Hydraulic modelling study - Huon Valley, Tasmania
Client: Huon Valley Council
Location: Huon Valley, Tasmania
Date: July 2017 – July 2018
Supporting flood estimation, mitigation and planning in a flood-prone region
The Huon Valley, south of Hobart, has experienced a number of major flood events over the last century. In July 2016, the Huon River peaked at 4.3 m – its highest level in 20 years – damaging 30 buildings and requiring evacuation of 20 people.
The Huon Valley Council had previously engaged Entura to undertake a flood study and emergency management planning for the Huon River. Previous work also included mitigation options for Huonville Main Drain, which flows through Huonville and can cause areas to be inundated.
In 2017, Entura was engaged to calibrate the Huon River XP SWMM flood model to the 2016 flood extents, and to create hydrologic and hydraulic models for Mountain River, Kermandie River and Skinners Creek. The studies included three mitigation options, flood hazard assessment and preliminary evacuation planning.
The Huon River flood model did not match the 2016 flood extents due to an incorrect rating having been adopted to generate the inflow hydrographs. Entura developed a more representative rating which provided more realistic inflow hydrographs matching the flood extent. The Manning’s roughness coefficients were also adjusted to match the calibration data.
Entura’s modelling and site visit to Skinners Creek, which flows through Huonville, uncovered a flow split into the adjacent Huonville Main Drain catchment. Huonville Main Drain causes inundation and hazards in Huonville even without any additional flow from Skinners Creek.
To address the hazards in Huonville caused by the Main Drain, Entura designed a mitigation concept which diverts the Main Drain into Skinners Creek, with appropriately sized open channels and reinforced concrete pipes to cope with a 1% AEP flood accounting for climate predictions.
The key findings and mitigation concept design were critical as a new subdivision was beginning to be developed in the flood plain.