Salinity Forecasting on Raw Water for Water Supply in the Chao Phraya River

Abstract

Frequent saltwater intrusions in the Chao Phraya River have had an impact on water supply to the residents of Bangkok and nearby areas. Although relocation of the raw water station is a long-term solution, it requires a large amount of time and investment. At present, knowing in advance when an intrusion occurs will support the waterworks authority in their operations. Here, we propose a method to forecast the salinity at the raw water pumping station from 24 h up to 120 h in advance. Each of the predictor variables has a physical impact on salinity. We explore a number of model candidates based on two common fitting methods: multiple linear regression and the artificial neural network. During model development, we found that the model behaved differently when the water level was high than when the water level was low (water level is measured at a point 164km upstream of the raw water pumping station); therefore, we propose a novel multilevel model approach that combines different sub-models, each of which is suitable for a particular water level. The models have been trained and selected through cross-validation, and tested on real data. According to the test results, the salinity can be forecasted with an RMSE of 0.054g/lat a forecast period of 24 h and up to 0.107g/lat a forecast period of 120 h.

Changes in slow-onset climate events in Thailand

“…Our results are consistent with the observed situation in early 2020 when salt water climbed up the Chao Phraya River and reached the city's main municipal water intake, threatening the quality of the raw water supply [57,[66][67]. Seawater intrusions have frequently occurred in the Gulf of Thailand due to the low-lying area's proximity to the sea and the combined effects of sea level rise, deep well pumping and land subsidence [57,[66][67]. In addition to seawater intrusion in the major rivers, the underlying multi-layered Bangkok aquifer system has been growing saltier from seawater intrusion for many years [68][69][70].…”

“…Salinity at the Samlae pumping station of water supply for Bangkok and its surrounding provinces, which is approximately 96 km upstream of the mouth of the Chao Phraya River, exhibits an increasing trend with statistical significance at a 95% confidence level. Our results are consistent with the observed situation in early 2020 when salt water climbed up the Chao Phraya River and reached the city's main municipal water intake, threatening the quality of the raw water supply [57,[66][67]. Seawater intrusions have frequently occurred in the Gulf of Thailand due to the low-lying area's proximity to the sea and the combined effects of sea level rise, deep well pumping and land subsidence [57,[66][67].…”

“…This problem remains a major concern for Bangkok, the Kingdom's capital, as a large amount of the daily water supply which is around 4.55 Mm 3 with groundwater amounting to slightly over 11,000 m 3 has to provide for a population of approximately 13 million [105]. Saline water supply can also cause long-term health effects on people who regularly consume it [66][67]104].…”