Water Discharge and Total Suspended Sediment Data
We generated daily water discharges at the three sites using rating curves and water level data provided by the Cambodian Ministry of Water Resources and Meteorology (MOWRAM) for the period 1993 to 2018. We obtained sediment data from MOWRAM under the Mekong River Commission framework: Water Quality Monitoring Network (WQMN). Total suspended sediment (TSS) concentration was obtained from the water quality sampling conducted on a monthly basis by MOWRAM from 1995 to 2018 at Kratie station and 1993 to 2017 at Chroy Changvar station. For Tonle Sap River, the monthly basis water sampling (once every month) also carried out from 1995 to 2018. Table 1 summarizes the data (TSS and water discharge) coverage period and number of sampling used in this study. In WQMN database, the TSS samples were collected at 0.3 m below the water surface in the middle of the mainstem cross-section at each station. The samples were at the designated laboratories by MRC and recommended analytical method for TSS analysis (2540-D-TSS-SM) (Kongmeng & Larsen, 2016). The reader should bear in mind that these were not depth-integrated samples, but single, near-surface samples from the approximate mid-point of the river. To the extent that the suspended sediments in the river are well-mixed, the samples may be representative of true loads, but if concentrations are heterogeneous in the vertical columns or across the channel, the measured TSS may not be representative of the average sediment concentration channel-wide, and may under-represent suspended sand especially, as sand concentrations would tend to greater near the bed. Note that since we analyzed flow and sediment records based on the hydrological year, our period of record analysed (by hydrological year) is one year shorter than period of available data expressed in calendar years (i.e. if the calendar year is 1995-2018, thus the study expressed as hydrological year 1995-2017).
Table 1 : Data coverage period and the number of Total suspended sediment (TSS) sampling and water discharge data used in the study.