The three-dimensional groundwater salinity distribution and fresh groundwater volumes in the Mekong Delta, Vietnam, inferred from geostatistical analyses

Over the last decades, economic developments in the Vietnamese Mekong Delta have led to a sharp increase in groundwater pumping for domestic, agricultural and industrial use. This has resulted in alarming rates of land subsidence and groundwater salinization. Effective groundwater management, including strategies to work towards sustainable groundwater use, requires knowledge about the current groundwater salinity distribution, in particular the available volumes of fresh groundwater. At the moment, no comprehensive dataset of the spatial distribution of fresh groundwater is available. To create a 3D model of total dissolved solids (TDS), an existing geological model of the spatial distribution and thickness of the aquifers and aquitards is updated. Next, maps of drainable porosity for each aquifer are interpolated based on the sedimentological description of the borehole data. Measured TDS in groundwater, inferred TDS from resistivity measurements in boreholes and soft incomplete data (derived from measurements in boreholes and data from domestic wells) are combined in an indicator kriging routine to obtain the full probability distribution of TDS for each (x,y,z) location. This statistical distribution of TDS combined with drainable porosity yields estimates of the volume of fresh groundwater (TDS < 1 g L−1) in each aquifer. Uncertainty estimates of these volumes follow from a Monte Carlo analysis (sequential indicator simulation). Results yield an estimated fresh groundwater volume for the Mekong Delta of 867 billion cubic metres with an uncertainty range of 830–900 billion cubic metres, which is somewhat higher than previous assessments of fresh groundwater volumes. The resulting dataset can for instance be used in groundwater flow and salt transport modelling as well as aquifer storage and recovery projects to support informed groundwater management decisions, e.g. to prevent further salinization of the Mekong Delta groundwater system and land subsidence, and is available at https://doi.org/10.5281/zenodo.4441776 (Gunnink et al., 2021).

The 3D groundwater salinity distribution and fresh groundwater volumes in the Mekong Delta, Vietnam, inferred from geostatistical analyses

Over the last decades, economic developments in the Vietnamese Mekong delta have led to a sharp increase in groundwater pumping for domestic, agricultural and industrial use. This has resulted in alarming rates of land subsidence and groundwater salinization. Effective groundwater management, including strategies to work towards sustainable groundwater use, requires knowledge about the current groundwater salinity distribution, in particular the available volumes of fresh groundwater. At the moment, no comprehensive dataset of the spatial distribution of fresh groundwater is available. To create a 3D model of Total Dissolved Solids (TDS), an existing geological model of the spatial distribution and thickness of the aquifers and aquitards is updated. Next, based on the sedimentological description of the borehole data, maps of drainable porosity for each aquifer are interpolated. Measured TDS in groundwater, inferred TDS from resistivity measurements in boreholes and soft incomplete data from domestic wells are combined in an indicator kriging routine to obtain the full probability distribution of TDS for each (x,y,z) location. This statistical distribution of TDS combined with drainable porosity yields estimates of the volume of fresh groundwater (TDS

Existence and Uniqueness Results for Two-Dimensional Stochastic Linearised Boussinesq Equation

The water flow in saturated zones of the soil is described by two-dimensional Boussinesq equation. This paper is devoted to investigating the linearised stochastic Boussinesq problem in the presence of randomness in hydraulic conductivity, drainable porosity, recharge, evapotranspiration, initial condition and boundary condition. We use the Sabolev spaces and Galerkin method. Under some suitable assumptions, we prove the existence and uniqueness results, as well as, the continuous dependence on the data for the solution of linearised stochastic Boussinesq problem. Keywords: linearised stochastic Boussinesq equation, Galerkin method, existence and uniqueness results, and continuous dependence on the data.

Hydromorphological analysis and water balance modelling of ombro- and mesotrophic peatlands

The hydromorphological analysis (HMA) is a method to quantify the potentials of mire revitalisation. In this study, the HMA is combined with the new peatland-tool of the water balance model AKWA-M®. This peatland-tool includes as well depth functions of the hydraulic conductivity and drainable porosity for several mire-ecotope-types as specific equations for mire evapotranspiration. The calculations were applied in several peatlands and mires of the German-Czech Ore Mountains (Erzgebirge/Krušné hory). The simulation results show that the chosen depth functions are valuable for the water balance calculation of mire ecotopes with a fully developed akrotelm like ombro- and mesotrophic peatlands. For degenerated peat soil or regenerating mires it is necessary to improve the model and the parameter calibration, especially the depth functions, with additional measured data in different peatlands.

