Takaaki Uda

River mouth improvement using artificial reef - an example of Kinoto-Dainichi river-

An artificial reef is applied to the river mouth improvement.Numerical simulation of wave, nearshore currents and flood currents were conducted under the condition, in which an artificial reef is installed in front of the mouth in order to reduce wave height in the river and to induce outward currents to enhance scouring in the reef gap so as to be safely used for navigation channel of small fishing boats. As a result of the numerical simulation optimum design of artificial reef as a river mouth improvement was determined.

Soreline recession accompanied with the construction of a headland on its surrounding beaches and its measures

On the Mochiishi coast in Shimane Prefecture a headland was built as a countermeasure against beach erosion. Original beach width was narrow and the distance from the shoreline to the seawall was less than 20m. After the completion of the headland beach erosion proceeded on the surrounding beaches and wave overtoppoing above the seawall increased. This paper summarizes this situation and shows further measure to prevent from beach erosion and wave overtopping.

Local Change in Water Level in a River with a Shallow Lack of Flood Plane

In a river with a lack of flood plane so called wando, water level rises up locally during flood. It is important to predict this change in water level for preventing the flood disaster. By using the two-dimensional shallow-water-flow model, it isable to estimate the plane distribution of water level and flow pattern in a river with a wandand it is shown that the calculation results on the longitudinal distribution of water level agree with the model experimental those. It becomes clear that the change in water level occurs mainly due to the local change in cross sectional area and its value relates to the velocity and the length, width, depth of lack. The convenient evaluating method of the change in water-level due to a lack of flood plane is proposed.

Transition of grasses and management of river dike

Evaluation of protective function of grasses covering a river bank against erosion due to flood flow is important for grasses to be used for the protective measures instead of concrete armoured bank. On the real river, however, transition of grasses takes place and the preffered kind of grasses may change from the turf being planted at the construction time. Thus the understanding of transition process is very important in such an evaluation of protective function of grasses. This study aims to investigate this transition process of grasses through a field observation in the Iwai River in Iwate Prefecture. Annual change in covarage rate of grasses was observed at river banks of various stages after the construction.

Field Experiment on Erosion-Resistance of Embankment of Ichinoseki Flood Detention Basin against Overflow.

Erosion resistance of a river bank slope with variety of plants was exeperimentally investigated. The experiment was carried out on a natural embankment of Ichinoseki Flood Detention Basin under rapid overflow condition. It is found that erosion resistance of embankment is governed by not only difference of distribution of plants but also mole holes in the bank.

An analysis of past coastal disasters in Japan by the slides collected by Prof. O.Toyoshima

Slides showing past coastal disasters collected by Prof. O. Toyoshima were analyzed. 378 pictures were selected. All photos were classified into four categories; (1) Disasters due to tsunami, storm surges and high waves and countermeasures, (2) Beach erosion and damage of coastal facilities, (3) Sea cliff erosion, and (4) Coastal utilization. Damaging process of coastal revetments is revealed for a typical example.