Modeling Effects of Floating Curtain Weirs and Controlling Algal Blooms in a Subtropical Reservoir of China

Ranojit Kumar Dutta,Baishakhi Das,Defu Liu,Jun Ma

doi:10.12691/ajwr-7-2-1

Abstract

Algal blooms occur frequently in Xiangxi Bay (XXB), which is one of the largest tributaries of the Three Gorges Reservoir (TGR). Floating curtain weirs (FCWs) are hydraulic structures that act as a barrier to divert density currents and diffuse heat across the width of the water body. Numerical modeling of FCWs is become a widely accepted method for controlling algal blooms. A laterally averaged two-dimensional hydrodynamic and water quality model (CE-QUAL-W2) was used to simulate the effects of FCWs, including those on water temperature, hydrodynamics and chlorophyll-a concentrations, for XXB. The developed model was calibrated using data collected in XXB from January to December 2010. The results indicated that the maximum chlorophyll-a concentrations observed were 74-154 mg/m3 at the XX09, XX06 and XX01 sampling sites. The performance of the FCWs suggests that the overall chlorophyll-a concentrations are markedly reduced by more than 85% as a function of the FCW heights and locations. Seasonally, an algal bloom reduction rate of more than 62% was observed in the summer. FCWs with heights of 3, 5, and 7 m reduced algal blooms by up to 99% at XX09 during March 26-28, April 24-27, July 18-26, August 5-20, and 23-28, and September 3-8 and 12-16, respectively. Therefore, the proposed FCWs can reduce algal blooms and improve water quality to save domestic water and aquatic ecosystems in XXB.

Highlights

Algal blooms occur seasonally in XXB of the Three Gorges Reservoir (TGR)
The maximum chlorophyll-a concentrations were 74-154 mg/m3 according to the scenario with no Floating curtain weirs (FCWs) at XX09, XX06 and XX01 from July 11 to August 9, 2010
FCWs were installed at three different upstream, midstream and downstream corresponding to XX09, XX06 and XX01 in XXB of the TGR, respectively

Summary

Introduction

Algal blooms occur seasonally in XXB of the Three Gorges Reservoir (TGR). Geographically, the TGR is located in a subtropical monsoon climate region where the summer is warmer and wet and the winter is cooler and dry [1]. Long-term data show that more severe algal blooms occur at midstream than upstream and downstream in XXB [1,4,10]. Density currents are affected by the upstream inflow and separate into two paths over the surface as overflows (warm water float) and under the bottom as an underflow (cold water underneath) in XXB [11]. Density currents intrude into XXB from the mainstream of the Yangtze River (YR) through the surface, middle and bottom as overflows, interflows and underflows [1,4]. The cold inflow submerges to the bottom as an underflow, which creates differences in the density between the surface and bottom. The upstream inflow and downstream intrusive density current interact at midstream to cause severe algal blooms at midstream

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