Abstract: The objective of this study was to retrieve daily composite soil moisture by jointly using brightness temperature observations from multiple operating satellites for near real-time application with better coverage and higher accuracy. Our approach was to first apply the single-channel brightness radiometric algorithm to estimate soil moisture from the respective brightness temperature observations of the SMAP, SMOS, AMSR2, FY3B, and FY3C satellites on the same day and then produce a daily composite dataset by averaging the individual satellite-retrieved soil moisture. We further evaluated our product, the official soil moisture products of the five satellites, and the ensemble mean (i.e., arithmetic mean) of the five official satellite soil moisture products against ground observations from two networks in Central Tibet and Anhui Province, China. The results show that our product outperforms the individual released products of the five satellites and their ensemble means in the two validation areas. The root mean square error (RMSE) values of our product were 0.06 and 0.09 m3/m3 in Central Tibet and Anhui Province, respectively. Relative to the ensemble mean of the five satellite products, our product improves the accuracy by 9.1% and 57.7% in Central Tibet and Anhui Province, respectively. This demonstrates that jointly using brightness temperature observations from multiple satellites to retrieve soil moisture not only improves the spatial coverage of daily observations but also produces better daily composite products.
Abstract: Although many studies have evaluated the impacts of bioretention cell (BRC) design elements on hydrologic performance, few have investigated the role site characteristics and rainfall patterns play. The objectives of this study were to assess the impacts of rainfall and catchment with different characteristics on the hydrologic performance of BRCs and identify important factors in sizing bioretention when hydrologic performance was oriented for the design using a modeling approach. A 10-year record of rainfall data was used to identify the frequency and magnitude of rainfall events. The results showed that although the small and medium rainfall events were dominant they contributed less to the total rainfall depth compared with the large rainfall events. The ratio of runoff coefficient to imperviousness can be used as an indicator to explain the reasons why BRCs perform differently with the same design strategy under the same rainfall events. Rainfall patterns had significant impacts on the hydrologic performance of BRCs by influencing the overflow and underdrain flow. BRCs performed better for rainfall events with a longer duration and smaller rainfall intensity because they generated smoother runoff processes into the BRCs. On the basis of these results, the runoff coefficient is suggested to be considered for BRC surface design.
Abstract: In this study, a two-dimensional flow-pollutant coupled model was developed based on a quadtree grid. This model was established to allow the accurate simulation of wind-driven flow in a large-scale shallow lake with irregular natural boundaries when focusing on important small-scale localized flow features. The quadtree grid was created by domain decomposition. The governing equations were solved using the finite volume method, and the normal fluxes of mass, momentum, and pollutants across the interface between cells were computed by means of a Godunov-type Osher scheme. The model was employed to simulate wind-driven flow in a circular basin with non-uniform depth. The computed values were in agreement with analytical data. The results indicate that the quadtree grid has fine local resolution and high efficiency, and is convenient for local refinement. It is clear that the quadtree grid model is effective when applied to complex flow domains. Finally, the model was used to calculate the flow field and concentration field of Taihu Lake, demonstrating its ability to predict the flow and concentration fields in an actual water area with complex geometry.
Abstract: The reverse osmosis method is one of the most widely used methods of seawater desalination at present. Hydrophilic and desalting membranes in reverse osmosis systems are highly susceptible to the input pollutants. Various contaminants, including suspended organic and inorganic matter, result in membrane fouling and membrane degradation. Fundamental parameters such as the turbidity, the amount of chlorine injection, and silt density index (SDI) are the most predominant parameters of fouling control in the membranes. In this study, the operation system included a water intake unit, a pretreatment system, and an RO system. The pretreatment system encompassed a clarifier, a gravity sand filter, pressurized sand filters, and a cartridge filter. The correlation between the amount of chlorine injection in terms of the oxidation-reduction potential (ORP) and the SDI value of the input water was investigated at a specified site next to the Persian Gulf. The results showed that, at certain intervals of inlet turbidity, injection of a certain amount of chlorine into the raw water has a distinct effect on the decrease of SDI
Abstract: In this paper, an analytical model that represents the streamwise velocity distribution for open channel flow with submerged flexible vegetation is studied. In the present vegetated flow modelling, the whole flow field has been separated into two layers vertically: a vegetated layer and a non-vegetated free-water layer. Within the vegetated layer, an analysis of the mechanisms affecting water flow through flexible vegetation has been conducted. In the non-vegetated layer, a modified log-law equation that represents the velocity profile varying with vegetation height has been investigated. Based on the studied analytical model, a sensitivity analysis has been conducted to assess the influences of the drag () and friction () coefficients on the flow velocity. The investigated ranges of and have also been compared to published values. The findings suggest that the and values are non-constant at different depths and vegetation densities, unlike the constant values commonly suggested in literature. This phenomenon is particularly clear for flows with flexible vegetation, which is characterised by large deflection.
