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NSW Coastline Management Manual

New South Wales Government
September 1990

ISBN 0730575063

Section 5: Hazard Management Options - continued

5.3 SELECTION OF MANAGEMENT OPTIONS

The intention of this section is to provide an indication of the more likely management options which may be appropriate in a range of circumstances. The approach used is to adopt the two broad categories of "low" and "high" development and to indicate the application of management options in addressing the hazards in each case.

A "high" level of development refers to a coastline characterised by intense urban use (e.g. residential, commercial) supported by substantial urban infrastructure (roads, water supply, sewerage, etc.). Surfers Paradise and Collaroy are examples of high levels of coastline development.

A "low" level of development is taken to mean a coastline characterised by rural or other non-urban uses. An important characteristic is also that land holdings are large single ownerships rather than urban sized allotments.

In fact there is a continuum between one extreme and the other. The subdivision into the two categories is convenient for discussion purposes and is intended as a starting point for consideration of options. Each situation on the coastline is unique and in the final analysis needs to be considered individually.

The above classifications are largely synonymous with "damage potential". Obviously a coastline with a high level of development has a high damage potential. Whether or not this damage potential is realised depends upon the extent of the hazards and the presence and effectiveness of any protective works.

It must be stressed that each situation along the coastline is unique and that individual solutions will emerge for each, depending on the particular degree of hazard and the economic, social and ecological conditions applying. Nevertheless it is considered that there are specific characteristics of each situation similar to those for the "high" and "low" development cases which can be used to broadly group options.

The discussion that follows might be considered as two case studies of a very general nature which provide some guidance in the selection of options for consideration in specific situations.

5.3.1 Low Development

Areas in the category of "low" existing development will usually, but not always, be outside the urban areas with existing land use zonings being non-urban, rural, open space or similar. The obvious characteristic will be little if any physical development and thus a low level of asset value. An important social consideration will be that landholdings will tend to be large single ownerships, even if subdivision has taken place. Where there is little or no existing development the conservation of ecological values is more likely to be a significant consideration.

(a) Environmental Planning

Where there is little or no development already existing the opportunity presents itself to manage the area by avoiding the potential coastline hazards. It is likely therefore that environmental planning will provide the most appropriate management strategies. While avoidance of the hazards is the most likely approach, should there be reasons for planning some forms of development within hazardous areas, other options are available to manage the coastline hazards.

Options available within the general category of environmental planning include restrictive land use zonings, planned retreat and voluntary purchase. This latter option would usually be associated with other options to cater for whatever development may exist or to provide for some specific purpose. These options were discussed in detail in Section 5.2.1.

The way in which land use zoning can be used to manage individual hazards is discussed below:

(i) Beach Erosion

Beach erosion, that is the short term fluctuation of the beach, without any shoreline recession can readily be managed by planning options. The extent of the hazard can be defined to within reasonable limits and is not progressive. The concept of creating land use zones encompassing the hazard area and precluding most development is an appropriate option.

(ii) Shoreline Recession

The progressive nature of shoreline recession puts a qualification on planning options as a means of managing the hazard. In broad terms, unless any zone encompasses the ultimate extent of the recession, the hazard area will at some future time extend beyond the zone.

Any zone which seeks to provide long term protection is likely to unnecessarily prevent development of land in the short term. A less conservative approach is likely to lead to property becoming threatened sooner than is acceptable. The accuracy of prediction of future recession is not high and as yet no techniques exist for predicting the ultimate shoreline location.

However, the concept of planned retreat does lend itself to accommodating the progressive nature of the hazard.

It is often the case that an area adjacent to the shoreline is to be zoned open space or environmental protection for reasons not related to the coastline hazards, (for example to conserve habitats or to provide for public recreation). The widths of such zones may be such as to contain any future shoreline movement and thus no further consideration of the hazard is necessary. However, it should be recognised, however, that these zones will become narrower as time progresses.

(iii) Coastal Entrances

The hazard presented by the wandering of coastal entrances can be managed by environmental planning options where there is little or no existing development. The only technical concern may be the difficulty of precisely defining the limits of movement.

