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Thematic paper: Coastal area planning and management with a focus on disaster management and the protective role of coastal forests and trees

Jane Preuss1

1 Introduction

Immediately after the 2004 tsunami, extensive efforts were mobilized to identify, characterize and map the devastating losses and impacts. The recovery process continues to generate awareness of the need for an integrated approach to decision-making in coastal regions that balances the need to accommodate seemingly conflicting objectives such as ecosystem management, housing and economic development. However, a model for this integration does not currently exist. Analysis of communities that have experienced disasters reveals that too often in the rush to return to “normal,” rebuilding occurs in such a way as to recreate, and often increase exposure to repeat hazards, while not taking into consideration lessons learned from the event such as the protective role of forests and dense vegetation buffers. Such rapid rebuilding tends not to be based on plans developed before the event that identified safety set-back distances, creation of buffer zones and optimal land uses.

Background information for the regional coordination workshop entitled Rehabilitation of Tsunami-Affected Forest Ecosystems: Strategies and New Directions (FAO, 2005) clearly defined the fundamental requirements for the integrated approach:

Rehabilitation and management of forests and trees are components of an integrated approach to coastal zone management in which the needs of people in urban and rural development need to be balanced with environmental considerations and natural resources management. Issues in forestry cannot be addressed in isolation of those in fisheries, aquaculture, agriculture, infrastructure, industry, tourism and residential development. Conflicts arise when different stakeholders lay claims on land and resources when appropriate institutional frameworks and policy and strategic planning mechanism are not in place to balance trade offs between different interests. There is an opportunity in the reconstruction, rehabilitation and restoration processes to promote multi-disciplinary and inter-sectoral approaches to coastal zone management. However, this will require close collaboration and coordinated efforts between stakeholders from community levels to work with Governments (local, provincial national), funding and technical agencies, NGOs and the private sector (FAO, 2005).

Multiple geological and atmospheric hazards tend to occur in the same places and exacerbate each other’s effects, thus increasing the risk of repetitive loss from all hazards. For individual communities, vulnerability to rare large-scale disasters such as tsunamis or earthquakes is low; however, medium and localized small-scale disasters such as floods, landslides and drought re-occur frequently. Cumulatively, these annual events result in significant losses. Reduction of this complex exposure can only be achieved through an integrated approach to coastal zone management. An integrated intersectoral approach consists of three primary phases:

1 Planwest Partners, United States.

2 Phase I: Hazard vulnerability and risk assessments

Phase I establishes the baseline context for integrated decision-making. It consists of four parts:

Part I: Define the boundaries of the project area (entire country, one community, etc.)

Part II: Hazard identification

Part III: Vulnerability assessment

Part IV: Risk assessment

2.1 Part I: Define the boundaries of the project area

Objectives: The coastal hazard assessment will be used as the foundation for long-term coastal management planning. Because of the multipurpose, multisectoral uses to which the assessment will be applied, a map of the study area is important.

Define mapping protocols: Define scale and reconcile data sets for baseline variables and features for orientation which could include:

·         coastline and offshore limits of interest;

Figure 5.1
A base map defines key features that will be addressed in detail through the planning process (Hikkaduwa, Sri Lanka) Source: USAID Sri Lanka Tsunami Reconstruction Program

2.2 Part II: Hazard identification

Objectives: Threats vary within comparatively short geographic distances and not all hazards constitute important threats to each community. It is therefore necessary to define hazards for further analysis and characterization.

Identify key hazards: On a national basis, the probability of specific hazards occurring in individual communities will differ depending on such variables as climate, geology, bathymetry/topography, coastal geometry and land-use patterns. For some hazards, the entire community will have similar susceptibility, such as from a cyclone. For others, such as flooding, some portions of the community may be impacted more than others; for example, low-lying areas are more susceptible to inundation. For this reason it is important to obtain maps for as many types of hazards as possible and to clearly delineate the specific characteristics and small-scale location-based variables that will become important considerations when developing a mitigation strategy. Table 5.1 differentiates hazard exposure between two countries (i.e. Indonesia and Sri Lanka).

Table 5.1 Key hazard identification

Major hazard


Sri Lanka**

Earthquake (ground motion, landslides and/or subsidence

Tsunami x x
Severe storms x x
Floods x x
Cyclones x
Landslides x x

Coastal erosion

x x

* Personal communication with Dr Paul Grundy, July 2006

** Identified by the Sri Lankan Parliament Select Committee on Natural Disasters

Define incidence of previous disasters and document impacts: There are extensive data on damage from the 2004 tsunami. In addition to the tsunami, it is important to analyse damage from lesser, but more frequent, events to begin assessing cumulative past losses. An electronic version of data sets will facilitate correlation of multiple variables using GIS. In some cases GIS maps may not be available, in which case it will be necessary to rely on qualitative information such as oral histories. For each hazard, variables could include, but not be limited to:

2.3 Part III: Vulnerability assessment

Objectives: The vulnerability assessment identifies features that are susceptible to damage including ecosystems and artificial structures. Societal variables, including demographic profiles and sites of potential human mortality such as hospitals and schools, are also defined.

Identify and characterize impacts from prior events: Within the area identified during the Hazard Analysis, identify and characterize damage and impacts of prior disasters as well as those impacts that can be expected from future events such as coastal flooding, riverine flooding, landslides, cyclones and tsunamis.

Correlate effects with coastal geometry: Tsunami behaviour varies in relation to topography, location (especially with respect to islands) and coastal geometry (Figure 5.2). In areas where the coastline is relatively even, vegetation can buffer the effects of the wave; in areas where there is considerable articulation, wave forces can be considerably higher.

Figure 5.2 Wave intensity and inundation area may vary significantly depending on whether the coastal area is relatively straight, or whether waves are refracted off points or headlands, or funnelled into narrow bays

Some harbours may be in protected locations from the standpoint of wind energy because they are in narrow bays or have headlands that dissipate wind energy. On the other hand, such features can also focus or amplify the wave, in which case tsunami energy is focused against the infrastructure, causing extensive damage to harbour facilities and boats. This appears to have been the experience of Hamatsumae on Okushiri Island, Japan, in 1993. Tsunamis treat rivers the same as harbours; once they enter the mouth, the wave travels significant distances upriver.

