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Myanmar is endowed with abundant water resources, but here are problems,related to their uneven spatial and temporal distribution. The monthly distribution of river flows closely follows the pattern of rainfall, which means that about 80 percent flows during the monsoon season (May-October) and 20 percent in the dry season (November-April).
The north-south direction of Myanmar’s mountain ranges is reflected in the flow of its major rivers, of which two are international. There are six river basins:
- Ayeyarwady (Irrawaddy)-Chindwin river basin, which is almost entirely located in Myanmar, drains 58 percent of the territory. It can be divided into three sub-basins: Upper Ayeyarwady, Lower Ayeyarwady and Chindwin.
- Sittaung river basin, which is also entirely located in Myanmar to the east of the downstream part of the Ayeyarwady, drains 5.4 percent of the territory.
- Thanlwin (Salween in Thailand, Nu in China) river basin drains 18.4 percent of the territory, mainly the Shan plateau in the east. The source of the river is inChina and, after entering the country, forms the border with Thailand for about 110 km.
- Mekong (Lankang in China) river basin drains 4.2 percent of the territory in the far east and forms the border with Lao People’s Democratic Republic. Myanmar is not a member of the Mekong River Commission.
- Rakhine (Arakan) coastal basin in the west drains into the Bay of Bengal.
- Tanintharyi (Tenasserim) coastal basin in the south drains into the Andaman Sea.
Total surface water produced internally is an estimated 992.1 km3/year. Groundwater resources have been estimated as 453.7 km3/year; but a large part of this water (about 443 km3/year) comprises the base flow of the rivers and is also accounted for as surface runoff. This gives a total internal renewable water resources (IRWR) of 1002.8 km3/year (992.1+453.7-443).
The annual inflow from other countries is about 128.186 km3: with 20 km3 coming from India, 68.74 km3 (Nu to Thanlwin) and 31.3 km3 (rivers in west Yunan) from China, and 8.156 km3 from Thailand. The Mekong river forms the over 170 km border with Lao People’s Democratic Republic. The source of the river is in China, the total annual flow is 73.63 km3, half of which or 36.815 km3 can theoretically be considered as an additional external resource. The total natural renewable water resources (including flow from incoming or border rivers) are therefore an estimated 1 167.8 km3/year (Table 2).
There are two major natural lakes. The largest is tInle lake in Shan state which runs some 24 km from north to south and 13 km from east to west, covering an area of 155 km2. The Indawgyi lake in Kachin state stretches about 22 km from north to south and 11 km from east to west.
The Irrigation Department, which was established to coordinate the development and management of water resources for irrigation, has constructed about 200 irrigation projects, which receive water t from constructed dams, weirs and sluices. A surface water runoff of about 15.46 km3 has been stored in the constructed reservoirs and can irrigate about 1 million ha (Naing, 2005).
The implementation of the Ngamoeyeik Dam Project started in 1992-1993 and the dam opened in 1995. It is an earth embankment measuring 4 724 m by 23 m with a reservoir capacity of 0.222 km3 (MIC, 2006). The dam was built to facilitate double cropping to supply additional water to farmlands in the rainy season if necessary, to take flood prevention measures on the Ngamoeyeik creek, and to supply around 600 000 m3 of water to Yangon City daily. Arrangements are being made to supply water to Ngamoeyeik dam by building the Mahuya dam and Paunglin dam to ensure that the Ngamoeyeik dam is able to work at full capacity. Measures have been taken to generate electricity from Ngamoeyeik dam (The new light of Myanmar, 2003a).
The Thaphanseik dam on the Mu river in Sagaing division, completed in 2001 is, 6 km long making it one of the largest dams in Southeast Asia. It is a multi-purpose dam, providing water for irrigation and for power for the nation’s developmental needs. The dam enables year-round irrigation of over 200 000 ha with feeder canals extending to eight townships (Earth Snapshot, 2009).
The Sedawgyi dam, used for hydropower, is on the right bank of the Chaunginagyi river and has a capacity of 25 MW; itbecame commercially operational in 1989. The Ngalaik dam in Pyinmana township was completed in 1987, with a full capacity of 0.093 km3. The Chaungmagyi dam for irrigation, also in Pyinmana township, was completed in 2003 and is able to store 0.05 km3 (The new light of Myanmar, 2003b). Another important dam for irrigation is the Yezin dam with a total capacity of 0.074 km3, which is able to irrigate 6 400 ha of agricultural land.
The Kataik dam, is 71 m high with a total capacity of 0.07 km3, was constructed in 2007 in Paung township. It is able to supply water to 4 050 ha of farmland and contributes much to regional development, since local people are able to engage in double cropping cropping (The new light of Myanmar, 2007).
According to studies by the United Nations and other sources, the hydropower potential of Myanmar is estimated to be as much as 40 000 MW. By 2002, 35 hydropower stations (including 15 medium-scale projects) had been completed with a total capacity of 390 MW, which is just 1 percent of the potential.
The government signed an agreement with China Power Investment Corporation in 2007 for the construction of seven large dams along the Ayeyarwady, Mali, and N’Mai rivers in Kachin state. The largest one, the Myitsone dam, will be located at the confluence of the Mali and N’Mai rivers, which then become the Ayeyarwady river and will be 152 m high with an installed capacity of 6 000 MW. The reservoir will flood an area larger than Singapore in one of the world’s most disputed biodiversity ‘hotspots’. An estimated 10 000 people will have to be displaced (BRN, 2010).
Two important hydropower dams, the Hatgyi and Tasang dams, are proposed to be constructed on the Thanlwin river (BRN, 2009).
Yangon wastewater treatment plant has been operational since 2005 and is designed to treat 12 300 m3/day (Than, 2010).