We have heard a lot in recent years a lot about economic migration... the problem of illegal immigration in Europe with boat loads of desperate people risking everything to get into the EU. In the states it largely relates to people from Latin America attempting to get into the perceived promised land of the USA. Just last week tough new immigration laws were passed in the US state of Arizona in attempt to combat an estimated half million illegal residents in a state with a population of 7 million.
One concern however, that is increasingly coming to the fore, is the role of environmental degradation as a driving force behind what is broadly termed economic migration. A poorly managed and degraded environment provides fewer services and supports less life and resources that can in turn support viable incomes for people. Environmental disasters also play their role and certainly can greatly exacerbate the situation in already poor circumstances and even make life untenable in certain areas.
The earthquake in Haiti is requiring the decampment and relocation of hundreds of thousands of people, the same will doubtless be true though on a smaller scale in Quinghai province, China after the recent quake.
Another quite extreme example of this has been the mudslides last month in Uganda. The mudslides on 1st March in the east of Uganda on the slopes of Mount Elgon swept away three villages killed up to 300 hundred people and rendered several thousand homeless. It has further raised concerns about outbreaks of cholera and malaria due to submerged pit latrines and pools of stagnant water.
Uganda has one of the highest population growth rates in Africa which has driven people ever higher up the mountainsides in search of land to eke out a subsistence living. The resulting deforestation and land clearance has left large areas vulnerable to landslides. The recent landslides have been labelled a ”wake-up call” by the Ugandan Minister for Disaster Preparedness, Mr. Musa Ecweru, and prompted him to state that some half-a-million people will need to be moved from their homes in mountainous areas because of the risk of landslides.
For such a statement to be made and only a year before national elections shows how serious the situation is being viewed. It remains to be seen however where provision can be made to re-settle so many people in such a relatively small and poor country.
The terrain of the main populated islands of Seychelles also means that landslides are a risk that needs to be mitigated. The heavy rains of 1997/98 saw several roads being washed out and gradual shifting of soil on some slopes has been and remains a problem in some areas. The most infamous disaster in Seychelles – the 1862 La Valasse - was a landslide. This too was likely coupled with significant environmental degradation of the time with several contemporary writers referring to the extensive deforestation that was prevalent in the 19th century. Today the mountainsides are generally quite heavily forested, though not necessarily by the most desirable species. Nevertheless the Seychelles Disaster Preparedness and Response Project will be, as one of its activities, undertaking a geological risk assessment of the three main islands in order to identify areas where mitigation actions or precautionary measures are required.
Showing posts with label Landslides. Show all posts
Showing posts with label Landslides. Show all posts
Friday, April 30, 2010
Monday, January 11, 2010
Addressing Landslides
Hidden beneath all the recent headlines about the big freeze in the northern hemisphere have been news items on the occurrence of land/mudslides in both Brazil and the Solomon Islands.
The slides in the Solomon Islands were following an offshore earthquake whilst those in Brazil were the results of very heavy rain. Now whilst freezing weather is clearly not a risk factor in the Seychelles, landslides are. The very steep terrain to be found in areas of the four main granite islands coupled with tropical rainfall provide the basic ingredients for landslide events.
The most famous natural disaster recorded in the human history of Seychelles is the landslide that occurred on the 12th October 1862 known locally as “La Valasse”. Accounts vary as to whether it was very heavy rain, brought on by a tropical cyclone, or a waterspout releasing its contents on the mountainside, either way, a huge landslide resulted. Originating from the east face of the Trois Frères mountains, sweeping down a swathe of land along the St Louis river valley, the boulders, mud and debris battered into the parts of the town of Victoria below. Many lives were lost and much infrastructure engulfed and submerged.
Looking at the photos of the landslide that took place at the beach resort of “Angra Dos Reis” on the island of “Ilha Grande” in Brazil I was struck by the similarity with the Seychelles scenario (see photo in sidebar). The landslide has occurred leaving the bare rock face – or glacis as we would call it locally – behind. Local readers will recall exactly the same thing happening, though on a much smaller scale, on the Beau Vallon Baie by-pass road a few years ago. What happens of course is quite simple, with very heavy rainfall the soil saturates and water actually starts to flow down the rock surface underneath the soil. This serves to lower the friction coefficient between the soil and the mountainside whilst increasing the weight of the soil. If sufficient water flows the soil and boulders can actually begin to slip down over the surface of the rock due to gravitational force.
A more gradual occurrence of this is one of the underlying problems affecting and causing great concern at the Vista-do-Mar estate in recent years.
One of the key activities of the GFDRR project in Seychelles will be a geological survey of the 3 main inhabited islands in order to assess the stability of steep hillsides in particular those that host or are above key residential and infrastructure areas. The findings of this work will enable better guidance to be provided to developers that are building in such areas and also allow the level of risk to be reduced or mitigated in existing developed areas.
These aspects of risk assessment and reduction are a key component of the raison d’etre of the Department of Risk and Disaster Management and the results of this study, when undertaken, should help provide a risk baseline upon which their other activities can be designed and targeted.
The slides in the Solomon Islands were following an offshore earthquake whilst those in Brazil were the results of very heavy rain. Now whilst freezing weather is clearly not a risk factor in the Seychelles, landslides are. The very steep terrain to be found in areas of the four main granite islands coupled with tropical rainfall provide the basic ingredients for landslide events.
The most famous natural disaster recorded in the human history of Seychelles is the landslide that occurred on the 12th October 1862 known locally as “La Valasse”. Accounts vary as to whether it was very heavy rain, brought on by a tropical cyclone, or a waterspout releasing its contents on the mountainside, either way, a huge landslide resulted. Originating from the east face of the Trois Frères mountains, sweeping down a swathe of land along the St Louis river valley, the boulders, mud and debris battered into the parts of the town of Victoria below. Many lives were lost and much infrastructure engulfed and submerged.
Looking at the photos of the landslide that took place at the beach resort of “Angra Dos Reis” on the island of “Ilha Grande” in Brazil I was struck by the similarity with the Seychelles scenario (see photo in sidebar). The landslide has occurred leaving the bare rock face – or glacis as we would call it locally – behind. Local readers will recall exactly the same thing happening, though on a much smaller scale, on the Beau Vallon Baie by-pass road a few years ago. What happens of course is quite simple, with very heavy rainfall the soil saturates and water actually starts to flow down the rock surface underneath the soil. This serves to lower the friction coefficient between the soil and the mountainside whilst increasing the weight of the soil. If sufficient water flows the soil and boulders can actually begin to slip down over the surface of the rock due to gravitational force.
A more gradual occurrence of this is one of the underlying problems affecting and causing great concern at the Vista-do-Mar estate in recent years.
One of the key activities of the GFDRR project in Seychelles will be a geological survey of the 3 main inhabited islands in order to assess the stability of steep hillsides in particular those that host or are above key residential and infrastructure areas. The findings of this work will enable better guidance to be provided to developers that are building in such areas and also allow the level of risk to be reduced or mitigated in existing developed areas.
These aspects of risk assessment and reduction are a key component of the raison d’etre of the Department of Risk and Disaster Management and the results of this study, when undertaken, should help provide a risk baseline upon which their other activities can be designed and targeted.
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