NSW Government Floodplain Management Program Grant funding was provided for the investigation and design of the upgrade of the existing Aberdeen levee. The upgrade will provide a 1% Annual Exceedance Probability (AEP) standard of protection for the township of Aberdeen to mitigate the flood risk to the town. The proposed Aberdeen levee upgrade works was recommended in the Aberdeen Floodplain Risk Management Plan 2015.
The Wallalong Levee forms part of the Hunter Valley Flood Mitigation Scheme and is designed to reduce the impacts of minor to moderate floods to 450 hectares of agricultural land.
Flood modelling shows there are some potential changes to the way the floodwaters will behave. According to this modelling flooding may occur earlier than previously experienced and may be deeper. No two floods are the same and the modelled effects on flood behaviour vary for different flooding scenarios.
The Department has undertaken a process of investigating levee remediation design options that would return flood behaviour to pre-2016 levels. The investigation was informed by input from the community through a Community Reference Group which included landholders from areas surrounding the levee.
Stage one remediation work was completed in 2020
Stage 2 bank protection works are yet to be planned due to the impacts of recent flooding.
Wallis Creek floodgates were constructed in the 1940s and forms part of the Hunter Valley Flood Mitigation scheme (Scheme, HVFMS). The floodgates are located on Wallis Creek, approximately 1km east of Maitland. Wallis Creek meanders across a low-lying floodplain to connect with the Hunter River downstream of Maitland. The floodgates are one of the most significant flood-mitigation infrastructures among the Scheme assets and comprise 10 floodgates with sizes 4.2mX3.3m each. In 2018, departmental floodplain engineers investigated its structural integrity and determined its solidness with the recommendation to improve stilling basin re-instalment. Improved stilling basin will reduce the flood velocity downstream, thereby reducing erosion at the confluence zone of the Hunter River. Works are yet to be scheduled.
In 2018 the Department engaged Royal Haskoning DHV (RHDHV) to undertake an assessment of Scott’s Dam levee as per Dam Safety NSW guidelines. The assessment determined a very unlikely scenario exists where the dam could fail. The likelihood of failure from this event is considered low; occurring with a major flood event on the Paterson River with no flooding in the Hunter River. Following the criteria the Department has been engaged Molino Stewart to develop an Emergency Management Plan (EMP) for the Scotts Dam. Building community resilience and raising awareness of the site-specific emergency response plans is the main focus for the Department.
The EMP is due to be finalised in 2022.
There have been significant population and land use changes throughout the catchment and particularly the floodplain since the Scheme’s commencement. The population has more than doubled and future growth within the floodplain is forecast. Being the largest regional economy in Australia, the Hunter Valley is a complex region with highly diverse natural, cultural, social, and economic values.
Changing land use and community expectations will affect how the Scheme is managed into the future.
A strategic review of the Scheme is currently underway to assess whether it will be fit for purpose into the future. The review will also assess whether current management arrangements are aligned with government policy and community expectations. The review will provide the information required to efficiently prioritise future investment in the Scheme, and inform decisions about future funding sources. It must ensure that the government and Hunter Catchment Contribution Levy payers receive maximum value for their investment in the Scheme.
The strategic review will be available through the have your say page in late 2022.
The heritage floodgate structure was built by the Eales family as part of the Brisbanefields Estate, possibly as early as 1874 and certainly by 1894. Due to the nature of the damage to the structure over the years it is necessary to undertake remedial works. Public Work Advisory (PWA) was engaged by the Department for structural integrity assessment options in July 2019. The assessment determined the culvert-floodgate is structurally unsafe mainly due to excessive foundation settlements and return wall displacements. Following this, the Maitland City Council has imposed a 10-tons load limit on the structure as an immediate response to their structural weakness. Simultaneously, a temporary access road is under construction for heavy vehicle use until remediation. The remedial construction is expected to commence in 2022.