# Singh, Vijay P.

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Item Quantifying the effect of land use and land cover changes on green water and blue water in northern part of China(Copernicus Publications on behalf of the European Geosciences Union, 2009-06-12) Liu, X.; Ren, L.; Yuan, F.; Singh, V. P.; Fang, X.; Yu, Z.; Zhang, W.Show more Changes in land use and land cover (LULC) have been occurring at an accelerated pace in northern parts of China. These changes are significantly impacting the hydrology of these parts, such as Laohahe Catchment. The hydrological effects of these changes occurring in this catchment were investigated using a semi-distributed hydrological model. The semi-distributed hydrological model was coupled with a two-source potential evaportranspiration (PET) model for simulating daily runoff. Model parameters were calibrated using hydrometeorological and LULC data for the same period. The LULC data were available for 1980, 1989, 1996 and 1999. Daily streamflow measurements were available from 1964 to 2005 and were divided into 4 periods: 1964–1979, 1980–1989, 1990–1999 and 2000–2005. These periods represented four different LULC scenarios. Streamflow simulation was conducted for each period under these four LULC scenarios. The results showed that the change in LULC influenced evapotranspiration (ET) and runoff. The LULC data showed that from 1980 to 1996 grass land and water body had decreased and forest land and crop land had increased. This change caused the evaporation from vegetation interception and vegetation transpiration to increase, whereas the soil evaporation tended to decrease. Thus during the period of 1964–1979 the green water or ET increased by 0.95%, but the blue water or runoff decreased by 8.71% in the Laohahe Catchment.Show more Item Kinematic wave model for transient bed profiles in alluvial channels under nonequilibrium conditions(American Geophysical Union, 2007-12-27) Tayfur, Gokmen; Singh, Vijay P.Show more Transient bed profiles in alluvial channels are generally modeled using diffusion (or dynamic) waves and assuming equilibrium between detachment and deposition rates. Equilibrium sediment transport can be considerably affected by an excess (or deficiency) of sediment supply due to mostly flows during flash floods or floods resulting from dam break or dike failure. In such situations the sediment transport process occurs under nonequilibrium conditions, and extensive changes in alluvial river morphology can take place over a relatively short period of time. Therefore the study and prediction of these changes are important for sustainable development and use of river water. This study hence developed a mathematical model based on the kinematic wave theory to model transient bed profiles in alluvial channels under nonequilibrium conditions. The kinematic wave theory employs a functional relation between sediment transport rate and concentration, the shear-stress approach for flow transport capacity, and a relation between flow velocity and depth. The model satisfactorily simulated transient bed forms observed in laboratory experiments.Show more Item Hybrid fuzzy and optimal modeling for water quality evaluation(American Geological Union, 2007-05-08) Wang, Dong; Singh, Vijay P.; Zhu, YuanshengShow more Water quality evaluation entails both randomness and fuzziness. Two hybrid models are developed, based on the principle of maximum entropy (POME) and engineering fuzzy set theory (EFST). Generalized weighted distances are defined for considering both randomness and fuzziness. The models are applied to 12 lakes and reservoirs in China, and their eutrophic level is determined. The results show that the proposed models are effective tools for generating a set of realistic and flexible optimal solutions for complicated water quality evaluation issues. In addition, the proposed models are flexible and adaptable for diagnosing the eutrophic status.Show more Item Kinematic wave model of bed profiles in alluvial channels(American Geophysical Union, 2006-06-21) Tayfur, Gokmen; Singh, Vijay P.Show more A mathematical model, based on the kinematic wave (KW) theory, is developed for describing the evolution and movement of bed profiles in alluvial channels. The model employs a functional relation between sediment transport rate and concentration, a relation between flow velocity and depth and Velikanov's formula relating suspended sediment concentration to flow variables. Laboratory flume and field data are used to test the model. Transient bed profiles in alluvial channels are also simulated for several hypothetical cases involving different water flow and sediment concentration characteristics. The model‐simulated bed profiles are found to be in good agreement with what is observed in the laboratory, and they seem theoretically reasonable for hypothetical cases. The model results reveal that the mean particle velocity and maximum concentration (maximum bed form elevation) strongly affect transient bed profiles.Show more Item Downstream hydraulic geometry relations: 2. Calibration and testing(American Geophysical Union, 2003-12-04) Singh, Vijay P.; Yang, Chih Ted; Deng, Zhi-QiangShow more Using 456 data sets under bank-full conditions obtained from various sources, the