Diagnostic Tools to Protect Coastal Areas | Disaster Management

The development of “diagnostic tools” to assist in identification of situations under which forests and trees would be suitable to protect coastal areas against: 1. Tsunamis 2. Cyclones 3. Wind and Salt Spray 4. Coastal Erosion.

Diagnostic Tool # 1. Tsunami Working Group Results:

The tsunami working group began with the same objectives as the other groups, but in spite of the concerted efforts all members, the meeting ended in deadlock with little movement towards the objectives owing to fundamental disagreement over the validity of the question.

Several opposing points of view were fielded by different sections and individuals.

In summary:

I. Physicists and engineers were ready to entertain the question given there is no reason to deny the notion that obstacles such as trees could modify the motion of tsunami waves and potentially provide protection for people and assets.

II. Pragmatists were unwilling to concede that planting mangroves and other coastal forests could be proposed as a serious solution to alleviate damage from tsunamis – trees take years to grow, occupy valuable space and the return period for tsunamis may be 200 years in much of the Indian Ocean.

III. Sceptics did not think that the scientific evidence for tree and forest protection against tsunamis was strong enough to support planting for this reason.

IV. Field-based practitioners with funding to plant trees in coastal areas who, because their mandate removed several of the aforementioned obstacles, reasoned that if trees could provide even a limited degree of protection, then so much the better.

V. Those believing that trees are good in all areas and at all times, and therefore, that it is inherently “good” to plant whenever and wherever possible.

Limitations on using trees and forests as coastal protection measures against tsunamis:

I. Coastal green belts cannot provide complete protection.

II. Tsunamis rarely strike areas where mangrove forests occur.

III. Land would have to be available and people would have to be prepared to live behind the forest for green belts to be proposed as a protective measure.

IV. Trees and forests are not relevant where the shore is steeply sloping.

V. Trees and forests are less relevant where local bathymetry provides protection or where other means of protection are present.

VI. Exposed high risk areas are often the most attractive for development and in such cases trees and forests are not appropriate to provide protection.

VII. Governance structures and institutions are frequently unable to enforce regulations governing construction in green belts.

Interactions between trees/forests and tsunamis:

I. Although trees can significantly slow a tsunami, flooding can still occur.

II. Although a porous barrier can reduce the height of a tsunami, the speed of flow may increase in nearby areas.

III. Trees and forest are likely to reduce the penetration of water inland as the period of tsunami waves is in the same order as the time it takes a wave to travel across a few hundred meters of land.

IV. Gaps and channels through vegetation can increase the intensity of a tsunami as a result of funneling of waves and intensification of backwash. The frequent presence of habitations along such channels may amplify catastrophic effects (river gates may provide protection).

V. Larger tsunamis are overwhelming and trees and forests would not provide protection in these cases. For smaller tsunamis, a wide belt of vegetation may provide protection; width estimates vary between 20 and 100 meters.

VI. Tsunamis can break trees, turning them into projectiles, although the possibility of broken trees acting as projectiles should not be relevant given that evacuation from danger areas should be the priority.

VII. Broken trees and branches can become lodged in vegetation and provide greater resistance against passage of water.

VIII. Trees with strong roots and trunks are likely to provide the most effective resistance to tsunamis; undergrowth also slows the advance of water.

IX. Reef maintenance, dune protection and protection and establishment of other protective structures should be considered in addition to possible establishment/protection of trees and forests.

The wealth of information and viewpoints makes summary problematic. Overall, the consensus during the workshop was that trees and forests can provide protection against tsunamis. The main questions, therefore, revolve around the quantity and quality of forest necessary to provide protection against a tsunami under a set of local conditions, and whether the result can be implemented under the prevailing socio-economic conditions.

To make the diagnostic tool operational, and notwithstanding questions of feasibility, it would be necessary to bring together detailed information quantifying the physical parameters that define the effectiveness of trees and forests in protecting against tsunamis. This basic information could then be applied at the local level prior to implementation of analyses to assess environmental, social and economic costs and benefits of trees and forests in comparison with other forms of coastal protection.

