Drainage Scenarios Research Articles

A macro-level life cycle environmental-economic impact and benefit assessment of sponge cities in China

Urban runoff source control facilities (URSCFs) are integral components of Sponge City (SC), playing a pivotal role in providing ecosystem services and managing water quality and quantity. To accurately assess the performance of URSCFs, it is crucial to quantify their environmental and economic impacts. However, previous studies have predominantly focused on location-specific case studies, lacking a macro-level perspective necessary for informing public policy development pertaining to SC initiatives. This study aims to bridge this gap by conducting a macro-level life cycle assessment across China's 16 initial pilot SCs, categorized into three zones based on their annual rainfall volume control rate α (i.e., Zone II (80 % to 85 % for α), Zone III (75 % to 85 % for α), and Zone IV (70 % to 85 % for α)). By simulating five rainfall drainage scenarios, we delve into the environmental benefits of SC construction. The results indicate that Zone III incurs the highest environmental and economic costs during the construction phase, followed by Zones II and IV. In Zone III, bioretention contribute significantly to the environmental impact and economic cost, while constructed wetland and detention cells are the key contributors for Zone II. During the operation phase, Zone III demonstrates the largest environmental and economic benefits, with Zone IV and II trailing behind. The investment payback period for SCs in all zones is less than eight years, with Zone IV recovering costs the fastest (3.9 years) and Zone II the slowest (7.5 years). Facilities like detention cells, green roofs, and permeable pavements tend to have longer payback periods. Based on our findings, we recommend that Zone II exercise caution in constructing detention cells, permeable pavements, and wetlands, while Zone III should carefully consider green roofs and bioretention to optimize SC investments. Due to the fewer URSCFs constructed in Zone IV, it exhibits the lowest environmental impact compared to Zones II and III. Our research provides valuable insights to support policymaking with regards to future SC planning and development.

Numerical solutions of thin film flows of non-Newtonian fluids via optimal homotopy asymptotic approach

The objective of this research is to recover new solutions in the lifting and drainage cases of thin film flows involving non-Newtonian fluid models namely Pseudo-Plastic (PP) and Oldroyd 6-Constant (O6C). Both of the considered fluids exhibit numerous uses in industry when coupled with thin film phenomena. Some of the industrial applications include decorative and optical coatings, prevention of metallic corrosion and lithography of various diodes, sensors and detectors. For solution purpose, a modified version of Optimal Homotopy Asymptotic Method (OHAM) is proposed in which Daftardar–Jafari polynomials will replace the classical OHAM polynomials in nonlinear problems and provide better results in terms of accuracy. The paper includes a comprehensive application of modified algorithm in the case of thin film phenomena. To validate the obtained series solutions, the paper employs a rigorous assessment of convergence and validity by computing the residual errors in each scenario. For showing the effectiveness of modified algorithm, numerical comparison of classical and modified OHAMs is also presented in this study. Furthermore, the study conducts an in-depth graphical analysis to assess the impact of fluid parameters on velocity profiles both in lifting and drainage scenarios. The results of this investigation demonstrate that the proposed modification of OHAM ensures better accuracy of solutions than the classical OHAM. Consequently, this method can be effectively utilized for tackling more advanced situations.

Modeling the Potential Influence of Subsurface Tile Drainage Systems on Downstream Flooding in a Midwestern Agricultural Watershed