geometric relations, derived in part 1 [ Singh et al., 2003 ], are calibrated and verified using the split sampling approach. The calibration of parameters shows that the change in stream power is not shared equally among hydraulic variables and that the unevenness depends on the boundary conditions to be satisfied by the channel under consideration. The agreement between the observed values of the hydraulic variables and those predicted by the derived relations is close for the verification data set and lends credence to the hypotheses employed in this study.Show more Item Downstream hydraulic geometry relations: 1. Theoretical development(American Geophysical Union, 2003-12-04) Singh, Vijay P.; Yang, Chih Ted; Deng, Z. Q.Show more In this study, it is hypothesized that (1) the spatial variation of the stream power of a channel for a given discharge is accomplished by the spatial variation in channel form (flow depth and channel width) and hydraulic variables, including energy slope, flow velocity, and friction, and (2) that the change in stream power is distributed among the changes in flow depth, channel width, flow velocity, slope, and friction, depending on the constraints (boundary conditions) the channel has to satisfy. The second hypothesis is a result of the principles of maximum entropy and minimum energy dissipation or its simplified minimum stream power. These two hypotheses lead to four families of downstream hydraulic geometry relations. The conditions under which these families of relations can occur in field are discussed.Show more Item Solute transport under steady and transient conditions in biodegraded municipal solid waste(American Geophysical Union, 1999-08) Bendz, David; Singh, Vijay P.Show more The transport of a conservative tracer (lithium) in a large (3.5 m3) undisturbed municipal solid waste sample has been investigated under steady and fully transient conditions using a simple model. The model comprises a kinematic wave approximation for water movement, presented in a previous paper, and a strict convective solute flux law. The waste medium is conceptualized as a three-domain system consisting of a mobile domain (channels), an immobile fast domain, and an immobile slow domain. The mobile domain constitutes only a minor fraction of the medium, and the access to the major part of medium is constrained by diffusive transport. Thus the system is in a state of physical nonequilibrium. The fast immobile domain is the part of the matrix which surrounds the channels and forms the boundary between the channels and the matrix. Owing to its exposure to mobile water, which enhances the biodegradation process, this domain is assumed to be more porous and loose in its structure and therefore to respond faster to a change in solute concentration in the mobile domain compared to the regions deep inside the matrix. The diffusive mass exchange between the domains is modeled with two first-order mass transfer expressions coupled in series. Under transient conditions the system will also be in a state of hydraulic nonequilibrium. Hydraulic gradients build up between the channel domain and the matrix in response to the water input events. The gradients will govern a reversible flow and convective transport between the domains, here represented as a source/sink term in the governing equation. The model has been used to interpret and compare the results from a steady state experiment and an unsteady state experiment. By solely adjusting the size of the fraction of the immobile fast domain that is active in transferring solute, the model is capable of accurately reproducing the measured outflow breakthrough curves for both the steady and unsteady state experiments. During transient conditions the fraction of the immobile fast domain that is active in transferring solute is found to be about 65% larger than that under steady state conditions. It is therefore concluded that the water input pattern governs the size of the fraction of the immobile fast domain which, in turn, governs the solute residence time in the solid waste. It can be concluded that the contaminant transport process in landfills is likely to be in a state of both physical, hydraulic, and chemical nonequilibrium. The transport process for a conservative solute is here shown to be dominated by convective transport in the channels and a fast diffusive mass exchange with the surrounding matrix. This may imply that the observed leachate quality from landfills mainly reflects the biochemical conditions in these regions. The water input pattern is of great importance for the transport process since it governs the size of the fraction of the immobile fast domain which is active in transferring solute. This may be the reason for leachate quality to be seasonally or water flux dependent, which has been observed in several investigations. The result also has a significant practical implication for efforts to enhance the biodegradation process in landfills by recycling of the leachate.Show more Item Kinematic wave model for water movement in municipal solid waste(American Geophysical Union, 1998-11) Bendz, David; Singh, Vijay P.; Rosqvist, H?