【正文】 Feasibility Study of Yan Oya Reservoir Project in Sri Lanka Chapter 1 China CAMC Engineering Co., LTD. 1 1 General Description The basis and principles 1) Feasibility study report of the project and advance report on updating the Feasibility study of Yan Oya project are provided by Ministry of Irrigation and Water Management of Sri Lanka 2) Topographic maps of the project region and other project files were provided by Sri Lanka authorities. 3） The agreement of the technical aspects of the project which the two sides reached Project Location The proposed project is located in the Anuradhapura and Trinalee districts in the NorthEast of Sri Lanka, about 300 km from Colombo, the capital city of Sri Lanka. The proposed dam is located about 70 km downstream from Hurulwewa tank. Its geographic coordinates are: 7176。55‘00‖ ～ 8176。55‘00‖NL, 80176。41‘27‖～ 81176。2‘10‖ at EL. Hydrological Meteorology The irrigation water resource for this project es from Yan Oya River with 1,500km2 catchment area and 150km length. The project area belongs to tropical marine climate zone with distinct rainy season and dry season. The annual mean precipitation is 1644mm. The rainy season is from October to next February. Engineering Geology The project area is covered with wide alluvial plain, with characteristics of flat ground and the alluvial layer in surface. The upper layer is highly plastic anic clay, and the lower layer consists of bands and clayey silt or clayey sand or very fine sandy silt. The slopes of the hill and adjacent areas of both abutments are covered with talus material which consists of hillside waste and debris up to 5m depth. Low flat topped hills are covered with residual soils. Total thickness of overburden including residual soil and pletely weathered rock layer varies from to . Scale of the Project The irrigation area of the project is 6346 ha. Feasibility Study of Yan Oya Reservoir Project in Sri Lanka Chapter 1 China CAMC Engineering Co., LTD. 2 Scope work of this Project An earth dam is proposed to be built on Yan Oya to raise properly normal water level of the river. Main building of the project include the earth fill main dam, saddle dam with spill way, watercarriage system , etc. Project Construction Schedule The project implementation period is 48 Months, and expected to start in January of first year and pleted in December of the fourth year due to impact of the rainy season. Feasibility Study of Yan Oya Reservoir Project in Sri Lanka Chapter 1 China CAMC Engineering Co., LTD. 3 Project Characteristics Table Item and No. Unit Qty. Remarks (1)Catchment area whole catchment km2 1500 Upstream of the dam site km2 1341 (2)Annual mean runoff flow 109m3 (3)Representation flow Annual mean flow m3/s Flood peak flow (design flood， P＝ 1％ ) m3/s 2344 Flood peak flow（ check flood standard，P＝ ％） m3/s 3650 2. Reservoir Check Flood level with P=% m Design Flood level with P=1% m Normal storage level m irrigation water level Minimum irrigation level m Total Capacity MCM 214 benefit index Irrigation area ha 6346 4. Major structures (1)Earth fill dam Type Homogeneous earth fill Crest elevation m Upstream slope ratio 1: Downstream slope ratio 1: Crest Length of the main dam m 2347 Crest width m Crest Length of Saddle dam m 580 Including spillway (), max height of the dam is 20m Feasibility Study of Yan Oya Reservoir Project in Sri Lanka Chapter 1 China CAMC Engineering Co., LTD. 4 Project Characteristics Table Item and its No. Unit Qty Notes Crest Length of Saddle dam m 1912 max height of the dam is 18m Crest Length of Saddle dam m 1027 max height of the dam is 10m Crest Length of Saddle dam m 99 max height of the dam is 2m (2).spillway Orifices pcs 5 Dimension of one orifice m 12 Energy dissipation underflow energy dissipation baffle pond Form of working gate Liftingtilting ogee steel gate Dimension(B H) 12m Quantity 5 Type of hoist QHLY2 Capacity kN 2 500 Quantity 5 (3).watercarriage system Type of water intake Tower structure Tunnel diameter m Liner diameter length m 82 Including intake and outlet (1)Construction Diversion Type stage by stage cofferdam diversion Structure of Cofferdam Earth structure (2)Construction schedule The whole construction period Month 48 Feasibility Study of Yan Oya Reservoir Project in Sri Lanka Chapter 2 China CAMC Engineering Co., LTD. 5 2 Hydrology Summary of Watershed The island of Sri Lanka lies in the Indian Ocean， to the southwest of the Bay of Bengal. It is separated from the South Asia subcontinent by the Gulf of Mannar and the Palk area amounts to 65,610 are many hydrographic s in this island, such as Mahaweli Ganga, Duduru Ganga, Aruvi Aru, Kalu Ganga, Yan Oya and so on. Mahaweli Ganga is the biggest river. The basin of Yan Oya is located in the northeast of Sri Lanka between the cathment of Ma Oya in the north and Amban Ganga, Kalu Oya in the south, between Malwathu Oya in the west and Kunchikumban aru in the east. The Yan Oya cathment is extended in form with a total length of 120km and the mean width of topography of the watershed is stretching high in the southwest and low in the northeast. In the upper catchment there is a considerable degree of development and human settlement especially around the Huruluwewa scheme while the most areas in the lower catchment are non cultivated lands covered by shrubs. There are two reservoirs