Diagnostic Tool # 2. Cyclone Working Group Results:

The diagnostic tool developed by the cyclone group is given below. The key decisions relate to the size of the expected storm surge. If the surge is expected to be above five meters, other measures should be taken as trees and forests will have little impact on influxes of water of this magnitude.

There is a further important point: Where coasts are eroding, trees will not secure the coastline in the long term and engineered measures are required. This point also relates more generally to the other coastal hazards.

Other key points relating to the potential protection provided by trees and forests against cyclones were:

I. Trees should only be considered as appropriate protection against the effects of cyclones for low intensity storms.

II. During cyclones, water (i.e., from the related heavy rains) kills in order of magnitude more people than wind does.

III. If the coastal bathymetry is predominantly shallow, the storm surge is greater.

IV. Barrier islands, although affording protection against tsunamis, do not attenuate cyclone- related surges.

V. Although a band of around ten kilometers of mangroves is required for protection against cyclones, they can provide protection, as in the case of the Sunderbans. However, forests with less breadth are useful in reducing the strength of storm waves.

VI. Penetration of floodwater cannot be stopped by trees and flood levels may remain for a day or more.

VII. Storm waves related to cyclone winds can be attenuated by trees.

VIII. Cyclones and tsunamis do not usually affect the same areas.

A major misapprehension concerning the effects of cyclones is that wind is the main threat to life. As stated earlier, water kills many more people than wind and this has important repercussions on the protective functions of trees and forests. Because flood levels are likely to remain for a day or more, porous structures such as forests will not prevent the influx of water.

They will, however, attenuate wind-driven waves. Given these observations, it is clear that a broad breadth of tree cover would be necessary to provide protection from cyclones. It is commonly held, for example, that the Sunderbans in Bangladesh afford cyclone protection and recent data from Orissa, India indicate that a 0.5-kilometre band of mangroves can protect lives with a statistical confidence level of 95 per cent, whereas a 1.5-kilometre strip can protect lives with a confidence level of 99 per cent.

More data are likely to emerge to further inform on this issue, but with the large areas of land required for tree planting, apropos protection of people and assets, it would be more likely that the above arguments would be used in calls for conservation rather than the establishment of forests exclusively as protective measures against cyclones.

Diagnostic Tool # 3. Wind and Salt Spray Working:

The diagnostic tool developed for wind and salt spray followed a similar approach to that adopted by the cyclone group. Information required for the tool relating specifically to wind and salt spray included the nature of the local winds, whereby coastal shelterbelts would only be appropriate where onshore winds occurred.

It was also noted that deep-rooted trees should be used to enable water uptake and to provide adequate support in sandy soils; moreover, they should also be sturdy and salt-resistant. Further information could be included in the tool to specify the degree to which salt spray and wind effects could be alleviated by using shelterbelts and also the area over which benefits would be experienced.

It should be noted in this context that salt may be suspended throughout the boundary layer and transported inland. Larger crystals of salt are likely to fall out of the air mass under less turbulent conditions, but smaller particles may be carried far inland. Therefore, the effects of coastal shelter belts may be fairly localized and tree planting would probably be best for protecting specific valuable structures or assets.

Diagnostic Tool # 4. Coastal Erosion Working:

The coastal erosion group developed a tool based on a coastal protection strategy including possible short- and long-term measures in combination with prioritization of areas according to the severity of erosion. The group agreed that economic, environmental, social and cultural values are likely to be subjects of protection from coastal erosion, and that national governments should determine priorities, depending on their specific situations.

In the short term, it was proposed that engineering solutions should be targeted at critical areas, according to prioritization of all areas. In the long term, guidelines, shoreline management plans within Integrated Coastal Zone Management (ICZM) initiatives and coastal laws should be developed to support short-term measures and overall aims.

The following levels were categorized to facilitate prioritization:

a. Critical:

Erosion is serious and is immediately threatening:

(i) Property and human activity of high economic value; and

(ii) Sensitive irreplaceable ecological systems.

b. Significant:

Erosion serious, entities same as above will be threatened in five years or more if nothing is done (the situation will become critical).

c. Acceptable:

Erosion affecting areas with no economic, ecological or heritage value.

