Field investigations were conducted at the north salt marsh of Osaka Nanko bird sanctuary (ca. 43100 m2) in high water temperature seasons of 2012-2014 and the amount of net CO2 absorption was estimated along with the characteristic of CO2 absorption and emission on the surface of the sediment. Gross CO2 absorption flux was closely related to sediment temperature, chlorophyll a and photon flux density, while CO2 emission flux changed depending on the sediment temperature and groundwater level. The groundwater level was thought to be indispensable for estimating the flux of CO2 emission on the sediment. For instance, when it was supposed groundwater level was equal to tidal level, the CO2 emission flux from the sediment reached 29 tons. It showed 2.1 times higher than the value which was estimated by using actual ground water level. Using the relationship of CO2 flux with sediment temperature, chlorophyll a, photon flux density and groundwater level, the total CO2 absorption and/or emission of the north salt marsh of Osaka Nanko bird sanctuary was estimated as ca. 23 tons for absorption and ca. 14 tons for emission in May to September, 2014. These results suggest that a net of 9 tons CO2 was absorbed and this salt marsh plays the role of a CO2 sink in the high temperature season of a year.
Oxygen consumption experiment was performed in two fixed points in order to clarify the fractionation of oxygen consumption in the bottom layer of the bay head of Ariake Sea. Chemical oxygen consumption in Hamakawa offshore (T14) showed 28% of the total oxygen consumption, has been shown to vary by the mortality of benthic animals and sediment reduction due to the formation of hypoxic water. In contrast, in an oceanographic observation tower of the Saga University chemical oxygen consumption accounted for 77% of total oxygen consumption. In addition, aerobic decomposition by microorganisms, so-called "oxygen consumption associated with the decomposition of the direct organic matter" did not show a big contribution. Differences of contribution rate of chemical oxygen consumption has been suggested to be due to the difference of suspended material composition. From these, oxygen consumption process was suggested significantly different in the two observation points.
The nonlinear steady wave equations based on the variational principle, were solved using the Newton-Raphson method, to find the numerical solutions for both surface and internal solitary waves. The ratio of kinetic energy to total energy for surface solitary waves increased, as the ratio of wave height to the still water depth increased. Conversely, the ratio of kinetic energy to total energy for internal solitary waves increased, when the ratio of wave height to the maximum wave height is average. The solitary waves propagation also was numerically simulated, by applying the time-dependent model, with the initial conditions obtained using the present method for the large-amplitude surface and internal solitary waves.
Under the Great East Japan Earthquake, Mound type Tsunami Evacuation Facility is focused in the reason of the survivors by being evacuated to Mound type Facility from Tsunami. In Fukuroi-city, Shizuoka-prefecture, Mound type Tsunami Evacuation Facility is planned. In present, although there is the design method of Mound type in various standards, there is not the design method of Mound type Tsunami Evacuation Facility. This report examines the design method of Mound type Tsunami Evacuation Facility. It proposes the items to be examined, on the basis of evacuation area, crest height, scouring depth and slope of Mound type to be decided to the precondition of number of candidates, inundation area and site form. Especially, examination methods of crest height and mound design are considered as the matters of highly novelty.
A series of hydraulic model experiments were carried out to investigate tsunami wave load acting on a tsunami evacuation building with openings. We have found that 1) wave impact force can be dominant only under restricted conditions, 2) existing design formula predicts tsunami wave pressure values on the safe side, and 3) due to the openings, tsunami wave force acting on the building decreases by a factor of (1-aperture ratio) or smaller. We also carried out a numerical experiment, succeeding to reproduce the results of physical experiments.
The massive March 11th Tohoku tsunami showed that the Teizan canal in Miyagi Prefecture acted to reduce the velocity and delay the arrival time of the tsunami. The Teizan canal in now attracting attention for being a symbol of the revival in the area. The purpose of this study is to clearly demonstrate experimentally the mitigation ability of a canal. Comparing its effects with that of a seawall, it is shown that inundation depth reduction, tsunami arrival time delay, velocity and specific energy reduction are equal to or greater than the mitigation effects of a seawall. After showing accuracy by comparison with the experimental results, the MPS method is applied to discuss the mitigation effects of a canal with dunes at both banks.
Tsunami risk was analyzed on the basis of tsunami flood simulation for three towns, Heda, Toi and Matsuzaki located on the west coast of the Izu Peninsula, Shizuoka Prefecture. Existing annual tsunami risks for the three towns were found to be in the range from 180 to 230 million yen/year. Risk reduction due to quick evacuation was compared with that due to seawall construction. Long-term risk reduction in 50 years was projected by considering population decrease and relocation encouragement from flooding zones. It is considered that the risk analysis in this study helps to establish a comprehensive and rational tsunami mitigation plan.
In order to clarify the relative contributions of bottom-layer water and sediments to oxygen consumption, theoretical considerations of oxygen consumption rates were analyzed based on existing experimental results. The contribution of bottom-layer water to oxygen consumption increased with the height of the bottom-layer increased. In addition, the contribution of bottom-layer water to oxygen consumption varied significantly depending upon the relative rates of oxygen consumption by the sediments and the bottom-layer water. The height of the bottom-layer water column where the rate of oxygen consumption was 50% (H50) was also calculated and compared with the height of the bottom-layer water. Offshore measurements taken near Takezaki in the inner Ariake bay showed that the height of the water column of bottom-layer water was always greater than H50, suggesting that high levels of oxygen consumption occurred in the bottom layer water. Conversely, the relationship between the water column height of the bottom-layer water and H50 was variable at the tidal flat margin, suggesting that both sediments and the bottom-layer water need to be considered in case of oxygen consumption processes.
Crest heights of storm surge barriers and seawalls in Japan are determined based on either wave runup or overtopping discharge. Authors have proposed integrated formula of wave runup and overtopping for seawalls constructed on land or in very shallow water. This study verified the applicability of Integrated Formula of Wave Overtopping and Runup Modeling for Seawalls (IFORM) for CLASH datasets as well as using other two prediction models of Goda (2009) and Van del Meer and Bruce (2014). The comparison of predictions with measurements of CLASH data showed that IFORM is enough to employ as the overtopping prediction. IFORM almost covers installation condition of Japanese seawalls and is capable to estimate runup and wave overtopping discharge of compound cross-sectional vertical and slope seawalls. For convenience and ease of use, this study summarised calculation diagrams for wave runup on seawalls with various kinds of slope gradient and toe depth installed on a uniform slope seabed.