Sri Lanka’s southeast coast, which is characterized by riverine estuaries, narrow-mouthed bays and lagoons bordered by sand dunes, flat sandy beaches and headlands, experienced significant damage from the 2004 Indian Ocean tsunami. In four case study locations that suffered particularly severe damage, nearshore transformation processes interacted with the shoreline geometry. In each location, tsunami waves were funnelled into a narrow bay or lagoon where the younger sand dunes in low-lying land between older dunes were breached. The combined interaction contributed to extensive damage to buildings and the devastation of vegetation, including mangroves, palm trees and shrubs (Hettiarachchi and Samarawickrama, 2006; Jinadasa and Wijerathne, 2005).

Plate 5.1 Smooth low-lying lands and young dune areas are particularly vulnerable because of the lack of frictional dissipation. Note the sparse vegetation and lack of low-lying undergrowth (shrubs and grasses)

Tsunami effects are also increased in the lee of circular-shaped islands, as demonstrated by the devastation to Aone on Okushiri Island in 1993, and Babi Island in Indonesia (Yeh et al., 1994).

Ecosystem features (offshore and onshore): Ecological features in the offshore and nearshore environments have dual importance because: (a) they are prone to damage — such as coral reefs, dunes and vegetation including trees, shrubs and grasses; and (b) they can reduce damage farther inland. They are the first line of protection against most coastal hazards because they create friction, thereby mitigating the forces of strong winds and waves.


Plate 5.2 Coastal bank erosion

Plate 5.3 Multiple varieties of littoral woodlands and dense vegetation can be effective in stabilizing soil and retarding erosion, thereby protecting inland uses (note the relatively straight coastal configuration)

Artificial features (land use and infrastructure): Land-use patterns are a reflection of changing demographics and settlement trends. In some instances,  lack of institutional oversight contributes to, or even creates, unsafe conditions by allowing such practices as encroachment into floodplains, inadequate drainage provisions, filling of wetlands and destruction of coastal vegetation, including dune grasses and mangrove forests. All of the above practices may further exacerbate the impacts of natural hazards including slope instability, erosion and siltation which, in turn, lead to increased frequency and losses from small- and medium-size disasters.

Current conditions and practices must be documented as benchmarks that can be compared with past land-use patterns. To monitor trends, the documentation will identify changes that have occurred during a specified time period, for example, over the last 25 years. Land management practices that could influence the future will also be identified, for example, encroaching urbanization which threatens forested lands.

Inventory elements include:

Plate 5.4 One aspect of land use is access. Without proper guidance, access to beaches can destroy dune vegetation

2.4 Part IV: Risk assessment: potential loss assessment

Objectives: Risk provides the basis for decision-making and institutional acceptance of protective measures. Risk is calculated by correlating information derived from the Hazard Assessment and the Vulnerability Assessment, i.e. Hazard + Vulnerability = Risk. The characteristics of risk are then analysed in terms of estimated probability of occurrence, magnitude and incidence of losses, which can be calculated both in quantitative or qualitative terms.

Synthesis (“hot spots”): Spatially correlate hazards and designate “hot spots” where multiple occurrences or types of events occur, for example, coastal erosion or coastal flooding.

Calculate probability of occurrence: Frequency of events is an important indicator of both past and future loss patterns. Because cumulative implications are important, the analysis must consider not only a large event such as a cyclone or tsunami, but also multiple and less severe events such as winter storms. Annualized losses over a ten- or 20-year time frame from lesser events may equal or even exceed the losses from a large event.

The probability of occurrence is based on frequency, as documented by historical records and scientific evidence. The time period for re-occurrence is based on criteria selected for a specific plan, for example over 30 years, the frequency that an event may occur will be of high, medium or low probability

Communities in close proximity to each other often have different probabilities of hazard occurrence. A comparison of two communities in the southern and eastern portions of Sri Lanka illustrates similarities and differences in probable occurrences. Community #1 (Table 5.2), Hikkaduwa, is flat; prone to coastal and riverine flooding, bank erosion and storm surge. Riverine flooding is often accompanied by channel migration with extensive sediment transport and/or deposition. The probability of coastal storms, riverine flooding and coastal erosion is high because the return period is annual. The historical experience of cyclones impacting Hikkaduwa is moderate; the geological evidence indicates that the probability of another tsunami impacting the area is also low, because the frequency is very rarely greater than every 15 years. Community #2, Arugam Bay, on the other hand, is characterized by variable flat areas, which, unlike Hikkaduwa, are not prone to landslides. On the other hand, Arugam Bay is prone to both riverine and lagoon flooding. Some high probability events may have low consequence individually, but may occur many times each year. Over a 20- or 30-year period, losses such as from coastal erosion could be significant. Conversely, the consequences (losses) from a single cyclone or a tsunami would be high. The consequences from the more severe event may — or may not — exceed the more frequent lesser hazards. Weighting of the consequences is therefore an important aspect of the risk assessment and the ensuing development of the mitigation strategy plan.

Tables 5.2 and 5.3 compare the probability/frequency and consequences of hazard occurrence for the two communities in Sri Lanka. Note that the vulnerabilities differ for the two communities, and thus, eventual priorities for mitigation strategies, such as forest planting, will also differ. 

Table 5.2 Probability and consequences of hazard occurrence:
Community #1 in Sri Lanka



Level of consequence

Return period

1–15 years
>15 years
>15 years

Coastal flooding


Riverine flooding**

Coastal storms

Coastal erosion


*USAID Sri Lanka Reconstruction Program (July 2006)

**Hikkaduwa River, Rathgama Lake, Gin Ganga

Table 5.3 Probability and consequences of hazard occurrence:
Community #2 in Sri Lanka
*(Arugam Bay)



Level of consequence

Return period

Less frequent
1–15 years
>15 years

Coastal flooding


Riverine & lagoon flooding**

Coastal storms

Coastal erosion


*USAID Sri Lanka Reconstruction Program (July 2006)

**Arugam Lagoon floodplains and associated rivers (Kirimitiya Aru, Karanda Oya, Sittu Aru and Goda Oya)

Comparison of characteristics and the approximate magnitude of potential loss under alternative event scenarios are important factors to help evaluate the consequences of various scenarios. The consequences should be evaluated in terms of the four variables identified during the Vulnerability Assessment: ecosystems, influences of geomorphology, and societal and economic variables (land use and infrastructure, existing protection (breakwaters, dykes, revetments, etc. demographic profiles, economic variables.

