Saigon river's response to Typhoon Usagi

A good understanding of the hydrological cycle, and discharge in particular, in tidal rivers enables reliable forecasting and decision making by researchers and policy makers. We develop the work of Camenen et al. 2021 where the hydrological dynamics of the tidal
Saigon river are studied. The study proposes a low-cost technique to estimate tidally influenced river discharge based on high- frequency in-situ measurements. This technique estimates discharge based on a stage-fall-discharge rating curve (Camenen et al., 2017) which requires the estimation of the river’s slope. The application to the Saigon river as in Camenen et al. 2021 shows that its hydrological dynamics are ruled by a complex combination of factors. This technique pointed out a paradoxical behavior during typhoon
USAGI (Nov. 2018): despite the heavy rain and increased water levels in the river, the net water discharge decreased substantially (figure 9a, 9c). Furthermore, the tidal-averaged water levels presented a seasonal variability (figure 9b) compatible with the seasonality of the nearby Mekong river’s discharge. We propose an in-depth study of in-situ water level time series at several locations in the Saigon river and in the surrounding coastal area. The tidal signal obtained via harmonic analysis is extracted from the water level time series and the residual signal is then filtered using a low-pass filter as proposed in Trinh et al. 2020. This discriminates non-tidal fluctuations of water level and thus, permits the analysis of the propagation of the non-tidal signal between different locations.  Additionally, the same technique as in Camenen et al. 2021 is used to separate the factors influencing the water discharge using both the residual signal and the tidal signal. This permits a sensitivity analysis of the Saigon’s discharge to tides and to other factors such as storm surge or precipitation. We expect to better characterize the hydrological pattern of the Saigon river and disentangle the factors that influence its discharge as well as provide insights on tidal river interaction with an extreme event.