Yoshihiko Maeno

Evaluation of Wave-Induced Pore Pressure in Sand Layer by Wave Steepness

ABSTRACTThe attenuation of wave-induced pore water pressures inside sand beds is investigated experimentally in a wave tank. It is found that the pore water pressure depends on the wave steepness. ...

In-Situ Measurements of Wave-Induced Pore Pressure for Predicting Properties of Seabed Deposits

ABSTRACTThis paper proposes a new method for predicting physical and mechanical properties of deposits near the surface of seabeds by means of in-situ measurements of wave-induced pore pressure. Fi...

Flood control and small-scale reservoirs

Flood control defenses such as levees, dams, reservoirs, and weirs are used to prevent rivers from bursting their banks. Among these defenses, the construction of large-scale dams has recently become an important topic of discussion in countries around the world. It is important to construct large dams to secure water for drinking, irrigation, electricity, and industrial use. However, leaders and well-informed persons in many fields have argued that the development of large-scale dams destroys the natural environment, forces residents of entire villages to leave their homes, and consumes too much time and money. In Japan, large-scale dams were initially constructed mainly to supply electric power, but the purpose of dams has now shifted to water supply or flood defense. Whether large-scale dams are necessary is now a source of contention throughout the world, with several advanced nations calling for the removal of dams. The present paper, taking as an example a small-scale reservoir for flood control in a small river in Funabashi City, Japan, makes the following main conclusions: small-scale reservoirs were used as a measure of flood control in many parts of Japan in the past; terraced paddy fields as well as small-scale reservoirs play an active role in flood control measures in place of large dams; flood control measures are reinforced by connecting small-scale reservoirs; small-scale reservoirs spare the environment from destruction caused by the construction of large dams; and small-scale reservoirs can be utilized as recreation sites for fishing, swimming, and walking.

Attitudes of residents in the Tokyo Bay area toward flood hazards.

There have been many recent reports of flood disasters from around the world. Many countries attempt to prepare for disaster situations, but one difficulty that exists in terms of preparing for flooding is that despite the level of flood hazard that may exist, many people living within river basins are unable to leave their homes or seek to return to their homes as soon as the immediate danger has passed. We distributed a questionnaire concerning flood hazards to residents within the basin of the Arakawa River in the old-town area of Tokyo, Japan. The Arakawa River, which drains into Tokyo Bay, was planned in 1911 with the aim of protecting the citizens of Tokyo from flooding; it was completed in 1930. All local residents are assigned a specified evacuation area by the local administrative body. The questionnaire was given to a random sample of about 1000 people living along the Arakawa River. The obtained answers make it clear that many people living along the river are unaware of their designated evacuation area in the case of flooding. This is an issue that must be dealt with by administrative guidance and efforts on the part of the residents. Consequently, the local administrative body must ensure that residents are well informed in terms of hydrological information and the locations of areas that provide refuge from flooding.

Infrastructure maintenance and disaster prevention measures on isolated Islands: the case of the Izu Islands near Tokyo

Of the 6,852 islands that make up the Japanese archipelago, 261 are inhabited but there are isolated islands with a total population of approximately 434,000 people scattered over an area of 5,255 km 2 . In the five years from 2001 to 2005, the population of these islands decreased by 8.3% compared to a 0.7% increase in the national population. The Tokyo Metropolitan Government administers some of these, including the Izu Islands. The Izu group consists of nine separate islands with a total population of 24,645 people spread over 296.56 km

Restoration projects and mitigation of post-flood hazards - a case study on the Maruyama River in Japan.

The hazardousness of potential flooding and environmental deterioration face river basins throughout the world. Rivers in Japan are relatively short in length and steep in elevation along the banks, which are supposed to funnel rainwater and create floods due to heavy rain from typhoons/hurricanes. In addition, the clearing of forested areas due to widespread residential development in Japan and a lack of forestry workers have led to a broad decline in the riparian forest ecosystems. The study examined the recovery of the Maruyama River basin following the flood disaster in 2004. The Maruyama River disaster-relief and restoration projects addressed the mitigation of environmental damage as well as economic impacts. The Maruyama River basin is a noted habitat of the Oriental white stork, which became extinct in 1971, and was reintroduced as the basin through the breeding program in 2003. The 2004 flood destroyed the stork habitat. As a part of the recovery effort, the Japanese government has worked with the Toyooka City government and the Maruyama River Basin Committee to rebuild and expand the habitat of the stork. Preserving the habitat of another endangered species, the committee has added the Japanese giant salamander into a species name list in the restoration plan. These projects are expected to reinvigorate the local economy and preserve the environment of the river basin.

FIELD MEASUREMENTS OF THE HOLDING POWER OF MOORING ANCHORS FOR SILT CURTAIN

Field verification of the holding power of mooring anchors was conducted on a seabed composed of soft mud located in Tokyo Bay, Japan. The observed holding power of the anchors was compared with the estimates based on the current design. The holding power depends strongly on the properties of the seabed deposit, the type of anchor and the duration of service. The coefficient of holding power, which is defined as the ratio of the maximum holding power to the submerged weight of the anchor, was introduced to examine the effects of the loading rate and angle of the mooring wire of the anchors. Because of the action of the overturning moment, the effect of a loading rate was negligible for concrete block anchors with a loading angle of 45 degree or less. The coefficient of holding power was 0.6 or less for the above case . The holding power for suction anchors increased with the suction inside anchor. There was a weak correlation between the holding power and the loading rate for soft mud.

Survey Of Small Fisheries In Japan

The coast in Japan is dotted over with many fishing ports. The former coastal fishery had been flourishing remarkably in Japan. However, many fishing villages have been declining gradually because of successors falling off and other industries developing. As a result, an aging and an under-population are making progress in the present circumstances of fishing villages in Japan. The fishing villages have enough motivation to be developed as a base of marine resort and recreation, since they have sufficient human and physical resources. The actual conditions of population movements, industrial structures, welfare facilities, public services, medical facilities, first-aid and rescue works, commerce and business, transportation, water works and sewer, etc. in fishing villages along the coast of Chiba and Kanagawa prefectures closing by the Tokyo Metropolitan area is investigated in this study.

A CONSIDERATION ON HOLDING POWER OF MOORING ANCHORS

The holding power of the mooring anchors were verified by comparing the estimation with the results by the field test. The field tests on the silty sand seabed were carried out for the holding power of two different types of anchor, the concrete block anchor and the suction anchor. The pressure distributions were measured at the bottom of the concrete block anchors and inside the suction anchor by varying the drawing angles of the anchor line, the drawing speed. The holding power of both anchors for the drawing angle of θ=90°increases with the drawing speed, and approaches to the constant value. The holding power for the drawing angle of θ<45° approaches to the constant value independently of the drawing speed. The concrete block anchor shows a peak of the largest holding power when the drawing speed is large. The suction anchor always shows a peak of the largest holding power independently of the drawing speed. It was also confirmed that the internal pressure inside the suction anchor changes in proportion to the holding power.

SEDIMENT MOVEMENT AND STRESS CONDITION IN SEA BED

A study of alternatives including a shoreline evolution numerical modelization has been carried out in order to both diagnose the erosion problem at the beaches located between Cambrils Harbour and Pixerota delta (Tarragona, Spain) and select nourishment alternatives.