Plate 5.5 The risk assessment correlates conditions such as levelled dunes and removal of vegetation prior to the tsunami with damage to homes, livelihoods (fishing) and ecosystems (erosion, destruction of trees)

3 Phase II: Mitigation strategy planning

Phase II establishes the means to reduce the risk of losses. Such loss reduction is achieved through the application of mitigation tools and implementation strategies that address risk characteristics that are defined during the risk assessment. The Mitigation Phase consists of two parts: Part I: Identify mitigation tools; Part II: Evaluate and select mitigation tools.

3.1 Part I: Identify mitigation tools

Objectives: A variety of actions to reduce the likelihood of losses are identified. Specific objectives and implementation priorities are tailored to community needs and the characteristics of hazard exposure.

Engineered approaches: Engineered barriers must be able to withstand overtopping wave forces at crest level. Such barriers are expected to remain stable during the progression of the storm event, including during tsunami runup and rundown. If such a system is breached at a weak point, there is a high possibility of progressive collapse leading to greater inundation.

Breakwaters and seawalls: A breakwater is an offshore structure providing protection from wave energy or by deflecting currents. A seawall is a hard coastal defense constructed onshore to prevent the passage of waves and to dissipate energy. Modern seawalls tend to be curved to deflect wave energy back, thereby reducing forces. In the event of overtopping, designs typically incorporate drainage systems.

Seawalls can be effective defenses in the short term. In the long term, however, the backwash tends to be reflected to the beach material beneath and in front of the seawall, which is erosive. Specific design solutions and ongoing maintenance are important considerations to reduce such negative effects.

Dykes and levees: A dyke (also known as a levee) is an artificial earthen wall built along the edge of a body of water such as a river or the sea to prevent flooding. Dykes are often found where low banks or dunes are not strong enough to protect against flooding. Dykes and levees require regular maintenance, which, if neglected, can have disastrous consequences.

Revetments: Revetments on banks or bluffs are placed in such a way as to absorb the energy of incoming waves. They may be either watertight, covering the slope completely, or porous, to allow water to filter through after the wave energy has been dissipated.

Waves break on revetments as they would on an unprotected bank or bluff, and water runs up the slope. The extent of runup can be reduced by using stone or other irregular or rough-surfaced construction materials.

Plate 5.6 Breakwaters and revetments are often used to protect critical infrastructure such as boat harbours and coastal roadways

Ecosystem management: Ecosystem management, including the use of vegetation, has been recognized as an important means to reduce exposure to multiple hazards. Non-structural tools through ecosystem management create friction to slow velocity; they constitute porous barriers against wind and waves (Urban Development Authority, 2006). The underlying purpose is to prevent or reduce the erosion of coastlines, estuaries and riverbanks through three main processes:

Enhance coral reefs: Coral reefs are the first line of defense to attenuate wave energy.

Preserve and enhance dune formation and sand bars: Dune formation and restoration is achieved by stabilizing the soil. The first colonizers on bare sand are a species of plants known as creepers. Wind-borne sand collects in and around them as they grow, forming small hummocks, which are then colonized by fresh seedlings. Gradually sandy hillocks are formed and additional species colonize and stabilize the sand, preventing wind-induced erosion. Gradually, the soil quality improves to establish suitable conditions for the growth of more substantial shrubs, which in turn create favourable conditions for the growth of trees.

Planned forests (porous barriers): Dense plantings of trees (planned forests) have multiple functions. The natural porous structure of littoral woodlands with deep roots generates a stable barrier against wind and wave forces. They can be an efficient natural energy absorber of steady flows and long waves. They are also an effective means to stabilize banks from erosion and scouring. Such stabilization will also reduce downstream siltation (Urban Development Authority, 2006).

Many communities impacted by the Indian Ocean tsunami have cited the presence of mangroves as positive contributions to the mitigation of wave velocity and amplitude. It is essential to recognize that some species of mangroves are more appropriate than others, because each species has differing characteristics. It is also vital to consider that the geometry of the site will influence the behaviour of the vegetation.

When the 1998 Papua New Guinea tsunami occurred, many people were killed or maimed as they became impaled on splintered mangrove trees. Others took refuge in palm trees that became flying missiles when uprooted. Reports indicate that people who took refuge in Casuarina trees survived (Dengler and Preuss, 1999). A number of uncertainties remain to be investigated, including whether the palm trees were shallow-rooted or whether the instability resulted from geological conditions such as a shallow clay layer, or the width of the forest was too narrow.

Plate 5.7 Mangroves splintered by the 1998 Papua New Guinea tsunami injured or killed many victims. Damaged trees in frontal tiers of the forest apparently protected those further back

Wetlands: Wetlands of various types provide coastal protection functions which are similar to the protective functions of vegetation. Both features create friction, which slows the speed of the waves. They also create opportunities for water detention and retention. 

Hybrid strategies: The relative effectiveness of mitigation tools is evaluated in relation to specific community benchmarks or goals and priorities, which are defined by local stakeholders based on the risk assessment. Priorities are established to minimize risk, based on the probability of occurrence(s) and/or anticipated consequences. Table 5.4 illustrates the correlation of goals with alternative mitigation strategies.

