Abstract:The present work examines the possible use of major ion chemistry and multivariate statistical techniques as a rapid and relatively cost-effective method of identifying the extent of groundwater and surface water (GW-SW) interaction in an urban setting. The original hydrogeochemical dataset consists of groundwater (n D 114), stream water (n D 42) and drain water (n D 24) samples, collected twice in a year for the pre-and post-monsoon seasons, for three successive years along an 8 km reach of the Delhi segment of River Yamuna, India. The dynamic and similar seasonal changes of hydro-geochemical facies and major ion trends of river, drain and groundwater samples indicate the existence of an empirical relationship between GW and SW. Results of both R-and Q-mode factor and cluster analyses highlight multi-scale control of the fluid exchange distributions, with distinct seasonal alteration in mode and extent of GW-SW interaction, namely, the influence of the mixing zones between urban river and groundwater and the pattern of groundwater flow through the river bed. Hierarchical cluster analysis (HCA) of sampling locations efficiently illustrates different groups that comprise samples severely influenced by contaminated surface water downstream and the upstream fresh water samples. These results substantiate the strong exchange processes between GW and SW all along the stretch. The study shows that the combination of an empirical and statistical relationship between different ionic species and sampling locations can provide greater confidence in identifying the extent of GW-SW interaction/exchange processes.

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Remote sensing techniques are becoming powerful tools for efficient management of irrigation systems in large irrigated areas. The objectives of management of irrigation systems, although they vary widely, may be defined as high crop productivity per unit land per unit applied water with equity in distribution. Some of the key elements of irrigation system management are: (i) performance monitoring and evaluation, (ii) diagnostic appraisal, (iii) action research, and (iv) farmers' participation. The objective of this paper is to present the state of the art on applications of satellite remote sensing that support management of irrigation systems and to identify emerging approaches that focus on future directions of research which may pave the way to operationalise the remote sensing techniques in practice. Firstly, a brief review on different approaches being utilized for management of irrigation systems is dealt with. Subsequently, the present status of remote sensing applications in irrigated agriculture is reviewed. The paper also presents future perspectives of remote sensing applications in determining hydrological variables and quantifying irrigation system performance indicators for better management of water use in irrigated agriculture. Copyright © 2002 John Wiley & Sons, Ltd.KEY WORDS: remote sensing; irrigation system management; performance monitoring; large irrigated commands; spatial hydrological modelling RÉ SUMÉ Les techniques de télédétection deviennent des outils puissants pour la gestion efficace des systèmes d'irrigation dans de grands périmètres irrigués. Les objectifs de la gestion des systèmes d'irrigation, bien que très variés, peuvent être définis en tant que productivité par hectare et par unité d'eau appliquée avec l'équité de la distribution. Certains des éléments principaux de la gestion de systèmes d'irrigation sont (i) la surveillance et l'évaluation de la performance, (ii) le diagnostique, (iii) la recherche active, et (iv) la participation des agriculteurs. L'objectif de cet article est de présenter la situation actuelle des applications de la télédétection par satellite appliquée aux systèmes d'irrigation et d'identifier les directions futures de la recherche pour préparer le terrain pour les techniques de télédétection dans la pratique. Premièrement, une brève revue des différentes approches utilisées pour la gestion des systèmes d'irrigation est traitée comme prétexte. La suite présente le statut actuel des applications de télédétection dans l'agriculture irriguée. La communication présente également quelques perspectives futures des applications de télédé-tection pour la détermination des variables hydrologiques et pour mesurer les indicateurs de performance des systèmes d'irrigation.

Simulation models are used to aid the decision makers about water pollution control and management in river systems. However, uncertainty of model parameters affects the model predictions and hence the pollution control decision. Therefore, it often is necessary to identify the model parameters that significantly affect the model output uncertainty prior to or as a supplement to model application to water pollution control and planning problems. In this study, sensitivity analysis, as a tool for uncertainty analysis was carried out to assess the sensitivity of water quality to (a) model parameters (b) pollution abatement measures such as wastewater treatment, waste discharge and flow augmentation from upstream reservoir. In addition, sensitivity analysis for the "best practical solution" was carried out to help the decision makers in choosing an appropriate option. The Delhi stretch of the river Yamuna was considered as a case study. The QUAL2E model is used for water quality simulation. The results obtained indicate that parameters K(1) (deoxygenation constant) and K(3) (settling oxygen demand), which is the rate of biochemical decomposition of organic matter and rate of BOD removal by settling, respectively, are the most sensitive parameters for the considered river stretch. Different combinations of variations in K(1) and K(2) also revealed similar results for better understanding of inter-dependability of K(1) and K(2). Also, among the pollution abatement methods, the change (perturbation) in wastewater treatment level at primary, secondary, tertiary, and advanced has the greatest effect on the uncertainty of the simulated dissolved oxygen and biochemical oxygen demand concentrations.

Groundwater quality problems have emerged in many geographical areas due to natural environmental processes and human intervention in the geosystems. Hydrogeochemical appraisal of fluoride contaminated groundwater in Mehsana District, Gujarat State, India is carried out by means of groundwater quality investigations together with X-ray diffraction analysis of soil samples in the delineated high fluoride areas. Results show that fluoride has negative relationships with calcium, whereas relationships with sodium, alkalinity and sulphate are positive. Results obtained from aqueous speciation modelling using PHREEQC reveal that the groundwater is undersaturated with fluorite and oversaturated with calcite. The factor analysis indicates that sodium plus potassium bicarbonate groundwater have high factor loading for fluoride, whereas that for calcium chloride and magnesium chloride groundwater is low. The plausible geochemical reactions in the study area are precipitation of calcite and dissolution of dolomite, carbon dioxide and sulphate minerals with ion exchange.