Volume fluctuation and flow reversal
Tonle Sap Lake over the course of one year
Inflow starts in May/June with maximum rates of flow of around 10,000 m3/s by late August and ends in October/November, amplified by precipitation of the annual monsoon. In November the lake reaches its maximum size. The annual monsoon coincides to cease around this time of the year. As the Mekong river begins its minimum around this time of the year and its water level falls deeper than the inundated Tonle Sap lake, Tonle Sap river and surrounding wetlands, waters of the lake's basin now drains via the Tonle Sap river into the Mekong. As a result the Tonle Sap River (length around 115 km/71 mi) flows 6 months a year South-East (Mekong) to North-West (lake) and 6 month a year in the opposite direction. The mean annual reverse flow volume in the Tonle Sap is 30 km3 (7.2 cu mi), or about half of the maximum lake volume. A further 10% is estimated to enter the system by overland flow from the Mekong.[20][21] The Mekong branches off into several arms near Phnom Penh and reaches Vietnamese territory south of Koh Thom and Loek Daek districts of Kandal Province.
Inflow starts in May/June with maximum rates of flow of around 10,000 m3/s by late August and ends in October/November, amplified by precipitation of the annual monsoon. In November the lake reaches its maximum size. The annual monsoon coincides to cease around this time of the year. As the Mekong river begins its minimum around this time of the year and its water level falls deeper than the inundated Tonle Sap lake, Tonle Sap river and surrounding wetlands, waters of the lake's basin now drains via the Tonle Sap river into the Mekong. As a result the Tonle Sap River (length around 115 km/71 mi) flows 6 months a year South-East (Mekong) to North-West (lake) and 6 month a year in the opposite direction. The mean annual reverse flow volume in the Tonle Sap is 30 km3 (7.2 cu mi), or about half of the maximum lake volume. A further 10% is estimated to enter the system by overland flow from the Mekong.[20][21] The Mekong branches off into several arms near Phnom Penh and reaches Vietnamese territory south of Koh Thom and Loek Daek districts of Kandal Province.
There is extreme hydrodynamic complexity in both time and space and it becomes impossible to measure channel discharge. Water levels, not flow rates and volumes, determine the movement of water across the landscape.
