December 11, 2017

The lessons of traditional irrigation agriculture: learning to live with nature

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Published as Chapter 26 of The Social and Environmental Effects of Large Dams: Volume 1. Overview. Wadebridge Ecological Centre, Worthyvale Manor Camelford, Cornwall PL32 9TT, UK, 1984. By Edward Goldsmith and Nicholas Hildyard.


At a recent meeting on water development schemes, Raymond Nace, a hydrologist, issued a stern rebuke to his assembled colleagues.

“Three sins beset water planners and their advisors: faith in science and technology; worship of bigness; and arrogance towards the landscape. The belief that technology can solve any water problem . . . is wrong. It seems essential that a new frame of mind, some new perspective, be applied to water planning.” [1]

Strong words indeed – and ones with which we would not disagree. But what principles should govern the “new frame of mind” that Dr. Nace calls for? To answer that question, it is not enough to examine only those features which have caused modern irrigation schemes to fail: much more important is an understanding of the features which have made traditional irrigation societies succeed.

Why, for example have the El Shabana, the Sonjo or the Chagga proved themselves capable of practising sustainable irrigation agriculture over thousands of years, whilst modern irrigation schemes have frequently lasted no more than a few decades? Is it, as Fernea suggests, because tribal societies have achieved “a congruence of fit” between their methods of cultivation, their land tenure systems and “the nature of land, water and climate”? [2] And, if so, what is the basis of that ‘congruence of fit’?

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Size: a critical factor?

One of the most striking features of traditional irrigation systems is that they operate on a very small scale. By contrast, most modern irrigation schemes cover large areas of land and are geared towards maximum production. In that respect, it is hardly surprising that their ecological impact is greater than that of traditional systems. The point is well made by Dr. Desmond Anthony:

“Experience has shown . . . that the extent and degree of modification (of ecological systems) and the magnitude of the resultant impact are usually directly proportional to the size of the project, and are related to the nature of the environment and its sensitivity to modifications of the kind brought about by construction, operation and maintenance of such projects.” [3]

Robert Goodland is of the same mind. Indeed, in his opinion, “the size of hydro projects is almost exponentially related to environmental impact”. [4] That general rule, he writes, is true of “the area of fertile soil removed from annual production by flooding; the number of people displaced and houses, infrastructure lost to the reservoir; and the opportunities for proliferation of aquatic disease vectors (e.g. malarial mosquito, schistosomiasis snail) and nuisance organisms (e.g. water hyacinth, gnats)”.

He goes on to point out that large reservoirs “trigger or exacerbate the perils of induced seismicity” and “produce less fish per unit volume than small reservoirs”. Moreover, “water quality deteriorates gravely in large reservoirs while remaining acceptable in small ones”.

For those reasons alone, says Goodland, dams should be as small as possible. Better still, tube turbines should be installed:

“These cheap, low-maintenance, sparkless sources of power are easy to manufacture in the 100kw to 1,000kw range, and 20mw to 100mw sizes also can be feasible with minor environmental impact.”

Indeed, Goodland claims, the smaller turbines cause “practically no environmental problems since little or no reservoir is created”.

Despite the environmental advantages of building small dams, small-scale irrigation and hydropower schemes are rarely favoured over large-scale schemes. One reason, undoubtedly, is that large-scale projects earn greater kudos for politicians and engineers alike: the more grandiose the scheme, the more prestige accrues to those involved in building it. So too, as William Ackermann points out, small-scale dams are frequently seen as being ‘uneconomic':

“From the viewpoint of power generation and large-scale water storage, only relatively large and deep reservoirs are economically attractive. One horsepower is generated by dropping 1 cubic foot of water per second through a height of 3.34 metres. Thus there are obvious advantages to constructing power dams with as much ‘head’ as possible. Similarly, for water storage, the approximately parabolic shape of most lake basins, ensures that each increase in the height of a dam progressively increases the storage benefits. In consequence, major reservoirs are usually made as extensive as possible and thus they tend to be in the large-scale range.” [5]

