• Journal of Korea Water Resources Association
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• v.34 no.4
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• pp.289-301
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• 2001

A fractional step finite difference model for the longitudinal dispersion of nonconservative pollutants is applied to the Nakdong River to simulate the phenol spill accident which occurred on March, 1971. Prior to the dispersion calculation, the flow conditions are simulated to provide inputs to the dispersion model. An unsteady flow model based on Preissmann's four-point scheme is used for this purpose. Sensitivities of the dispersion calculation to empirical equations for dispersion coefficient and to the first-order decay coefficient are analyzed. The time to peak concentration at a downstream location is significantly different depending on the formula for the dispersion coefficient. Although the decay coefficient does not affect the shape of the temporal concentration distribution, the concentration values depend on the decay coefficient verb significantly. An optimization technique is used to calibrate the dispersion model as well as the flow model. The time to the peak concentration is simulated for major positions of water intake along the Nakdong River.

• Water for future
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• v.28 no.3
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• pp.205-216
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• 1995

Existing equations for dispersion coefficient are analyzed in depth to select proper dispersion coefficient which can represent dispersion characteristics of natural streams. Several equations are tested with measured data which were collected in 26 streams in the United States. Findings of this study are as follows. Elder's equation should not be used to estimate dispersion coefficient of the one-dimensional dispersion model because it underestimates significantly. McQuivey and Keefer's equation is overestimating, whereas Magazine et al.'s equation is underestimating. However, Iwasa and Aya's equation predicts relatively well. Fischer's equation is generally overestimating. Liu's equation predicts quite well. The performance of Liu's equation is the best of all especially in terms of accuracy. However, Liu's equation is generally overestimating in case of large river because the square of channel width is included in the equation. Therefore, it is recommended not to use Liu's equation in case of large rivers, especially rivers of which channel width is larger than 200m.

• Journal of Soil and Groundwater Environment
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• v.11 no.6
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• pp.28-34
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• 2006

Laboratory column tests using $Cl^-$ tracer were conducted to study the correlation of soil particle distribution and hydrodynamic dispersion mechanism with three kinds of ununiformed soil samples, in which the ratio of gravel and sand versus silt and clay is 24.5 for S-1 soil, 4.48 for S-2 soil, and 0.4 for S-3 soil. Chloride breakthrough curves with time were fitted with gaussian functions. The relative concentrations of chloride were converged to 1.0 after 0.7 hours for S-1, 6.3 hours for S-2, and 389 hours for S-3. Average linear velocity, longitudinal dispersion coefficient, and longitudinal dispersivity were calculated by chloride breakthrough curves. Longitudinal dispersion coefficients were $1.20{\times}10^{-4}\;m^2/sec$ for S-1, $8.87{\times}10^{-7}\;m^2/sec$ for S-2, and $1.94{\times}10^{-9}\;m^2/sec$ for S-3. Peclet numbers calculated by the molecular diffusion coefficient of chloride and the mean grain diameters of soils were $2.59{\times}10^2$ for S-1, $6.27{\times}10^0$ for S-2, and $1.35{\times}10^{-4}$ for S-3. Mechanical dispersion was dominant for the hydrodynamic dispersion mechanism of S-1. Both mechanical dispersion and molecular diffusion were dominant for the hydrodynamic dispersion mechanism of S-2, but mechanical dispersion was ascendant over molecular diffusion. Hydrodynamic dispersion in S-3 was occurred mainly by molecular diffusion. When plotting three soils on the graph of $D_L/D_m$ versus Peclet number produced by Bijeljic and Blunt (2006), the values of $D_L/D_m$ for S-1 and S-2 were more than 2.0 order compared to their graph. S-3 was not plotted on their graph because the Peclet number was as small as $1.35{\times}10^{-4}$.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.14 no.1
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• pp.131-141
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• 1994

Three characteristics-based split-operator methods were applied to a longitudinal pollutant dispersion problem, and the results were compared with those of several Eulerian schemes. The split-operator methods consisted of generalized upwind, two-point fourth-order and sixth-order Holly-Preissmann schemes, respectively, for the advection calculation, and the Crank-Nicholson scheme for the diffusion calculation. Compared with the Eulerian schemes tested, split-operator methods using the Holly-Preissmann schemes gave much more accurate computational results. Eulerian schemes using centered difference approximations for the advection term resulted in numerical oscillations, and those using backward difference resulted in numerical diffusion, both of which were more severe for smaller value of the longitudinal dispersion coefficient.

