Nachchaduwa Tank

Location: 80 18’ 0 N and 800 27’ 0 E to 80 17’ 0 N and 800 32’ 0 E; 917506 N and 439435 E to 915651 N and 448609 E; about 10 km southeast of Anuradhapura town in the Anuradhapura District, of the North-central Province.

Area: 1,780 ha at full supply level

Altitude: Around 100 m above sea level (asl) while the highest point in the area, the Ritigala hills are 572 m asl.

Overview: Nachchaduwa is a recently rehabilitated ancient irrigation tank. It is situated in the upper regions of the Malwatu Oya basin and forms a part of the cascading tank system of the Mahaweli scheme. The conservation significance of the wetland stems not only from its support to wildlife but also from the multiple uses it provides in the form of irrigated agriculture, domestic usage and fisheries. The tank catchment forms a part of the Ritigala Strict Nature Reserve, which is notably high in floral and faunal diversity.

Physical features: The tank is moderately deep (7.62 m asl at bund) and is surrounded by an undulating plain (at about 100 – 350 m asl) with isolated hillocks. The Malwatu Oya feeds the Nachchaduwa tank, which has three sluices to control its water levels. The main sluice is located near the southern end of the bund and releases water mainly to Tissa Wewa. The other two sluices release water to Nuwara Wewa. The tank has a storage capacity of 55.68 million m3. The reservoir and its catchment lie within the dry zone and receive an annual rainfall of 1,219 mm, mainly through the northeast monsoon. Mean monthly temperature is 27.9oC and the mean monthly relative humidity varies from a low of 60% (March) to 90% (December/January).

Ecological features: The landscape surrounding Nachchaduwa was part of the ancient Anuradhapura kingdom and has been influenced by human activities for centuries. Few patches of natural forests remain in the southern boundary of the tank. The aquatic vegetation in the tank consists of phytoplankton and rooted vegetation, while certain parts of the tank and its borders, which are seasonally inundated, are important feeding and breeding habitat for birds. Four types of terrestrial vegetation (dry mixed evergreen, riverine, scrub land and home gardens) are present in the area. A total of 105 plant species have been recorded. 65 bird species have been documented in the area of which 18 can be considered aquatic. This reservoir contributes to water quality regulation through the retention of pollutants and sediments.

Noteworthy fauna: The freshwater fishes in this tank are dominated by exotics such as Oreochromis mossambicus, Labeo rohita and Ctenopharyngodon idella. Indigenous species such as Channa striata are commercially important. Other indigenous fish species in the tank mainly comprise of Puntius spp, and Rasbora spp. Noteworthy reptiles include Crocodylus palustris, Geochelone elegans, Lissemys punctata and Melanochelys trijuga. The tank also serves as important habitat for water birds, where Pelecanus philippensis, Anhinga melanogaster and Haliaeetus leucogaster are among the noteworthy birds associated with the tank. Mammals such as Canis aureus, Lutra lutra, Elephas maximus and Prionailurus viverrinus are among the noteworthy mammals

Noteworthy flora: At least five species of endemic plants, Anisophyllea cinnamomoides, Diospyros ebenoides, Vernonia zeylanica and Willughbela cirrhifera have been recorded from the adjacent forests of the Nachchaduwa tank. Additionally, species such as Diospyrus malabaricus and Terminalia arjuna have also been noted in these habitats.

Land use: The local communities collect fish and shrimp from the tank. Paddy and chena cultivations and brick-making activities are common in the surrounding areas.

Possible changes in land use: Information not available

Hydrological and biophysical values: This tank acts as a store of water that is released according to the downstream irrigation requirements

Social and cultural values: The majority of the workforce in the immediate vicinity are self-employed and engage in the seasonal cultivation of paddy and chena, which are dependent upon the rainfall patterns. Due to the shortage of water, agricultural expansion is hindered. A small segment of the population depends on the tank fishery for their livelihood. Several important archaeological remains including an ancient diversion weir have been discovered from the vicinity. The Aruvil Aru, which is the second largest river in Sri Lanka, was one of the earliest sites of human settlement in the country. Settlements in the region can be traced back to prehistoric times. The exact time frame of the construction of Nachchaduwa is unknown, but the reservoir was possibly already in existence in the early part of the first millennium A.D.

Scientific research and monitoring: Information not available

Conservation education: Information not available

Recreation and tourism: The catchment area of the tank, Ritigala, is being promoted as a nature-based tourism destination.

Conservation measures taken: A portion of the catchment of the reservoir, Ritigala hill, has been declared as a Strict Nature Reserve under the FFPO. Community-based forestry management projects have been practiced in the area. The CEA published a wetland site report in 1994 under the Wetland Conservation Project. The Forest Department has been involved with teak planting in the surrounding areas. Under the ADB funded PAM Project, management measures for Ritigala will be implemented aiming to enhance its status as a Strict Nature Reserve.

Conservation measures proposed: The wetland site report produced by the CEA suggests a number of conservation measures.

Disturbance and threats: Rapid destruction of the wetland and surrounding forests for chena cultivation, illegal timber extraction and the expansion of human settlements are major problems in this area. Tortoise hunting by villages for food and indiscriminate killing of snakes mainly due to wrong identification is a major threat to their survival in the tank area. Invasive alien plant species such as Eichhornia crassipes also pose a threat to native aquatic plants in the tank.

Land tenure: The tank and the Strict Nature Reserve are state owned, while the homesteads and paddy fields are privately owned.

Management authority and jurisdication: Divisional Secretariat Division at Thirappane is responsible for all matters related to land tenure and distribution and five government departments (Irrigation, Agriculture, Forest, Wildlife, Archaeology) play important roles with respect to land management and resource use.

References: CEA/ARCADIS Euroconsult (1994g); CEA/ARCADIS Euroconsult (1999)