Since 1997, rainfall has been measured by using tipping-bucket rain gauges in a mountainous area as a part of GAME-Tropics (the Global Energy and Water Cycle Experiment (GEWEX) Asian Monsoon Experiment (GAME)). Orographic precipitation tends to occur when easterly or southeasterly wind is predominated, wind speed is relatively strong (Average: 4.6m/s, S. D.: 2.1m/s), and the lifted condensation level is low. By investigating orographic precipitation using a regional atmospheric model under various atmospheric conditions, 1) comparatively strong monsoon westerly in the lower troposphere and complex terrain and 2) moist condition in the lower atmosphere including evapotranspiration from the wet ground are significant factors to the spatial pattern of precipitation in the mountainous region.

View full abstract

Effectiveness of distributed rainfall information by weather radar was investigated through runoff analyses with a distributed runoff model and radar information., To achieve this purpose, actual rainfall distribution and virtual basin model are used in runoff simulation using a distributed runoff model by developing a method ofvirtually extending a small actual basin. As results, we found as followed;
Effectiveness of distributed rainfall information is different between rainfall by front and Typhoon.
up-scaling beyond size of basin brings vital error in hydrograph.
method of up-scaling also brings vital error in hydrograph.
location of up-scaled mesh is also bring vital error in hydrograph.
utilization of hourly rainfall brings same degree of error by spatial up-scaling of 13km.

View full abstract

Dense Non Aqueous Phase Liquids (DNAPLs) are common sources of groundwater contamination in the subsurface where they remain entrapped within the pore space and dissolved in aqueous phase during long tarm. In this study a new experiment to predict the entrapped DNAPL is introduced and their results are reported. Three types of randomly packed glass beads with different diameters (1, 2, 3mm) were used on fingering penetration of TCE (trichloroethylene) into saturated porous media to evaluate two main parameters governing with DNAPL transport and entrapment within pores. The results suggest that the first parameter; the relative permeability coefficient (k_D) accounting for fingering, is related to finger Reynolds number (wd/v) and the second parameter; the entrapment rate coefficient K [T^-1] ranged from 1.2×10^-2 to 7.3×10^-2 (sec.^-1) and proportional to the ratio of the Reynolds number to the intrinsic permeability. The one-dimensional numerical computation with those parameters is used to compare with the experimental results.

View full abstract

To understand the influence of heterogeneity on rainfall infiltration and seepage, the governing equations of twophase flow through porous medium are employed and the finite element formulation is carried out. And 1/f-^ζmodel is introduced as the geostatistical model of hydraulic conductivity. It was shown that when ground surface was under the ponded condition, surface water reached water table faster because of heterogeneity. However, when ground surface was in non-ponded condition, the influence of heterogeneity depended on analysis scale. Moreover, distribution of pore water pressure was highly related to distribution of saturated hydraulic conductivity of ground surface.

View full abstract

Recently as a new governing equation of solute transport, a fractional advection dispersion equation (fADE) has been proposed, which includes non-integer derivatives for the mass-transport phenomena in heterogeneous geologic media by Benson et al.(1998, 2000). Using this equation, heterogeneitycan be taken into account effectively without scale dependency. We solved the fADE numerically by thefinitc difference method, and compare with new experimental data. The data were taken in a sand box with Tohoku silica sand and 3% of NaCl solution. Breakthrough curves are obtained from the experimental result, and we found that the experimental result is essentially different from the ordinary Gaussian profiles and the order of derivative is about 1.5 for our experiments.

View full abstract

The present study is concerned with feasibility of the rainfall infiltration facilities in Takamatsu city and offers newly obtained fundamental data such as geological map of surface soil layer, hydraulic conductivity of surface soil layer and groundwater level during rainy seasons. Four issues are discussed. First, a new geological map is presented for surface soil layer at lm depth, which is closely related to infiltration facilities, basedon the re-examination of the existing borehole logs and new boring survey. In urbanized area surface soils of lm thickness show multiple layers of different soil types, reflecting the past land use change. Secondary, an in-situ permeability test was carried out at 39 locations to correlate the hydraulic conductivity of the surface soil layer at lm depth and its soil type. Thirdly, the depth of groundwater table from the ground surface is reported with water level variation corresponding to rainfall. Finally, the effective areas for infiltration facilities in Takamatsu city are discussed.

