|Vewa - The man-made reservoirs
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|Author:||Percy [ Tue Sep 20, 2005 4:03 am ]|
|Post subject:||Vewa - The man-made reservoirs|
Vewa - The man-made reservoirs
Ancient Singhalese were a people who had a close relationship with nature. They were not worshiping it like primitive people nor they tried to conquer it as Western cultures still do. They simply followed the principles of coexistence. The Singhalese are patient observers. By understanding the fundamental rules of nature, they managed to develop a world where they could 'live'. The blending into the environment is clearly shown in their constructions, art, culture.. etc. This is the legacy left by ancient Singhalese to the world.
The striking thing about these is that these marvels were achieved by Singhalese while many nations (mostly Western) in the world were living a primitive barbarian lives. It is quite sad that once the barbarians became 'civilized', they destroyed the knowledge of the ancient cultures from Americas to East.
King Parakramabahu the Great said "No drop of water that falls from sky should be allowed to flow to the sea unused" and that's what they actually did.
The man-made reservoirs that uses western engineering, holds back water with the use of 'Dam's and are widely used in all over the world for generating electricity, irrigation.. etc. The 'vewa' I speak of is not a pond, a lake or a reservoir like that. This fact is accepted by the Europeans who closely examined them. After 'Lanka' came under British rule in 1815, goals of building "weva" was sought by governors (Sir Henry Word), Government Agents (Mr. Baileys, Sir Emerson Tent), Scientists (R. L. Brohier) and Engineers (Mr. Blair, Sir Henry Paker, Sir Ivors). What they found could only be categorized as something unique only to a 'weva'.
It may appear to be such a simple matter to raise a long bank of earth in order to hold back certain quantity of rain water for bathing/ watering adjoining rice fields after the rain has ceased, that any people living in hot countries where the rain is only seasonal and are followed by several almost rainless months might be expected to be struck by the idea...When I visited West Africa, the natives of Gambia valley who have cultivated rice for so long a period...,informed me that such and idea as storing water for its irrigation had never crossed their minds. They have never heard of such a practice...
(pg.352-353 Ancient Ceylon-H. Paker).
It has been found that lower dams are constructed inside the lake to prevent the dual disaster of loosing water and flooding the villages in failure of main dam. Also, smaller wev are constructed to filter the incoming water before it reaches the main tank; this ensures that the main weva has clean water in it. Apart from battling the pubic health, they were famous for using a technology that is still used in reservoirs. The'Biso-Kotuwa' was mastered by them around third century B.C. (300 B.C.).
Since about the middle of last century, open wells, called 'valve-towers' when they stand clear to the embankment and 'valve-pits' when they are in it, have been built at numerous reservoirs in Europe. Their duty is to hold the valves, and their lifting-gear for working them, by means of which the outward flow of the water is regulated or totally stopped. Such also was the function of 'biso-kotuwa' of the Singhalese engineers; they were the first inventors of the valve-pit, more than 2100 years ago. And that it must have been no easy task to control the out-flow of water at reservoirs which had a depth of 30 or 40 feet...if not those of an earlier period, had mastered the problem so successfully that all others were satisfied to copy their designs.
(pg 376-377 Ancient Ceylon-H. Pak er)
North-east monsoon rain fills the lakes in Dec-Feb season and in almost all the other months, the zone receives little or no rain. But in the May-Sep season ((South-west monsoon), central hills receives rain and the kings built a man-made network of rivers & canals and integrated it to the natural rivers running down in all directions of the country to fill up the main 'wev'. Those in turn were used to fill the small-tanks to supply water to the fields below in a quota basis. The water was directed to canals using Amunu, a small dam built across the river just to its water-level (The Beaver type dam & NO, Beaver is not found in Asian countries), thus shows a advance water management system (quota is automatically managed)..
...The reservoir of Kohrud at Ispahan, the artificial lake of Ajmeer or the tank of Hyder in Mysore can no more be compared in extent or grandeur with 'Kalaweva' or 'Padaviya' than the conduits of Hazekiah, the canals of the Persians, or the subterranean water-courses of Peru can vie with the 'Ellahara canal', which connected the lake of 'Minneri' and the 'sea of Parakrama' with the 'Aban-ganga' river. (Sir E. Tent)
The natural forests were located at the high locations on land and in the area surrounding the wev are to be protected as gold. They enable the soil to absorb water (i.e. act as water-containers) and enrich the underground water levels. The paddy-fields or cultivated land were located below the wev to utilize the water. The forests were guarded at all costs and villages were also located at high grounds near the fields. This helped to minimize the destruction of forests and the contamination of water. If the Dam comes too low, the goal of providing water for fields would be worthless because, there won't be much area left to cultivate. Therefore the engineers had to know the amount of water that would be supplied from forests, area to be cultivated.. etc before a 'weva' is being built.
