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Papua New Guinea
Geologically, Papua New Guinea is a young country. The presence of high mountain ranges and abundant rainfall leads to high runoff over most of the country.
There are nine hydrological drainage divisions (basins). The largest river basins are the Sepik, Fly, Purari and Markham. Even though the Sepik has the lowest annual discharge, it has the largest catchment area, 78 000 km2, followed by the Fly River with 61 000 km2, Purari with 33 670 km2, and Markham with 12 000 km2. The other catchments are less than 5 000 km2 in area and very steep.
The internal renewable water resources are an estimated 801 km3/year (Table 2). As the country has an abundance of surface water resources and as there are few large-scale consumers, groundwater resources have not been developed. However, there is evidence that groundwater is being used increasingly as a source of reliable high-quality water. In 1974, a surveyed 34 percent of the villages relied on groundwater from boreholes, dug-wells or springs. In the 1970s and 1980s, groundwater was developed for urban water supply schemes in seven major towns. Groundwater resources have not been assessed but it is assumed that most groundwater returns to the river systems and is therefore included in the surface water resources.
There are 5 383 mostly small natural freshwater lakes, only 22 have a surface area exceeding 1 000 ha. Lake Murray is the largest with a surface area of 64 700 ha.
In 1986, there were three dams over 15 m high. The gross theoretical hydropower potential for Papua New Guinea is 175 000 GWh/year. In 1990, the total installed capacity was 163 MW and the annual generation was 438 GWh. In 2008, of the country’s total power generating capacity of 580 MW, hydropower comprises 220 MW (ADB, 2008). The Sirinumu dam, which was officially opened in 1963, provides water for consumption and electricity for Port Moresby (NLA, 1963). The Yonki dam, a 60 m high dam of zoned earth-fill construction, is a hydroelectricity dam located on the Ramu river in Eastern Highlands Province. In 2009, total dam capacity has been estimated at 665 million m3.