Proceedings of the Institution of Civil Engineers -

Engineering Sustainability

ISSN 1478-4629 | E-ISSN 1751-7680
Volume 159 Issue 1, March 2006, pp. 23-30

 

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In developing countries many houses are built by the most vulnerable persons in unplanned settlements on land that is marginal in construction terms and often subject to high landslide risk. This paper outlines a low-cost, community-based approach to landslide risk reduction undertaken in St Lucia, West Indies. The process of establishing a Government management team integrated with joint community implementation is described. Three key elements comprising a mapping methodology for landslide risk, identification of dominant slope instability controls and implementation of low-cost sustainable measures are described. The successful pilot project demonstrates the feasibility of such a low-cost approach to landslide risk reduction and offers a major step forward in establishing appropriate preventative measures for minimising landslide risk in vulnerable communities.

The World Bank estimates that the number of urban poor living below the poverty line in 2000 was 1500 million and that this number is set to grow.1 The occurrence of a landslide can seriously affect individual residents living in poor urban conditions, cause disruption to essential services and involve a significant cost to the authorities in terms of engineering intervention. In the more extreme cases major landslide occurrence can be expensive to governments in the context of rehousing and relocation costs. To reduce social and financial costs to a community, as well as financial costs to governments, it is desirable that landslide risk reduction measures are identified and implemented wherever possible. This paper outlines the results of a pilot study in St Lucia, West Indies, which had the twin objectives of establishing a sustainable management structure to reduce landslide risk and implementing specific strategies within communities to begin to address those risks. We address two general factors–institutional weakness and the efficacy of local stakeholders in reducing risk. The main problems faced by Caribbean countries are the same factors that contribute to natural disaster vulnerability: relatively low institutional strength, rapid and often unregulated urbanisation, persistence of poverty and possibly climate change.2 In particular, lower levels of institutional strength in respect of risk reduction can have very negative effects on the country's economy in terms of debt and fiscal balance. Local populations should be made aware of landslide risk reduction–such knowledge can provide a very effective way of reducing risk.3 In developing a sustainable approach to landslide risk reduction, in this pilot study we have therefore explicitly sought to provide mechanisms for institutional strengthening and to link them directly with community involvement and public awareness.

The increasing level of construction activity (both domestic and infrastructural) in developing countries is giving rise to a growing frequency of small- and medium-scale disasters related to patterns of human environmental intervention, indicating that disaster risk is accumulating.4 These disasters may have a larger cumulative impact than the spectacular but occasional large catastrophes. The problem faced by many of the most vulnerable communities is illustrated in Fig. 1. This example, from St Lucia, West Indies, shows a house that has had to be demolished because of the occurrence of a landside undermining the foundations. Unplanned housing developments built on steep slopes frequently lack any form of adequate slope drainage, hence making steeper slopes particularly vulnerable to landslides. Of course, the majority of unplanned or squatter-type settlements are frequently to be found on just such steeper, marginal, slopes and so intrinsically there is already a high risk of slope instability. Matters can, however, be more complicated. In certain circumstances the steeper slopes have shallow soil cover and hence piling can readily reach intact parent rock material. Conversely, at shallower downslope locations, the soil regolith may be substantially greater, large-scale topographic convergence may cause locally high pore water pressures and accordingly the shallower slopes may provide a significant slope stability risk. Fig. 2 shows a landslide on a 15° slope threatening unplanned housing in the immediate vicinity, caused by upslope topographic convergence of surface water resulting in locally high pore pressures.

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Fig. 1. A landslide in an unplanned area of housing in St Lucia. The house shown has since had to be demolished

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Fig. 2. A landslide (marked) caused by upslope soil water convergence on a shallow slope, threatening unplanned housing

While appropriate mitigation measures can be extremely costeffective in both social and financial terms, a major issue that needs to be tackled is the multi-disciplinary nature of slope stability problems. The identification of appropriate landslide risk reduction measures can most appropriately begin with learning from communities as to the particular areas of greatest concern (of which, of course, they have detailed knowledge). Using this background information, the subsequent involvement of engineers, hydrologists and planners is essential to discuss, analyse and then define possible best measures to mitigate landslide risk.5

Landslide risk reduction requires a multi-disciplinary holistic approach. Information needs to be gathered from a variety of sources, integrated in a manner that allows the correct identification of process controls on slope stability, and resultant mitigation measures presented that allow residents in part of a community to understand why one particular measure is adopted in one slope zone and (because of subtle differences in the dominant slope stability control processes) different interventions may be recommended in another.

