Storm‐coverage effect on dynamic flood‐frequency analysis: empirical data analysis

In this study, a dynamic flood‐frequency analysis model considering the storm coverage effect is proposed and applied to six sub‐basins in the Pyungchang River basin, Korea. The model proposed is composed of the rectangular pulse Poisson process model for rainfall, the Soil Conservation Service curve number method for infiltration and the geomorphoclimatic instantaneous unit hydrograph for runoff estimation. Also, the model developed by Marco and Valdes is adopted for quantifying the storm‐coverage characteristics. By comparing the results from the same model with and without the storm‐coverage effect consideration, we could quantify the storm‐coverage effect on the flood‐frequency analysis. As a result of that, we found the storm‐coverage effect was so significant that overestimation of the design flood was unavoidable without its consideration. This also becomes more serious for larger basins where the probability of complete storm coverage is quite low. However, for smaller basins, the limited number of rain gauges is found to hamper the proper quantification of the storm‐coverage characteristics. Provided with a relationship curve between the basin size and the storm coverage (as in this study), this problem could be overcome with an acceptable accuracy level. Copyright © 2003 John Wiley & Sons, Ltd.     

Acoustic tomography for monitoring the Sea of Japan: a pilot experiment

A pilot experiment was conducted in the Sea of Japan (also called the East Sea) in September-October 1999, to assess the possibility of using acoustic tomographic techniques for monitoring water mass structure and dynamics. Acoustic m-sequence signals at various frequencies between 250 and 634 Hz were transmitted from bottom-mounted acoustic sources in shallow water off the coast of Vladivostok to vertical-array receiving systems deployed off the north coast of Ulleung-Do island (S. Korea), 558 km to the south. The data are analyzed for temporal correlation, time spread, and transmission loss and are interpreted in terms of a tomographic system for monitoring the East Sea.     

Application of generalized contaminant retardation factor to a multi‐phase system

In this study, a generalized contaminant retardation factor applicable to a multiphase system where various types of colloids exist simultaneously with contaminants is derived and incorporated into an equilibrium model which is successfully applied to experimental data for which phenanthrene was used as hydrophobic organic contaminants and dissolved organic matter (DOM) or bacteria as mobile carriers. Based on the parameter values for the experimental data regarding the association of phenanthrene with solid matrix, DOM and various bacterial isolates, numerical experiments are performed to examine the transport behaviour of hydrophobic organic contaminants in various types of the multiphase system. Numerical experiments demonstrate that the extent of contaminant transport enhancement depends on the adsorption affinity of the colloid, its concentration and its mobility, and that the importance of a third phase to contaminant transport needs to be evaluated carefully with respect to the relevance of experimental conditions applied to realistic environmental conditions. Copyright © 2003 John Wiley & Sons, Ltd.     

The hydrocarbons in the Isla Vista marine seep environment

Hydrocarbon analyses on samples of sediment, interstitial water, and dissolved and particulate fractions of the water column from the vicinity of the Isla Vista seep near Santa Barbara, California, are presented. The results demonstrate that a very heterogeneous distribution of hydrocarbon composition and concentration exists in the seep environment and that the life-style and feeding habits of the organisms in this environment will have a dramatic effect on their hydrocarbon exposure.     

Numerical analysis of bacterial transport in saturated porous media

A mathematical model to describe bacterial transport in saturated porous media is presented. Reversible/irreversible attachment and growth/decay terms were incorporated into the transport model. Additionally, the changes of porosity and permeability due to bacterial deposition and/or growth were accounted for in the model. The predictive model was used to fit the column experimental data from the literature, and the fitting result showed a good match with the data. Based on the parameter values determined from the literature experimental data, numerical experiments were performed to examine bacterial sorption and/or growth during bacterial transport through saturated porous media. In addition, sensitivity analysis was performed to investigate the impact of key model parameters for bacterial transport on the permeability and porosity of porous media. The model results show that the permeability and porosity of porous media could be altered due to bacterial deposition and growth on the solid matrix. However, variation of permeability due to bacterial growth was trivial compared with natural permeability variation. Copyright © 2005 John Wiley & Sons, Ltd.     

Analysis of Cryptosporidium parvum oocyst transport in porous media

Cryptosporidium parvum is a protozoan parasite, transmitted through aqueous environments in the form of an oocyst. In this study, a transport model into which sorption, filtration and inactivation mechanisms are incorporated is applied to simulate laboratory column data, and the suitability of a kinetic model to describe the C. parvum oocyst transport and removal in porous media is compared with an equilibrium model. The kinetic model is applied to simulate previous column experimental data and successfully simulates the concentration peak; the late time tailing effect appeared in the breakthrough curves, indicating that the kinetic model is more suitable than the equilibrium one at simulating the fate and transport of the oocysts in porous media. Simulation illustrates that sorption causes retardation along with a tailing in the breakthrough curve. Additionally, filtration acts as a major mechanism of removing the oocysts from the aqueous phase, whereas the role of inactivation in reducing the viable oocyst concentration is minimal. Copyright © 2004 John Wiley & Sons, Ltd.     

