Sri Lanka it is well known for its history of irrigation technology since centuries ago. About 2500 years old irrigation structures and systems are the silent witnesses of the marvellous irrigation technology of our proud nation.
Among all these ancient irrigation systems all over the country, mainly in the Dry Zone, Anuradhapura is popular as the Wew Bendhi Rajjaya for the large number of tanks built by kings governed from time to time including the world heritage irrigation masterpiece the Abhayawewa tank still quenching the heat of the Anuradhapura sacred city and the suburb.
The marvel of irrigation systems in Sri Lanka especially in Rajarata alias the kingdom of tanks is a consequence of the unbelievable unique engineering skills showcased to the world. The progressive erection of a colossal and artistic systems of interconnected canals, dams and tank cascades (ellangas) system for collecting water of rivers from different locations in the country displays the notable achievements of our great ancestors in the water management component.
According to the Chronicles and legends, resulting from the destructions caused by South Indian invaders and abandoning during the colonial rule over 400 years, the overall irrigational system and the associated civilisation tragically ruined leaving admirable remnants as witnessed today.
Later since the independence gained in 1948, the economic development of the country was centered on major, medium and minor irrigation systems. Over time, the ancient hydraulic structures including reservoir dams built by our ancestors faced an with interdependent challenge due to aging of structures suffering from various architectural and irrigational deficiencies and shortcomings concerning operation and maintenance of such work.
Irrigation marvels
Under these circumstances as the modern pioneers of the country’s irrigation development sector, the Irrigation Department now on the move to unveil many irrigational marvels in Rajarata. In the Anuradhapura district alone, there are around 3,000 tanks, most of them dilapidated, abandoned or not regularly maintained and filled with sediment.
According to Irrigation Department information, Rs. 8,000 million has been allocated to continue renovation work in 14 irrigation schemes in various locations under which around 14,000 hectares are being cultivated. It is reported that there are around 16,000 working tanks and 2,100 abandoned tanks in the country, in addition to 15,800 anicut schemes. In this context, on the instructions of President Gotabaya Rajapaksa and under the guidance of Irrigation, Minister Chamal Rajapaksa, the Irrigation Prosperity or the Wari Saubhagya program has been launched for renovation and the revival of dilapidated rural tanks.
Under the first phase, the renovation work on 5,000 tanks has begun and the overall cost for the renovation program is estimated as Rs. 12.5 billion. In the Anuradhapura district, 200 ruined tanks have been selected for repairing at a cost of Rs. 3,000 million and construction work progressing on 20 tanks.
An abandoned tank namely Kudawilachchiya in the Northeast corner of the Wilpatthu National Park about three kilometres from the Mahawilachchiya reservoir, has been found while hidden in the thick forest cover of the Wilpatthu National Park extending for around 131,879 hectares. At a recently conducted survey, 38 Irrigation structures mainly ruined tanks and abandoned paddy fields have been identified in this landscape. It is found that the tank was breached at several places when it was recovered.
The latest surveys conducted by the Irrigation Department have identified that this massive earthen dam is 2.55 k.m. in length and the maximum height of the dam is nearly 32 feet.
As other ancient reservoirs, the Kudawilachchiya tank too consists of two sluices (Bisokotuwa in ancient Sinhala terminology) which have been destroyed by treasure hunters. But fortunately, the original structural features of the sluices remain intact. Plenty of stone pillars are aligned precisely to form the sluice well.
All structures have been covered with two - metres to four metres thick brick masonry to arrest any leakage. It is amazing that these nearly 2,000 year old bricks and cement motor also remain as they were without any harm or significant damage. The stone curved sluice tunnels and groves are also seen intact and still in good working condition.
Earthen dam
According to Irrigation Engineers, the two steps of the retaining wall type providing riprap protection along the entire tank bund, show the great structural knowledge used in ancient irrigation technology. However, the question is this massive earthen dam which is around three km long has a spill length of 15m which is odd in dimension when compared to other reservoirs holding the same capacity. This structural situation is interpreted that though the entire dam could hold more than 46,000 acre feet of water, the annual inflow to the reservoir might be less than 28,000 acre feet. This hydrological analysis proves that those ancient irrigation technicians have had knowledge of hydrological features of the upper catchment which may cope with the shorter length of the spill built at the Kudawilachchiya tank.
