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NSW Coastline Management Manual

New South Wales Government
September 1990

ISBN 0730575063

Appendix D: Hazard Management Options

Appendix D5 - Dune Management Options

1 INTRODUCTION

Effective dune management is based on maintenance of a satisfactory vegetative cover. Specific dune management techniques are described in the Soil Conservation Service's "Coastal Dune Management" manual (SCS, 1990). This appendix considers the principles of coastal dune management and complements the discussion of dune vegetation as a coastal process given in Appendix B8. This appendix is based generally on the more comprehensive work of Chapman (1989).

2 VEGETATION AND DUNE MANAGEMENT

The interactions between coastal processes and dune vegetation are, in natural circumstances, very positive. The principal species are well suited to stabilising dune sands and initiating beach recovery following severe storms. During storms, sand is removed from the beach to form an offshore bar, and during intense storms, a demand for dune sand is created which involves reserves held by primary species.

Beach vegetation, such as Spinifex, provides some resistance to the removal of sand during the storm, but its principal role is to quickly stabilise the sand which returns within a few weeks of the return of fine weather. With loss of vigour of primary species, sand is free to move inland, where it impacts vegetation which does not have the capacity to tolerate burial and further dieback results.

Secondary species (as seen in Figure B8.1), have an important function of stabilising seaward of the of the permanent dune crest. Their survival mechanism relies on an adaptable growth habit and capacity to reseed prolifically; they cannot develop quickly and require the stabilising influence of primary species to establish successfully. Degradation of species composition ultimately leads to monocultures and catastrophic losses of dune cover. The loss of vegetation zonation also contributes to a change in dune conformation, reducing the capacity of the dune barrier to absorb high wave energy.

Permanent tertiary species on and behind the crest of the foredune are slow growing and highly interdependent in that they need to cooperatively maintain an unbroken canopy. Wherever wind and light penetrate, die-back occurs and weed species volunteer. Some beaches, particularly those which are receding, depend on close-knit communities of permanent species standing high above the dune escarpment for their stability. Vantage points, access tracks, housing and parking take heavy toll on these stands and caution is required before urbanisation is allowed. Management of vegetation on a receding coast is discussed in some detail by Wickham (1984).

Coastal dunes have been and are used for a variety of purposes including mining (both placer mining and sand extraction), water extraction, waste water disposal, housing, agriculture and recreation. Problems that have arisen from some of these uses include sand drift, shoreline recession, soil over-nutrification, loss of species, destruction of archaeological sites and reduced recreational amenity. Past experience indicates that coastal dune vegetation has limited capacity to recover from some of these uses. Much of the coast has already sustained some loss of intrinsic value which may be costly and difficult to rehabilitate. There is potential for heavy mineral sands mining to stabilise and rehabilitate unstable or eroded dune systems and in appropriate situations this could be used as a positive management concept.

If remaining intact coastal dunes are to retain their natural plant and animal communities there exist a limited number of compatible land use options. Existing vegetated dunes can be utilised for recreation, education, research, and conservation with little permanent damage if such use is correctly managed. Other uses such as sand extraction, housing and waste disposal are more disruptive and permanent loss of vegetation is unavoidable. Where dune development is still demanded in spite of expected permanent loss of dune value, thorough evaluation of trade-offs is required.

Heavy mineral sand mining requires complete removal of existing vegetation but experience shows that a stable vegetation cover can be re-established on mined areas.

3 MANAGEMENT OBJECTIVES AND OPTIONS

Management of coastal dunes, as with the management of any land system requires the planning and control of desired human activity within the limits imposed by physical, biological and cultural resources. A fundamental goal of the management of dune vegetation is to provide the means for the community to enjoy the widest possible range of coastal orientated activities without degrading the resource base which supports them. In the case of vegetation management, an objective which follows from the above goal is that of maintaining populations that are self perpetuating, so as to minimise maintenance.

