TEAMS
POSITION PAPER ON THE EARTH MOVEMENT CRISIS OF
BLACK MALLET AND MAYNARD HILL
TABLE OF CONTENTS
TEAMS - Total Environmental Assessment and Management Solutions Range of action proposed by TEAMS and their benefits
Launching a public sensitization and education campaign to encourage slope stabilization and the importance of adherence to hazard legislation
Identification of landslide prone areas and mapping of them according to position and character
Identification and development of controls and remedial measures
Define the need for further investigation
Development of a legislative response to protect against future landslide crisis
TEAMS POSITION PAPER ON THE EARTH MOVEMENT CRISIS OF
BLACK MALLET AND MAYNARD HILL
Over the past month residents of Black Mallet and Maynard Hill have experienced significant earth movements which have
caused structural damage to buildings, utilities and roads. The lack of information regarding the reason for the sudden
movement and its potential for future damage to human life and property in the area is also causing concern among residents.
By all indication this situation has affected more than 40 houses as of October 15, 1999 with at least five families relocated.
The situation started during the first week of October where the residents started noticing small cracks in the roads and some
homes. In a matter of three days, the cracks widened causing extensive damage to some homes and the roads, and breaking
underground water pipelines. As of this week, a substantial portion of the newly built Castries River Wall has fallen, threatening
to compromise the success of this Disaster Preparedness Project. The situation in Black Mallet and Maynard Mll requires an
appropriate response but it more emphatically calls attention to the problem of slope instability in St. Lucia and the need for
appropriate sustainable action to protect human life and property.
Filling in of these cracks is not a meaningful or long-term response. The situation requires study of the geomorphological forces in the Black Mallet-Maynard Hill landslippage immediately.
The Black Mallet Maynard Hill Disaster confronts us all with the complex issues involved with construction on landslide-prone
areas, which describes much of St. Lucia's slopes. Landslides are a dynamic manifestation of the unchecked confrontation
existing between humans and other natural forces.
The amount of investment that already exists on our hillsides is enormous. So too, the complex issues involved
with construction and development on St. Lucia's landslide-prone slopes.
Landsliding takes place when slope materials are no longer able to resist the force of gravity. This increase in shear resistance
may result from either internal or external causes. Internal causes involve changes in either the physical or the chemical
properties of the material (rock or soil) or its water content. External factors that lead to increases in sheer stress on the slope
usually involve a form of disturbance that may either be natural or induced by man. Essentially these two elements (shear
resistance and shear stress) work to create conditions for slope material failure and forces that actually cause it to &d
respectively.
| Examples of factors leading to an increase in shear stress |
Removal of lateral; or underlying support |
| Examples of factors leading to a decrease in shear resistance |
Materials |
Therefore, Fs the safety factor for the stability of a slope can be defined as
1Fs= The sum of forces resisting slope failure | Fs= Shear strength |
--------------------------------------------------------------------------------------------------------------------------------
IF Fs> 1.0 STABILITY IS LIKELY BUT IF Fs < 1.0 INSTABILITY EXISTS (OR IS INMMINENT).
The propensity toward landslides on the St. Lucian landscape is influenced by the combination of factors. They include: steep
slopes, high slopes, concentrated soil water (high pore-water pressure), deeply weathered soil cover, undercutting of the base
of slopes, and weak incoherent material outcropping below stronger more coherent material and deforested slopes. Because
St. Lucia's landscape is subject to both tropical rainstorms and earthquake /tremor activity, the potential for landsliding
is even-higher.
From an environmental perspective, landslides are frequent and natural occurrences. From a human perspective, they seem
rare and traumatic events. Dramatic changes in land use patterns and density, and the absence of mitigation measures facilitate
landslide episodes. And as flat becomes increasingly scarce, the appeal of unsuitable land begins to outweigh the risks. In
short.
| 1The calculation of F, depends upon the on-site measurement of the geotechnical properties of the slope materials or the analysis of rock or soil samples in the laboratory (see Petley, 1984). These geotechnical properties tend to identify the state of preparation, as defined above, and may fail to consider factors (such as river undercutting) which may be present but have not yet transmitted their influence to the site being investigated. In such situations a geomorphological study can make a significant contribution to the assessment of slope stability, by identifying those characteristics of the situation of a slope that are likely to have an external influence upon stability. |
We forget. We live under the false belief that we are in control of these forces and in our action undermine the already precarious state of slope balance. As a result, when landslides occur and recur, we are shocked and disbelieving, as though unaware of our natural reality.