According to this prioritization, critical and significant erosion areas are protected first to prevent loss of land, natural resources and heritage, to avoid displacement of population and to maintain/improve tourism value. Once consensus is reached on the areas in which protection is needed, processes are initiated to consult local residents and stakeholders, collect and analyse data and develop an understanding of erosion and key coastal processes in the area.

Following this process, available options, including hard engineering, soft engineering, re-forestation and combined measures are considered for a period according to the urgency of the situation, with critical situations requiring more immediate action.

Points considered include:

I. The effectiveness of each option in overcoming/ reducing the threat.

II. Socio-economic and environmental impacts of each option (hard engineering structures generally cause more serious environmental impact than soft solutions).

III. Engineering parameters (hydraulics/hydrodynamics, geotechnical matters, construction materials/ techniques).

IV. Time needed for construction.

V. Funds available.

In summary, it was noted that reforestation is not appropriate for all areas and the following criteria are mandatory:

a. Sufficient time frame.

b. Local participation.

c. Available space.

Following this assessment, an identification of minimal data requirements for reforestation is carried out and reviews are undertaken by experts at critical decision-making stages throughout the process. A note was made that the tool focuses on continental coastlines and mangroves, and that small islands require different approaches and considerations as the environmental conditions and guiding principles are different.

Little information was included in the diagnostic tool on the circumstances under which trees could be suitable for arresting or reversing coastal erosion. In relation to this, it should be noted that trees may not decelerate the pace of erosion at all on naturally eroding coastlines, and therefore, local circumstances should be reviewed before decisions are made.

Conclusions and Further Refinements:

A number of elements contained in each diagnostic tool were generic and could be used for a variety of coastal hazards with minor adjustments made to accommodate technical information.

The following questions were central:

1. What is the coastal hazard?

2. Are valuable assets at risk?

3. Are trees effective in protecting against the type and intensity of hazard expected?

4. Is the coast undergoing erosion?

5. Is land available in terms of area and possible lost opportunity costs?

6. Are finances available to establish trees?

7. Are different types of protection more environmentally or socially preferable?

8. Do trees or forests offer comparative advantages over other types of structure in terms of protective capacity, cost, environmental benefits or social benefits?

To further develop and operationalize these diagnostic tools, a greater level of technical detail is required to quantitatively define the relationships underlying points 2 and 8 above. This information has proved to be unavailable in forms readily accessible to foresters and policy-makers, but discussions during the workshop indicated that there is further information available to quantify the degree to which trees can protect against a coastal hazard under given sets of coastal conditions.

A number of the technical experts present at the workshop supported follow-up work to unearth, consolidate and make public such information, and by doing so, resolve some of the controversy over the protective capacity of trees and forests — especially in relation to tsunamis.

Conclusive remarks and recommendations:

1. Coastal forests and trees can, under certain conditions, act as bioshields to protect lives and valuable assets against coastal hazards, including: tsunamis, cyclones, wind and salt spray and coastal erosion.

2. The degree of protection offered by coastal bioshields depends on a number of variables, including:

(i) The characteristics of the hazard itself (e.g., type, force, frequency);

(ii) The features of the site (e.g., bathymetry, coastal geomorphology); and

(iii) The characteristics of the bioshield (e.g., type of forest/tree, width, height and density of the forest).

3. Care must be taken to avoid making generalizations about the protective role of forests and trees based on evidence from one or a few areas; the many factors that influence the protective role of the forests/trees must be understood and taken into consideration before lessons can be learned and applied elsewhere.

4. Coastal forests and trees are not able to provide effective protection against all hazards (e.g., extremely large tsunami waves, flooding from cyclones and certain types of coastal erosion); provisions for other forms of protection and (in extreme events) for evacuation must be relied upon. Care must be taken not to create a false sense of protection against coastal hazards.

5. The importance of incorporating coastal protection as an integral part of coastal area planning and management is recognized.

6. The options for protection include: soft and hard solutions and a hybrid of the two. If none of these is appropriate and viable, it may be necessary to zone coastal land use to prevent (further) settlement and construction of valuable assets in the vulnerable zone.

7. It is important to match the species with the site in order to avoid high mortality and low performance of the planted trees. Some forest types and tree species cannot survive or thrive in areas exposed to specific coastal hazards; therefore, they are not candidates for protective measures.