However, it is also important to retain diversity, preserve endemic and rare species, and protect the structural integrity of plant communities in a manner which satisfies strategies for their conservation.

Maintenance of existing plant populations and processes by means of management is necessary, given the vulnerability of dunes and dune vegetation to disturbance. However, there is still much to be learned about management measures that best enhance natural maintenance of plant populations. The simple exclusion of people and vehicles from the vegetated sections of dunes does not necessarily ensure the maintenance of plant populations.

With these objectives in mind land use options can be considered in terms of their likely impact on the vegetation and ultimately the whole dune system. Land use options may first be considered in the light of their effect on the removal or retention of vegetation:-

i) Vegetation Removed

ii) Vegetation Retained

Those options which require vegetation removal can be further subdivided on the basis of being extensive (as dwellings and infrastructure development and cultivation), or intensive (as sand extraction and heavy mineral sands mining). Furthermore, those options which allow retention of vegetation may be subdivided into a disruptive class (as active recreation, water extraction, effluent disposal, and grazing might be), or non-disruptive, (as passive recreation, education, research and commercial fishing should be).

The potential effects of disruptive activities or those that require vegetation removal include changes in species diversity, loss of structural complexity, extinction of rare and endangered species, introduction of exotic weeds, and interference to population dynamics and critical life cycles. Any of these outcomes would result in loss of vegetation which would require costly and careful rehabilitation which, although it may never replicate the original situation, may achieve a stable vegetative cover. Therefore, land development and management decisions must be made with full cognisance of their potential effect on dune environments. Management decisions at both the land use planning scale and the site scale should be based on a sound knowledge of the vegetation resources of the area.

Special attention is needed with regard to human impact on the critical parts of life cycles of dune plants (such as reproduction), the influence of fire, and establishment and growth of plants under conditions of constant physical disturbance. In the absence of such information, it is possible that one or more of the following outcomes will ensue:

a) Development and management policy will be over-restrictive.

b) The community will have to commit more resources to dune management programs.

c) Irreparable dune damage will completely change the intrinsic values of the New South Wales coastline.

In order to forestall problems as far as possible, it is recommended that priority should be given to the formulation of conservative policies with respect to permanent dune vegetation, with the onus on the proponents of development to provide proof of development acceptability.

Where it is not possible to preserve the pristine state of a natural dune system, management must be concerned with both the form and function of the dunes. The concept of maintained "function" includes the preservation of a reservoir of sand close to the foreshore to meet the demands of short term fluctuations in sea level and storm wave attack.

Problems arise when human usage interrupts the "symbiosis" which exists between the dune form and its vegetation. In these situations use may be made of devices which complement natural sand accretion and accommodate erosion with minimal damage to plants and fixtures (e.g. board and chain pavement, protective or dune forming fencing, and "managed" vegetation). Dune forming fences may be utilised where a loss of dune form has created a focus for wind and drifting sand to develop a blowout.

A further management option where economic quantities of heavy mineral sands are present is to allow mining. The statutory requirement would ensure rehabilitation of damaged or disturbed dunes at no cost to the State or local council. Rehabilitation would be subject to a Mining Rehabilitation and Environmental Management Plan in accordance with the Rehabilitation Policy of the Department of Minerals and Energy and would require annual review to critically assess the status and suitability of the rehabilitation programme. Such land use would enable re-establishment of a vegetative cover which may eventually resemble the natural state.

Where it is not possible to establish a complete self sustaining cover of vegetation, dune maintenance programs should be introduced to ensure the persistence of vegetative protection. Such programs may include enclosure of primary and secondary vegetation by fencing, and the institution of an ongoing program of fertilising, plant replacement and pest control. The cost of such a program is the price of beach usage.

4 SITE SPECIFIC MANAGEMENT CONSIDERATIONS

The coastal manager is concerned with three broad categories of on site management problems:

 (a) Minimising disturbance to dunes.

 (b) Management of access by humans and their vehicles.

 (c) Rehabilitation of damaged dunes.


