Sustainable groundwater resources developmenthydrologie.org/hsj/420/hysj_42_04_0565.pdfSustainable groundwater resources development A. DAS GUPTA & PUSPA R. ONTA School of Civil Engineering,

Hydrological Sciences-Joumal-des Sciences Hydrologiques, 42(4) August 1997 565

Sustainable groundwater resources development

A. DAS GUPTA & PUSPA R. ONTA School of Civil Engineering, Asian Institute of Technology, PO Box 4, Klongluang, Pathumthani 12120, Thailand

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.

Aménagement durable des ressources en eaux souterraines Résumé L'aménagement durable des ressources en eaux souterraines implique que l'utilisation à long terme des eaux souterraines pour l'alimentation en eau soit réalisée de manière efficace et équitable tout en conservant leur qualité et leur diversité environnementale. La compréhension du fonctionnement d'un système aquifère et de ses relations avec son environnement est nécessaire pour formuler un plan de gestion durable. Les modèles mathématiques nourris par des données de terrain jouent un rôle fondamental pour prévoir le comportement futur d'un système soumis à des sollicitations et pour déterminer les conditions les plus efficaces pour un aménagement et une gestion durable des ressources en eaux souterraines. On a insisté sur les principes fondamentaux d'un aménagement durable et fourni une brève analyse d'une étude de cas afin d'illustrer comment une approche systémique et sa traduction informatique en termes de modèles mathématiques peuvent être utilisées pour aborder le grand problème d'une allocation de l'eau satisfaisant certaines contraintes techniques et environnementales.

INTRODUCTION

Groundwater has always been considered to be a readily available source of water for domestic, agricultural and industrial use. In many parts of the world, groundwater extracted for a variety of purposes has made a major contribution to the improvement of the social and economic circumstances of human beings. Management strategies have been focused on the development of groundwater resource while projects of various types and scales have been developed and managed in response to the growing demand for water by communities and industries. In spite of bringing many benefits, with the increase in demand, this resource is being overexploited in many areas resulting in a permanent depletion of the aquifer system and associated environmental consequences like land subsidence and water quality deterioration. Moreover, with changes in land use and a vast increase in the quantities and types of

Open for discussion until 1 February 1998

566 A. Das Gupta & Puspa R. Onta

industrial, agricultural and domestic effluent entering the hydrological cycle, a gradual decline in water quality is observed due to surface and subsurface pollution.

Concurrently with the development in field investigation, monitoring and evaluation, mathematical modelling has emerged as a powerful tool for groundwater planning and management. The systems approach and its computational framework of mathematical models have been developed and proposed for the optimum development and management of groundwater resources (Gorelick, 1983; Willis & Yen, 1987). As the world is becoming more concerned with sustainable and environmentally sound development, there is a need to highlight key principles of sustainable groundwater resources development and illustrate how a systems approach can be used in addressing the main issue of water allocation satisfying some of the technical and environmental constraints. The emphasis is on systems analysis and planning for achieving sustainable groundwater resources development.

SUSTAINABILITY

Sustainable development, as presently understood, had its origin in the World Conservation Strategy (IUCN, 1980). This strategy sets out some now widely accepted principles of environmental sustainability and identified three essential life support systems: soil, air and water. The sustainable development concept was subsequently promoted to a high level of international prominence in the report Our Common Future (WCED, 1987), known as the Brundtland Report. It defined sustainable development as "development which meets the needs of the present without compromising the ability of future generations to meet their own needs". Water resources projects are sustainable, if water of sufficient quantity and quality at acceptable prices is available to meet demands and quality standards of the region now and in the future without causing the environment to deteriorate (Plate, 1993).

Water resources come from systems which include rivers, lakes, wetlands and aquifers. The planning for utilization of these resources must be considered in association with their functions in the hydrological cycle and their interactions with the physical, chemical and biological processes in terrestrial ecosystems. Planning and decision making for groundwater development is a continuous dynamic process. When one addresses the question of sustainable development, the objectives and concerns of development will change over time and the development planning must adjust with the changing conditions. Short term socio-economic gains may have to be traded with long term sustainability, with its varied dimensions. This again is not an easy task because of the complex interactions involved and the difficulties of specifying various noncommensurate criteria.

