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Numerical Simulation of the Water Temperature Distribution in a Tropical Large, Deep Reservoir on the Lancang River

Author(s): Shibo Guo, Dejun Zhu, Yongcan Chen

Linked Author(s): Shibo Guo, Dejun Zhu, Yongcan Chen

Keywords: The Nuozhadu Reservoir; Lancang-Mekong river; Water temperature; Delft3D;

Abstract: The thermal structure of a lake or reservoir can affect the surrounding environment, such as the meteorological and hydrological characteristics. In recent years, a series of reservoirs have been and are still being constructed along the Lancang-Mekong River. The Nuozhadu Reservoir (NZDR) is the largest reservoir on the middle-lower reach of the Lancang River. The NZDR was completed in 2014 and its impoundment started in 2011. The thermal structure in the reservoir and the possible influences on the downstream reaches of the river has been a great concern of researchers and stakeholders. A three-dimensional (3D) numerical model Delft3D was used to simulate the water temperature distribution of NZDR. Observed water temperature data in 2015 were used to calibrate and tune the parameters of the model. Then the results were analyzed and the analysis demonstrated that: (1) The thermal stratification exists all the year round in NZDR. (2) The surface simulated temperature in front of the dam varies between 18 ℃ and 30 ℃, and the peak temperature occurs in June, however, the peak temperature in the deep water occurs in October. (3) The daily average temperature of the surface water is higher than the daily average air temperature in most time of the year, meaning that the air absorbs energy from the water during these periods, which is different from general reservoirs and lakes in temperate or subtropical zones. (4) The solar radiation plays a dominant role in surface thermal energy transfer. Moreover, the solar radiation makes the water warmer and the air makes the water colder. (5) Obvious longitudinal (along the riverway) temperature gradient exists in upstream, then the isotherms are close to be horizontal near the dam. (6) There is a water temperature rising phenomenon (+4.2 ℃/100 km on the water surface) along the riverway in NZDR. The increase of the shortwave radiation absorption and the decrease in latitude are probably the reason of the temperature rising. (7) The annually average outflow temperature is warmer than that of the inflow by 1.2 ℃.

DOI: https://doi.org/10.3850/38WC092019-0715

Year: 2019

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