Table 5.4 Correlating goals with alternative mitigation tools
(using a tsunami as a sample hazard)

Sample goals

Barrier Management

Reduce the impacts of tsunami waves prior to reaching the shoreline


Coral reef protection and enhancement

Reduce the inland movement and velocity of tsunami waves

Dyke revetments

Dune protection vegetation, planting littoral forests, land-use policies including set-backs

Facilitate access to/from the water to preserve dune vegetation


Maintain trails

3.1 Part II: Selecting and evaluating integrative mitigation strategies

Objectives: Mitigation strategies are typically hybrid approaches that combine a number of measures to maximize benefits while addressing the unique characteristics and requirements of a site and a community. It is incumbent on each community to identify alternative actions potentially appropriate to its requirements, and to evaluate these strategies in relation to its unique priorities.

Integrative mitigation strategies: No mitigation tool is responsive to all hazards or appropriate for all locations. Hybrid approaches integrate diverse tools, for example, forest planting with land use and infrastructure planning and vegetation management programmes.

Mitigation entails difficult choices between competing claims on fragile areas. Choices will involve trade-offs and the need to reconcile opportunities for ecosystem enhancement or restoration such as forests, preserving wetlands, re-establishing dunes or mangroves; securing infrastructure; and re-establishing tourist, agricultural or fishing industries.

Evaluation criteria must address such variables as frequency of hazard occurrence, as well as consequences which are quantifiable (for example, the number of hectares of destroyed ecosystems, potential lives lost, cost to construct and maintain) and others that are qualitative (for example, social dislocation and opportunity costs in terms of lost opportunities).

A word of caution at this point is important. Land-use decisions pertaining to the coastal zone are invariably complex and often highly politicized. The thumbnail summaries below are only intended to exemplify complex considerations addressed by the decision-making process. They therefore do not capture the subtleties of political processes that erupt over allocation of scarce land uses.

Case study #1: Hilo, Hawaii Tsunami Reconstruction: Central Urban Core


In 1946, Hilo, Hawaii, was struck by a tsunami generated by an earthquake in the Aleutian Islands; it was struck again in 1960 by a tsunami generated by the great Chilean earthquake. Both events inflicted significant damage on Hilo’s downtown urban core, located at the head of Hilo Bay. Because of its crescent shape, wave forces were focused at the narrow end of the bay. In both events, the tsunami overtopped the Hilo breakwater.

The two Hilo case studies illustrate differing approaches to hazard mitigation that have been adopted for Hilo’s coast. The differences, in part, reflect different timing for plan preparation; Project A was prepared in the immediate recovery period after the 1960 tsunami, while Project B (located outside of the urban renewal area but within the tsunami experience area) was prepared approximately 18 years after the tsunami.

Mitigation concept

After the second tsunami in 1960, a multicomponent plan was proposed to rebuild Hilo’s downtown core consisting of the following activities (Figure 5.3):

Figure 5.3 Hilo Redevelopment Proposal included plans for a tsunami forest (prepared in 1960, included in Hawaii County, 1974)

Project status and evaluation considerations

Breakwater: Prior to the tsunami, Hilo was protected by a breakwater that had been designed and constructed against winter storms. It had been constructed between 1908 and 1929 upon a submerged reef in Hilo Bay. Immediately after the tsunami, the US Army Corps of Engineers (COE) approved funding to extend the breakwater by 4 000 feet (1 219 metres) and raised its height to 20 feet (six metres) above mean sea level. During the 1960s and 1970s, the community debated the advisability of increasing the breakwater height, because modification of the breakwater would become a strong visual statement. Public opinion viewed the breakwater as a “towering” wall that would block views to sea. Business interests also questioned the aesthetics of the breakwater, which they feared could negatively impact tourism. While the controversy brewed, the COE continued to evaluate the economics of the breakwater, including the inability to assure complete protection from another seismic wave. In the late 1970s, the tsunami breakwater was de-authorized.

Outcome: Not implemented.

Mall and civic centre: A high percentage of Hilo’s commercial and office space was destroyed by the tsunami, thus, the top priority of decision-makers responsible for recovery was economic recovery. To stimulate the “rebirth” of the city, Kaiko’o Mall and a new county office complex were developed upland of the old town centre, on land that was elevated with fill.

Outcome: Implemented.

Community park: The Bayfront Park was developed on land that was mandated to remain as open space under the redevelopment plan. The park became an important site for a wide range of community activities. The open space was also considered to be the visual connection between the town and the bay.

Outcome: Implemented.

Tsunami forest: The tsunami forest consisted of a dense band of tall trees to create friction and provide a buffer against waves. The tall trees were to be supplemented by low shrubs to provide soil stabilization. Feasibility of the fully functional forest as planned was hampered by the importance of the coastal highway and connector roadway with major streets leading almost to the bay’s edge. The forest, as proposed, would have provided no protection for the coastal highway. Re-aligning the roadway to create the necessary depth for the forest would have reduced the size of the park. Re-alignment would also have necessitated extensive additional land acquisition. Finally, implementation of the tsunami forest would have created a visual buffer to the sea. The complexity of implementation, plus lack of public support reduced commitment to implementation. A thin band of coco palms was planted — rather than dense forest.

Outcome: Not implemented.

Case study # 2: Hilo Long Term Recovery Planning, Keaukaha Shoreline Plan

Mitigation concept

In 1979, Hilo adopted the Keaukaha Shoreline Plan for the portion of the Hilo shoreline that adjoined the commercial core. The Keaukaha coast experienced damage in the 1946 and 1960 tsunamis; the community hospital was destroyed in 1961 by a winter storm (presumably it had been damaged, but survived the tsunami). The coast is regularly impacted by winter storms and coastal flooding. The county’s major tourist area was located at one edge of the coast; the remainder accommodates the port as well as residential uses and beach parks.

Project status and evaluation considerations

Area-wide concept:

The County of Hawaii adopted a policy to create a forested green belt along the Keaukaha coast. The dense vegetated buffer had multiple purposes. On the one hand, a string of parks and trails would be developed and on the other hand the forested parks would provide protection against recurrent storms and future tsunamis (Figure 5.4).

Figure 5.4 Keaukaha Shoreline Planning Area indicating a forested belt along the Keaukaha Coast; the dimensions of the forest are not specified (Hawaii County, 1978)

Subarea concept:

Activities and land uses on Keaukaha coast were grouped into eight overlapping, but identifiable, character areas that were used as the basis for the integrated park and trail system, interspersed with residential uses — interrupted by the port. Division of the coast into subareas was one planning tool used to identify and address specific needs or conflicts between uses.

