2. Conjunctive Use of Surface and Groundwater
2.1 The Concept of Conjunctive Use
As broadly outlined above, a critical problem that mankind has to face and cope with is how to manage the intensifying competition for water among the expanding urban centres, the agricultural sector and instream water uses dictated by environmental concerns. Confronted with the prospect of heightened competition for available water and the increased difficulties in constructing new large-scale water plants, water planners must depend more and more on better management of existing projects through basin-wide strategies that include integrated utilization of surface and groundwater. Todd (1959) defined this process as conjunctive use. Lettenmaier and Burges (1982) distinguished conjunctive use, which deals with short-term use, from the long-term discharging and recharging process known as cycle storage.
Until the late fifties, planning for management and development of surface and groundwater were dealt with separately, as if they were unrelated systems. Although the adverse effects have long been evident, it is only in recent years that conjunctive use is being considered as an important water management practice.
In general terms, conjunctive use implies the planned and coordinated management of surface and groundwater, so as to maximize the efficient use of total water resources. Because of the interrelationship existing between surface and subsurface water, it is possible to store during critical periods the surplus of one to tide over the deficit of the other. Thus groundwater may be used to supplement surface water supplies, to cope with peak demands for municipal and irrigation purposes, or to meet deficits in years