Tidal Tree by the Qiantang RiverJialei CaoAward: Top 100
School: the summit country day school This is an aerial photograph shot on the banks of the Qiantang River in Hangzhou, Zhejiang, China. The natural phenomenon demonstrated by the photo is called tidal tree, referring to the tidal grooves, a typical depositional landform, formed on the tidal flats. From the sky, the tidal grooves resemble towering trees growing on the beach. The formation of this landform is related to the erosive action of ebb currents on the tidal flats and needs to satisfy two conditions: first, the internal factor, which is the soft and easily eroded texture of the tidal flats, generally with abundant silt and sand; second, the external factor, which requires hydraulic action. Tidal trees usually grow in association with tidal movements, as the rising and falling tides bring in and wash away sediment. Day in and day out, the continuously eroded tidal grooves become deeper and longer. Tidal trees guard the tidal flat ecosystem. They can sustain biodiversity and provide abundant nutrients, food, and safe shelter for organisms, serving as a habitat for numerous species. Additionally, tidal trees have the ability to degrade pollutants. When heavy metal pollutants flow into the tidal grooves, the salinity changes in the water cause coagulation, resulting in the combination and settling of pollutants with suspended particles. As a passage for the ebb and flow of tides between the sea and the land, tidal trees provide favorable conditions for drainage and tidal intake in coastal areas, reducing the risk of coastal flooding. 
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