Mirei Shige-Eda

Relationship between Pressure Fluctuations on the Bed Wall and Free Surface Fluctuations in Weak Hydraulic Jump

The relation of time averaged conjugate depth and the characteristic of the length of hydraulic jump have been almost clarified. The time averaged pressure distributions around the end sill are also measured by several researchers. On the other hand, bed materials near the roller of hydraulic jump are sometimes picked up by the pressure fluctuations, so that it is quite important to investigate characteristics of the pressure fluctuations in and around the hydraulic jump. In this study, the fluctuations of bed pressure in and around roller and also instantaneous flow depth are measured with the pressure gauges and supersonic wave gauges, respectively. It was found that oscillations of roller influences on the instantaneous flow depth and bed pressure and also that the instantaneous bed pressure concerns with the instantaneous free surface fluctuations.

ASSESMENT OF FLOOD CONTROL EFFECTS OF DRAINAGE PUMPS AND THE MUTABE RETARDING BASIN IN THE ROKKAKU RIVER BY NUMERICAL ANALYSIS

A retarding basin is one of the most effective countermeasures to mitigate existing downstream flooding problems. Effectiveness of the basin is strongly dependent on design of an overflow levee. Experimental works have been commonly employed for the overflow levee design. The primary objective of this study is to demonstrate that a numerical model, which are comprised of the distributed hydrological model, the 2D unsteady flow model based on flux-difference splitting scheme as well as unstructured finite-volume method, and operation of drainage system, is an effective tool to evaluate the stage-discharge relationship of the Mutabe retarding basin in the Rokkaku River under the given conditions of rain-fall and tidal level of the Ariake Sea.

ON THE EXAMINATION AND EVALUATION OF BREACH DISCHARGE IN INUNDATION ANALYSIS

The breach discharge by overtopping flows is examined experimentally and numerically. The process of breach erosion is reproduced, employing laboratory-scale non-cohesive homogeneous embankments. The relationship between breach discharge and effective width of breach cross-section is identified by using experimental results. The relationship is compared with the one obtained from the on-site overflow experiments at Chiyoda conducted in 2010~2011. Breach discharge is calculated by the numerical model that simultaneously solves flood flows in a channel and inundation flows in a flood plain with the dynamic inundation model, which comprises the finite volume method on unstructured grid using FDS technique. It shows that breach discharge can be predicted comparatively by the use of the model with the h-q boundary condition and effective width of breach cross-section.

ECONOMIC LOSS ESTIMATION IN IIZUKA CITY USING NUMERICAL SIMULATOR FOR RAINFALL-RUNOFF/FLOOD INUNDATION PROCESS IN URBAN AREA WIT RIVER AND SEWER NETWORK

Economic loss estimations for flooding in the Iizuka-city area in the Onga river basin were performed using numerical simulator for rainfall-runoff in watershed and flood inundation process in urban area with rivers and sewer network. The rain-fall runoff was simulated by a distributed hydrological model. The flood flow in rivers and inundation flows on the ground were simulated simultaneously by the 2D freesurface flow model. The dynamic network model for free-surface-pressurized flow combined with the Preissmann slot was used for the sewer network. The economic loss estimation based on the simulated inundation area and depth was compared with the reported value. The effects of flood disaster-reduction system were also examined based on the numerical results.

ESTIMATION OF OVERFLOW DISCHARGES BY SIMULTANEOUS ANALYSIS OF FLOOD AND INUNDATION FLOWS IN A MEANDERING CHANNEL

The overflow discharges, under the overflow as well as submerged overflow conditions, from a meandering channel with or without retarding plantations into a flood plain are investigated experimentally and numerically. The analysis is directed toward the examination of the overflow discharges by the overflow discharge formula as well as the numerical analysis, simultaneously solving flows in a channel and inundation flows in a flood plain. The dynamic inundation analysis model used in the analysis comprises the finite volume method on unstructured grid using fluxdifference splitting (FDS) technique. We found that the model is much superior to the formula in predicting the overflow discharges with or without retarding plantations.

STUDY ON MANAGEMENT OF VEGETATIONS USING EXTENDED QUASI TWO-DIMENSIONAL ANALYSIS IN THE OONO AND OTOTSU RIVER

The management of the vegetation in the Oono and Ototsu River were examined using extended quasi 2D simulations. Firstly, the relation between the boundary mixing coefficients f and vegetation density in the Oono River is examined through comparison of numerical results between quasi 2D and 2D simulations. From the relation, a value of f is found to be 0.11 in the Oono River. And the effects of deforestation to the boundary mixing coefficient f were also examined. It showed that deforestation is not effected significantly on the value of f in the Oono River. Finally, management map of the vegetation in the Oono and Ototsu River was made using extended quasi 2D analysis.

ESTIMATION OF OVERFLOW DISCHARGES BY SIMULTANEOUS ANALYSIS OF FLOOD AND INUNDATION FLOWS

The overflow discharges, under the overflow as well as submerged overflow conditions, from a river with or without retarding plantations into a flood plain are investigated experimentally and numerically. The analysis is directed toward the examination of the overflow discharges by the overflow discharge formula as well as the numerical analysis, simultaneously solving flows in a channel and inundation flows in a flood plain. The dynamic inundation analysis model used in the analysis comprises the finite volume method on unstructured grid using fluxdifference splitting (FDS) technique. We found that the model is much superior to the formula in predicting the overflow discharges with or without retarding plantations.

EXAMINATION OF BOUNDARY MIXING COEFFICIENTS BEFORE AND AFTER DEFORESTATION IN THE OTOTSU RIVER BASED ON NUMERICAL SIMULATIONS

The boundary mixing coefficients, which is used for estimation of boundary shear stress due to vegetation in quasi 2D simulations, in the Ototsu river is investigated numerically. Firstly, the relation between the boundary mixing coefficients f and vegetation density is examined through comparison of numerical resuts between quasi 2D and 2D simulations. From the relation, a value of f is found to be 0.08 in the Ototsu river. And it is shown that the quasi 2D model can reproduce the observation data of the water level in the three different flooding when the f=0.08 is used. The effects of deforestation to the boundary mixing coefficient f is also examined. It shows that deforestation is not effected significantly on the value of f in the Ototsu river.

FLOOD SIMULATIONS IN THE OTOTSU RIVER WITH VEGETATIONS BY A TWO-DIMENSIONAL NUMERICAL MODEL

Two-dimensional numerical simulations of flood flows in the Ototsu River were performed to examine the effects of the vegetations on the flood flows. A two-dimensional numerical model, based on finitevolume method with unstructured grid system and flux-difference splitting, was used for the simulations. The model was verified through the observation data of the water level in the flooding. The effects of the vegetations on the behavior of flood flows at the design flood discharge were also examined based on the numerical results. It shows that the 2D numerical model is useful in the examination of the effects of the vegetations on the flood flow behavior.

DYNAMIC FLOOD SIMULATION FOR INUNDATION FLOW OF THE URBAN AREA IN THE ONGA RIVER BASIN

A filed study and dynamic flood simulation on the Onga River heavy rainfall disaster in July 18-21, 2003 were conducted. Firstly, the flood process in the Iizuka-city area, which suffered the greatest damage in the Onga basin, was examined based on field study. Secondly, the flood simulation model was applied to the Iizuka-city area. The water movement in the urban area including the Onga River, main branch rivers was simulated simultaneously and the computed results compared with the flood process examined in the field study. Finally, the effect of the river improvements on the flood damage was examined through the numerical simulation. It shows that the model is a useful tool for examining the effects of the improvement work of a main river to inundation flows from tributary rivers.