Water Resources Management - Practices of Irrigation and On-farm Water Management - page 164

If the total basin inflow, I s , is defined as the sum of natural recharge and induced
recharge by pumping, Eq. (5.2) can be rewritten as

P s = I s − D R (5.3)

where P s is the basin sustainable yield.
The basin sustainable yield should be a compromised pumping rate, which can be
sustained by groundwater recharge and will not cause unacceptable environmental,
economic, or social consequences. Therefore, the basin sustainable yield should
satisfy the following conditions (Zhou, 2009 ) :

(a) It is a sustainable pumping rate defined by water balance equation (Eq. 5.2).
However, the water balance equation is only a necessary condition but not an
absolute condition. Other constraints must be satisfied.
(b) Environmental constraints require considering groundwater as a part of an
integral water and ecological system. Pumping capture should not cause the
excessive depletion of surface water and the excessive reduction of groundwa-
ter discharge to spring, rivers and wetlands. The cone of depression induced
by pumping should not cause the intrusion of undesirable quality water, land
subsidence, and the damage of groundwater dependent terrestrial ecosystems.
(c) Economic constraints require maximizing groundwater development to fulfill
water demand for irrigation and industrial use.
(d) Social constraints require safe access of good quality groundwater for drink-
ing water supply and equitable distribution of shared groundwater resources by
all.

Maimore ( 2004 ) proposed a practical approach to define the sustainable yield. The
approach includes considerations of spatial and temporal aspects, conceptual water
balance, influence of boundaries, water demand and supply, and the stakeholder
involvement.
Assessments of sustainable yield must reach beyond hydrogeology to encompass
the interdisciplinary synthesis of surface water hydrology, ecology, geology, and cli-
matology. In addition, since groundwater is a resource held in common, sustainable
yield assessments must consider the socioeconomic context (Hardin, 1968 ) . In gen-
eral, different communities will have different perceptions of what constitutes an
acceptable rate of groundwater withdrawal, and these perceptions may vary over
time.
From the above discussion, it is clear that the basin sustainable yield cannot
be simply calculated as a single value using the water balance equation (Eqs. 5.1
or 5.2). How much groundwater is available for use depends on how changes in
recharge and discharge affect the surrounding environment and the acceptable trade
off between groundwater use and these changes. Achieving this trade off in the long
term is a central theme in the evolving concept of sustainability.