Clogging of unsaturated gravel permeated with landfill leachate

The results of an experimental investigation into the clogging of unsaturated, uniformly graded 50 mm gravel permeated with municipal solid waste landfill leachate are reported. The flow of leachate within the unsaturated gravel was heterogeneous and occurred in free-draining flow pathways. The leachate experienced reductions in the concentrations of both the organic and inorganic constituents after passing through the unsaturated gravel although there was very little clogging within the unsaturated gravel. The average drainable porosity was reduced by 8% after 8 years permeation. The biofilm was limited to areas on the gravel where leachate could be retained; predominantly on top of lateral gravel surfaces and near particle-to-particle contacts. As a result, only a small fraction of the total surface area of the unsaturated gravel was covered with biofilm. The short leachate retention time and the sporadic distribution of biofilm limited the degree of contact between the bacteria and the leachate and hence limited biologically induced clogging within the unsaturated gravel. The data suggest that leachate collection systems should be designed and operated such that the drainage material of the leachate collection system remains unsaturated for as long as possible.

DETERMINAÇÃO A CAMPO DA POROSIDADE DRENÁVEL UTILIZANDO MODELOS MATEMÁTICOS COM BASE NO FLUXO DE DRENAGEM

Determinação A campo da porosidade drenável utilizaNdo modelos matemáticos com base no fluxo de DRENAGEM Antonio Ricardo Santos Andrade; Ivan Amaral Guerrini; Marcio Furlan Maggi; Wagner Martins da Cunha VilellaDepartamento de Engenharia Rural, Faculdade de Ciências Agronômicas, Universidade Estadual Paulista, Botucatu, SP, [email protected] 1 RESUMO Este estudo objetivou estimar da porosidade drenável por meio de equações de estimativa utilizando dados de carga hidráulica e descarga de drenos medidos obtidos a campo. O experimento foi conduzido em solos aluviais da área experimental do Departamento de Engenharia Rural da Faculdade de Ciências Agronômicas – Universidade Estadual Paulista, Botucatu, SP. Em uma área piloto, foram caracterizadas as propriedades hidráulicas do solo, determinado a carga hidráulica e descarga dos drenos subterrâneos. Os dados foram analisados com o uso das equações de Hooghoudt, para fluxo permanente, e a de Glover-Dumm, para fluxos não permanentes. Nas condições locais deste estudo a equação para fluxo permanente não permitiu uma boa estimativa da porosidade drenável na profundidade que contribui para o fluxo aos drenos. O uso da equação para fluxo não permanente proporcionou um valor de porosidade drenável mais próxima de um valor médio representativo desta propriedade para o dimensionamento de sistema de drenagem, quando comparado ao método de laboratório (mesa de tensão). Contudo, e devido à variabilidade espacial textural do solo ser ampla, vindo a dificultar a estimativa de valores mais representativos da porosidade drenável a ser utilizados nas equações para o dimensionamento de drenos. Assim, um grande número de medições pode ser requerido em condições de recarga e carga hidráulica, para levar em conta esta variabilidade, permitindo, portanto, uma estimativa mais fidedigna da porosidade drenável, no sentido de definir o melhor procedimento de análise dos resultados. UNITERMOS: Equações de drenagem, carga hidráulica, coeficiente de descarga. Andrade, A. R. S.; Gerrini, I. A.; MAGGI, M. F.; Vilella, W. M. C. field estimate of drainable porosity usING mathematical models based on the DRAINAGE flow 2 ABSTRACT This study aimed to determine the drainable porosity through estimate equations using field data from hydraulic head charge and drain discharge. The experiment was carried out in an alluvial soil area at the Agricultural Engineering Department in the School of Agronomy Sciences of Paulista State University, Botucatu, SP, Brazil. In an experimental area, the hydraulic properties of the soil were characterized through the hydraulic head charge and discharge of the underground drains. The data were analyzed with the use of Hooghoudt equations for steady-state flow and Glover-Dumm equation for non-steady-state flow. Under local conditions, the figures for steady-state flow did not allow a good estimate of the drainable porosity in the depth that contributes to the flow towards the drains. When compared to laboratory method (tension table), using an equation for non-steady-state flow, to calculate the dimension of drainage systems, provided a drainable porosity value closer to the significant average value of this property. However, and because the spatial and textural soil variability be wide, it is more difficult to estimate more significant values for drainable porosity to be used in equations for the drain dimensioning. Therefore, to take this variability into consideration and, thus, allow a more accurate estimate for drainable porosity in order to define the best procedure for result analysis, a large number of tests, under conditions of recharge and hydraulic head can be requested. KEYWORDS: drainage equations, hydraulic head charge, discharge coefficient