Yeywa Dam

The Yeywa Hydropower Station (ရဲရွာရေအားလျှပ်စစ်ဓာတ်အားပေးစက်ရုံ), located on the Myitnge River, 52 km southeast of Mandalay city, at Yeywa village in Kyaukse Township, Mandalay Region in central Myanmar, is the country's first roller-compacted concrete (RCC) dam, and the site of a 790 MW hydroelectric power plant, the largest in the country.

Background
The plant feasibility study was comepleted in 1999. In May 2001, agreement of consulting service between MEPE and COLENCO Power Engineering, Ltd. was signed. In 2003 agreement part 2 for Detail Design, preparation of tender documents and guidance services for construction supervision was signed. The river diversion was completed on December 12, 2004 and RCC placement began on February 8, 2006. The Burmese government announced plans for the Yeywa Dam in late 2001. In 2004, Burma's Ministry of Electric Power (MEPE) signed a Memorandum of understanding with a consortium of Chinese companies created by China International Trust & Investment Co. (CITIC) and Sinohydro Corporation for implementation of the project. On September 2, 2005, a ceremony to mark the signing of contract between the Hydroelectric Power Department under the Ministry of Electric Power and the China National Heavy Machinery Corporation (CHMC) for the Yeywa Hydroelectric Power Project was held in Yangon [Rangoon], Site work began in 2004 and all four generators were commissioned in 2010. The project was completed in November 2011.

Design
The dam design comprises a 137 m high RCC embankment gravity dam, built of 2800000 m3 of concrete. The dam includes an ungated spillway of reinforced conventional concrete cast after RCC placement, located in the central section of the dam for a design flood water discharge of 6600 m3/s. The 448 ft wide spillway consists of eight 56 ft wide and 39 ft high outlets.

There is a 790 MW (4 × 197.5 MW) powerhouse at the toe of the dam on the south bank of the river. The power house containing the turbines and generators is 510 ft long, 148 ft wide and 197 ft high. The power house and dam structures are designed to withstand earthquakes of up to eight on the Richter scale.

The power generation facilities consist of four water intakes, each consisting of 22 ft diameter and 492 ft long high tensile steel pipe penstocks and four vertical axis Francis turbines and generator units and associated electro-mechanical and auxiliary equipment installed in an open air powerhouse. Four water intake towers were built as conventional reinforced concrete structures abutting the upstream (east) face of the RCC dam. This enabled the contractor to build the towers above the penstock inlets before the start of RCC construction in order to minimise interference with the RCC construction activity.

There is one permanent 10 m diameter, 450 m long, diversion tunnel in the north river bank serving as a bottom outlet. This outlet tunnel enables reservoir drawdown and control during reservoir filling, maintenance of downstream riparian river flow during the impounding period and, together with the spillway, serves to redirect flood waters of the Myitnge river and maintain river flow during an emergency when all turbines are closed down.

Two double circuit 230 kV transmission lines connect the main transformers located on the downstream side of the powerhouse to an open-air switchyard, located on the south river bank 550 m downstream of the powerhouse. The Yeywa Dam will supply electric power to the Meiktila Sub-Power Station through the 110 km long Yeywa-Meiktila 230 kV double power line link to the southwest and to the Bellin Substation through another 50 km long 230 kV double power line link in the west. The Bellin and the Meiktila Sub-Power Stations will be linked to each other with 100 km long 23 kV double power lines. US$45.8 million worth of 230 KVA cables and equipment were used for construction and linking of these sub- power stations.

Construction
Several construction companies from China, Switzerland, and Britain and Myanmar have been involved in various stages of the Yeywa Dam, including the Chinese companies: Export-Import Bank of China (China Exim Bank), China Gezhouba Group Co. (CGGC), China National Electric Equipment Co., Hunan Savoo Overseas Water & Electric Engineering Co. and China National Heavy Machinery Co. The Swiss company Colenco Power Engineering, the Germany-based company Voith Siemens, and the British Malcolm Dunstan & Associates.

A key aspect in the successful construction of the Yeywa RCC dam was comprehensive training of the local staff during preparative for and initial stages of the construction. High-Tech Concrete Technologies (HTCT), a member of Shwe Taung Group, was the one who has been succeeding the knowledge from local perspective. Up to 5,000 workers were employed on this large construction project. Equipment selected for the concreting operations include Putzmeister's MX 32 stationary boom, an M 38 truck-mounted concrete pump and two BSA 2,109 HP stationary pumps.

A bridge was built across the river, just downstream of the dam, to replace the ferry system, which had been the only means for transport across the river.

Various studies were conducted during construction, and identified risk factors, one of them was "Key Organizational Risk Factors: A Case Study of Hydroelectric Power Projects in Myanmar".

Impact
3550 GWh of electricity per year will be supplied to the Mandalay Division regional power grid for public and private consumption.

In 2005 the Myanmar Times reported that three villages near the dam had been relocated. The villagers had depended on the Myitnge River for their fishing, farming and logging livelihoods, the sources of which will be flooded by the dam. Ancient cultural sites like the Sappa Sukha Htattaw Temple will also be flooded and forever lost.