PRINCIPLES OF SUSTAINABLE GROUNDWATER DEVELOPMENT

The goal of environmentally sound and sustainable development of water resources is to develop and manage them in such a way that the resource base is maintained and

Sustainable groundwater resources development 567

enhanced over the long term. Groundwater development begins typically with a few pumping wells and initially the groundwater management practice, in many cases, is geared to facilitate usage and development. As development progresses with more and more drilled wells scattered over the basin, issues such as overexploitation, equitable sharing of water and degradation of water quality become apparent in many basins. Thus, the emphasis of groundwater management practice has to be changed so that the available resource is utilized in an efficient, sustainable and equitable manner contributing to the economic and social well being of the broader community. A sustainable groundwater development depends on the understanding of processes in the aquifer system, quantitative and qualitative monitoring of the resource and the interaction with land and surface water development. The following key principles reflect different aspects of concern in the evolution of sustainability in groundwater development: (a) long term conservation of groundwater resources; (b) protection of groundwater quality from significant degradation; and (c) consideration of environmental impacts of groundwater development.

Long term conservation of groundwater resources

Groundwater development must be sustainable on a long term basis which implies that the rate of extraction should be equal to or less than the rate of recharge. When the rate of extraction is higher than the rate of recharge, a continual lowering of water level or potentiometric level is expected and this situation has to be carefully considered for some specific cases. A continual lowering of the water table will steadily increase the pumping cost and then, at a certain level, it would no longer be economical to pump for many uses such as agricultural production. An assessment of the natural recharge is thus a basic prerequisite for an efficient groundwater resources development planning.

At the initial stage of development, conventional water balance studies based on the classical theory of a hydrological budget and soil moisture balance are conducted to estimate the groundwater recharge. However, with the availability of hydrogeo-logical data and monitoring information as development progresses, the long term availability of a resource for development is assessed based on the dynamic response of the groundwater system. As the requirement of sustainable development is attached with the quantity aspect of groundwater availability and the related economic consequences, the operational concern will be to limit the anticipated decline of the water table or potentiometric level. This restriction may also be related to the environmental consequences of development as stressed in the subsequent principles.

A comprehensive discussion on various methods that are available to estimate recharge can be found in Simmers (1988). Rushton & Ward (1979) outlined the conventional method of analysis and suggested several modifications to the classical theory. Khan & Mawdsley (1988) introduced the concept of reliable yield and proposed a lumped model to estimate the yield of an unconfined aquifer. Das Gupta & Amaraweera (1993) illustrated an approach, using an example from the island of


Mannar in Sri Lanka, to assess the long term safe withdrawal from a coastal aquifer. The time frame for long term evaluation was not long enough for most of the studies to consider the implications for future generations.

Protection of groundwater quality

The quantitative aspect of resource availability for sustainable use is a basic concern for the evolution of resource management. However, the quality aspect is also of critical importance and is closely linked with the quantity aspect. The quality of groundwater in aquifers can be affected by natural and human activities while the extent to which the quality is affected varies with the hydrogeological and climatic settings (Todd, 1980; Fetter, 1993). A deterioration of groundwater quality is detected only when there is a characteristic odour, colour or taste in consumed water or when the presence of pollutant has an immediate impact on users of water. With the presence of various sources of contamination and with the complexity of the hydrogeological environment and transport processes, sometime it is difficult to establish a simple, straight forward cause and effect relationship. Moreover the impact of groundwater quality deterioration could be widespread and difficult to control.

Ideally, contamination should be prevented. Successful prevention means that the potential contaminants must be controlled so that they cannot react with the groundwater system. Land use planning is a major form of prevention in which the producers of hazardous wastes are kept away from the areas overlying groundwater resources so that in the event of an accidental leakage, little damage will occur. Once contamination of a local groundwater supply has occurred, action must be taken to find and eliminate the sources, contain the contaminants in the area already affected and restore the water quality of the aquifer. As groundwater resources may be the only freshwater resource in many areas, restoration of the aquifer may be of the highest priority regardless of the cost involved. The problem of groundwater contamination has been approached by different investigators from different points of view. The resulting achievements are very extensive and scattered. A practical handbook of assessment, prevention and remediation of groundwater contamination is provided by Boulding (1995). Khondaker et al. (1990) provided the state-of-the-art of groundwater contamination studies.

