As part of SARFIIP, Jacobs and Kingfisher Research prepared designs for two integrated regulator and fishway structures at the Pike floodplain for SA Water, DEW and the MDBA. These structures will enable the future managed inundation watering of Pike during regulated river flows to restore floodplain health and fish passage connectivity through the floodplain.
A successful floodplain flow regulator and fishway design requires that fish are able to readily locate and enter the downstream entrance. The entrance must be located at the ‘limit of fish migration’, represented by either a wall or a line of turbulence below the regulator gate that fish cannot pass. The upstream fishway exit must be located where fish are not drawn back downstream over the gates.
To confirm the optimal fishway entrance and exit arrangements, a 1:15 scale physical model was constructed and tested at the UniSA AFMG facilities. The model was designed to enable the performance of critical elements to be identified and if necessary, quickly adjusted.
The sheet-metal model incorporated six lay-flat regulator gates and an adjustable downstream fishway entrance. The model was tested for variable scaled passing flows up to 3,000 ML/d.
The modelling revealed the existence of complex hydraulics and the need to maintain the integrity of attraction flows to the fishway entrance. A ‘flow straightening wall’ was incorporated to ensure positive velocity vectors downstream of the entrance. A nib wall was provided across the regulator below the overshot gates to form the ‘limit of fish migration’, aligning with the fishway entrance. The location of the fishway upstream exit was also confirmed and the optimised arrangements demonstrated to the client.
In summary, low-cost physical modelling was undertaken to optimise the fishway designs and provide certainty to the biological functionality of the structures and this helped maximise ecological value for investment.