Hung Tao Shen

Evolution and hydraulic resistance of anchor ice on gravel bed

This paper presents a laboratory study on anchor ice evolution and its hydraulic effect in channels with a gravel bed. The study revealed that anchor ice is initiated by frazil ice accumulation on bed gravel from half a gravel diameter below the crown level of the gravel. No in-situ ice growth within the frazil accumulation or downward growth towards the bed was observed. During the initial stage of growth anchor ice grew in the forms of tails, scales, or balls, depending on the flow velocity and Froude number. During the final stage of growth, when the gravel bed was covered by ice, the growth rate increased with the heat loss rate and Froude number, and inversely proportional to the flow depth. The overall hydraulic resistance of anchor ice was smaller for smaller bed gravel sizes and decreases with the increase in flow rate and flow depth. The rate of increase of the gross Mannings resistance coefficient decreases with the increase in Reynolds number. The bed/ice surface roughness first increases with anchor ice growth, then decreases to a minimum value after the initial stage of growth, when anchor ice grew out of the gravel bed.

Modeling oil spills in a river—lake system

Abstract A general model shell, ROSS3, is developed for simulating oil spills in complex river systems using techniques which have not been previously exploited in oil spill models. ROSS3s new approach has several advantages over the approach to model oil spills in the past: (a) The use of a time-varying boundary-fitted coordinate system that allows accurate accounting for complex river/lake boundary as well as the river boundary changes as its water levels fluctuate; (b) The ability to confine two-dimensional hydrodynamic computations to a limited river reach; (c) The ability to interactively layout the channel networks for setting up the model, define extra cross sections to increase the accuracy if needed, in addition to the traditional data entry and visualization interfaces. ROSS3 is a two-layer two-dimensional oip spill model that can simulate the mechanism of advection, horizontal diffusion, mechanical spreading, shoreline deposition, evaporation, dissolution, vertical mixing, resurfacing and sinking. In ROSS3 spilled oil may be a surface slick or suspended oil droplets, or a combination of both. Both free surface and ice cover conditions can be simulated. The flow of conditions can be varied and the unsteady flow model can be run within ROSS3 to simulate the flow conditions in both the river and the lake. The ice conditions can be added or removed from the model input using easy interactive procedures.

Frazil evolution in channels

A simulation model for the formation and evolution of frazil in open channels is developed. In this model, the primary nucleation is assumed to be due to mass exchange of seeding crystals at the free surface. The model of frazil crystals growth is based on the rate of heat transfer between crystals and the ambient turbulent flow. Secondary nucleation and flocculation are simulated based on binary collisions of frazil particles. The model is validated with existing experimental data. It is capable of simulating the variation of water temperature during the frazil formation period and the evolution of size and concentration distributions of frazil in the flow. Effects of the surface heat exchange, the rate of seeding, and the flow condition are examined.

Shokotsu River ice jam formation

A spring ice jam occurred in the Shokotsu River in March 1995. This has been the only known ice jam in this river since 1955. This paper discusses the ice jam processes and investigates the causes of the Shokotsu River ice jam by analyzing the available hydrometeorological data as well as hydraulic and geometric characteristics of the river. This analysis showed that this breakup event was triggered by a sudden increase in basin runoff produced by the rainfall during a warm spell. Snowmelt resulting from warm air temperature alone would not be sufficient to produce the discharge increase for the breakup. The jam was initiated at a section with rapid reductions in channel slope, flow velocity, as well as the top width as the ice run approached from upstream. Numerical simulation carried out to analyze the ice jam dynamics showed that the model is capable of reproducing the jam event and supplemented the limited information obtained from the field observation.

Modelling river oil spills: a review

The risk of oil spills in rivers has increased due to oil storage facilities along rivers, inland navigation, major oil transport pipelines that cross rivers. Inland oil spills are more frequent than ocean oil spills but are usually of smaller volumes. Oil spills in inland waterways can have enormous environmental and economical impacts because of their closeness to populated areas and economic centres. Previous review studies on oil spill modelling have concentrated on ocean oil spill modelling. In this paper all existing major river oil spill models are reviewed. The specific needs of the river oil spill models that are different from the ocean oil spill models are identified. The physico chemical oil spill processes which form the model are discussed. A comparison of the different models are presented. Simulations are presented to demostrate state-of-the-art in river oil spill models.

