Field experiment on water circulation performance of continuous diffusion-type air-lifting tower in reservoir (Measurement of deep- and shallow-layer flow using equipment of different sizes)

Abstract

To enhance the water quality in stratified reservoirs in summer, a novel air-lifting tower for destratifying water has been deployed since the 2010s in Japan. Compared to conventional water mixing systems that intermittently diffuse air into water bodies to induce water circulation, this air-lifting tower is equipped with nozzles that diffuse air continuously. Simulations using the newly developed system have shown that it is more efficient than conventional systems for increasing the flow rate of water. However, despite the potential benefits of the new system, empirical evaluations are scarce because of limited implementation in reservoirs. Here we present the results of field experiments designed to evaluate the performance of new air-lifting towers that were installed in 2012 as upgrades to conventional air-lifting systems in Yamaguchi Regulating Reservoir in Fukuoka Prefecture. The experiment utilized four air-lifting towers with different diameters (0.5 m, 1.0 m) and lengths (4.0 m, 8.0 m), and water flow velocity was measured at their bottom intakes and near the water surface where the emitted bubble plumes ascend. The data facilitated an estimation of the volume of water flowing into the bottom intakes and rising up to the reservoir surface. Finally, the data were compared with predictions of a previous study, and it was found that they generally corroborated each other.