Abstract: Gravity currents exist widely in nature and engineering. In this study, a series of laboratory experiments were conducted to investigate lock-release gravity currents through vegetation patches into different ambient environments. The head position, front velocity and entrainment coefficient of gravity currents were analyzed by using the images acquired by a high-speed camera. The results show that the front velocity in linearly stratification environments is smaller than that in constant-density ambient. Both stratified environment and vegetation patches can inhibit the entrainment between gravity current and ambient water. As stratified environment and vegetation patches exist simultaneously, the mixing and entrainment of gravity currents are related to the ratio α of vegetation height to water depth. When α=0.43, the entrainment and mixing between gravity current and ambient water are the strongest. The particle image velocimetry (PIV) technique was applied to study the velocity and vorticity fields in detail. The results show that the stratification environment can restrain the development of the vorticity both at the upper and lower interfaces between current and ambient water. However, when α=0.20, i.e. some gravity currents climbs to the top of vegetation patches, the combined effects of the stratified water and the vegetation patch strengthen the vorticity near the top of vegetation patches.

Key words: gravity current, stratified water, vegetation patch, particle image velocimetry