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Volume 13
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Water, Volume 13, Issue 2 (January-2 2021) – 135 articles

Cover Story (view full-size image): Spring freshet is the dominant annual discharge event in all major Arctic-draining rivers, with large contributions of freshwater inflow to the Arctic Ocean. Studies have shown that the total freshwater influx to the Arctic Ocean has increased as the Arctic climate changes at a significantly higher rate than in other parts of the globe. This study assesses the large-scale atmospheric and surface climatic conditions that affect the magnitude and timing of the spring freshets by analyzing daily discharges from sub-basins within the four largest Arctic-draining watersheds (i.e., Mackenzie, Ob, Lena, and Yenisei). Results reveal that climatic variations closely match the observed regional trends of increasing cold-season flows and earlier freshets. Freshet characteristics are also influenced by several large-scale atmospheric/ocean teleconnections. View this paper
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19 pages, 11278 KiB  
Article
Mechanisms of Flood-Induced Levee Breaching in Marumori Town during the 2019 Hagibis Typhoon
by Nguyen Xuan Tinh, Hitoshi Tanaka, Gen Abe, Yuka Okamoto and Kwanchai Pakoksung
Water 2021, 13(2), 244; https://doi.org/10.3390/w13020244 - 19 Jan 2021
Cited by 3 | Viewed by 2765
Abstract
Typhoon Hagibis, which occurred at the beginning of October 2019, was one of the largest and most powerful tropical cyclones and was considered to be the most devastating typhoon to hit Japan in recorded history. Extreme heavy rainfall caused massive impacts to Japan [...] Read more.
Typhoon Hagibis, which occurred at the beginning of October 2019, was one of the largest and most powerful tropical cyclones and was considered to be the most devastating typhoon to hit Japan in recorded history. Extreme heavy rainfall caused massive impacts to Japan in general and to Marumori Town, Miyagi Prefecture in particular. In the present study, the detailed flood characteristics at Marumori Town were investigated by using field observation and numerical simulations. The obtained data immediately after the flood has clearly shown that most levee breaches were caused by the water overflow on the river embankment at the constriction areas such as the tributaries’ junction and the intersection of the river embankment. Numerical simulations were performed to investigate the mechanism of levee breaching in Marumori Town. According to the simulation results, the flooding water from the upstream levee breach locations flowed into the paddy field area and caused the levee to breach at the river embankment interaction in the downstream area. A new levee breach criterion in terms of overflow depth and its duration on the river embankment was proposed. In addition, a sensitivity analysis was also performed to understand the effect of the backwater and phase lag of water level rise between the mainstream and tributaries. Although there have been many studies on flood disasters, the typhoon’s flood-induced disasters on the river and coastal infrastructures have still remained a big challenge. The present study outcomes provide useful information not only to understand how the river embankment of tributaries is vulnerable to water level rise, but also to support the river authorities to prepare better mitigation plans for future flood disasters. Full article
(This article belongs to the Section Water Erosion and Sediment Transport)
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33 pages, 4414 KiB  
Article
SWMM-UrbanEVA: A Model for the Evapotranspiration of Urban Vegetation
by Birgitta Hörnschemeyer, Malte Henrichs and Mathias Uhl
Water 2021, 13(2), 243; https://doi.org/10.3390/w13020243 - 19 Jan 2021
Cited by 14 | Viewed by 4934
Abstract
Urban hydrology has so far lacked a suitable model for a precise long-term determination of evapotranspiration (ET) addressing shading and vegetation-specific dynamics. The proposed model “SWMM-UrbanEVA” is fully integrated into US EPA’s Stormwater Management Model (SWMM) and consists of two submodules. Submodule 1, [...] Read more.
Urban hydrology has so far lacked a suitable model for a precise long-term determination of evapotranspiration (ET) addressing shading and vegetation-specific dynamics. The proposed model “SWMM-UrbanEVA” is fully integrated into US EPA’s Stormwater Management Model (SWMM) and consists of two submodules. Submodule 1, “Shading”, considers the reduction in potential ET due to shading effects. Local variabilities of shading impacts can be addressed for both pervious and impervious catchments. Submodule 2, “Evapotranspiration”, allows the spatio-temporal differentiated ET simulation of vegetation and maps dependencies on vegetation, soil, and moisture conditions which are necessary for realistically modeling vegetation’s water balance. The model is tested for parameter sensitivities, validity, and plausibility of model behaviour and shows good model performance for both submodules. Depending on location and vegetation, remarkable improvements in total volume errors Vol (from Vol = 0.59 to −0.04% for coniferous) and modeling long-term dynamics, measured by the Nash–Sutcliffe model efficiency (NSE) (from NSE = 0.47 to 0.87 for coniferous) can be observed. The most sensitive model inputs to total ET are the shading factor KS and the crop factor KC. Both must be derived very carefully to minimize volume errors. Another focus must be set on the soil parameters since they define the soil volume available for ET. Process-oriented differentiation between ET fluxes interception evaporation, transpiration, and soil evaporation, using the leaf area index, behaves realistically but shows a lack in volume errors. Further investigations on process dynamics, validation, and parametrization are recommended. Full article
(This article belongs to the Special Issue Rainwater Management in Urban Areas)
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11 pages, 5224 KiB  
Article
Soil Water Dynamics Under Different Land Uses in Loess Hilly Region in China by Stable Isotopic Tracing
by Kang Du, Beiying Zhang and Linjuan Li
Water 2021, 13(2), 242; https://doi.org/10.3390/w13020242 - 19 Jan 2021
Cited by 5 | Viewed by 2451
Abstract
Exploring soil water dynamics under different land use types is important for water resource management and vegetation restoration in the Loess Plateau. In this study, we investigated the hydrogen and oxygen isotopic compositions of soil water from four different land use types to [...] Read more.
Exploring soil water dynamics under different land use types is important for water resource management and vegetation restoration in the Loess Plateau. In this study, we investigated the hydrogen and oxygen isotopic compositions of soil water from four different land use types to explore the mechanism of soil water movement and transformation and analyse the influence of land use. The results show that the range of stable isotopes (δD and δ18O) in soil water was smaller than that in precipitation. Values for δD and δ18O in soil water showed relatively similar temporal variation, heavy isotopes were enriched in the soil water in July and depleted in October. Stable isotope values in shallow (<100 cm depth) soil water and deep (>200 cm depth) soil water were low. The δD and δ18O values in woodlands decreased gradually with increasing depth. Across the four land use types, the maximum variation in δD and δ18O was in the shallow depth of the soil profile. Groundwater was recharged mainly from precipitation and then from soil water. The ratio of groundwater recharge by soil water under different land use types followed this rank order: woodland (35.70%) > grassland (31.14%) > shrubland (29.47%) > cropland (29.18%). Matrix flow and preferential flow coexisted during infiltration, and the occurrence of preferential flow was related to the land use type. The main reason for the variation in isotopic composition in soil water is the difference in soil evaporation, which is influenced by different vegetation cover. Owing to the difference in soil evaporation and fractionation, precipitation on cropland, shrubland, and grassland can recharge more soil water than on woodland. Full article
(This article belongs to the Section Hydrology)
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27 pages, 6797 KiB  
Article
Flood Susceptibility Assessment Using Novel Ensemble of Hyperpipes and Support Vector Regression Algorithms
by Asish Saha, Subodh Chandra Pal, Alireza Arabameri, Thomas Blaschke, Somayeh Panahi, Indrajit Chowdhuri, Rabin Chakrabortty, Romulus Costache and Aman Arora
Water 2021, 13(2), 241; https://doi.org/10.3390/w13020241 - 19 Jan 2021
Cited by 99 | Viewed by 5790
Abstract
Recurrent floods are one of the major global threats among people, particularly in developing countries like India, as this nation has a tropical monsoon type of climate. Therefore, flood susceptibility (FS) mapping is indeed necessary to overcome this type of natural hazard phenomena. [...] Read more.
