Agriculture in Sri Lanka is the cornerstone in the economic and social development of the country. A colossal sum of money is spent annually to import food, most of which can be produced locally.
In 2017, around Rs. 250 billion worth food including milk food has been imported. Sri Lanka has a wide variation in soil and climate with 24 agro-ecological zones, each characterized by specific climate and soil, making it possible to cultivate different crops. With about 2.5 million hectares of hitherto uncultivated/partly cultivated land and nearly one million unemployed people, importing food costing Rs. 250 billion annually is an anomalous situation.
The productivity of the domestic food sector has been static or declining during the recent past and the total production and average yields of most crops, except rice, have decreased. With the increase in population growth and development, water is playing a key factor in socio-economic development and tends to be a limiting factor.
In the Rajarata, hydraulic civilisation thrived in the past. However, at present, an appreciable percentage of people in the dry zone are affected by water shortage. The dry zone, which covers the lowlands of the northern, north-central and eastern areas of the country, is subjected to several months of dry spell extending from May to September. In order to overcome the limited water availability during this period, a water management system which is called Tank Cascade System or ellangawa was developed by our forefathers. In this system, rain water which runs off is collected in individual small tanks, with each having its own micro-catchment. A ‘tank cascade’ constitutes 4-10 series of small tanks in a meso-catchment basin which could vary from 10-20 ha.
Irregularly rainfall
The total catchment area of a cascade determines the amount of runoff that could be collected. The run-off in a catchment area depends on factors such as, gradient of the land, soil characteristics such as soil depth, organic matter level, the type of crop in the catchment, etc. The benefit of tank cascade system is that the excess water from a tank along its command area is captured by the next downstream tank. Thus, water is not wasted as King Parakramabahu I said, “let not even one drop of water that falls on the earth in the form of rain be allowed to reach the sea” Tank cascade system helps to overcome problems related to irregularly distributed rainfall and make water available throughout the year.
Availability of water in several locations of the cascade help to overcome water scarcity even during dry seasons which enable to maximize land use. Storage of water in the upstream tanks in a cascade, reduces the risk of breaching of the bunds of those on the downstream when the rainfall is excessive. Regulated release of only excess water, reduces flood damages downstream.
Tanks at several locations provide water for all domestic water needs. It also meets the water needs of cattle and other animals in the area. Cascade system keeps the ground water level high to provide water in wells for domestic uses. It also improves the micro-climate in the immediate tank environment which brings relief to the tree crops in adjacent areas during dry seasons.
There are about 12,500 such small tanks scattered throughout the dry zone with an irrigation potential of over 100,000 ha. Most of these tanks are shallow mini reservoirs with an average depth of 2.5 to 3.5 metres with micro-catchments of less than 20 sq.km. The feeding streams are non-perennial and water flow is available for relatively short periods following monsoon rains. Rehabilitation of Small Scale Irrigation Schemes (SSIS) is of importance mainly because these small tanks in addition to supplying water for irrigation, are also an effective water source for domestic needs, livestock and fish.
Storage process in the cascade system, would promote crop and animal production, enhancing farmer income.
Small tanks are of much relevance in development programmes when the agricultural, social and environmental benefits are considered. The sustainability of the village depends on the small tanks. These tanks functioned and served the community for more than a thousand years and will continue to do so. Amid the current large scale irrigation and agricultural development projects, the small tanks continue to contribute to maintain the socio-economy of the village and upkeep the agricultural economy of the country. Despite various irrigation projects implemented in the country, the people living in the Wayamba Province face many difficulties without an adequate supply of water. The living standard of the people decreased, as the farmers suffered from a severe shortage of water for their cultivation, and the clean drinking water shortage led to the proliferation of kidney disease among the people in the region.
Safe drinking water
The initiative taken by President Maithripala Sirisena to launch the second phase of the Rs. 23 billion Moragahakanda-Kaluganga reservoir project in the North Western Province is highly commendable. It will provide safe drinking water to people in the province and enable irrigation of 12,500 hectares. The project will provide direct dividends to around 13,500 farmer families, and indirect benefits to another 80,000 farmer families.
As a part of this project, 91 tanks of Ahutuwewa Divisional Secretariat, 119 tanks of Polpithigama Divisional Secretariat, 107 tanks of Mahawa Divisional Secretariat, 30 tanks of Galewela Divisional Secretariat, one tank at Palagala Divisional Secretariat and 5 tanks in Dambulla Divisional Secretariat will be developed.
Rehabilitation/development of irrigation schemes alone is not likely to contribute to growth in the agriculture sector. The need to protection and sustainable use of water resources is important. Appropriate agricultural systems and practices are necessary to increase efficiency in the irrigational schemes. Production of the staple food crop, rice, depends largely on irrigated agriculture and the yield of rice has increased during the decade, except the last few years due to prolonged drought.
The catchment areas of the tanks need to be properly managed and in this regard establishment of a Catchment Management Unit would be appropriate. This Unit will work together with local authorities, other public authorities, government agencies, and local communities in establishing effective integrated catchment management.
The main purpose of the Unit is to protect and improve water resources. This approach also would ensure that those involved in land use planning, natural resource management, crop production etc. work together in planning and implementing catchment management policies which would ultimately result in socio-economic development of the area.