Highlights Tile flow was simulated to study the impacts of tile drainage on watershed hydrology and downstream flood days. Three tile drainage scenarios with varied extents of drained land were compared with a baseline scenario. The depth of tile flow contributing to streamflow was found to increase as the area of drained land increased. Results suggest that drainage systems decrease flood days when compared to the baseline scenario. Abstract. Subsurface tile drainage systems are common in agricultural regions of the Midwestern United States. Drainage systems remove excess water from the surface and soil profile of agricultural fields, allowing crop production in previously unsuitable locations. However, these systems impact watershed hydrology and could influence flooding events. Therefore, this study aimed to determine whether tile drainage systems influence downstream flood days in a Midwestern agricultural watershed, specifically the Skunk Creek watershed. The Soil and Water Assessment Tool (SWAT) model was used to simulate the hydrologic processes of the Skunk Creek Watershed for an 18-year period (2004–2021). The model was calibrated and validated using observed daily streamflow data with the SWAT Calibration and Uncertainty Program (SWAT-CUP) software and through the manual modification of missed precipitation data. Three tile drainage scenarios—ranging from 15% to 75% tile-drained agricultural land—were individually incorporated into the model. Results indicated that with increased tile drainage, surface runoff, groundwater flow, deep aquifer recharge, and percolation decreased, whereas lateral soil flow, tile flow, evapotranspiration, and water yield increased. A comparison of tile drainage scenarios suggests that increasing the area of tile-drained agricultural land decreases total flood days. However, the impact of tile drainage systems on downstream peak flood flows varied by event, with large precipitation events initiating flood days across all scenarios. While tile flow decreased flood days on a daily time step, flash floods might have occurred on a sub-daily time step but were not captured in this study. Future studies can replicate the approach with a sub-daily time step for simulating hourly flood events with various tile drainage scenarios. Keywords: Midwestern United States, Streamflow, SWAT, Tile drainage, Watershed hydrology.

Chemical composition of arsenic-based acid mine drainage in the downstream of a gold mine: Fuzzy regression and clustering analysis

This study employs fuzzy regression and fuzzy multivariate clustering techniques to analyze arsenic-polluted water samples originating from acid rock drainage in waste rock dumps. The research focuses on understanding the complex relationships between variables associated with arsenic contamination, such as water arsenic concentration, pH levels, and soil characteristics. To this end, fuzzy regression models were developed to estimate the relationships between water arsenic concentration and independent variables, thus, incorporating the inherent uncertainties into the analysis. Furthermore, multivariate fuzzy k-means clustering analysis facilitated the identification of fuzzy-based clusters within the dataset, providing insights into spatial patterns and potential sources of arsenic pollution. The pairwise comparisons indicated the strongest correlation of 0.62 between soil total arsenic and pH, while the weakest correlation of 0.13 was observed between soil-soluble arsenic and soil iron, providing valuable insights into their relationships and impact on water arsenic levels. The associated uncertainties in the relationships among the variables were determined based on the degree of belongingness of each data point to various fuzzy sets. Three distinct clusters emerged from the analysis: Cluster 1 comprised Points 5, 6, and 7; Cluster 2 included Points 1, 2, 3, 4, 8, and 9; and Cluster 3 consisted of Points 10, 11, 12, and 13. The findings enhance our understanding of the factors influencing arsenic contamination to provide an effective mitigation strategy in acid rock drainage scenarios. This research also demonstrates the applicability and effectiveness of fuzzy regression and fuzzy multivariate clustering in the analysis of arsenic-polluted water samples.

Geomorphologic evidence of jökulhlaups along the Hvítá River, southwestern Iceland

Glacial outburst floods (jökulhlaups) have been a significant driver of landscape evolution, environmental change, and geohazards throughout the Quaternary. Iceland experiences more frequent jökulhlaups than nearly anywhere else on Earth, though most research focuses on subglacial volcanogenic floods that drain across outwash plains. Abundant geomorphologic evidence exists for largescale jökulhlaups that drained along the modern-day course of the Hvítá River in southwestern Iceland during early Holocene deglaciation, originating from ice-dammed Glacial Lake Kjölur; yet only one previous publication has investigated these events. This study uses a combination of field mapping and remote sensing to identify new jökulhlaup geomorphologic evidence along the Hvítá River, including erosional landforms such as scoured bedrock, anastomosing channel networks, cataracts, and canyons, and depositional features such as boulder bars and channel infill. We synthesize new findings with previously reported work to: 1) present an updated geomorphologic map of Hvítá jökulhlaup evidence; 2) reconstruct flood drainage routes, landscape impact, hydrology, and relative chronology; and 3) hypothesize scenarios of ice margin position and glacial lake evolution. Interpreting flood landform assemblages reveals a more extensive geomorphologic record than previously reported, with a complex drainage pattern along four separate routes from two potentially different sources. Reconstructed peak flow discharges span four orders of magnitude from 10² to 10$^5$ m³/s. Geomorphologic and paleohydraulic results introduce four hypothesized drainage scenarios, though absolute geochronology is necessary to determine whether multiple floods drained along each route. The Hvítá jökulhlaups yield insight into the timing and dynamics of the final phase of Icelandic Ice Sheet decay, advancing understanding of Iceland’s Pleistocene–Holocene transition, demonstrating the importance of high magnitude, low frequency floods in landscape evolution, and serving as an analogue to ice and meltwater response to past, present, and future climate warming in glaciated regions worldwide.

