OSS Saint Louis
Assessing the vulnerability of coastal populations and economic activities
Coastal environments are complex systems with a particularly high degree of interaction between the physical, ecological and social components. Around one-third of West Africa’s inhabitants live on the coast, and the population is growing at a rate of 4% per year. Coastal areas produce 56% of regional GDP. Fishing is a particularly important activity, with sales totalling an estimated 2.5 billion dollars on the wholesale market. Moreover, a number of major cities are located along this coastline, including Dakar and Saint-Louis in Senegal, as well as several key ports (trade and fishing).
These coastal ecosystems are under threat, not only from the development of non-sustainable infrastructure, poor management of resources and natural habitats and pollution, but also from the impacts of climate change. Ineed, phenomena such as sea level rise, storm surges and overflowing coastal rivers are leading to greater coastal flooding and erosion, thus increasing the vulnerability of the region and its population.
In some areas, the coastline is receding by up to 10 metres every year. Between 20% and 30% of mangroves have been destroyed or severely damaged over the past 25 years. This is also true in Senegal, where the coastline is receding at an estimated 0.5m to 2m every year. At the same time, the country has been impacted by flooding caused by high rainfall, overflowing rivers and/or storm surges, industrial and domestic pollution, saltwater intrusion and mangrove destruction.
To address these issues and establish the necessary balance between ecosystem protection and economic development, it is vital to precisely track hydrodynamics, morphology and sedimentology on different scales in time and space, and to combine this process with modelling, in order to better understand, plan and manage the changes taking place in these environments.
The project team therefore selected a region of study that is representative of the hazards and risks encountered in Senegal and, more widely, in West Africa as a whole. That region is the coastline of Saint-Louis, which is particularly exposed to coastal erosion and flooding (from the Senegal River and storm surges).
The Saint-Louis OSS project has four complementary objectives:
- Provide more information on the many hazards (flooding by storm surges or the Senegal River, the receding coastline) and associated risks experienced by coastal areas, based on an approach combining existing in-situ data (on the water level, DGPS surveys, etc.), with dedicated population surveys and multi-sensor data from satellites (including coastal altimetry) and in-situ sources (video camera, DGPS topographical surveys), statistical processing and mapping simulations;
- Identify current and future high-risk hotspots relating to climate change and linked to rising sea levels;
- Supply tools and indicators of population vulnerability, economic activities and infrastructure based on a cross-cutting approach combining the processing of satellite, in-situ and socio-economic data with mapping simulations;
- Raise the awareness of players and encourage a multi-risk vision to address the problems of coastal areas and to jointly build the coastline and coastal cities of the future.
TERRITORY FOR EXPERIMENTATION
Saint-Louis coastline in Senegal
The project will involve observations, measurements and simulations at three working sites:
- the breach (the new river mouth, a highly turbulent zone where it is impossible to acquire in-situ measurements of coastal hydrodynamics and bathymetry),
- the Langue de Barbarie sand spit,
- the lower estuary (Saint-Louis island and residential areas close to the river mouth).
Located at the mouth of the Senegal River (seen here by the Pleiades satellite), Saint-Louis is sensitive to coastal erosion and subject to both the Senegal River floods and storm surges. © CNES 2012, Distribution Airbus DS
Multi-source in-situ data including:
- tide-gauge data,
- video camera data
- results of social surveys.
RESULTS - FINAL PRODUCTS
- Identify the main floods that have caused damage in the past
- Establish scenarios for flood mapping simulation
- Quantify the rise in the sea level near the coastline based on existing altimetry data
- Conduct flood mapping simulation with several scenarios of rising sea levels
- Establish the reference DTM for shallow water bathymetry and the topography of intertidal zones
- Develop an automatic algorithm for coastline detection
- Create a geospatial database of high-risk areas and high-risk factors, including the mapping of current and future hotspots.