2020 Vol. 13, No. 2

Display Method:
Climate change and human activities have changed a number of characteristics of river flow in the Taihu Basin. Based on long-term time series of hydrological data from 1986 to 2015, we analyzed variability in precipitation, water stage, water diversion from the Yangtze River, and net inflow into Taihu Lake with the Mann-Kendall test. The non-stationary relationship between precipitation and water stage was first analyzed for the Taihu Basin and the Wuchengxiyu (WCXY) sub-region. The optimized regional and urban regulation schemes were explored to tackle high water stage problems through the hydrodynamic model. The results showed the following: (1) The highest, lowest, and average Taihu Lake water stages of all months had increasing trends. The total net inflow into Taihu Lake from the Huxi (HX) sub-region and the Wangting Sluice increased significantly. (2) The Taihu Lake water stage decreased much more slowly after 2002; it was steadier and higher after 2002. After the construction of Wuxi urban flood control projects, the average water stage of the inner city was 0.16 m to 0.40 m lower than that of suburbs in the flood season, leading to the transfer of flooding in inner cities to suburbs and increasing inflow from HX into Taihu Lake. (3) The regional optimized schemes were more satisfactory in not increasing the inner city flood control burden, thereby decreasing the average water stage by 0.04 m to 0.13 m, and the highest water stage by 0.04 m to 0.09 m for Taihu Lake and the sub-region in the flood season. Future flood control research should set the basin as the basic unit, and decreasing diversion and drainage lines along the Yangtze River can take an active role in flood control.
Urban flooding in Chittagong City usually occurs during the monsoon season and a rainwater harvesting (RWH) system can be used as a remedial measure. This study examines the feasibility of rain barrel RWH system at a distributed scale within an urbanized area located in the northwestern part of Chittagong City that experiences flash flooding on a regular basis. For flood modeling, the storm water management model (SWMM) was employed with rain barrel low-impact development (LID) as a flood reduction measure. The Hydrologic Engineering Center’s River Analysis System (HEC-RAS) inundation model was coupled with SWMM to observe the detailed and spatial extent of flood reduction. Compared to SWMM simulated floods, the simulated inundation depth using remote sensing data and the HEC-RAS showed a reasonable match, i.e., the correlation coefficients were found to be 0.70 and 0.98, respectively. Finally, using LID, i.e., RWH, a reduction of 28.66% could be achieved for reducing flood extent. Moreover, the study showed that 10% to 60% imperviousness of the subcatchment area can yield a monthly RWH potential of 0.04 to 0.45 m3 from a square meter of rooftop area. The model can be used for necessary decision making for flood reduction and to establish a distributed RWH system in the study area.
In our previous study, we prepared the granules by embedding artemisinin into alginate-chitosan using microcapsule technology. These
granules can release artemisinin sustainably and have a strong inhibitory effect on the growth of both single Microcystis aeruginosa and mixed
algae. To safely and effectively use artemisinin sustained-release granules to control algal blooms, the ecotoxicity was studied by assessing their
acute and chronic toxicity to Daphnia magna (D. magna) and Danio rerio (D. rerio), along with their antioxidant activities. The results showed
that the 48-h median effective concentration (EC50) of pure artemisinin to D. magna was 24.54 mg/L and the 96-h median lethal concentration
(LC50) of pure artemisinin to D. rerio was 68.08 mg/L. Both values were classified as intermediate toxicity according to the Organization for
Economic Co-operation and Development (OECD). The optimal algae inhibitory concentration of artemisinin sustained-release granules (1 g/L)
had low acute toxicity to both D. magna and D. rerio. The sustained-release granules had higher chronic toxicity to D. magna than to D. rerio.
Partial indices of D. magna were inhibited by granules when the concentrations were larger than 0.1 g/L. Low granule concentration had an
inductive effect on antioxidant enzyme activities in D. magna and D. rerio. With the increase of the exposure concentration and time, the enzyme
activity presented a trend of first increasing and then decreasing, and the overall changes were significant. The change trend and range of enzyme
activity indicated that the granules could cause serious oxidative stress to D. magna and D. rerio, and the changes were consistent with the results
of toxicity experimentation.
To achieve the greatest leaching efficiency, water movement must occur under unsaturated flow conditions. Accordingly, the water application intensity of irrigation must be chosen carefully. The aim of this study was to evaluate the impact of the water application intensity of micro-sprinkler irrigation on coastal saline soil with different salt contents. To achieve this objective, a laboratory experiment was conducted with three soil salinity treatments (2.26, 10.13, and 22.29 dS/m) and three water application intensity treatments (3.05, 5.19, and 7.23 mm/h). The results showed that the effect of soil salinity on soil water content, electrical conductivity, and pH was significant, and the effect of the water application intensity was insignificant. High soil water content was present in the 40–60 cm profile in all soil salinity treatments, and the content was higher in the medium and high water application intensity treatments than in the low-intensity treatment. Significant salt leaching occurred in all treatments, and the effect was stronger in the high soil salinity treatment and medium water application intensity treatment. In the medium and high soil salinity treatments, pH exhibited a decreasing trend, with no trend change in the low soil salinity treatment, and the pH value was higher in the medium water application intensity treatment than in the other two treatments. These results indicated that the three intensities evaluated had no statistically different effect on the electrical conductivity of saturated soil-paste extracts (EC) in the upper 20 cm of the soil profile, and it would be better to maintain a lower value of the water application intensity.