Environmental impacts of groundwater development

The essential requirement in the evolution of sustainable development for water resources system is the recognition of the objective of environmental sustainability. By making changes to the groundwater system, changes in the broader context of the water system may result. On the other hand, by making changes in the environment of other components of the water cycle, changes in the groundwater system can result. This is particularly evident where the groundwater system has hydraulic links


with the surface water systems such as rivers, lakes, springs and swamps. A continual lowering of water table or potentiometric level can result in land subsidence due to formation compaction in some hydrogeological environments. Many associated and potential problems like flooding, loss of property and human lives, severe deterioration of infrastructure facilities, groundwater pollution and health hazards have been attributed to the effects of excessive groundwater withdrawal and land subsidence (Nutalaya et al., 1989; Ramnarong & Buapeng, 1991). Also the most common environmental impact of uncontrolled pumping, particularly in coastal areas, is the intrusion of saline water.

For environmental sustainability, the development and management of groundwater resources should be considered as a part of the integrated water management pursuing two main objectives, namely: provision of water for beneficial uses at minimum cost and avoidance of adverse effects on the environment. Groundwater resources planning as part of the water resources system is strongly interrelated with other planning areas, e.g. agricultural development, industrial development and urbanization. The development perspectives of these various sectors have strong implications on the sustainability of groundwater development. Attempts are being made to develop a comprehensive modelling approach for water resources systems at basin scale for water management with due regard to the interactions between different sub-systems of water resources and their interactions with other development sectors (Sivapalan et al, 1996a,b,c; Refsgaard et al., 1995a,b). However, a major effort in applying these methodologies to the field scale has been hampered due to lack of field information on individual systems and their interactions. Major challenges exist in accommodating changing social values and in understanding better the relationship between the biota and the occurrence, behaviour, and quality of water.

USE OF MATHEMATICAL MODELS

Mathematical models have long been developed and proposed in analysing complex water resources systems, including those involving conjunctive water use (Gorelick, 1983; Willis & Yeh, 1987). Broadly speaking, these models may be categorized into two groups based on the two basic analytical techniques viz. simulation and optimization. Simulation models solve the governing mathematical equations (in one, two or three dimensions) of flow and solute transport in heterogeneous systems using numerical techniques such as finite difference, finite element, or method of characteristics (Anderson & Woessner, 1992). A simulation model is used many times repeatedly for each management alternative to predict the spatial and temporal distribution of state or response of the system (e.g. hydraulic heads, concentrations in aquifers and rivers).

Although simulation can be very detailed, provide a wide range of performance indicators and explain complex relationships, its computational demands are very high. Since simulation often fails to consider important objectives and constraints, it is unlikely to yield optimal decisions. In contrast, an optimization model uses a

570 A. Das Gupta & Puspa R. Onla

mathematically based search procedure to find the decision that maximizes or minimizes certain objectives or criteria. In order to relate systematically the detailed hydraulic behaviour of the system to management plans and policies, simulation and optimization have also been linked.

Critical literature reviews of planning and management models considering quantity and quality aspects as well as for the conjunctive use of surface water and groundwater were presented by Das Gupta & Onta (1994), and Onta et al. (1994). The computational approaches for estimating land subsidence due to fluid withdrawal and for solving sea water intrusion problems in coastal areas are well established. Full mathematical simulation of regional subsidence has been carried out in many areas, e.g. for the case of Venice by Gambolati & Freeze (1973), and Gambolati et al. (1974); for the case of Mexico City by Rivera et al. (1991); and for the case of Bangkok City by AIT (1981). A historical perspective of the quantitative analysis of sea water intrusion problems and a review of mathematical models were provided by Reilly & Goodman (1985) and Bobba (1993).

