Author(s): Naito Yuta, Umeda Makoto, Tetsuya Shintani
Linked Author(s): Tetsuya Shintani
Keywords: Reservoir; Stratified Flow; Flow Structure; Thermocline; Velocity;
Abstract: Prolonged discharge of high turbidity water to the downstream of reservoirs is an environmental problem that has long been unsolved due to the function of reservoirs of storing water for flood control. It is, however, necessary to take possible measures to reduce high turbidity in downstream rivers. For that purpose, field observation and numerical simulation on thermal stratification and water flow were conducted in a large reservoir.
The numerical model used in this study is Fantom 3-D, which is an environmental hydrodynamic simulator for lakes, reservoirs. The model was applied to Isawa Dam Reservoir, located in the Kitakami River System in the northeast part of Japan Main Island. Water flow condition was first measured in the reservoir prior to simulation in this study. The measurement was done from the end of August through September, 2016. Middle scale flood that did not destroy the stratification occurred in the first half of the measurement period, while in the latter half of the measurement, initiation of mixing regime that might lead to whole circulation was observed. The results of the simulation were not able to express the layered flow structure revealed in the measurement, but the flow pattern of horizontal velocity induced by the wind observed in the first half of the measurement period of the epilimnion of the reservoir is able to reproduce roughly. Distributions of vertical velocity and eddy viscosity that seem to correspond to the surface mixing which seen in the second half of the measurement period were identified.