Water — Open Access Journal

Hydraulic structures are often complex and in many cases their designs require attention so that the flow behavior around hydraulic structures and their influence on the environment can be predicted accurately. Currently, more efficient computational fluid dynamics (CFD) codes can solve the Navier–Stokes equations in three-dimensions and free surface computation in a significantly improved manner. CFD has evolved into a powerful tool in simulating fluid flows. In addition, CFD with its advantages of lower cost and greater flexibility can reasonably predict the mean characteristics of flows such as velocity distributions, pressure distributions, and water surface profiles of complex problems in hydraulic engineering. In Ethiopia, Tendaho Dam Spillway was constructed recently, and one flood passed over the spillway. Although the flood was below the designed capacity, there was an overflow due to superelevation at the bend. Therefore, design of complex hydraulic structures using the state-of- art of 3D hydrodynamic modelling enhances the safety of the structures. 3D hydrodynamic modelling was used to verify the safety of the spillway using designed data and the result showed that the constructed hydraulic section is not safe unless it is modified. Full article

Flood classification is an important basis for flood forecasting, flood risk identification, flood real-time scheduling, and flood resource utilization. However, flood classification results may be not reasonable due to uncertainty, the fuzziness of evaluation indices, and the demerit of not comprehensively considering the index weight. In this paper, based on the fuzzy clustering iterative model, a sensitivity coefficient was applied to combine the subjective and objective weights into a combined weight, then the fuzzy clustering iterative model with combined weight (FCI-CW) was proposed for flood classification. Moreover, an immune grey wolf optimizer algorithm (IGWO) based on the standard grey wolf optimizer algorithm and an immune clone selection operator was proposed for the global search of the optimal fuzzy clustering center and the sensitivity coefficient of FCI-CW. Finally, simulation results at Nanjing station and Yichang station demonstrate that the proposed methodology, i.e., FCI-CW combined with IGWO, is reasonable and reliable, can effectively deal with flood classification problems with better fitness and a comprehensive consideration of the subjective and objective aspects, and has great application potential in sorting, evaluation, and decision-making problems without evaluation criteria. Full article

The concept of a traditional return period has long been questioned in non-stationary studies, and the risk of failure was recommended to evaluate the design events in flood modeling. However, few studies have been done in terms of multivariate cases. To investigate the impact of non-stationarity on the streamflow series, the Yichang station in the Yangtze River was taken as a case study. A time varying copula model was constructed for bivariate modeling of flood peak and 7-day flood volume, and the non-stationary return period and risk of failure were applied to compare the results between stationary and non-stationary models. The results demonstrated that the streamflow series at the Yichang station showed significant non-stationary properties. The flood peak and volume series presented decreasing trends in their location parameters and the dependence structure between them also weakened over time. The conclusions of the bivariate non-stationary return period and risk of failure were different depending on the design flood event. In the event that both flood peak and volume are exceeding, the flood risk is smaller with the non-stationary model, which is a joint effect of the time varying marginal distribution and copula function. While in the event that either flood peak or volume exceed, the effect of non-stationary properties is almost negligible. As for the design values, the non-stationary model is characterized by a higher flood peak and lower flood volume. These conclusions may be helpful in long-term decision making in the Yangtze River basin under non-stationary conditions. Full article

The SWOT (Surface Water and Ocean Topography) mission, to be launched in 2021, will provide water surface elevations, slopes, and river width measurements for rivers wider than 100 m. In this study, synthetic SWOT data are assimilated in a regional hydrometeorological model in order to improve the dynamics of continental waters over the Garonne catchment, one of the major French catchments. The aim of this paper is to demonstrate that the sequential assimilation of SWOT-like river depths allows the correction of river bed roughness coefficients and thus simulated river depths. An extended Kalman filter is implemented and the data assimilation strategy was applied to four experiments of gradually increasing complexity regarding observation and model error over the 1995–2000 period. With respect to a “true” river state, assimilating river depths allows the proper retrieval of constant and spatially distributed roughness coefficients with a root mean square error of 1 m^1/3 s⁻¹, and the estimation of associated river depths. It was also shown that river depth differences can be assimilated, resulting in a higher root mean square error for roughness coefficients with respect to the true river state. Finally, the last experiment shows how one can take into account more realistic sources of SWOT error measurements, in particular the importance of the estimation of the tropospheric water content in the process. Full article