Despite our natural preponderance for slope collapse, the significance of human activity cannot be understated. Through our
ignorance and false beliefs we undertake activities in areas clearly unsuitable and undermine shear strength and increase shear
stress on our already unstable slopes. This may occur through excavating at the base of the slope, creating a steeper slope and
removing some of the basal support. Another action that has far reaching implications for slope protection is clearing slopes of
vegetation cover, which would normally have resisted shallow slope failures, not only through the binding effects of roots but
also through the absorption and evapotranspiration of water drawn out of the soil. Building of houses on unmanaged slopes
oversteepens the slope and overloads the surface, greatly increasing the chances of slope failure. The list of human
mismanagement goes on. Building densities that exceed the natural limits of the slope, improper channeling of household waste
water, and even construction of roads and highways with the associated environmental impacts. It is imperative that we take
immediate action to make the connection between our action and its impact on environmental health and its sustainability.
With each landslide episode, the impacts worsen because of the increased density of development and the escalating costs of infrastructure replacement and relocation of residents. Solutions are difficult to implement for many reasons including:
TEAMS-Total Environmental Assessment and Management Solutions
TEAMS is an environmental management consultancy that is concerned with the broad range of activities involving human use of land, air, plants, and water. Our interest in the Black Mallet/Maynard Hill disaster developed out of our assessment that this issue is the epitome of an environmental crisis. We also believe that the Black Mallet/Maynard Hill disaster is not an isolated incident but one that serves as an indication of our ill preparedness to deal with environmental management issues from a holistic and sustainable perspective. The Landslide inventory map produced after Tropical Storm Debbie, 1995 inventoried the slopes of weakness across St. Lucia. In conjunction with any contour map of St. Lucia, the magnitude of the earth movement issue for the entire nation can be properly grasped in its enormity (See figures 1 &2).
Action taken with this disaster has the potential to impact not only the residents of Black Mallet/Maynard Hill and the surroundings but the entire island. Within this disaster lies the opportunity for the analysis not only on the Black Mallet/Maynard Hill disaster but on the slope safety factor of other slopes across the island which holds high densities of our population. It is essential we move beyond this crisis to protecting the thousands of lives and the millions of dollars in property and infrastructure and that are currently held on our slopes.
TEAMS acknowledges the need for a multidisciplinary taskforce to work on environmental management issues and our
TEAM designated to work on this concern includes:
- An environmental scientist and computer scientist
- A physical planner
- A physical geographer (specializing in hydrology and geomorphology)
- An environmental policy developer
- Two environmental geographers
- An engineer
TEAMSproposes that any management strategy of the Black Mallet/Maynard Hill disaster must go beyond crisis management and look toward long term solutions that have applicability to the entire island and communities that potentially face the slope failure.
Range of action proposed by TEAMS and their benefits
IMMEDIATE PRODUCTION OF, A NATIONAL LANDSLIDE PROGRAMME which will comprise of :
Statements like those found in the Mirror Oct 15th, 1999Vol. 6 No. 07 stated "I believe this has to do with the river project which is taking place. {The building of 1,250 metre Castries River wall} You see they dug the river to build these walls and took too long to fill it up so the earth has shifted to fill in the space, " and Pat Brown's statement "This is as a result of the excavation at the toe of the hill," (The toe meaning the Castries River bank in the area of Marchand) ... "You see this whole area from Bois Cachette right across to Pavee and Black Mallet is made up of rock. Over the rock there is loose soil and when the clay reaches saturation point this causes a sliding plate over a solid rock. What aggravated this thing was the excavation at the toe of the slip, this excavation was kept open for quite a while and this is what aggravated this problem." Neither reality nor scientific study supports the widespread belief posited by both layman and engineer of a single causal factor as responsible for the landslides.
