Management plans for coastal erosion should be based on the principle of working with natural processes. The EUROSION recommendations [1] propose four concepts to assist in making this principle operational:

1. Coastal sediment cell
We already encountered the coastal sediment cell in the previous chapter, where it was defined as a coastal compartment that contains a complete cycle of sedimentation including sources, transport paths and sinks. The cell boundaries delineate the geographical area within which the budget of sediment is determined, providing the framework for the quantitative analysis of coastal erosion and accretion. In this respect, coastal sediment cells constitute the most appropriate units for achieving the objective of favourable sediment status and hence coastal resilience. The application of coastal sediment cells requires the establishment of a sand budget for a coastal area. This gives an insight into the relative importance of the various sediment sources and losses, resulting in deposition and erosion. The determination of the correct fluxes for specific coastal environments is sometimes surrounded with large uncertainties which could make the job of the coastal manager more difficult.

2. Coastal resilience
Coastal resilience is the inherent ability of the coast to accommodate changes induced by sea level rise, extreme events and occasional human impacts, whilst maintaining the functions fulfilled by the coastal system in the longer term [1]. Because resilience is based on natural processes, it varies between different coastal types: a beach dune coast is obviously more resilient than a cliff coast because of the self restoring capacity of dunes.

Note that this definition does not require a coastline to remain in an equilibrium state. Especially on longer time scales most coasts are evolving systems an are not necessarily in equilibrium [11]. Coastal resilience therefore should refer to coastal functions: compatibility and adaptability of uses to coastal erosion management which allows natural fluctuations of the coastline.

3. Favourable sediment status
EUROSION proposed the introduction of the concept of favourable sediment status as the cornerstone for sustainable shoreline management to European legislation but this was not realised. It is defined as the situation where the availability of coastal sediments support the objective of promoting coastal resilience in general and of preserving dynamic coastlines in particular. A neutral or positive sediment balance is often required to arrive at this favourable status. As we can see from the diagram on page 9, we can expect that the impact of sea level rise results in a higher demand, which - if not supplied - will lead to coastline retreat.

A favourable sediment status for the coastal zone shall be achieved for each coastal sediment cell principally through sediment management including nourishments and the designation of strategic sediment reservoirs in combination with traditional measures such as spatial planning, building regulations and environmental assessment procedures. As we will see later, not only the availability of sufficient sediment is required, but also the spatial distribution needs attention.

4. Strategic sediment reservoirs
Strategic sediment reservoirs are supplies of sediment of ‘appropriate’ characteristics that are available for replenishment of the coastal zone, either temporarily (to compensate for losses due to extreme storms) or in the long term (at least 100 years). They can be identified offshore, in the coastal zone (both above and below low water) and in the hinterland.

It is recognised that many coastal erosion problems are caused by a human induced imbalance in the sediment budget. Natural sediment sources are depleted by sand mining activities, trapped in river reservoirs upstream or fixed by coastal engineering structures. Restoring this balance will require identifying areas where essential sediment processes occur, and identifying strategic sediment reservoirs from where sediment can be taken without endangering the natural balance.

5. Why are these concepts important?
These concepts are interlinked through coastal processes but they also have a policy and management dimension. Take for instance the favourable sediment status. It refers to the sediment balance and distribution within a coastal cell, but also to a certain desired state. To describe the sediment balance as ‘favourable’ depends on the objective for erosion management. If erosion is not acceptable, the sediment balance should be such that there is no net loss of sediment out of the coastal cell. Due to the dynamic character of soft coasts also the sediment balance is dynamic. For instance in the stormy season the sediment balance can be negative, while during calm weather it may be positive. Therefore, coastal erosion management should consider both a short and long time frame. The short time frame that addresses hours to days is needed to anticipate extreme events, such as storms, which can lead to sudden erosion. The long time frame of decades to centuries is important when considering the impact of climate change, which is likely to significantly increase coastal erosion in the future.

For a sediment status to remain favourable, a strategic sediment reservoir is required. Sediment reservoirs can fulfil two roles in this respect. In the first place they should be conserved as a source of sediment when needed in the future to maintain the proper sediment balance. The coastal cell receives a sediment input from the reservoir, either through natural transport mechanisms or artificial nourishment. Typically, such a sediment reservoir is located outside of the coastal cell.

Secondly, a sediment reservoir may also be defined within a coastal cell. This is when the actual location of the sediment is important. It may be necessary to spatially define a sediment reservoir within a coastal cell in fairly great detail. For instance as a volume of sand above storm surge water level to prevent flooding of the hinterland.

Working as much as possible with natural processes implies that the favourable sediment status will fluctuate: the status need not to be sufficient at any point in time. As a consequence, managers should anticipate a certain fluctuation of the coastline. Therefore, coastal resilience is imperative for sustainable coastal erosion management. Coastal resilience should be maintained as much as possible by ensuring sufficient buffer between the coastline and the built up area. Implementing set-back lines is a useful measure for this [see "How are setback lines defined?"].

6. How does management of coastal erosion relate to ICZM?
Many of the principles of good ICZM contained in the EU Recommendation [12] are relevant to the implementation of a sustainable approach to erosion management. These principles include taking a long term perspective, local specificity, involving all the relevant parties and working with natural processes. Therefore, management plans for coastal erosion should be part of a broader policy on ICZM. Such policy provides the objectives for coastal erosion management, such as whether or not to hold the line, or allow some coastline retreat to a certain extent. In the next chapter we will show how important it is to formulate policy objectives for erosion management.