Modeling Effects of Bottom Curtain Weirs and Controlling Algal Blooms in Xiangxi Bay, Three Gorges Reservoir, China

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

doi:10.12691/ajwr-7-2-2

Abstract

A bottom curtain weir (BCW) is a hydraulic structure that acts as a barrier to the flow and diffusion of heat across the width of a water body. Algal blooms occur frequently in the largest tributary of Xiangxi Bay (XXB) of the Three Gorges Reservoir (TGR). A laterally averaged two-dimensional hydrodynamic and water quality model was used to simulate BCWs, including water temperature, hydrodynamics and chlorophyll-a concentrations, for XXB. The numerical models show that BCWs are a much more attractive, much less expensive and time-saving algal bloom controlling technique for subtropical reservoirs. The developed model was calibrated using data collected in XXB from January to December 2010. The maximum chlorophyll-a concentrations observed were 125-154 mg/m3 according to sampling sites such as XX09, XX06 and XX01. Overall chlorophyll-a concentrations were markedly reduced by 4-44% as a function of BCWs height and location. A seasonal algal bloom reduction rate of more than 37% was observed in summer. In some periods, such as May 27-31, June 2-4, June 16-18, August 16-18 and August 23-24, BCWs with heights of 3 m, 5 m and 7 m reduced algal blooms by up to 99% at XX09 and XX06 in XXB. Therefore, the proposed BCWs can reduce algal blooms and improve water quality to save domestic water and aquatic ecosystems in XXB of TGR.

Highlights

Density currents occur frequently over the year in XXB of the Three Gorges Reservoir (TGR)
bottom curtain weir (BCW) were installed at heights of 3 m, 5 m and 7 m at three parts of XXB, i.e., upstream, midstream and downstream corresponding to XX09, XX06 and XX01, respectively (Figure 2)
The upstream and midstream velocities varied more than the downstream velocity because the downslope bottom density currents are blocked by the BCWs with height of 3 m, 5 m and 7 m at XX09 and XX06 (Figure 2)

Summary

Introduction

Density currents occur frequently over the year in XXB of the Three Gorges Reservoir (TGR). Intrusive density currents are entering XXB from the mainstream Yangtze River (YR) of TGR along the surface, middle and bottom as overflow, interflow and underflow [1,2,3]. Floating curtain weirs have been used to control algal blooms in reservoirs such as the Terauchi Dam Reservoir in Japan, Daceheong Reservoir in Korea, and So-oak River in Korea [9,11,12,13,14]. We previously studied floating curtain weirs (FCWs) for controlling algal blooms in XXB subtropical reservoir. FCWs divert overflow density currents, whereas internal curtain weirs (ICWs) affect interflow and control algal blooms without changing underflow.

Objectives

Results

Discussion

Conclusion