5.1 Possible approaches
The earlier sections of this Guide have looked at the processes and risks related to beach-dune systems, and have pointed towards the need to treat each site as a unique situation; generic dune management approaches are not appropriate. This Chapter sets out the underlying issues involved in selecting a management approach that will achieve the specific objectives established for each site.
It is assumed throughout this section that all sites being considered have assets at risk from erosion and that protection of these assets will be balanced against impacts on the environment. Most approaches to erosion management are damaging to the environment to a greater or lesser extent. This is particularly so for projects entailing civil engineering operations such as revetment and sea-wall construction or major beach renourishment schemes. The inclusion of such approaches herein does not, therefore, indicate approval or commendation of them from SNH in all circumstances. Rather, they are included to provide a comprehensive guide to the options available to coastal managers and to promote good practice, from an environmental perspective, in the design and implementation of coastal defences, whatever approach is adopted.
Questions to be answered include:
- What are the objectives?
- Will the scheme achieve the objectives?
- Over what time scale will it be effective?
- What will be the impacts on the natural environment and the landscape over different timescales?
- Are the resources (materials, equipment, labour, funding) available for both initial implementation and long term maintenance?
- Are the short and long term costs justified by the benefits?
- What will be the impacts on adjacent areas?
- Are there more appropriate options?
There are four general approaches to managing dune erosion:
- Non-interference, allowing natural processes to continue while accepting losses or taking appropriate action to relocate any backshore assets at risk.
- Delay erosion using small scale, short term (5-10 year life) schemes that can be implemented at relatively low cost and that will have a minimum impact on the coastal environment.
- Defend the frontage selectively using methods that may require the involvement of specialist consultants and may have a high impact on the immediate environment and coastal landscape; these may be short term, but are more likely to have a longer life expectancy (5-30 year life).
- Establish a fixed shoreline using large scale, long term (20-50 year life) defences that will require the involvement of specialist consultants and will significantly alter the coastal environment, landscape and recreational use of the beach.
There is obviously some overlap between these approaches and some differences of opinion as to what may be short term or long term, and what their impact on the environment may be. Schemes that have a life expectancy (without maintenance) of up to 10 years are considered short term in relation to the natural environment. In addition it should be noted that these approaches are not independent – indeed it may well be advantageous to combine small scale, short term management with engineered schemes to encourage dune systems to redevelop after being damaged.
Selection of the appropriate approach, or combination of approaches depends on the objectives and constraints relevant to the site. Scheme options suitable to each approach are set out in a series of Summaries presented in Appendix 1. These include:
Non-interference
- Adaptive management
Small scale, short term
- Dune grass planting
- Dune thatching
- Dune fencing
- Beach re-cycling
- Sand bag structures
- Beach nourishment
- Beach drainage
- Gabion structures (see note below)
Selective frontages
- Rock or gabion headlands
- Groynes
- Nearshore breakwaters
- Artificial reefs
Large scale, long term
- Rock revetments
- Timber revetments and breastwork
- Impermeable revetments and seawalls
(Note. Gabions are often associated with poor shoreline management practice, and should only be used in specific circumstances. If they are regularly exposed to wave attack then they will have a short life before becoming ineffective and an eyesore. However, used as a buried defence or within sheltered areas of an estuary they can be both effective and unobtrusive. Their position in the short-term, small scale category is debatable as they can be used over long frontages, and if well maintained can last for longer than 10 years before needing substantial renovation.)
The Summaries set out sufficient information about each option for the reader to make an informed decision about their appropriate use. The Summaries of small scale, short term operations provide information that will allow implementation, possibly using volunteer or unskilled labour. It is assumed that larger schemes will only be put in place following preliminary appraisal and design studies by a competent coastal consultant; the relevant Summaries present information to allow the proposed designs to be assessed for appropriateness and potential long term impacts.
Appendix 1 also includes a summary of “novel” methods, providing a brief indication of the reasons for not giving them serious consideration.