View full abstract

Pipeflow is recognized as an important hydrologic control as well as a landslide initiation factor, and the development of a theoretical method to analyze pipeflow process is needed. However, there are few modeling studies of pipeflow, and a general simulation technique for water dynamics in the hillslope scale with soil pipes has not yet been developed. In this study, a general model that describes lateral pipeflow in a hillslope was developed. In the model, matrix flow and pipeflow were calculated by their respective governing equations (Richards' equation and Manning's equation), considering the interaction between t hese two flow systems. Numerical experiments were conducted to analyze the effect of pipeflowon slope stability. Results indicated that pipe clogging decreases the factor of safety and couldbe a factor that triggers landslides, and that pipeflow affects the initiation of debris flow after landslides.

View full abstract

An applicability of quinone biomarker to the analysis of hillslope runoff was investigated. Atfirst, quinone profiles of three types of stream as well as a hillslope runoff in a forest head were compared. The quinone composition of hillslope runoff differed from others. Moreover, there were remarkable differences in quinone profile of hillslope runoff under different rainfall conditions. Then, the behavior of quinone biomarker accompanying the increase and decrease of hillslope runoff after a rainfall event was examined. Q-9 (1-12), Q-10 (H2), Q-11, MK-6 and MK-10 can be key biomarkers for the analysis of intedlow.

View full abstract

Few studies have addressed the runoff mechanism in volcanic basins, because the flood discharge in such basins tends to be small. However, after volcanic eruptions it is important to review therunoff characteristics of the basin, because eruptions can profoundly alter the runoff mechanism. This study analyzes the runoff mechanism during rainfall in an experimental basin at Volcano Tarumae, according to field survey results. We reached these conclusions: 1) The runoff in the upper part of a basin is composed of runoff from areas adjacent to the river channel and large-scale groundwater runoff (mainly spring water at the riverhead). 2) Changes in rainfall have little influence on the runoff source area. 3) The discharge of spring water depends on average rainfall intensity and ground moisture in thebasin.

View full abstract

A new numerical analysis method has been developed for groundwater flow in rocks considering fracture network. In the numerical method, large or high permeable fractures, which greatly affect on the groundwater flow, and the other fractures are modeled as disks and pipes, respectively. The groundwater flow in crystalline rocks can be estimated easily and accurately by using the numerical method.
The numerical code was applied to a fictitious rock mass in which 2, 000 fractures had been generated. The groundwater flow rate was calculated by modeling a few percent of the fractures and the other fractures as disks and pipes respectively. The flow rate was almost the same as the one calculated by modeling all the fractures as disks. As a result, it was considered that the numerical code was validated.

View full abstract

This paper evinces a great performance of geostatistically estimating the modeling errors and a spatial distribution of permeabilities for two-dimensional groundwater flow. The exact variation in the water levels, which is equivalent to the accurate modeling errors, is formulated from the series solution of the finite element equation. A hypothetical aquifer into twenty piecewise zones, each of which has a constant permeability, is designed to allow assessing the errors and the level-variations in the homogeneous and heterogenous aquifers. Spatial estimation of the error complements and distributed structure identification of inhomogeneous permeabilities are herein carried out. A geostatistical model of the distributed permeabilities is integrated into the physical-based model. The statistical-based parameters in the integrated system are successfully identified from the physical-based observed data. It can be proven that such estimation and identification approaches are powerful and helpful in perfectly modeling.

View full abstract

In coastal areas, a subsurface dam has been planed to ensure a constant extraction of water without causing saltwater intrusion into fresh groundwater. The movement and removal of residual saltwater in the storage area of the subsurface dam have not been investigated because of difficulties in monitoring and predicting saltwater dynamics under ground. Experimental and numerical studies were performed to understand the fundamental mechanism of saltwater movement after the dam construction. Experimental results indicate that the residual saltwater in the storage area is gradually flushed out under the conditions of freshwater overflow above the cut-off wall. Numerical results show that the circulation flow is appeared in the residual saltwater region immediately after the installation of the cut-off wall, and then the diluted saltwater in the freshwater-saltwater mixing zone is transported with freshwater flow into the sea side. The results obtained in this study will be a useful guideline to manage groundwater in subsurface dam.

