Detached breakwaters have been used as coastal protection structures. In sandy beaches, group of breakwaters that have openings are constructed. According to the analysis of the bottom sounding, it is known that tombolos are formed behind detached breakwaters. And local scour will occur in an opening or offshore after the detached breakwaters construction. It is difficult to estimate the amount of sand trapping effect because the shoreline data is few. Thus the purpose of this study is to research the relationship wave field and shoreline profiles. The results of this research are follows. 1) If a rate of wave height decreases, erosion will occur. 2) Some detached breakwaters are not applied it. Even if rate of wave height does not change, erosion will occur.
A simple model for predicting change in sand bar of a river mouth was developed. Topographic changes of a river mouth bar were investigated first, taking the case of Sagami River and a river mouth facing the Pacific Ocean as the example. The equilibrium state of the profile of a sand bar is assumed and the strength of the recovery of river mouth topography is determined depending upon the shift from this equilibrium state. The offshore sand transport due to flood current and shoreward sand transport due to waves were modeled to predict three-dimensional change of a sand bar. Dynamic changes in a river mouth bar responding flood current and waves can be predicted by this model.
Field tests of BaNK system were performed in an artificial semi-enclosed beach. We have proposed 'Beach and Navigation Keeper: BaNK system' in order to cope with beach erosion and shoaling of fairway. The system is a method to control sediment transport due to wave-induced residual currents produced by plural submerged asymmetrical structures. In the beach, seashore transformation owing to waves has occurred and been restored every year by a coastal protection work. The transformation of the beach has been investigated on the basis of the field survey from December 2000. Afterwards, half cut old tires as BaNK blocks were set in the beach in 2002 and in 2003 for the tests. As a result of this research, it becomes clear that the BaNK system is very effective as a beach erosion control work in a beach.
A digital still camera with 6 to 8 mega pixels has been commercially available nowadays and has been commonly applied to image sensing. In addition, the resolution of digital camera has developed to be higher as much as 12 mega pixels. These cameras would be applied to an aerial photogrammetry. However, an aerial photography processing for survey purpose has not been standardized especially for nearshore zone for which normal land survey techniques are also difficult to apply, because it is too deep and rough to conduct a human survey, and is too shallow to carry out a ship (sounding) survey. It sounds that an aerial photogrammetry by using a commercially available high resolution camera has much potential to apply for a nearshore survey. Therefore, the Bundle adjustment is applied to a set of obliquely snap-shot digital aerial photographs for obtaining (x, y, z) data and accuracy in this paper. As a result, reasonable accuracy is obtained if the digital point for survey exists inside a benchmarked area. The resolution would be better if any benchmarked points (targets) can be placed on either sea bottom or water surface.
On the basis of conservation equations of mass and momentum fluxes of waves, a predictive equation of intervals of rip currents was proposed. The equation was compared with the field data and the effectiveness was confirmed. The interval of rip currents is given by Yr=0.197·T·√gHb (tanβ)-1 using the parameters of wave characteristics and seabed slope. Also the ratio of the interval of rip currents relative to the breaker width is given by Yr/B=0.79·(Ho/Lo)-0.535(tanβ)0.27
An analytical model for long shore transient current and a numerical model for transient current are proposed. The time evolution of long shore current by oblique incident waves shows analytically and asymptotic long shore velocity in the surf zone is defined the function of bottom friction coefficient. Numerical simulation of near shore current evolution by oblique incident wave groups shows periodic low-frequency current motion is driven by periodic and phase aligned motion of wave groups.
A number of inlets exist mainly in the eastern coast of Hokkaido, Japan, however relatively small number of inlets, for instance Imakirekuchi Inlet of Lake Hamana, can be seen in the rest of Japan coast. Here, tidal prism data (P) and cross sectional area (A) of inlet in Japan, China, U.S.A., New Zealand, Vietnam, and India are collected from the available literatures to study local character of inlets and global character of inlets. A modified inlet A-Prelationship in Japan is derived first, then inlet A-Prelationships in each countries are considered separately. Finally, global A-Prelationship, for which tidal prism ranges from 105 to 109 and cross sectional area ranges 101 to 104 in metric units, is derived with reasonably good correlation. So far, this global A-Pequation could be applied to an inlet in other countries as the first order approximation, but also necessary to improve the equation by incorporating more field data.
On September 1, 2001 a lady was drowned and killed at the Pansea beach on Phuket Island in Thailand. We set up an investigation team and carried out a field investigation on this drowning accident on September 18-21, 2002. Beach topography and rip currents were observed as well as the grain size test of the beach materials. Observed nearshore currents were compared with the numerical simulation. A rip current induced by the existence of shallow rock-exposed bed in the vicinity of the location where the accident occurred was the main cause of the drowning accident.
