction of waterway at the culvert Shallow depth due to: gradient culverts wide culvert bases that disperse flow Lack of resting place or shelter due to: simplified channel form lack of substrate complexity Excess turbulence due to: steep gradient culverts constriction of water at culvert inlet upstream build up low tailwater levels Excessive head loss due to: sudden change in bed profile Low levels of light due to: long, narrow culverts Culvert velocities pose a barrier to fish passage when the distance between rest points is greater than the maximum distance fish can swim at burst speeds. Shallow water can inhibit fish swimming effectively, particularly larger species. Fish may become injured, especially in high flow conditions. Lack of resting places pose a barrier to upstream fish passage if the length between shelter areas is greater than the maximum distance fish can swim between resting. Turbulence levels may exceed tolerance of particular fish and therefore present a barrier to upstream movement. Fish lose ability to navigate through the culvert and they are unable to recognise primary flow direction. Many Australian native fishes have little capacity to jump and are therefore unable to negotiate small water surface drops. Many Australian native fishes have a tendency to avoid dark areas and may not enter culverts with reduced light levels relative to the stream outside of the culvert. Figure 2.2: The impacts of culverts across culvert zones (from Kapitzke 2010). 6 Guidelines for fish passage at small structures
ARI-Technical-Report-276-Guidelines-for-fish-passage-at-small-structures.docx