投棄 浚渫土의 擧動解析에 관한 硏究

Abstract

Although the dredging work is an ancient art which can be traced back for several thousand years, it is only relatively new science covering the design of dredgers and dredging techniques. The primary purpose of dredging work is to maintain navigational readiness and to increase environmental amenity. Therefore the dredging project, which is composed of excavating, removing, transporting and storing or dumping dredged material, must be carefully managed to insure that dredging works are completed in a cost-effective and environmentally safe manner.

The most important point in dumping operations is evaluating and decreasing the impacts of dumping works at the dumping area. One of the most effective method for this purpose is using the schematic process composed of the sophisticated plan, precise work and predicting/reducing the impacts based on an numerical model being closely linked with field observation.

In this study, we first introduce the state of art of dredging work being done in the world including Korea, the environmental impacts of dredging activities at both dredging area and dumping area and the features of treatment methods. After this, the numerical model is used to predict the spatial transport and fate of dredged materials which is dumped by the hopper dredger or barge into an open receiving water area and the effluents behavior discharged from the confined dumping facility(CDF) located at a coastal area. To do this purpose, numerical models were used for reappearing the tidal current of concerned area and for analysing long-term diffusion of effluent. These models were then applied to Mokpo harbor where capital dredging and maintenance dredging are being conducted simultaneously and the CDF is under construction.

In series of model case study, we found that the behavior of dredged materials dumped in open water area was governed by the receiving water conditions, the operating condition of dredging equipment as well as the characteristics of materials. The sand moved 2,700 meters from the dumping point and 90 percent settled on bottom in 20 minute. The silt moved 4,000 meters from the dumping point after an hour. All of clay suspended in water until an hour and moved 4,200 meters.

The effluent discharged from CDF was governed by the receiving water condition and outfall geometry, so that limit of near-field was 14∼750 meter down stream and 5 ∼250 meter in transverse direction. Dilution ranged from 1.1 to 8.7 by the model cases. Long-term diffusion characteristics was governed by the dilution rate during near-field behavior, ambient conditions and CDF operation mode.

Also the results revealed that there are needs to reform intensively existing domestic regulations. Mixing zones created by discharge from dredging operations would be one of the criteria for environmental regulatory for dredge operation management.