2.1. Establishing the cross-ministry team

In construction, there is now a substantial body of work that identifies sustainability indicators and key performance indicators that assist in project performance and raise awareness of sustainability.6,7 Clear evidence-based policy (i.e. a circumstance in which significant evidence is available to support a given policy direction) and appropriate ethics and values need to be embraced if sustainable developments are to be successful.8 In the context of formulating a sustainable process of landslide risk management for lower income countries, however, there is comparatively little by way of evidence-based policy information available to guide us as to the best ways of establishing and delivering sustainable management. Indeed, so far, most environmental performance research has focused on Organisation for Economic Cooperation and Development (OECD) countries; there is very scarce knowledge available in the academic literature on how environmentally related policy is institutionalised in single developing nation states.9

The aim of this paper is to begin to contribute to evidence-based policy in the area of sustainable landslide risk management by reviewing the establishment of a within-government cross-ministry management team and the implementation of community-based risk reduction measures. It is the multi-disciplinary nature of landslide risk that led us in 2003 to form a cross-ministry committee in St Lucia, West Indies. The role of the committee was to address the management of slope stability in communities (the MoSSaiC management committee) and was structured to comprise representatives from eight government ministries and agencies to tackle landslide risk reduction (Fig. 3). This structure was central to the belief that in order to tackle risk reduction in a successful and sustainable way, a holistic view needed to be taken and the committee itself needed to both reflect and own that belief. A core mission of that committee is capacity-build within government. Specifically, the MoSSaiC vision is to

  1. build local capacity in the broad area of slope stability while simultaneously seeking to minimise resource expenditure

  2. achieve the vision by identifying key environmental projects that can be undertaken by existing governmentbased staff and local communities

  3. establish team structures that are key to delivering the vision; a management team that develops and communicates the vision; field teams that develop project strategies and implement specific project plans.

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Fig. 3. The cross-ministry management team configured in St Lucia

Since its inception in July 2003, the MoSSaiC management committee has comprised members from Government of St Lucia ministries and agencies (Agriculture; Communications, Works, Transport & Public Utilities (MCWT&PU); Physical Development; Planning; Social Transformation), National Emergency Management Organisation (NEMO), Organisation of East Caribbean States (OECS), Water and Sewerage Company of St Lucia (WASCO), Sir Arthur Lewis Community College, and the University of Bristol, UK. The management committee comprises ten members from these groups. In 2004 the Government of St Lucia formalised the committee, instigating terms of reference and the requirement for the committee to provide annual reports direct to Cabinet. The committee, currently under the chairmanship of the University of Bristol representative, has now been tasked with overseeing budgets assigned under the 2005/6 annual Government Budget Announcement.

For certain projects there will always be an absolute need for international level expertise to be ‘brought in’ to a country to supply specialised knowledge (usually design, but not necessarily site investigation). For example, tunnel construction and associated stability issues will very likely exceed the technical experience of local engineers (government or private). However, focusing on an internal management team we believe ensures the best approach to sustainable risk reduction, since it

  1. creates a ‘learning organisation’ dynamic

  2. promotes cost minimisation

  3. provides secure links from government through to community that are themselves sustainable

  4. ensures optimal assimilation of appropriate background data

  5. provides for a coherent connection with social development funds that deliver intervention at the community level.

2.2. Community Project Committee

In St Lucia, the World Bank (and other donors) established a social development fund (the Poverty Reduction Fund, PRF) to target assistance to the most vulnerable communities. The projects submitted to that fund from communities require the establishment of Community Project Committees (CPCs). Elected members from the community, having complementary skills and a willingness to promote best practice through a public awareness approach appropriate to that community, are key qualities for CPC members. Such committees are instrumental, indeed pivotal, in providing the link between the cross-ministry management team and community members. Sohail and Baldwin comment on the relationship between community-level involvement and sustainability being very important: ‘maximising the community involvement at all stages means that people contributed readily and were more willing to take care of the facilities once installed’.1 Additional evidence from public participation procedures shows that the public are capable of reaching technically and socially complex decisions that are neither irrational nor zero-risk based.10 Accordingly, in the pilot study reported here, close liaison was maintained between the MoSSaiC team and the CPC nominated by the community in which the pilot was based.

