Proposed flood diversion canal cross sections, 1896

Proposed flood diversion canal cross section, 1896. After the ‘Great Flood’ of February 1893, the Water Supply Department and its director, J.B. Henderson, investigated the possibility of building flood diversion canals to protect the city. This cross section map shows one canal leaving from Oxley and the other leaving from Yeronga, both with a common outlet at Tingalpa Creek at the ocean. This map shows that the maximum depth of cutting for the upper canal would be approximately 252 feet and, for a length of around 8.5 miles, the average depth would be about 120 feet. For the lower canal, the maximum cutting depth would be about 170 feet while for a length of around six miles the average depth would be 100 feet. According to Henderson’s report, both canals would have ‘colossal dimensions’ and rival some of the largest canals in the world. As shown by another map depicting the proposal, either canal would require purchasing land between the Brisbane River and Moreton Bay. The canals would also require the construction of several new rail and road bridges, revetting to protect embankments, and finally an inlet weir. According to Henderson’s calculations, the excavation alone would cost £9,523,194 for the upper canal, and about £7,138,000 for the lower canal. In addition to affecting navigability and tidal behaviour of the Brisbane River, the canals would need frequent dredging. Henderson advised parliament to abandon consideration of this and other similar schemes. Queensland votes and proceedings, vol.4, 1896