Exploring Freshwater Regimes and Impact Factors in the Coastal Estuaries of the Vietnamese Mekong Delta

Abstract

Freshwater resources make an essential contribution to the livelihoods of millions of local people in the coastal estuaries of the Vietnamese Mekong Delta (VMD). However, coastal freshwaters currently face numerous threats, not least (i) changing tidal dynamics due to sea level rise and (ii) changes in river regimes due to dam construction upstream. This research explores the evolution of freshwater regimes in these coastal estuaries. Using process diagrams, freshwater distributions are mapped and analyzed. Application of statistical methods provides insight into freshwater flow cycles and variations in water regimes upstream at various measurement points within the estuaries. A previously calibrated and validated hydraulic model is used to simulate drought-year scenarios and spatial changes in freshwaters over time. Findings indicate decreasing river discharges in the flood season, but increasing discharges in the dry season, due to the impacts of hydropower dams. In addition, the driest months are shifting earlier. From this data, we derive rules of thumb regarding freshwater distributions in the coastal estuaries of the VMD. These relate to (i) the boundary beyond which freshwater is always found; (ii) the boundary where freshwater appears daily; (iii) the start of the freshwater season; (iii) the boundary where freshwater appears until February and until April; (iv) the end of the flood season; and (v) the number of days without freshwater per year. The trends discerned will help local freshwater users and decision makers formulate forward-looking, flexible strategies for freshwater exploitation, while also providing avenues for further research.

GRACE-Derived Time Lag of Mekong Estuarine Freshwater Transport in the Western South China Sea Validated by Isotopic Tracer Age

“…Driven by the southwest monsoon, the downstream area of the Mekong basin normally generates a flood pulse in summer, which contributes~84% of the annual total river discharge [30]. During wet and dry conditions, the Tonle Sap Lake in Cambodia and dam operations also help regulate the seasonal river flux along the main stream [31][32][33].…”

Assessing and Forecasting Saline Intrusion in the Vietnamese Mekong Delta Under the Impact of Upstream flow and Sea Level Rise

“…The saline intrusion in the VMD under the impacts of upstream flows, climate change and SLR has been presented in previous studies [5,6,[9][10][11][12][13][14]. They have indicated that the impacts of climate change, SLR and upstream flow changes increased the saline intrusion and negative impacts on water supply and agricultural products.…”

Statistical and Hydrological Evaluations of Water Dynamics in the Lower Sai Gon-Dong Nai River, Vietnam

“…Updated versions of the MK test (so-called Modified MK test) such as the variance correction [41,42], trend-free prewhitening [43], and the block bootstrap method (BBS) [44] are also widely used to eliminate the effect of autocorrelation in time series data. In particular, trend detection using the MK test has received high attention in recent decades [45][46][47][48]. In the SGDNrb, the MK and Modified MK trend determination methods have been and still are commonly being used in a number of studies on precipitation variability [49][50][51], and water levels [29,52].…”