Recurrent floods are one of the major global threats among people, particularly in developing countries like India, as this nation has a tropical monsoon type of climate. Therefore, flood susceptibility (FS) mapping is indeed necessary to overcome this type of natural hazard phenomena. With this in mind, we evaluated the prediction performance of FS mapping in the Koiya River basin, Eastern India. The present research work was done through preparation of a sophisticated flood inventory map; eight flood conditioning variables were selected based on the topography and hydro-climatological condition, and by applying the novel ensemble approach of hyperpipes (HP) and support vector regression (SVR) machine learning (ML) algorithms. The ensemble approach of HP-SVR was also compared with the stand-alone ML algorithms of HP and SVR. In relative importance of variables, distance to river was the most dominant factor for flood occurrences followed by rainfall, land use land cover (LULC), and normalized difference vegetation index (NDVI). The validation and accuracy assessment of FS maps was done through five popular statistical methods. The result of accuracy evaluation showed that the ensemble approach is the most optimal model (AUC = 0.915, sensitivity = 0.932, specificity = 0.902, accuracy = 0.928 and Kappa = 0.835) in FS assessment, followed by HP (AUC = 0.885) and SVR (AUC = 0.871). Full article
(This article belongs to the Special Issue Flash-Flood Susceptibility, Forecast and Warning)
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16 pages, 3607 KiB  
Article
Preparation, Performances and Mechanisms of Co@AC Composite for Herbicide Atrazine Removal in Water
by Yongpan Liu, Danxia Liu, Huijun He, Jinxiao Zhang, Jie Liu, Dunqiu Wang, Liangliang Huang and Zhihong Tu
Water 2021, 13(2), 240; https://doi.org/10.3390/w13020240 - 19 Jan 2021
Cited by 8 | Viewed by 2155
Abstract
In this study, a high-performance adsorbent Co@AC was prepared by loading cobalt ions (Co2+) on activated carbon (AC) via solution impregnation and high-temperature calcination technology, and was used to remove atrazine in water. The preparation factors on the adsorbent properties were [...] Read more.
In this study, a high-performance adsorbent Co@AC was prepared by loading cobalt ions (Co2+) on activated carbon (AC) via solution impregnation and high-temperature calcination technology, and was used to remove atrazine in water. The preparation factors on the adsorbent properties were studied, and the characteristics were analyzed by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and Fourier transform infrared spectrometer (FTIR). The results showed that Co@AC possessed the best performance when the factors were 7.0% of Co2+ (w/v), 7.0 h of immersing time, 500 °C of calcination temperature and 4.0 h of calcination time. The adsorption conditions and mechanisms for atrazine removal by Co@AC were also studied scientifically. As the conditions were pH 4.0, reaction time 90 min and temperature 25 °C, Co@AC had the largest adsorption capacity, which was 92.95 mg/g, and the maximum removal rate reached 94.79%. The correlation coefficient of the Freundlich isotherm was better than that of the Langmuir isotherm, and the adsorption process followed the pseudo-second-order kinetic model. Cycle experiments showed that the removal efficiency of atrazine by Co@AC remained above 85% after five repeated experiments, indicating that Co@AC showed a strong stable performance and is a promising material for pesticides removal. Full article
(This article belongs to the Section Wastewater Treatment and Reuse)
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22 pages, 9268 KiB  
Article
Application of Convolution Neural Networks and Hydrological Images for the Estimation of Pollutant Loads in Ungauged Watersheds
by Chul Min Song
Water 2021, 13(2), 239; https://doi.org/10.3390/w13020239 - 19 Jan 2021
Cited by 3 | Viewed by 2188
Abstract
River monitoring and predicting analysis for establishing pollutant loads management require numerous budgets and human resources. However, it is general that the number of government officials in charge of these tasks is few. Although the government has been commissioning a study related to [...] Read more.
River monitoring and predicting analysis for establishing pollutant loads management require numerous budgets and human resources. However, it is general that the number of government officials in charge of these tasks is few. Although the government has been commissioning a study related to river management to experts, it has been inevitable to avoid the consumption of a massive budget because the characteristics of pollutant loads present various patterns according to topographic of the watershed, such as topology like South Korea. To address this, previous studies have used conceptual and empirical models and have recently used artificial neural network models. The conceptual model has a shortcoming in which it required massive data and has vexatious that has to enforce the sensitivity and uncertain analysis. The empirical model and artificial neural network (ANN) need lower data than a conceptual model; however, these models have a flaw that could not reflect the topographical characteristic. To this end, this study has used a convolution neural network (CNN), one of the deep learning algorithms, to reflect the topographical characteristic and had estimated the pollutant loads of ungauged watersheds. The estimation results for the biochemical oxygen demand (BOD) and total phosphorus (TP) loads for three ungauged watersheds were all excellent. However, prediction results with low accuracy were obtained when the hydrological images of a watershed with a land cover status different from the ungauged watersheds were used as training data for the CNN model. Full article
(This article belongs to the Section Hydrology)
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18 pages, 5599 KiB  
Article
Numerical Study of Fluctuating Pressure on Stilling Basin Slab with Sudden Lateral Enlargement and Bottom Drop
by Yangliang Lu, Jinbu Yin, Zhou Yang, Kebang Wei and Zhiming Liu
Water 2021, 13(2), 238; https://doi.org/10.3390/w13020238 - 19 Jan 2021
Cited by 5 | Viewed by 3128
Abstract
A stilling basin with sudden enlargement and bottom drop leads to complicated hydraulic characteristics, especially a fluctuating pressure distribution beneath 3D spatial hydraulic jumps. This paper used the large eddy simulation (LES) model and the TruVOF method based on FLOW-3D software to simulate [...] Read more.
A stilling basin with sudden enlargement and bottom drop leads to complicated hydraulic characteristics, especially a fluctuating pressure distribution beneath 3D spatial hydraulic jumps. This paper used the large eddy simulation (LES) model and the TruVOF method based on FLOW-3D software to simulate the time-average pressure, root mean square (RMS) of fluctuating pressure, maximum and minimum pressure of a stilling basin slab. Compared with physical model results, the simulation results show that the LES model can simulate the fluctuating water flow pressure in a stilling basin reliably. The maximum value of RMS of fluctuating pressure appears in the vicinity of the front of the stilling basin and the extension line of the side wall. Based on the generating mechanism of fluctuating pressure and the Poisson Equation derived from the Navier–Stokes Equation, this paper provides a research method of combining quantitative analysis of influencing factors (fluctuating velocity, velocity gradient, and fluctuating vorticity) and qualitative analysis of the characteristics of fluctuating pressure. The distribution of fluctuating pressure in the swirling zone of the stilling basin and the wall-attached jet zone is mainly affected by the vortex and fluctuating flow velocity, respectively, and the distribution in the impinging zone is caused by fluctuating velocity, velocity gradient and fluctuating vorticity. Full article
(This article belongs to the Special Issue Physical Modelling in Hydraulics Engineering)
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37 pages, 3730 KiB  
Article
Hazards, Vulnerability, and Risk Analysis on Wave Overtopping and Coastal Flooding in Low-Lying Coastal Areas: The Case of Costa da Caparica, Portugal
by José Carlos Ferreira, Fábio Santos Cardona, Catarina Jóia Santos and José António Tenedório
Water 2021, 13(2), 237; https://doi.org/10.3390/w13020237 - 19 Jan 2021
Cited by 10 | Viewed by 5874
Abstract
Coastal areas are densely populated areas, and they have been experiencing increasing pressures as a consequence of population growth, but also because of climate change aggravation. For this reason, hazard, vulnerability, and risk indexes have been becoming more recurrent, especially to study and [...] Read more.
