Hydrogeology and Resource Availability

This explosive growth in groundwater irrigation has had little relationship with the pattern of occurrence of the groundwater resource. Figure 2.1 presents the first ever groundwater recharge map of the world prepared by researchers at the University of Kassel (Germany). It shows that in terms of long-term groundwater recharge, South Asia and the North China Plain are less well endowed compared to South America, pockets of sub-Saharan Africa and South-east Asia.

Many scientists argue that in the long run, groundwater development is self-regulating; people cannot pump more water than there is in the aquifers. According to them, long before the hydrogeology of aquifers imposes a check on further development, the economics of pumping water from deep aquifers would do so.2 It is therefore ironic that global pockets of intensive groundwater use have emerged in regions that are not amongst the best endowed for it. Many of these regions have alluvial aquifers of high quality. The entire Indo-Gangetic plain that encompasses Pakistan Punjab and Sind, all of Northern India, Nepal Terai and Bangladesh are examples; so are areas of the North China Plain. However, all these are arid or semiarid, receiving little rainfall to provide natural recharge. Two-thirds of India (nearly half of the Indian subcont inent), in contrast, is doubly disadvantaged: it has semiarid climate with limited rainfall for recharging the aquifers; and hard-rock, basaltic aquifers with low storativity values. Peninsular India therefore is amongst the worst candidates for intensive groundwater irrigation; and yet, this is the region that has followed the Indo-Gangetic plain in ushering in a tube well revolution.

This paradox is global. High levels of sunlight combined with frequently lower levels of pest and disease problems can create optimal conditions for intensive agriculture - as in California, Spain and Israel. In contrast, many humid regions do not have as intensive agriculture despite - or perhaps because of - abundant water from groundwater or other sources (M. Moench, 2005, e-mail communication). In arid areas without resources for recharge, however, stringent limits to intensive groundwater irrigation are accessed early, leading to severe depletion, and at times, corrective measures as in Israel (which achieved high agricultural water productivity) and Saudi Arabia (which for some time had a vibrant wheat economy based on irrigation with fossil groundwater that has been progressively shrunk (Abderrahman, 2003)).

With this backdrop in mind, Fig. 2.2 attempts to highlight the irony of Asia's groundwater boom in the last 50 years. It is a common knowledge that hydro-geologic features of a terrain vary greatly even within a square mile, especially in hard-rock aquifers. So the classificatory approach we have used in Fig. 2.2 oversimplifies the great hydrogeologic diversity found in Asia, and can be justified only from the viewpoint of understanding aggregate patterns at a sub-

Central Indian plateau, western and eastern ghat

Humid

Eastern India, Nepal Terai,

Bangladesh most of South-east Asia, parts of South China, coastal regions of India

Aquifers with low storativity or natural quality problems

Good aquifers

Pakistan Punjab; India Punjab, Haryana, Sind; peninsular India

Rajasthan, north Gujarat, Kutch, Yellow River basin

Arid or semiarid

Fig. 2.2. Hydrogeologic patterns in Asia.

Fig. 2.2. Hydrogeologic patterns in Asia.

continental level. Regions best suited for this boom are those with high rainfall and good aquifers (North-West quadrant); however, except for Bangladesh and parts of eastern India, the groundwater boom has left these regions untouched. The groundwater irrigation economy is insignificant in South China and much of South-east Asia, which can sustain much more intensive groundwater irrigation than they currently practise. In contrast, it has assumed boom proportions in all the other three quadrants, none of which has 'appropriate' hydrogeologic and climatic conditions for intensive groundwater irrigation.

Around the world, intensive groundwater development without appropriate resource management regimes has resulted in resource degradation. In South Asia, this threat is growing. Besides non-point pollution of groundwater through chemical fertilizers and pesticides, intensive use of groundwater in agriculture gives rise to four resource management challenges: (i) controlling resource depletion; (ii) optimal management of conjunctive use of surface and groundwaters; (iii) managing the productivity impacts of secondary saliniza-tion; and (iv) managing natural groundwater quality concerns. The seriousness of each of these varies across regions depending upon their hydrogeology and the degree of groundwater development as set out in Fig. 2.3. It is clear that even in upper-right quadrant regions, which provide robust hydrogeologic platforms for intensive groundwater irrigation, socio-ecological and public health problems need to be managed as groundwater irrigation expands. In the eastern Gangetic basin, for instance, groundwater development is associated with mobilization of (geogenic) arsenic. Coastal areas are typically humid and have good alluvial aquifers; but salinity ingress or sea-water intrusion into coastal aquifers is a common problem, sometimes even at early stages of groundwater development. Likewise, in all humid areas (or arid areas with large volumes of surface water movement) with intensive groundwater irrigation, conjunctive management of surface and groundwaters remains a major challenge as well as an opportunity.

Socio-economic and Management Challenges

Hydro-geological Settings

Resource Depletiona

Optimizing conjunctive useb

Secondary salinizationc

Natural Groundwater Quality Concerns

Major alluvial plants

Arid

• •

• O

Humid

a • •

• •

Coastal plains

• •

• • o

Inter-Montane valleys

• •

o

Hard-rock areas

• •

O

• • •

aRelated to aquifer recharge rates and storate availability.

bImplies both abundant surface and groundwater availability.

cImplies limited fresh groundwater availability and presence of saline groundwater and/or land drainage problems.

Fig. 2.3. Resource management challenges of intensive groundwater use in Asian agriculture.

Fig. 2.3. Resource management challenges of intensive groundwater use in Asian agriculture.

As mentioned earlier, the geology of central and peninsular India is different and far more complex compared with that of the Indo-Gangetic basin, which consists of extensive alluvial aquifers throughout. Figure 2.4, showing a map of major aquifers of India by the Central Ground Water Board, suggests the dominance of basalt and crystalline rock formation in peninsular India. The water-bearing and -conveying properties of these aquifers vary greatly even over small distances, making scientific resource management critical and difficult at the same time (GoI, 1995). Overall, however, the yields of these aquifers are quite modest and, in fact, much smaller than much of sub-Saharan Africa; yet, there is a heavy and growing dependence on groundwater irrigation even in these regions.

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