The organic sediment moves with water flowing in estuary. It is carried to the river with flood tide from river mouth, and settles on the riverbed at a tidal flat. The organic sediment settled there causes the environment deterioration and loss of waterside scene value. Then, the environmental quality improvement technology was proposed using fly ash for consolidated sediment. We established the construction technology for environmental improvement at riverbed covered by organic sediment. The column bucket method and the vacuum pump method were proposed for the infiltration-pillar installation. The efficient construction method corresponding to riverside could be validated by these constructions. The infiltration-pillar was constructed as a method of supplying oxygen into consolidated sediment by the water movement in the pipe with the ebb and flood tide.
A new method for the dehydration of dredging sludge with high efficiency was developed. This new hydration method produces hydrated sludge with relatively high water content and low strength, which is enough for tidal flat construction, and achieve the increase of the efficiency of treatment and the reduction of the cost and the working space for the treatment. Using paper sludge as main content of flocculation material, a large scale of flock of dredging sludge can be produced. This results in the high efficiency of dehydration processes which consists of the first flocculation process in a tank and the second dehydration process by belt press. A small scale laboratory test and a large scale field test were carried out and verified the efficiency of this hydration method.
A manufacturing technique of high quality stabilized dredging soil is newly presented in this study. In the technique, a simple drumstyle mixer without power-driven machinery is used at the process of mixing dredging soil with cement through a compressed-airmixture pipeline in order to improve the mixing of two materials. The prototype tests for the producing of stabilized dredging soil are conducted in the cases with and without the drumstyle mixer, and it is found that the strength of the stabilized dredging soil using this new technique becomes greater comparing with the case using the previous technique without the mixer under the same transporting distance of two materials. The systematic tests are also conducted with different mixer's height h and diameter d, for the discussions about the optimal mixer's shape. Furthermore, the practicalness of this technique is discussed through the test producing the amount of stabilized dredging soil per hour that is needed under actual construction of reclamation.
The immersed tunnel project crossing over the Bosphorus Strait located in Istanbul, Turkey, is under construction. The immersion procedure was carefully examined by mans of a physical model test, because the current field of the Bosphorus Strait is complicated and has two-layer system consisting of surface southwards flow and bottom northwards flow. The objectives of the model test are: to measure the mooring forces for all immersion processes, to check behavior of a placing barge and a tunnel element during immersion process, and to confirm immersion procedure using winch work. A seventeen mooring wires are used for completing the immersion of a tunnel element, and the mooring forces of all wires in each immersion process were measured. Based on the average/maximum forces of wires through the all model tests, the designed winch capability was determined.
Many follow-up studies have already been carried out and they reported the effectiveness of the water-route to enhance exchange of water and improve water quality. However, at the planning stage of the construction of water-route, it is not easy to determine the appropriate plain arrangement of the water-route. In this study, the authors proposed a procedure for evaluating the effectiveness of the plain arrangement of water-route using the shear velocity in the objective region through numerical simulations of tidal current. Three types of plane arrangements were examined and found that the shear stress at the bottom clearly increased in the cases where the water-routes exist. However, we could not found any significant difference between three types of arrangements.
An onboard vacuum suction oil recovery system has been developed. The system employs a high-power vacuum blower to suck and transfer oil slicks from the sea surface together with large amount of water and air in the gas-liquid multiphase form. This paper mainly presents the performance test results with a large-size model in the Simulation Tank for Oil Recovery in Maritime Situations (STORMS) in PARI. The tests covered various aspects including oil recovery performance such as sensitivity to sea condition or emulsification as well as design issues such as power required for driving blowers, how to cool the blower or how to control the suction rate, etc. Throughout the whole tests, the system generally worked well. The test results have been applied to the oil skimming system mounted on ISHIZUCH--an oil recovery vessel owned and operated by MLIT, which has been fully refitted and has come back in service this spring.
This research shows results of some tests about a developed skimmer which recovers the spilled oil from water surface by a raking system. It stores and separates water from oil/water mixture in its tank. The separated water is drained out from its tank by a diaphragm pump. The tests were operated in the large wave basin of STORMS with bunker C heavy oil and its emulsion. The grab-buckets have been used often as the oil skimming tool when viscous oil spilled at the coast, and it is appreciated its good recovery rate and poor efficiency. So that our objective of this research is to develop the skimmer for persons who normally construct marine structures by crane and work vessel like the grab-bucket, and to improve its recovery efficiency by separating water in its bucket tank by draining with pump.
In Hokkaido, more than 30 semi-closed water areas exist, and aquaculture has been performed in many of those water areas. Since semi-closed water areas connected to open sea by a narrow inlet are very calm water area, such areas are suitable for the aquaculture. However there is also the risk that the water quality may suddenly decrease. For permanent use for aquaculture, maintenance of the water quality is needed. As one of the water quality preservation methods, improvement of water quality by promotion of water exchange has been pointed out. Many of these water areas are located on the coast of the Okhotsk Sea. Ice floes normally reach the coast in winter, tides cause ice floes to pass through lagoon inlets into the lagoon. These ice floes have caused serious damage to aquaculture facilities. To prevent such damage, ice booms had started to be installed. However, these facilities have been used only during winter. In this paper, it proposes that the method of water quality improvement by use of these facilities.