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The objective of this study was to explore the higher-order turbulence statistics of flow and turbulent length scales around a complex pier (CP) and compare the results with those for a simple pier (SP). The velocity data were recorded in a laboratory flume using particle image velocimetry (PIV). The PIV data were analysed to estimate the velocity fluctuations of third order, turbulence production and dissipation rates, turbulent length scales and the contributions of burst–sweep events to the total Reynolds shear stress around the piers mounted on a rigid flat surface. The skewness and advection coefficients indicated a more asymmetric distribution of velocity fluctuations for the SP than for the CP. Ejection and sweep events illustrated the dominance of similar strengths for an extended period, downstream of the piers. The upstream turbulent kinetic energy production was similar for both piers, while the upstream dissipation rate was higher for the CP. The length scales were greater at the upstream for the case of the SP while, downstream, they were greater for the CP. The findings of this work demonstrate the importance of a pile cap in restricting downward-moving flow by showing a lower magnitude of scour-inducing turbulence parameters for the CP as compared with the SP.

Groundwater flow problems are generally solved using analytical or numerical methods. Though analytical solutions are exact and preferable, they are not available for complex field problems. Hence numerical methods such as Finite Element and Finite Difference methods are used to solve complex groundwater problems. These conventional mesh/ grid-based numerical methods need construction of a detailed mesh/ grid. On the other hand, the meshless approach creates a system of algebraic equations on a collection of distributed nodes in the problem area and the boundary. As a result, it is easy to incorporate any modifications to the model at a later time by simply adding nodes to the domain. In this study a weak form meshless method known as local radial point interpolation method (LRPIM) which uses radial basis functions for approximation or interpolation is developed to solve the groundwater flow problems in a confined aquifer. The results obtained from the LRPIM model has been compared with other numerical methods for benchmark and real field problems, and are found to be satisfactory. Implementation of the essential boundary conditions was relatively easier in LRPIM and gave good accuracy for the problems considered. LRPIM can potentially be used as an alternative to the other conventional methods, especially where the domain boundary is irregular or varying with time.

Air-entrainment from surface vortex at critical submergence for hydraulic intakes adversely affects the withdrawal efficiency and intake performance. In this study, flow at the lateral dual square bottom intake placed in a row operating under uniform approach flow is numerically simulated. The dual intakes are subjected to perpendicular approach flow making the withdrawal condition more complex. The interface of the air–water phase is tracked using the volume of fluid (VOF) model, both coupled and decoupled with the level-set method with different spatial discretization methods for identifying the best interface interpolation. This study is focused on the development of a methodology for the determination of critical submergence for dual intakes numerically. Surface vortex causing air-entrainment at lateral dual intake was identified using three distinct approaches and a novel methodology involving the use of volume fraction study combined with a swirling-strength based vortex detection mechanism is proposed to compute the critical submergence for the safe operation of the intakes. Further, the effect of intake pipe blockage on the critical submergence is studied using differential intake protrusions and identified that a differential protrusion of the downstream intake can reduce the critical submergence with an enhanced withdrawal capacity of the upstream intake. The computed critical submergence is validated using experimental results on lateral dual intakes and found to be within ±10% error. The results of this study will be helpful to practicing engineers in the rational design of hydraulic intakes for various diversion projects.

This study investigates the turbulent flow properties experimentally in the vicinity of two side-by-side circular cylinders, along with the influence of the third cylinder of the same dimension placed in the upstream and successively in the downstream forming an equilateral triangle. Three-dimensional stereoscopic particle image velocimetry (PIV) was employed to collect the instantaneous velocity data around the arrangements. The study highlights the prime parameters of turbulence such as the mean velocities, Reynolds stresses, turbulent kinetic energy (TKE), quadrant analysis, and Q-criteria for vortices, which are responsible for the development of various problems such as scour-hole around the cylindrical pier arrangements, disturbance around industrial and marine structures. The spectral analysis was performed to examine the energy distributions, vortex-shedding frequencies with corresponding Strouhal numbers. Dominant vorticity locations were identified from the contours of Q-criteria. The magnitude of turbulence characteristics was reduced by 15–20% (turbulence intensity reduced by 20% and TKE by 15%) when the third cylinder was placed the upstream of side-by-side cylinder group. Streamlines are also studied to visualize the flow patterns for a better understanding of physics in the presence of the third cylinder. The maximum energy of vortices obtained from the spectrum analysis showed that the vortices generated were less when the third cylinder is placed upstream.

