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

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/m 3 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,

Application of 2D Hydrodynamic Model for the Assessment of the Influencing Factor in Xiangxi Bay of the Three Gorges Reservoir, China

“…XXB is located (from 110°25′E to 111°06″E and from 30°57′N to 31°34′N) in Hubei Province, China. The bay has a watershed area of 3095 km 2 and an annual average ow of 47.4 m 3 /s [1,2,3,4]. Eleven eld stations were considered for the model developed from upstream to downstream.…”

“…A computational grid of XXB was developed based on the bathymetric and geometric data. The XXB was represented by 64 longitudinal segments, each 500 m in length, and 109 vertical layers, each 1 m thick [1,4]. CE-QUAL-W2 has several coe cients that can be adjusted in the calibration process [17,18,19,20,21].…”

“…1a). The Three Gorges Project (TGP) has created substantial social and economic bene ts, such as power generation, ood control, river navigation, drought prevention and freshwater impoundment in central China [1,2,3,4]. However, the aquatic environment of the area has signi cantly changed since impoundment (2003) [1,2,3,5].…”

“…Additionally, density currents are in uenced by the thermal strati cation of the reservoir [2,8,9,10,15]. Analyses of long-term data records suggest that algal blooms in the tributaries of TGR are sensitive to changes in thermal strati cation, hydrodynamics and nutrient loads [1,4,7]. Based on long-term eld observations, Ji et al…”

“…Je et al (2010) also noted that the water in the TGR mainstream owed backward into XXB at different plunging depths due to the water temperature differences between the TGR mainstream and XXB. Density currents are also affected by upstream in ows into XXB and intrusion ows from the TGR mainstream and these currents affect the algal blooms and aquatic ecosystems in XXB [1,2,3,4]. Density currents exist below the ambient water level and form different ows, such as over ows, inter ows and under ows [8,11,12].…”