Terunori Ohmoto

Effects of Water Surface oscillation on Turbulent Flow in an Open Channel with a Series of Spur Dikes

Spur dikes have been used as hydraulic structures to suppress bank erosion by flood flow, waves generated by ship and to maintain flow depth as a navigation channel. Recently, it’s noticed that they have functions to produce diversified attractive environments in river. In this study, experiments were executed to clarify water and momentum exchange between main flow and non-submerged spur-dikes regions. The results showed that prominent water surface oscillations happened in an arrangement of spur -dikes and the variations obviously correlated with velocity fluctuations, enhanced the water exchange, but did not influence on Reynolds shear stress.

Three-Dimensional Flow Structure in an Open Channel with a Flexible Vegetation Zone

Laboratory experiments were conducted using two-components electromagnetic current meter and particle image velocimetry (PIV) to clarify the interaction between main flow and flexible artificial vegetation zone, which was attached to the central bottom and sidewall of an open channel. Experimental results showed that in the main flow region under equilibrium horizontal components of secondary currents pointed in the direction toward the vegetation zone near the bottom, and in vegetation zone vertical components directed the upward. Furthermore, horizontal periodical components of velocity variations activated the momentum transport from main flow region to vegetation zone.

Turbulent structure in open channel with permeable and impermeable side cavities

The cavity zone along riverside is expected to produce native habitats of various ecosystems and water-friendly environment. However, effects of side cavities on flow resistance and turbulent flow structures are ambiguous. In this paper, effects of aspect ratio of side cavity on open-channel flow with permeable and impermeable side cavities were examined experimentally. Velocity fluctuations were measured by using a particle image velocimetry. Results showed that the flow resistance significantly depended on the longitudinal length of cavity between vegetation zones or blocker zone and the reason could be explained by the difference of momentum transport through the interaction among main flow, discontinuous vegetation and cavity. Moreover, we revealed the flow resistance could be explained by the difference of mass exchange and momentum transport through the interaction between the side cavity and main flow region.

Effects of Hyper-concentrated Sediment on Flow Resistance in an Open Channel with Three-dimensional Square Ribs

The necessity to understand and predict flows that carry large suspended sediment and wash loads has become acute in river basins where significant erosion and siltation associated with hyper-concentrated flood give rise to many river problems. Mud flows, debris flows or slurries, made up of a large amount of clay and/or silt particles suspended in water, often show non-Newtonian properties but remain poorly understood concerning the impacts of their rheological properties on fully developed turbulent structure. In this paper, we experimentally investigated resistance and momentum transport of hyper-concentrated sediment laden-flow in an open channel with three-dimensional square ribs by using Particle Image Velocimetry (PIV). The results showed that rheological properties significantly dissipated the turbulent flow fluctuations over three-dimensional square ribs and augmented the flow resistance by comparison with the clear water flow.

FLOW PATTERN AND SUSPENDED SEDIMENT TRANSPORT AROUND SPUR DIKES IN THE KIKUCHI RIVER ESTUARY

A series of spur dikes was constructed to reinforce an embankment at bends in the lower reach of the Kikuchi River. In recent years, eutrophicated fine sediment accumulation around spur dikes has caused a serious problem in estuary ecosystem. Therefore, Ministry of Land, Infrastructure and Transport has developed the renaturalization project of sand beach in the estuary. In this study, we have particularly investigated flow patterns and fine sediment transport around these spur dikes by using Stream-pro Acoustic Doppler Current Profiler (ADCP) and radio-controlled model boat equipped with Workhorse ADCP in the period of spring tide. The results show that these spur dikes weakened flow and SS transport in the concave, and strengthened them in the convex of the bend. In addition, fine sediment accumulation were discussed through streamwise distribution of SS transport in both cases of flood and ebb tide.

Effects of Relative Groine Height in Bed Configurations and Flow Structure in an Open Channel Flow

A lot of non-overflow groynes that do not sink under the water at the ordinary water flow are used, and it is known to it does working that keeps away the water current form the river bank..On the other hand, when the water level is surpassing of the height of the groyne, it becomes to sink.. In this study, the height of the groyne was made constant, depth was changed systematically, and it aimed to clarify the characteristic of the bed level variation and the flow velocity profile of the flowfield with a single groyne by the laboratory experiment under the condition to assume the Froude number to be 0.2. As a result, the maximum depth of scour has become small as the relative groyne higher. The groyne height when relative height grows, the ratio of the main flow velocity to the mean flow velocity has grown.

FLOW RESISTANCE AND MOMENTUM TRANSPORT IN OPEN CHANNEL WITH LONGITUDINALY DISCONTINUOUS VEGETATION

Vegetation communities are often observed to grow in stripe pattern or patches within many stream channels. In such a situation, hydraulic engineers should examine an appropriate vegetation management system paying attention to flood control and vegetation ecosystem. In this paper, the flow resistance and momentum transport in open channel flow with discontinuous vegetation in longitudinal direction were examined experimentally. Velocity fluctuations were measured using a particle-image-velocimetry (PIV). Results showed that the flow resistance significantly depended on the longitudinal length of cavity between vegetation zones and the reason could be explained by the difference of momentum transport through the interaction among main flow, discontinuous vegetation and cavity.

AN OUTLINE OF THE FLOOD DISASTERS IN THE SEADAI RIVER IN JULY 2006 AND THE REVIEW OF FLOOD CONTRORL BY DAM OPERATION

Recently, a heavy rainfall in a short period of time occurs often and causes severe damage from a flood in various regions. The heavy rainfall due to the Baiu front gave severe damage to the southern region of Kyushu Island from July 19 to 23 in 2006. In this paper, an outline of flood disasters for the Sendai river basin in Kagoshima Prefecture from this heavy rainfall was reported. Furthermore, an improvement of the flood control operation of Tsuruda Dam in Kagoshima Prefecture was considered. By introducing the improved operation technique, it is expected that the flood control of Tsuruda Dam works well not only under usual flood conditions but also under unexpected heavy flood conditions.

FLOW RESISTANCE AND TURBULENT STRUCTURE IN OPEN CHANNEL FLOW WITH SUBMERGED VEGETATION

Vegetation colonies are often observed to grow in stripe pattern or patches within many stream channel. In this paper, the influence that interaction of longitudinal vegetation zones gave to the flow resistance in an open-channel was examined experimentally. Laboratory experiments were conducted using a two-component electromagnetic current-meter to clarify the momentum transport between main flow and flexible artificial vegetation. Results showed that the flow resistance significantly depended on the lateral distance between longitudinal vegetation zones and the reason could be explained by the difference of convective momentum transport through the interaction between longitudinal vegetation zones.

IMPROVEMENT ON THE GROWTH ENVIRONMENT OF ENDANGERED SPECIES

Vallisneria higoensis which is an aquatic plant peculiar to Kumamoto Prefecture is on the verge of the present extinction. In this study, it aimed at an improvement of the growth environment of a water plant by making the flow velocity increase using groyne. The indoor experiment considered groyne arrangement. Consequently, it turns out that the one-bank groynes increases the flow velocity of a mainstream part by about 5% compared with a case without a groyne, and it is increasing about 10% in the both-banks groynes. It was admitted by the result of a field survey that the flow velocity in main flow region after both-bank groynes installation was increasing about 11 to 23% compared with before installation. It turns out that 5m distribution expansion was seen at the maximum about growth of aquatic plant, and the area of a aquiherbosa is also expanded.