Coastal areas are densely populated areas, and they have been experiencing increasing pressures as a consequence of population growth, but also because of climate change aggravation. For this reason, hazard, vulnerability, and risk indexes have been becoming more recurrent, especially to study and analyze low-lying coastal areas. This study presents an analysis on wave overtopping and coastal flooding, using an Analytic Hierarchy Process (AHP) multicriteria methodology, in Costa da Caparica (Portugal). The definition of the different criteria, as well as their respective weighting for the overall problem and index calculation, was carried out with the help of experts in the subject. By following this methodology, and by using Geographic Information Systems (GIS), hazard, vulnerability, and risk indexes were obtained. The most hazardous areas are located closest to the sea, where the elevation is the lowest, whereas the most vulnerable areas are in neighborhoods with specific socioeconomic characteristics (high urban and economic density). Overall, around 30% of the study area displays moderate to very high risk regarding the occurrence of overtopping and flooding events. The results of this study will be helpful in decision-making processes in matters of coastal zone management and monitoring. Full article
(This article belongs to the Section Oceans and Coastal Zones)
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16 pages, 1124 KiB  
Article
Implications of Experiment Set-Ups for Residential Water End-Use Classification
by Nora Gourmelon, Siming Bayer, Michael Mayle, Guy Bach, Christian Bebber, Christophe Munck, Christoph Sosna and Andreas Maier
Water 2021, 13(2), 236; https://doi.org/10.3390/w13020236 - 19 Jan 2021
Cited by 8 | Viewed by 3215
Abstract
With an increasing need for secured water supply, a better understanding of the water consumption behavior is beneficial. This can be achieved through end-use classification, i.e., identifying end-uses such as toilets, showers or dishwashers from water consumption data. Previously, both supervised and unsupervised [...] Read more.
With an increasing need for secured water supply, a better understanding of the water consumption behavior is beneficial. This can be achieved through end-use classification, i.e., identifying end-uses such as toilets, showers or dishwashers from water consumption data. Previously, both supervised and unsupervised machine learning (ML) techniques are employed, demonstrating accurate classification results on particular datasets. However, a comprehensive comparison of ML techniques on a common dataset is still missing. Hence, in this study, we are aiming at a quantitative evaluation of various ML techniques on a common dataset. For this purpose, a stochastic water consumption simulation tool with high capability to model the real-world water consumption pattern is applied to generate residential data. Subsequently, unsupervised clustering methods, such as dynamic time warping, k-means, DBSCAN, OPTICS and Hough transform, are compared to supervised methods based on SVM. The quantitative results demonstrate that supervised approaches are capable to classify common residential end-uses (toilet, shower, faucet, dishwasher, washing machine, bathtub and mixed water-uses) with accuracies up to 0.99, whereas unsupervised methods fail to detect those consumption categories. In conclusion, clustering techniques alone are not suitable to separate end-use categories fully automatically. Hence, accurate labels are essential for the end-use classification of water events, where crowdsourcing and citizen science approaches pose feasible solutions for this purpose. Full article
(This article belongs to the Special Issue Water and the Ecosphere in the Anthropocene)
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18 pages, 13583 KiB  
Article
An Assessment of Lake Ecology on the Basis of the Macrobenthos Multi-Metric Index (MMI) in 11 Lakes in the Western Region of Jilin, China
by Yi-fan Ding, Shi-jun Sun, Jiang Feng, Peng Cui, Dan Zhang and Zhen-yu Long
Water 2021, 13(2), 235; https://doi.org/10.3390/w13020235 - 19 Jan 2021
Cited by 5 | Viewed by 2542
Abstract
The western region of Jilin Province is located at the northeastern part of China. A large number of lakes are distributed in this region, where is one of five large lake regions within China, supporting both drinking water and agricultural water. The frequent [...] Read more.
The western region of Jilin Province is located at the northeastern part of China. A large number of lakes are distributed in this region, where is one of five large lake regions within China, supporting both drinking water and agricultural water. The frequent human activities and scarce rainfall in this region have resulted in weaker lake connectivity and enrichment of the pollutants within the lakes. The lake ecosystems in the region have been degraded to varying degrees, and thus it is necessary to assess its ecological health. Macrobenthos multi-metric index (MMI) is a mature ecological health assessment method that has been widely used in the lake ecosystem assessment all over the world. However, it has not been well developed for assessing the lake water ecosystem in China. In this study, 11 lakes affected by human activities to different degrees were selected as the research objects. They were categorized into three types on the basis of trophic level. Through the comparison and screening of different biological indicators among different lake types, we selected appropriate indicators to construct the MMI. Four core indicators were selected from 58 candidate indicators to construct the MMI: the total number of taxa, Simpson index, percentage of Diptera + Mesogastropod, and percentage of pollution-intolerant species. MMI could distinguish lakes that are seriously and slightly disturbed by humans. The results of regression analysis also showed that the degree of lake eutrophication caused by human activities had a significant correlation with MMI, effectively explaining its changes. MMI can characterize the disturbance and influence of eutrophication on macrobenthos. The results of MMI can also be affected by the land use type and the coverage of aquatic vegetation around the lake, which are important factors affecting the ecological health of the lake. Research on the application of MMI method to assessment of the ecological health of lakes is very rare in Northeast China. This research can provide supplementary information beyond the traditional water environment assessment for the formulation of management strategies. Full article
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21 pages, 11544 KiB  
Article
Spatial and Temporal Characteristics of Precipitation and Potential Influencing Factors in the Loess Plateau before and after the Implementation of the Grain for Green Project
by Jichao Wang, Miao Sun, Xuerui Gao, Xining Zhao and Yong Zhao
Water 2021, 13(2), 234; https://doi.org/10.3390/w13020234 - 19 Jan 2021
Cited by 4 | Viewed by 2454
Abstract
Since the implementation of the Grain for Green Project (GFGP) in the 1990s, the warming and wetting trend in the Loess Plateau is becoming statistically significant in the context of climate change. However, the correlation between precipitation increase and the regional vegetation restoration [...] Read more.
Since the implementation of the Grain for Green Project (GFGP) in the 1990s, the warming and wetting trend in the Loess Plateau is becoming statistically significant in the context of climate change. However, the correlation between precipitation increase and the regional vegetation restoration is still controversial. To explore the main factors influencing the regional precipitation change, this study selected five potential influencing factors including potential evapotranspiration (PET), normalized difference vegetation index (NDVI), precipitable water (PW), surface temperature (ST), and water vapor transport (WVT). We used the statistical methods to analyze the spatial-temporal distribution of precipitation before and after the GFGP and to quantify the relative influence degree of different factors to precipitation change. The results show that: (1) The precipitation increased significantly (95% confidence level) after the GFGP, with an increase rate of 4.96 mm a−1; (2) from the perspective of spatial-temporal distribution, the precipitation in the southern part of the Loess plateau was significantly increasing with an increase rate of 20–50 mm in the period of 2000–2014; (3) the relative influence degree of NDVI to precipitation increased after the GFGP, and the annual precipitation (PREA) and summer precipitation (PRES) was more influenced by NDVI (relative influence degree of 30.18% and 31.37%, respectively) compared with winter precipitation. In winter, the PW and the PET are the main influencing factors for the precipitation change with relative influence degrees of 30.13% and 27.64%, respectively. Based on this study, we speculate that the warming and wetting trend of the Loess Plateau in recent years is not only closely related to global climate change, but also significantly affected by local climate change brought by vegetation restoration. The above conclusions are important for future ecological restoration and water resources management in the water-scarce Loess Plateau. Full article
(This article belongs to the Special Issue Hydrological Modeling in Water Cycle Processes)
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15 pages, 8150 KiB  
Article
Distribution Uniformity in Intensive Horticultural Systems of Almería and Influence of the Production System and Water Quality
by Juana Isabel Contreras, José Roldán-Cañas, Maria Fatima Moreno-Pérez, Pedro Gavilán, David Lozano and Rafael Baeza
Water 2021, 13(2), 233; https://doi.org/10.3390/w13020233 - 19 Jan 2021
Cited by 7 | Viewed by 2570
Abstract
The high productivity and efficiency of the use of irrigation water that characterizes greenhouse horticultural crops can be affected by poor irrigation distribution uniformity. The objective of this work was to estimate the average irrigation distribution uniformity (DU) of the greenhouses in Almería, [...] Read more.
