人为扰动下河流复氧激增现象及机制分析

Reaeration surging phenomenon with artificial disturbance and theimplication for the impact of turbulent kinetic energy in river

为探究河流复氧规律及其机制,研制出改变河道局部水流流速的深控型水平推流曝气装置,并使用该装置在天津市外环河中进行原位试验,探究人为扰动对河流复氧系数的影响.试验结果表明,装置工作时纵向流速提高至40cm/s,最大增幅22倍;水体溶解氧浓度提高0.6~1.7mg/L,约10%.研究发现,经典的Owens等5组河流复氧系数经验公式均低估了扰动下的复氧系数,试验均值约为49.5d-1,是理论值的10~100倍,即河流复氧在人为扰动下发生激增现象.分析成因表明,湍流动能与河流复氧系数显著正相关,区别于自然流动,人为扰动提升了水体纵向和垂向湍流动能,加速了中下层水体溶解氧扩散,提高了复氧率,进而发生了复氧激增现象.研究成果为提升城市河流水质的水力学方法提供了科学依据.

Nowadays,the disturbance aeration device widely used in the ecological restoration of rivers and lakes.However,it is still not clear how the artificial stir influences the reaeration in rivers.To address this issue,we developed a deep-controlled horizontal push-flow aeration device,which can change the flow velocity of the local water flow in the river channel.In order to investigate the effects of artificial disturbance on the reaeration coefficient of the river,the device was used to conduct an in-situ experiment in the Waihuan river of Tianjin.The results showed that the water velocity increased to 40cm/s and 22 times higher than the original velocity when the device operated.Similarly,the dissolved oxygen concentration increased by 0.6~1.7mg/L(10%).Moreover,five groups of classical rivers reaeration coefficient empirical formulae underestimated the reaeration coefficients.It can be called the river reaeration surging phenomenon under artificial disturbance.There was a significantly positive relationship between the turbulence kinetic energy and reaeration coefficient in the river.Compared with the natural flow,the artificial disturbance enhanced the vertical and longitudinal turbulence kinetic energy and accelerated the dissolved oxygen diffusion in the middle and bottom water,respectively.The increase of the turbulence kinetic energy increased reaeration rate and contributed to reaeration surge.This study provides a scientific basis for the hydraulic methods of improving water quality in urban rivers.