• Journal of Korea Water Resources Association
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• v.36 no.4
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• pp.673-689
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• 2003

Field tests were conducted to investigate characteristics of the transverse mixing and to evaluate the dispersion coefficients in the meandering natural streams. The Sum River and the Cheong-mi Creek, tributaries of Han River, were selected as the test site, and measurements of the hydraulic and dispersion data were performed. In the tracer tests, the radioisotope was used as a tracer and injected into a flow on the instantaneous point source. Using the measured data, the longitudinal and transverse dispersion coefficients were evaluated and compared with the previous studies. The longitudinal dispersion coefficients, which were evaluated by application of the analytical solution, were about 0.5 $m^2$/s at the Sum River and 0.2 $m^2$/s at the Cheong -mi Creek. The transverse dispersion coefficients, which were evaluated by the analytical solution and the moment method, were ranging from 0.01 to 0.06 $m^2$/s for the Sum River and from 0.01 to 0.05 $m^2$/s for the Cheong-mi Creek.

• Journal of Soil and Groundwater Environment
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• v.13 no.4
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• pp.1-7
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• 2008

This study analyzed for hydrodynamic dispersion characteristics of multi-soil layer (Silt and clay, Find sand, Coarse sand), data of a field tracer test on the multi-soil layer and data of laboratory column experiments on the samples on each soil layers. Through the analysis of permeability and flow, MS (Silt and clay) and FS (Fine sand), which were low effective porosity, were higher average linear velocity while CS (Coarse sand), which was high effective porosity, was higher hydraulic conductivity. Hydraulic conductivity function based on average soil particle diameter was assumed Y=$3.49{\times}10^{-8}e^{15320x}$ and coefficient of determination was 0.90. Average linear velocity function based on average soil particle diameter was assumed Y=$1.88{\times}10^{-7}e^{11459x}$ and coefficient of determination was 0.81. Longitudinal dispersivity function based on average soil particle diameter was Y = 0.00256$e^{5971x}$ and coefficient of determination was 0.98. According to the linear regression analysis of average linear velocity and longitudinal dispersivity, assumed function was Y = 21.7527x + 0.0063, and coefficient of determination was 0.9979. The ratio of field scale/laboratory scale was 54.09, it exhibited scale-dependent effect of hydrodynamic dispersion. Field longitudinal dispersivity (1.39m) was 7.47 times as higher than longitudinal dispersivity estimated by the methods of Xu and Eckstein (1995). Hydrodynamic dispersion on CS layer was occurred mainly by diffusion flow in the test aquifer.

• Journal of Soil and Groundwater Environment
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• v.11 no.6
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• pp.53-60
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• 2006

Single well injection withdrawal tracer tests with bromide were carried out at two wells developed in a horizontally heterogeneous fractured rock. The hydraulic conductivity of TW-1 well was 5 times larger than TW-2 well, and the average linear velocity of TW-2 well was 1.8 times faster than TW-1 well. The difference of hydrodynamic dispersions of two wells in the fractured rock was studied with the analysis of concentration breakthrough curves and cumulative mass recovery curves of bromide with withdrawal time, and the estimation of average travel distance, pore velocity, longitudinal dispersivity and longitudinal dispersion coefficient. The average travel distances of bromide were estimated to be 3.00 m in TW-1 well and 5.62 m in TW-2 well. The average pore velocities for the injection/withdrawal phase were estimated to be $4.31\;{\times}\;10^{-4}\;m/sec$ in TW-1 well and $8.08\;{\times}\;10^{-4}\;m/sec$ in TW-2 well. Average travel distance and pore velocity were higher in TW-2 well because of small effective porosity. Longitudinal dispersivities were estimated to be 28.73 cm in TW-1 well and 18.49 cm in TW-2 well, and bromide transport was 1.55 times faster in TW-1 well. Longitudinal dispersion coefficients were estimated to be $5.14\;{\times}\;10^{-6}\;m^2/sec$ in TW-1 well and $6.06\;{\times}\;10^{-6}\;m^2/sec$ in TW-2 well, and diffusion area was 1.18 times larger in TW-2 well.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.29 no.6B
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• pp.551-560
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• 2009