A review of two case studies is provided in the following sections with a view to present modelling approaches on the basis of which a sustainable development policy can be developed. The first study deals with the application of a groundwater quantity management model for a large-scale physical system. The management model is formulated for a situation in which the available surface water is not adequate to meet the demands and the deficit amount would be the minimum groundwater supply requirement. The second case study is on the conjunctive use of surface water and groundwater for irrigation. The need for integrating groundwater use in the irrigation scheme exists because natural rainfall and surface sources, due to their seasonal variability and inherent uncertainties, cannot meet the irrigation requirement of the study area.

Application of a groundwater quantity management model

The management model is applied to the complex multiaquifer system underlying the city of Bangkok. The city is situated on the delta and flood plain of the Chao Phraya River which traverses the Lower Central Plain of Thailand. The extent of the metropolitan area is approximately 1500 km2 and the population is over 6 million. To meet the increasing water demand in the city, the groundwater resources have been extensively developed, rather in an unplanned manner, resulting in adverse economic-environmental problems such as continual decline of potentiometric levels, land subsidence and groundwater quality deterioration by salt water encroachment. Efforts are being undertaken to increase the surface water supplies substantially whereby groundwater pumpage can be curtailed. Under this circumstance, it was desirable to know the maximum withdrawal economically feasible considering a certain rate of potentiometric head recovery. However, data on the cost of pumping and the benefit derived from water were not available. Nevertheless, the applicability of the model was demonstrated with assumed cost and benefit factors. For analysis, the minimum allowable heads at different location at different time periods were


specified in two ways: (a) considering a linear recovery of potentiometric level achieving the target level at the end of the eighth year and then remaining constant; and (b) achieving the target level of potentiometric head at the end of the tenth year with a quadratic rate of recovery. The details of model development and application results can be found in Das Gupta et al. (1996). Only a brief description of the approach with some selected results are presented herein.

Management model The hydraulic response of the multiaquifer system was simulated through the convolution of unit response functions generated by solving numerically the quasi-three dimensional flow equation with leakage fluxes between aquifers. The objective function of the management model was defined as maximizing the relative net benefit or minimizing the operational cost, subject to a specified allowable drawdown, a specified minimum pumping requirement and a maximum allowable recharge. For a multiaquifer system, the number of variables and constraints would be large. The quadratic model was, therefore, applied through a hierarchical approach by decomposing the original problem into sub-problems at different levels and the solution procedure was iterative encompassing both quadratic and linear programming problems. For details on the schematization for the physical system as well as for modelling, reference can be made to Das Gupta et al. (1996).

Results As mentioned earlier, the optimal distribution of the pumping pattern was determined considering certain assumed cost and benefit factors and defined rate of recovery of potentiometric head. With a uniform benefit rate of 16 cents per m3 of water and a pumping cost of 24 cents per 1000 m3 per m lift of water, the total optimum water withdrawals over respective time periods considering the linear rate of potentiometric head recovery are given in Table 1 as Case A. This result was, however, identical with the safe yield considering a linear rate of recovery (indicated as Case B in Table 1), which implies that the benefit rate was relatively higher than the pumping cost and the lifting head was not enough to make the economic factor influence the optimal decision. With pumping cost four times that of Case A, the total withdrawal volume and benefit were less, and the results on withdrawal rates over respective time periods are given in Table 1 as Case C. The optimal pumping distribution was also changed though the target rate

Table 1 Optimal pumpage considering potentiometric head recovery.

