Padza (or badlands) around the village of Dapani on Mayotte. These padzas are the result of weathering of volcanic rock. The island's coral reef can be seen in the distance (Dapani, Mayotte, 2012). © BRGM - Dominique Tardy

LESELAM: action against soil erosion and lagoon siltation in Mayotte

The LESELAM project is a stepping stone in the Erosion Road Map developed for Mayotte. The aim is twofold: to understand the phenomena causing soil erosion, and to raise awareness of the problem among the population, elected officials and associations and thus encourage the adoption of techniques to limit soil losses, in both urban and agricultural areas.

Soil erosion in Mayotte is caused by the impacts of heavy tropical rainfall on unprotected soils:

  • in cities and building sites, along road embankments and bare earth roads and in and parks and gardens with insufficient plant cover,
  • in agricultural area, fields on medium to steeply sloping ground and fields managed as monocrops without plant cover or mulch,
  • in natural areas, forest parcels clear-cut or burned to make way for crops, and badlands (padzas, etc.).

High human pressure tends to accelerate soil erosion: more or less unregulated urban sprawl, deforestation, shift from extensive farming (Mahorese gardens) to monocultures that leave soils unprotected, etc. Erosion becomes very active in the rainy season and is a serious threat to Mayotte's lagoon, one of the most beautiful in the world.

The LESELAM project was designed to better understand, prevent and remedy these soil erosion problems in Mayotte.

From 2015 to 2017, the project was involved the BRGM, CAPAM, IRSTEA, Les Naturalistes de Mayotte and the CAPAM. Leselam 2 (2018-2020) is run by the BRGM and Les Naturalistes de Mayotte, with subcontractor support (University of Tours, Kermap, Capam, Agrikagna, ADINM).

Quantifying erosion phenomena in several pilot catchment basins

The LESELAM projects aims first of all to produce the necessary knowledge to respond to questions raised by those directly concerned on the ground: what are the main sources of erosion and to what extent do they worsen siltation in the lagoon? How efficient are the remedial measures proposed?

This aim was achieved by establishing an observatory to quantify the phenomena. The two pilot catchment basins initially proposed (Dzoumogné for the erosion problem in agricultural and natural areas and M'Tsamboro for urban areas) were identified in consultation with local players and in accordance with numerous environmental, technical and logistical criteria. In 2016, a third catchment basin, Salim Bé, was brought into the project.

Setting up a demonstrator of remedial practices

To implement, monitor and evaluate remedial measures, demonstrators were set up in an agricultural zone (control plot compared with a plot under agri-conservation techniques), a natural zone (padza) and a village zone (control gardens with planted buffer strips, cover plants, etc.).

Raising awareness and training

Multi-player workshops were organised to help the different populations concerned (farmers and city dwellers, elected representatives, associations, schools) to adopt techniques that limit soil erosion. The aim was to help socialise the issues and the solutions proposed as a preliminary step towards organising communal action, by looking beyond the purely technical approach of projects that fall by the wayside because stakeholders are not properly involved in developing the right solutions.


Visit the LESELAM project website

BRGM - 3 avenue Claude-Guillemin - BP 36009 45060 Orléans Cedex 2 - France Tel.: +33 (0)2 38 64 34 34