China
Africa
Explore chapters and articles related to this topic
Dynamic state of river-mouth bar in the Yuragawa River and its control under flood flow conditions
Published in Silke Wieprecht, Stefan Haun, Karolin Weber, Markus Noack, Kristina Terheiden, River Sedimentation, 2016
H. Miwa, K. Kanda, T. Ochi, H. Kawaguchi
The topology of river mouths, which are defined as regions where river runoff enters an ocean, is characterized by the combined influence of sediment transported by the river and near shore currents associated with tides and sea waves. River mouths along the coast of the Sea of Japan are particularly affected by the action of winter sea waves, and tidal prisms are small. Under these conditions, river-mouth bars tend to develop under conditions of longshore sediment transport, and blocking of river-mouths is frequent. Floods tend to breach the river-mouth bars that develop during dry periods, and complex changes occur in bar behavior during floods and in post-flushing river-mouth channel width. These changes vary depending on flood hydrodynamics, fluvial morphology near the river mouth, and the presence or absence of harbor facilities and other man-made structures along the coast.
River action and control
Published in F.G. Bell, Geological Hazards, 1999
River channels may be improved by dredging. When a river is dredged its floor should not be lowered to such a degree that the water level is appreciably lowered. In addition, the nature of the materials occupying the floor should be investigated. First, this gives an indication of which plant may be suitably employed. Indeed removal of unconsolidated material usually revolves around the selection of suitable floating equipment for the dredging work. Of special importance is the possible presence of boulders. Suction dredgers should always be fitted with a simple trap device in the suction line for catching boulders and rock fragments. Underwater rock excavation can be carried out by underwater drilling and blasting or from a floating rock breaker. Second, it provides information relating to the stability of the slopes of the channel. The rate at which sedimentation takes place provides some indication of the regularity with which dredging should be carried out. Dredging of river mouths and depositing the sediment at sea, however, may lead to erosion of neighbouring beaches subjected to reduced sediment supply.
Hydraulic Aspects of River Training Works in Tidal Rivers
Published in S.N. Ghosh, Tidal Hydraulic Engineering, 2017
Improvement of river mouths requires installation of artificial works such as training walls or jetties to increase velocities for carrying the river load farther down. The load will either go directly into the deep sea or be moved by the littoral or other current system. Conversely, a high river discharge emptying into the sea may be arrested on its way by a littoral current. This will result in the formation of a sandspit parallel to the coastline, through which the river can break during flood. Control of littoral drift is the main problem in channel improvement.
Collapse and recovery process of the sand spit at the Tenryu River mouth on the Pacific Coast of Japan
Published in Coastal Engineering Journal, 2018
Yoshimitsu Tajima, Tomohiro Takagawa, Shinji Sato, Satoshi Takewaka
Six field cameras were installed to capture the dynamic morphology changes around the Tenryu River mouth. Recorded successive still images with a time interval of 1.2 s were rectified based on the XY-coordinate system on the horizontal plane at the water level, T.P. +0 m. Time-varying shoreline profiles were then extracted from these rectified images. During the flood induced by Man-Yi, floating debris, captured by the field cameras, was traced to obtain the time-varying surface flow velocity at the river mouth. The obtained velocity was then compared with the recorded time-varying water levels inside and outside of the river mouth and with profiles of the sand spit. It was found through comparisons of these data that there was a 4-h time lag between the two characteristic deformation processes of the sand spit: (i) erosion of the eastern tip of the spit and (ii) breach of the western part of the spit. The erosion of the eastern tip of the spit started when the observed surface water velocity reached its peak, while the breach of the sand spit was initiated 2 h after the water head difference between the inside and outside of the estuary reached its peak. It was also found that the observed morphology changes of the river mouth have a significant impact on the surrounding hydrodynamic characteristics, such as flow velocities, tidal responses, and water levels.