Discharge-salinity relationships in Modaomen waterway, Pearl River estuary

Abstract

There are many parameters determining salt intrusion in alluvial estuaries, including river discharge, channel shape, tidal forcing. In this paper, according to a well-tested theory for the calculation of salt intrusion in estuary regions, the salt intrusion length can be computed by the model that drives from this well-tested theory. There is an analytical method that presented for the salt intrusion in a funnel-shaped estuary. The method is tested against monitoring data from 6 stations during dry season in 2005 in the Modaomen water way. The average value of salt intrusion length to the point where the salinity on the cross section is 0.5‰ is 37.0 km. When the projects of the water transfer to meet the emergency stemming from salty tide put into effect, the salt intrusion length is decreased, which is 20.7 km on average. According to the length which is predicted by the model, we establish two optimal regression equations for the discharge-salt intrusion relationship at slack after flood tide during dry season (using the calculated length and measured length to discharge, respectively), one is an exponential regression equation, xL0 = 104.13 e-0.0007Q (R2=0.8276); the other is a power-law regression equation, xL0 = 106 Q-1.401 (R2=0.8007). Our results suggest that the salt intrusion length is dependent on the river discharge. The two regression equations used to determine discharge in the Modaomen water way which can explain river discharge-salt relationships, and offer a useful tool for predicting the relationships between estuarine salinity and river freshwater discharge.