Institute Dingenierie Of Lenvironnement

Cheseaux, Switzerland

Institute Dingenierie Of Lenvironnement

Cheseaux, Switzerland
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Jin G.,Hohai University | Tang H.,Hohai University | Li L.,Hohai University | Li L.,University of Queensland | Barry D.A.,Institute Dingenierie Of Lenvironnement
Geophysical Research Letters | Year: 2011

Small density variations across streambeds due to low solute concentrations in stream water exist commonly in streams and rivers. Using laboratory experiments and numerical modeling, we demonstrated that even small density variations can influence hyporheic flow in streambeds with periodic bed forms. The circulating pore water flow patterns in the bed were modified constantly as the solute front moved downward. Density-induced head gradients eventually overwhelmed the regional hydraulic gradient and drove the circulating flow below a hydraulic divide that would have existed without the density influence. The density-modified hyporheic flow provided a relatively fast solute transport mechanism and enhanced the overall mass exchange between the stream and bed. These results highlight the important role of weak, upward density gradients in modulating hyporheic flow. Copyright 2011 by the American Geophysical Union.

Xin P.,Hohai University | Xin P.,University of Queensland | Wang S.S.J.,University of Queensland | Robinson C.,University of Western Ontario | And 4 more authors.
Geophysical Research Letters | Year: 2014

Submarine groundwater discharge (SGD) is an integral part of the hydrological cycle and represents an important aspect of land-ocean interactions. We used a numerical model to simulate flow and salt transport in a nearshore groundwater aquifer under varying wave conditions based on yearlong random wave data sets, including storm surge events the results showed significant flow asymmetry with rapid response of influxes and retarded response of effluxes across the seabed to the irregular wave conditions. While a storm surge immediately intensified seawater influx to the aquifer, the subsequent return of intruded seawater to the sea, as part of an increased SGD, was gradual. Using functional data analysis, we revealed and quantified retarded, cumulative effects of past wave conditions on SGD including the fresh groundwater and recirculating seawater discharge components the retardation was characterized well by a gamma distribution function regardless of wave conditions the relationships between discharge rates and wave parameters were quantifiable by a regression model in a functional form independent of the actual irregular wave conditions. This statistical model provides a useful method for analyzing and predicting SGD from nearshore unconfined aquifers affected by random waves. Key Points Cumulative effects of antecedent wave conditions on SGD Long memory of past wave conditions back to over a hundred days found in the SGD Wave effects characterized well by a gamma distribution function © 2014. American Geophysical Union. All Rights Reserved.

Zanganeh M.,Iran University of Science and Technology | Yeganeh-Bakhtiary A.,Iran University of Science and Technology | Bakhtyar R.,Institute Dingenierie Of Lenvironnement
Journal of Hydroinformatics | Year: 2011

In this paper the capability of Particle Swarm Optimization (PSO) is employed to deal with an Adaptive Network based Fuzzy Inference System (ANFIS) model's inherent shortcomings to extract optimum fuzzy if-then rules in noisy areas arising from the application of nondimensional variables to estimate scour depth. In the model, a PSO algorithm is employed to optimize the clustering parameters controlling fuzzy if-then rules in subtractive clustering while another PSO algorithm is employed to tune the fuzzy rule parameters associated with the fuzzy if-then rules. The PSO model's objective function is the Root Mean Square (RMSE), by which the model attempts to minimize the error in scour depth estimation with respect to its generalization capability. To evaluate the model's performance, the experimental datasets are used as training, checking and testing datasets. Two-dimensional and nondimensional models are developed such that in the dimensional model the mean current velocity, mean grain size, water depth, pipe diameter and shear boundary velocity are used as input variables while in the nondimensional model the pipe, boundary Reynolds numbers, Froude number and normalized depth of water are set as input variables. The results show that the model provides an alternative approach to the conventional empirical formulae. It is evident that the developed PSO-FIS-PSO is superior to the ANFIS model in the noisy area in which the input and output variables are slightly related to each other. © IWA Publishing 2011.

Jin G.,State Key Laboratory of Hydrology Water Resources and Hydraulic EngineeringHohai UniversityNanjing China | Tang H.,State Key Laboratory of Hydrology Water Resources and Hydraulic EngineeringHohai UniversityNanjing China | Li L.,Water Resources University | Barry D.A.,Institute Dingenierie Of Lenvironnement
Water Resources Research | Year: 2015

A laboratory experiment and numerical modeling were used to examine effects of density gradients on hyporheic flow and solute transport under the condition of a solute pulse input to a river with regular bed forms. Relatively low-density gradients due to an initial salt pulse concentration of 1.55 kg m-3 applied in the experiment were found to modulate significantly the pore-water flow and solute transport in the riverbed. Such density gradients increased downward flow and solute transport in the riverbed by factors up to 1.6. This resulted in a 12.2% increase in the total salt transfer from the water column to the riverbed over the salt pulse period. As the solute pulse passed, the effect of the density gradients reversed, slowing down the release of the solute back to the river water by a factor of 3.7. Numerical modeling indicated that these density effects intensified as salt concentrations in the water column increased. Simulations further showed that the density gradients might even lead to unstable flow and result in solute fingers in the bed of large bed forms. The slow release of solute from the bed back to the river led to a long tail of solute concentration in the river water. These findings have implications for assessment of impact of pollution events on river systems, in particular, long-term effects on both the river water and riverbed due to the hyporheic exchange. © 2015. American Geophysical Union.

Bakhtyar R.,Institute Dingenierie Of Lenvironnement | Razmi A.M.,Institute Dingenierie Of Lenvironnement | Barry D.A.,Institute Dingenierie Of Lenvironnement | Yeganeh-Bakhtiary A.,Iran University of Science and Technology | Zou Q.-P.,University of Plymouth
Advances in Water Resources | Year: 2010

Wave breaking and wave runup/rundown have a major influence on nearshore hydrodynamics, morphodynamics and beach evolution. In the case of wave breaking, there is significant mixing of air and water at the wave crest, along with relatively high kinetic energy, so prediction of the free surface is complicated. Most hydrodynamic studies of surf and swash zone are derived from single-phase flow, in which the role of air is ignored. Two-phase flow modeling, consisting of both phases of water and air, may be a good alternative numerical modeling approach for simulating nearshore hydrodynamics and, consequently, sediment transport. A two-phase flow tool can compute more realistically the shape of the free surface, while the effects of air are accounted for. This paper used models based on two-dimensional, two-phase Reynolds-averaged Navier-Stokes equations, the volume-of-fluid surface capturing technique and different turbulence closure models, i.e., k-ε, k-ω and re-normalized group (RNG). Our numerical results were compared with the available experimental data. Comparison of the employed method with a model not utilizing a two-phase flow modeling demonstrates that including the air phase leads to improvement in simulation of wave characteristics, especially in the vicinity of the breaking point. The numerical results revealed that the RNG turbulence model yielded better predictions of nearshore zone hydrodynamics, although the k-ε model also gave satisfactory predictions. The model provides new insights for the wave, turbulence and means flow structure in the surf and swash zones. © 2010 Elsevier Ltd.

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