Acknowledgement Goulburn-Murray Water
Broken Creek in north-central Victoria flows into the River Murray upstream of Barmah. There are 10 low-head (\u3c2 m high) weirs on Broken Creek which all have vertical slot fishways however these have high turbulence (i.e. 75 W/m3) and thus limited functionality for several species of native small and medium sized fish (i.e. \u3c300 mm long).
In late 2017, the Victorian government (DELWP) engaged Jacobs and Kingfisher Research to hydraulically model the Rices and Kennedy’s Weir fishways to prepare conceptual designs for retro-fitted ‘key-hole’ slots to reduce pool turbulence and demonstrate potential for improvement in functionality to pass much smaller fish (i.e. \u3e50 mm long).
Jacobs applied a Microsoft Excel based fishway model which takes fishway geometry, calibrated slot discharge coefficient data, and headwater/tailwater ranges, and uses these data to predict individual pool turbulence, depth and slot velocity. These hydraulic outputs were combined with fish swimming ability, maximum allowable turbulence, and minimum water depth to graphically demonstrate water level ranges for which each fishway could pass small, medium and large-sized native fish. Conceptual level ‘key-hole’ slot designs were then developed, reducing slot areas and flow rates and enabling passage of all fish sizes.
The modelling showed that The theoretical implementation of ‘key-hole’ slots effectively halved the fishway discharge and reduced the pool turbulence to 35 W/m3, the known threshold suitable for passage of small-sized native fish.
This project demonstrated the efficiency of Microsoft Excel based modelling to bring together both fishway hydraulics and fish biology, with novel design options rapidly evaluated for a low cost. Graphical fishway operation tables were automatically produced for the full range of site operational conditions without the need for costly post-processing of model results.
GBCMA propose to retrofit key-hole slots to Rice’s and Kennedy’s weir fishways to improve their performance during 2018