Aquatic plant harvest has been widely considered a plant management measure, as it can physically remove the targeted plants quickly and efficiently. Few empirical studies have examined the effects of harvesting on water quality or the aquatic plant community in a complete lake ecosystem. A large area (196 km²) of floating-leaved Nymphoides peltata was harvested in Lake Taihu in 2013. The effects of harvesting on the coverage and biomass of N. peltata and on the submerged plant community were evaluated. The quantities of nitrogen and phosphorus removed by harvesting were calculated. Harvesting caused an immediate reduction in N. peltata coverage, and its coverage in the following year ranged from 29.2% to 95.1%. Wave conditions and interspecific competition were the main factors that influenced the response of the submerged plant community to N. peltata harvesting. Harvesting may favor the dominance of Hydrilla verticillata, which expands quickly at an average growth rate of 53 ± 14 g m⁻² day⁻¹. Harvesting a large amount of N. peltata has a positive effect on total nitrogen (TN), ammonium nitrogen (NH₃-N), and chemical oxygen demand (COD_Mn) control but can lead to different consequences (e.g., increase in total phosphorus (TP) and algal concentration). Full article

Flash flood is a significant threat to those who live in China and beyond. Reproducing them with distributed hydrological models is an effective measure for preventing flash floods. This paper introduces the China flash flood hydrological model (CNFF-HM); explores its principles, key steps, and applicability; and validates its simulation effects in two typical, small ungauged catchments (UCs), namely, Tiezhuling and Qianyangxi. First, the applicability of the model and the portability of the parameters were verified in Qianyangxi. Then, in Tiezhuling, the model parameters were comprehensively determined based on the measured values and simulation results, and the influence of the reservoir on the simulation effect was analyzed. Using the model’s different parameters in different catchments, the characteristics of the basin were compared and analyzed from the aspects of evapotranspiration, runoff, water distribution, and confluence. Finally, the early warning effect was evaluated. The results indicated the following: (1) The reservoir has a significant impact on model simulation. (2) The two UCs have similarities in evapotranspiration, runoff, and water source, and the difference in convergence is obvious. (3) With better early warning effect, the warning can achieve full coverage. These positive results suggest that this method should be further developed and tested. Full article

In this study, we estimate monthly variations of surface-water storage (SWS) and subsurface water storage (SSWS, including groundwater and soil moisture) within the Lower Mekong Basin located in Vietnam and Cambodia during the 2003–2009 period. The approach is based on the combination of multisatellite observations using surface-water extent from MODIS atmospherically corrected land-surface imagery, and water-level variations from 45 virtual stations (VS) derived from ENVISAT altimetry measurements. Surface-water extent ranges from ∼6500 to ∼40,000 km${}^2$ during low and high water stages, respectively. Across the study area, seasonal variations of water stages range from 8 m in the upstream parts to 1 m in the downstream regions. Annual variation of SWS is ∼40 km${}^3$ for the 2003–2009 period that contributes to 40–45% of total water-storage (TWS) variations derived from Gravity Recovery And Climate Experiment (GRACE) data. By removing the variations of SWS from GRACE-derived TWS, we can isolate the monthly variations of SSWS, and estimate its mean annual variations of ∼50 km${}^3$ (55–60% of the TWS). This study highlights the ability to combine multisatellite observations to monitor land-water storage and the variations of its different components at regional scale. The results of this study represent important information to improve the overall quality of regional hydrological models and to assess the impacts of human activities on the hydrological cycles. Full article