In this study, the local scour and the associated flow hydrodynamics around a complex pier with rectangular pile-cap at three different pile-cap elevations are investigated. The pile-cap elevations...

In this study, we assess the soil erosion susceptibility at the sub-basins scale using remote sensing data with the integration of the Geographical Information System (GIS) for the Netravati river basin in Western Ghats, India. The Cartosat digital elevation model was used for the calculation of morphometric parameters, and Landsat satellite images were used for land cover classification. The whole river basin was divided into five sub-basins for identifying the spatial variation of morphometric parameters and different land use categories. A weighted sum approach (WSA) was used for the ranking of each morphometric parameter and land use types. Then each sub-basin was assigned as very low, low, medium, high, and very high priority ranking. The final prioritization map based on the combined (morphometric and land cover) analysis showed erosion susceptibility is very high for sub-basin 4, high for sub-basin 2, medium for sub-basin 5, low for sub-basin 1, and very low for sub-basin 3. Further, the soil erosion susceptibility analysis has been done separately for morphometric and land cover at the sub-basins scale. The results of this study will be useful for the water resource manager and policymaker while considering the soil erosion-prone areas in the region, and the methodology can be adapted for other river basins.

In this paper, the meshless element-free Galerkin method (EFGM) based coupled model is developed to simulate the groundwater flow and multispecies reactive transport coupled with sequential decay reactions in unconfined aquifers. The use of moving least squares (MLS) approximation in approximating the head and concentration variables in EFGM tends to provide the solutions with better numerically stability than the finite difference (FDM) and finite element methods (FEM). Therefore, the proposed model is less affected by numerical dispersion unlike FDM/FEM based models. For the validation of the proposed model, it is applied to multispecies transport equations coupled with sequential reactions, reversible reactions, spatially or temporally varying transport velocities, time dependent decay rates and species concentration at the boundaries. EFGM solution is matching very well with the available analytical solutions for all the selected problems. However, FEM model fails to converge to the analytical solution for the selected problems with the time dependent transport coefficients. Finally, the developed EFGM coupled model is used to simulate groundwater flow and transport of chlorinated solvents in hypothetical and synthetic field unconfined aquifers. The EFGM solutions are compared with those from MODFLOW-RT3D simulations. The good comparison between both solutions indicates the applicability of the proposed model to multispecies transport.

In this study, a meshless simulation model based on the element-free Galerkin method (EFGM) is proposed for the coupled simulation of groundwater flow and contaminant transport (GFCT) in the two-dimensions. EFGM discretizes the governing GFCT equations using the Galerkin integral approach and shape functions generated through the moving least squares (MLS) approximation method. It results into the stable system of equations for estimating the groundwater head and contaminant concentration values. EFGM computes the several global matrices using the spatial information of the scattered and unconnected field nodes and hence, terminates the meshing procedure unlike the finite difference (FDM) and finite element (FEM) methods. The Kronecker delta function property is missing in EFGM shape functions and hence, the Dirichlet boundary conditions are enforced with some special methods. We have used the penalty method to include them into the presented EFGM model. This method is straightforward and computationally useful for the real field simulations. The proposed model is first validated using both the one- and two-dimensional analytical solutions. The developed coupled model is then applied to solve the hypothetical and real field problems. EFGM results for both the problems are compared with the MODFLOW and MT3DMS results for the head and concentration values respectively. EFGM results are found to be satisfactory for both the cases, and it shows the potential of the proposed approach for the coupled GFCT simulations.

In this study, the impacts of changes in land use/ land cover (LULC) and climate on surface runoff are investigated in the Kadalundi river basin, Western Ghats, India. Land Change Modeller (LCM) wa...

This study investigated the impacts of changes in land cover and climate on runoff and sediment yield in a river basin in India. Land Change Modeler was used to derive the future land cover and its...

For physically based spatially distributed models which rely on a grid based representation of the spatial variability in a river basin, choice of an appropriate grid-size without compensating mode...

