2012 – We need flood protection in WA too!

Graeme Mann, Michael Smith, Louise Thomas

Regular flooding around the coastal town of Busselton, south of Perth, led to the construction of large rural drains in the 1920s to divert two of the major rivers around the town. Hydrologic studies after major floods in 1997 and 1999 showed that the existing drains were providing much less than the desired 1 in 100 AEP flood protection, particularly as subdivisions were being developed along both sides of the Vasse River Diversion Drain (VDD).
Three compensating basins constructed in rural land south of Busselton provide a total storage capacity of 4.4 GL. The banks that form the three basins have a total length of 8.5 km, vary in height up to 6 m and are either zoned earthfill embankments, with a clay foundation cut-off through sandy soil horizons to a depth of 1 to 2 m below ground level or homogeneous earthfill embankments. The spillways are overflow sections on the embankments using concrete revetment mattresses. The outlet works are uncontrolled box culverts with a capacity of up to 14 m3/s. Peak outflows are typically about 30% of peak inflows to the basins.
The paper discusses the Busselton Flood Protection Project and associated diversion drains, including the design of long embankments for the compensating basins on very flat terrain that are required to survive their “first filling period” during each flood emergency.
Keywords: Earth embankments, flood mitigation, flood compensating basins, levee banks, diversion drains, Busselton, piping failures.