The high productivity and efficiency of the use of irrigation water that characterizes greenhouse horticultural crops can be affected by poor irrigation distribution uniformity. The objective of this work was to estimate the average irrigation distribution uniformity (DU) of the greenhouses in Almería, determining the influence of the irrigation water quality as well as the production system on this uniformity. A prospective study was carried out in which commercial farms were selected that used different water qualities (groundwater vs. reclaimed) with different production systems (organic vs. conventional/integrated). The average irrigation distribution uniformity in the greenhouses of Almería was 80%. The farms with organic production systems presented a drastic DU reduction with respect to conventional farms (48% vs. 88%). The DU of the irrigation water presented in commercial farms irrigated with reclaimed water presented a lower DU than those irrigated with groundwater (76% vs. 86%). The distribution of irrigation depth of water in the greenhouses showed slight variations (from 3.2 to 2.9 mm) depending on the emitter position, with the highest values being at the head of the sub-main pipe and dripper line and the lowest at the end of the sub-main pipe and dripper line. The depth of water values was very close to the theoretical average of 3 mm. Water quality affects the distribution pattern of the depth of water in greenhouses. Installations irrigated with reclaimed water showed greater oscillation of the water depth within the sub-unit, varying from 3.6 to 2.0 mm, although the average depth was located close to the theoretical depth (3 mm). The production system affected the distribution of the depth of water—in the organic system, the depth underwent greater variation depending on the position of the emitter in the sub-unit, ranging from 1.7 to 3.3 mm. In addition, within this production system, the median depth of water was close to 2.5 mm, lower than the theoretical depth (3 mm), which denoted a certain generalized filling that was accentuated at the end of the dripper line and sub-main pipe. Full article
(This article belongs to the Special Issue Water and Irrigation Management in Arid and Semiarid Zones)
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20 pages, 7380 KiB  
Article
Impact Force of a Geomorphic Dam-Break Wave against an Obstacle: Effects of Sediment Inertia
by Cristiana Di Cristo, Massimo Greco, Michele Iervolino and Andrea Vacca
Water 2021, 13(2), 232; https://doi.org/10.3390/w13020232 - 19 Jan 2021
Cited by 2 | Viewed by 2231
Abstract
The evaluation of the impact force on structures due to a flood wave is of utmost importance for estimating physical damage and designing adequate countermeasures. The present study investigates, using 2D shallow-water approximation, the morphodynamics and forces caused by a dam-break wave against [...] Read more.
The evaluation of the impact force on structures due to a flood wave is of utmost importance for estimating physical damage and designing adequate countermeasures. The present study investigates, using 2D shallow-water approximation, the morphodynamics and forces caused by a dam-break wave against a rigid obstacle in the presence of an erodible bed. A widely used coupled equilibrium model, based on the two-dimensional Saint–Venant hydrodynamic equations combined with the sediment continuity Exner equation (SVEM), is compared with a more complex two-phase model (TPM). Considering an experimental set-up presented in the literature with a single rigid obstacle in a channel, two series of tests were performed, assuming sand or light sediments on the bottom. The former test is representative of a typical laboratory experiment, and the latter may be scaled up to a field case. For each test, two different particle diameters were considered. Independently from the particle size, it was found that in the sand tests, SVEM performs similarly to TPM. In the case of light sediment, larger differences are observed, and the SVEM predicts a higher force of about 26% for both considered diameters. The analysis of the flow fields and the morphodynamics shows these differences can be essentially ascribed to the role of inertia of the solid particles. Full article
(This article belongs to the Special Issue Fluvial Hydraulics and Applications)
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17 pages, 2790 KiB  
Article
Evaluation and Correction of IMERG Late Run Precipitation Product in Rainstorm over the Southern Basin of China
by Chen Yu, Jianchun Zheng, Deyong Hu, Yufei Di, Xiuhua Zhang and Manqing Liu
Water 2021, 13(2), 231; https://doi.org/10.3390/w13020231 - 19 Jan 2021
Cited by 5 | Viewed by 2158
Abstract
Satellite precipitation products play an essential role in providing effective global or regional precipitation. However, there are still many uncertainties in the performance of satellite precipitation products, especially in extreme precipitation analysis. In this study, a Global Precipitation Measurement (GPM) Integrated Multi-satellite Retrievals [...] Read more.
Satellite precipitation products play an essential role in providing effective global or regional precipitation. However, there are still many uncertainties in the performance of satellite precipitation products, especially in extreme precipitation analysis. In this study, a Global Precipitation Measurement (GPM) Integrated Multi-satellite Retrievals for GPM (IMERG) late run (LR) product was used to evaluate the rainstorms in the southern basin of China from 2015 to 2018. Three correction methods, multiple linear regression (MLR), artificial neural network (ANN), and geographically weighted regression (GWR), were used to get correction products to improve the precipitation performance. This study found that IMERG LR’s ability to characterize rainstorm events was limited, and there was a significant underestimation. The observation error and detection ability of IMERG LR decrease gradually from the southeast coast to the northwest inland. The error test shows that in the eastern coastal area (zone I and II), the central area (zone III), and the western inland area (zone IV and V), the optimal correction method is MLR, ANN, and GWR, respectively. The performance of three correction products is slightly better compared with the original product IMERG LR. From zone I to V, correlation coefficient (CC) and root mean square error (RMSE) show a decreasing trend. Zone II has the highest relative bias (RB), and the deviation is relatively large. The categorical indices of inland area performed better than coastal area. The correction product’s precipitation is slightly lower than the observed value from April to November with a mean error of 8.03%. The correction product’s precipitation was slightly higher than the observed values in other months, with an average error of 12.27%. The greater the observed precipitation, the higher the uncertainty of corrected precipitation result. The coefficient of variation showed that zone II had the highest uncertainty, and zone V had the lowest uncertainty. MLR had a high uncertainty with an average of 9.72%. The mean coefficient of variation of ANN and GWR is 7.74% and 7.29%, respectively. This study aims to generate a set of precipitation products with good accuracy through the IMERG LR evaluation and correction to support regional extreme precipitation research. Full article
(This article belongs to the Section Water Resources Management, Policy and Governance)
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21 pages, 6172 KiB  
Article
Impact of the Grid Resolution and Deterministic Interpolation of Precipitation on Rainfall-Runoff Modeling in a Sparsely Gauged Mountainous Catchment
by Paweł Gilewski
Water 2021, 13(2), 230; https://doi.org/10.3390/w13020230 - 19 Jan 2021
Cited by 12 | Viewed by 2777
Abstract
Precipitation is a key variable in the hydrological cycle and essential input data in rainfall-runoff modeling. Rain gauge data are considered as one of the best data sources of precipitation but before further use, the data must be spatially interpolated. The process of [...] Read more.