Optimum pumpage (103 m3 day') Total Net benefit volume (US$106) (106 m3)

Case 1991-1992 1993-1994 1995-1996 1997-1998 1999-2000

A 988.2 999.4 948.1 865.8 927.3 3451.9 539.5 B 988.2 999.4 948.1 865.8 927.3 3451.9 C 923.1 1002.0 944.2 860.6 923.5 3397.0 492.6 D 1109.0 1179.7 1089.5 1051.4 902.1 3892.1 606.4


of potentiometric head recovery was the same in both cases. The reduction in withdrawal was mostly in the first time period; after that the optimal pumping distributions and the total pumping became almost equal to those of Case A. At the beginning of the planning horizon, due to a high lifting head, the pumping cost was higher and influenced the decision. Later as the potentiometric head recovered, the lifting head decreased and the influence of cost on the decision was reduced. With a quadratic rate of potentiometric head recovery, the optimum total withdrawal and benefit were higher than those of Case A, as indicated in Table 1 by Case D. For a higher recovery rate at the later part of the planning horizon, the total pumping in Case D was reduced rapidly, whereas in Case A and C, since the allowable head was considered to be constant from the fourth to the fifth time period, the total pumpage increased during the fifth time period. These variations and the net benefit with total withdrawal volume are shown diagrammatically in Fig. 1.

(a) 4°°° E3 Total \A>I. Pumped E3 Nef Benefit

400

200

(b) 1200

a Case : A S B a Case : C o Case : D

6001 1991-92 1995-96

Year

Fig. 1 Comparisons of (a) net benefits and total withdrawal volume; and (b) total pumping rates for different cases considered.


Application of conjunctive water use planning model

The study area is from the Bagmati Irrigation Project located in the southern Terai region of the Bagmati River Basin in Nepal (Fig. 2). The Bagmati River, which is predominantly rain fed, is the primary source of surface water. The principal aquifer unit being currently used by local farmers (and planned for integration by the government authorities) is the underlying shallow aquifer, which is alluvial and unconfined in nature. The study considered only the first development phase in which intensive agricultural development plans existed for 68,000 hectares of the net command area of the Bagmati Irrigation Project. The details of model development and results for the case study are described elsewhere (Onta, 1991; Onta et al., 1991). Only a brief description of the approach with some typical results are presented herein.

The three-step modelling approach consisted of first using a stochastic dynamic programming (SDP) model to determine the long term operation (pumping and river diversion) policy for a given pumping capacity and irrigation water demand. Using this policy, the conjunctive use system simulation model was run over a 50-year time period with several synthetic rainfall and streamflow series. The actual average annual operation cost and estimates of several reliability measures were obtained.

T r

85°00 'E 86°0O'E Fig. 2 Bagmati case study area.


The procedure was repeated for other alternatives to find out their performance indices. Finally, a multiple criteria decision making (MCDM) method was used to suggest the most satisfactory alternative (i.e. pumping system capacity) considering several performance measures of the alternatives simultaneously.

SDP model The objective function of the SDP model was to minimize the expected value of annual operating costs for a specified pumping (and diversion) capacity subject to the constraints on system capacities, water availability, irrigation water demand, maximum and minimum permissible aquifer storage states to avoid excessive drawdown and waterlogging, mandatory downstream water requirements, and the state transformation equation. This equation described the water balance of the lumped groundwater system on a seasonal (four-monthly) basis and considered most of the interacting processes such as évapotranspiration, natural and irrigation recharge, groundwater loss, and inflow. Natural recharge from rainfall and stream-flow was regarded as a stochastic variable. A recursive backward-looking SDP algorithm was used to solve the multistage discrete-time optimal control problem. Figure 3 shows the SDP-derived operation policies in different seasons as a function of initial depth of groundwater level from the surface for the pumping capacity of 450 x 106 m3 (Alternative 3). Similar results were observed for other pumping capacities. Groundwater pumpage generally decreased (and river diversion increased) with greater water table depth, signifying the strong influence of nonlinear pumping cost. Higher pumpage in the wet season (June-September) was due to higher water demand, higher recharge and the specified upper control level of the groundwater table.

Simulation model The simulation model, lumped in character, was based upon the same state transformation equation, constraints and set of input data as the SDP model. Actual values of the state and decision variables were used, rather than the class values. Simulation basically consisted of routing the generated mutually related

1200

1000

800

600

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Fig.

o GW Dry Season o GW Wet Season A GW Winter Season • SW Dry Season • SW Wet Season A SW Winter Season

ni im ift mk A A A ' A

0 2 4 Groundwater Level from Surface (m)

SW : Surface Water ; GW : Groundwater

3 SDP operation policies (pumping capacity = 450 Mm3).


300 400 500 600 Pumping Capacity (Mm3)

0C : Annual Operating Cost TAC : Total Annual Cost TABE : Total Annual Benefit Equivalent NRS : Nepalese Rupees

( 1 U.S. $ =25.30NRs,Conversion Factor in 1988) Fig. 4 Cost and benefit equivalents of planning alternatives.