�kan; Bengtsson, LarsShow more The movement of water in a large (3.5 m3) undisturbed sample of 22-year-old municipal solid waste has been modeled using a kinematic wave approximation for unsaturated infiltration and internal drainage. The model employs a two-parameter power expression as macroscopic flux law. The model parameters were determined and interpreted in terms of the internal geometry of the waste medium by fitting the model to one set of infiltration and drainage data. The model was validated using another set of data from a sequence of water input events. The results of the validation show that the model performs satisfactorily, but further development of the model to incorporate spatial variability would increase its capability.Show more Item An entropy-based morphological analysis of river basin networks(American Geophysical Union, 1993-04) Fiorentino, Mauro; Claps, Pierluigi; Singh, Vijay P.Show more Under the assumption that the only information available on a drainage basin is its mean elevation, the connection between entropy and potential energy is explored to analyze drainage basins morphological characteristics. The mean basin elevation is found to be linearly related to the entropy of the drainage basin. This relation leads to a linear relation between the mean elevation of a subnetwork and the logarithm of its topological diameter. Furthermore, the relation between the fall in elevation from the source to the outlet of the main channel and the entropy of its drainage basin is found to be linear and so is also the case between the elevation of a node and the logarithm of its distance from the source. When a drainage basin is ordered according to the Horton-Strahler ordering scheme, a linear relation is found between the drainage basin entropy and the basin order. This relation can be characterized as a measure of the basin network complexity. The basin entropy is found to be linearly related to the logarithm of the magnitude of the basin network. This relation leads to a nonlinear relation between the network diameter and magnitude, where the exponent is found to be related to the fractal dimension of the drainage network. Also, the exponent of the power law relating the channel slope to the network magnitude is found to be related to the fractal dimension of the network. These relationships are verified on three drainage basins in southern Italy, and the results are found to be promising.Show more Item A stochastic model for sediment yield using the Principle of Maximum Entropy(American Geophysical Union, 1987-05) Singh, V. P.; Krstanovic, P. F.Show more The principle of maximum entropy was applied to derive a stochastic model for sediment yield from upland watersheds. By maximizing the conditional entropy subject to certain constraints, a probability distribution of sediment yield conditioned on the probability distribution of direct runoff volume was obtained. This distribution resulted in minimally prejudiced assignment of probabilities on the basis of given information. The parameters of this distribution were determined from such prior information about the direct runoff volume and sediment yield as their means and covariance. The stochastic model was verified by using three sets of field data and was compared with a bivariate normal distribution. The model yielded sediment yield reasonably accurately.Show more Item A kinematic model for surface irrigation: Verification by experimental data(American Geophysical Union, 1983-12) Singh, Vijay P.; Ram, Rama S.Show more A kinematic model for surface irrigation is verified by experimental data obtained for 31 borders. These borders are of varied characteristics. Calculated values of advance times, water surface profiles when water reaches the end of the border, and recession times are compared with their observations. The prediction error in most cases remains below 20% for the advance time and below 15% for the recession time. The water surface profiles computed by the model agree with observed profiles reasonably well. For the data analyzed here the kinematic wave model is found to be sufficiently accurate for modeling the entire irrigation cycle except for the vertical recession.Show more Item A kinematic model for surface irrigation: An extension(American Geophysical Union, 1982-06) Sherman, Bernard; Singh, Vijay P.Show more The kinematic model for surface irrigation, reported previously by Sherman and Singh (1978), is extended. Depending upon the duration of irrigation and time variability of infiltration, three cases are distinguished. Explicit solutions are obtained when infiltration is constant. When infiltration is varying in time, a numerical procedure is developed which is stable and has fast convergence. A rigorous theoretical justification is developed for computation of the depth of water at and the time history of the front wall of water advancing down an infiltrating plane or channel. A derivation is given of the continuity and momentum equations when there is lateral inflow and infiltration into the channel bed.Show more Item A distributed converging overland flow model: 3. Application to Natural Watersheds(American Geophysical Union, 1976-10) Singh, Vijay P.Show more The proposed distributed converging overland flow model is utilized to predict surface runoff from three natural agricultural watersheds. The Lax-Wendroff