8. Development of bioshields is not possible in all situations owing to, inter alia, biological limitations, space constraints, incompatibility with priority land uses and prohibitive costs.

9. The level of knowledge and understanding of the functions of forests and trees in coastal protection is still insufficient and there is a lack of multidisciplinary research and cooperation in this field. Specific areas needing further attention include research in non-mangrove coastal forests and collection of data and development of models on interaction between the physical and ecological parameters.

10. There is a need to recognize that many years are required to establish and grow bioshields to a size and density that could offer protection against coastal hazards.

11. Considerable research and field initiatives related to forests and coastal protection have been carried out over the past several years; they provide a useful foundation for further work to improve understanding of the protective role that forests can offer.

Recommendations:

Assessment and design of bioshields:

1. The following analysis sequence is recommended to assess the potential for protection:

(a) Identify the areas that are subject to coastal hazard(s) and the characteristics of the hazard(s).

(b) Identify and prioritize the assets that need protection.

(c) Identify the options for protection (hard, soft and hybrid measures).

(d) Consider the costs and benefits of the protective measure(s).

When a conclusion has been reached that forests and trees should be used for protection, the bioshield should be designed using best practice.

2. The following broad approaches are recommended:

(a) Protecting and managing existing coastal forests that provide protection to people and valuable assets against coastal hazards in order to maximize their protective role.

(b) Rehabilitate existing degraded forests whose protective function has been impaired.

(c) Plant new forests and trees in sites where they have the potential to provide protection.

3. The design of protective measures using trees and forests must take into consideration not only physical and biological features, but also the economic, social and cultural factors of the site.

4. Local people should be involved in the design and development of the bioshield so that they have a stake in protecting and maintaining it over the long term.

5. The multiple functions of coastal forests and trees (i.e., economic/livelihood protection, wildlife habitat, aesthetics) need to be recognized and prioritized in establishing and managing coastal forests to enhance protection. It should be recognized that these functions and objectives may be compatible and mutually supportive, or they may be mutually exclusive.

Institutional and policy support and outreach:

1. National governments should review existing coastal forest management policies and regulations to assess their practicality, e.g., regarding set-back (no construction) zones and protected forests.

2. National and local governments should develop/revise policies on coastal forest management and, as appropriate, ICZM policies, regulations and guidelines so that they adequately reflect the role of coastal forests/vegetation in enhancing coastal protection and improving livelihoods.

3. National/local governments should develop national/local coordination bodies for coastal area management and establish realistic integrated and participatory coastal management plans, incorporating bioshield development and management, as appropriate.

4. All sectors involved in the management of coastal forests and related natural resources should be involved in the development of disaster management policies and plans and be included in national disaster management committees (where they exist) to ensure that the role of forests and trees is adequately addressed.

5. National Disaster Management Committees should identify the link between disaster management and environmental management with special emphasis on the role of coastal forests and trees.

6. Additional research and multidisciplinary cooperation is needed to improve scientific knowledge and understanding of the protective functions of forests and trees against coastal hazards.

7. Efforts should be made to translate scientific knowledge into practical guidelines and technical information for use by coastal forest managers and other relevant coastal land managers.

8. Capacity in coastal forest management for protection should be strengthened through education, training and extension.

9. Efforts should be made to raise awareness of the importance of forests and trees, apropos coastal protection among disaster management decision-makers, natural resource managers, NGOs, the private sector, local communities and the general public (e.g., through demonstration sites, published materials and mass media such as videos, comic books and “pocket books”).

National, regional and international cooperation:

1. National agencies, the private sector and international donors should provide financial support for research, capacity strengthening and field implementation related to forest management for enhanced coastal protection.

2. FAO should support enhanced regional cooperation, including through workshops, working groups and technical networks.

3. A regional database should be developed on best practices, suitable species and other relevant information for improved management of coastal forests for enhanced protection.

4. FAO should collect and publish information on local and indigenous knowledge, attitudes and practices related to the use of forests and trees for coastal protection.

5. Support should be provided to initiatives (e.g., Mangroves for the Future, Green Coast and Asian Greenbelt) that provide a framework for national actions and regional cooperation to address the issue of coastal rehabilitation for protective purposes.