A. Das Gupta

Sustainable groundwater resources development

Abstract Sustainable groundwater resources development implies use of groundwater as a source of water supply, on a long term basis, in an efficient and equitable manner sustaining its quality and environmental diversity. An understanding of the behaviour of a groundwater system and of its interaction with the environment is required to formulate a sustainable management plan. Mathematical models supported by field information play a key role in assessing the future behaviour of a system to stresses and to find effective operating conditions for sustainable development and management of groundwater resources. Basic principles for sustainable development are stressed and a brief review of two case studies is provided to illustrate how a systems approach and its computational framework of mathematical models can be used in addressing the main issue of water allocation satisfying some of the technical and environmental constraints.

Fingered preferential flow in unsaturated homogeneous coarse sands

The occurrence of fingered preferential flow depends on both flow and porous media characteristics. The boundary condition of unsaturated infiltration has been investigated to assess whether it produces unstable wetting in homogeneous coarse sands. Laboratory tracer experiments were conducted in two coarse sand materials; for each sand material two initial conditions of air dry and field capacity were considered. Results indicate that the commonly occurring process of nonponding rainfall can provoke fingered preferential flow in homogeneous sandy soils. This phenomenon is very predominant in dry as compared to wet initial conditions. Models of water flow and solute transport in uniform coarse soils should incorporate the effects of such fingered flow phenomenon.

A nonlinear chance constrained model for irrigation planning

Abstract A general nonlinear optimization model for irrigation planning and management comprising a production function, chance constraints due to stochastic streamflows and a loss function to represent the economic implications of the chance constraints is proposed. A computationally feasible approach is suggested to resolve a complex problem of agricultural water management with stochastic streamflow. This is possible by transforming the chance constraints and the loss function which are originally in the form of cumulative probability distribution functions of the streamflow into equivalent nonlinear deterministic forms.

Heavy Metal Adsorption in Soil: Comparison of Bisolute Adsorption Models and Laboratory Experiments

The effect of Zn and NH4 on the adsorption of Cd has been studied at a pH of 6 for two soils. The experiments were carried out for concentrations of Zn and NH4 in the ranges present in most industrial wastewaters. The competitive experiments were conducted also with wastewater from a zinc refinery. It was found that both Zn and NH4 suppressed the ability of Cd to adsorb onto soil. The adsorption of Cd and Zn was determined to be less in the refinery wastewater than that in the single solute batch experiments. Different theories have been proposed to predict the equilibrium concentrations of solutes in the bisolute system using single solute isotherm constants. Four simple mathematical models to predict equilibrium concentrations in the bisolute system have been tested for their applicability, viz., Competitive Freundlich Adsorption Model (CFAM), Modified Competitive Freundlich Adsorption Isotherm Model (MCFAM), Ideal Adsorbed Solution Theory (IAST), and the one given by Sheindorf et al. (1981), (SM). The MCFAM and the SM were found to be satisfactory in predicting the concentrations in the bisolute system and at the same time more easily incorporated into bisolute transport models.

Search Beam Method. A promishing way to define non-dominated solutions in multi-objective groundwater development.

An interactive multi‐objective decision‐making (MODM) model based on the Search Beam Method (SBM) and a finite‐difference groundwater flow model (GWM), is developed for analysing groundwater resources development and management problems. The SBM utilizes one‐dimensional search in the objective space to (systematically) identify the non‐dominated solutions. The steady‐state GWM determines the aquifer response due to well withdrawals. Three competing objectives of maximizing total yield, minimizing maximum compression and minimizing total pumping cost are considered. Applicability of the MODM model is demonstrated on a simplified confined aquifer system resembling one of the water‐bearing layers underlying Bangkok.

Estimating aquifer recharge and parameters from water level observations

This paper is concerned with the development of a technique to estimate recharge from rainfall, and to estimate aquifer parameters, using groundwater level records and available climatological data. The methodology combines a hydrometeorological model which links rainfall and evapotranspiration to the effective groundwater recharge, and a geohydrologic model which links the recharge to the water level in the aquifer. Results of field application are presented to illustrate the usefulness of the technique.

A pilot-scale investigation of particle retention during artificial recharge

For longtime storage of water in the pores of sand, it is important to study physical clogging. An experimental investigation was conducted using a pilot-scale artificial recharge model to study the temporal and spatial variation of particle retention in the sand pores. The experimental results were compared to a mathematical model characterizing physical clogging in artificial recharge.

River basin water quality assessment and management: case study of Tha Chin River Basin, Thailand

The water quality improvement plan for the Tha Chin river basin in central Thailand has been studied by using integrated land-use and water quality modelling. There has been little research on water quality planning in this basin due to the complex and intensive data requirements and also due to modelling difficulties. This research attempts to apply the integrated land-use and water quality modelling to the Tha Chin river basin. Loading reduction scenarios were applied to find out the appropriate loading reduction target and hence the improved water quality in the main stream.

Simulation of stable and unstable flows in unsaturated homogeneous coarse sand

Abstract A numerical model developed to simulate stable and unstable flows in unsaturated porous media is described. Results of numerical studies carried out to simulate laboratory experiments with the assumption of stable flow demonstrate the occurrence of unstable flow for the initial conditions of both air dry and field capacity for unsaturated infiltration in sands. This indicates that the Richards flow equation based on moisture content and potential variables averaged over total crosssectional area may not be applicable for flow under instability-prone boundary conditions. The unstable flow due to wetting front instability is modelled using the steady-state theory proposed by Hillel & Baker (1988). Simulation results for fingered flux calculated with the theory represent the experimental data reasonably well. The pore water velocity remains constant irrespective of the incident flux as long as the flux is smaller than the hydraulic conductivity value at the water entry suction of the porous media. T...

Saltwater transport in a heterogeneous formation: A case study

Historical information of the hydraulic and salinity aspect, detailed geological information, and information on the physical characteristics of the different layers comprising the formation, are needed for simulating the saltwater transport process in aquifers. In most simulation studies of field situations, there is an inadequacy of data and the modeller has to make justifiable assumptions to analyze a particular situation in order to provide an insight into the problem.A quasi-three-dimensional solute transport model is used to analyze the saltwater encroachment phenomena in aquifers underlying the City of Bangkok; first by calibrating the models performance with available historical data and then by assessing the extent of future saltwater encroachment with the implementation of the regulatory pumpage to be followed in order to restrict the alarming rate of land subsidence. Model simulation indicates a substantial reduction in the rate of encroachment of the saltwater front with a reduction of pumpage after 1987.