2.2. Tonle Sap River System

2.2.1. Introduction

The Tonle Sap Great Lake lies in the centre floodplain of Cambodia and is connected to the Mekong River at Chakdomuk (the four conjunctions in front of the Royal Palace) by the Tonle Sap River, which is approximately 120 km long. The Tonle Sap Great Lake is the largest permanent freshwater lake in Southeast Asia. The Tonle Sap River is the connection between the Tonle Sap Great Lake and the Mekong River.

The total catchment of the Tonle Sap Great Lake is 67,600 km² (Mekong River Commission Secretariat, 1993). The Tonle Sap Great Lake has several input rivers, the most important being the Tonle Sap River during the rainy season, which contribute to 62 percent of the total water supply. Other major rivers are the Stung Sen, Stung Sreng, Stung Pursat, Stung Sisophon, Stung Mongkul Borey, and Stung Sâng Kae. The rivers on the watershed area and direct rainfall on the lake contribute the remaining 38 percent (Mekong Secretariat, 1993). The Tonle Sap Great Lake and the Tonle Sap floodplain start in the western part of the country, continue to areas around the Tonle Sap Great Lake, and conjoin with Mekong River at Phnom Penh Municipality. This wetland covers an area of 2,500 km² in the dry season and about 13,500 km² in the rainy season.

The Mekong River Commission Secretariat (1993) reports that hydrological data for the rivers of the Tonle Sap Great Lake watershed, the Tonle Sap River and the Mekong River are simultaneously available for only one hydrological year, that of 1962-63. Carbonnel and Guiscafré derived the following water balance for that period:

Table 1: Water balance of the Tonle Sap Great Lake Basin: Surface water availability

Because of the flat topography of the plain around the Tonle Sap Great Lake, variations in water volume stored in the lake result in large fluctuations of the flooded surface. Two national highways around the lake (national road No. 5 and No. 6) correspond approximately to the limit of the expansion of the lake water at its highest level. The storage volume of the lake estimated by Carbonnel and Guiscafré (1963) by the water balance method (which is not very accurate) is 72 x 109 m³. More accurate estimations of the lake storage capacity would require bathymetric and topographic surveys of the lake, which have never been carried out.

The Tonle Sap Great Lake provides water, soil, inundated forest, fish, waterfowl and diversity in supporting the livelihoods of much of the Cambodian population. It is the most productive lake in terms of fish and almost 60 to 70 percent of fish consumed throughout the country is derived from the Tonle Sap Great Lake. Varied flooded forests play many roles in sustaining biodiversity and the Tonle Sap ecosystem. Flooded forests are the breeding and feeding habitats for fish and other forms of wildlife. It is also considered one of the wetlands of international significance in Southeast Asia, in which many waterfowl, including a dozen of rare and endangered water birds such as the pelican, lesser adjutant, greater adjutant, etc. are found. Other wild animals such as snakes, turtles, crocodiles, wild pigs, monkeys, otters, and macaques are also found in the Tonle Sap Great Lake.

The importance of the Tonle Sap Great Lake goes far beyond the national boundary. Many species migrate back and forth within the Mekong-Tonle Sap floodplain. Therefore, Tonle Sap is an important part of the Mekong River ecosystem, the management of which requires cooperation and participation from the Mekong sub-regional countries.

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Table of contents > 2. River Basins > 2.2. Tonle Sap River System

2.2.1. Introduction

2.2.2. The World network of biosphere reserves

2.2.3. The Royal Decree

2.2.4. Tributaries of the Tonle Sap Great Lake

2.2.5. Detailed survey of surface water in the Tonle Sap Great Lake catchment