A. Ghosh Bobba

Numerical modelling of salt-water intrusion due to human activities and sea-level change in the Godavari Delta, India

Abstract The effects of human activities and sea-level changes on the spatial and temporal behaviour of the coupled mechanism of salt-water and freshwater flow through the Godavari Delta of India were analysed. The density driven salt-water intrusion process was simulated with the use of a SUTRA (Saturated-Unsaturated TRAnsport) model. Physical parameters, initial heads, and boundary conditions of the delta were defined on the basis of available field data, and an areal, steady-state groundwater model was constructed to calibrate the observed head values corresponding to the initial development phase of the aquifer. Initial and boundary conditions determined from the areal calibration were used to evaluate steady-state, hydraulic heads. Consequently, the initial position of the hydraulic head distribution was calibrated under steady-state conditions. The changes of initial hydraulic distribution, under discharge and recharge conditions, were calculated, and the present-day position of the interface was predicted. The present-day distribution of hydraulic head was estimated via a 20-year simulation. The results indicate that a considerable advance in seawater intrusion can be expected in the coastal aquifer if current rates of groundwater exploitation continue and an important part of the freshwater from the river is channelled from the reservoir for irrigation, industrial and domestic purposes.

Application of environmental models to different hydrological systems.

In recent years global problems such as climatic change, acid rain, and water pollution in surface and subsurface environments dominate discussions of world environmental problems. In this paper, the roles of hydrologic processes and hydrogeochemical processes are investigated through development, modification, and application of mathematical models for addressing point and non-point source water quality modelling of receiving waters: surface water, subsurface water and lake water. The paper describes the use of models to simulate the movements of pollutants and water: subsurface water, surface water and lake sediments. A hydrological model was applied to Northeast Pond River watershed to understand climate change effects in the watershed. Four watershed acidification models were applied to compute hydrogen ion, alkalinity and sulphate concentrations from Turkey Lakes watershed, Canada. The computed hydrogen ion was used to estimate acidic events, magnitude of hydrogen ion, and duration using a stochastic model. There exist uncertainties in environmental models due to imperfect knowledge of processes controlling water quality parameters as well as errors in data. Monte Carlo, first order, and inverse method analyses were used to assess uncertainty in models. SUTRA (saturated-unsaturated transport) and SUTRA(-1) models were applied to Lambton county, Ontario, Canada to locate groundwater discharge areas for St. Clair River, calculate discharge rates, and hydrogeologic parameters. A sediment contamination model was developed and applied to Great Lakes sediment data to estimate transport parameters by Pb-210 data. It was then coupled with fatty acid data and results were compared with observed data. A contaminant transport model was developed and applied to two North American streams to compute stream water concentration. The computed data was compared with observed data using a simple statistical method. A hydrological model was coupled with water quality models and RAISON (regional analysis by intelligent systems on) expert system and applied to Canadian watersheds. Digital satellite data was used to locate groundwater discharge and recharge areas in the watershed. This data is useful as observed data for hydrological modelling and GIS (Geographical Information System) system

Ground Water-Surface Water Interface (GWSWI) Modeling: Recent Advances and Future Challenges

Ground water-surface water interface (GWSWI) represents the interconnection of ground water and surface water in the hydrologic continuum. Interactions between these two water masses result in unique gradients and/or transitions of contaminant concentration profiles, biological populations, chemistry, flow, mixing characteristics, redox potential, dissolved oxygen, organic content, and thermal properties across GWSWI. In addition, many unique biogeochemical processes occur in this zone that can have significant impact on the fate and transport of contaminants across the GWSWI. Prediction of the distribution and concentrations of contaminants across the GWSWI is challenging, but is essential for evaluating human health and environmental risk, including remedial alternatives at contaminated sites. The objective of this paper is to review and assess existing modeling capabilities to recognize (a) the need for development of new modeling tools, (b) knowledge gaps, and (c) challenges required to address contaminant transport within GWSWI. Currently, the most important needs for future model development are, (a) linkage between ground water and surface water models; (b) integration of process-level models within the framework of large-scale models; and (c) understanding ground water-surface water interactions within a spatial and temporal framework.

Sensitivity of Hydrological Variables in the Northeast Pond River Watershed, Newfoundland, Canada, Due to Atmospheric Change

Watershed runoff modelling techniques were developed and applied for assessing climatic impacts, and tested for a watershed in the Northeast Pond River basin using atmospheric-change scenarios from a series of hypothetical scenarios. Results of this research strongly suggest that possible changes in temperature and precipitation caused by increases in atmospheric trace-gas concentrations could have major impacts on both the timing and magnitude of runoff and soil moisture in important natural resources areas. Of particular importance are predicted patterns of summer soil-moisture drying that are consistent across the entire range of tested scenarios. The decreases in summer soil moisture range from 10 to 50% for different scenarios. In addition, consistent changes were observed in the timing of runoff – specifically dramatic increases in winter runoff and decreases in summer runoff. These hydrologic results raise the possibility of major environmental and socio-economic difficulties and they will have significant implications for future water-resource planning and management.