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300 400 500 600 Pumping Capacity (Mm )

OR : Overall Reliability ; DSR : Dry Season Reliability VUL : Vulnerability ; RES : Resilience

Fig. 5 Reliability indices of planning alternatives.

rainfall and streamflow sequences through the conjunctive use system, season by season, obeying the SDP operation policies as far as possible and keeping an account of the actual water use, failure measures and annual operating costs. For each alternative, five different sets of synthetic sequences were used in the simulation, and average values of the performance indices were computed. The average economic measures (i.e. annual operating and total costs, and benefit equivalent to total water use) for each alternative are presented in Fig. 4. Similarly, the average reliability measures (i.e. overall and dry season reliability, vulnerability, and resilience) against each alternative are shown in Fig. 5. These figures indicate conflict or trade-off among different performance measures or alternatives.

MCDM model The results of the previous step was used by the MCDM model, using the technique of compromise programming (Zeleny, 1982). The analysis


showed that Alternative 3 was the most stable alternative and hence preferred. Depending upon the relative preferences of the decision maker or the weights of various criteria, the choice of the most satisfactory alternative may change. The important point to note, however, is that the selected sets of management alternatives, along with their performance measures, supports and improves the decision making process.

An appropriate modelling strategy

A variety of groundwater flow, solute transport and consolidation models are being used quite extensively to simulate the dynamics of the aquifer systems and to evaluate the long term impact of sustained groundwater withdrawal and associated consequences. In contrast, management models are not widely applied owing to their complexity, and lack of credibility and field testing. A groundwater system management model should identify and incorporate important environmental, socioeconomic and institutional factors, in addition to the physical ones, characterizing the specific problem. At the same time, it should also be balanced with regards to the sophistication of modelling, accuracy of output and simplicity. For complex systems, use of conventional systems analytical techniques, within the framework of multi-objective and multicriteria-based decision analysis, provides more insight into the decision making process in general. Uncertainty is a key issue and predominant uncertainties must be considered in any system analysis. It must, however, be remembered that no model is without its limitations. Models provide important additional information, inferences due to probable changes in conditions to support, but do not substitute for the judgement of experienced planners and managers.

In many countries, there is certainly a limitation on financial resources and technical expertise to address and overcome the problems of unplanned groundwater resources development as mentioned earlier. Even an effective groundwater monitoring system will not be realized in many cases, except perhaps in specific locations such as urban and industrial areas where there is an increasing evidence of environmental degradation affecting the economic growth. Although it is difficult to generalize specific situations in different countries which vary considerably, a pragmatic approach towards an appropriate modelling strategy is to evolve the modelling concept as development progresses and to adapt models according to the specific situation and problems in each country. As a general recommendation, the following two groundwater management modelling strategies can be adopted: (a) a simulation model in conjunction with decision analysis; and (b) a two-step optimization-simulation modelling approach combined with decision analysis.

For very complex and dynamic systems management as well as for policy development, the first strategy may be considered. On the other hand, for operational management studies of simpler systems or for regional studies, the second strategy may be appropriate. Typically, a simplified optimization model (e.g. lumped, steady state) is initially used to screen the possible management alternatives. The optimal policies of the first-level model are then evaluated in a more detailed simulation


model of the groundwater system at the second level. The simulation model would more clearly define the performance of the system in terms of various criteria (e.g. hydrological and environmental impacts), for each alternative policy. If the policies are not feasible, the iterative process continues with updated conditions until an acceptable set of policies is found. Additional criteria (e.g. benefits, cost, risks) can then be considered simultaneously under a decision analysis framework in order to evaluate the management alternatives and select a set of most satisfactory solutions.