In order to implement the coastal green belt concept it was important to retain the unique ecosystems that characterized the coast. Most important were a large lagoon and major stands of trees. The lagoon was heavily used by local fisherfolk and was therefore considered by the community to be an important resource. During the Keaukaha plan preparation phase, the county was simultaneously developing plans to expand the coastal road within the existing right of way, which would have destroyed the lagoon and trees. Transportation planners were persuaded to re-align the route inland outside of the tsunami experience zone. This decision retained the lagoons while maintaining water detention and reducing vulnerability to recurring disruption from winter storms — which reduced maintenance costs. The coast route was partially funded with federal funds because it was considered to be a component of the interstate highway system (Figure 5.5).

Figure 5.5 The Keukaha subarea concept with the lagoon saved by roadway realignment to provide additional depth for planting and safety from disruption caused by storms or tsunami (Hawaii County, 1978)

Project site:

Public and private development is required to comply with set-back and landscape requirements — irrespective of the owner. Plantings on the hotel/resort site (Figure 5.6, right) are in required set-backs and are the responsibility of private landowners. These dense plantings are intended to provide protection from storms and from tsunami. Buildings in both graphics below existed prior to adoption of the plan.

Figure 5.6 Left: Coastal land form (Urban Regional Research 1982); right, project area site plan — set-backs with protective buffers (Hawaii County, 1978)

Outcome: All components of the Keaukaha plan implemented. The county acquired the parklands, which are maintained as part of the overall county park budget.

Case study # 3: Sri Lanka — reducing river bank erosion

Mitigation concept

Bank erosion caused by riverine flooding has been a recurring problem. Multiple seasonal flooding events can result in incremental bank erosion, loss of neighbouring property, and degradation of water quality. Sediment transport to the sea leads to channel migration, which can result in siltation of corals and other marine organisms. Cumulatively, these effects can be extremely damaging. Plates 5.8 and 5.9 juxtapose mitigation in two settings compared to approaches to bank stabilization when priorities differ.

Project descriptions and evaluation considerations

Project A: Mangrove forest, Hikkaduwa, Sri Lanka

A mangrove forest has been planted to reduce low bank erosion, while also protecting adjoining wetland areas that accommodate water detention and drainage. Costs are generated in the planting, because maintenance is minimal. Some continued erosion occurs during maturation of the buffer forest.

Plate 5.8 Mangrove forest used for bank stabilization: Hikkaduwa Sri Lanka

Project B: Weligama (Mirissa) roadway stabilization:

Continuous bank erosion threatens to undermine the roadway. To reduce the threat of access disruption, a retaining wall was constructed to protect the road from erosion caused by the migrating channel. Because of the location of the erosion other solutions, such as vegetation planting, were not feasible. The benefit of this solution was the immediate protection; a “soft” solution would necessitate re-aligning the roadway.

Plate 5.9 Retaining wall to stabilize a roadway: Weligama (Mirissa), Sri Lanka

Case study # 4: Coastal erosion mitigation

Mitigation concept

To provide protection against coastal erosion, thereby reducing threats to the critical roadway. The project consists of a raised embankment and revetment with planting on the shore side of the embankment.

Project description and evaluation considerations

Project A: Coastal hardening — Sri Lanka

Critical segments of Sri Lanka’s coastal roadway are at or below sea level. Restoration and maintenance of safe access was the prime consideration; a “hard solution” was selected as an economic imperative. Some trees have been planted between the embankment and the road; however, there is insufficient area for a deep tsunami forest. Seasonal fluctuation in beach sand has been reported; during periods of low sand there is reduced access to the water by fisherfolk and others and it becomes impossible for fisherfolk to pull their boats onto land.

Plate 5.10 Left: Bank revetment, Sri Lanka. Right: Tree planting on the inland side of the revetment

Project B: Hybrid protection, Hawaii

Required set-backs from the high water, together with retaining walls and low dune planting, permit buffering from winter storms while encouraging continued beach nourishment. The project continues the use of private property with government enforcement of standards and regulations.

Plate 5.11 Vegetation protection — low retaining walls and set-backs
for residential development

Case study #5: Multiple uses with forest buffers

Mitigation concept

Forest buffers are combined with other uses to: (a) provide protection against tsunamis and coastal storms; and (b) accommodate private property-based uses.

Project A: Forest buffer and wetland agriculture (rice paddies) –— Sanriku coast, Japan

This is a combination of tsunami forests with wetland and other land use that facilitate water detention to absorb storm water runoff and tsunami inundation. This scheme also deters people from moving into the hazard zone.

Plate 5.12 Combination of protective planting with agriculture to provide detention for storm water and coastal flooding water (Japan)

Projects B & C: Residential projects rearward and tsunami forest

Dense tsunami forests have been planted to protect homes from tsunamis and from the more frequent storm waves. In the case of Hawaii, the forests have been planted along the shoreline in the area mandated by state law as set-back buffers from the coast.

Plate 5.13 Left: Sanriku coast, Japan
Right: Kauai Island, Hawaii

In both cases, homes are located behind tsunami forests planted along the shore. Houses are located inland of the forest. In the Kauai example (Plate 5.13, right), houses are elevated above the projected tsunami elevation.

Case study # 6: Dune preservation and restoration programme

Mitigation concept

A first step towards improving the environment for forests is to stabilize soil conditions through dune enhancement. Such dune management programmes are multifaceted because they include restrictions on levelling and on access, as well as planting programmes and maintenance.

Evaluation considerations

Costs include the need for enforcement because such programmes will initially be unpopular in many sectors. Hotel developers often maintain that dunes block views or pathways to the beach; housing constructed by the informal sector is often located in dune areas — which must be prohibited and alternative locations must be found. In addition, access routes, including paths and standards, must be developed and clearly marked.

Benefits will include stabilized soils and reduced coastal erosion, including sediment deposition and siltation. These benefits, in turn, reduce degradation of corals and related environmental assets.

