Geography
Sri Lanka is situated in the Indian Ocean, near the southern tip of India, between latitude 60N and 100 N and longitudes 800E and 820E. It has a maximum length of 432 km and width of 224 km with a total area of 65,610 sq.km. of land and 870 sq.km. of water. Its coastline is 1,340 km long. Its terrain is mostly low, flat to rolling plain, with mountains in the southcentral interior. Three zones are distinguishable by elevation: the Central Highlands, the plains, and the coastal belt. The coastal belt about thirty meters above sea level surrounds the island. Much of the coast consists of sandy beaches. Most of the island&&39;s surface consists of plains between 30 and 200 meters above sea level. Hundred and three rivers rise in the Central Highlands and flow in a radial pattern toward the sea. 

Population and Land Use
The population was more than 21.9 million in 2021. The population density is highest in the Colombo city in the Western province. Sri Lanka is ethnically, linguistically and religiously diverse country.
The present land use pattern in Sri Lanka is a legacy of land policy of the colonial past where export based commercial plantation agriculture was superimposed on a traditional subsistence farming system. At present about 40% of the total land area is used for agriculture while another 30% is forest and wildlife reserves. The balance is used for all other activities as urban and infra-structure development. 
Out of the available 2.1 million ha arable lands, about one million ha is used for paddy cultivation. Other area is utilized for Tea, Rubber, Coconut, Palm oil, Cinnamon, Banana, Pineapple and other seasonal crops. Other field crops such as maize, green gram, finger millets, black gram, cowpea, soya beans, gingerly, chilies, potatoes and big onions are grown in uplands in both seasons (Yala & Maha) and low lands in Yala season.

Climate and Rainfall
Sri Lanka’s climate is tropical and quite hot. The mean temperature ranges from a low of 16°C in Nuwara-eliya in the Central Highlands to a high of 32°C in Trincomalee in the northeast coast. The average yearly temperature for the country as a whole is between 28 and 30°C. Rainfall producing mechanisms in Sri Lanka are convectional activity, monsoon and weather systems formed in Bay of Bengal. Sri Lanka’s annual rainfall varies from 850mm to 5500mm with an average of 1861 mm. Sri Lanka is mainly divided into 3 climatic zones depending on the rainfall they receive. They are dry zone (annual rainfall<1750mm), intermediate zone (2500mm>annual rainfall>1750mm) and wet zone (annual rainfall > 2500mm).

Food and Agriculture
Rice being the staple food in Sri Lanka it is the most vital food crop cultivated in the country. The major rice growing areas of the country are located in the Dry Zone and the Intermediate zones and are the most vulnerable to droughts. Thus, high variability of rainfall will have negative impacts on the rain fed paddy cultivation. Furthermore, the wet zone paddy fields are badly affected during floods. 
Sri Lanka’s primary form of agriculture is rice production. Tea, rubber, fruits, vegetables, and other cash crops are cultivated in the country. Rice occupies 34% of the total cultivated area in Sri Lanka. Sri Lanka currently produces 2.7 million tons of paddy rice annually and satisfies around 95% of the domestic requirement. From the expected production of non-rice annuals, a major portion of green gram and maize can be produced under rainfed conditions. However, for crops such as onions, potato and chilies, most of the production is expected from irrigated fields under crop diversification. 

Water Resources Management
Annual water resources of Sri Lanka are estimated at 45 km3 of the surface water in the country. 103 distinct river basins are available in country which flow through the wet and dry zones. Rivers in wet zone are perineal and carry nearly 50% of surface runoff. 
There are 73 major reservoirs and about 160 medium reservoirs which are managed by the Irrigation Department (ID) where more than 14,000 minor tanks are managed by the Department of Agrarian Services Department (DAD) and Provincial Councils. 7 Multipurpose reservoirs and 7 major reservoirs in Mahaweli basin and Walawe basin are managed by the Mahaweli Authority Sri Lanka (MASL). 7 Hydropower reservoirs in Kelani and Kalu basins are managed by the Ceylon Electricity Board (CEB). 2 medium reservoirs in Kelani basin are managed by the National Water Supply and Drainage Board (NWSDB). Most of the reservoirs have been constructed during Sinhalese Kings’ period and rehabilitated and augmented by Irrigation Department during last 122 years from time to time. 
The groundwater resources are considered to be lesser compared to surface water resources. Seven main types of groundwater aquifers have been identified. The estimated groundwater potential is 7,800 MCM per annum. Both the quantity and quality issues limit the use of groundwater. It is widely used for domestic, small-scale irrigation, industrial and other uses.

