One of Thailand's most important rivers has been prone to saltwater intrusions because of natural occurrences and human influences, affecting the well-being of surrounding ecosystems and cities.
What's happening?
According to a study published last January, Thailand's Chao Phraya estuary has experienced several saltwater flooding events, which have increased the salinity of the water and the duration of contamination.
Though saltwater inundation is affected by estuary length, width, depth, and meandering, the river's discharge and tidal range, winds, and tropical storms, human activity has exacerbated the issue.
A warming planet, rising sea levels, and water regulation and abstraction through sand mining and the construction of irrigation canals, navigation canals, gates, and dams have allowed tidal waves to move further upstream and increase saltwater intrusion.
The researchers collected information on water level, salinity, river discharge, and wind from multiple spots along the Chao Phraya Estuary over 500 days from October 2020 to February 2022 through public sources and a three-dimensional hydrodynamic model.
The data showed that water intake at Bangkok's Metropolitan Waterworks Authority 98 kilometers (nearly 61 miles) from the river's mouth showed that "salt intrusion contaminated the municipal water with salinity higher than 0.25 [practical salinity units]," which is the standard for drinking water, from December 2020 to March 2021 and again in June 2021.
Why is the saltwater flooding concerning?
According to the researchers, "severe saltwater intrusion will affect people's health, contaminate soil … cause crop harvest reduction, and economic loss on a wide scale." Furthermore, "saltwater intrusion can change the species abundance and diversity of terrestrial and aquatic communities, affecting the estuary's function and services."
The Chao Phraya is the nation's largest river and one of the largest rivers in Southeast Asia. It's a freshwater source for agricultural and industrial areas and cities like Bangkok, which has a population of over 14 million people.
It's also crucial for rice production — and, therefore, Thailand's economy — as the country is sixth in global rice production,
As such, demand for water has been inversely proportional to the Chao Phraya Estuary's quality, and this issue will continue to worsen with increasing sea surface temperatures and stronger El Niños.
Similar instances of saltwater intrusion have taken place in Vietnam and Brazil.
What's being done to help?
The researchers called for the improvement of freshwater allocation by limiting its usage in the irrigation and city sectors and increasing freshwater input into the Chao Phraya by diverging it from other catchments.
They also mentioned the need for accurate river discharge measurements, as they "effectively manage the saltwater intrusion problem because the saltwater intrusion in the CPE is very sensitive to freshwater discharge."
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