(a) Disturbance

Removal or excavation of foredunes or incipient foredunes can cause instability, render the sand mobile, and reduce the sand storage capacity which augments the beach during storm wave erosion. No excavation of foredunes should be permitted unless plans are developed for their rehabilitation which are acceptable to the appropriate authority. In addition, no excavation of incipient dunes should be permitted unless designed with the objective of correcting dune instability or a dune restoration problem identified in the Coastline Management Plan.

The following criteria are suggested to guide the manager in deciding whether a form of land use should be encouraged:

Essentially all disturbance to incipient foredunes and foredunes should be prevented, as any damage to the vegetation will affect dune stability. Once the vegetation has been destroyed in one part, a blowout may result which in turn may become a transgressive dune or sand sheet. Where there is considerable human activity the dunes should be fenced and access controlled and limited. Stock should not be allowed to graze, and during nesting and breeding periods of bird species using dune habitats, very careful control is necessary to prevent their disturbance. Cooking facilities, firewood and toilets should be provided where appropriate to prevent the use of the dunes for these purposes.

Ideally, no buildings should be sited in the coastal hazard zone, but if encroachment is absolutely unavoidable, structures should be relocatable, or elevated on deep anchored piles, or expendable structures may be used. Contractors in control of access to building sites should take responsibility for protecting and stabilising the dunes in and around their sites.

(b) Access

Dunes are held together by plants and damage to these by excess traffic can cause total destruction of a stable area and greatly increased mobility of unstable dunes. Both public access paths and vehicle tracks need to be carefully sited and controlled. Rotation of access points can help. Pedestrian access should be via properly constructed walkways if traffic is moderately high. Elevated walkways of boards are perhaps the best and most aesthetically pleasing solution as they can be built above the vegetation, but less expensive and equally effective access may be provided with board and chain walkways.

Hard paving or fill should be avoided in dune areas since it is not consistent with the concepts of maintained form and function, and inflexible elements can provide focal points for wind erosion. In addition, if the hard surfacing is attacked by storm waves, the incorporation of fragments of paving or fill into the beach can reduce amenity.

Vehicles travelling on the beach between high and low water marks have little impact on the sedimentary beach system. However vehicles can readily damage or destroy vegetation on coastal sand dunes. Plants growing on newly forming dunes are particularly sensitive to vehicle impact. Beach traffic should be diverted around drift lines and other zones of embryonic dune formation. The closure of beaches to vehicles during periods of 'king' tides, which would force drivers to run up the face of dunes or through bird nesting sites and embryonic dunes, is recommended. So too is the closure of beaches that are so narrow as to force drivers to run along the very toe of the dunes at high tide; bypass routes around such sections should be provided.

(c) Rehabilitation

Techniques for the rehabilitation of coastal dunes are discussed by the Soil Conservation Service (SCS, 1990). In any dune rehabilitation program it is important to appreciate that the incipient dune, and occasionally the foredune, are destined to be eroded during storms, with inevitable damage to vegetation, walkways and fences. An important objective of good rehabilitation practice is, therefore, to minimise maintenance commitments by providing vegetation which regenerates naturally and by using flexible or expendable structures which can accept storm attack or be replaced at minimum cost.

The Department of Minerals and Energy has produced general guidelines for the management and rehabilitation of heavy mineral sands mining. Guidelines are also determined for each individual heavy mineral sands mining operation in NSW.

5. REFERENCES

Chapman, D.M., (1989). "Coastal Dunes of New South Wales, Status and Management", University of Sydney, Coastal Studies Unit Technical Report No. 89/3.

SCS (1990), "Coastal Dune Management - A Manual of Coastal Dune Management and Rehabilitation Techniques", eds Conacher P.A., Joy D.W.B., Stanley R.J., and Treffry P.T., Soil Conservation Service of NSW 1990.

Wickham H.G. (1984). "Management of vegetated Dune Reserves on a Receding Coast". J. Soil Cons. NSW 40(i). pp 46-55.