2.1 The Mekong River System (Basin)

2.1.1 Introduction

The Mekong River Basin stretches about 4,500 km from the Tibetan Plateau to the South China Sea and comprises some 795,000 km², ranking it the 21st largest river basin worldwide. It incorporates the areas of six countries (Table１), including six broad hypsographic regions.

The Mekong River passes Cambodia about 480 km from the border with Lao PDR in the North and Viet Nam in the South, and it has an average width of about 1.5 km in the territory of Cambodia (See attached map of Cambodia and other MRC member countries in the lower Mekong River Basin.) It crosses Stung Treng and Kratie Provinces in the upper part of the country, Kampong Charm Province, Phnom Penh Municipality--the capital of Cambodia, and flows down towards Kandal Province to the South China Sea.

Table 1: Territory and water flow of the six Mekong River Basin countries
within the catchments

The mean annual discharge of the Mekong River is approximately 475 x 109 m³. China contributes 16 percent of the discharge and Myanmar two percent, with the remainder coming from the four countries in the lower basin (Table 2). About 55 percent of the water in the lower basin comes from the mountainous regions along the eastern rim of the basin, with Northeast Thailand contributing only 10 percent.

Table 2: Approximate distribution of Mekong River Basin’s water
resources by country

The Mekong River, flowing down to Cambodia from Lao PDR, has rapid flows and shallows as far as Kratie Province, and it is difficult to navigate, while from Kratie Province to Phnom Penh Municipality, the current flows moderately with a deep water depth and is suitable for navigation. The Mekong River joins the Tonle Sap River and then branches off the Bassac River, which can support the passage of 3,000- ton class vessels bound for ports overseas.Water quantities during the annual wet season amount to about twenty times as that of the dry season.

The average flow is 2,860 m³/s, equal to 18% of the average flow for the Mekong River Basin. The average annual discharge into Cambodia is more than 300 billion m³ and it is estimated that with contributions from the downstream tributaries, some 500 billion m³ is discharged into the South China Sea annually (FAO, 1994).

Table 3: Mekong River flow

Remarkably, the Cambodia Mekong River receives approximately 25 percent of its total water volume from Tibet and China, a further 50 percent from northeast Thailand and Lao PDR and 20 percent from northeast Cambodia and neighbouring parts of Lao PDR and Vietnam. The remaining ten percent is derived from the nine rivers that drain the waters of greater Cambodia into the Tonle Sap Great Lake. The rivers that flow from the coastal ranges flow south directly into the sea.

This river system passes through the alluvial plain, the centre of the major cultivated land for paddy rice and upland crops in Cambodia. It plays a major role in agriculture through the maintenance of soil moisture and utilization of Colmatage is affecgted by the inundation, not withstanding the insufficiencies of irrigation facilities. In addition, the river is the habitat of a variety of fish and other aquatic species with rich nutrients for their proper living conditions. It also supports domestic water and irrigation water supplies, and contributes an important transport medium.

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Table of contents > 2. River Basins > 2.1. The Mekong River System (Basin)

2.1.1. Introduction

2.1.2. Mekong River tributaries and Rainfall

2.1.3. Detailed survey of rainfall and surface water in the Mekong catchment

2.1.4. Water environment in the Mekong River systems