RUSLE

BSc International Land and Water Management Wageningen University

Supervisors:
WU Supervisor: Klaas Metselaar
Host supervisor: Sabine Engel

Abstract
Mangrove forest systems and coral reefs are vital ecosystems with ecological, economic, and societal importance. However, they face threats such as excessive sediment inflow from human activities, endangering their health and resilience. This report explores sediment-related issues in the Lagun Bay catchment area on Bonaire and proposes dams as sediment control measures. Potential soil erosion was assessed and dams were designed to reduce sediment transport effectively. However, maintenance is essential for dam functionality. Though not definitive, these dam designs offer potential solutions. Sustainable land and coastal management, coupled with improved data and regular maintenance, can protect these valuable ecosystems and preserve biodiversity. Further research is needed to enhance data quality and expand the study area.

Abstract: Over the past decades coastal ecosystems have been increasingly threatened and have been reducing at alarming rates. Similar is happening on Bonaire, where increased sediment transport and decrease in the freshwater inflow is responsible for high mortality of the mangrove forest in Lac Bay. Factors, such as Bonaire’s arid climate, past deforestation and overgrazing by feral animals have left the island bare which furtherly increases erosion and sediment rich runoff towards the bay. To come up with interventions to reduce mangrove mortality quantitative and qualitative data on the erosion potential and on the rainfall runoff relationship is required. This research provides information on spatial distribution of potential erosion rates in the catchment of Lac Bay, using the RUSLE equation. Moreover, a portable mini rainfall simulator is used to estimate the surface runoff coefficient and to validate RUSLEs potential erosion rates. Unfortunately, no correlation has been found between the measured data and the estimated soil erosion rates. Median annual potential soil loss is 19,3 t ha1 corresponding to annual soil loss of 41678 t. Spatial variation of potential erosion rates is homogeneous, implying catchment wide conservation measures. Measures such as reduced grazing could decrease the potential erosion rates in Lac Bay up to 5%, by increasing vegetation cover in the catchment. Structural measures such as earth dams could furtherly reduce sedimentation at the point of deposition, however before implementation further research needs to be conducted on the impact of such structures on freshwater inflow to the bay. The median runoff coefficient is 0,24 with 76% of the catchment having runoff coefficients between 0,16 and 0,33.