Présentations Colloques

    Oral Presentation
    Session 2.02: Groundwater for sustainable water supplies in developing countries
    Pfunt Helena
    Numerical modeling for groundwater management and protection - The case of the Nyanzare well field in Gitega, Burundi
    The majority of the water supply for Gitega city, located in the center of Burundi, is derived from the Nyanzare well field which produces around 5000 m3 day. The study area is characterised by hills of ancient formations composed of metamorphic rocks as alternating schist, quartzite, and phyllite. Due to population growth, the water demand for the second largest city of Burundi is increasing. Concurrently, progressive urbanization, clay mining, agriculture, coffee industry, and fuel depots represent a growing risk for drinking water quality. To provide for a groundwater management tool, a 3D numerical groundwater flow model of the Nyanzare catchment was developed. The model was set up using the finite element software SPRING. It contains the relevant lithological units of the highly inhomogeneous valley as well as lineaments that act as preferential flow paths leading to great efficiency in some of the pumping wells. A transient recharge calculation was carried out taking into account spatial and climate data of the area. The model was successfully calibrated using water level data from three observation wells collected during the past 3 years. The resulting flow field in the valley was applied to determine average flow velocities and to establish protection zones based on the 50 day travel time around each well. A strategy for sustainable use requires an assessment of available groundwater resources combined with changes in socio-economic and climatic conditions. Several scenarios were tested to simulate the effects of (1) increased water demand after the installation of another well and (2) the variation of pumping intervals. Furthermore, a decline in recharge caused by (3) stresses from climate change and (4) the expansion of build-up areas spreading further into the catchment area was simulated. Results show that scenarios (1) and (3) are the most hazardous.


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