Regional assessment of groundwater recharge in the lower Mekong Basin

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

Agri-commerce and agroecological baseline data compilation and review

The document provides a summary review of selected policies and policy perspectives in Laos that guide agriculture development in the country. The review looks into selected priority areas that are relevant to agro-commerce and agroecology

Is roof-top rainwater harvesting a viable solution to develop small-scale agriculture? (A case study in Laos)

This study assessed the feasibility of using roof-top rainwater harvesting system (RWHS) to irrigate home-based vegetable gardens in Laos. Surveys were conducted in three villages located in the provinces of Vientiane and Savannakhet to gather quantitative data on irrigation and farming practices. A model combining a RWHS water balance and a crop water balance was developed to simulate various scenarios of cropping cycles irrigated by a RWHS with varying dimensions. This model ran at a daily time step aimed to assess how the roof and vegetable garden areas and tank capacity influence crop yields, for different cropping calendars and rainfall years

Mapping irrigated areas in the dry zone of Myanmar by differentiating evapotranspiration from irrigated and rain-fed areas [Abstract only]

In the Dry Zone of Myanmar, variability in water resources and insufficient capacity to manage that variability is one of the main causes of food insecurity. Seasonal water scarcity is widely acknowledged to be a key constraint to livelihoods and peoples’ wellbeing. This paper describes analyses conducted as a contribution to a detailed water resource assessment of the Dry Zone of Myanmar, which sought to provide information on current water availability and its use in agriculture. A key unknown is the area of dry season irrigation. The paper describes an attempt to estimate the actual area irrigated during the dry seasons (2011-2012) and to determine effective irrigation volumes by differentiating actual evapotranspiration (ET) in irrigated and rain-fed areas. The results indicate that 256,578 ha were irrigated. This contrasts with the total irrigable area of 344,257 ha as stated by the Irrigation Department (ID), the JICA estimate of 382,110 ha, and the FAO estimate of total irrigated area of 685,246 ha. ET in rain-fed and irrigated areas in conjunction with potential evapotranspiration (PET) were compared between three different areas located in the north, the center and the south of the Dry Zone. Actual water volume utilized by crops is much smaller than the volume of water diverted for irrigation, suggesting significant scope for improving irrigation efficiency

Analyzing economic tradeoffs of water use in the Nam Ngum River Basin, Lao PDR. [Abstract only].

In German Aerospace Center (DLR); Germany. Federal Ministry of Education and Research (BMBF). Mekong Environmental Symposium, Ho Chi Minh City, Vietnam, 5-7 March 2013. Abstract volume, Topic 02 - Hydropower development and impacts on economy. Wessling, Germany: German Aerospace Center (DLR); Bonn, Germany: Federal Ministry of Education and Research (BMBF)

Regional Assessment of Groundwater Recharge in the Lower Mekong Basin

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

Geochemical characteristics and groundwater quality in the Vientiane Plain, Laos

Groundwater from the shallow aquifers of the Vientiane Plain, Laos is used for domestic needs including to some extent for drinking and for household gardening. The objective of this study is to assess the groundwater quality for drinking and irrigation activities and to determine the processes that lead to the presence of major ions in groundwater. Twenty groundwater samples were collected from a village on the Plain in December 2014, January 2015, and May 2015, and analysed for major ions and selected suite of minor ions and heavy metals. Groundwater is largely acidic, fresh and soft in nature. Geochemistry showed dominant Ca–Mg–HCO3 and mixed Ca–Na–HCO3 groundwater. Sodium impacts the suitability of water for irrigation to some extent. Hydrogeochemical processes identified and verified through factor analysis indicate weathering, carbonate dissolution, ion exchange, and anthropogenic sources including salinisation, due to irrigation and use of fertilizers as sources for the occurrence of major ions at such concentrations in this area. Only concentrations of lead and iron were above the permissible limits with arsenic, copper, zinc, mercury, and uranium found to be within safe limits. Background sample (groundwater) collected 5 km from the study area and the bottled water sample were all within suitable limits for drinking. This study is the first to provide a local-level assessment of geochemical processes in groundwater of this area indicating that the groundwater does not pose any threat to human health if used for drinking based on major ions, minor ions and a suite heavy metals except for iron and lead