Coastal erosion risk is rising as sea-levels accelerate and storms intensify, threatening beaches and infrastructure. To address this, strategic planning for the sandy shore must replace outdated hazard mapping with data-driven, regionally consistent methods that account for sediment movement and geomorphic variability to identify high-risk areas and guide adaptation. The sediment compartment approach can help with this planning.

This sediment compartment approach is a practical framework for use in coastal management and regional planning. The framework divides the coast into areas with interconnected landforms and sediment processes. The boundaries serve as natural barriers to sediment transport, allowing each compartment to be treated as a semi-closed system with identifiable sources and sinks of sediment.

A coastal sediment compartment is a section of coastline that shares a common sediment resource with clearly defined physical boundaries. These compartment boundaries are natural landmarks such as headlands or river mouths, which limit the movement of sediment between adjacent areas.

Australia’s coastline has been mapped as series of compartments based on landforms and patterns of sediment (sand and other beach material) movement. There are three main levels of compartments, each suitable for different types of decision making:

• primary level based on the influence of large landforms and offshore processes, suitable for regional planning or large-scale engineering such as ports
• secondary level on medium landforms and regional sediment processes, useful for smaller engineering or local planning decisions
• tertiary level based on individual beaches, suitable for very small projects unlikely to restrict sediment movement, such as deciding the exact location of a groyne or sea wall within a broader management plan.

A nested hierarchy of compartments has been developed to reflect the variability in sediment transport over time and space. Large primary compartments set the context for analyzing smaller secondary and tertiary compartments, and are useful for understanding historical trends, current processes, and broader risks such as erosion and accretion.

This approach is useful for open coastlines and does not cover detailed sediment dynamics in estuaries or coastal lakes.

The sediment compartments approach was developed by a team of coastal experts in 2015. A similar model is already in use in countries like the United States, the United Kingdom, and Europe, helping to manage sediment movement across administrative borders.

CoastAdapt includes maps of primary and secondary coastal compartments and their attributes, together with further information on their use.

CoastAdapt's sediment compartment approach also provides a susceptibility rank, which is a useful development. The rank - numbered from 1 to 5 - indicates the likelihood and nature of coastal change in each secondary compartment.

1. Accreting at present, and likely to continue in future
2. Stable and likely to start accreting in the future
3. Stable and likely to stay stable
4. Stable but likely to start eroding in future
5. Receding and likely to continue eroding in future.

Your local government may have available more detailed coastal information related to your location that you may also wish to consider.

A sediment compartment approach can be used for:

• strategic planning: to identify high-risk areas for development and infrastructure using geomorphology and sediment connectivity, not simple buffers.
• forecasting change: to model long-term shoreline recession under sea-level rise and sediment redistribution.
• adaptation prioritisation: to guide protection, retreat, or nourishment projects without disrupting sediment-sharing systems.
• hazard mapping: to refine erosion zones for local planning, especially in complex or data-poor areas.
• uncertainty communication: to provide probabilistic hazard zones (e.g., 50%, 10%, 1% exceedance) for transparent decision-making.

The following steps can help to make use of coastal compartments information in coastal management and adaptation.

1. Review coastal compartment data:
   1. Start by looking at the coastal datasets information.
   2. Identify the level of susceptibility for the compartments that relate to your local government area or location of interest. This is in a scale of 1 to 5, with higher numbers indicating a greater susceptibility to erosion, and lower numbers a greater susceptibility to accretion.
   3. Note it is important to not place infrastructure that could disrupt coastal processes in highly sensitive compartments.
2. Assess susceptibility levels
   1. If the susceptibility to change is medium to high - for example 4 or 5 - it is useful to get expert advice on the cause of the erosion risk. It is important to understand whether it is from high volumes of longshore sediment transport, or a deficient offshore sand supply.
   2. Limited offshore sources of sand are often revealed in beaches where recovery from storm erosion is slow or incomplete.
   3. A high level of susceptibility suggests that planning may need to consider adjacent compartments.
3. Seek expert advice for high value development or high risk areas
   1. If a compartment has a high ratings (4 or 5), then consult coastal experts to determine the cause of erosion risk.
   2. Key factors may include:
      1. High volumes of longshore sediment transport or Limited offshore sand supply.
      2. Slow or incomplete beach recovery after storms often indicates a deficient offshore sand source.
      3. High susceptibility may also require consideration of adjacent compartments.
4. Evaluate development scale and impact
   1. Consider the scale of planned development in the coastal compartments. If you are planning for a large or high-value development or piece of infrastructure - for example a hospital - it is useful to consider the implications of that development at all compartment scales.
   2. Use detailed impact modelling using local data will also be needed for large developments or for critical infrastructure.
   3. For many smaller decisions, it is appropriate to consider implications up to secondary compartments.
5. Consider compartment boundaries.
   1. If a planned development is near a compartment boundary, it is also useful to consider the adjacent compartment and adjoining councils in planning, assessment and decision-making.

You will also need other sources of information for effective coastal planning and management, particularly where the compartment sensitivity rating is high. Some local councils may have available more relevant and detailed coastal information.

Example: Sediments and two adjacent compartments

• You will need to understand the local sources and behaviour of sediments to design effective coastal protection measures.
• In sediment deficient compartments, such as around Old Bar in New South Wales, there are limited sources of sand that can replenish eroding beaches without other consequences.
• This is in contrast to the neighbouring Foster-Tuncurry secondary compartment which is rich in sediment.