Precipitation is a key variable in the hydrological cycle and essential input data in rainfall-runoff modeling. Rain gauge data are considered as one of the best data sources of precipitation but before further use, the data must be spatially interpolated. The process of interpolation is particularly challenging over mountainous areas due to complex orography and a usually sparse network of rain gauges. This paper investigates two deterministic interpolation methods (inverse distance weighting (IDW), and first-degree polynomial) and their impact on the outputs of semi-distributed rainfall-runoff modeling in a mountainous catchment. The performed analysis considers the aspect of interpolation grid size, which is often neglected in other than fully-distributed modeling. The impact of the inverse distance power (IDP) value in the IDW interpolation was also analyzed. It has been found that the best simulation results were obtained using a grid size smaller or equal to 750 m and the first-degree polynomial as an interpolation method. The results indicate that the IDP value in the IDW method has more impact on the simulation results than the grid size. Evaluation of the results was done using the Kling-Gupta efficiency (KGE), which is considered to be an alternative to the Nash-Sutcliffe efficiency (NSE). It was found that KGE generally tends to provide higher and less varied values than NSE which makes it less useful for the evaluation of the results. Full article
(This article belongs to the Special Issue Modelling Precipitation in Space and Time)
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31 pages, 7315 KiB  
Article
Improving Thermal Distribution in Water-Cooled PV Modules and Its Effect on RO Permeate Recovery
by Mario F. Suzuki Valenzuela, Fernando Sánchez Soto, María Magdalena Armendáriz-Ontiveros, Ian M. Sosa-Tinoco and Gustavo A. Fimbres Weihs
Water 2021, 13(2), 229; https://doi.org/10.3390/w13020229 - 19 Jan 2021
Cited by 7 | Viewed by 2832
Abstract
Among the most notable emerging hybrid technologies for water treatment are those that combine reverse osmosis (RO) membrane systems with alternative energy sources such as solar photovoltaic (PV). Solar PV modules can enable systems disconnected from the electricity grid, and in some locations [...] Read more.
Among the most notable emerging hybrid technologies for water treatment are those that combine reverse osmosis (RO) membrane systems with alternative energy sources such as solar photovoltaic (PV). Solar PV modules can enable systems disconnected from the electricity grid, and in some locations can also be used for water heating as photovoltaic-thermal (PVT) units, a process in which water removes heat from the PV module, increasing its electrical generation efficiency. When combined with RO, the higher temperature feed water can increase RO permeate flux, improving recovery but decreasing the rejection of dissolved salts. Although the decrease in efficiency of PV modules at higher temperatures is a well-known issue, this is usually under conditions of uniform temperature. However, the temperature distribution in water-cooled PV modules is usually not uniform and, given the anisotropy of the distribution and electrical connection of the PV cells in the module, this factor has not been the focus of much study. In this context, a PVT unit that focuses on increasing the output water temperature with a high global heat transfer coefficient will not necessarily be the most electrically efficient system. This study experimentally assesses several proposed heat-exchange configurations for PVT systems where the PV modules are cooled by forced convective water flow. A simulation model of PVT performance is then validated and used to predict the productivity of the PVT-RO coupling, both in terms of electrical generation and permeate flux of the hybrid system under different conditions. The results suggest that water-cooled PV modules have several potential applications for off-grid and remote water treatment, as well as water transportation systems. Full article
(This article belongs to the Special Issue Water Systems Using Affordable and Clean Energy)
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19 pages, 3239 KiB  
Article
The Human Rights to Water and Sanitation in Policy Responses to the COVID-19 Pandemic: An Analysis of Brazilian States
by Davi Madureira Victral and Léo Heller
Water 2021, 13(2), 228; https://doi.org/10.3390/w13020228 - 19 Jan 2021
Cited by 5 | Viewed by 2683
Abstract
The outbreak of the new coronavirus disease (COVID-19) led to an unprecedented number of policy responses from public institutions involved in the health and economic sectors. Nonetheless, the water, sanitation, and hygiene (WASH) sector remained in the background of this decision-making arena. The [...] Read more.
The outbreak of the new coronavirus disease (COVID-19) led to an unprecedented number of policy responses from public institutions involved in the health and economic sectors. Nonetheless, the water, sanitation, and hygiene (WASH) sector remained in the background of this decision-making arena. The objective of the study presented herein was to observe and discuss political responses to the new coronavirus pandemic in the context of WASH during the first 40 days of the outbreak, using as cases the five Brazilian states most affected by the pandemic. We addressed this issue with a quali-quantitative exploratory study using content analysis to discuss the direction (for whom and how?) of those policy responses, through the framework of the human rights to water and sanitation. The paper also introduces a timeline to map the reactivity and proactivity of the studied institutions. We identified two major priorities in policy responses to the coronavirus pandemic: population protection and financial and economic sustainability of service providers. In regard to population protection, the findings show that it often did not contemplate all of the population, and that equality and non-discriminations were partially ignored in the laws and regulations. In addition, institutions more attached to service providers were more committed to the provider’s economic and financial sustainability than to measures to directly protect the population. Full article
(This article belongs to the Special Issue The Politics of the Human Right to Water)
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20 pages, 6971 KiB  
Article
The Morphological and Functional Organization of Cattails Typha laxmannii Lepech. and Typha australis Schum. and Thonn. under Soil Pollution by Potentially Toxic Elements
by Tatiana Minkina, Grigoriy Fedorenko, Dina Nevidomskaya, Elizaveta Konstantinova, Tatiana Pol’shina, Aleksei Fedorenko, Victor Chaplygin, Saglara Mandzhieva, Tamara Dudnikova and Tara Hassan
Water 2021, 13(2), 227; https://doi.org/10.3390/w13020227 - 18 Jan 2021
Cited by 9 | Viewed by 3221
Abstract
The aim of this study is to investigate the adaptation of two species of cattail Typha australis Schum. and Thonn. and Typha laxmannii Lepech. based on analysis of the morphological and anatomical features of their vegetative and generative organs to soil pollution with [...] Read more.
The aim of this study is to investigate the adaptation of two species of cattail Typha australis Schum. and Thonn. and Typha laxmannii Lepech. based on analysis of the morphological and anatomical features of their vegetative and generative organs to soil pollution with potentially toxic elements (PTE) in the riparian zones of the sea edge of the Don River delta (Southern Russia). Both species of the cattail are able to accumulate high concentrations of Ni, Zn, Cd, Pb and can be used for phytoremediation of polluted territories. The pattern of PTE accumulation in hydrophytes has changed on polluted soils of coastal areas from roots/rhizomes > inflorescences > stems to roots/rhizomes > stems ≥ inflorescences. The comparative morphological and anatomical analysis showed a statistically significant effect of the environmental stress factor by the type of proliferation in T. australis, and species T. laxmannii was visually in a depressed, deformed state with mass manifestations of hypogenesis. These deformations should be considered, on one hand, as adaptive, but on the other, as pathological changes in the structure of the spikes of the cattails. Light-optical and electron microscopic studies have shown that the degree and nature of ultrastructural changes in cattails at the same level of soil pollution are different and most expressed in the assimilation tissue of leaves. However, these changes were destructive for T. australis, but for T. laxmannii, these indicated a high level of adaptation to the prolonged technogenic impact of PTE. Full article
(This article belongs to the Special Issue Geochemistry of Landscape and Soil)
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25 pages, 9879 KiB  
Article
Checking the Plausibility of Modelled Nitrate Concentrations in the Leachate on Federal State Scale in Germany
by Tim Wolters, Nils Cremer, Michael Eisele, Frank Herrmann, Peter Kreins, Ralf Kunkel and Frank Wendland
Water 2021, 13(2), 226; https://doi.org/10.3390/w13020226 - 18 Jan 2021
Cited by 13 | Viewed by 2789
Abstract
In Germany, modelled nitrate concentrations in the leachate are of great importance for the development of scenarios for the long-term achievement of the groundwater quality target according to the specific requirements of the EU Water Framework Directive as well as within the context [...] Read more.
