Characterizing Density Flow Regimes of Three Rivers with Different Physicochemical Properties in a Run-Of-The-River Reservoir

Sewoong Chung,Soonju Yu,Ingu Ryu

doi:10.3390/w12030717

Sewoong Chung, Soonju Yu + Show 1 more

Open Access

https://doi.org/10.3390/w12030717

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Abstract

Inflow mixing affects the spatiotemporal heterogeneity of water quality in reservoirs. Reservoir water quality management requires accurate prediction of density flow regimes to understand the spatiotemporal distribution of dissolved and particulate nutrients and organics. This study aims to characterize the mixing and circulation of three rivers with different physicochemical properties in a run-of-the-river (ROR) reservoir, using high-frequency monitoring and three-dimensional (3D) hydrodynamic modeling. The Aquatic Ecosystem Model (AEM3D) was constructed for the reservoir and calibrated with high-frequency data obtained from May–June 2016, accurately reproducing the observed spatiotemporal variations of flow velocity, water temperature, and electrical conductivity (EC) in the reservoir. High-frequency data and 3D model results showed that mixing of the rivers in the ROR reservoir is governed by density flow regimes formed by influent water temperature differences. At the confluence, colder and warmer river influents formed underflows and surface buoyant overflows, respectively. The spatial arrangement of flow direction, water residence time, and EC concentration were largely controlled by the buoyancy-driven flow. Stagnant areas with long residence times corresponded with areas of observed algal blooms and hypoxia. High-frequency sensor technology, combined with 3D hydrodynamic modeling, is effective for understanding the complex flow regimes and associated water quality characteristics in ROR-type reservoirs.

Highlights

Human beings have created dams in running water to supply municipal, agricultural, and industrial water needs, and to produce electricity
The Aquatic Ecology Model 3D (AEM3D) model reproduced well the spatiotemporal variations of flow velocity, water temperature, and electrical conductivity (EC) observed in the reservoir, with acceptable error rates, and was used to analyze the mixing and circulation characteristics of the river flows into the reservoir
The spatiotemporal arrangement of the inflows and their mixing in the reservoir are largely controlled by the buoyancy force resulting from the water temperature difference in the North Han (NH)- and South Han (SH)-rivers

Summary

Introduction

Human beings have created dams in running water to supply municipal, agricultural, and industrial water needs, and to produce electricity. Water quality problems caused by dam construction include, but are not limited to, prolonged discharge of turbid water to downstream areas after flood events and during flushing events [4], eutrophication and over proliferation of algae due to the accumulation of nutrients and increased residence time, and the depletion of dissolved oxygen (DO) in the lower layers under thermal stratification [5,6]. These problems are complex in time and space, due to physical, chemical, and biological interactions.

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