An Application of Homotopy Perturbation Method to Fractional-Order Thin Film Flow of the Johnson–Segalman Fluid Model

Thin film flow is an important theme in fluid mechanics and has many industrial applications. These flows can be observed in oil refinement process, laser cutting, and nuclear reactors. In this theoretical study, we explore thin film flow of non-Newtonian Johnson–Segalman fluid on a vertical belt in fractional space in lifting and drainage scenarios. Modelled fractional-order boundary value problems are solved numerically using the homotopy perturbation method along with Caputo definition of fractional derivative. In this study, instantaneous and average velocities and volumetric flux are computed in lifting and drainage cases. Validity and convergence of homotopy-based solutions are confirmed by finding residual errors in each case. Moreover, the consequences of different fractional and fluid parameters are graphically studied on the velocity profile. Analysis shows that fractional parameters have opposite effects of the fluid velocity.

Hybrid Approach for Excess Stormwater Management: Combining Decentralized and Centralized Strategies for the Enhancement of Urban Flooding Resilience

Urban sprawl and soil sealing has gradually led to an impervious surface increase with consequences on the enhancement of flooding risk. During the last decades, a hybrid approach involving both traditional storm water detention tanks (SWDTs) and low-impact development (LID) has resulted in the best solution to manage urban flooding and to improve city resilience. This research aimed at a modeling comparison between drainage scenarios involving the mentioned hybrid approach (H-SM), with (de)centralized LID supporting SWDTs, and a scenario representative of the centralized approach only involving SWDTs (C-SM). Results highlighted that the implementation of H-SM approaches could be a great opportunity to reduce SWDTs volumes. However, the performances varied according to the typology of implemented LID, their parameterization with specific reference to the draining time, and the rainfall severity. Overall, with the increase of rainfall severity and the decrease of draining time, a decrease of retention performances can be observed with SWDTs volume reductions moving from 100% to 28%. In addition, without expecting to implement multicriteria techniques, a preliminary cost analysis pointed out that the larger investment effort of the (de)centralized LID could be, in specific cases, overtaken by the cost advantages resulting from the reduction of the SWDTs volumes.

Seasonal effects of controlled drainage on field water balance and groundwater levels

Abstract Adaptive water management solutions such as controlled drainage have raised interest in Nordic areas due to climate variability. It is not fully known how controlled drainage affects seasonal field water balance or can help in preventing water scarcity during dry growing seasons (GSs). The objective was to simulate the effects of controlled drainage on field hydrology using a well-tested, process-based hydrological model. The FLUSH model was calibrated and validated to an experimental field. The model performance with non-local input data was moderate but acceptable for running the controlled drainage scenarios to test the response of the water management method to meteorological forcing. Simulation results showed that controlled drainage reduced drain discharge while increasing surface layer runoff and shallow groundwater outflow. Groundwater depths from the scenario simulations demonstrated that controlled drainage could keep the depth closer to the soil surface, but the effect diminished during the dry conditions. Controlled drainage can be used to change the water flow pathways but has a secondary effect compared with the primary meteorological drivers. The field data set and FLUSH formed a novel computational platform to study the impacts of different water management options on the whole water balance and spatial variability of groundwater depths.