In Germany, modelled nitrate concentrations in the leachate are of great importance for the development of scenarios for the long-term achievement of the groundwater quality target according to the specific requirements of the EU Water Framework Directive as well as within the context of the recently adopted general administrative regulation for the designation of nitrate-polluted areas in Germany. For the German federal states of North Rhine-Westphalia (NRW) and Rhineland-Palatinate (RLP), an area-covering modelling of mean long-term nitrate concentrations in leachate with high spatial resolution was carried out using the model system RAUMIS-mGROWA-DENUZ. Hotspot regions with nitrate concentrations in the leachate of 50 mg NO3/L and more were identified for intensively farmed areas in the Münsterland, Lower Rhine, and Vorderpfalz. The validity of modelled values was checked using measured values from 1119 preselected monitoring stations from shallow springs and aquifers filtered near to the surface with oxidizing properties. For the land use categories of urban areas, arable land, grassland, and forest, an at least good agreement of modelled nitrate concentrations in the leachate and measured nitrate concentrations in groundwater was obtained at numerous sites. An equally good agreement was obtained for 1461 measuring stations from the area of responsibility of the Erftverband, which is a major water supplier in the Lower Rhine region. Here, discrepancies have been analyzed in detail due to profound regional knowledge on observation sites. It turned out that in most cases, accuracy limitations of input data (e.g., N balance surpluses of agriculture at the municipal level, 1:50,000 soil map) have been the reason for larger deviations between observed and modelled values. In a broader sense, the case study has shown on the one hand that the model system RAUMIS-mGROWA-DENUZ is able to reliably represent interrelationships and influencing factors that determine simulated nitrate concentrations in the leachate. On the other hand, it has been proven that observed nitrate concentrations in groundwater may provide a solid data source for checking the plausibility of modelled nitrate concentrations in leachate in cases where certain preselection criteria are applied. Full article
(This article belongs to the Special Issue Geo-Environmental Approaches for the Analysis and Assessment of Groundwater Resources at Catchment-Scale)
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20 pages, 1619 KiB  
Review
A Critical Review of Methods for Analyzing Freshwater Eutrophication
by Yan Zhang, Mingxuan Li, Jiefeng Dong, Hong Yang, Lukas Van Zwieten, Hui Lu, Aref Alshameri, Zihan Zhan, Xin Chen, Xueding Jiang, Weicheng Xu, Yanping Bao and Hailong Wang
Water 2021, 13(2), 225; https://doi.org/10.3390/w13020225 - 18 Jan 2021
Cited by 45 | Viewed by 9831
Abstract
Water eutrophication is a global environmental problem that poses serious threats to aquatic ecosystems and human health. The evaluation of eutrophication provides a theoretical basis and technical guidance for the management and rehabilitation of water ecosystems. In the last four decades, dozens of [...] Read more.
Water eutrophication is a global environmental problem that poses serious threats to aquatic ecosystems and human health. The evaluation of eutrophication provides a theoretical basis and technical guidance for the management and rehabilitation of water ecosystems. In the last four decades, dozens of evaluation methods have been applied to freshwater eutrophication, but there is a clear need to optimize and standardize the most suitable methods. We have addressed this gap by presenting a systematic review of methodologies. Due to the diversity and complexity of water bodies, no single evaluation method was identified that would adequately represent eutrophication under all scenarios. We demonstrate that lakes can best be assessed using the trophic level index (TLI) method, reservoirs and wetlands the trophic state index (TSI) and fuzzy comprehensive evaluation (FCE) method, respectively, and rivers the FCE method or back propagation (BP) neural network methods. More recently applied methodologies including spectral imaging and 3-D mapping of water quality using underwater gliders allow greater resolution and can be effective in managing waterbodies to avoid future eutrophication. The aim of this review is to guide future studies on the most appropriate methods available for assessing and reporting water eutrophication. Full article
(This article belongs to the Special Issue The Impact of Climate Change and Human Activities on Aquatic Environments)
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21 pages, 2555 KiB  
Review
The Status of Arsenic Pollution in the Greek and Cyprus Environment: An Overview
by Spyros K. Golfinopoulos, Soterios P. Varnavas and Dimitrios E. Alexakis
Water 2021, 13(2), 224; https://doi.org/10.3390/w13020224 - 18 Jan 2021
Cited by 21 | Viewed by 5222
Abstract
This study presents an overview about the arsenic (As) contamination and its sources in two European countries. Arsenic is a highly toxic element in its inorganic form and it is carcinogenic to human seven in low concentrations. The occurrence of As in surface [...] Read more.
This study presents an overview about the arsenic (As) contamination and its sources in two European countries. Arsenic is a highly toxic element in its inorganic form and it is carcinogenic to human seven in low concentrations. The occurrence of As in surface water, stream and marine waters, groundwater, bottled water, sediment, soil, mines, and seafood, its environmental origin, and its impacts on human health are discussed. The classes of Geoaccumulation Index for As in Greece ranges from practically uncontaminated to extremely contaminated, and in Cyprus varies between practically uncontaminated and heavily contaminated. In many cases, the As contamination reaches very high concentrations and the impacts may be crucial for the human health and ecosystems. Physicochemical properties, regional climate and geological setting are controlling the occurrence and transport of As. In Greece and Cyprus, the geology, lithology, and ore-deposits are the most important factors for the variation of As contents in water, soil, and sediment. The dominant As species are also determined by the location and the redox conditions. The findings of this paper may be useful for scientists and stakeholders monitoring the studied areas and applying measures for protection of the human and terrestrial ecological receptors (plants, avian, mammals). Full article
(This article belongs to the Special Issue Water Quality Indices: Current and Future Trends in Evaluating Contamination of Groundwater Resources)
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18 pages, 4903 KiB  
Article
How to Assess the Ecological Status of Highly Humic Lakes? Development of a New Method Based on Benthic Invertebrates
by Dāvis Ozoliņš, Agnija Skuja, Jolanta Jēkabsone, Ilga Kokorite, Andris Avotins and Sandra Poikane
Water 2021, 13(2), 223; https://doi.org/10.3390/w13020223 - 18 Jan 2021
Cited by 8 | Viewed by 2982
Abstract
Highly humic lakes are typical for the boreal zone. These unique ecosystems are characterised as relatively undisturbed habitats with brown water, high acidity, low nutrient content and lack of macrophytes. Current lake assessment methods are not appropriate for ecological assessment of highly humic [...] Read more.
Highly humic lakes are typical for the boreal zone. These unique ecosystems are characterised as relatively undisturbed habitats with brown water, high acidity, low nutrient content and lack of macrophytes. Current lake assessment methods are not appropriate for ecological assessment of highly humic lakes because of their unique properties and differing human pressures acting on these ecosystems. This study proposes a new approach suitable for the ecological status assessment of highly humic lakes impacted by hydrological modifications. Altogether, 52 macroinvertebrate samples from 15 raised bog lakes were used to develop the method. The studied lakes are located in the raised bogs at the central and eastern parts of Latvia. Altered water level was found as the main threat to the humic lake habitats since no other pressures were established. A multimetric index based on macroinvertebrate abundance, littoral and profundal preferences, Coleoptera taxa richness and the Biological Monitoring Working Party (BMWP) Score is suggested as the most suitable tool to assess the ecological quality of the highly humic lakes. Full article
(This article belongs to the Special Issue Freshwater Macroinvertebrates: Main Gaps and Future Trends)
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27 pages, 4609 KiB  
Article
Evapotranspiration Response to Climate Change in Semi-Arid Areas: Using Random Forest as Multi-Model Ensemble Method
by Marcos Ruiz-Aĺvarez, Francisco Gomariz-Castillo and Francisco Alonso-Sarría
Water 2021, 13(2), 222; https://doi.org/10.3390/w13020222 - 18 Jan 2021
Cited by 12 | Viewed by 2847
Abstract
Large ensembles of climate models are increasingly available either as ensembles of opportunity or perturbed physics ensembles, providing a wealth of additional data that is potentially useful for improving adaptation strategies to climate change. In this work, we propose a framework to evaluate [...] Read more.