Plate 5.14 (left) Pedestrian trail with sign stating “Please keep off the dunes” — soil stabilization project (Oregon, USA)
Plate 5.15 (right) Structure pathway for a particularly sensitive dune (Oregon, USA)

4 Phase III: Institutional issues to encourage planting of forests and trees as part of coastal management

Objectives: Forest and tree planting, as well as management programmes, must become integrated with overall institutional processes associated with coastal management.

4.1 Part I: Institutional issues relating to forests and trees in comparison with other structures

4.1.1 Institutional overview of case studies

Using forests and trees for hazard mitigation is inherently a multidisciplinary and multisectoral field that requires commitment and cooperation among multiple agencies and donors. The first step towards integrating forests and other planting programmes into coastal management is to assess if current institutional practices positively or negatively influence vegetation management.

Case study # 1: Hilo Bayfront reconstruction plan after the 1960 tsunami

Implementing responsibility

There was no oversight body responsible for coordinating all components of the project on a long-term basis. Multiple components of the project were not developed by local planners. The planning process did not consider the feasibility of the recommendations.

Case study # 2: Hilo–Keaukaha shoreline plan

Implementing responsibility

A single oversight body was responsible for all components of the project on a long-term basis. It was also responsible for coordinating with multiple departments and stakeholders including private parties (hotels, residents, shop owners and others).

Case study # 3: Riverine bank erosion

Implementing responsibility

Both projects have single purpose objectives — not part of a comprehensive plan.

Case study # 4: Coastal bank erosion

Implementing responsibility

Case study # 5: Multiple uses with forest buffers

Implementing responsibility for all projects (in Japan and the United States)

Case study # 6: Dune restoration and access, Oregon

Dune preservation and restoration goals part of the state land-use law; individual dune restoration projects administered locally.

Implementing responsibility

4.1.2 Themes of successful implementation

The case studies indicate that inclusion of forests and trees as part of an integrated strategy most often occurred under the following conditions:

  1. Multiple proponents: Part of an overall plan with commitment from multiple stakeholders. Successful efforts have reflected intersectoral “buy in” and have been multidisciplinary in their objectives. For example, the Keaukaha Shoreline Plan and forest/rice paddies in Japan demonstrate multiple proponents in preserving and enhancing vegetation.
  2. Land availability: Land must be available for a forest project to be feasible. Where land acquisition is problematic or where immediate shore protection is necessary, hard solutions tend to be preferred. In communities where coastal set-backs are enforced, such lands have been used, for example in Hawaii and Japan.
  3. Management programme: A coordinating body must exist to oversee multisectoral projects from their inception through implementation and long-term management. Environmental management must be grounded on coordinated policy implementation and institutional consistency.

4.2 Part II: Create a management programme for enforcement and oversight

Coastal areas are traditionally among the most intensively used portions of a community with many competing objectives and stakeholders for limited resources. Coastal management therefore requires a consistent framework for decision-making. Prerequisites to coordinated implementation of vegetation management programmes include the following actions.

4.2.1 Create and empower an oversight body to oversee the management programme

Implementation of objectives that promote planting of trees and forests highlights the need to integrate ecosystem management with other development or economic objectives. Such integration requires a mechanism to coordinate planning and decision-making. An oversight body is essential to orderly coastal management. This body would integrate and coordinate forest management with coastal management and disaster management. This body with also have the mandate and authority to coordinate policies between different jurisdictional authorities (including local/national/or different ministries with differing priorities, e.g. forestry and transportation).

4.2.2 Institute regulatory consistency

Enforcement of standards on both public and private property development — including prohibitions on building in designated areas, is essential to the long-term implementation of vegetation management programmes.

Predictable regulatory oversight is based on three factors:

  1. A designated coastal management zone: Administrative zones are defined within which mitigation strategies are applied that are sufficiently large to encompass both the direct hazard and the area influenced by the potential hazard.
  2. Tier 1 (coastal zone): Define the land area directly impacted by each hazard such as coastal flooding, riverine flooding, landslides, cyclone or tsunami during the hazard analysis. Where applicable, subzones should also be defined, for example, the floodway and the floodplain — the floodway is an ideal location for planting.

    Tier 2 (coastal influence zone): Define the area that includes features that are vulnerable to damage and which potentially can reduce wave and wind impact, thereby reducing susceptibility to collateral damage. The area includes offshore and nearshore environments in which ecological influences such as trees and forests are or could be located.

  3. Standards and rules for allowable and preferred uses in the coastal management zone: Articulated goals must guide future development to desired locations, and building construction must comply with standards. (Note: Many of the “successful” case study examples in this paper have used mandated set-back areas to plant forest buffers.)
  4. Adopt and enforce regulations: Enforcement of laws such as set-back regulations and construction laws, as well as prohibition of practices such as coral or sand mining, will significantly contribute to reduced exposure to hazards. It is essential that commitment to regulations be enforced; for example, no construction of any kind (including by the informal sector) or building in designated areas.

4.2.3 Facilitate integrated planning processes through data sharing

A fundamental aspect of coordinated coastal management is the ability to correlate baseline data collected by many stakeholders, including national ministries, local agencies and NGOs. Review of planning processes in many countries throughout Asia indicates that data sets are not readily available to departments and agencies that have not collected them. This lack of data sharing is a serious impediment to integrative management.

4.2.4 Public education on the importance of coastal management

Sustained coastal management, including implementation of planting forests, requires local commitment. It is crucial that all sectors (public and private) accept that the implementation of planting programmes is long term. Before forests reach maturity, extensive land management may be required to prevent the use of young trees for fuelwood or other purposes.

5 Economic social and environmental costs and benefits

Objectives: Institutionalize coastal hazard management policies to maximize economic, social and environment benefits while reducing costs. This evaluation process will also develop a framework within which to explicitly demonstrate the long-term benefits of forests and trees as vehicles to achieve damage reduction.