With the MoSSaiC team in place and the CPC structure recognised, a pilot was established by the MoSSaiC management team in the Skate Town area of Castries, St Lucia, West Indies. Skate Town is a zone of unplanned housing on generally steep slopes, with no significant managed slope drainage. The community is among the most vulnerable in terms of social needs and housing conditions. A relatively recent major landslide had occurred in a broadly similar topographic and social context that involved the relocation of numerous residents and a cost to the Government of EC$2 million, funded in the form of a loan from the regional banking system.11 It was particularly timely therefore to pilot a landslide risk reduction strategy in the Skate Town Community. We followed three logical steps in the development of the strategy, all of which were designed to focus on sustainability of the political process, community engagement and appropriate physical interventions.

3.1. Slope zonation mapping

The initial step taken was that of talking with community residents on site to ascertain precise information on landslide occurrence, structures showing signs of distress, identification of areas of the slope prone to surface water and the main natural slope drainage lines. All this information was then incorporated on a site plan and supplemented by a walk-over survey to examine locations of large-scale topographic convergence (and hence the likely generation of high pore pressures).12 Fig. 4 illustrates the field plan produced as a result of this process. In particular, the following five zones were identified

  1. Zone A: steep slopes (50°) with high-density housing (roof coverage approximates 70% of slope area); shallow soil regolith with bedrock within 1 m of the slope surface

  2. Zone B: steep slopes with small footpath drains that could apparently be easily overtopped in moderate rainfall events

  3. Zone C: evidence of previous slope failure due to topographic soil water convergence

  4. Zone D: steep slopes with unfinished culverts that could result in houses being flooded and structurally undermined in moderate rainfall events

  5. Zone E: footpath drain junctions could be blocked, causing generation of surface water and consequential slope infiltration.

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Fig. 4. Initial landslide risk zonation mapping undertaken in the Skate Town community, Castries, West Indies. The circle indicates an area of potential landslide risk identified in the mapping zonation process. This area was subjected to a landslide some three months after the mapping exercise was undertaken (see Fig. 5)

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Fig. 5. Landslide and retaining wall failure in Skate Town—a location previously identified as high risk in the risk map developed for the community (Fig. 4)

The process of zonation in this manner sought to engage the local community in the process and identify (with their help) the likely processes dominant in landslide risk in specific areas of the community. Such a process was considered important in that it would facilitate, at a later date, explanations within the community as to why one type of intervention would be needed in one sector, while a different intervention might be proposed in another. The survey indicated the apparent significance of the need to introduce effective surface water management on the slope if the landside risk was to be reduced. This included the need, in public awareness terms, to convey to residents the importance of installing roof guttering and connecting all waste water from houses to drainage lines.

The zonation mapping exercise undertaken with the community identified two areas of potential landslide risk (Fig. 4). Some three months after compilation of the zonation map, a slide occurred in one of the two risk areas previously identified (Fig. 5). Heavy rainfall accentuated by topographic convergence caused a significant slide and the overturning of a retaining wall. Retaining walls in communities typical of that of Skate Town are usually constructed by individual residents and are vulnerable to failure. The design often fails to capture the highly dynamic pore pressure regime at the back of the wall, which plays such a vital part in the overall stability of the structure.13 However, the occurrence of this event demonstrated the appropriateness of the zonation mapping process to the community, the PRF and to Government.

While this landslide event apparently served to indicate the importance of infiltration-induced slope instability, prior to looking at appropriate intervention methods the community could embrace, any intervention methods would only really be effective if the dominant instability processes were indeed likely to be infiltration-induced. This would mean that managing the surface water would be an effective macro landslide risk reduction strategy.

3.2. Instability process identification using CHASMTM software

A major component of the correct identification of landslide risk reduction approaches is the application of slope stability software. For this purpose an integrated slope hydrology and slope stability software package such as CHASMTM is appropriate. Full details of this coupled fully dynamic slope hydrology/ stability software have been given elsewhere.1417 CHASMTM is designed to help estimate the effects on slope stability of selected storm events, surface covers, slope plan curvatures and other important slope and material properties. CHASMTM key capabilities include

  • unsaturated and saturated slope hydrology modelled using a finite-difference formulation directly coupled to slope stability slip search

  • fully dynamic slope hydrology implemented for convergent, divergent or rectilinear slope geometries

  • incorporation of vegetation cover effects for both slope hydrology and slope stability

  • Microsoft Windows slope draw facility that is user defined

  • specification of multiple soil strata and associated properties.

