Présentations Colloques

    Oral Presentation
    8.03
    Session 8.03: Geometrical structure and hydrogeological properties of Hard-Rock aquifers.
    Gaut Sylvi
    Combining geological mapping, aerial photos and geophysical methods to enhance groundwater abstraction
    Urbanization, intensifying agriculture, industrial and population growth are changing groundwater extraction patterns in India. Human actors are also rapidly altering catchments by building thousands of recharge structures. At the same time, climate change is altering rainfall patterns. ****Our research in the upper Arkavathy watershed in South India (1447 sq km) aims to disaggregate the influence of climatic and anthropogenic stressors on hydrologic partitioning -- the ratio of runoff, recharge and evapotranspiration -- and consequently water availability. The interdisciplinary study involved secondary (census, agricultural statistics, satellite imagery and meteorological data) and primary data (weather stations, stream gages, borewell monitoring, borewell camera scans, isotopic analyses, and farm surveys) over two years.**Secondary data show that both stream flow and groundwater levels have declined since the 1970s but these historical trends cannot be explained by past climate change+ groundwater over-exploitation and eucalyptus plantations are the most likely causes. Additionally, the shallow weathered rock aquifer dried up in the early 1990s and current pumping is from deep fracture aquifers.****Models calibrated using primary data show that interventions like farm bunds and check dams have increased percolation and decreased stream flow, especially during low to moderate rain events. Paradoxically, the shallow aquifer has not recovered despite hundreds of recharge structures because dewatering has induced flow into deeper fracture aquifers which are being pumped. Total evapotranspiration has increased considerably over the last three decades driven by market demand for produce from nearby Bangalore.****Climate models project a decrease in moderate rainfall events and an increase in intense rain events. Under such a regime, the strategy of distributed recharge structures could in principle allow a greater fraction of rainfall to percolate, improving climate adaptation. The problem remains however, the inability to control pumping. Severe groundwater overexploitation, not climate variability, remains the primary concern.******
    Norway

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