Extreme cold and meteorological drought in the Mongolian Plateau (MP) were investigated during 1969–2017. Several drought indices were evaluated by analyzing recorded historical drought data in the Chinese region of the MP. The evaluated drought indices were then applied to detect drought characteristics in the entire MP. The trends of extreme cold indices showed that the climate of the MP has warmed during the past 49 years; however, the frequency of cold day/night has increased in the Mongolian region. The climate of Mongolia has also become colder in the spring season. The comprehensive meteorological drought index (CMDI) and the standardized precipitation index with a six-month scale (SPI6) exhibited better performances, showing high consistency between the spatial patterns of the two indices. However, drought represented by the SPI6 was enhanced greater than that expressed by the CMDI. Drought in the MP has been enhanced during the past 49 years, particularly in the Ordos and Alashan plateaus and the Xiliao River basin in China. Moreover, drought has been enhanced from August to October, particularly in the Mongolian region. However, spring drought has shown a weakening trend, which has been beneficial for agriculture and husbandry sectors in some regions of the MP. Full article

The aim of this study is to introduce a novel method which can separate sand- or gravel-dominated bed load transport in rivers with mixed-size bed material. When dealing with large rivers with complex hydrodynamics and morphodynamics, the bed load transport modes can indicate strong variation even locally, which requires a suitable approach to estimate the locally unique behavior of the sediment transport. However, the literature offers only few studies regarding this issue, and they are concerned with uniform bed load. In order to partly fill this gap, we suggest here a decision criteria which utilizes the shear Reynolds number. The method was verified with data from field and laboratory measurements, both performed at nonuniform bed material compositions. The comparative assessment of the results show that the shear Reynolds number-based method operates more reliably than the Shields–Parker diagram and it is expected to predict the sand or gravel transport domination with a <5% uncertainty. The results contribute to the improvement of numerical sediment transport modeling as well as to the field implementation of bed load transport measurements. Full article

Drought monitoring is one of the significant issues of water resources assessment. Multiple drought indices (DIs), including Percent of Normal (PN), Standardized Precipitation Index (SPI), statistical Z-Score, and Effective Drought Index (EDI) at 18 different timesteps were employed to evaluate the drought condition in Wuyuer River Basin (WRB), Northeast China. Daily precipitation data of 50 years (1960–2010) from three meteorological stations were used in this study. We found DIs with intermediate time steps (7 to 18 months) to have the highest predictive values for identifying droughts. And DIs exhibited a better similarity in the 12-month timestep. Among all the DIs, EDI exhibited the best correlation with other DIs for various timesteps. When further comparing with historical droughts, Z-Score, SPI, and EDI were found more sensitive to multi-monthly cumulative precipitation changes (r² > 0.55) with respect to monthly precipitation changes (r² ≤ 0.10), while EDI was more preferable when only monthly precipitation data were available. These results indicated that various indices for different timesteps should be investigated in drought monitoring in WRB, especially the intermediate timesteps should be considered. Full article

This special issue on Antimicrobial Resistance in Environmental Waters features 11 articles on monitoring and surveillance of antimicrobial resistance (AMR) in natural aquatic systems (reservoirs, rivers), and effluent discharge from water treatment plants to assess the effectiveness of AMR removal and resulting loads in treated waters. The occurrence and distribution of antimicrobials, antibiotic resistant bacteria (ARB), antibiotic resistance genes (ARGs) and mobile genetic elements (MGEs) was determined by utilizing a variety of techniques including liquid chromatography—mass spectrometry in tandem (LC-MS/MS), traditional culturing, antibiotic susceptibility testing (AST), molecular and OMIC approaches. Some of the key elements of AMR studies presented in this special issue highlight the underlying drivers of AMR contamination in the environment and evaluation of the hazard imposed on aquatic organisms in receiving environments through ecological risk assessments. As described in this issue, screening antimicrobial peptide (AMP) libraries for biofilm disruption and antimicrobial candidates are promising avenues for the development of new treatment options to eradicate resistance. This editorial puts into perspective the current AMR problem in the environment and potential new methods which could be applied to surveillance and monitoring efforts. Full article

