Water Harvesting Structures -  Need To Draw Pragmatic Lessons

Natural resource management in the post-independence era has been marked by ‘standardisation’: monoculture plantations replaced mixed forests; large scale irrigation systems replaced the diverse indigenous water harvesting systems and the Green Revolution replaced the different local agricultural practices.  This no doubt helped to raise productivity levels substantially but the consequent environment degradation and widening gap between the rich and the poor has led many to question its efficacy.

Consequently, in recent times, the thrust in development circles has been on the need to revisit traditional systems of resource management especially those which have survived modernisation.  The purpose is to draw pragmatic lessons from them in terms of technological development and management practices.

There are two common elements in these ‘traditional and indigenous’ systems which have ensured their sustainability. One is that they have built on local or more popularly known as ‘indigenous knowledge’ of resources, tested over time.  Second, they have knit local communities in strong economic and social ties to ensure rational and equitable use of resources.  In addition, a striking feature of these systems is the diversity in terms of the technological aspects, resources use patterns and management practices.

The indigenous water harvesting structures in Asia display this diversity and a scientific understanding of water resources and local environment.  With the current thrust on the need to understand indigenous resource management systems, it becomes important to respect these aspects of diversity and scientific knowledge acquired over centuries and transmitted through informal channels of dissemination.

A preliminary glance across diverse indigenous water harvesting structures in Asia would show that these are essentially site-specific and are limited by their regional condition.  The choice of an indigenous water harvesting structure is a response to the source and availability of water and, topographic characteristics.  Availability of water depends on the average annual precipitation, groundwater potential and water carried by rivers.  Most of these structures are managed by communities benefiting from them.   Compared to large scale systems, these also appear to be technologically and environmentally more suitable.

The different indigenous water harvesting structures in the Asian countries can be broadly classified into:
1. Diversion Systems
2. Storage Systems
3. Lift Irrigation Systems

Diversion Systems

Diversion of natural springs, waterfalls and rivers is the most widespread system in the hilly regions and plains of Asia.  It is commonly seen in the Himalayan region stretching between the gorges of the Indus and the Brahmaputra and in the Western Ghats running along the west coast of India.  Although a number of rivers originate in these regions (Indus, Ganga, Tista, Kaveri, Krishna etc.), they are highly turbulent and cannot be tapped.  Therefore, perennial streams and springs are the main sources of water.

At higher elevations, the main system of water harvesting is diversion through channels.  These channels are usually unlined and are constructed along the contours to distribute water to the fields located at accessible altitudes.  At lower elevations, the diversion channels use the sloping terrain to carry water or the depth of the channel itself is reduced gradually to permit downward flow.  In the Himalayan region, the diversion system is known by different local names such as ‘kuhl,’ ‘gul’, ‘kulo’ and ‘diggi’.  Open pipes made from split bamboo or arecanut are also used to bring water from natural springs for drinking and other household purposes.

Diversion by checkdams is another widespread system in the foothills and sloping plains.  A river (and its major branches) is diverted at different points by temporary weirs made of stone and mud.  They are referred to as ‘pat’, ‘dong’, ‘kalvai’ and ‘korambo’.

In the plains rivers carry more discharge than the hill springs and so diversion structures are more sturdy and complicated.  The material used to construct the diversion structures on river beds to check water flow, range from clay, stone, cement and bamboo to palm and banana leaves.  This system is widespread in the plains if Indus, Ganges and Brahmaputra.  Malaysia has heavy rainfall for seven to eight months in a year and therefore diversion of water to paddy fields and rubber and palm plantations is the predominant water harvesting system.  Small earthen and stone checkdams are also constructed on individual fields to store rain water.

Diversion systems always tend to enlist local support in construction and maintenance of channels and to permit equitable distribution of water.  Regular interaction and co-operation is essential not only with a village benefiting from a particular stream of river but also with villages located downstream which too depend on the same water source for irrigating their fields.

Storage Systems
In regions with low rainfall (,120 cm. Annually), non-perennial rivers and undulating terrain, the predominant water harvesting structures are the storage works.  The design of these structures depends a great deal on the physiographic features of terrain and availability of water.  In the case of India, 90 percent of the annual run-off in the peninsular rivers occurs during the four months of the monsoons.  Hence, storage both round the year and for short duration is very important for irrigation and for drinking purposes by human beings and livestock.