Synergetic Tl and As retention in secondary minerals: An example of extreme arsenic and thallium pollution

Secondary minerals could be effective scavengers of toxic arsenic (As) and thallium (Tl). In environments polluted by mining, these elements are abundant both in acid rock/mine drainage scenarios, as well as in carbonate-buffered environments. In this study we have investigated the behavior of As and Tl during weathering in mine waste dumps and an associated technosol sample from the Crven Dol locality (Allchar Tl–As–Sb–Au deposit, North Macedonia) contaminated with up to 142 g kg−1 of As and 18 g kg−1 of Tl, making it an As- and Tl-extreme environment. We identified As and Tl reservoirs and discuss their difference from those observed in other naturally As- and Tl-rich environments. The pore waters show high concentrations of As (up to 196 mg L−1) and Tl (up to 660 μg L−1). Mild extractions mobilized up to 46% of the total Tl and 11% of the total As, indicating that a large amount of these toxic elements is weakly bound and can be easily mobilized into the environment. Apart from the recognition of Tl storage in several secondary phases (mainly as Tl(I) in members of the pharmacosiderite and jarosite groups, as well as Mn oxides, but also as very minor Tl(III) in other secondary phases), this study also provides the first evidence of Tl uptake by previously unknown thallium arsenate phases (with Tl:As ratios ∼ 2 and 4), detected in carbonate-buffered (near-neutral pH) As- and Tl-rich technosols and waste dumps. These results indicate the need for further studies on Tl speciation in extremely As- and Tl-rich environments.

Hydrologic and suspended sediment effects of forest roads using field and DHSVM modelling studies

Forest road hydrologic and surface erosion effects were evaluated using a two-step approach in South Fork Caspar Creek: (1) road runoff and suspended sediment measurements and (2) use of the Distributed Hydrology Soil Vegetation Model (DHSVM) to examine road scenarios at the watershed scale. Statistical evaluation showed the best multiple linear regression (MLR) model to predict Log10 suspended sediment load (SSL) was from road runoff event peak flow and cube root of maximum turbidity combined with road characteristics of either cutslope cover or road surface type. MLR using road dimensions and event precipitation, without runoff or turbidity, suggested the best model to predict Log10 SSL used road length times slope squared (LS2), road surface type, and cutslope area. DHSVM simulations for three different road drainage scenarios for two road networks were used to evaluate hydrologic and suspended sediment effects. The 2018 road network represented road networks placed high on slopes away from watercourses and a pre-1974 road network lower on the hillslopes with high numbers of watercourse crossings and streamside roads. Forest harvest of South Fork Caspar Creek (SFC) was predicted by DHSVM to increase storm peak flows by 1.5% to 11% relative to pre-harvest, no-road peak flows. The 2018 road network, with 13% of road length adjacent to watercourses, was predicted to make < 2% increase in peak flows. In contrast, the pre-1974 road network scenario, with 58% of road length adjacent to watercourses, was predicted to increase peak flows as much as 46%. There were low levels of suspended sediment contributions, 23–86 kg/ha/yr, predicted from the 2018 road network scenario with few road watercourse crossings. The pre-1974 road network was predicted to contribute 347 – 2158 kg/ha/yr, depending on road drainage scenario.

Pore-Scale Dynamics of Liquid CO2–Water Displacement in 2D Axisymmetric Porous Micromodels Under Strong Drainage and Weak Imbibition Conditions: High-Speed μPIV Measurements