The Three Gorges Project (TGP) has changed the flow-sediment process in the middle Yangtze River. For navigation purposes, there is an urgent need to study the changes of the river regime over a long-term period and the shoal-channel evolution over different seasons since the completion of the TGP. Based on analysis of the measured data and the results of a two-dimensional mathematical model, the changes of the river regime and river bed evolution in the Yaojian reach downstream of the TGP were studied. Results show that a high sediment transport flux helps to keep the main flow in the North Branch, while a low sediment transport flux helps to keep the main flow in the South Branch. Thus, the main branch will not change in the near future because of the low sediment transport load. In this study, the flow-sediment process adjusted by the TGP was restored to the conditions before the TGP, and the river bed evolution under the adjusted and non-adjusted flow-sediment conditions was calculated. After the completion of the TGP, the reservoir storage accelerated the flood recession process and decreased the erosion by 11.9% under the flow-sediment conditions in 2010, and the deposition in the flood season decreased by 56.4%
Based on conventional particle swarm optimization (PSO), this paper presents an efficient and reliable heuristic approach using PSO with an adaptive random inertia weight (ARIW) strategy, referred to as the ARIW-PSO algorithm, to build a multi-objective optimization model for reservoir operation. Using the triangular probability density function, the inertia weight is randomly generated, and the probability density function is automatically adjusted to make the inertia weight generally greater in the initial stage of evolution, which is suitable for global searches. In the evolution process, the inertia weight gradually decreases, which is beneficial to local searches. The performance of the ARIW-PSO algorithm was investigated with some classical test functions, and the results were compared with those of the genetic algorithm (GA), the conventional PSO, and other improved PSO methods. Then, the ARIW-PSO algorithm was applied to multi-objective optimal dispatch of the Panjiakou Reservoir and multi-objective flood control operation of a reservoir group on the Luanhe River in China, including the Panjiakou Reservoir, Daheiting Reservoir, and Taolinkou Reservoir. The validity of the multi-objective optimization model for multi-reservoir systems based on the ARIW-PSO algorithm was verified.
Based on a self-developed hydrodynamic cavitation device with different geometric parameters for circular multi-orifice plates, turbulence characteristics of cavitating flow behind multi-orifice plates, including effects of orifice number and orifice layout on longitudinal velocity, turbulence intensity, and Reynolds stress, were measured with the particle image velocimetry (PIV) technique. Flow regimes of the cavitating flow were also observed with high-speed photography. The experimental results showed the following: (1) high-velocity multiple cavitating jets occurred behind the multi-orifice plates, and the cavitating flow fields were characterized by topological structures; (2) the longitudinal velocity at each cross-section exhibited a sawtooth-like distribution close to the multi-orifice plate, and each sawtooth indicated one jet issuing from one orifice; (3) there were similar magnitudes and forms for the longitudinal and vertical turbulence intensities at the same cross-section; (4) the variation in amplitude of Reynolds stress increased with an increase in orifice number; and (5) the cavitation clouds in the flow fields became denser with the increase in orifice number, and the clouds generated by the staggered layout of orifices were greater in number than those generated by the checkerboard-type one for the same orifice number. The experimental results can be used to analyze the mechanism of killing pathogenic microorganisms through hydrodynamic cavitation.
Estimation of scour dimensions below submarine pipelines is a vital step in designing offshore infrastructure. Extreme events like tsunami waves produce strong erosive forces below the underwater pipes, apt to create scour holes, jeopardizing the safety of the structure. Despite the importance of this issue, previous studies have mainly focused on steady flow cases, and the scour pattern below submarine pipes induced by high-amplitude transient waves has rarely been investigated. This paper reports the results of 40 experimental runs on transient wave-induced scour below a model pipe in a laboratory flume under a variety of initial conditions. The variables included the bed particle size and gradation, initial water depth, wave height, and slope of the bed layer. Waves were generated by a sudden release of water from a sluice gate, installed in the middle of the flume. A pressure transducer data acquisition system was used to record the wave heights at different time steps. The results indicate that, with a shallower initial depth of flow, the scour depth is relatively large. It was also found that there exists a direct correlation between the induced wave height and the size of the scour hole. It was observed that, in clear water conditions, the size of the scour hole in coarse sediments is smaller, while in live-bed conditions, larger scour holes are created in coarser sediments. It was also observed that at high wave amplitudes, the live-bed conditions are dominant, and consequently the bed elevation is altered.
A combined dam structure using different concrete materials offers many practical benefits. There are several real-world cases where large-volume heterogeneous concrete materials have been used together. From the engineering design standpoint, it is crucial to understand the deformation coordination characteristics and mechanical properties of large-volume heterogeneous concrete, which affect dam safety and stability. In this study, a large dam facility was selected for a case study, and various design schemes of the combined dam structure were developed by changing the configurations of material zoning and material types for a given dam shape. Elastoplastic analysis of the dam-foundation-reservoir system for six schemes was carried out under dynamic conditions, in which the concrete damaged plasticity (CDP) model, the Lagrangian finite element formulation, and a surface-to-surface contact model were utilized. To evaluate the mechanical properties of zoning interfaces and coordination characteristics, the vertical distribution of the first principal stress at the longitudinal joint was used as the critical index of deformation coordination control, and the overall deformation and damage characteristics of the dam were also investigated. Through a comparative study of the design schemes, an optimal scheme of the combined dam structure was identified: large-volume roller-compacted concrete (RCC) is recommended for the dam body upstream of the longitudinal joint, and high-volume fly ash conventional concrete (CC) for the dam body downstream of the longitudinal joint. This study provides engineers with a reference basis for combined dam structure design.