..high pitch of perfection... was that which held within its scope a knowledge of surveying & leveling. Most of their irrigation schemes .. when estimated by eye appear to all purpose quite flat. Yet,...channels were traced mile upon mile on gradients that would call into use the most precise instruments of the modern age to establish. ...a system of measuring heights and distances must have attained a very high level of efficiency...,that on organization which functioned much on the lines of our modern service for survey existed from earliest times of the Christian era if not even before..."so far had the renown of their excellence in this branch (irrigation) reached, that in 8th century A.D., the King of Ashmir (Djaya-pida) [Rajatharangane -Indian chronicle] sent to Ceylon for engineers to form a lake.
(pg 3 Ancient Ceylon-H. Paker)
As the water pass over steep land of the mountains a set of smaller dams were made to break the speed of water and to to filter-out the mud. This enabled them to control the water and minimize the possibility of mud filling out the lakes. The magic in the smaller dams was the mountain bodies can be used! I.e. the people will not have a problem with water in anytime of the year, whether it is rainy or dry.
By the 6th century A.D., engineering milestones included the 'Kantalai Weva' [King Mahasena (274-302)] which covered 4,560 acres was fed by a canal 25 miles long and was contained by a dam 50 feet high. Even more superior in technology was the 'Kala Weva' [King Dhatusena(460-478)]. It encompassed seven square miles and had a dam 3,1/2 miles long and 36 to 58 feet high with a Spill of hammered granite. A canal 54 miles long and 40 feet wide linked it to the city of Anuradhapura and played an integral role in the development of that ancient capital. The first 17 miles of this canal had a gradient of only six inches slope per mile.The bund of the 'Parakrama Samudra (=sea)' was nearly nine miles long and rose to an average height of 40 feet.
When it comes to irrigation, kings of "Lambakarna" dynasty were the major contributors. It is noteworthy that "Indians never introduced this technology to Singhalese (If so, why isn't there any Wev in India?". The Southern India had enough kingdoms too!). It is because the climate and geography of Ceylon made the Singhalese look at the world with a different eye.
In the south, technology needed customization. They received more rain than the 'Rajarata (Land of Kings)' did. Therefore, instead of the building chains of lakes interconnected by crisscrossing grid of canals, they developed thousands of small scale lakes. Striking thing about these is that they did not contain mechanisms to take water in or out. It is now found that the tips were curved to lift the water to the high-lands to do it. As the secondary purpose they fed the soil with water. According to Choolawansa, the two brothers Kiththisirinaga and Siriwallabha of the southern kingdom are said to have ruled the Dwadhahassaka rata (Land of 12000 lakes) and Aththadhahassaka rata (Land of 8000 lakes) respectively.
Parts of a Weva Description
Usually was built in stone, mud and brick, on natural hard rock (quartzite, granite). Therefore it had no specific shape and the needed mud was taken from the area of the future lake bed. The shape in the cross-section view is trapezoid and a vertical layer of mud was used inside the dam to prevent leakages. Inner wall was covered with stone to prevent the dam from erosion due to waves.
Biso Kotuwa (Valve-pit)
Though the actual function is quite unclear, it is evident that this served the purpose of modern-day valve pit (A pressure control device). The technology is believed to be found 2100 years ago by the native Engineers. This was built in stone and a index (Kata Pahana) laid in it to show the water levels.
This was used to take water into the lake, into the Biso-kotuwa and to issue water to the fields.
This was used to release the extra amount of water, when the lake is filled and is threatening the dam.
It should be noted that most of these lakes and their dams are still in function.
|Author:||akilada [ Fri Jul 14, 2006 4:53 pm ]|
I think this a very informative article. This should not be limited to lanka library. So please put this is wikipedia and let the world know how developed and self-depedent we were in one time.
|Author:||LankaLibrary [ Tue Dec 26, 2006 11:52 pm ]|
|Post subject:||Socio-ecological Significance of the Village Tanks|
Socio-ecological Significance of the Village Tanks (small reservoirs)Systems of Sri Lanka
A Study of Society Water and Environment
By G.M. Badaranayake, Sri Lanka
Abstract from 3rd IWHA conference, Egypt 2003
Sri Lanka is a tropical island located in the Indian Ocean. It’s climate is mainly determined by weather patterns of South-Asian region particularly by two monsoons called Northeastern and Southwestern.