View full abstract

Whole of people living in KUMAMOTO area are using groundwater for drinking water. The amount of groundwater for drinking use is over 200 million cubic meter per year. Main recharging area of this groundwater bain is farm area which exists in middle SHIRA-River. But recently, groundwater level shows a yearly decrease. In this paper, the authors shows the change of groundwater level in KUMAMOTO groundwater basin and discuss the cause of this decrease of groundwater level. As the results, we show that decrease of groundwater level is mainly caused by decreasing of paddy field area. Moreover, we show the plan for recovering the groundwater and estimate the effect of this plan by field experiment.

View full abstract

When predicting the impact on the hydrological environment by land development, the surface runoff and groundwater recharge rates are the most important quantities. The change in land use leads to an increase in the flood peaks and a decrease in the rainwater infiltration into the underground. In order to assess the effect of the alteration on the groundwater recharge rate in the weathered granite area, the response of the groundwater level is studied at several observation wells, which are linked with the quasithree dimensional groundwater flow. As a result, it is found that the maximum surface runoff coefficient, F_∞, is the most affective parameter followed by the shape parameter, (r) _1/2, used in the surface runoff coefficient as a function of rainfall intensity. Besides, it is also found that a change in the ground surface elevation affects the soil water loss height R₀, which is used in the recharge model. In conclusion, the present approach is useful for predicting the change in the hydrological processes of the land use alteration in the weathered granite area.

View full abstract

A river running through an alluvial area does not flow in the channel only; rather, the stream-water has some interaction with riparian groundwater, such as infiltration into an aquifer or exfiltration from the aquifer. Especially in case of the stream flowing with small discharge due to an artificial intake, the interaction between stream and aquifer may be important factor governing the stream condition. Because remarkable decrease of the discharge affects not only hydraulic quantities but also water quality and temperature, it is necessary to keep a minimum stream discharge in order to preserve the river environment. In this paper, toward evaluation of the minimum discharge, relationships between stream and aquifer are investigated through field investigations and hydraulic analyses. According to the observations in the Yasugawa alluvial fan, it is supposed that variation of the stream discharge may be caused by water exchange with the aquifer. The finding from the computed results indicates that this hydraulic model can become a useable tool for quantitative evaluation of the minimum discharge to keep the stream condition suitable.

View full abstract

In Sarobetsu Mire, the groundwater level has dropped because of drying. There is concern regarding increase in the area occupied by Sasa bamboo and displacement of the original vegetation. The mire basin has seen decreases in snowfall and river water level during the snowmelt season. For mire conservation, it is necessary to understand how changes in the hydrological cycle affect the groundwater in the basin.
In this research, to determine howSasabamboo has spread, we employed remote sensing data collected over the last 23 years as well as ground truth data. We separated river runoff components to clarify water balance in the basin and estimated rates of rainfall and snowmelt water recharge into groundwater. These estimates were used as simulation inputs. The simulation was designed to analyze groundwater responses to changes in rainfall, snowmelt water volume, and river water level, toward revealing a causal relationship with the increase inSasabamboo-covered area.

View full abstract

A major flood occurred in the city of Koriyama at the end of August 1998, after which a flood control facility project called the Heisei Abukuma River Project was speedily carried out from 1999 to 2001 in the Abukuma river basin, which includes Koriyama. Shortly afterwards, however, Typhoon No.6 hit the city in July 2002 and caused flood disaster.
The purpose of this study is to examine how these disasters affected Koriyama residents' perception with respect to floods. Analysis results given here are based on a questionnaire survey conducted among Koriyama residents.
The results clearly indicate that the city residents are more concerned about inland flooding than levee breaks as a potential cause of floods. They also show that the city residents' evaluation of the Heisei Abukuma River Project relates to their perception of flood risk, and that their evaluations are affected little by the actual experience they have had with floods.