In the inverse groundwater modelling problems, the objective functions generally used contain several local minima which render the conventional gradient-based optimization unsuitable for such problems. The recently used individual population-based evolutionary methods such as differential evolution (DE) algorithm and particle swarm optimization (PSO) are often observed to get stuck into sub-optimal solution. In this study to address this issue, a hybrid- metaheuristic Differential Evolution- Particle Swarm Optimization (DE-PSO) is proposed to obtain aquifer parameters. PSO introduces a perturbation in each generation to increase the diversity in the population of DE to improve its fitness value. The developed hybrid DE-PSO optimization is coupled with finite element method (FEM) based simulator to get a simulation-optimization (SO) model. Initially, the proposed SO model is tested on a synthetic irregular domain problem to estimate aquifer transmissivity values which are compared with available zonation pattern values. Later, the SO model is applied to the Mahi Right Bank Canal (MRBC) heterogeneous unconfined aquifer system and the optimally obtained results are compared with the DE, PSO and genetic algorithm (GA) methods respectively. The performance of the hybrid DE-PSO model is also tested using various fit- independent statistics for the reliability and accuracy. The results of this study show that the hybrid-metaheuristic based DE-PSO optimization algorithm is an efficient and robust tool for inverse groundwater problem of estimating the aquifer parameters.

We herein propose a simulation-optimization model for groundwater remediation, using PAT (pump and treat), by coupling artificial neural network (ANN) with the grey wolf optimizer (GWO). The input and output datasets to train and validate the ANN model are generated by repetitively simulating the groundwater flow and solute transport processes using the analytic element method (AEM) and random walk particle tracking (RWPT). The input dataset is the different realization of the pumping strategy and output dataset are hydraulic head and contaminant concentration at predefined locations. The ANN model is used to approximate the flow and transport processes of two unconfined aquifer case studies. The performance evaluation of the ANN model showed that the value of mean squared error (MSE) is close to zero and the value of the correlation coefficient (R) is close to 0.99. These results certainly depict high accuracy of the ANN model in approximating the AEM-RWPT model. Further, the ANN model is coupled with the GWO and it is used for remediation design using PAT. A comparison of the results of the ANN-GWO model with solutions of ANN-PSO (ANN-Particle Swarm Optimization) and ANN-DE (ANN-Differential Evolution) models illustrates the better stability and convergence behaviour of the proposed methodology for groundwater remediation.

Droughts are the major natural disasters affecting water availability leading to social, economic, and environmental challenges. Due to climate variability, investigation of climate change impact on droughts is of vital importance for sustainable societal and ecosystem functioning. Western Ghats, a humid tropical region of India is selected as a case study to investigate the change in drought characteristics subjected to future climate change. In the last few decades, due to monsoon failure, the intensity of droughts has been identified to increase in this region making this study important. For future climatic variables, the ensemble of five Global Climate Models (GCMs) in the Coupled Model Intercomparison Project (CMIP5) are considered for the Representative Concentration Pathways (RCPs) 4.5 and 8.5. Standardized Precipitation-Evapotranspiration Index (SPEI) for the 12-month accumulated period is considered to assess the change in the drought characteristics during near (2011–2040), mid (2041–2070), and far future (2071–2100). The results indicate an increase in drought events in the future with maximum change during the far future for both RCP 4.5 and 8.5 scenarios. The major areas affected are in the southern part of Kerala and Karnataka. The change in total severity and duration of these drought events are high during the near future, moderate during the mid-future, and very high during the far future in both scenarios with RCP 8.5 being more severe. The findings show the variability in drought characteristics both spatially and temporally across the study area. The results will be helpful in identifying the hotspots prone to drought risk. This will serve as important guidance in improving the identification of causes, minimizing impacts, and enhancing the resilience to droughts in the study area. Further, the important implication of the study will be for water resource planning and management to strategize policies that emphasize on providing water in water-scarce regions during extreme drought situations.

Coastal regions have the most challenging aquifer systems because of their geometry and the flow behavior of groundwater with tidal oscillations. Studies have focused on tide-induced ground...

In this paper, two meshless methods, namely, a weak form Meshless Local Petrov Galerkin (MLPG) method, and Meshless Weak Strong (MWS) form method, obtained by combining MLPG with a strong form Radial Point Collocation Method (RPCM), are presented for simulation of advection-dispersion-reaction phenomena of the contaminants in the porous media. The first-order decay and sorption reactions are considered in this study. The Crank Nicolson scheme is applied for the time discretization. The weak form MLPG is a truly meshless and robust numerical technique, that can be applied to complex aquifer systems with derivative boundaries. However, in this method, the computational time is increased due to the integration, which is not essential for simple problems. Thus, the MLPG method is further coupled with a strong form RPCM with an aim of decreasing the background integration, by modelling only the nodes around the derivative boundaries using MLPG method and the other nodes by a direct RPCM which do not require integration. The proposed MWS model automatically converts into a complete RPCM model if there are no derivative boundaries. Thus, this model being both accurate and computationally efficient is suitable for simple and moderately complex aquifer systems and MLPG is the most stable and reliable method for modelling the most complex aquifer problems. Both the developed models are tested with available analytical solutions and applied for hypothetical case studies. The results prove the efficiency of the models and the applicability of each model is described in detail.

