Présentations Colloques

Oral Presentation
8.03
Session 8.03: Geometrical structure and hydrogeological properties of Hard-Rock aquifers.
Tindimugaya Callist
Evolution of fluvial, weathered and fractured basement aquifers in Uganda
The evolution of aquifers in deeply weathered environments throughout the tropics is closely related to the long-term development of the landscape via tectonically controlled cycles of deep weathering and stripping. Deep weathering of the bedrock yields a thick weathered regolith and induces sub-horizontal fissures through isostatic uplift. Cycles of stripping partially erode the unconsolidated weathered overburden, producing a discontinuous regolith, and deposit coarse-grained clasts in river channels. We present evidence for the evolution of weathered regolith, fissued-bedrock and fluvial aquifers by tectonically controlled stripping and weathering based on historical observations and detailed studies in Uganda. Critically, field investigations identify, for the first time, a highly productive fluvial aquifer in addition to the primarily in situ weathered regolith and fissured bedrock aquifers that have commonly been described and exploited in deeply weathered terrain. The fluvial aquifer consists of well rounded, coarse sands and gravels with well yields of over 5 m3 per hour that significantly exceed well yields of < 1 m3 per hour typically experienced in weathered regolith and fissured bedrock aquifers. Fluvial aquifers are of limited extent on stripped surfaces but can feature significant thicknesses along former river channels on deeply weathered surfaces. The revised conceptual model of the evolution of aquifers in deeply weathered environments represents a key contribution to the understanding of the hydrogeology of these terrains and provides an important new target for the development of groundwater in Uganda and similar environments where groundwater resources are limited by the low permeability and storage of weathered and fissured crystalline rock aquifers.
Uganda