scheme is used to obtain numerical solutions. For determination of the kinematic wave friction relationship parameter a simple relation between the parameter and topographic slope is hypothesized. The simple relation contains two constants which are optimized for each watershed by the Rosenbrock-Palmer optimization algorithm. The model results are in good agreement with runoff observations from these watersheds. It is shown that if the model structure is sound, it will suffice to optimize model parameters on hydrograph peak only even for prediction of the entire hydrograph. The model results suggest that a distributed approach to kinematic wave modeling of watershed surface runoff is potentially promising and warrants further investigation.Show more Item Granulometric characterization of sediments transported by surface runoff generated by moving storms(Copernicus Publications on behalf of the European Geosciences Union and the American Geophysical Union, 2008-12-16) de Lima, J. L. M. P.; Souza, C. C. S.; Singh, V. P.Show more Due to the combined effect of wind and rain, the importance of storm movement to surface flow has long been recognized, at scales ranging from headwater scales to large basins. This study presents the results of laboratory experiments designed to investigate the influence of moving rainfall storms on the dynamics of sediment transport by surface runoff. Experiments were carried out, using a rain simulator and a soil flume. The movement of rainfall was generated by moving the rain simulator at a constant speed in the upstream and downstream directions along the flume. The main objective of the study was to characterize, in laboratory conditions, the distribution of sediment grain-size transported by rainfall-induced overland flow and its temporal evolution. Grain-size distribution of the eroded material is governed by the capacity of flow that transports sediments. Granulometric curves were constructed using conventional hand sieving and a laser diffraction particle size analyser (material below 0.250 mm) for overland flow and sediment deliveries collected at the flume outlet. Surface slope was set at 2%, 7% and 14%. Rainstorms were moved with a constant speed, upslope and downslope, along the flume or were kept static. The results of laboratory experiments show that storm movement, affecting the spatial and temporal distribution of rainfall, has a marked influence on the grain-size characteristics of sediments transported by overland flow. The downstream-moving rainfall storms have higher stream power than do other storm types.Show more Item A distributed converging overland flow model: 1. Mathematical solutions(American Geophysical Union, 1976-10) Sherman, Bernard; Singh, Vijay P.Show more In models for overland flow based on kinematic wave theory the friction parameter is assumed to be constant. This paper studies a converging geometry and allows continuous spatial variability in the parameter. Parameter variability results in a completely distributed approach, reduces the need to use a complex network model to simulate watershed surface runoff, and saves much computational time and effort. This paper is the first in a series of three. It develops analytical solutions for a converging geometry with no infiltration and temporally constant lateral inflow. Part 2 discusses the effect of infiltration on the runoff process, and part 3 discusses application of the proposed model to natural agricultural watersheds.Show more Item A fractional dispersion model for overland solute transport(American Geophysical Union, 2006-03-18) Deng, Zhi-Qiang; de Lima, M. Isabel P.; Singh, Vijay P.; de Lima, Jo?�o L. M. P.Show more Using the kinematic-wave overland flow equation and a fractional dispersion-advection equation, a process-oriented, physically-based model is developed for overland solute transport. Two scenarios, one consisting of downslope and the other of upslope rainstorm movements, are considered for numerical computations. Under these conditions, the hydrograph displays a long-tailed distribution due to the variation in flow velocity in both time and distance. The solute transport exhibits a complex behavior. Pollutographs are characterized by a steep rising limb, with a peak, and a long, stretched receding limb; whereas the solute concentration distributions feature a rapid receding limb followed by a long stretched rising limb. Downslope moving storms cause much higher peak in both hydrographs and pollutographs than do upslope moving storms. Both hydrographs and the pollutographs predicted by the fractional dispersion model are in good agreement with the data measured experimentally using a soil flume and a moving rainfall simulator.Show more Item A distributed converging overland flow model: 2. Effect of infiltration(American Geophysical Union, 1976-10) Sherman, Bernard; Singh, Vijay P.Show more The overland flow on an infiltrating converging surface is studied. Mathematical solutions are developed to study the effect of infiltration on nonlinear overland flow dynamics. To develop mathematical solutions, infiltration and rainfall are represented by simple time and space in variant functions. For complex rainfall and infiltration functions, explicit solutions are not feasible.Show more