Computer-based modeling of impacts of Prunus africana on groundwater in Northwestern Cameroon

The community of Ntisaw in Northwestern Cameroon originally partnered with the Engineers Without Borders chapter at the University of Illinois at Urbana-Champaign in 2008 to design a gravity-fed distribution network for an existing groundwater source. The system, which was completed in 2012, continues to provide year-round access to clean water via public tapstands placed at convenient locations throughout the village, thereby reducing the time and labor needed to carry water and the threat of waterborne disease. However, the source itself is still at risk from contamination from cattle fecal matter. To ensure the water remains clean, the community has completed construction of a wood and barbed wire fence around the catchment area. In partnership with Agence Nationale d'Appui au devloppement FORestier (ANAFOR), the Cameroonian forestry agency, Ntisaw has also begun planting a grove of Prunus africana (African almond) trees that will provide income for the community as well as protection for the catchment from wandering cattle. However, it is uncertain how much of an impact planting a large number of these deep-rooted trees will have on the unconfined aquifer that currently feeds the water system. Simplified models of the catchment were created using the modeling program MIKE SHE, a coupled surface-subsurface model that allows the modeling of infiltration, evapotranspiration, and surface water and groundwater flow. Model calibration was completed using existing field data previously measured on location. The calibrated model was then combined with information regarding the potential spacing, root depth, and leaf area index of the African almond grove. From this simulation, a qualitative analysis of the impact of mature trees near the existing water supply was developed, providing feedback for the appropriate spacing required to avoid negative impacts on the system. Although the results of these modeling efforts are specific to the catchment in question, the methods of analysis used to obtain them can be broadly applied to similar small-scale situations of water resource management elsewhere in the developing world.