Large ensembles of climate models are increasingly available either as ensembles of opportunity or perturbed physics ensembles, providing a wealth of additional data that is potentially useful for improving adaptation strategies to climate change. In this work, we propose a framework to evaluate the predictive capacity of 11 multi-model ensemble methods (MMEs), including random forest (RF), to estimate reference evapotranspiration (ET0) using 10 AR5 models for the scenarios RCP4.5 and RCP8.5. The study was carried out in the Segura Hydrographic Demarcation (SE of Spain), a typical Mediterranean semiarid area. ET0 was estimated in the historical scenario (1970–2000) using a spatially calibrated Hargreaves model. MMEs obtained better results than any individual model for reproducing daily ET0. In validation, RF resulted more accurate than other MMEs (Kling–Gupta efficiency (KGE) M=0.903, SD=0.034 for KGE and M=3.17, SD=2.97 for absolute percent bias). A statistically significant positive trend was observed along the 21st century for RCP8.5, but this trend stabilizes in the middle of the century for RCP4.5. The observed spatial pattern shows a larger ET0 increase in headwaters and a smaller increase in the coast. Full article
(This article belongs to the Special Issue Evapotranspiration Measurements and Modeling)
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16 pages, 4950 KiB  
Article
A New Method for Wet-Dry Front Treatment in Outburst Flood Simulation
by Dingzhu Liu, Jinbo Tang, Hao Wang, Yang Cao, Nazir Ahmed Bazai, Huayong Chen and Daochuan Liu
Water 2021, 13(2), 221; https://doi.org/10.3390/w13020221 - 18 Jan 2021
Cited by 9 | Viewed by 2339
Abstract
When utilizing a finite volume method to predict outburst flood evolution in real geometry, the processing of wet-dry front and dry cells is an important step. In this paper, we propose a new approach to process wet-dry front and dry cells, including four [...] Read more.
When utilizing a finite volume method to predict outburst flood evolution in real geometry, the processing of wet-dry front and dry cells is an important step. In this paper, we propose a new approach to process wet-dry front and dry cells, including four steps: (1) estimating intercell properties; (2) modifying interface elevation; (3) calculating dry cell elevations by averaging intercell elevations; and (4) changing the value of the first term of slope limiter based on geometry in dry cells. The Harten, Lax, and van Leer with the contact wave restored (HLLC) scheme was implemented to calculate the flux. By combining the MUSCL (Monotone Upstream–centred Scheme for Conservation Laws)-Hancock method with the minmod slope limiter, we achieved second-order accuracy in space and time. This approach is able to keep the conservation property (C-property) and the mass conservation of complex bed geometry. The results of numerical tests in this study are consistent with experimental data, which verifies the effectiveness of the new approach. This method could be applied to acquire wetting and drying processes during flood evolution on structured meshes. Furthermore, a new settlement introduces few modification steps, so it could be easily applied to matrix calculations. The new method proposed in this study can facilitate the simulation of flood routing in real terrain. Full article
(This article belongs to the Special Issue Soil–Water Conservation, Erosion, and Landslide)
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15 pages, 5285 KiB  
Article
Spatio-Temporal Analysis of Surface Water Quality in Mokopane Area, Limpopo, South Africa
by Mmasabata Dolly Molekoa, Ram Avtar, Pankaj Kumar, Huynh Vuong Thu Minh, Rajarshi Dasgupta, Brian Alan Johnson, Netrananda Sahu, Ram Lal Verma and Ali P. Yunus
Water 2021, 13(2), 220; https://doi.org/10.3390/w13020220 - 18 Jan 2021
Cited by 21 | Viewed by 6121
Abstract
Considering the well-documented impacts of land-use change on water resources and the rapid land-use conversions occurring throughout Africa, in this study, we conducted a spatiotemporal analysis of surface water quality and its relation with the land use and land cover (LULC) pattern in [...] Read more.
Considering the well-documented impacts of land-use change on water resources and the rapid land-use conversions occurring throughout Africa, in this study, we conducted a spatiotemporal analysis of surface water quality and its relation with the land use and land cover (LULC) pattern in Mokopane, Limpopo province of South Africa. Various physico-chemical parameters were analyzed for surface water samples collected from five sampling locations from 2016 to 2020. Time-series analysis of key surface water quality parameters was performed to identify the essential hydrological processes governing water quality. The analyzed water quality data were also used to calculate the heavy metal pollution index (HPI), heavy metal evaluation index (HEI) and weighted water quality index (WQI). Also, the spatial trend of water quality is compared with LULC changes from 2015 to 2020. Results revealed that the concentration of most of the physico-chemical parameters in the water samples was beyond the World Health Organization (WHO) adopted permissible limit, except for a few parameters in some locations. Based on the calculated values of HPI and HEI, water quality samples were categorized as low to moderately polluted water bodies, whereas all water samples fell under the poor category (>100) and beyond based on the calculated WQI. Looking precisely at the water quality’s temporal trend, it is found that most of the sampling shows a deteriorating trend from 2016 to 2019. However, the year 2020 shows a slightly improving trend on water quality, which can be justified by lowering human activities during the lockdown period imposed by COVID-19. Land use has a significant relationship with surface water quality, and it was evident that built-up land had a more significant negative impact on water quality than the other land use classes. Both natural processes (rock weathering) and anthropogenic activities (wastewater discharge, industrial activities etc.) were found to be playing a vital role in water quality evolution. This study suggests that continuous assessment and monitoring of the spatial and temporal variability of water quality in Limpopo is important to control pollution and health safety in the future. Full article
(This article belongs to the Special Issue Water Quality Assessments for Urban Water Environment)
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13 pages, 3265 KiB  
Article
Characterizing Preferential Flow Paths in Texturally Similar Soils under Different Land Uses by Combining Drainage and Dye-Staining Methods
by Youyan Zhang, Zhe Cao, Fang Hou and Jinhua Cheng
Water 2021, 13(2), 219; https://doi.org/10.3390/w13020219 - 18 Jan 2021
Cited by 5 | Viewed by 2227
Abstract
Preferential flow paths have been widely characterized by many visualization methods. However, the differences in preferential flow paths under various land uses and their relationships to hydraulic properties remain uncertain. The objectives of this study are to (1) characterize preferential flow paths under [...] Read more.
Preferential flow paths have been widely characterized by many visualization methods. However, the differences in preferential flow paths under various land uses and their relationships to hydraulic properties remain uncertain. The objectives of this study are to (1) characterize preferential flow paths under various land uses (forest and orchard) by combining drainage and dye-staining methods and to (2) build a connection between preferential flow paths and hydraulic-related parameters and extract the proportion of preferential flow paths from the compounding effects of matrix flow and preferential flow. The dye-staining experiments were conducted in five sandy soils and one sandy clay loam in situ, including four soils from forest and two soils from orchards. A total of 47 soil cores, 4 cm in height and 9 cm in diameter, were collected in each layer of the dye-stained soils for drainage experiments in the laboratory. Dye coverage and hydraulically equivalent macropore parameters (macroporosity, pore size distribution, and number of macropores) and their relationships were analyzed. The results show that the volume of preferential flow is partly affected by the total macropore volume. The effect of macropores on preferential flow varies by macropore size distribution. Dye coverage exhibited a significant (P < 0.01) correlation with macroporosity (correlation coefficient 0.83). Based on the value of macroporosity or steady effluent rates, the part of the dye coverage that was due to preferential flow on the surface dye-stained soil (resulting from both matrix and preferential flow) could be identified in this study. Compared with orchards, forestland has more preferential flow paths in both surface soil and subsoil. Further studies are needed to quantify the 3-D preferential flow paths and build a connection between preferential flow paths and hydraulic properties. Full article
(This article belongs to the Section Hydrology)
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25 pages, 945 KiB  
Article
Planning the Urban Waterfront Transformation, from Infrastructures to Public Space Design in a Sea-Level Rise Scenario: The European Union Prize for Contemporary Architecture Case
by Francesca Dal Cin, Fransje Hooimeijer and Maria Matos Silva
Water 2021, 13(2), 218; https://doi.org/10.3390/w13020218 - 18 Jan 2021
Cited by 13 | Viewed by 6492
Abstract
Future sea-level rises on the urban waterfront of coastal and riverbanks cities will not be uniform. The impact of floods is exacerbated by population density in nearshore urban areas, and combined with land conversion and urbanization, the vulnerability of coastal towns and public [...] Read more.
