The mapping of monthly soil erosion risk on Mauritius Island
Paper Presenter: Rody Nigel, Department of Physics
Authors:

Rody Nigel
Department of Physics

Soonil D.D.R. Rughooputh
Pro-Vice RC&I, Prof. of Physics
ABSTRACT:
The rugged topography, extensive sugarcane cultivations and tropical
climate of Mauritius are the ingredients required to make the island
potentially at risk to soil erosion. Also, its radial drainage system and the
torrential flows and turbidity in its rivers during intense rainfall events
make its coastal wetlands, estuaries and lagoon potential sinks for
sediments. For a sustainable management of the environment,
measurement and modelling of soil erosion are called for to study the
erosion processes occurring on the island and to formulate conservation
measures to reduce the soil erosion on-site and its damages off-site.
However, these require substantial funding and resources and, therefore,
focal areas (and their corresponding basins) will need to be chosen for
pilot studies and priority actions from soil and water conservation
programmes (Vrieling et al. 2006).
This paper reports the production of soil erosion risk maps for Mauritius
Island that will help identify such priority action areas. The mapping is
done using a simple but yet effective model which is based on a
framework consisting of scores and decision rules within a GIS. The model
is termed the ‘Mauritius Soil Erosion Risk Mapping’ (MauSERM) model and
is an expansion of a soil erosion risk mapping model for the island by
Kremer (2000). Monthly erosion risk maps have been produced based on
four crucial parameters namely; monthly rainfall amount, soil erodibility,
topographic slope gradient and monthly land cover protection. Erosion risk
classes have been labelled: ‘None’, ‘Very Low’, ‘Low’, ‘Moderate’, ‘High’
and ‘Very High’. Monthly erosion sensitivity maps, an intermediate result
derived from soil, slope and land cover consideration, have also been
produced.
Results show that, in general, whilst the island is highly sensitive to
erosion from November to February, the erosion risk is highest from
December to April. These correspond to the months of the summer period
whence the island is subjected to intense tropical cyclones and sugarcane
crop has the lowest annual canopy cover. November is the month with the
highest sensitivity island-wide (None: 7%, Very Low: 47%, Low: 34%,
Moderate: 8%, High: 3% and Very High: 1%) and February is the month
with the greatest risk island-wide (None: 7%, Very Low: 12%, Low: 44%,
Moderate: 27%, High: 9% and Very High: 1%). For the remaining
months, the island in general has low erosion sensitivity and risk. Most of
the high/very high erosion risk areas are sugarcane cultivations on steep
slopes in the humid and the super-humid climatic zones of the island.
The basins of the island have been delineated with the use of spatial
hydrologic tools. The delineated basins have been used to aggregate the
soil risk mapping results in order to identify basins with the greatest
distribution of high erosion risk areas. Thereafter, with the help of
hydrographic data, basins that also contain erosion-at-risk water bodies
have been further identified. An example is Riviére Champagne basin that
has a coastal wetland located at its outlet and with 7 Km2 (39%) of
basin’s surface area having high/very high erosion risk areas.
Erosion risk mapping models similar to the one presented in this paper
can be easily set-up in other developing countries that have scarce data
and limited funding. This will permit the identification of their high erosion
risk areas, which could eventually become their priority action and focal
areas.
Keywords: soil erosion, risk mapping, GIS, Mauritius
REFERENCE
KREMER, M., 2000. Aspekte der Bodenerosion in Mauritius – Analysis
verschiedener EinfluBfaktoren an ausgewahlten Standorten mit hilfe
Geographischer Informationssysteme (GIS). Thesis (Diplomarbeit).
Philips-University Marburg. [In German].
VRIELING, A., STERK, G., VIGIAK, O., 2006. Spatial evaluation of soil
erosion risk in the West Usambara Mountains, Tanzania. Land Degradation
& Development, 17 (3): 301-319.