Three‐Dimensional Effects of Artificial Mixing in a Shallow Drinking‐Water Reservoir

Abstract

AbstractStudies that examine the effects of artificial mixing for water‐quality mitigation in lakes and reservoirs often view a water column with a one‐dimensional (1‐D) perspective (e.g., homogenized epilimnetic and hypolimnetic layers). Artificial mixing in natural water bodies, however, is inherently three dimensional (3‐D). Using a 3‐D approach experimentally and numerically, the present study visualizes thermal structure and analyzes constituent transport under the influence of artificial mixing in a shallow drinking‐water reservoir. The purpose is to improve the understanding of artificial mixing, which may help to better design and operate mixing systems. In this reservoir, a side‐stream supersaturation (SSS) hypolimnetic oxygenation system and an epilimnetic bubble‐plume mixing (EM) system were concurrently deployed in the deep region. The present study found that, while the mixing induced by the SSS system does not have a distinct 3‐D effect on the thermal structure, epilimnetic mixing by the EM system causes 3‐D heterogeneity. In the experiments, epilimnetic mixing deepened the lower metalimnetic boundary near the diffuser by about 1 m, with 55% reduction of the deepening rate at 120 m upstream of the diffuser. In a tracer study using a 3‐D hydrodynamic model, the operational flow rate of the EM system is found to be an important short‐term driver of constituent transport in the reservoir, whereas the duration of the EM system operation is the dominant long‐term driver. The results suggest that artificial mixing substantially alters both 3‐D thermal structure and constituent transport, and thus needs to be taken into account for reservoir management.