Resolving pore-scale transient flow dynamics is crucial to understanding the physics underlying multiphase flow in porous media and informing large-scale predictive models. Surface properties of the porous matrix play an important role in controlling such physics, yet interfacial mechanisms remain poorly understood, in part due to a lack of direct observations. This study reports on an experimental investigation of the pore-scale flow dynamics of liquid CO2 and water in two-dimensional (2D) circular porous micromodels with different surface characteristics employing high-speed microscopic particle image velocimetry (μPIV). The design of the micromodel minimized side boundary effects due to the limited size of the domain. The high-speed μPIV technique resolved the spatial and temporal dynamics of multiphase flow of CO2 and water under reservoir-relevant conditions, for both drainage and imbibition scenarios. When CO2 displaced water in a hydrophilic micromodel (i.e., drainage), unstable capillary fingering occurred and the pore flow was dominated by successive pore-scale burst events (i.e., Haines jumps). When the same experiment was repeated in a nearly neutral wetting micromodel (i.e., weak imbibition), flow instability and fluctuations were virtually eliminated, leading to a more compact displacement pattern. Energy balance analysis indicates that the conversion efficiency between surface energy and external work is less than 30%, and that kinetic energy is a disproportionately smaller contributor to the energy budget. This is true even during a Haines jump event, which induces velocities typically two orders of magnitude higher than the bulk velocity. These novel measurements further enabled direct observations of the meniscus displacement, revealing a significant alteration of the pore filling mechanisms during drainage and imbibition. While the former typically featured burst events, which often occur only at one of the several throats connecting a pore, the latter is typically dominated by a cooperative filling mechanism involving simultaneous invasion of a pore from multiple throats. This cooperative filling mechanism leads to merging of two interfaces and releases surface energy, causing instantaneous high-speed events that are similar, yet fundamentally different from, burst events. Finally, pore-scale velocity fields were statistically analyzed to provide a quantitative measure of the role of capillary effects in these pore flows.

The importance of subsurface drainage on model performance and water balance in an agricultural catchment using SWAT and SWAT-MODFLOW

Artificial subsurface drainage impacts the hydrological system, but its spatial distribution is typically uncertain, hindering the understanding of the hydrological behaviour of a certain catchment. In this study, the effects of using four different sources to delineate the spatial distribution of subsurface drainage systems on hydrological modelling performance and simulated water balance were assessed. This work was addressed using SWAT and SWAT-MODFLOW (that is, four SWAT models and four SWAT-MODFLOW models were set up and evaluated). The spatial distribution of subsurface drainage systems were based on (1) low electrical resistivity (as a proxy for clay content) in the top 4 m of the subsurface; (2) historical maps from contractors, which conducted the drainage work; (3) settings from previous successful SWAT set-ups in Denmark; and (4) similar settings as in scenario 3, but adjusted according to the national drained area probability map in Denmark. Scenarios 1 and 4 and scenarios 2 and 3, respectively, showed similar fractions of subsurface drained areas out of the total catchment area (large and small, respectively). Scenarios 2 and 3 showed better statistical performance with SWAT, while scenarios 1 and 4 performed better using SWAT-MODFLOW. Best statistical and graphical performances were obtained with the large drain fraction scenarios and when using the coupled model. First, low drain fraction scenarios underestimated subsurface drainage flow to the stream. Besides, SWAT-MODFLOW performed better than SWAT because MODFLOW was able to simulate groundwater flow across the surface catchment, whereas SWAT by default is not capable of doing so. All things considered, impacts of different subsurface drainage scenarios on catchment hydrology are assessed using both SWAT and SWAT-MODFLOW for the first time in this work, revealing the relevance of this input step for satisfactory hydrological modelling and reinforcing previous authors findings regarding the better performance of the coupled model over SWAT, but being even more relevant in this none-zero balance catchment. The proposed method of modelling coupling, and delineating subsurface drained areas using geophysical data, is promising and can be adopted by other researchers to evaluate the water balance impact of land-use and climate changes around the world.

Characterization of prairie pothole inundation using AnnAGNPS under varying management and drainage scenarios

Farmed prairie potholes are small, isolated depressions frequently classified as semi-permanent wetlands that make up a significant portion of land area in the Des Moines Lobe (DML) of the larger Prairie Pothole Region (PPR). Historically, these depressions have been subjected to significant drainage to improve their agricultural capacity. However, many assessments of the economic return of continuing to farm these depressions suggest that continued attempts to produce conventional row crops is not profitable and has other ecological consequences beyond crop drownout. This study expands the existing discussion of land use and drainage alternatives in a watershed modeling context. This study utilized the Annualized Agricultural Non-Point Source (AnnAGNPS) model to individually simulate the long-term hydrology of 6 prairie potholes using a matrix of land use and drainage modifications. Results suggest the presence of artificial drainage is the dominant factor in prairie pothole hydrology, while retirement and no-till practices can provide moderate reductions in flood inundation. Conservation tillage induces minimal change on flood metrics. Results show that average annual maximum inundated surface area is reduced by at most 50% across all simulations and the median annual days flooded could be reduced by 25 days, though this is less consistent when isolating high-precipitation years. Regardless of drainage status, in all scenarios there are, on average, more than two inundations events per year lasting 2–4 days. Longer events occur approximately once per year on average. Area inundation frequency curves suggest up to a 20% reduction in maximum pothole area inundated annually can be achieved at the 2-year return frequency. The availability of this data helps characterize the hydrology of farmed potholes more generally over a wide range of conditions, providing a reference for the prioritization of potholes for conservation or alternative management.

