“ Do not let a single drop of water flow to the sea without being made use of ”
EXCELLENCE IN IRRIGATION ENGINEERING
Lessons from the Past irrigation systems those found in Sri Lanka are unique .
The irrigation system in Sri Lanka can be considered as a sustainable soil - water eco system . There are canals that interconnect large and small reservoirs spreading all over the dry zone where this wide network helps to enrich ground water , maintains the eco system and the water table .
Source - amazinglanka . com
“ Do not let a single drop of water flow to the sea without being made use of ”
~ King Parakramabahu the First
T he unique irrigation system and the hydro engineering knowledge in the past prove the excellence in irrigation of our nation .
Ancient civilizations were based on river valleys - for example , river Nile in Egypt , Upreties and Tigris rivers ( Babylon ), Indus and Ganges ( India ). Even in Sri Lanka , the first kingdom Anuradhapura was based on the valley of Malwathu Oya . Our ancestors built a number of reservoirs , anicuts , and canals in the dry zone establishing their civilizations . Engineering skills in such marvels still never fail to amaze today ’ s engineers .
Source - amazinglanka . com
The concept “ Wewai dagebai-gamai pansalai ”( the tank , village and the temple ) implies that the hydro engineer had quite a responsible role in the ancient society . Eventhough Sri Lankan culture was influenced largely by parallel civilizations in India , the advance
In the late 1970s , when Maduru Oya reservoir was constructed under Mahaweli Project , the old anicut and the sluice which dates back to 5th or 6th century A . D . were found in exactly the same position . The same was observed in Urithissa Tank ( Ridiyagama ) which very well proves the excellence of ancient engineers . Kala Wewa spillway ( the tank ), Minipe Anicut are also some examples of the skillful engineering work of our ancestors .
Kirindi Oya dam is another ancient engineering product , built at an oblique angle of nearly 45 degrees , instead of going across the shortest possible route . It is found that this design increased the discharging power and the ability to withstand shocks .
THE SLUICE AND SLUICE GATES Sluice and sluice gates are the most important parts of an irrigation tank . It ’ s purpose is to control the outflow of water without damaging the dam . ( It ’ s found that the ancient engineers used a ‘ Keta Sorowwa ’( Removable part of a pipe in smaller tanks ). The sluice was connected to a number of keta , which were kept on top of another , such that the water head of the sluice inlet could be controlled by removing the ‘ keta ’. Hence , the flow rate through the sluice could be controlled to the desired level .
However , when it comes to larger tanks like Parakramasamudraya , Kala Wewa etc . keta sorowwa could not be used , as the water head was much greater . As a solution for this problem , ancient engineers used “ bisokotuwa ”. It is one of the greatest engineering techniques in the history of irrigation . It is square in shape , with a length of 8-12ft and a width of 8-10ft ( placed inside the dam ). When the inlet gates are opened , water flows into the bisokotuwa through a conduit . When water reaches the head to a safer level , the outlet gate opens and the water flows through the sluice smoothly .
10 University of Peradeniya Gauge Magazine