Experimental studies of sediment enrichment of arctic ice covers due to wave action and frazil entrainment

Two processes are investigated that are believed to contribute to the sediment enrichment of ice covers in coastal arctic waters. One process results from wave action which pumps sediment rich underlying water into the surface cover. The other enriching mechanism is produced by rising frazil that entrains suspended sediment which subsequently becomes incorporated in the surface ice layer. In both processes the sediment enrichment of the ice cover is found to depend upon the sediment size and concentration in the underlying water column. In the wave dependent process the rate of sediment enrichment is influenced by the period, amplitude, and duration of the wave action as well as the size of the ice particles and motion of the cover. Frazil rising through sediment laden water was found to entrain particles of sand far more effectively than silt. Sand laden frazil floe would often become so loaded with sediment that the floe would eventually settle to the floor of the water column.

An Integrated Computer Model for Simulating Oil Spills in the Upper St. Lawrence River

Abstract An integrated oil spill model MICROSS2 has been developed for simulating the fate and transport of spilled oil in rivers and is applied to the upper St. Lawrence river bordering the United States and Canada. This model considers the physico-chemical mechanisms of advection, horizontal diffusion, mechanical spreading, evaporation, dissolution, vertical mixing, and shoreline deposition in simulating the oil slick transformation. It can simulate the oil slick transformation on the water surface and in the water column, in transient flow conditions with varying wind and air temperature. The integrated model consists of the following modules: a) a menu based interface for interactive data preparation, and execution of other modules; b) flow model to compute the velocity distribution in the river; c) a two-dimensional two layer oil spill model; d) a graphics interface for visualizing the results from the flow model and the oil spill model. The integrated model is operational on a micro-computer, and can be used as a part of an oil spill response program to assist cleanup, environmental impact assessment, and contingency planning.

Dynamics of Ice Jam Formation and Release

Abstract The numerical model DynaRICE and its application to ice jam formation and release is presented. The model is a two-dimensional coupled flow and ice dynamic model. The ice dynamic component, which includes both the internal ice resistance and boundary friction on ice motion, uses a Lagrangian SPH method. The hydrodynamic component of the model uses a streamline upwind finite element method, which is capable of simulating trans-critical flow conditions. The model is validated with field observed ice jam data. The phenomena of ice jam formation and release dynamics are examined using the validated model.

A preliminary laboratory study of motion of floating debris generated by solitary waves running up a beach

Destructive tsunamis can destroy coastal structures and move huge amounts of tsunami debris. Our current understanding of motion of tsunami debris in tsunami flows is limited. In this paper, we present a preliminary laboratory study of motion of model debris under the action of solitary waves running up a beach. The difference between the waterline of maximum inundation and the final position of debris was examined under various conditions. Effects of solitary wave height, water depth, and the distance of debris source to the shoreline on the maximum inundation, the debris limit, and the final position of debris were examined. In general, the final positions of the debris are different from the waterline at maximum inundation and there is a low possibility that a large amount of debris can be carried by retreating water offshore into the sea.

A Simulation Model for Chemical Spills in the Upper St. Lawrence River

Abstract A two-dimensional Lagrangian computer model to simulate the transport of chemical spills in the upper St. Lawrence River is developed. The model considers the spilled chemical to be transported in the river as a mixed layer over the depth of the flow and a bottom layer along the bed, with continuous exchange between the two layers. The transport and fate processes include advection/diffusion, sorption/desorption, settling, resuspension, diffusive exchange between sediment/water interface, and can include volatilization, photolysis, hydrolysis, and biodegradation. The model is an integrated part of contingency plan for containment, control and cleanup of possible chemical spills in the upper St. Lawrence River.