Homotopic fractional analysis of thin film flow of Oldroyd 6-Constant fluid

The analysis of Oldroyd fluids; a class of Maxwell fluids which also bears Newtonian properties under some conditions, has important implications for different scientific and engineering/industrial applications. Examples of these fluids are typically dilute polymer solutions which demonstrate both viscous and elastic behaviors when subjected to strain. For unidirectional steady flows, the Oldroyd-B (3-Constant) model is the simplest when it comes to describing these behaviors. This model is not sufficient in certain cases, for instance, convergent flow channels, pulling effects, and other extensional flows. In all such scenarios, its application may lead to having out of bound tensile stresses. Hence, in all practicality, higher constants of the Oldroyd model are required to include different tensorial invariants. In this article, we perform this analysis in fractional space on Oldroyd fluids in thin-film flow context using the Oldroyd 6-Constant model for both lifting and drainage scenarios. Solutions to the highly non-linear fractional differential equations are obtained by means of the Homotopy Perturbation Method (HPM) along with fractional calculus. Validation and convergence of the solutions are confirmed by finding residual errors. To the best of our knowledge, the given problem has not been attempted before in fractional space. Various physical aspects, such as the velocity profile, volumetric flux and average velocities are determined and analyzed both graphically and in tabulation form as part of this analysis.

A Two‐Phase, Pore‐Scale Reactive Transport Model for the Kinetic Interface‐Sensitive Tracer

AbstractPrevious laboratory experiments with the kinetic interface sensitive (KIS) tracers have shown promising results with respect to the quantification of the fluid‐fluid interfacial area (IFA) under dynamic, two‐phase flow conditions. However, pore‐scale effects relevant to two‐phase flow (e.g., the formation of hydrodynamically stagnant/immobile zones) are not yet fully understood, and quantitative information about how far these effects influence the transport of the tracer reaction products is not yet available. Therefore, a pore‐scale numerical model that includes two‐phase, reactive flow, and transport of the KIS tracer at the fluid‐fluid interface is developed. We propose a new method to quantitatively analyze how the mass of the KIS‐tracer reaction product in the flowing water is affected by the presence of the immobile zones. The model employs the phase field method (PFM) and a new continuous mass transfer formulation, consistent with the PFM. We verify the model with the analytical solutions of transport involving advection, reaction and diffusion processes. The model is tested for two‐phase flow conditions in a conceptual 2D slit. The applicability of the model is demonstrated in NAPL/water drainage scenarios in a conceptual porous domain, comparing the results in terms of the spatial distribution of the phases and solute concentration. Furthermore, we distinguish the mobile and immobile zones based on the local Péclet number, and the corresponding IFA, and solute mass in these two zones is quantified. Finally, we show that the solute mass in flowing water can be employed to selectively determine the mobile part of the IFA.