View full abstract

The framework of decision-making process and the way to make a consensus among residents and river administrators are pursued. Interviews were held to river administrators and representatives of NPOs that typical three cases of river planning concern. The results of this research revealed three points to improvement the ongoing river administrative. The first is changing framework of river administrative that doesn't allow public involvement in flood control. The second is NPOs' working with river administrators for educational activities. The third is NPOs' continual acts in neutral position.

View full abstract

Public works for preventing disaster must be implemented for emergency. But if confrontation between construction of safety and environment preservation is once caused, the propriety of public work tend to be decided by most residents' consciousness and an opinion of few people who actually met emergency such as floods damage and are afraid of a coming disaster is often neglected.
This interview research was carried out for the residents who live around Daiju barrage in the lower Yosino river for investigating the residents' consciousness about the referendum on public works, disaster prevention, environment preservation, and so on. As a result of analysis, it was shown up that there are some difficulties in the referendum which asks the right or wrong of a disaster prevention work.
This paper offers the alternative way to treat the result of referendum to compensate the faults.

View full abstract

Yodo river park, the first government-managed river park in Japan, has annual visitors of about 5 million and has become one of the most important parks in Osaka and its neighboring prefectures. The park also plays a role to protect or preserve natural river environment and is composed of four types ofareas according to purposes. The actural condition of various functions and utilization of the park has never been investigated sufficiently since the park was open to the public. The purpose of this study is to evaluate the utilization of the park economically using a questionnaire survey result and visitors number data by the park administrator. A relation between characteristics of the areas and the benefit of the utilization is investigated. Annual benefit of the park is over 2.7 billion yen.

View full abstract

There is a great concern for water resources scarcity all over the world, and global modeling of water resources assessment is required for many reasons. Environmental flow has become one of major water users in some part of the world and is estimated to grow rapidly in other part of the world, but its global estimation has not been carried out. Many studies and practices in various countries are overviewed to pick up significant factors which affect the setting procedure of environmental flow in a wide variety of regions. Those factors are then categorized into three types; climate, geographical, and human dimensions. The world can be divided to sub regions using these factors, and then appropriate environmental flow methods will be applied to each sub region to assess environmental flow requirement.

View full abstract

The satellite images are expected to use for monitoring and identification of the disaster area. A differential image is basic method to distinguish the surface change. It is considered that the differential image is useful to extract the disaster area in which surface condition changed between before and after disaster. However the differential images have not been used efficiently due to seasonal change. This paper proposed a new method to produce a differential image using fine and coarse resolution image. Sensors with coarse spatial resolution can acquire the images with higher temporal frequency. However such coarse image does not have enough spatial resolution to investigate flood disaster area. On the other hand, fine spatial resolution sensor can not acquire the images with higher temporal frequency. The new method simulates the fine resolution image which has the surface reflectance when coarse image was acquired (just before disaster or no seasonal change), using the linear mixture model. New method can exclude the effect of seasonal change and has a good capability to identify only flood disaster area

View full abstract

Since the “Flood Fighting Act” was revised in 2001, the flood hazard map has positively been promoted by many local municipalities, and as of March 2002, 217 flood hazard maps had been produced. The effectiveness of flood hazard maps has already been verified in several cases. However, there are some issues on residents' understanding of flood hazard maps.
In this study, we review the effectiveness of flood hazard maps and issues on residents' understanding of them, and we examine the role that flood hazard maps serve. Then, we grasp the state of residents' recognition of flood hazard maps. Moreover, we analyze the effect of the explanation meeting of the flood hazard map on residents' recognition.

View full abstract

The purpose of this paper was to investigate how to collect and use real-time rainfall and water-level information obtained at the time of Kyusyu heavy rainfall disaster between July 19 and 21, 2003. In Fukuoka city, heavy inundation damage was caused by the rainfall. The Hakata Miyako Hotel, located in the centrala rea of Fukuokacity, was protected against inundation damage; this hotel collected had rainfall and river water-level information through the “Fukuoka city disaster prevention homepage” and established rules for an inundation prevention plan. The hotel suffered heavy inundation damage in 1999, and took action to safeguard against a reoccurrence. Duringthe heavy rainfall of 2003, 19 persons in Minamata city were killed by debris flow. Although the Minamata city office had real-timer ainfall and water-level information teiminals, an evacuation counsel had not ordered before the debris flow occurred. It is possible that this was due to the following: the an nouncement of a heavy rainfall alarmwas overdue, the municipal staff had not yet mastered usage of the information terminals, etc.Construction of areal-time information system alone is not effective for disaster prevention. It is necessary to provide thorough and continuous education for users of that real-time information system.