TOWARDS ACHIEVING A SUSTAINABLE DEVELOPMENT

In the past, the professionals and decision makers have been concerned more with resource development to meet users needs without paying much attention to the environmental concern. However, as development has progressed, many countries have been faced with declining groundwater availability as well as deteriorating groundwater quality owing to the increased water demand and a concomitant increase in the amount and types of pollutants entering the hydrological cycle resulting from urban, industrial and agricultural development. If groundwater resources are to be developed and managed sustainably so that they can continue to contribute as long term water supply sources, three important operational management strategies should be implemented: (a) understanding of resources availability and its vulnerability should be enhanced; (b) resource managers and decision makers should recognize groundwater as a

crucial component of water resources and the environment; and (c) knowledge and understanding of the groundwater system and the environment

should be transferred to the groundwater users so that consensus-driven, sustainable management plans will be achieved.

Strategy 1

Efficient management of groundwater has to start with an understanding of the occurrence and behaviour of groundwater and groundwater quality. It must include consideration of aquifer capabilities, water needs and water quality requirements. Identification and control of sources of contamination are necessary to limit impacts on groundwater quality; control on the location and construction of wells and the withdrawal of water at appreciable rates are necessary to prevent aquifer depletion and to avoid the occurrence of adverse environmental consequences. It has to be realized that a substantial amount of data and information are required to accomplish these requirements. The implication of the first strategy is that organizations overseeing the groundwater development in a particular area should possess the capability and expertise to institute a cost-effective data collection and evaluation scheme as groundwater development takes place. In this regard, a close cooperation and coordination are essential among the various government departments dealing

578 A. Das Gupta & Puspa R. Ont a

with groundwater. Also the team responsible for resource assessment and evaluation of development strategies taking into consideration the environmental implications should be of multidisciplinary and interdisciplinary nature. Depending on the local hydrogeological conditions, a combination of the following approaches would be useful: (a) define the groundwater system by mapping the available stratigraphie informa

tion to identify aquifers, confining layers and their possible interconnection; (b) establish the hydraulic head and groundwater quality variation from the collected

field data and correlate with variations of exploitation in space and time; (c) determine the susceptibility of the groundwater system to overexploitation and

related environmental consequences in a qualitative way, using empirical assessment approaches based on sample hydrogeological criteria (Adams & MacDonald, 1995; Prokopovich, 1991; Foster & Hirata, 1991; Canter & Knox, 1985);

(d) initially define a target potentiometric level to be maintained, based on the vulnerability analysis in step (c), to minimize the probability of occurrence of adverse environmental consequences; and

(e) monitor and evaluate the changes in hydraulic head and groundwater quality, establish the cause and effect relationship through appropriate modelling to determine the regional distribution of abstractions and their limitations to avoid significant depressions of hydraulic heads, particularly in areas vulnerable to adverse consequences like water quality degradation and/or land subsidence.

Strategy 2

The implication of the second strategy is that the groundwater issues become a part of the social, legislative and scientific conscience. With increasing demand for water, dependence on groundwater has increased considerably in different parts of the world. However the ensuing problems of overexploitation and environmental degradation are not reflected as major concerns in the development policy of many nations. Thus more proactive management and protection of groundwater resources are urgently required to avoid permanent depletion of the resource in both quantity and quality aspects. This implies that an effective control on groundwater exploitation is necessary and that proper land use planning is essential for protecting groundwater quality. For land use planning, standards must be defined for land based on the underlying hydrogeological conditions and the potential for migration of contaminants from the land surface to the groundwater and within groundwater to abstraction points. Recent articles on groundwater quality management have stressed the importance of delineating recharge zones to the aquifer since these zones are at great risk.

Policies and land use planning are only effective when regulatory measures are implemented through by-laws. In many situations, institutional and regulatory measures need to be strengthened to implement necessary controls. Moreover, proper monitoring and evaluation are to be undertaken to check the effectiveness of various


control measures adopted as well as to identify new or emerging threats. For these efforts to be successful there is a need of coordination and collaboration of different agencies dealing with technical, administrative, regulatory and legislative aspects for implementation of methods for groundwater protection. For aquifer systems already suffering significant degradation, it is necessary to lay stress on the recognition of the existing problem by the authorities using water as well as by authorities discharging contaminants. A concerted effort must be put forward by all concerned for the development of alternative technologies for remediation and for the establishment of a long term strategy to contain and reduce existing pollution through detection, correction and preventive methodologies.