Monitoring of drawdown pattern during pumping in an unconfined physical aquifer model

In this study, we attempted to analyse a drawdown pattern around a pumping well in an unconfined sandy gravelly aquifer constructed in a laboratory tank by means of both experimental and numerical modelling of groundwater flow. The physical model consisted of recharge, aquifer and discharge zones. Permeability and specific yield of the aquifer material were determined by Dupuit approximation under steady‐state flow and stepwise gravitational drainage of groundwater, respectively. The drawdown of water table in pumping and neighbouring observation wells was monitored to investigate the effect of no‐flow boundary on the drawdown pattern during pumping for three different boundary conditions: (i) no recharge and no discharge with four no‐flow boundaries (Case 1); (ii) no recharge and reservoir with three no‐flow boundaries (Case 2); (iii) recharge and discharge with two no‐flow boundaries (Case 3). Based on the aquifer parameters, numerical modelling was also performed to compare the simulated drawdown with that observed. Results showed that a large difference existed between the simulated drawdown and that observed in wells for all cases. The reason for the difference could be explained by the formation of a curvilinear type water table between wells rather than a linear one due to a delayed response of water table in the capillary fringe. This phenomenon was also investigated from a mass balance study on the pumping volume. The curvilinear type of water table was further evidenced by measurement of water contents at several positions in the aquifer between wells using time domain reflectometry (TDR). This indicates that the existing groundwater flow model applicable to an unconfined aquifer lacks the capacity to describe a slow response of water table in the aquifer and care should be taken in the interpretation of water table formation in the aquifer during pumping. Copyright © 2001 John Wiley & Sons, Ltd.     

Case Studies of PSDDF for Phased Placement of Dredged Soils

Use of Terzaghi's one-dimensional consolidation theory is not suitable for consolidation of highly deformable soft clays such as dredged soils. To model this condition, it is necessary to consider non-linear finite strain consolidation behavior, i.e., changes in compressibility and permeability with increasing stress. A one-dimensional non-linear finite strain numerical model, Primary Consolidation, Secondary Compression, and Desiccation of Dredged Fill (PSDDF), has been used to predict the stress-dependent settlement of fine-grained dredged materials. In this paper, two case studies of using PSDDF are discussed to illustrate the applicability and accuracy of PSDDF. The first case study involves PSDDF simulations of laboratory-phased placement of a marine clay dredged from Busan, Korea. PSDDF results are in good agreement with the corresponding results of the laboratory large strain consolidation tests. The other involves estimating the service life of the Craney Island Dredged Material Management Area near Norfolk, Virginia, in the United States. The excellent agreement between measured and calculated values shows that PSDDF is a reliable tool for predicting settlement of dredged material.     

3D magnetotelluric modelling including surface topography

An edge finite‐element method has been applied to compute magnetotelluric (MT) responses to three‐dimensional (3D) earth topography. The finite‐element algorithm uses a single edge shape function at each edge of hexahedral elements, guaranteeing the continuity of the tangential electric field while conserving the continuity of magnetic flux at boundaries. We solve the resulting system of equations using the biconjugate gradient method with a Jacobian preconditioner. The solution gives electric fields parallel to the slope of a surface relief that is often encountered in MT surveys. The algorithm is successfully verified by comparison with other numerical solutions for a 3D‐2 model for comparison of modelling methods for EM induction and a ridge model. We use a 3D trapezoidal‐hill model to investigate 3D topographic effects, which are caused mainly by galvanic effects, not only in the Zxy mode but also in the Zyx mode. If a 3D topography were approximated by a two‐dimensional topography therefore errors occurring in the transverse electric mode would be more serious than those in the transverse magnetic mode.     

Reductive dechlorination of polychlorinated biphenyls (PCBs) by ultrasound-assisted chemical process (UACP)

The dechlorination of aqueous polychlorinated biphenyls (PCBs) using the ultrasound-assisted chemical process (UACP), which is a combination of ultrasonic irradiation and radical generations using di-tert-butyl peroxide as a radical initiator and ferrous ion as a catalyst at moderate temperature in alkaline 2-propanol, was demonstrated with a high reduction of PCBs. A commercial PCB-containing compound, Aroclor 1260, was also decomposed with the removal efficiency of 97 % achieved within 3 h of UACP. The gas chromatograph was used as a quantitative method to measure the decomposition rate of PCBs. The competitive elimination among the ortho (2-position), meta (3-position), and para (4-position) chlorine atoms of PCB was also identified.