5.1 Phase 1 for cost benefit: Review hazard, vulnerability and risk assessment findings

The benefit–cost analysis is an outgrowth of the multiphase approach outlined by this paper. Hazard and vulnerability analysis identifies key items of exposure in terms that, so far as possible, are spatially and quantifiably defined. For example, the Hikkaduwa base map in Figure 5.1 indicates environmental features such as wetlands and marshes and economic parameters such as transportation linkages, built up areas, agricultural areas and coral reef mining. The vulnerability analysis explicitly correlates interactions between social, environmental and economic variables.

5.2 Establishing a structure for cost–benefit-based decision-making

Typically, a cost–benefit analysis evaluates the viability of a project in relation to the costs of construction vs. revenue generated. An integrated cost–benefit analysis such as is being discussed in this paper will evaluate disparate alternatives. Costs and benefits will be evaluated for specific courses of action in relation to considerations summarized in Table 5.5.

Table 5.5 Cost–benefit criteria

Cost–benefit evaluation


Does not solve problem effectively

Is moderately effective in solving problem

Is very effective in solving problem

Time to implement

Many years
Several years

Three or fewer years


Short life span

Relatively permanent


Very expensive

Moderately expensive


Technical feasibility

Difficult to implement

Moderately able to implement

Easily implemented

Social/political feasibility

Unpopular/affects few

Able to implement with political cost

Popular/affects many

Environmental impact

Significant impact


Low/positive impact

Clallam County 2004.

Based on an approved ratio of implementation and maintenance costs to quantifiable benefits that can include damage avoidance.

6. Applying insights from previous analyses to cost–benefit decision-making

6.1 Dune and vegetation preservation

6.1.1 The formal sector

Plates 5.4 and 5.5 illustrate the potential impacts of economic uses on dune vegetation which is a prerequisite for soil stabilization (important for tree growth). An important difference between the two plates is a significant difference in the social profile of the economic sector. In Plate 5.4, social and economic impacts fall primarily on the formal sector, while in Plate 5.5 social and economic impacts fall primarily on the informal sector. These differences will lead to significant differences in mitigation strategies and in the cost–benefit analysis that will be required to implement the strategy.

In Plate 5.4, the main building complies with coastal development set-back guidelines. Intrusion onto dunes can be mitigated by the property owner using the strategies illustrated in Plates 5.11, 5.13 and 5.14. These solutions would all rate high in compliance with the goals in Table 5.5.

6.1.2 The informal sector

In Plate 5.5 dune vegetation was destroyed for home and fishing-support construction by the informal sector within the immediate littoral zone, and as such was environmentally damaging. Strategies to mitigate conditions in Plate 5.5 are complex and the cost–benefit analysis must take into consideration non-quantifiable issues. Social and political issues reflect difficult choices because the land is not owned by the party experiencing the social impacts. Strategies to mitigate social impacts require alternative sites for housing as well as for the fishing industry — which will have significant cost implications. A new fishing harbour was constructed in the vicinity, for which long-term economic impacts are intended to eventually improve housing options. Environmental issues for this site were also weighed against economic requirements. Instead of preserving vegetation and creating a site for forests and trees, the coast was hardened to protect the road.

6.2 Bank stabilization (choosing between forests and retainage)

6.2.1 Mangrove forest

Plate 5.8 (mangrove forest used for bank stabilization) and Plate 5.9 (retaining wall to stabilize roadway) are both located in Sri Lanka on rivers that are prone to channel migration.

For the mangrove forest site in Plate 5.8, the effectiveness of mangrove planting was rated very high, while the time to implement was not a factor. The adjacent uses were agricultural; thus, some continued erosion and bank overflow were not considered to be critical issues during the implementation period. Cost was not an issue because land for planting was available. All of the other ratings were high.

6.2.2 Retaining wall to stabilize roadway

The top community priority was to maintain access. It was therefore necessary to choose an effective means to retard bank erosion caused by the migrating river channel. The retaining wall had a high rating with respect to effectiveness and time to implement, as the river will continue to migrate; thus, its permanence depends on continued maintenance. Hybrid solutions (not represented in the plates) could be considered to reduce erosive velocity, such as giving the river additional overflow area further upstream (see forest/rice paddies in Plate 5.12). The cost of such a solution would depend on land availability and current uses along the channel.

7 Conclusions

Coastal regions will always be focal points for societal use, inter alia commerce, tourism, recreation, housing and fishing. Integrated coastal zone management balances ecosystem preservation and restoration against the short- and long-term needs of society. Such balancing of disparate and seemingly conflicting requirements necessitates establishing priorities to which participating stakeholders can ascribe. Strong leadership that is sensitive to integrative management will be required to “champion” the long-term effectiveness of forests and trees over the more expedient effectiveness of short-term “fixes” such as hard solutions. Integrative multisectoral planning has the merit of institutionalizing societal needs with the needs of healthy ecosystems. Unfortunately, the needs of society are multifaceted, with differing values held by differing constituencies. The value of forests and other vegetation buffers has been clearly demonstrated by recent disasters.

Multisectoral integrative planning establishes a framework within which to structure such a systematic programme. Clear identification of risk factors is only the first step in establishing locations for forests and vegetation buffers to maximize protection. The next step is to develop the management plan with an institutionalized administrative structure that will achieve the following:


Bryant, E. Undated. Ted Bryant HomePage. Questions and Answers about Tsunami UOW Earth & Environmental Sciences Tsunami Research Q & A


Dengler, L. & Preuss, J. 1999. Reconnaissance report on the Papua New Guinea tsunami of July 17, 1998. EERI Special Earthquake Report. Earthquake Engineering Research Institute.

Clallam County. 2004. Clallam County hazard mitigation plan. Prepared by GeoEngineers Inc. for Clallam County, Washington.

County of Hawaii. 1974. Hilo downtown development plan. Prepared by Belt Collins and Associates for County of Hawaii Planning Department.

County of Hawaii. 1978. Keaukaha shoreline plan. Prepared by Walters, Kimura and Associates, Inc. for County of Hawaii Department of Parks and Recreation.

FAO. 2005. Rehabilitation of tsunami-affected forest ecosystems: strategies and new directions. Background information regional coordination workshop, 7–8 March 2005. Bangkok, Thailand, FAO.

