¹School of Construction, Urban, & Environmental Engineering Handong University, Pohang City, KOREA

knahn@handong.edu

　

²Civil & Coastal Engineering Department, University of Florida Gainesville, Florida, USA

　

This paper presents the effect of turbulence on the fall velocity of sand particles. The equation of motion for a single suspended spherical particle in homogeneous turbulence is solved numerically and compared with experimental data. The average fall velocity in homogeneous turbulence is shown to be reduced considerably compared to fall velocity in still water. The effects of added mass, pressure force, non-linear drag forces, and frequency of turbulent fluctuations on the average fall velocity are discussed.

　

The average turbulence level in the surf zone is shown to be dependent on the incoming wave period. And in consequence, the average fall velocity of sand particle in surf zone should be influenced by wave period such that the average fall time of sand particles increase as wave period decreases. The possible implication of these results on the Dean number (D= H / wT, H: wave height, T: wave period, w: fall velocity of sand particle) as an index to discriminate the storm/normal beach profile is discussed.

　

　

¹Coastal and Harbor Engineering Laboratory Korea Ocean Research and Development Institute Ansan, Kyunggido, KOREA

jyjin@kordi.re.kr

　

²Department of Oceanography, Inha University Incheon, KOREA

　

Indirect measurements of suspended sediment concentration (SSC) using optics or acoustics have replaced traditional filtering method. In spite of their convenience, however, optical backscatter sensors (OBSs) and acoustic Doppler current profilers (ADCPs) of the representative indirect methods, require rigorous calibration procedures because of their sensitivity to particle size, SSC, seawater temperature and salinity etc. The calibration of the indirect instruments should be conducted in-situ, of which the primary task is seawater sampling at the same depths as their sensing depths.

　

Various kinds of water sampler such as general water samplers including the Nansen, Van Dorn and Niskin bottles activated by the dropping messengers as well as some automatic samplers of syringe and pump types, may be used for the calibration. However, all the existing water samplers have their own inherent restrictions in that the water sampler for the in-situ SSC calibrations of the indirect instruments should be isokinetic. Additionally, a time-selective and self-triggering sampler is also required for the calibration in estuaries or macrotidal environments where the particle size varies with the tidal phase.

　

A time-selective self-triggering and isokinetic water sampler has been developed for the in-situ calibration of indirect SSC values obtained with the OBSs, transmissometers or ADCPs. The new sampler (Auttle) could be said as the automatic and mooring version of the Niskin bottle. The Auttle's performance has been successfully confirmed through various field tests including an intensive field campaign for the study of the sedimentary processes around a harbor suffering from heavy siltation. This paper will describe the operational principle, the test results, and the applicability of the Auttle in the various fields of oceanography and coastal engineering.

　

　

¹Coastal and Harbor Engineering Research Laboratory, KORDI Seoul, KOREA

swkang@kordi.re.kr

　

²Department of Civil and Environment, Hannam University Daejeon, KOREA

　

Dredging operation is common practice in port and harbor construction sites for deepening navigational channels. In recent years it has received increasing scrutiny because of potential impacts on marine environment by impairing water quality and surrounding habitat. To estimate these impacts, it is necessary to predict the fate and transport of disposed sediments, and also the changes of sediment transport patterns due to port construction. A three-dimensional particle-tracking model has been developed to predict the fate and transport of suspended sediment loads resulting from a port construction in Asan Bay, Korea. Numerical simulations for the transport of suspended sediments with multi-component mixtures were conducted. Changes in tidal currents before and after the port construction and the resulting bottom shear stresses in Asan Bay were obtained to assess the influence on sediment transport due to port and harbor constructions.

　

　

U.S.Army Engineer Research and Development Center Vicksburg, Mississippi, USA

parchut@wes.army.mil

　

Most of the harbors and navigation channels in the world have shoaling problems, which result in loss of water depth needed for safe navigation of vessels. The major sources of shoaling include littoral transport, deposition of suspended sediment, sliding down of soft top layer along the slope of channel bank, sediment transport originating from adjacent areas, and slope instability. Catching sediment before it enters the sensitive area is one of the effective methods for management of sediment deposition. Under favorable site and climatic conditions this can be achieved by providing a sediment trap at carefully selected location.

　

Sediment traps do not catch all the sediment moving in the area. Hence dredging cannot be completely avoided but the frequency and quantity of dredging can be significantly reduced. This increases the efficiency of use of harbor facilities and results in significant cost savings on maintenance dredging. The sediment trap itself must be emptied periodically to keep it functional. Sediment traps are not very common because they can be effective only at highly selective locations and cannot be provided as a general solution to channel sedimentation problem. Physical or numerical model studies are very useful in designing sediment traps. The paper describes the circumstances under which sediment traps can be effectively designed and operated for maximum benefit. Design of sediment trap proposed at Rollover Pass, Texas is described. Practical examples of sediment traps functioning successfully at Channel Islands Harbor, California, USA, Visakhapatnam Port, India, and at Carolina Beach Inlet, North Carolina, USA are described.

　

　

¹Department of Ecosystem Engineering, University of Tokushima Tokushima-city, Tokushima, JAPAN

Yamachan@eco.tokushima-u.ac.jp

　

²Port and Airport Technical Investigation Office. The Shikoku Regional Development Bureau. Ministry of Land, Infrastructure and Transport, JAPAN

　

Recently, the construction of harbor and seashore structures for the economical development and protection against disasters has led a constant eutrophication in coastal enclosed sea areas. Especially when stratification progresses in summer, red tide and low oxygen water column occur with a bloom of phytoplankton. One of the causes promoting these phenomena is supposed to be the influence of sediment. However, there are a few methods of controlling a secondary influence of low oxygen concentration and release of nutrients in sediments.

　

In this research, we focused the sustainable ecological function. We specially paid its attention to a deposit feeding sea cucumber Stichopus japonicus, which is a fishery useful species, to improve sediment quality. In this experiment, deposited seston is used as food for sea cucumbers. The amount of assimilation and the assimilation efficiency were measured in order to compare effects of water temperature and each size. We tried to estimate the amount of organic matter removed from sediment. In addition, a possibility that sea cucumber selectively ingests deposited organic matter is also considered. The alimentary canal of sea cucumber was dissected into three parts, stomach+first intestine, second intestine, large intestine and changes in the material concentrations of these contents and food and feces were measured. We compared changes of Chl.a, Pheo.a, TOC and TN, after measurements.

　

TOC and TN concentrations increased from stomach to first small intestine, but decreased from second small intestine to large intestine. These results suggested that S. japonicus selected dense organic matter patches in the feeding behavior. The amount of assimilation showed the decreasing tendency before estivation, but increased after estivation, indicating lower temperature affects the amount of assimilation. S. japonicus had high assimilation efficiency (68.7±22.8%) before estivation, whereas it was about 35% after estivation.