Strategy 3

Water users play a dual role in water resources planning : on the one hand they are the ultimate beneficiaries, but on the other hand they are the ultimate managers, whose behaviour plays a dominant role. As has been pointed out, organizations concerned with groundwater development should acquire, through monitoring and evaluation, an understanding of the functions of a groundwater system with due regard to environmental implications in order to achieve sustainable management. Any control to be imposed on water withdrawal and on land use planning to ensure sustaining the available resource for future generations will have an immediate impact on the present water users. In this regard, the effectiveness of any regulation will certainly depend on the acceptance and credibility attached to the decisions by the water users. As such, the knowledge and information on the groundwater system and its interaction with the environment gained by the authorities should be transferred to the users in a form that they can understand. Unless an effort is made to provide the community with such information, the needs to limit the pumpage and/or change the land use activities are not obvious to them, similar to the perception in general they have about groundwater: "out of sight, out of mind". In the long run, through a continuous information exchange, a realization of the ensuing problems and the need for sustainable management will certainly ensure the acceptance of social and economic inconveniences associated with these restrictions. A long term proposition of developing public awareness on the need of regulating certain development activities to ensure sustainability of the resource for future generations is to introduce this at an early age in primary school curricula, especially within a general introduction to protection of the environment.

CONCLUDING REMARKS

Groundwater is an important natural resource with high economic value and sociological significance. It is important that this resource be utilized in such a manner that a permanent depletion of the resource in both quantity and quality aspects is avoided and that any other environmental impacts like land subsidence or sea water

580 A. Das Gupta & Puspa R. Onto

intrusion in coastal areas are restrained within acceptable limit. In most of the aquifer systems, unplanned and uncontrolled water withdrawal, waste disposal and pollution have already led to situations of excessive stress and water shortage. In some cases, the adverse consequences could be so severe that remediation would be difficult and the future use of the resource will be permanently constrained. In some other cases, there may still be an opportunity for corrective measures and it may be desirable to consider sustainable management as an option for development planning in the future.

The key principles in the evolution of sustainability in groundwater development are addressed as: (a) providing sustainable water use; (b) protecting groundwater resources from degradation, i.e. sustaining quality; and (c) controlling environmental impacts of development, i.e. sustaining environmental diversity. The basic need is to understand the functioning of the groundwater system, as development progresses, through monitoring and evaluation and to adjust the utilization pattern spatially as well as in time as need arises to sustain this resource on a long term basis for future generations. In this regard, mathematical models provide a quantitative framework to synthesize data obtained from monitoring of the groundwater system and play a significant role in assessing the system's behaviour when subjected to future stresses and changing conditions.

However, not only technical factor but also institutional and social acceptance are important in addressing sustainability. In order to achieve these factors, the authorities concerned should have adequate and properly trained manpower to monitor and evaluate the system response and should take the responsibility to transfer this knowledge and understanding of the system's performance through proper means to groundwater users and the community. The resource planners and decision makers should recognize groundwater as an important component of water resources and the environment and it is required that necessary regulations are implemented for the protection of the resource.

The foregoing remarks present a number of challenges under the pressures of economic growth. Technically, the complexity of the system requires special efforts to develop the monitoring network and modelling tools needed for predictive analysis. Another challenge is to find alternative methods of protection and effective methods of treatment in the case of protecting groundwater quality. However, the most important challenge is to understand the interaction and interdependency between groundwater and ecosystems. It has to be realized that a substantial amount of time, manpower and funding is needed to acquire all necessary data and information through monitoring as well as through quantitative analysis. However, all these efforts and costs are insignificant compared with the cost of remedying the adverse impacts of overexploitation or contamination of groundwater, or even of providing an alternative water supply.

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