Flood Pulse and Water Level

This chapter evaluates the flood-induced water level change in Tonle Sap Lake (TSL) and the Tonle Sap River (TSR) based on the long-term record of water levels for 15 years from 1998 to 2013. The water level was monitored at Kampong Luong (KL), located in TSL, Prek Kdam (PK) in TSR, and Phnom Penh Port (PPP), at the intersection between Mekong River (MR) and TSR. The water levels at the three stations periodically fluctuate with an approximately annual cycle. The water level (surface altitude) is in the order of PPP > PK > KL during wet seasons and KL > PK > PPP during dry seasons. The reverse flow occurs mainly from May to October, and its duration ranged from 80 to 120 days at PPP and from 110 to 150 days at PK. In both the long-term (i.e., annual cycle) and local rainfall-derived short-term variations, the water level at PPP was correlated with those at PK and KL. During the reverse flow, the short-term variation of the water level is weakened in TSL because of the widened water surface in the lake. The long-term trend revealed that the average water levels at TSL and TSR decreased for 20 years from 1999 to 2018, which is caused by the reduction in the discharge in MR and the reverse flow in TSR.