Precipitation climatologies for the period 1961–1990 were generated for all climatic regions of Costa Rica using an irregular rain-gauge observational network comprised by 416 rain-gauge stations. Two sub-networks were defined: a high temporal resolution sub-network (HTR), including stations having at least 20 years of continuous records during the study period (157 in total); and a high spatial resolution sub-network (HSR), which includes all HTR-stations plus those stations with less than 20 years of continuous records (416 in total). Results from the kriging variance reduction efficiency (KRE) objective function between the two sub-networks, show that ordinary kriging (OK) is unable to fully explain the spatio-temporal variability of precipitation within most climatic regions if only stations from the HTR sub-network are used. Results also suggests that in most cases, it is beneficial to increase the density of the rain-gauge observational network at the expense of temporal fidelity, by including more stations even though their records may not represent the same time step. Thereafter, precipitation climatologies were generated using seven deterministic (IDW, TS2, TS2PARA, TS2LINEAR, TPS, MQS and NN) and two geostatistical (OK and KED) interpolation methods. Performance of the various interpolation methods was evaluated using cross validation technique, selecting the mean absolute error (MAE) and the root-mean square error (RMSE) as agreement metrics. Results suggest that IDW is marginally superior to OK and KED for most climatic regions. The remaining deterministic methods however, considerably deviate from IDW, which suggests that these methods are incapable of properly capturing the true-nature of spatial precipitation patterns over the considered climatic regions. The final generated IDW climatology was then validated against the Global Precipitation Climatology Centre (GPCC), Climate Research Unit (CRU) and WorldClim datasets, in which overall spatial and temporal coherence is considered satisfactory, giving assurance about the use this new climatology in the development of local climate impact studies. Full article

Recently, the number of extreme rainfall events has increased because of climate change. The ever-widening impervious area in urban watersheds also continuously augments runoff volume. Most measures to prevent urban inundation are structural, such as the construction, rehabilitation, and replacement of urban drainage facilities. Because structural measures require time and money, nonstructural measures are also required for the efficient prevention of urban inundation. Current operations in Korea focus on the individual operation of urban drainage facilities while neglecting the status of effluent streams. A study on urban drainage facilities that considers the status of urban streams is necessary to improve the operation of drainage facilities in urban areas. A revised resilience index is suggested to evaluate measures. For the historical rainfall event in 2010, the system resilience for current and integrated operations was 0.199 and 0.238, respectively. For the 2011 event, the system resilience for current and integrated operations was 0.064 and 0.235, respectively. The integrated operation exhibited good performance for the 2010 and 2011 events. Based on the results of this study, an operation as a nonstructural measure for the total management of urban areas is proposed. The revised resilience index could support decision-making processes for flood-management plans. Full article

Incremental ecological service value is an important assessment indicator for ecosystem restoration projects, such as the interconnected river system network project in western Jilin Province, China. In this paper, a fuzzy two-stage chance-constrained stochastic programming (FTSCCP) model is proposed for the optimization of regional incremental ecological service value through adjustments to the original water diversions and ecological water supplement schemes for ecosystem restoration under different management requirements and scenarios. The proposed method can effectively address uncertainties such as fuzzy parameters, probability distributions, and random variables in optimizing processes simultaneously. The results reveal that, under the requirement of meeting the original plan, a decrease in restoration scale would mainly appear under low-flow scenarios, and for the other scenarios, the original plan would be fully realized with an increase in flood utilization and a decrease in normal water supplementation. For the requirement of maximizing the incremental ecological service value, the adjustments would mainly be increases in water supplementation for reed wetlands and marsh wetlands and decreases in water surface area, including fish ponds and crab ponds. The ecological service values would be 11,256.79 million CNY (Chinese Yuan), 16,465.11 million CNY and 17,639.59 million CNY under low-, normal- and high-flow scenarios, respectively, with increases of 3.2%, 6.9% and 14.5% compared to the values based on the requirement of meeting the original plan. The results would be helpful for guiding regional ecosystem restoration and water resource management in the western Jilin Province. Full article

Using the conventional XAD 8/4 method with general columns to isolate dissolved organic matter (DOM) is extremely time-consuming and labor-intensive. This study presents a rapid and effective method using solid-phase extraction (SPE) cartridges packed with XAD 8/4 resins for isolating various DOMs. The relative fraction (percentage hydrophobic, transphilic, and hydrophilic) of the various DOMs processed by both methods showed similar values. Moreover, changes in the molecular weight distribution of effluent from XAD 8/4 resins processed by both methods showed the same ultraviolet (UV) and fluorescence absorbance pattern s. The biopolymer compositions of eluates from XAD 8/4 resins also showed no significant difference between the two methods. However, higher carbon recovery of the isolation method using SPE cartridges was found (with columns: 88.9%; with SPE: 95.9%). In addition, the proposed method using SPE cartridges packed with XAD 8/4 resins is much faster than that using general columns (with columns: 1468 min; with SPE: 485 min). The proposed isolation method is highly efficient and accurate; it is an excellent candidate method for isolating various DOMs. Full article

