Saltwater intrusion in Chao Phraya Estuary: A long, narrow and meandering partially mixed estuary influenced by water regulation and abstraction

Abstract

Study area: The Chao Phraya Estuary (CPE) (100° 28'−100° 36'E, 13° 30'−14° 15'N) in the central part of Thailand. Study focus: To systematically study characters of the CPE, saltwater intrusion and its responses to natural and water regulation and abstraction using high resolution 3D hydrodynamic model with along-the-river measurements. New hydrological insights for the region: Findings show that: (i) the CPE is a partially mixed estuary regulated by the tide, river discharge, local and remote winds, and seasonal sea level that is substantially influenced by the Asian-Australian monsoon and human factors. (ii) Low freshwater discharge, prevailing down-estuary winds, and the highest annual sea level are the natural causes for the enhancement of estuarine circulation and the greatest saltwater intrusion distance, which both occur in January. (iii) Geometry of the CPE (long, narrow and meandering) enhances the tidal wave energy dissipation through horizontal turbulence and riverbank roughness which should be considered when modelling any similar estuary elsewhere. (iv) Water regulation and abstraction are likely to be responsible for severe intrusion events during 2020 and 2021, which adversely affected more than 14 million people in and around Bangkok. The freshwater discharge rate and saltwater intrusion distance from the river mouth have a negative relation (R = - 0.72, p-value = 0). Improvement of freshwater allocation within the river basin are primary ways to effectively manage the saltwater intrusion problem.

Keywords

• Partially mixed estuary
• Hydrodynamics
• Monsoons
• Freshwater abstraction
• Numerical model
• Sidewall roughness