A generalized analytical model for estimating the rate of imbibition/drainage of wetting/nonwetting fluids in capillaries

Displacing one fluid by another immiscible with it is a phenomenon of greatest importance and exists in various applications from large scale oil productions to small scale microfluidics. Modeling this phenomenon is crucial, particularly, with respect to estimating penetration rates. Although considerable amounts of research works have been conducted to understand the physics involved in this phenomenon, they remain adherent to particular applications. This includes, for example, imbibition scenarios in which a wetting fluid imbibes inside a capillary tube even without the need to initiate the penetration. On the other hand, drainage scenarios, in which a nonwetting fluid displaces a wetting one, requires such initiation by providing external boosting. There are several external factors that influence the rate at which the meniscus advances inside a capillary tube. The most common such forces include pressure force, capillary force, and gravity force. Several of the modeling approaches have considered the case in which the displaced fluids are gases (e.g., air), particularly in applications related to infiltration studies in porous media. This allowed researchers to ignore the frictional resistance of the displaced fluid and only considers the other denser fluid. However, there exists other applications in which this is not correct and it may not be appropriate to ignore the displaced fluid. In this work, a new generalized model is introduced that accounts for all the physics involved in this process and also does not ignore the displaced fluid. For validation, it is shown that the derived model reduces to all the special cases for which analytical solutions exist, (including that of a single-phase flows). Furthermore, comparisons with computational fluid dynamics simulation (CFD) of drainage/imbibition scenarios show very good match with the results of the derived model, which builds confidence in the modeling approach.

A method for determining reasonable water area ratio based on flood risk and cost-effectiveness in Rainy City

Urban flooding is increasingly pervasive, with the decreasing water area in cities and the dreadful impact on people. Therefore, it is necessary to carry out a quantitative evaluation of the area of urban water and analyze the threshold of the reasonable water ratio under different drainage scenarios. In this research, simulations were performed by using the Personal Computer Storm Water Management Model (PCSWMM), and the model parameter calibration method was based on the runoff coefficient as a contribution to meeting the data-poor urban areas. Then, urban flood control standards were divided into four classes, and the rainfall scenario once in 200 years and historical maximum were selected to build future extreme inundation scenarios in the case study. Simultaneously, methods for the reasonable water area ratio estimation were decided. The cost-effectiveness of all possible solutions was examined across the two scenarios based on the assessment method. The results show that the range of reasonable ratios of the water area under traditional planning is 5.78–6.02% to meet the standard of urban drainage. Similarly, the range of reasonable ratios of water area under the LID (low impact development) plan combined with the sponge city concept is 5.63–5.88%.

Analysis of three-dimensional ponded drainage of a multi-layered soil underlain by an impervious barrier

A general analytical model is proposed for predicting three-dimensional seepage into ditch drains through a soil column comprising of three distinct vertical anisotropic soil layers and underlain by an impervious barrier, the drains being fed by a distributed ponding head introduced at the surface of the soil column. The problem is solved for three different situations resulting from three different locations of the water table in the ditches, namely, when the water level lies in the first layer, when it lies in the second layer and finally when it falls in the third layer. The derived solutions are validated by comparing with analytical solutions of others for a few drainage scenarios; in addition, a few numerical checks on them have also been carried out by making use of the Processing MODFLOW environment. From the study, it is seen that ponded drainage of a multi-layered soil is mostly three-dimensional in nature, particularly in locations close to the drains and that the directional conductivities of the layers play a pivotal role in deciding the hydraulics of flow associated with such a system. Further, it has also come out of the study that by suitably altering the ponding distribution at the surface of the soil, the uniformity of water movement in a multi-layered drainage system can be considerably improved mainly if the directional conductivities of the bottom layers are relatively lower than those of the top layer. As soils in nature are mostly stratified and as no analytical solution to the three-dimensional ponded ditch drainage problem currently exists for a layered soil, the proposed solutions are expected to be important additions to the already existing repertoire of drainage solutions on the subject, particularly when looked in the context of reclamation of water-logged and saline soils in layered field situations.

Synergistic arsenic(v) and lead(ii) retention on synthetic jarosite. I. Simultaneous structural incorporation behaviour and mechanism.