Benefits: A lack of knowledge among the general public, civil service and the construction industry is a challenge to any
meaningful change required to protect the stability of slopes. No single factor causes landslides although the construction at the
base may well have been the feather that broke the camel's back. It is imperative that the public is informed of their
contribution to undermining the shear stress and shear strength of the slopes. This proactive action more dm any will contribute
to St. Lucian's acting more environmentally and thorough the application of remedial measures support their safety, the
protection of their property and sustainable development. The information will be meaningful to the public so that can act on it
in their everyday lives and recognize the need for their responsible participation.
Ø Identification of local, and national concern and define the extent of the area of concern
Ø Identify areas of active or past landsliding and Identify slopes which are potentially unstable
Benefits: Identification of slopes that face imminent instability and assessment of the number of lives at risk and the value of
property also at risk. Also assess what public utilities, buildings or properties are at risk and provide an evaluation of the
potential economic, social and environmental costs of landsliding.
Ø Relate the assessment of landslides and sites of potential failure to their impact and produce a hazard zoning map
Ø Indicate in the short term, the need for avoidance, prevention, or correction of landslides
Benefits: Since landslide policies are concerned with future development and if landsliding is to be taken into account this must be based on some form of landslide hazard map and the introduction of controls to support the law.
1. Analysis of existing legislation
2. Incorporate the results in planning and legislation
Benefits: Also required, as part of the process of Landslide Hazard Assessment is a legislative response. Where an area is
prone to landslides like many sites in St. Lucia are prone, several reactions are possible. These range from ignoring the
conditions until a crisis to avoiding the site completely. In areas already occupied like the Black Mallet-Maynard Hill area, it is
sometimes possible to introduce remedial measures that will reduce the risk of slope failure. This is imperative in St. Lucia at
this juncture as the crisis situation presents a window where residents appreciate the need for balance with the natural
environment for their safety and the protection of their property. The inability of the state to carry sustained losses from
landslides considering the island's propensity to the hazard, the absence of enforceable legislation required to prevent or at
least restrict the unwise use of landslide prone slopes with planners taking a more pro-active stance.
Conclusion
The damage caused by landslides can range from the catastrophic to the minor. Locally, partial cost of this phenomenon can
be plotted in terms of human life, infrastructural damage but the true cost remains unknown. The implications for the future of
inaction in the present can potentially be so widespread that it is imperative that it not be ignored as an essential part of
environmental management. The Black Mallet-Maynard Hill Areas provide an indication of the hazard that exists in a like a
multiplicity of other communities like Ravine Poisson, Augier, and Monchy. Landslide hazard assessment is a necessity for St.
Lucia because of our particular environmental conditions. This assessment and the related geomorphological studies are an
important contribution to the evaluation of environmental risk that should feature in both planning and policy decisions
(including legislation).
Crozier, M.J., 1984, Field assessment of slope instability, in D. Brusden and D.B. Prior (eds.),
Slope Instability, Wiley Press, Chichester, p. 103-142,
Landslide Hazards Reduction Program, http://usgs.gov/html-files/landslide/oueb2/landslide.htm
Panizza, M., 1987, The Geomorphological Hazard Assessment and the Analysis of Geomorphological Risk in V.
Gardiner (ed.) Intentional Geomorphology, 1986, Wiley Press, London, pp. 2-25-229.
Petley, D.J., 1984, Ground Investigation, Sampling and Testing for Studies of slope Stability, in D. Brusden and D.B.
Prior (eds.), Slope Instability, Wiley Press, Chichester, pp.67- IO L
Schuster R.L., 1978, Introduction, in R.L. Schuster and R. J. Krizek (eds.), 1978, Landslides: Analysis and a port Research
Board Special Report, 176, National Academy of Sciences, Washington D. C, pp. 1 - 10.
Seed, H.B., Whitman, R.V., Defulzian, H., Dorby, R., and Idriss, J,M., Soil Conditions and Building Damage in 1967
Caracas Earthquake, JOURNAL OF SOIL MECHANICS. Div. Amer. Soc. Civil Eng. 98, pp. 787-806.
TEAMS (Total Environmental Assessment and Management Solutions), Belmar Lane, Morne Fortune, Castries, P O Box 1161, Castries, Saint Lucia, WEST INDIES. Phone/Fax 758-452-3274
November 1999