It is widely known that land use/land cover (LULC) changes significantly alter watershed hydrology and sediment yields. The impact, especially on erosion and sedimentation, is likely to be exacerbated in regions dominated by high rainfall patterns such as monsoons. This study analyzed the hydrological responses of LULC changes in terms of streamflow (SF) and sediment yield (SY) in a monsoon-dominated tropical watershed, the Periyar River Watershed (PRW) in Kerala, India. This watershed drains an area of 4793 km2 characterized by an average monsoon rainfall of 2900 mm from June to November. The watershed hydrology and sediment dynamics were simulated using the Soil and Water Assessment Tool (SWAT) model for the impact assessment at the watershed outlet and the sub-watershed level. Historical LULC data were analyzed for 1988, 1992, 2002, and 2016 using the maximum likelihood method, and future LULC changes were projected for 2030, 2050, 2075, and 2100 using the Markov chain–cellular automata technique. Between 1988 and 2016, the urban area increased by 4.13 percent, while plantation and forest coverage decreased by 1.5 percent. At this rate, by 2100, the urban area is expected to grow by 16.45% while plantations and forest area will shrink by 13.7% compared to 1988. The effects of these changes on SF and SY were found to be minimal at the watershed outlet; however, at the spatial scale of sub-watersheds, the changes varied up to 70% for surface runoff and 200% for SY. These findings highlight the potential impacts of LULC changes in a monsoon-dominated watershed and may contribute to the development of successful LULC-based watershed management strategies for prevention of flooding and sediment loss.

Climate change (CC) affects millions of people directly or indirectly. Especially, the effect of CC on the hydrological regime is extensive. Hence, understanding its impact is highly essential. In this study, the Bharathapuzha river basin (BRB) lying in the Western Ghats region of southern India is considered for CC impact assessment, as it is a highly complex and challenging watershed, due to its varying topographical features, such as soil texture, land use/land cover types, slope, and climatology, including rainfall and temperature patterns. To understand the CC impact on the hydrological variables at BRB in the future, five downscaled global circulation models (GCMs) were used, namely BNU-ESM, Can-ESM, CNRM, MPI-ESM MR, and MPI-ESM LR. These GCMs were obtained for two representative concentration pathway (RCP) scenarios: 4.5 representing normal condition and 8.5 representing the worst condition of projected carbon and greenhouse gases concentration on the lower atmosphere. To obtain the continuous simulation of hydrological variables, the SWAT hydrological model was adopted in this study. Results showed that rainfall pattern, evapotranspiration, and soil moisture will increase at moderate to significant levels in the future. This is especially seen during the far future period (i.e., 2071 to 2100). Similar results were obtained for surface runoff. For instance, surface runoff will increase up to 19.2% (RCP 4.5) and 36% (RCP 8.5) during 2100, as compared to the average historical condition (1981–2010). The results from this study will be useful for various water resources management and adaptation measures in the future, and the methodology can be adopted for similar regions.

First-order reaction networks are often encountered in groundwater pollution problems. The members of the network transform/degrade from one species to another. In this paper a strong form meshfree numerical method named radial point collocation method (RPCM) is introduced to model such reactions. In the proposed method, the entire domain is decomposed into a number of overlapping local support domains surrounding each node. The concentrations of species at each node and its directional derivatives are approximated using multiquadrics radial basis functions (MQ-RBF) within the local support domain. 1D models are verified against existing analytical solutions. Further, the 2D model simulations are compared with widely used RT3D (Reactive Transport in 3 Dimensions) for a benchmark problem. Sensitivity analysis is also performed for model parameters. The proposed model solves species-wise governing equations and boundary conditions without operator splitting, unlike the popular grid/mesh-based models. The RPCM-based models are found to be very effective in modeling first-order reaction network problems.

In this study, experimental investigations of the flow pattern around an oblong pier (OP) mounted on a rigid flat surface are carried out in a laboratory flume and the results are compared with tha...