Abstract:

A 2D 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.