Since the software includes surface cover, leakage, dynamic rainfall, unsaturated and saturated soil water modelling and a slip search algorithm, it allows the determination of dominant instability processes, be they hydrological, geotechnical or bioengineering in nature. Appropriate application of this software can provide guidance as to the potential causes of slope instability at a site and thereby indicate the type of mitigation methods that should be examined. The software has been installed in the Ministries of Agriculture, MCWT&PU and Planning for research purposes in St Lucia as part of the MoSSaiC programme.

The CHASMTM software was configured for scenario testing on the Skate Town slope using two soil types from field observations and related laboratory testing the Skate Town slope using two soil types from field observations and related laboratory testing (c′ = 3, φ 18; c′ = 15, φ = 40; φb = 15 and with a 24-hour rainfall of 10 mm/h corresponding to a recurrence interval of 10 years, where c′ is effective cohesion (kPa), φ is the angle of internal friction and φb is the unsaturated friction angle (degrees))18,19 (Fig. 6). The results from this scenario gave minimum factors of safety of 0·98 with a maximum failure surface depth of 2·5 m using an automated grid search technique. These results demonstrated that infiltration-induced slides are likely to be the relevant processes for which risk reduction strategies need to be addressed, and thus that intervention methods should be focused on appropriate surface water management improvements.

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Fig. 6. Main dialogue window of the CHASMTM software used for the assessment of infiltration-controlled

3.3. Sustainable Intervention measures

Identification of surface drainage issues using the zonation procedure outlined above facilitated the deployment of five intervention methods

  1. installation of low-cost water table monitoring

  2. installation of low-cost drainage designs

  3. construction of additional culverts in key locations

  4. configuration of a ‘show home’ within the community to demonstrate good drainage practice

  5. field- and ‘classroom-’ based training for PRF community technical officers.

The MoSSaiC management team directly facilitated the collaboration between the MCWT&PU, the PRF and the Skate Town community to install low-cost groundwater monitoring methods. Configuring an MCWT&PU field team (Fig. 7) allowed the installation of inexpensive piezometer tubing from which community residents are able to monitor water levels themselves. The process of residents monitoring groundwater levels in the immediate vicinity of their property provides an important component for public awareness initiatives because residents are made keenly aware of the role of groundwater levels in slope stability.

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Fig. 7. Field team from the MCW&PU who, under the MoSSaiC team management, assisted in the installation of low-cost groundwater monitoring piezometers

Removal of surface water to existing culvert drains is a very high priority on such steep slopes. The MoSSaiC team designed a low-cost drainage system comprising sunlight-resistant polythene overlain by a locally purchased wire mesh to facilitate the provision of a soft engineering approach to surface drainage (the STARTM drainage system). Costing less than 10% of comparable concrete drains and capable of being constructed by community residents themselves, this drainage system has been trialled in the community. Fig. 8 shows a section of drain at the time of construction. This system affords a major opportunity to improve drainage at low cost, provides a soft engineering solution and uses readily available local materials. In a similar manner to groundwater monitoring, the fact that the community constructed the drain again assists the public awareness dynamic and the likely sustainable nature of the intervention. Thus the cost base comparison is definitively low first cost and the near certainty of low lifecycle cost.

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Fig. 8. Community members constructing the low-cost STARTM drainage system in the Skate Town community

The zonation mapping exercise identified three major additional drains that were required to link with existing culverts and to which the low-cost STARTM drains could then be connected. Once these were identified the MoSSaiC team facilitated subsequent rapid discussions with the PRF and community residents to implement the recommendations for culvert construction.

A fifth low-cost intervention was implemented following Government, PRF and CPC agreement to the value of selecting a ‘show home’ within the community that would illustrate all aspects of low-cost good practice as far as drainage of water from the house was concerned. The Fig. 8. Community members constructing the low-cost STARTM drainage system in the Skate Town community CPC consulted with community residents to determine an appropriate location. As a result of this process, a show home is now configured in which kitchen and other waste water is piped directly to the newly constructed STARTM drain (Fig. 9(a)) adjacent to the property and roof guttering is connected to a 400 gallon tank with an overflow connected to the intercept drain at the rear of the house (Fig. 9(b)).

