Water Discharge and Total Suspended Sediment Dynamic in the Lower Mekong River at Kratie and Chroy Changvar
Figure 2 shows the hydrographs of the daily water discharge and observed total suspended sediment concentrations (TSS) at Kratie from 1995 to 2018 and Chroy Changvar from 1993 to 2017. The daily water discharge clearly reflects the annual dry and rainy seasons, with low flows in March and April (down to approximately 2,000 m3/s), followed by onset of the rainy season and increased discharges in May, and high flows in August and September (up to approximately 30,000 m3/s). At Kratie, the maximum discharge reached 58,205 m3/s in the rainy season of 1996 while the minimum discharge was 1,073 m3/s in the dry season of 1995. At Chroy Changvar station, maximum discharge reached 40,556 m3/s in the rainy season of 2014, while minimum lowest discharge was 405 m3/s in the dry season of 1995.
We calculated descriptive statistics such as minimum, maximum, mean, and standard deviation to show tendency and variation of water quality parameters to illustrate the temporal distribution of important basic water quality parameters and for highlighting the specific characteristics. Additionally, we calculated skewness and kurtosis to determine if the data were skewed with positive or negative tails, and to determine the peakedness of the distributions, respectively. The summary statistics of TSS concentrations from 1993-2017 at Kratie and Chroy Changvar are summarized in Table 4 . Between June and October, water in the Mekong River was opaque, with TSS concentrations from 90 to 200 mg/l as it carried sediments derived from erosion across the land surface. On the falling limb beginning in December, the TSS concentration drop to less than 20 mg/l on average. Figure 3illustrated the rating curve of observing water discharge and daily water discharge and observed total suspended sediment concentrations (TSS) at Kratie and Chroy Changvar station (1993 to 2017). Discharge and TSS concentrations showed significant statistical relations, with R2=0.53 for Kratie station and R2=0.65 for Chroy Changvar.