Dams / Reservoirs
It is estimated that there are about more than 13,000 man-made reservoirs in the country. Out of these about 131 are classified as large dams. Most of the large dams are earthen dams and few concrete gravity dams can be seen. There are about 99 Major and Medium diversion structures in Sri Lanka. In addition, about 20,723 minor reservoirs (including village tanks) and about 15,866 minor diversion weirs (anicuts) are available to divert water to minor tanks or irrigable area. The large reservoirs have been built for mainly irrigation and hydro power generation. The village reservoirs provide several services such as water for agriculture, drinking, sanitation, inland fishing and livestock. The ‘Senanayake Samudraya’ which was built between 1949-1952 remains the largest reservoir in Sri Lanka, having 959 Mm3 capacity.

River Basins
There are 103 distinct river basins in Sri Lanka. 36 major river basins have been classified into three groups based on monsoonal rainfall pattern: 1. south – west monsoonal, 2. Northeast monsoonal and 3. Both monsoonal basins. The important rivers in group 1 are Kelani, Kalu, Benthota, Gin, Nilwala, Maha Oya and Attanagalu Oya. There are 26 rivers that fall into group
2 and cover a significant spatial extent of the country. There are two river basins that fall into the group 3 receiving rainfall from both monsoons. They are Mahaweli and Walawe rivers. The Mahaweli River is the longest river with a length of 355 km and basin area is 10,488 sq.km.

Irrigation and Drainage
Sri Lanka as an agricultural country has two main cropping seasons associated with rainfall; one from October to December coincides with the initiation of the primary cultivation season recognized as “Maha” (October – March) and the April to June rainfall coincides with the secondary cultivation season recognized as “Yala”(April – September). 
The Irrigation systems in Sri Lanka are mainly classified into three main types; Major, Minor & Rain fed irrigation systems. Irrigation systems having a command area of more than 400ha are classified as Major Irrigation systems. The major irrigation systems are spread over 350,000 ha. The second system, which has more than 57,000 ha of paddy land is called Medium irrigation schemes. Their commend is area is between 400 ha and 80 ha. The schemes which the command area is less than 80 ha are Minor schemes. There are more than about 291,000 minor irrigation schemes in Sri Lanka. The Rainfed cultivation system is also dominant in wet zone of Sri Lanka having about 260,000 ha of paddy lands. Rice is the main crop cultivated in major irrigation schemes in dry and intermediate zones. About 90% of the irrigated lands are cultivated with paddy. In Yala, the drier season, the contribution from irrigation is more pronounced, highlighting the positive impact of irrigation on food security and livelihoods. A critical issue in the drainage of irrigation schemes is the excessive growth of water weeds in those drainage channels. Therefore, seasonal maintenance of those is needed. Most of the time those drainage canals are overflowing and therefore flooded. Drainage canals and irrigation reservations are subjected to encroachment with the growing demand for lands. Therefore, drainage canals are not functioning as expected.

Water Governance
The Irrigation department, established in 1900, has played a major role in Sri Lanka’s irrigation development. Participatory management in irrigated agriculture is accepted as the government policy, and several programmes have been implemented to encourage and facilitate better participation of farmers in the management process. The implied policy emphasizes that irrigated agriculture will be supported financially by the state, while farmers actively participate in decision making. There are over 40 acts of parliament with relevance to the water sector. Accordingly, the Comprehensive Water Resources Management in Sri Lanka Report done in 1994 lists 29 legislations as directly linked to water. Irrigation Ordinance, National Environmental Act, Coast Conservation Act, Agrarian Services Act are coming under them. Traditionally the cost of infrastructure development and their maintenance have been borne by the state. However, several well-functioning farmer organizations have developed their own methodologies to recover the costs of maintaining the canals under their management.

ICID and National Committee
Sri Lanka joined the ICID as a founder member in the year 1950. The current Chairman of the Sri Lanka National Committee, ICID (SLNICID) is Eng.K.D.N.Siriwardana and can be contacted at dgiirrigation@gmail.com

---

References

Strategic Plan for Water Resources Development & Management database updated 2022, Irrigation Department
National Drought plan for Sri Lanka, Ministry of Environment, Sri Lanka-September 2020
Department of Meteorology - Sri Lanka (https://www.meteo.gov.lk)
Irrigation Department - Sri Lanka (https://www.irrigation.gov.lk)
Department of Census and Statistics (http://www.statistics.gov.lk)

---

[Updated 12 July 2022]