There is another question being posed as to why they had constructed a bigger dam wasting a massive amount of materials and human resources when the annual inflow is low. This could have been a difficult and somewhat rather inconvenient task those days. An interesting justification for this question can be found when walking along the Kudawilachchiya tank bund.
We are aware that in the Dry Zone, the annual yield might be less than 1,750 mm. But when we take in to consideration the period 1,000 years or more, it could yield more water. That might be the reasons behind the massive earthen dam of this tank. By the time those ancient engineers knew that the length of the spillway is not enough to cope with such an event and so they might have introduced a breaching section artificially to the bund where geological features are not supported for a natural safe breaching section.
“It can be observed that 275 metres away from the spillway, there is a stone abutment that can be considered as protecting the bund from breaching in the event of a massive flood. Even at present, the downstream protection by dress stone masonry which may be providing convincing evidence that our ancestors provided wisely, adequate room for excessive water by preventing the dam from erosion.
On top of this massive dress stone abutment, there are ruins of an ancient building which could be assumed as the operation room for dam controlling staff that would have been a vital factor for operating the breaching section in case of a severe flood threat,’’ a spokesman for the Irrigation Department said.
Hydrological expertise
Chief Resident Project Engineer in charge of the Kudawilachchiya Renovation Project, Eng: Prasanna Tilakaratne said that it seemed this would be the first evidence of the unique hydrological expertise of our ancient irrigation engineers. Archaeological findings that were being unearthed and discovered at the work site which remained hidden for centuries in the Wilpatthu National Park was bearing precious evidence about the excellent irrigational engineering skills of our ancient Irrigation Engineers who saved every drop of rain water in the kingdom of tanks they had created for achieving sustainable development in Sri Lanka.
It is learnt that this tank was constructed under the supervision of Saliya - Asokamala about 1900 years ago and believed that Prince Saliya and Asokamala used to visit the tank for relaxation. The ruined building structure adjoining the spill of the tank is supposed to be a pavilion reserved for the royalties.
According to the resource inventory of the Wilpattu National Park produced by the World Conservation Union the area identified as Galbendhi Neeravia which is located Northeast of the Maradanmaduwa tank close to Kudawilachchiya in the national park is supposed to be the place where Prince Saliya, the son of King Dutugemunu lived with his bride of low caste Asokamala some 19 decades ago.
Kudawilachchiya Chief Resident Project Engineer Prasanna Tilakaratne said that the estimated cost for the completion of the renovation, rehabilitation and restoration project is Rs 6,000 million. Once completed the capacity of the tanks will be around 18,500 acre-feet. The project includes a 3.5 km canal way for emitting tank water to Sadasarana Wewa when necessary.
Tilakaratne said that around 25,000 families will get drinking water facilities from the tank and Irrigational water will be provided for cultivating 800 acres in both Yala and Maha cultivation seasons. The wildlife in the Wilpaththu national park suffering from water scarcity are benefited since the Kudawilachchiya tank is situated within the park boundaries. The tank has been built across the Ittikulama canal, a tributary canal of Modaragan Aru river flowing via the Wilpatthu national park. The project is targeted to be completed within the next three years.
The Irrigation Department has arranged to implement the constructions with precautionary action to preserve and protect all monuments of unique historic importance on the instructions of the Archaeology Department. The surveying of the project area is nearing completion and the environmental impact study report is pending. Archaeology Departmental approval has been granted to start the headwork construction of the project.
In this project, mainly the haedworks (includng earth dam, spllway structure wth five radial gates, sluce structure), supply canal from Kudawlachchiya reservoir to Sadasaranawewa, Access roads are constructed.
The main dam is an earth dam and 2.6m long. Average hieght 12 m.
The supply canal is 3.2 km and includes 350 m close conduit and 250m trough, other sectons are earthen. In the supply canal, there is a tank called Walantheliyawa. It also rehaltated by the project.
There are two access roads. One is from Kiralpetyawa to the Right bank of the Kudawilachchya dam. The other one is from Kukulkatuwa side to the proposed spill of the reservoir.
Costruction work on access roads and part of the supply canal started.
Under the supply canal, the Walanthelyawa minor tank is being rehabilitated with its spill tail canal.
Both access roads are constructed with 5m width. The RB access road is going through the Kiralpetiyawa tank bund. Two sluices of the tank are rehabltated.