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Why small is not enough

But even supposing that, in future, only small-scale dams were to be built, would that enable us to avoid the problems associated with today’s ‘superdams’? The answer is undoubtedly a guarded ‘No’. Small is certainly preferable to big – and on that point we should be quite clear – but smallness does not in itself provide a foolproof insurance against ecological damage. Indeed, the record makes it quite clear that even small-scale projects can cause significant ecological and social harm. In some cases, the damage done is the result of poor design: in others – as in the first of the following three examples – it arises from the very fact that the schemes involved are small-scale.

  • According to John Hunter, the small dams which have been built in the Volta Valley provide a more suitable niche for the vector of onchocerciasis than large dams. “In many areas,” he reports, “the construction of small dams has already augmented the spread of river blindness rather than the reverse”. [6] The reason is clear enough: the more dams there are, the more spillways there will be – and hence the more breeding places for the black flies which carry the disease.
  • In Jamaica, bad design led to the failure of a series of small dams which had been built across various shallow valleys in order to make reservoirs for irrigation from modest creeks. Because the sub-soil of the region is particularly porous – a fact which the dams’ promoters failed to take into account – the water simply leaked away from the reservoirs. As a result, reports Brian Johnson of IIED, the dams now “sit high and dry, a series of embarrassing embankments”. [7]
  • In Eastern Nepal, a small hydro-dam silted up so quickly that the turbines stopped functioning. According to far-away economic experts, the dam was supposed to have repaid its initial investment within 15 years: in just five years, however, it had become “a millstone of modernity around the Nepalese neck”.
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Seasonal vs. perennial irrigation

Even the small-scale irrigation schemes built today aim at replacing seasonal irrigation with perennial irrigation. Such perennial irrigation, however, invariably entails higher social and ecological costs – whatever the size of the scheme involved.

Perennial irrigation schemes create a permanent (rather than a temporary) niche for the vectors of the principal water-borne diseases – thus inevitably causing an escalation in the incidence of those diseases. That problem is exacerbated by the fact that perennial irrigation drastically increases the amount of time that local farmers must spend in the irrigation waters – and hence the amount of time that they are exposed to the vectors which those waters harbour. It also increases the moisture level of the atmosphere and the soil, and the vegetative period of crops, thus providing a permanent niche for pests.

Although perennial irrigation makes possible several harvests a year, that achievement quickly turns sour where the soil is too poor to support the extra demands being made upon it. In that respect, it is important to note that very few soils – and, in particular, the organically poor soils of the tropics – can be used to produce 2 to 3 identical crops a year for very long. Indeed, if multi-cropping is carried out over any significant period of time in such regions, it can only lead to the degradation of agricultural land – which, in turn, must lead to a reduction rather than an increase in yields.

Equally important, multi-cropping and perennial irrigation tend to raise the water table, inevitably giving rise to all the attendant problems of waterlogging and salinisation. Furthermore, multi-cropping cannot avoid increasing the workload of local farmers, to the detriment of their social lives. The resulting social impoverishment frequently exacerbates the problems of social disintegration, thus rendering impossible the co-operation which is so vital to the sound management and maintenance of a viable irrigation system.

For the above reasons, the very principle of perennial irrigation is unacceptable – on whatever scale it is carried out. That stark reality is tacitly recognised by traditional irrigation agriculturalists. Indeed, for them, irrigation is invariably seasonal and, moreover, it is limited to the shortest possible period. Thus, in the majority of traditional irrigation societies, we find that half the potential agricultural land is allowed to lie fallow on alternate years, thereby ensuring that irrigation is carried out for a short season every other year.

It goes without saying that such an apparent ‘waste’ of good land is considered intolerable by those who manage today’s modern irrigation systems. Indeed, the very idea of ‘fallow lands’ and ‘alternate year irrigation’ goes against all the cannons of the modern market system, geared as it is towards increasing production regardless of long-term ecological and social costs.