Groundwater contamination modelling

In the development of groundwater protection and rehabilitation strategies, mathematical models play an important role. This chapter discusses the role of groundwater contamination models in planning, management, and regulation of groundwater systems, with a focus on generic and site specific contamination. The various approaches for modelling groundwater contamination are reviewed. The applicability of various kinds of models to groundwater contamination is discussed and an overview of available models presented. A case history from Canada is used to demonstrate and illustrate current modelling methodology.

A microcomputer model of contaminant transport in an aquatic system

A micro computer model was developed for routing chemical waste contamination through a small aquatic system. The capabilities of this simulation model include the following characteristics: a) It distributes contamination by advection and dispersion along the longitudinal axis of the system. b) It may be discretized into any number of segments (vertical planes normal to the longitudinal axis) as may be appropriate to describe spatial variations in chemical contamination. c) It is capable of treating instantaneous, continuous, or time varying releases of chemical waste contamination. d) It provides for temporal description of contamination throughout the system. e) It provides for adsorption and desorption by both vegetation and bottom sediments. The model can be run on microcomputer with Fortran compiler. The model applied to two small streams which are located in U.S.A., and Canada. The model results compared well with observed data. The dispersion parameter was computed by the model.

Groundwater Development and Management of Coastal Aquifers (including Island Aquifers) through Monitoring and Modeling Approaches

More than half the world’s population now lives within 80 kilometres of a shoreline and human population in these regions is growing exponentially, such that it is expected to double or triple in the next two decades in North America alone. Human activities on coastal and island watersheds provide the major sources of nutrients and pollutants entering shallow coastal ecosystems. Contamination loadings from watersheds are the most widespread factor that alters structure and function of receiving aquatic ecosystems. Surface water in the coastal and island watersheds interacts with adjacent subsurface water. Subsurface water discharges are recognized as potentially significant contaminant pathway from the land to the coast by human activities. This interaction affects the water quality and quantity in both surface and subsurface waters. The diversity, in combination with the range of disciplines and of time and space scales involved; complicate the use of data for purposes other than those envisioned by the original investigators. As land and water resource development increases in the coastal watersheds, it is becoming readily apparent that subsurface and surface waters interaction must be considered in establishing water management policies. On a more regional scale, human activity has already demonstrated heavy impacts on coastal zones and further demands are increasingly threatening the integrity and health of biologically rich aquatic ecosystems, including coral reefs, mangroves, sea grass beds, lagoons, wetlands, bays and near shore waters.

Numerical simulation model of fatty acids in lake sediments

The finite element model was successfully applied to predict the Pb-210 and total extractable fatty acid concentrations at different depths in two sediment cores from Lake Ontario by using different transport parameters. The transport parameters were computed from Pb-210 data. These parameters were used to simulate the total extractable fatty acid concentrations at different depths. The computed results were compared with observed data and results were compared by statistical methods. Good agreement was achieved though improved results were observed in a two layer model accounting for bioturbation in the upper 4–6 cm of sediment. By modifying this model is useful to apply the contaminant transport in lake sediments, industrial waste disposal ponds, and fish ponds with different geological, physical, chemical and biological parameters at different depths.

Watershed acidification modelling

A wide variety of watershed acidification models are currently being used to address water quality issues from national to local field scale due to acid precipitation. The complexity of the watershed process and the need to provide information quickly has increased the reliance on these models. To properly utilize a watershed acidification model, the user must clearly understand the goals and objectives of the modeling project, and the capabilities and limitations of the watershed acidification model. An overview of process descriptions, assumptions, constraints and other considerations which enter into the development of deterministic watershed acidification models is given in this chapter. Various approaches to watershed acidification models from very simple lumped models to complex models describing flow and biogechemical reactions in watershed systems are described. Four watershed acidification models (TMWAM, ETD, ILWAS and RAINS) are reviewed and a comparison of model performance is presented for Turkey Lakes watershed, Ontario, Canada.

Computer program (shock) to predict acid shocks in watersheds using stochastic analysis

High hydrogen ion concentrations of runoff events were analyzed in terms of the probability distributions of frequency, duration, magnitude, and time of occurrence. Simple stochastic models were applied to the probability distributions of the annual frequency of high hydrogen ion concentration flows and their magnitudes. A consideration of the statistical properties of the given stochastic variables led to the development of a technique with which higher hydrogen flow events exceeding any higher level of interest may be investigated without resorting to reanalysis of the historical data. The proposed methodology was applied to the daily hydrogen ion concentration flow records of Mersey River Watershed, N.S., Canada, which is affected by acid precipitation. Copyright (C) 1996 Elsevier Science Ltd (Less)