Future sea-level rises on the urban waterfront of coastal and riverbanks cities will not be uniform. The impact of floods is exacerbated by population density in nearshore urban areas, and combined with land conversion and urbanization, the vulnerability of coastal towns and public spaces in particular is significantly increased. The empirical analysis of a selected number of waterfront projects, namely the winners of the Mies Van Der Rohe Prize, highlighted the different morphological characteristics of public spaces, in relation to the approximation to the water body: near the shoreline, in and on water. The critical reading of selected architectures related to water is open to multiple insights, allowing to shift the design attention from the building to the public space on the waterfronts. The survey makes it possible to delineate contemporary features and lay the framework for urban development in coastal or riverside areas. Full article
(This article belongs to the Special Issue Integrated Approaches to Manage Floods in Urban Environments)
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13 pages, 1459 KiB  
Article
Effect of Drip Irrigation on Soil Water Balance and Water Use Efficiency of Maize in Northwest China
by Yahui Wang, Sien Li, Yaokui Cui, Shujing Qin, Hui Guo, Danni Yang and Chunyu Wang
Water 2021, 13(2), 217; https://doi.org/10.3390/w13020217 - 18 Jan 2021
Cited by 17 | Viewed by 4422
Abstract
Drip irrigation (DI) has been widely utilized for crops and its water-saving effect has been confirmed by numerous studies. However, whether this technology can save so much water under the field scale during practical application is still uncertain. In order to answer this [...] Read more.
Drip irrigation (DI) has been widely utilized for crops and its water-saving effect has been confirmed by numerous studies. However, whether this technology can save so much water under the field scale during practical application is still uncertain. In order to answer this question, evapotranspiration (ET), soil water content, transpiration and evaporation over the DI and border irrigation (BI) in an arid area of NW China were continuously measured by two eddy covariance systems, micro-lysimeters, the packaged stem sap flow gauges and CS616 sensors during 2014–2018 growing seasons. The results showed that the DI averagely increased crop water use efficiency (CWUE) by 11% per year against BI. The deep drainage under DI treatment was lower than BI by 8% averagely for the five-year period. While for the ET, the DI averagely decreased ET by 7% and 40mm per year against the traditional BI. The decrease in ET was mainly due to the significant reduction in soil evaporation instead of transpiration. Oppositely, we found that DI may increase maize (Zea mays L.) transpiration in some year for the better preponderant growth of crop. Thus, the accelerating effect on transpiration of DI and its reducing effect on soil evaporation should be considered simultaneously. In our experiment, DI only improved CWUE and WUE (water use efficiency) by 11% and 15% on average in a large farmland scale, unable to always be more than a 20% improvement, as concluded by many other field experiments. Consequently, the water-saving effect of DI should not be overestimated in water resource evaluation. Full article
(This article belongs to the Section Water, Agriculture and Aquaculture)
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22 pages, 2954 KiB  
Article
Susceptibility to Gully Erosion: Applying Random Forest (RF) and Frequency Ratio (FR) Approaches to a Small Catchment in Ethiopia
by Selamawit Amare, Eddy Langendoen, Saskia Keesstra, Martine van der Ploeg, Habtamu Gelagay, Hanibal Lemma and Sjoerd E. A. T. M. van der Zee
Water 2021, 13(2), 216; https://doi.org/10.3390/w13020216 - 18 Jan 2021
Cited by 32 | Viewed by 3681
Abstract
Soil erosion by gullies in Ethiopia is causing environmental and socioeconomic problems. A sound soil and water management plan requires accurately predicted gully erosion hotspot areas. Hence, this study develops a gully erosion susceptibility map (GESM) using frequency ratio (FR) and random forest [...] Read more.
Soil erosion by gullies in Ethiopia is causing environmental and socioeconomic problems. A sound soil and water management plan requires accurately predicted gully erosion hotspot areas. Hence, this study develops a gully erosion susceptibility map (GESM) using frequency ratio (FR) and random forest (RF) algorithms. A total of 56 gullies were surveyed, and their extents were derived by digitizing Google Earth imagery. Literature review and a multicollinearity test resulted in 14 environmental variables for the final analysis. Model prediction potential was evaluated using the area under the curve (AUC) method. Results showed that the best prediction accuracy using the FR and RF models was obtained by using the top four most important gully predictor factors: drainage density, elevation, land use, and groundwater table. The notion that the groundwater table is one of the most important gully predictor factors in Ethiopia is a novel and significant quantifiable finding and is critical to the design of effective watershed management plans. Results from separate variable importance analyses showed land cover for Nitisols and drainage density for Vertisols as leading factors determining gully locations. Factors such as texture, stream power index, convergence index, slope length, and plan and profile curvatures were found to have little significance for gully formation in the studied catchment. Full article
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25 pages, 1428 KiB  
Review
Current and Emerging Adsorbent Technologies for Wastewater Treatment: Trends, Limitations, and Environmental Implications
by Fazila Younas, Adnan Mustafa, Zia Ur Rahman Farooqi, Xiukang Wang, Sadia Younas, Waqas Mohy-Ud-Din, Muhammad Ashir Hameed, Muhammad Mohsin Abrar, Ali Akbar Maitlo, Saima Noreen and Muhammad Mahroz Hussain
Water 2021, 13(2), 215; https://doi.org/10.3390/w13020215 - 18 Jan 2021
Cited by 106 | Viewed by 12583
Abstract
Wastewater generation and treatment is an ever-increasing concern in the current century due to increased urbanization and industrialization. To tackle the situation of increasing environmental hazards, numerous wastewater treatment approaches are used—i.e., physical, chemical, and biological (primary to tertiary treatment) methods. Various treatment [...] Read more.
Wastewater generation and treatment is an ever-increasing concern in the current century due to increased urbanization and industrialization. To tackle the situation of increasing environmental hazards, numerous wastewater treatment approaches are used—i.e., physical, chemical, and biological (primary to tertiary treatment) methods. Various treatment techniques being used have the risks of producing secondary pollutants. The most promising technique is the use of different materials as adsorbents that have a higher efficacy in treating wastewater, with a minimal production of secondary pollutants. Biosorption is a key process that is highly efficient and cost-effective. This method majorly uses the adsorption process/mechanism for toxicant removal from wastewater. This review elaborates the major agricultural and non-agricultural materials-based sorbents that have been used with their possible mechanisms of pollutant removal. Moreover, this creates a better understanding of how the efficacy of these sorbents can be enhanced by modification or treatments with other substances. This review also explains the re-usability and mechanisms of the used adsorbents and/or their disposal in a safe and environmentally friendly way, along with highlighting the major research gaps and potential future research directions. Additionally, the cost benefit ratio of adsorbents is elucidated. Full article
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