Experimental study of air curtains blocking saltwater intrusion under estuary dynamic conditions

Abstract

The saltwater intrusion seriously threatens the water supply security of estuaries, while the existing salty blocking measures (e.g., gates and dams) are rude and the dynamic mechanism is not fully considered. In order to investigate countermeasures to reduce the risk of the saltwater intrusion, as well as enrichment blocking methods, in this paper, the salt-inhibiting properties of air curtain under tidal action was investigated based on a long-distance physical flume with dual tidal-salinity control capability. Experimental results indicate that air curtains significantly diminish distance of saltwater into estuaries. The bubble plumes, on the one hand, promote vertical mixing, elevating high-salinity water from the depths to the surface, thereby disrupting the vertical circulation structure of salt wedge. On the other hand, the energy dissipation and barrier effect produced by bubble bursting can significantly reduce the momentum of the invading saltwater. Meanwhile, the research emphasizes that the salt intrusion length is negatively correlated with the airflow discharge, whereas the salty-blocking effect prefer better of the weakly-mixed estuary than the strongly-mixed. Most importantly, the air curtain mixing coefficient ka were proposed at the first time to quantify the salty blocking effect. The mixing coefficient ka is the function of airflow discharge Qa and tidal current ut, demonstrating a direct proportionality to Qa and ut−1. Moreover, a quantitative relationship between ka and Qa/ut was obtained from experimental results. The research results would help inform the flexible salt-inhibiting measures of estuarine air curtain.