Salt intrusion in multi-channel estuaries: a case study in the Mekong Delta, Vietnam

Abstract

Abstract. There is a well-tested theory for the computation of salt intrusion in alluvial estuaries that is fully analytical and predictable, in the sense that it has well-tested analytical equations to predict the mixing behaviour of the estuary based on measurable quantities, such as channel topography, river discharge and tidal characteristics. This theory has been described in a range of publications (Savenije, 1986, 1989, 1993) and a recent book (Savenije, 2005). This theory applies to single-channel topographies and estuaries that demonstrate moderate tidal damping. The Mekong delta is a multi-channel estuary where the tide is damped due to a relatively strong river discharge (in the order of 2000m/s), even during the dry season. As a result the Mekong is a strongly riverine estuary. This paper aims to test if the theory can be applied to such a riverine multi-channel estuary, and to see if possible adjustments or generalisations need to be made. The paper presents salt intrusion measurements that were done by moving boat in 2005, to which the salt intrusion model was calibrated. The theory was expanded to cater for tidal damping. Subsequently the model was validated with observations made at fixed locations over the years 1998 and 1999. Finally it was tested whether the Mekong calibration fits the overall predictive equations derived in other estuaries. The test was successful and led to a slight adjustment of the predictive equation to cater for estuaries that experience a sloping bottom.

Simulated Impacts of Climate Change on Current Farming Locations of Striped Catfish (Pangasianodon hypophthalmus; Sauvage) in the Mekong Delta, Vietnam

“…Nguyen and Savenije (2006) pointed that the high sediment transport capacity of the Mekong river and the lack of updated topographical data will affect the results of salinity models like ours. In addition, topographical changes are very difficult to predict given that future infrastructure changes are likely to influence water discharge and drainage.…”

“…To assess sea level rise and salinity intrusion in the Mekong Delta, researchers have begun using hydrological models and GIS data since the start of this century. Specifically, the VRSAP model was used by Wassmann et al (2004) to map the vulnerable rice production areas and by Nguyen and Savenije (2006) to predict the salinity distribution in the Mekong river branches using topography, tide, and river discharge data. Hoa et al (2007Hoa et al ( , 2008 used an integrated hydraulic model, HydroGis, in tracking the impact of sea level rise and flooding in general.…”

New Analytical Form of Salt Intrusion Model in Funnel Shaped Estuaries: Application to the Abashiri River

“…The geomorphologic equilibrium form of the estuarine channel exhibits an evolution of the cross-sectional area, width, and depth toward the sea 4), 6) . It is often found that the increase in geometric parameters approximates to an exponential function of the form:…”

Simulating Future Flows and Salinity Intrusion Using Combined One- and Two-Dimensional Hydrodynamic Modelling—The Case of Hau River, Vietnamese Mekong Delta

“…Considerable differences in the 4.0 PSU isohaline between this study and Smajgl et al [53] can be attributed to differences between the scenario setups and boundary conditions in the two studies. Nguyen and Savenije [32] tested analytical solutions of salinity simulation in the Mekong estuaries based on observed data in 2005 for the Co Chien, Cung Hau and Hau estuaries. The results showed that salinity intrusion distances from the river mouth were 41 km and 23 km for spring tide and neap tide during the dry season in 2005, respectively.…”

“…The average discharge in the dry season fluctuates greatly, from 1700 m 3 /s to 6000 m 3 /s between January and May, and leads to water shortages for irrigating about 1.5 million hectares of irrigated crops [27]. The Mekong Delta experiences two types of tidal regime, namely the semi-diurnal and diurnal tides, affecting the hydraulic condition in estuaries of the East and West seas, respectively [32]. The salinity intrusion in the VMD-and in all the river networks-is substantial in recent years, particularly during the dry season, during which about 2.1 million hectares in the Mekong Delta suffered from salinity intrusion [21,27].…”