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Fig. 9. Show home completion in Skate Town illustrating good practice in house drainage: (a) connecting kitchen waste water to the STARTM drain; (b) provision of a 400 gallon tank to take water from roof guttering with an overflow connecting to an intercept drain at the upslope rear of the house

Having completed these five intervention elements within the community, this provided an ideal ‘laboratory’ in which to base a training course for community technical officers based in other regions of St Lucia. Participation of key local residents, who themselves had assisted with the construction of low-cost drains and the ‘show home’, provided on-site guidance to the course participants. This they were able to do in respect of outlining the advantages of taking a holistic view of risk reduction, as well as providing specific advice on detailed construction aspects of the interventions. This was seen as a most significant step in developing sustainable capacity build.

These five intervention methods demanded the coordination of community, the PRF, Ministry of Communications and Government to secure appropriate funding, gain acceptance of the proposals and deliver the specific recommendations on the ground, as well as to raise public awareness within this vulnerable community. All of this was achieved through the cross-ministry MoSSaiC management team (Fig. 3); since the process deployed existing staff, the interventions contribute significantly to sustainable improvements on the ground and to institutional strengthening in a manner that is ‘low cost/high return’.

The multi-disciplinary MoSSaiC committee, in focusing on delivering low-cost methods of reducing landslide risk at the community level, is an important and sustainable structure for government. The specific project we have outlined is an indicator of such a committee's ability to build capacity within government. With such a focus and vision, the MoSSaiC concept provides an instrument for communities and government alike which, as we have stressed, is ‘low cost/high return’ in regard to landslide risk reduction. The inter-ministry collaboration achieved and outcomes delivered to communities within the last 12 months are now being applied to other areas.

The MoSSaiC structure has facilitated a key community member from the Skate Town community providing assistance to establish exactly the same process within another community Trou Rouge) in Castries, St Lucia. This is an important catalytic achievement in terms of capacity build, which can be taken as evidence of the likelihood of the process we have outlined as being sustainable not only within government but also within communities. There is substantial evidence that risk reduction costs around 15% of the cost of repairs after a disaster has occurred,20 based on a United States Geological Survey. The assertion from that study is that preparing to avert disasters costs less than repairing damage caused (based on the period 1990–2000 for all disasters worldwide). In seeking to emphasise the importance of risk reduction we not only recognise this point, but extend it to demonstrate that a sustainable within-government management structure can deliver risk reduction strategies. Endorsement of the success of the pilot implementation has come from the Government of St Lucia, which has now ratified the MoSSaiC management committee as having a formal reporting line to Cabinet.

Figure 10 summarises the structure of the community–government linkages and the specific risk reduction implementation measures undertaken by the teams. In particular, there are five characteristics that render the pilot study a sound template for landslide risk reduction in lower-income countries

  1. a functioning within-government cross-ministry management team

  2. community involvement in the risk zonation process

  3. public awareness–accepted as significant by the community in the establishment of the ‘show home’

  4. cross-community participation established following the Skate Town pilot

  5. training courses delivered within a community context to ensure interaction between residents participating in the interventions and technical officers from other communities.

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Fig. 10. The organisation framework created by the MoSSaiC team to provide a sustainable community-based landslide risk reduction strategy. This structure provides a suitable template for implementation elsewhere

The original elements of this pilot study are the ability to create vertical integration from community to government, to achieve horizontal integration in ensuring community-to-community transfer, and taking a holistic view of landslide risk processes within communities. The success both of institutional strengthening and sustainability of the process we have established needs to be monitored over the coming two or three years. There is, however, sufficient encouragement at this point to consider that the pilot we have described provides a very positive model for other countries within the Caribbean region and beyond.

The low-cost community-based pilot programme of landslide risk reduction outlined in this paper provides a framework for innovative sustainable intervention in this important area of risk. In a period of just two years, socio-political aspects have been configured and technical on-the-ground delivery of both risk analysis and drainage interventions has been achieved. We see this as a major initiative in moving from a culture of reaction towards a culture of prevention: ‘preventative action is both more humane than curative measures, it is also more cost effective’.20 There is now the opportunity to learn from the successes within the pilot programme reported here, convert the pilot to a regional programme and begin discussions on government-level policies that support a landslide risk reduction strategy.

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