What is flood mitigation?

When considering structural solutions, it’s important to understand the effectiveness of individual measures in terms of flood mitigation impact. For example, some works may reduce flooding to a large area by centimetres which providing a minimal benefit to a large number of homeowners that are least affected by flooding and almost no benefit to those homeowners that are worst affected.

From Darwin to Alice Springs, many areas in the Northern Territory (NT) are prone to flooding, from storm surge in coastal areas to flash flooding in creeks. Flooding can happen in built up urban areas due to an increase in the rate of storm water runoff or towns and suburbs built within floodplains. Poor stormwater management can also cause localised flooding.

Depending on locality and the nature of the flooding, a number of structural (infrastructure) and non-structural (flood resilience) mitigation measures may be available. However, flood mitigation measures may only lessen the impact of flooding. No amount of intervention can stop heavy rain or high tides.

The community, local businesses, emergency services, local council and government need to work together to reduce the impact of flood waters. The Northern Territory Government is committed to assisting residents in flood-prone areas through a range of flood mitigation options.

Structural flood mitigation

Structural flood mitigation is where physical structures are constructed or modified to reduce the impact of flooding on individual properties or whole catchments and include:

Infrastructure, including dams, levees, bridges and culverts

When considering structural solutions, it’s important to understand the effectiveness of individual measures in terms of flood mitigation impact. For example, some works may reduce flooding to a large area by centimetres which provides minimal benefit to a large number of homeowners that are least affected by flooding and almost no benefit to those homeowners that are worst affected.

Maintenance of existing infrastructure

Ongoing maintenance to existing creeks and stormwater drainage systems is vital to maintain the hydraulic performance of the drain. Developing and reviewing a regular maintenance schedule for flood prone areas can provide significant benefit during seasonal rains. While clearing creek systems does not help always reduce the impact of large flood events, it does help reduce the impact of smaller, more frequent floods.

Individual flood proofing measures

Where the inundation of flood water is relatively low (nominally less than 700mm), it may be possible to keep flood waters out of homes by installing solid fences, raising windows, sealing doors with ‘stop boards’ and limiting sewage contamination through reflux valves.

Improved traffic access

Improving the flood resilience of roads provides a benefit to flood-affected residents by allowing residents to escape floods and emergency services to get in to assist. Key routes to essential services such as hospitals and emergency shelters should have at least a Q100 flood immunity.

Non-structural flood mitigation

Property surveys

Detailed survey of flood affected residences can increase the accuracy of flood modelling so that homeowners, insurers and buyers can understand the actual impact of flooding on each property.

Land use planning controls

Strategic land use planning will identify the extent of flood impacted land to limit the construction of urban and rural residential, commercial and industrial land. The NT Planning Scheme requires all new developments to undertake land suitability investigations to determine the extent of constrained land.

Building and development controls

Existing building controls require new homes or substantial renovations to construct habitable floor levels 300mm above Q100 year flood levels, in order to provide some level of protection from flooding.

Catchment flood modelling

Maintaining up to date flood models of developing catchments assists the Development Consent Authority to understand the impact of new development on existing residents in the catchment. New land developments are required to manage the rate at which stormwater leaves the development to maintain the pre-development rate of flow.

Early warning systems

As many floods occur at night, early warning systems are extremely important in flash flooding events to provide residents with the ability to respond to impending flood waters. This may include moving vehicles, collecting pets and valuables and implementing personal emergency plans.

Develop a household emergency plan

In conjunction with a household emergency kit, a household emergency plan is essential for all Territorians. Regardless of any mitigation measures, every household must be prepared for extreme weather, including flooding.

Access to information and warnings

The Northern Territory Government's Secure NT website gives advice on planning for emergencies and provides up-to-date information during and after emergencies including major flooding, extreme weather and cyclones. Other useful sites include:

Go to the Northern Territory Government website to view storm surge flood maps and flood plain maps.

Understanding and awareness

Knowing your local flood history and developing an understanding of how floods behave in your area provides you with the ability to respond in time to the impending flood. Watching tide and rainfall forecasts can alert residents when the conditions that may result in flooding could occur.

Last updated: 28 November 2017