岸线码头密度对河道水动力和污染物输移影响分析——以武汉河段为例

Analysis of the Effects of Varying Density in Wharf Groups on River Hydrodynamics and Pollutant Transport:A Case Study in Wuhan Reach

为研究岸线码头密度对河流水动力变化及污染物输移的影响,以武汉河段为例,基于Mike21模型建立了适用于该河段的平面二维水动力-水质模型,计算了长为9.6 km的岸线范围内布置不同密度码头群后引起的附近区域内水位、流速变化以及突发水污染事故后的自净能力变化,从空间差异性、最大变幅等角度对比了三者的差异,并归纳了码头密度与水动力条件、污染物浓度变幅之间的关系。结果表明:(1)随着码头密度增加,工程区上游水位变化较流速更敏感,工程区及下游局部位置水位变幅较小,而流速变化较为敏感,表现为前沿主流区流速增大,近岸区流速减小;当码头密度大于1.25~2.5座/km的临界范围后,水动力条件随码头密度的变幅逐渐减缓。(2)修建码头后,受水动力变化影响,工程区河段上游污染物浓度变化呈"峰前减、峰后增",但工程区下游呈"峰前增、峰后减"的特征;工程区间内表现为主流区浓度增大、近岸带浓度减小、高浓度滞留时间总体增加的变化特点。(3)受码头工程群影响,无论是区间整体上,还是局部范围内,污染物浓度相对水动力条件变幅更大,对河段内水源地的取水可能造成不利影响。以上认识对于河流岸线开发利用规模选取和效应评估具有参考意义。

A 2 D hydrodynamic and water quality model is established on the basis of a MIKE 21 model to examine the influences of wharf density on river hydrodynamics and pollutant transport.The water level,velocity,and pollutant concentration of the Wuhan reach caused by varying density in the wharf groups within the 9.6 km bank line are calculated.The differences among the three variables are compared from the perspective of spatial difference.Finally,conclusions are drawn regarding maximum variation and the relationship among wharf density,hydrodynamics,and pollutant concentration variation.The following results are presented.(1)The change in the upstream water level of the project area as the number of wharfs increases is more sensitive than that of flow velocity.The change in the water level of the project area and the local location downstream is smaller.Meanwhile,the change in flow velocity is more sensitive,indicating that flow velocity in the mainstream area of the front increases and that in the nearshore area decreases.When wharf density is greater than the critical range of 1.25-2.5 units/km,hydrodynamics slows down gradually with a change in wharf density.(2)After wharf construction,the pollutant concentration change upstream of the project area exhibits the characteristics of"decrease before peak and increase after peak"due to the change in hydrodynamics.By contrast,the region downstream of the project area exhibits the characteristics of"increase before peak and decrease after peak."In the project area,concentration increases in the mainstream zone and decreases in the nearshore zone.An overall increase occurs in high-concentration detention time.(3)Pollutant concentration,which is affected by wharf groups,whether in the entire or part of the section,changes more than hydrodynamics.This condition may have a negative effect on the water intake of the water source in the reach.The aforementioned knowledge has reference value for selecting the scale of development,utilizing river bank lines,and evaluating the effect of bank lines.