Abstract: A new equation is proposed for the design of armor units on protected river banks under the combined action of ship-induced waves and river flow. Existing observed field and experimental data in the literature have been examined and a valuable database has been developed. Different conditions, including the river water depth, flow velocity, river bank slope, Froude number, wave height, wave period, and wave obliquity have been considered. Results from an empirical equation (Bhowmik, 1978) that only considers the maximum wave height and river bank slope have been compared with the results calculated by the newly developed equation. Calculated results have also been verified against field data. Results show that not only the maximum wave height and river bank slope but also the water depth, flow velocity, wave length, wave obliquity, and wave period are important parameters for predicting the mean diameter of the armor units, highlighting the multivariate behavior of protecting the river bank in the presence of ship-induced waves and river flow velocity.
Abstract: The waterway in the middle and lower reaches of the Yangtze River has long been known as the Golden Waterway and has served as an important link in the construction of the Yangtze River Economic Belt. Therefore, expanding its dimensions is a significant goal, particularly given the long-range cumulative erosion occurring downstream of the Three Gorges Dam (TGD), which has been concentrated in the dry river channel. With the regulation of the volume from upstream reservoirs and the TGD, the minimum discharge and water level of the river downstream are increasing, and creating favorable conditions for the increase of the depth of the waterway. The discharge compensation effect during the dry season offsets the decline in the water level of the river channel caused by the down-cutting of part of the riverbed, but the minimum navigable water level of the segment near the dam still shows a declining trend. In recent years, several waterway remediation projects have been implemented in the downstream reaches of the TGD and although the waterway depth and width have been increased, the channel dimensions are still insufficient in the Yichang-Anqing reach (with a total length of 1026 km), as compared to the upstream reservoir area and the deep water channel in the downstream tidal reaches. A comprehensive analysis of the water depth and the number and length of shoals in the waterway indicates that its dimensions can be increased to 4.5 m × 200 m and 6.0 m × 200 m in the Yichang-Wuhan and Wuhan-Anqing reaches, respectively. This is also feasible given the remediation technologies currently available, but remediation projects need to be coordinated with those for flood prevention and ecological protection.
Abstract: Large eddy simulation (LES) explicitly calculates the large-scale vortex field and parameterizes the small-scale vortices. In this study, LES and κ-ε models were developed for a specific geometrical configuration of backward-facing step (BFS). The simulation results were validated with particle image velocimetry (PIV) measurements and direct numerical simulation (DNS). This LES simulation was carried out with a Reynolds number of 9000 in a pressurized water tunnel with an expansion ratio of 2.00. The results indicate that the LES model can reveal large-scale vortex motion although with a larger grid-cell size. However, the LES model tends to overestimate the top wall separation and the Reynolds stress components for the BFS flow simulation without a sufficiently fine grid. Overall, LES is a potential tool for simulating separated flow controlled by large-scale vortices.
Abstract: During reservoir operation, the erosion effects of groundwater change the porosity and permeability of the dam curtain, causing changes to the seepage field. To understand where the changes take place and to what degree the porosity and permeability change, a multi-field coupling model was built and solved. The model takes into account seepage, solution concentration, and solid structure. The model was validated using uplift pressure monitoring data. Then, the variations in curtain porosity, seepage flow, and loss quantity of Ca(OH)2 were calculated. The key time nodes were obtained through curve fitting of the variation of seepage flow with the BiDoseResp function. The results showed that the model could reflect the attenuation trend of curtain performance well. The process and position of the erosion were not homogeneous. Although erosion mainly occurred at the top and bottom of the curtain, it was most developed at the top. The erosion effects developed slowly during the early stage, much fast during the middle and late stages, and culminated in complete dissolution. The model results and the daily monitoring data can provide a scientific basis for the safe operation and management of reservoirs.
Abstract: Based on the characteristics of hydrodynamics and sediment transport in the bar area in the Modaomen Estuary, a flume experiment was performed to study the evolution of the longitudinal profile of the mouth bar. The mouth bar evolution was investigated under the impacts of floods with different return periods as well as flood-wave interaction. The results show that floods with different return periods had significant influences on the evolution of the river mouth bar. Particularly on the inner slope of the mouth bar, the sediment was substantially active and moveable. The inner slope and the bar crest tended to be remarkably scoured. The erosion was intensified with the increase of the magnitude of floods. Moreover, the bar crest moved seawards, while the elevation of the bar crest barely changed. Under the flood-wave interaction, a remarkable amount of erosion on the inner and outer slopes of the mouth bar was also found. The seaward displacement of the bar crest under the interaction of floods and waves was less than it was under only the impact of floods, while more deposition was found on the crest of the mouth bar in this case.
