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Flood study

East Hills Floodway Model Investigation

This Report details the results of a hydraulic model investigation into flooding along the Georges River at East Hills. The investigation was undertaken by Manly Hydraulics Laboratory as part of a study by the Rivers and Ports Branch for Bankstown City Council.

A physical model of horizontal scale 200 and vertical scale 50 was constructed using recent hydrosurvey and ground survey information.

The model study was conducted in two stages separated by a gap of three years. For the second stage, the design floods had been reassessed. An additional flood event in August 1986 was available tor verification.

The first stage involved:

  • Tuning the model using flood data from the 1956 and 1978 floods, as well as tidal data;
  • ModeI testing a range of flood discharges and tailwater levels encompassing an early estimate of 1 in 100 year flood;
  • Obtaining river channel water levels and velocities for the full range of tests;
  • Determining overbank velocities and detailed flow paths for a discharge of 2100m3/s and a 4.7m tailwater at Deadmans Creek;
  • Testing the effects of four flood mitigation options (i.e. Options I to 4) under the central design flow conditions.

The second stage was prompted by requirements to test additional management options for flood discharge and peak flood levels. This stage involved:

  • Testing the accuracy of the model with respect to Stage I using the previous I in 100 year flood condition of 2100m3/s discharge and 4.7m tailwater.
  • The verification of the model against the recent 1986 flood.
  • Testing a more recently derived 1 in 100 year flood with a discharge of 2300m3/s and corresponding tailwaters of 4.Sm and 4.Im at Deadmans Creek. Overbank velocities and flow paths were obtained in addition to water level measurements.
  • Testing the effects of several new flood mitigation options (i.e. Options 5 to 8) using the new I in 100 year flood discharge and both tailwater levels.

The model satisfactorily reproduced the 1986 floods and showed that, under existing conditions, approximately 80 properties in the study area experience inundation. Properties near the East Hills Footbridge experience depths of up to 4m. Flow velocities of up to 2.5m/s were measured adjacent to several houses.

By using several combinations of finger levees (Options 2, 3, 4, 6A and 6B) various degrees of flow velocity reductions were achieved without changing the level of inundation. The two options involving ring levees (1 and 5) prevented inundation up to 1 in 100 year flood conditions in the selected areas.

All of the levee options caused minor upstream afflux but this had attenuated to within the accuracy of measurement at Milperra Bridge.

Options 7 and 8 were purely non-structural, involving house removal and house relocation.

Additional Information

Field Value
Title East Hills Floodway Model Investigation
Publication Date 1 October 1987
Themes Land and Resource Management
Spatial Extent
Map data © OpenStreetMap contributors
Council/LGA Canterbury-Bankstown Council
Author/ Prepared by Sparkes and T. Vera-Cruz; MHL; Rivers and Ports Branch Public Works Department
Publish date 7 June 2017
Update date 27 June 2017
Place Name East Hills
Approval State Approved
Submitted for approval 8 June 2017
Submitted by John Silk
Approved 28 June 2017
Approved by plattns
Data Comment

Report only; no other data. Legacy data; may have been superseded.

Identifier fd930f1c-4728-403f-b1af-6be224c3e83a