Hydrology and Earth System Sciences www.hydrol-earth-syst-sci.net 1027-5606 1607-7938 10 5 2006 10.5194/hess-10-743-2006 http://www.hydrol-earth-syst-sci.net/10/743/2006/ http://www.hydrol-earth-syst-sci.net/10/743/2006/hess-10-743-2006.html http://www.hydrol-earth-syst-sci.net/10/743/2006/hess-10-743-2006.pdf 743 754 2006-10-16 Salt intrusion in multi-channel estuaries: a case study in the Mekong Delta, Vietnam A. D. Nguyen d.nguyen@unesco-ihe.org H. H.  Savenije Department of Management and Institutions, UNESCO-IHE Institute for Water Education, 7 Westvest, P.O. Box 3015, 2601 DA Delft, The Netherlands Water Resources Section, Faculty of Civil Engineering and Applied Geosciences, Delft University of Technology, Stevinweg 1, P.O. Box 5048, 2600 GA Delft, The Netherlands There is a well-tested theory for the computation of salt intrusion in alluvial estuaries that is fully analytical and predictive. The theory uses analytical equations to predict the mixing behaviour of the estuary based on measurable quantities, such as channel topography, river discharge and tidal characteristics. It 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 2000 m³/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 has been expanded to cater for tidal damping. Subsequently the model has been validated with observations made at fixed locations over the years 1998 and 1999. Finally it has been tested whether the Mekong calibration fits the overall predictive equations derived in other estuaries. The test has been successful and led to a slight adjustment of the predictive equation to cater for estuaries that experience a sloping bottom. Dyer, K. R.: "Estuaries, A Physical Introduction", second ed. John Wiley, London, 195 pp, 1997. Nguyen, A. N. and Nguyen, V. L.: Salt water intrusion disaster in Vietnam. UNDP Project No VIE/97/002, HCM City, Vietnam (in Vietnamese and English), 1999. Savenije, H. H. G.: A one-dimensional model for salinity intrusion in alluvial estuaries, J. Hydrol., 85, 87–109, 1986. Savenije, H. H. G.: Salt intrusion model for high-water slack, low-water slack and mean tide on spreadsheet, J. Hydrol., 107, 9–18, 1989. Savenije, H. H. G.: Rapid Assessment Technique for Salt intrusion in alluvial estuaries, Ph.D. thesis, IHE report series, No. 27, International Institute for Infrastructural, Hydraulic and Environmental Engineering, Delft, The Netherlands, 1992. Savenije, H. H. G.: Predictive model for salt intrusion in estuaries, J. Hydrol., 148, 203–218, 1993. Savenije, H. H. G.: A simple analytical expression to describe tidal damping and amplification, J. Hydrol., 243, 205–215, 2001. Savenije, H. H. G.: Salinity and Tides in Alluvial Estuaries, Elsevier, Amsterdam, 197pp, 2005. Savenije, H. H. G. and Veling, E. J. M.: Relation between tidal damping and wave celerity in estuaries, J. Geophys. Res., 110, C04007, 1–10, 2005. Van der Burgh, P.: Ontwikkeling van een methode voor het voorspellen van zoutverdelingen in estuaria, kanalen en zeeen, Rijkwaterstaat Rapport 10-72 (in Dutch), 1972.