Development of hydrogeological conceptual models of wetlands in data scarce regions - The Kilombero floodplain, Tanzania and the Namulonge inland valley, Uganda

Sonja Beuel1, Geofrey Gabiri2, Christine Stumpp3, Barbara Reichert1
1 Steinmann Institut für Geologie, Mineralogie und Paläontologie, Rheinische Friedrich-Wilhelms-Universität Bonn
2 Geographisches Institut, Rheinische Friedrich-Wilhelms-Universität Bonn
3 Institut für Grundwasserökologie, Helmholtz-Zentrum München

O 2.4 in Aquifer systems in Europe and beyond

14.04.2016, 15:00-15:15, Audimax B, Geb. 30.95

 

 

The BMBF-funded project “GlobE – wetlands in East Africa” focusses on reconciling future food production in East African wetlands with the concurrent environmental protection of these valuable ecosystems. As agriculture in wetlands strongly depends on water, there is a need to assess their hydrological functioning including interactions with groundwater. This helps to assess the effects of increasing agricultural use on wetland ecosystems.

This study assesses groundwater movement and quality as well as its interaction with other water compartments (stream-, flood-, soil-water, and precipitation) in two different East African wetlands and thus contributes significantly to a sound understanding of their respective hydrological functioning. The two study sites are a lowland floodplain in southern central Tanzania and an inland valley in central Uganda. In order to create a clear overview of the hydrogeological settings of these environments and to understand ongoing flow and mixing processes, summarizing conceptual hydrogeological models were developed. For this purpose, a comprehensive methodological approach combining the evaluation of literature and field data using graphical, statistical and modeling approaches was conducted.

The base of the conceptual models are hydrogeological maps and cross sections, derived from former maps, drilling campaigns and the evaluation of new and historical drilling logs. Hydraulic conductivities were determined by applying and interpreting pumping tests, infiltration tests and grainsize analyses. Groundwater level measurements were also carried out and yielded piezometric maps to determine prevailing groundwater flow directions. Furthermore, sampling campaigns of water from the different compartments were carried out, including measurements of in-situ-parameters and analyses of major ions and trace elements as well as stable water isotopes. Hydrochemical and isotope data were analyzed graphically and statistically. Hydrochemical modeling with PhreeqC was used to quantify flow and mixing processes.

The two study sites differ completely in their hydrogeological settings, but show comparable flow and mixing patterns. Groundwater in the floodplain of Tanzania flows through an unconfined sedimentary aquifer and is well mixed vertically. The inland valley in Uganda is comprised of a confined, layered aquifer system that is artesian in some parts, and shallow and deep groundwaters are clearly separated. Both study sites show interactions between stream water and groundwater depending on the meteorological conditions. Flood water in Tanzania is mainly derived from stream water, while flood water in Uganda originates from precipitation.



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