Introducing land use zones to accommodate entrance movement is not likely to affect large areas of land. Where isolated structures do exist, voluntary purchase may often be more appropriate than protective works.

(iv) Sand Drift

When dealing with areas of low development the most appropriate option for dealing with sand drift will be to implement appropriate dune management techniques to ensure that a well vegetated, stable dune system can be maintained. In order to do so, an adequate width must be provided for in land use zones etc. to allow for a self-sustaining vegetative system.

Voluntary purchase may well be an attractive way of dealing with isolated property threatened by extensive transgressive dunes.

(v) Coastal Inundation

The extent of land affected by inundation can usually be readily defined. Land use zoning and voluntary purchase of isolated, badly affected properties are appropriate options in a low development area. The zones required will often be an extension of those defined for beach erosion or shoreline recession, except where a dune system might be breached and the area affected may be more significant. Inundation alone may be insufficient reason to preclude development and other options exist to ensure compatibility with this hazard.

(vi) Slope and Cliff Instability

Buffer zones, restrictive zonings, and voluntary purchase will be appropriate where there is little development in areas subject to slope, bluff or cliff instability. It is particularly important to allow for the stability of dunes behind eroded beaches when considering zoning boundaries for other hazards.

(vii) Stormwater Erosion

Problems encountered from stormwater erosion in the low development case are likely to be encompassed within environmental planning options adopted to deal with other hazards. Voluntary purchase of badly affected structures may be considered.

It should be noted that in planning development near the coastline, even though the development itself may not be threatened, its impact on stormwater flows may be significant. The increased peak flows often resulting can have detrimental impacts on beaches.

Development control conditions are usually placed on development of an individual property at the time of granting development consent or building approval. In some cases, the types of controls which may be applied are outlined in a Development Control Plan (DCP).

In order to be applicable the property would need to be zoned in such a way as to allow development in an area subject to hazard. Given that areas of low development zonings are more likely to preclude development in a hazardous area, the use of development control conditions will be the exception rather than the rule.

There are cases where, for sound reason, zonings will permit development of some type in hazard prone areas and the application of development control conditions would then be appropriate. An example might be surf life saving facilities, tourist facilities or some other development where the purpose of the development dictates close proximity to the coastline. In such cases it is desirable that the extent and nature of the zoning is not unduly restrictive, to allow the greatest degree of flexibility in the application of development controls.

The options available in this category were discussed in section 5.2.2. The following sections outline the application of development control conditions to manage individual hazards in the context of low existing development scenarios.

(i) Beach Erosion

(b) Development Control Conditions

Whilst in areas of low development, zonings will usually restrict development of areas prone to threat from beach erosion, there may be cases either where the purpose of a structure dictates its location within a hazard zone, or a small part of a larger property falls within a hazard zone. Building setback lines and design conditions may then be appropriate options.

Where a small part of a property lies within the active beach zone setback lines can be used to exclude structures from the active area. Otherwise conditions such as foundation design and floor levels can be applied.

(ii) Shoreline Recession

Development control conditions related to building design and location are not particularly suited in the long-term where shoreline recession is one of the hazards. Difficulties with determining the extent of zonings discussed earlier apply also to the location of setback lines. Design conditions aimed at ensuring the integrity of a building may be effective so far as the safety of the structure is concerned, but a possible consequence is that, as time passes, the building's location may become socially unacceptable.

The use of conditions requiring buildings to be relocatable may be effective if used in conjunction with an overall policy of planned retreat. Specification of piled foundations may assist by ensuring that the building remains undamaged during a storm.

(iii) Coastal Entrances

Whilst development near mobile entrances is likely to be the exception rather than the rule in the low development situation, the application of development control conditions would have a place. Setbacks could be used to limit the location of development on large properties bordering on an entrance. Foundation design conditions could be applied as a safety measure where the extent of movement of the entrance is uncertain.

(iv) Sand Drift

Where other hazards do not dictate the exclusion of development, conditions relating to the maintenance of vegetation on a dune system might be appropriate. In the low development situation, land near the coast might be set aside for recreation (e.g. a golf course). Conditions requiring maintenance of the dune system or restriction of access would be appropriate measures to consider. In a rural situation grazing on fragile dune systems should be prevented.

