Coastal Zone Management (CZM) is an integrated system for development planning in the coastal zone. CZM recognises that coastal zone users depend on the same coastal resource base and so need to be managed together to achieve mutual sustainable development.
One important area of interaction between coastal use and the coastal environment is coastal protection. The need to understand and determine the behaviour of the coastline is critical to determine what new activities can take place there and how best to sustain those already in place.
Shoreline management concentrates on a narrow area (i.e. the nearshore seabed, beaches, dunes, cliffs and estuaries, and the immediately adjacent land). It is principally concerned with any necessary intervention in the natural development of the shoreline to preserve and enhance those of its attributes which are agreed to be of greatest importance whilst providing appropriate standards of protection of land from flooding or erosion by the sea. Shoreline management not only considers the techniques that provide the best coastal protection, but also the social, economic and environmental factors associated with a coastal protection strategy. This directly requires the input from, and cooperation between, the affected coastal users. It is suggested that adopting the idea of a Shoreline Management Plan (SMP) is a suitable way forward for strategic management of the coastline of the Western Isles.
A Shoreline Management Plan is usually built up in a number of stages.
1. Define the length of coastline that is to be considered in the Plan on the basis of natural divisions, i.e. coastal "cells".
2. Review the geology and geomorphological development of the coast,
Study the hydraulic regime of the coastline, drawing together information on the winds, waves and tides which influence its development,
Gather together information about the characteristics and attributes of the coastline and adjacent hinterland, for example existing coastal defences, land use and infrastructure, ecologically sensitive sites, amenity and recreational uses, sites of archaeological or geological importance etc.,
Identify the present and future risks to these attributes that would result from changes in the coastline, and the present trends in the evolution of the coast (eg erosion).
This will naturally result in the identification of a number of "stakeholders" in the coastal zone, i.e. organisations or individuals which have an interest in the development and management of the coastline. These will include central or local government departments, land-owners, those with commercial or industrial interests in the coastline, conservation organisations, representatives of the tourism and leisure industries, and often may more besides. These are likely to become consultees at later stages in the development of the Plan.
This study identifies the coastal "cells", gathering information on the hydraulic regime and attributes of the coastline, and identifies some of the present and future problems around the coast. It would be a useful next step to draw up a list of stakeholders for the coastline of the Western Isles, both in general and for the various islands.
Definition of Management Units and Objective setting
The next stage is to sub-divide the area considered into Management Units. These are much shorter lengths of coastline, typically a few hundred metres to a few kilometres long. They are chosen so that their whole length is of a consistent type, i.e. the hydraulic climate, beach morphology, hinterland level and usage are all reasonably similar along the length of the Unit. The Management Units become the basis for more detailed management planning, and the strategic management of the whole coastal cell is eventually derived by assembling the plans for each Management Unit.
This study has provided a useful starting point for the definition of Management Units (MU's) that include beaches. Further work is needed to define MU's for other parts of the coast, and to consider any necessary extensions or sub-divisions of the Units already defined.
Once the Management Units are chosen, work can start in earnest on the future plans for the coastline.
The first step in this is to decide on appropriate objectives for each Unit. In areas of residential property on low-lying land, for example, the principal objective will be to provide adequate levels of defence against flooding; aspects such as preserving or enhancing the recreational use of the coastline will also need to be considered, but will be of secondary consideration. On more remote stretches of coastline, the consequences of erosion or inundation may be much less serious, and the main objectives for the Management Plan may be to preserve the natural environment and aesthetics of the coast.
Drawing up plans for each Management Unit involves the following steps:
· predicting the future development of the coastline (and immediate hinterland) if no management action is taken,
· deciding whether this future development will adversely affect or positively help achieve the objectives for that Unit,
· deciding therefore whether any positive action needs to be taken in that Unit, together with a view on the urgency of that action,
· -drawing up, where necessary, a list of possible methods of management,
· carrying out a preliminary appraisal of these options, bearing in mind the likely feasibility, costs, and environmental impacts, also bearing in mind the potential effects on adjacent Management Units,
· consulting on the preferred management option(s) with the various consultees identified in the initial stages of the SMP,
· adjusting and re-consulting on the proposals as appropriate,
· finalising the management plans for the Unit, with more detailed costings, benefit analyses, and environmental impact assessments. At this stage, it may also be necessary to gather further information on the coastline, for example more refined studies of waves and tides, in order to produce a suitable design or any scheme.
· drawing up a programme of works for the whole coastline covered by the Shoreline Management plan, reflecting both the urgency of particular schemes and the available financial and other resources.
The Plan is seen as a "living" document, which will need to be revised as circumstances alter. In order to keep the Shoreline Management Plan up to date, there will need to be an element of monitoring the coastline, and of revising and refining the Plan at sensible intervals accordingly.
A useful method of assessing management options is a technique known as a Multi-Criteria Analysis. Two sites in the Western Isles are analysed in this way: Management Unit 3 (Aiginis to Melbost Point) and Management Unit 30 (Kirkibost and Baleshare Islands).