Jarosite [KFe3(SO4)2(OH)6] minerals are effective scavengers of potentially toxic elements (PTEs) and are abundant, for example, in acid rock/mine drainage scenarios. The retention process is highly relevant for environmental attenuation of heavy metals and metalloids since these are usually highly soluble and thus mobile under acidic conditions. We investigated both macroscopically and at the molecular scale the extent and the effects of concomitant incorporation of As(v) and Pb(ii) into synthetic jarosite at different As/Pb starting molar ratios, using XRD-Rietveld, SEM, ATR-FTIR spectroscopy and wet chemistry. The amount of arsenate substituted in the jarosite structure was larger when Pb(ii) was also incorporated, the former filling up to approximately 33% of the tetrahedral sites normally occupied by SO42-, as compared to 21% when Pb(ii) was absent. Similarly, the amount of Pb(ii) incorporated in the structure was larger when As(v) was also taken up. The jarosite unit cell volume increased as higher amounts of As(v) incorporated into its structure, but simultaneous Pb(ii) incorporation seemed to limit this increase due to its smaller size as compared to K+. The extent to which As and Pb can accommodate in the jarosite structure was found to be limited by concentration maxima under the imposed synthesis conditions. At As/Pb ratios up to 1, Pb-As-jarosites were the only crystalline products. Above this ratio, a mixture of Pb-As-jarosite, anglesite (PbSO4) and poorly-crystalline ferric arsenate (AFA) phases was observed. At the highest As/Pb ratio investigated of 1.80 Pb-As-jarosite was no longer formed. Infrared spectroscopy analysis was applied for the first time here to substituted jarosites with both cations and anions, showing spectral changes in the solids as the As/Pb ratio increased: a characteristic As-O doublet at ∼810 and ∼855 cm-1 was observed upon Pb incorporation, showing an indirect effect of Pb(ii) on the As-O bonds in the jarosite structure. Thus, structural incorporation of Pb plays a pivotal role in the unit cell environment of jarosite to balance the distortion caused by AsO4-for-SO4 substitution. The retention processes found in this work have important environmental implications and impacts: through the synergistic incorporation encountered, remediation enhancement of cationic pollutants such as Pb(ii) is possible in a concomitant fashion with As(v) attenuation in acidic mining and metallurgical environments.

DRAINMOD-simulated performance of controlled drainage across the U.S. Midwest

Controlled drainage (CD) has recently been proposed as a best management practice for reducing nutrient export from drained cropland in the U.S. Midwest to the Mississippi River and the Gulf of Mexico. We conducted a 25-year simulation study using the hydrological model, DRAINMOD, and the carbon and nitrogen (N) model, DRAINMOD-NII, to evaluate the performance of CD at 48 locations across the U.S. Midwest. Hydrological and Nitrogen predictions of this simulation study were compared to RZWQM-DSSAT predictions by Thorp et al. (2008). Simulation results showed that CD reduced annual subsurface drainage by 86mm (30%) and annual N drainage losses by 10.9kgNha−1 (32%), on average over the 48 sites. DRAINMOD predicted highest reductions in drain flow at the south and southeast locations and lowest reductions at the northwest locations. The large reductions in drain flow in the south and southeast locations resulted in a large increase in surface runoff, which could increase soil erosion and sediment transport to surface water. In the north and northwest locations, the smaller amount of water that did not pass through the drainage system because of CD was primarily lost as evapotranspiration. DRAINMOD-NII predictions of annual reductions in N drainage loss followed the same trend of annual reductions in drainage flow. DRAINMOD-NII predictions show that reductions in N drainage loss under CD were mainly attributed to increase in denitrification. The declining trend in predicted annual denitrification from the southern to the northern locations of the Midwest region is most likely attributed to the lower temperature and less precipitation at the northern locations. RZWQM-DSSAT predicted reductions in annual drainage and N loss under CD conditions showed a similar trend to DRAINMOD/DRAINMOD-NII predictions. RZWQM-DSSAT, however, predicted substantially higher reductions in both drain flow (regional average of 151mmyr−1, 53%) and N drainage losses (regional average of 18.9kgNha−1yr−1, 51%). The discrepancies between DRAINMOD/DRAINMOD-NII and RZWQM-DSSAT predictions of annual reductions in drain flow and N loss under CD conditions were caused by differences in model predictions of individual components of the water and nitrogen balances under both free drainage and controlled drainage scenarios. Overall, this simulation study showed that climate variation across the region has a substantial impact on CD efficacy for reducing N drainage loss.