(v) Coastal Inundation

Where minor coastal inundation is the only coastal hazard, development might be considered in such an area subject to the application of conditions relating to floor levels. Wave height and runup should be considered in setting levels. Possible damage to foundations from scour and floating debris should also be considered.

(vi) Slope and Cliff Instability

Whilst development in areas subject to slope, bluff and cliff instability is likely to be avoided in the "low" development areas, development control conditions may have a place in some circumstances. Building setback and foundation design aimed at overcoming the hazard are the conditions likely to be considered.

(vii) Stormwater Erosion

Stormwater erosion by itself is unlikely to be sufficient to preclude development and development conditions may be applied to render a particular development safe. Where new development is being considered conditions may be applied to regulate the discharge of stormwater.

(c) Dune Management

The objective of sound dune management is to sustain the role and value of the dunes as part of the coastal system. This role is multifaceted and includes the control of wind blown sand, the assurance of a buffer against short-term erosion, and the enhancement of the beach and coastal amenity. The basic principle is to maintain a satisfactory vegetative cover; this involves the application of land capability principles, organisation of recreational activity and rehabilitation of disturbed dunes.

In the "low" development situation there is usually ample scope for, and significant benefits to be derived from, the other applications of dune management principles.
The implications of dune management in respect of the various hazards are outlined in the following sections.

(i) Beach Erosion

The extent of the zone affected by short-term erosion is related to the volume of sand on the beach berm, incipient dune and foredune. If a good vegetative cover exists on the foredune a volumetric buffer against erosion is retained and the process of colonisation and building of the incipient dune is facilitated. In assessing the extent of the short-term erosion hazard, the existence of a well vegetated dune will reduce the width affected.

(ii) Shoreline Recession

One of the mechanisms for the loss of material from an area of coastline is by wind blown loss of sand. While this is not usually the major loss mechanism, it is significant in many cases. A well managed dune system will prevent this loss and thereby reduce the rate of shoreline recession.

(iii) Coastal Entrances

The existence or otherwise of a well maintained dune system is in itself not a major factor in limiting the movement of a coastal entrance. However, a mobile entrance may create instability on the surrounding area and managing these areas will assist in preventing further damage and also wind blown losses.

(iv) Sand Drift

Dune management and the maintenance of a satisfactory vegetative cover is the major management option for the control of sand drift.

(v) Coastal Inundation

The existence of a stable dune of appropriate height can be of major importance in the prevention of inundation of low lying coastal areas. The crest level of the dune should be determined by the likely elevated ocean water level and the wave runup level. It may be necessary to reform the dune to achieve the right crest level and thereafter manage the dune to ensure it remains stable.

(vi) Stormwater Erosion

Dune management does not have a significant direct impact on the management of stormwater erosion, except to the extent of limiting the instability that may be caused, and as part of rehabilitation if other options are used to relocate or control the discharge.

Figure 5.5 Severe Beach Erosion, 1974 Storms, Bilgola Beach, Sydney

Figure 5.5 Severe Beach Erosion, 1974 Storms, Bilgola Beach, Sydney.

(d) Protective Works

For the "low" development situation, major protective works are likely to be low on the list of options considered, environmental planning and voluntary purchase being the more likely options. Minor works to cater for some low level hazards might be considered, for example to protect one or two existing houses from stormwater erosion. The role of such works would be similar to the role performed in the case of the high development scenario and will be discussed in that section.

However, an option which should not be overlooked, however, is the case of protective works to allow a major development in an area now undeveloped or with little existing developments. It is always an option to allow development in an area prone to coastline hazards and to provide engineering works to protect or make the development secure.

If such an option is being considered there are some important aspects to take into account. Such a proposal should not be considered only in the context of development of a single property but at least in the context of a whole beach compartment or in the context of regional planning. The physical impacts of the necessary protective works on adjoining areas should be assessed and the proposal judged on its merits taking account of the physical impacts, social implications, economic benefits and costs and ecological implications.

Should this approach be considered as a management option for an area it is important that the land use zoning (both in extent and in description) allow a flexible approach to the use of protective works, setting of design conditions and accommodating public aspirations such as foreshore access.