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The preservation of forests

A further essential feature of traditional irrigation agriculture is that it is practised in areas where part, at least, of the natural forest cover has been allowed to remain intact. Such forests are particularly important in the uplands and in the watersheds of the river whose waters are abstracted.

Indeed, deforestation is by far the most important cause of the recurrent and ever more destructive droughts that today afflict vast and highly populous areas of the Third World.

It contributes to such droughts in a number of ways. Firstly, it reduces rainfall. Thus, in Amazonia, 75 percent of the precipitation is estimated to be derived from the transpiration of trees in the area, which means that once the Amazonian forest is cut down one can expect a significant reduction in rainfall throughout the region.

(The vast volume of water that is continuously being exchanged between the forest and the atmosphere, over an area of something like two million square miles, serves as a massive cooling system for the entire planet which means that the destruction of the Amazonian forest must seriously affect world climate. A preliminary mathematical model developed by one group of researchers suggests that the destruction of Amazonia should increase the mean temperature in the tropics to something like 50ºC, making them virtually uninhabitable. The United Nations University in Tokyo is currently studying this very alarming issue.)

It appears that the Harappan Desert in Pakistan was also once a vast rainforest whose rainfall was also largely self-generated, so that once the trees were cut down, rainfall was reduced to near zero. [8]

But the recurrent droughts are not necessarily the result of reduced rainfall. Droughts are regularly reported in areas where there has been no recent reduction in rainfall. Such droughts are simply the result of a lowered water-table caused by deforestation, excessive water-abstraction, or else they are due to the reduced water-retaining capacity of an overtaxed soil.

The general desiccation caused by deforestation in India was eloquently described by E. Wasburn Hopkins 80 years ago:

“All that great bare belt of country which now stretches south of the Ganges – that vast waste where drought seems to be perennial and famine is as much at home as is Civa in a grave-yard – was once an almost impenetrable wood.

Luxuriant growth filled it: self-irrigated, it kept the fruit of the summer’s rain till winter, while the light winter rains were treasured there till the June monsoon came again. Even as late as the epic period, it was a hero’s derring-do to wander through that forest-world south of the Nerbudda, which at that time was a great inexhaustible river, its springs conserved by the forest. Now the forest is gone, the hills are bare, the valley is unprotected, and the Nerbudda dries up like a brook, while starved cattle lie down to die on the parched clay that should be a river’s bed.” [9]

The deforestation of upland areas is even less tolerable, since forested uplands attract a great deal of rain and it is in the uplands that the sources of the rivers, which water the plains beneath, are situated.

We have seen how this is so in Sri Lanka and how the water required for the vast water-development schemes being built today, is unlikely to be available now that the uplands have been deforested. One might add that already, the autumn monsoon – which blows from the South West and which used to collect moisture from the forest uplands and deposit it on the dry zone beyond – now falls on denuded mountains. Hence, the autumn rains have largely vanished from the north east of the island.

We have also noted how such deforested slopes are, in the tropics in particular, very rapidly eroded and that the soil which is washed off them raises the river beds, causing floods that can be as devastating to agricultural production as are the droughts, to which the same areas have become so prone, during the dry season.

Ironically, deforestation is at once the cause of both the floods and the droughts that combine annually, to deprive the inhabitants of vast areas of the Third World of considerably more food than could conceivably be provided by the implementation of FAO’s plans to increase, by 50 percent or so, the agricultural area at present under irrigation.

What is more, the forests can provide water in perpetuity – not just temporarily – and at no social and ecological cost. On the contrary, they provide other equally precious benefits. For instance, they harbour a wealth of wildlife. They are a source of all sorts of wild fruits and berries, of humus for the fields and of timber for building houses.

On a wider scale, they generate oxygen and absorb carbon dioxide and generally exert a stabilising influence on climate. In addition, all these benefits are free and are thus available to all – not just to the urban elite which alone benefits from the building of large dams

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