Flow characteristics in curved open channel with partial suspended vegetation

Suspended vegetation in open channels such as natural river,lake,reservoir usually affect the flow structure,causing the change of the water environment,sediment transport,bed deformation.In order to study the water flow behavior in curved open channels under the influence of suspended vegetation,experiments were conducted in a Ushaped flume with 180°bend where the suspended vegetation substituted by cylindrical glass rods were partially placed.The particle image velocimeter(PIV)system was employed to measure the flow velocities of various cases with different vegetation arrangements and roots length.Comparison and analysis were conducted for measured data,such as water level,velocity,head loss,Reynolds stress,and turbulence kinetic energy(TKE)to obtain certain general rules of water flow in open curved channels with suspended vegetation.It can be found from the measured data that the water level and the head loss in the vegetation area are closely related to the arrangements of the suspended vegetation.Furthermore,the drag force of the vegetation can not only lead to smaller increments of longitudinal TKE above the vegetation tail than that below it,but also lead to the flow velocities in vegetation area much smaller than areas without vegetation.In addition,suspended vegetation weakens the vortex strength near the water surface and increases the vortex strength below the vegetation tail,and the flow velocity in the vegetation area has a close relationship with the suspended vegetation length in the water.Therefore,it can be concluded that the reasonable arrangements of suspended vegetation group in curved open channel can protect the concave bank from being scoured,and protect the convex bank from being deposited.

Optimized greenery configuration to mitigate urban heat:A decade systematic review

Urban vegetation is a nature-based solution for cooling cities.Under global warming and urban population growth,it is essential to optimize urban vegetation configuration in the urban area to bring maximum cooling benefit.This paper reviews 85 optimized urban vegetation configuration studies published from 2010 to 2020 to provide an insight into the most effective vegetation configuration for urban heat mitigation.Patterns and preferences in methods and the optimized greenery configurations are comprehensively analyzed.The results indicate that size,quantity,and layout of urban green space and the physiological characteristics and spatial arrangement of urban vegetation significantly influence their cooling effect.Additionally,two other research gaps were identified.First,more research needs to be done in southern hemisphere cities experiencing rapid urbanization and severe impacts of extreme weather.Second,a comprehensive method for quantifying interactions and cumulative effects of natural and artificial factors in the urban environment is required.Future study needs a holistic understanding of the interactive effects of vegetation spatial distribution on urban environment and climate for a more accurate analysis of optimal cooling greening layouts in large urban areas at multi-scales.