This technique allows the assessment of different management options. Criteria which are judged more important than others, for a particular stretch of coast, have this reflected by an appropriate weighting. In the example given for Aiginis, the comparative weighting of criteria for the frontage at Aiginis is given as follows:
|
Criterion |
A |
B |
C |
D |
E |
F |
Total Weight | |
|
A B C D E F |
Protection of land Modest capital costs Low maintenance cost Maintain beach levels Public acceptance Low environmental impact |
- 0 0 0 0 0 |
2 - 1 1 0 1 |
2 1 - 1 0 1 |
2 1 1 - 0 1 |
2 2 2 2 - 1 |
2 1 1 1 1 - |
10 5 5 5 1 4 |
If the criterion in a row is:
- more important than the criterion in the column, then score = 2
- equally important as the criterion in the column, score =1
- less important than the criterion in the column, score = 0
Next a list of feasible methods of managing the coastline is drawn up, including the "Do Nothing" option, i.e. to allow the coastline to continue to evolve without (further) intervention. A comparative assessment of the alternative schemes is made by marking how well each scheme is likely to achieve each criterion on a scale of 1 to 10 (where 10 means a very good achievement of the criterion). Finally, for each option, the rankings are multiplied by the weighting assigned to the relevant criterion (from the table above), and a total weighted score evaluated (bottom row).
For the Aiginis example, the comparative assessment of defence alternatives are as follows:
Option Description
Number
1 Do nothing, but rebuild infrastructure at Aiginis further inland
2 Build sea wall to protect eroding cliffs at Aiginis
3 Rock revetment to protect eroding cliffs at Aiginis
4 Offshore breakwaters/sill to protect eroding cliffs at Aiginis
5 Shingle recycling from western end to eastern end of frontage
(Note that there is no "Do Nothing" option here, since the continued erosion of the cliffs at Aiginis would result in serious threats to the infrastructure and possibly the village.)
|
Criterion |
Weight |
Alternative Options 1 2 3 4 5 |
||||||||||||||||||||||||||||||||||||||||
|
A Protection of land B Modest capital cost C Low maintenance cost D Maintain beach levels E Public acceptance F Low environmental impact |
10 5 5 5 1 4 |
1 1 1 4 3 7 |
9 1 5 2 7 3 |
8 3 5 5 8 4 |
7 3 5 8 7 4 |
4 6 3 8 7 6 | ||||||||||||||||||||||||||||||||||||
|
TOTAL WEIGHTED SCORE |
71 |
149 |
181 |
173 |
156 | |||||||||||||||||||||||||||||||||||||
Discussion of alternatives
From the table above the best two of the suggested alternatives for protecting the soft cliffs at Aiginis are ranked almost equally, namely the rock revetment (option 3) and the offshore breakwaters or rock sill (option 4). To separate these alternatives a more detailed analysis, including costing, would have to be conducted.
Future monitoring of the beaches allows the early identification of changes in the beach response. This can then used to detect which beaches are relatively stable and which are being eroded and hence where action may be required. The coastline of the Western Isles is presently poorly served with beach data. Beach surveys should be considered an integral part of any future coastal management policy. This will provide greater detail on the areas of coastline most at risk and hence allow the most effective use of any available resources.
Where developed areas are at possible risk, or where there are sites of conservational importance, detailed surveys may be required. However, on many parts of the Western Isles coastline where there is little infrastructure or other human development less expensive methods of surveying may be more cost effective.
On parts of the coastline where infrastructure, buildings, historic interests, cemeteries etc. may be affected, a profile survey of the beach and immediate hinterland should ideally be surveyed twice a year. Beach profile surveys should also be conducted at locations where coastal protection work has been installed to identify any effects on the beach due to these structures. Where any coastal protection work is planned, beach profile surveys should also be conducted for as long a period as possible before construction to gain an insight into the natural behaviour of the area. In addition visual surveys of all coastal defence work should be conducted at least twice a year. Such a survey should also be carried out after any severe storm events.
On parts of the coastline where there are little or no human influences or development, survey information does not have to be so detailed. Aerial photography surveys would be an ideal method of obtaining such information on much of the western coastline of the Western Isles. Surveys flown every five years would be sufficient to provide a qualitative record of beach development, but given the dynamic nature of the hydraulic conditions every two years would be advisable. To conduct an aerial survey of all the 'soft' coastline of the Western Isles may prove too expensive. There are other ways in which a regular survey can be conducted, for instance the comparison of site photographs taken at regular intervals. At some locations where coastal edge retreat of the machair is occurring, pegs may be driven into the machair and the distance to the eroding edge measured. The frequency of such surveys would depend on the particular site, but it would be advisable to conduct at least one survey at a set time during the year and ideally also after severe storm events. A further possibility is to get the local inhabitants involved in a neighbourhood watch scheme for the beach. This would also help focus public awareness on the importance of the coastal zone as an effective coastal defence and possibly help reduce any detrimental human effects.
Analysis of survey information is required. This needs to be carried out promptly (i.e. within a few weeks of the measurements), but can be done simply eg using a spread sheet to analyse rates of retreat or advance.