Federal Emergency Management Agency (FEMA). 2000. A coastal construction manual. FEMA 55CD. Third Edition, May, 2000.

Hawaii State Foundation on Culture and the Arts. 1969. Environmental and urban design proposals: East Hawaii project/city of Hilo.Prepared by the office of George S. Walters; funded by the US National Endowment of the Arts, with County of Hawaii and the State of Hawaii Department of Land and Natural Resources.

Hirashi, T. & K. Harada. 2003. Greenbelt tsunami prevention in South Pacific region. Report of the Port and Airport Research Institute, Japan, (PARI) Vol. 42, No. 2.

National Tsunami Hazard Mitigation Program. 2001. Designing for tsunamis. Seven principles for planning and designing for tsunami hazards. California, Hawaii, Oregon and Washington, NOAA, USGS, FEMA and NSF.

Hettiarachchi, S.S.L. & S.P. Samarawickrama. 2005. Experience of the Indian Ocean tsunami on the Sri Lankan coast. International Conference on Coastlines, Structures and Breakwaters, Institution of Civil Engineers, UK.

Hettiarachchi, S.S.L. & S.P. Samarawickrama. 2006. The tsunami hazard in Sri Lanka. Strategic approach for the protection of lives, ecosystems and infrastructure. Indian Ocean Tsunami, Special Issue. Coastal Engineering Journal, Society of Civil Engineers, Japan.

Jinadasa, S.U.P. & E.M.S. Wijerathne. 2005. Assessment of geo-morphological influences to protect the tsunami hazardous southeastern coastal belt of Sri Lanka. Asian and Pacific Coasts 4–8 September 2005.

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Sri Lankan Parliament Select Committee on Natural Disasters. 2005. Report of the select committee on natural disasters to recommend steps to minimize the damages from natural disasters.

UKLanka .net .June 6, 2005. (available at

Urban Development Authority Environment and Landscape Division. 2006. A basic guide to design, planting and establishment of coastal greenbelts in Sri Lanka. Published as Annex to USAID Sri Lanka Tsunami Reconstruction Program (SLTRP-00026), July 2006.

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Yeh, H., Liu, P., Briggs, M., & C. Synolakis. 1994. Propagation and amplification of tsunamis at coastal boundaries. Nature November 1994.

Field study presentation: Mangrove planting for coastline protection — to plant or not to plant?

Tan Kim Hooi, Centre for Coastal & Marine Environment, Maritime Institute of Malaysia and Ong Jin Eong, Universiti Sains Malaysia (retired)

The 2004 Indian Ocean tsunami was generated by a massive 9.3 Richter scale earthquake. The destruction wreaked by this tsunami was colossal in terms of loss of human life and coastal property. A number of anecdotal reports indicated that mangrove forest played a role in saving lives and property; destruction and degradation of mangroves were blamed for exacerbating the damage incurred. As a result, governments and NGOs are embarking on plans to plant mangrove belts along coastlines to provide protection from future tsunamis. This paper provides basic information on the natural distribution and regeneration of mangroves, examines the need for mangrove planting along coastlines in tsunami-affected areas based on field observations, repositions policy priorities for mangrove protection and rehabilitation, and offers options for coastal protection where mangrove planting is not possible.

Key points and observations emphasized in the discussions

An integrated approach is necessary in coastal area/disaster management planning to accommodate seemingly conflicting objectives such as ecosystem management, housing and economic development. This could lead to a reduction of exposure to disasters. Planning for coastal areas must often consider multiple hazards, as they tend to appear in the same places (with some exceptions).

An integrated sectoral approach comprises three stages:

  1. Hazard vulnerability and risk assessment
  2. Mitigation strategy planning
  3. Institutional issues to encourage planting of forests and trees as part of coastal management

Coordinated, integrated and participatory planning is an effective way to enhance coastal area management and the role trees and forests play in coastal protection. The use of bioshields should be considered within the framework of disaster management strategies, which also include effective early warning systems and evacuation plans.

Malaysian case study: Controversy existed over the protective capacity of mangroves following the tsunami, but decisions had to be made about protecting and rehabilitating mangroves, in the additional context of sea-level rise. Adequate protection of existing mangroves should be given priority.

Casualties from the tsunami occurred in estuaries and on open beaches, but rebuilding took place directly on the coast nonetheless.

Mangroves are not useful for protection near the epicentre of a tsunami/earthquake, or were degraded and mostly absent in tsunami-hit areas.

Mangroves may be rehabilitated and can self-repair if the hydrology is correct and natural seed recruitment is possible. Many efforts failed owing to a lack of technical information on how to establish mangroves. The correct species should be used in the right place; abandoned shrimp ponds should be rehabilitated, but this does not apply to mudflats or rocky coasts. Non-mangrove species may be used for beaches and sand dunes.

Additional points made in subsequent discussions: That there was less difficulty with reconstruction and rehabilitation after Hurricane Katrina in the state of Florida (where disaster management issues are taken very seriously) in comparison with the state of Lousiana (where there is no disaster management plan and no building codes), was reported as a recent example of the importance of coastal planning for the mitigation of natural hazards.

Apropos possible coastal planning approaches in localities where ownership is often unknown (for example, Aceh, Indonesia), and whether hard or soft structures should be used, it was stressed that each community is different and blanket recommendations are not possible; therefore, every site should be studied on a case-by-case basis.

It should also be taken into account that the planning process takes approximately five years due to the need for a consultative, participatory process, which is critical for beneficial outcomes.

Early warning systems, training and awareness-raising should be included in disaster management approaches and may be more appropriate than “tsunami shelters” (i.e. shelters similar to those used for protection against cyclones).

It was suggested that discount rates should be considered in determining the types of structure to be used in coastal protection.

In addressing rehabilitation and reconstruction needs after the 2004 Indian Ocean tsunami, several countries have called for the urgent restoration of mangroves. In some cases the high demand for mangrove seeds and propagules has led to overcollection, which has damaged the ability of natural mangroves to regenerate.

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