Abstract:Groundwater recharge remains almost totally unknown across the Mekong River Basin, hindering the evaluation of groundwater potential for irrigation. A regional regression model was developed to map groundwater recharge across the Lower Mekong Basin where agricultural water demand is increasing, especially during the dry season. The model was calibrated with baseflow computed with the local-minimum flow separation method applied to streamflow recorded in 65 unregulated sub-catchments since 1951. Our results, in agreement with previous local studies, indicate that spatial variations in groundwater recharge are predominantly controlled by the climate (rainfall and evapotranspiration) while aquifer characteristics seem to play a secondary role at this regional scale. While this analysis suggests large scope for expanding agricultural groundwater use, the map derived from this study provides a simple way to assess the limits of groundwater-fed irrigation development. Further data measurements to capture local variations in hydrogeology will be required to refine the evaluation of recharge rates to support practical implementations.
The carbonate areas of Southeast Asia are part of the global set of well-developed tropical-subtropical karst regions and form water-rich aquifers. Due to the strong development of karst features, groundwater in karst conduits flows rapidly and is susceptible to various environmental problems, including rocky desertification and socioeconomic impacts leading to poverty. Karst-related data for the region are scarce and scattered. Based on information contributed by training workshops of the International Research Center on Karst (IRCK) under the auspices of UNESCO, as well as published literature, this study summarizes karst hydrogeological data and waterrelated environmental issues in Southeast Asia, in an attempt to find commonality, and to form both generally valid and region-specific concepts that can be extended to data-deficient areas, where these concepts may serve as a guide for governments when managing the karst environment. Based on topographic differences, karst terrains in Southeast Asia were classified into four types: karst on plateaux, karst in mountains, karst in plains, and karst on islands. This approach was utilized to compile and classify the surveyed karsts. The examples shared by participants in the IRCK training workshops included karst information from their own countries, most of which have not been published in English. The case studies demonstrate that karst areas in Southeast Asia are widely and repeatedly exposed to droughts and floods, resulting in environmental constraints and development obstacles. These studies also show that environmental problems can be resolved and sustainable development can be achieved if appropriate management measures are taken.
The lowland floodplains of the Lao PDR experience prolonged dry seasons characterized by pronounced and common water scarcity, with water supplies increasingly offset with groundwater. Groundwater assessment is still at a very rudimentary stage in Laos, making it difficult to ensure that new water supplies are developed successfully and managed sustainably. The goal of this study was to apply a variety of field hydrogeophysical techniques to this problem, and in the process, help build and strengthen human and institutional capacity with various stakeholder groups from government, university and the community. The study area focused on a cross-section of the Vientiane Plain in the Lower Mekong Basin in central Lao PDR to identify and characterize the hydrogeology and groundwater quality. The research collaboration built and strengthened stakeholder capacity by developing and progressing the hydrogeological field mapping of the Vientiane Plain. It provided local undergraduate and postgraduate training opportunities using several different near-surface geophysical and hydrogeological techniques; some previously untested in Lao PDR. At one of the survey sites, the geophysics showed the spatial extent of the shallow aquifer, and in the process identified an extensive conductive zone, interpreted as more saline groundwater. Any groundwater development within this or similar zones is likely to be unsuitable as sources for drinking and irrigation water. Engagement with the local village authorities supported local community members and government to expand groundwater development for rural water supplies. Access to groundwater as a reliable, safe and secure resource provides an opportunity to strengthen the resilience of farmers to changing climatic conditions. Participatory research collaboration of this kind can positively enhance data and build capacity, which is a required precursor for improving knowledge and management of poorly understood groundwater resources.
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