This paper describes a newly developed pollutant transport model named ARPTM which was designed to simulate the transport and characteristics of pollutant materials after an accidental spill in upstream of river system up to a given position in the downstream. In particular, the ARPTM incorporated ADCP data to compute longitudinal dispersion coefficient and advection velocity which are necessary to apply one-dimensional advection-dispersion equation. ARPTM was built on top of the geographic information system platforms to take advantage of the technology's capabilities to track geo-referenced processes and visualize the simulated results in conjunction with associated geographic layers such as digital maps. The ARPTM computes travel distance, time, and concentration of the pollutant cloud in the given flow path from the river network, after quickly finding path between the spill of the pollutant material and any concerned points in the downstream. ARPTM is closely connected with a recently developed GIS-based Arc River database that stores inputs and outputs of ARPTM. ARPTM thereby assembles measurements, modeling, and cyberinfrastructure components to create a useful cyber-tool for determining and visualizing the dynamics of the clouds of pollutants while dispersing in space and time. ARPTM is expected to be potentially used for building warning system for the transport of pollutant materials in a large basin.

• Korean Journal of Soil Science and Fertilizer
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• v.43 no.3
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• pp.275-282
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• 2010

The laboratory column experiments were used to transport of metal elements by infiltration-related dispersion and/or diffusion in mine tailing of the Guryong gold mine. The mine tailing shows the neutral pH (for a pore water) and contains quartz, chlorite, pyrite and calcite. Both a non-reactive solute ($Cl^-$ of 100 mg $L^{-1}$) and a reactive solute (1N HCl), were injected continuously through columns. The breakthrough curve in the non-reactive experiment reached at a maximum under 1.5 pore volumes (PV). The longitudinal dispersion (0.607 cm) and hydrodynamic dispersion coefficient ($1.96{\times}10^{-7}cm^{2}sec^{-1}$) were calculated by the slope. In the reactive experiment, the plateau curve was appeared in the pH values of 5.3, 4.5 and 1.7. The releases of metal elements such as Fe, Mn, Al, Cu, Zn, Pb, and Cd were observed to be related to the pH buffering. High concentrations of Mn, Cd and Zn were observed at the first pH plateau (4 PV and pH 5.3), whereas Fe, Cu, Al and Pb were released as the pH decreased to 4.0 or less. The resulting order of metals mobility, based on the effluent water, is Mn=Cd>Zn>Cu>Fe>Al>Pb.

• Journal of the Korean Society of Hazard Mitigation
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• v.4 no.3 s.14
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• pp.43-50
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• 2004

This study had been performed to analyze flushing effects for instantaneous contaminants input with changing dam discharge in River. RMA-2 and RMA-4 models were applied to the downstream part of the Han River(from Jamsil submerged weir to Singok submerged one) The longitudinal dispersion coefficient of $50m^2/s$ was used. The four cases of dam discharges were selected as $500m^3/s,\;1000m^3/s,\;1500m^3/s$ and $2000m^3/s$, respectively, for 1 hour. The drought flow was fixed $200m^3/s$ in the Han River. The arrival time and the concentration of contaminant, the area of dispersion were estimated with RMA-4 model in the downstream part of the Han River. The arrival time which the concentration of contaminants become under 1ppm was analyzed with the stagnant and the instantaneous inflow contaminant at the section of Sungsan Bridge. The more increasing a dam discharge, the more short a dilution time of contaminant. The relation between the dam discharge and dilution time shows linearity. The instantaneous contaminant input was sensitively affected by the dam discharge than the stagnant contaminant one in the river. If it is tried to flush with a temporally increased dam discharge, it should be understood the range of overflowed contaminant dispersion from main channel to tributary channel.