A generalized 3-D geological and hydrogeological conceptual model of granite aquifers controlled by single or multiphase weathering

摘要: Summary The weathered layers of crystalline rocks form aquifers that are prime interest for water supply in hard rock areas. These weathering profiles generally develop under both stable geodynamic conditions (weathering rate ≫ erosion rate) and a hydrolysing climate. They composed thick stratiform follow the paleo-landscape (paleotopography) thus present gently dipping sequence at regional scale. structure hydrodynamic properties profile granitic area (53 km2 Maheshwaram catchment, state Andhra Pradesh, India) were characterized detail mapped from observations on outcrops, 80 vertical electric soundings lithologs 45 borewells which flowmeter measurements injection tests also performed to characterize hydraulic conductivities conductive fissure zones. results multiphase process: an ancient was partly eroded, down its fissured layer. It later re-weathered more or less parallel current topographic surface. This peculiar is linked history Indian Peninsula underwent alternate erosion-dominated phases. composed, top bottom, up total depth 35 m, sandy regolith saprolite (1–3 m), 10–15 m laminated containing unusual preserved fissures 15–20 m By comparing various case studies similar terrain, generalized 3-D geological hydrogeological conceptual model granite-type (granites, gneisses, etc.) proposed. In rocks, single erosion processes induce structures. A few main differences arise comparison phase profiles: (i) later, respective thicknesses can be deeply modified, (ii) layer re-weathered, resulting new may contain quite well fissures, (iii) upper part densely fissured. As result same processes, multi-phase exhibit very conductivities, show higher density within obliterated by recent weathering; their conductivity significantly reduced. Nevertheless, they do contribute borewell yield. weathering-induced provide most aquifer permeability. use such precise mapping appears prerequisite groundwater development management hard-rock areas as it answers several key issues.