In the plateau region of South India and Sri Lanka, storage works are the predominant water harvesting structures.  The rivers and streams in these regions carry a heavy supply of water in the form of a flash flood during the months of September to December.  A system of interconnected reservoirs divert river water and store rain water as well.  They are locally referred to as ‘system ery’ and ‘chain ery’ respectively.

In some regions, the undulating terrain promotes rapid run-off and therefore single-unit or isolated reservoirs are designed to divert and sore rain and river water.  These are locally referred to as ‘ery’, ‘kulam’ and ‘keri’.  Structures similar to isolate ery are also widespread in eastern parts of India, namely Chotanagar Plateau, where they are referred to as ‘ahar’, ‘chaur’, and ‘hir’.

These storage structures – interconnected and isolated – have embankment on three sides and the fourth side is left open to collect run-off.  Water stored in the reservoirs/tanks reaches field through a canal system or earthen channels.  Water from the tank is allowed into the canal through sluices.  Spillways are provided for passage of excess of water.

Storage structures below the surface or dug out ponds co-exist with diversion channels in the plains of Indus-Ganga which extends to Bangladesh.  Natural as well as artificial depressions known as ‘pokhar’, ‘talaab’, jhil, and ‘saagar’ are fed from all sides and store both rain and flood water.

In the western plains of India (including the Thar Desert) and adjoining parts of Pakistan, scanty rainfall (40-80 cm. Annually) and absence of rivers has led to construction of in-situ water harvesting structures.  These include elevated earthern embankment constructed on one side of a sloping terrain to arrest rain water run-off as well as depressions.  These are locally referred to as ‘johad’ and ‘khadin’ and ‘topa’ and ‘nadi’ respectively.  In the arid parts of Baluchistan, stone structures called ‘gabbar baandhs’ predominate.

Another type of storage called submerge tanks extend all the way from Central India to Baluchistan.  They are different from in-situ water harvesting structures in the sense that they have higher embankments and collect run-off from a wider catchment.  They are constructed in a series across the same stream and cultivation follows after submerge of the fields.  In India these are referred to as ‘bundhee’ and in Baluchistan, as ‘khushkaba’ and ‘sailaba’.

The storage structures discussed so far are characterised by multiple use.  They are used for irrigation fields, for drinking by livestock and human beings, for controlling evaporation, for better distribution and for reducing the flow of run-off.  Storage structures are labour intensive during both construction and maintenance and therefore involvement of local communities benefiting directly from them is imperative.  Annual desilting and repair of tanks is taken up at the community level and formal/informal groups monitor the distribution of water.

Lift Irrigation Systems
Lift irrigation systems (LIS) include lifting of ground water for irrigation and drinking purposes as well as for appropriating surface water sources for irrigation.

Dug well and tubewells are a common feature in all parts of Asia.  In the desert regions of India, dug wells are covered to reduce evaporation losses and are locally referred to as ‘tanka’.  Traditional methods of lift irrigation from rivers, streams, channels and tanks using human and animal energy have been replaced in most cases by diesel pumpsets.  However in western India (Kolhapur district of Maharashtra), the traditional system of ‘phad’ is still prevalent, where 8-10 bullocks and a similar number of men raise the water level to some 14-15 meters.

In Bangladesh, a minor revolution has taken place in the field of manual irrigation.  The treadle pump – human powered, twin cylinder pump head with a bamboo or PVC tubewell – was introduced by an NGO, in 1979 and has become one of the most successful irrigation pumps made in Bangladesh.  A modification of the indigenous ‘dekhi’ system, it is easily operated by men and women alike to lift water from ponds and channels to the paddy fields.

These various indigenous water harvesting systems are an important strand in current research in terms of their technical and management aspects so that they can be revived where relevant, upgraded where necessary and integrated with modern technology development. The underlying message here is not to eulogise indigenous system but serve as a reminder that one must not ‘overlook indigenous knowledge’.

Prema Gera
(The study has been funded by the Commonwealth Secretariat, London)
 

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