The South-west monsoon rainfall brings a higher amount of water for the western part of the island but less rainfall to the northern part called Dry Zone. North-east monsoon brings a little or no rainfall frequently.
As these monsoons confine to a very limited seasons( two or three months) the most part of the year experiences lack of water. Limited water, available on the surface is mostly subjected to evaporate due to high temperature throughout the year. When either one or both monsoons are failed, there would certainly be dry spells or droughts those seriously effect the environment as well as the societies whose socio-economic activities are entirely based on water.
Thus water is a limited, valuable and scarce resource in the Northern Dry Zone of Sri Lanka where a large number of rural communities live depending on irrigated agriculture. In the early times of the inhabitation the country, there was a hydraulic civilization based on a very sophisticated irrigation and water management systems called Village Tank (small reservoirs) System. Since very beginning of the civilization, people have built and improved this water utilization system to overcome the problems of water scarcity.
Tanks were built by damming the rivers and streams across at many places in order to collect, reserve, regulate and to use water in a sustainable manner. Village tank system, in it’s technical and hydro-meteorological aspect has a unique significance.
A tank is not a single component but a component of a well planned integrated water draining system made by the man called the cascade. Cascade is a chain of reservoirs located along the streams or tributaries of a river within a macro catchment or a watershed. Every tank connects to another by the same stream. Surplus water from one tank located in the upper part of the stream, flows to the other that is located in the lower part of the stream through the irrigation channel network on the paddy field. Ultimately water collected into a larger reservoir located in the lowermost the valley (fig 1).
Every tank has a settlement called village, located in close proximity to the tank. Settlement is consists of about 50 to 100 dwells belong to a few families who ever engage in cultivating the paddy field. They mostly belong to a single cast and expanded from a one or two nuclei families.
The paddy (rice) field is located just below the tank lying parallel to the stream .Paddy field is used mainly for rice cultivation by irrigated water issued from the tank The upper part of the tank’s water spread area is normally covered with forest, mostly with jungles or dry scrubs. People use this land for highland cultivation known as Shifting cultivation or locally called Chena cultivation. This land is also used for timber and firewood.
In terms of physical set up, village tank system is not only a water regulating system but also a better man-made adjustment to the environment of dryness in the Dry zone of Sri Lanka. It directly effects the soil, vegetation, surface and ground water, air moisture and bio-diversity of the environment.
Tanks play a vital role in reducing the dryness of the air, adding higher amount of water vapor in to atmosphere by evaporation from the water body . Present study reveals that the atmospheric humidity in tank villages are considerably higher than that of the outside area.
Natural environment surrounding the tank village system particularly dense vegetation cover around the tanks, along the streams and irrigation channels have created a micro-climatic condition. It has been mostly favorable for the bio-diversity. The people who lived in these environments achieved and gained many advantages from this environment. There was a good relationship between man water and environment.
The tank is the main source of water. Their social economic activities and culture was entirely linked with the tank. Sociologically, in these societies there were so many traditions, customs habits and attitudes in relation to the utilization of water. Their water utilization methods and practices have been entirely based on such attitudes. They are tightly bounded with the protection of the environment .
Placing an especial emphasize on the above mentioned conditions, present paper discusses the importance of the interrelationship of man water and environment in the Dry Zone of Sri Lanka from an ecological perspective.
In this attempt, the present paper deals mainly with three aspect as follows
1 The physical set-up of the tank cascade system and it’s environment, particularly hydro-meteorological significance
2 Sociological aspect of the utilization of water as a scare resource
3 Linkage of man water and environment
In the first step, physical set-up of the Tank Cascade System is analyzed by the method of Ariel photographs interpretation. It’s hydro-meteorological significance will be analyzed by data, collected from recorded sources as well as from the field research undertaken by the author.
Sociological aspect will be discussed on the basis data and information collected in the field by social data collecting methods such formal and informal discussions with people and study of life events. Linkage of man water and environment will be identified by utilizing both physical and social information.
The ecological significance of the social activities of village tank societies will be highlighted ultimately.
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