Nitin Joshi

Long-term historic changes in climatic variables of Betwa Basin, India

In this study, trend analyses of historic past climatic variables were investigated for the Betwa basin located in Central India. In the serially independent climatic variables, Mann–Kendall test (MK test) was applied to the original sample data. However, in the serially correlated series, pre-whitening is used before employing the MK test. The long-term trend analysis showed several of the meteorological stations to exhibit a decreasing trend in annual and seasonal precipitation in the study area. Seasonal and yearly numbers of rainy days are decreased. However, onset of effective monsoon (except for Shivpuri and Tikamgarh stations) did not show any trend during the study period. For maximum temperature, five out of 12 stations showed a decreasing trend in monsoon season whereas almost all other stations showed an increasing trend in winter and no trend in summer season. For minimum temperature, only two stations of the basin showed a decreasing trend in monsoon and all other stations exhibited a significant increase in winter and summer season. The increase of winter temperature may adversely affect the growth of Rabi crop (wheat and mustard) in the study area. Potential evopotranspiration (PET) did not show any trend in monsoon, except for Jalaun and Jhansi stations, showing decreasing trends. Raisen and Vidisha stations showed an increasing trend in winter only, and the trend for other stations were random in nature. In summer, five out of 12 stations showed an increasing trend in PET. Results of this study can be employed in preparation of water resources development and management plan in the Betwa Basin.

Application of nonequilibrium fracture matrix model in simulating reactive contaminant transport through fractured porous media

Nonequilibrium and nonlinear sorption of the contaminants in the fractured porous media could significantly influence the shape of the breakthrough curve (BTC). For the fracture-matrix system, there are very few studies which consider these processes. In this study, the nonequilibrium fracture-matrix model with two different nonlinear sorption isotherms, namely nonlinear Freundlich and Langmuir sorption isotherms were developed. The effect of sorption nonlinearity and nonequilibrium conditions on the shape of the BTC was studied using the temporal moments. The developed models along with the linear equilibrium, linear nonequilibrium fracture matrix models, and the multirate mass transfer model were used to simulate the BTC, which were compared with the experimental data available in the literature. Both sorption nonequilibrium and nonlinearity were found to significantly influence the shape of the BTC. Presence of sorption nonlinearity reduces the solute spreading, whereas presence of nonequilibrium conditions increases the solute spreading. Considering the sorption nonequilibrium along with the sorption nonlinearity leads to an improved simulation of the BTC. The nonequilibrium nonlinear sorption models could simulate the extended BTC tailing resulting from sorption nonlinearity and rate-limited interaction in the fracture-matrix system.

Reactive Transport in Fractured Permeable Porous Media

AbstractThe transport of reactive solutes can be influenced by transport-related and sorption-related nonequilibrium processes. The reactive contaminant transport model for fracture and the multiprocess nonequilibrium (MPNE) model for porous formation is considered. Two coupled transport equations, one for the porous formation and the other for the fracture, were solved numerically using a hybrid finite-volume method. The numerical model employs a globally second-order accurate explicit finite-volume method for the advective transport and a finite-difference method for the dispersive transport and coupled reaction terms. An attempt is made to investigate the effects of various MPNE model parameters on the concentration profile in the fracture. It was found that the higher values of mass transfer coefficient, sorption coefficient, matrix diffusion coefficient, fracture retardation coefficient, and matrix porosity in the advective and nonadvective regions of the porous matrix leads to a decrease in the solu...

Finite volume model for reactive transport in fractured porous media with distance- and time-dependent dispersion

Abstract There are very few studies of fractured porous media that use distance- and time-dependent dispersion models, and, to the best of our knowledge, none which compare these with constant dispersion models. Therefore, in this study, the behaviour of temporal and spatial concentration profiles with distance- and time-dependent dispersion models is investigated. A hybrid finite volume method is used to solve the governing equations for these dispersion models. The developed numerical model is used to study the effects of matrix diffusion coefficient, groundwater velocity and matrix and fracture retardation factor on concentration profiles in the application of constant, distance-dependent and time-dependent dispersion models. In addition, an attempt is made to evaluate the applicability of these dispersion models by using the models to simulate experimental data. It was found that a better fit to the observed data is obtained in the case of distance- and time-dependent dispersion models as compared to the constant dispersion model. Thus, these numerical experiments indicate that distance- and time-dependent dispersion models have better simulation potential than the constant dispersion model.

Reactive transport through porous media using finite-difference and finite-volume methods

In this paper, finite-volume method (FVM) and implicit finite-difference method (FDM) have been used to solve multiprocess nonequilibrium (MPNE) transport equation for reactive solute transport through porous media. A review of the literature reveals that the performance of the MPNE transport model for advection- and dispersion-dominant cases has not been analysed. The main objective of the present study is to asses the performance of both FDM and FVM in the presence of high value of Peclet number (Pe) for reactive transport through porous media. It has been shown that in case of advection-dominant transport (i.e. at high values of Pe), the FDM numerical model remains stable and oscillation free, when the values of mass transfer and sorption rate coefficient are high. Further, the FVM model is capable of simulating advection-dominant transport irrespective of the values of mass transfer and sorption rate coefficient. This is established through simulation of the experimental data of Strontium.