Currently, black-odor river has received great attention in China. In this study, the micro-nano bubble technology (MBT) was used to mitigate the water pollution rapidly and continuously by increasing the concentration of dissolved oxygen (DO) in water. During treatment, the concentration of DO increased from 0.60 mg/L to over 5.00 mg/L, and the oxidation reduction potential (ORP) also changed from a negative value to over 100.00 mV after only five days aeration. High throughput pyrosequencing technology was employed to identify the microbial community structure. At genus level, the dominant bacteria were anaerobic and nutrient-loving microbes (e.g., Arcobacter sp., Azonexus sp., and Citrobacter sp.) before, and the relative abundances of aerobic and functional microbes (e.g., Perlucidibaca sp., Pseudarcicella sp., Rhodoluna sp., and Sediminibacterium sp.) were increased after treatment. Meanwhile, the water quality was significantly improved with about 50% removal ratios of chemical oxygen demand (COD_Cr) and ammonia nitrogen (NH₄⁺-N). Canonical correspondence analysis (CCA) results showed that microbial community structure shaped by COD, DO, NH₄⁺-N, and TP, CCA1 and CCA2 explained 41.94% and 24.56% of total variances, respectively. Overall, the MBT could improve the water quality of urban black-odor river by raising the DO and activate the aerobic microbes. Full article

Low flow is a seasonal phenomenon which is a critical requirement for utilization of water resources under rapidly changing environmental conditions. The operation of the Three Gorges Dam (TGD) has had a great influence on downstream low flow in the Yangtze River. In this paper, the characteristics of low flow in the main Yangtze River were analyzed during the dry season before and after the TGD operation during the period of 1956–2016. The results show that: (1) the operation of the TGD has changed the spatial and temporal distribution of streamflow in the middle and lower Yangtze River and the annual mean low flow has increased significantly since the TGD operation. (2) The operation of the TGD could advance the date of the start of dry season in the lower Yangtze River basin. The start dates of the dry season in the Yichang, Hankou and Datong stations were advanced by 14 days, 10 days and 9 days, respectively. (3) The minimum streamflow in the lower Yangtze River has increased notably since the TGD operation. The minimum streamflow was raised by 42.91%, 13.76% and 6.06% at the Yichang, Hankou and Datong stations, respectively. The increasing number of dams in the world might have the potential effects on downstream low flow. More attention should be paid to investigating the influence of dam construction on low flow in rivers all over the world. Full article

Enterovirus 70 (EV70) is an emerging viral pathogen that remains viable in final treated effluent. Solar irradiation is, therefore, explored as a low-cost natural disinfection strategy to mitigate potential concerns. EV70 was exposed to simulated sunlight for 24 h at a fluence rate of 28.67 J/cm²/h in three different water matrices, namely, phosphate-buffered saline (PBS), treated wastewater effluent, and chlorinated effluent. In the presence of sunlight, EV70 decreased in infectivity by 1.7 log, 1.0 log, and 1.3 log in PBS, effluent, and chlorinated effluent, respectively. Irradiated EV70 was further introduced to host cell lines and was unable to infect the cell lines. In contrast, EV70 in dark microcosms replicated to titers 13.5, 3.3, and 4.2 times the initial inoculum. The reduction in EV70 infectivity was accompanied by a reduction in viral binding capacity to Vero cells. In addition, genome sequencing analysis revealed five nonsynonymous nucleotide substitutions in irradiated viruses after 10 days of infection in Vero cells, resulting in amino acid substitutions: Lys14Glu in the VP4 protein, Ala201Val in VP2, Gly71Ser in VP3, Glu50Gln in VP1, and Ile47Leu in 3C^pro. Overall, solar irradiation resulted in EV70 inactivation and an inhibition of viral activity in all parameters studied. Full article