View full abstract

This paper contributes to loss reduction due to inundation disasters in the underground area.
In this paper, we reported the results of questionnaire and interview surveys abo ut the present conditions of countermeasures against inundation disasters in the underground space. We found several problems such as information gathering and effectiveness of countermeasures. In order to improve them, efforts of governments are expected from view point of finance and regulation law. Then we discussed about necessary items for loss reduction due to inundation disasters in the underground markets, and showed the risk management system for loss reduction.

View full abstract

The Thomas-Fiering stochastic model for synthetic streamflow generation is used to determine monthly inflow scenarios for the watershed of the reservoir that supplies the city of Matsuyama, Ehime Prefecture.The scenarios are going to be used by a stochastic programming model which is being developed for the optimal operation of the reservoir. The Thomas-Fiering model allows for the non-stationarity of seasonal data. Twenty years of historical data are used for calibrating the model parameters and a new 20-year synthetic series is generated. The comparison between the statistics of historical and synthetic discharges shows that the model can preserve the characteristics of the historical series and effectivelyincorporate them into the generated data.

View full abstract

The influence of global warming to hazard risk is estimated from the results of regional climate change models by Japan Meteorological Agency and Meteorological Research Institute. The output size of the models is about 20km. Before risk assessment, the outputs were checked through comparisons among monitoring data, those from global climate change models and regional climate change models in 1981-2000. The comparison shows that the outputs of regional climate change models are meaningful only in the east parts of Japan, while those in the west need recalculation. Even though the recalculation are in the middle of process, the results hows that the annual maximum daily precipitation in 2081-2100 will increasei n the southern Hokkaido, Sanriku, southern Tohoku, and middle Kanto plain while the change on flood risk will differ region by region. It also shows that seasonal precipitation in 2081-2100 will decrease from winter and spring in many parts of the eastern Japan. This study implies that more detailed analysis in regional bases will be needed for flood and drought risk analyses.

View full abstract

A global river discharge simulation is conducted taking into account the operation of 500 individual reservoirs. The operating rule for each reservoir is estimated by newly developed algorithm and available global datasets since actual operating rule is not published globally. In this algorithm, reservoir operation is categorized into ‘irrigation purpose’ and ‘non-irrigation purpose.’ The latter decreases inter-annual and seasonal fluctuation of discharge, and the former, in addition, supplies irrigation water to meet the demand in downstream. The simulation result is validated with observed data in three reservoirs in three basins, and judged sufficient for global study. Finally, the impact of reservoir operation on river discharge is assessed globally, by comparing RES simulation, global river discharge simulation with reservoir operations, and CTRL simulation, without operations. The result indicates that reservoir operations increase by 4-43% of monthly discharge into oceans in maximum (the world ocean is dividedinto eight oceans), decrease by 1-7%.

View full abstract

This paper shows spatial distribution of merits and demerits of flood in the Mekong Basin. Firstly, the flood and inundation surrounding Phnom Penh, Cambodia in 2000 (thel arge flood) and 1994 (the normal flood), was simulated. Secondly, the benefits of the flood were calculated, combining the unit price of primary industry (agriculture and fishery) and the result of the flood simulation. As a result, the large flood gives high productivity of rice along rivers because it flowed out nutrition a lot It also expanded fish product area in the flood plain. Therefore, agriculture and fishery obtained higher benefits in 2000 than 1994. The spatio-temporal benefits and damages were constructed.

View full abstract

Many people request river environmental preservation and regeneration for nature conservation. Although it is important to assess the river environment on a planning stage, the evaluation method has not been established yet. Almost rivers are artificially influenced, therefore the method based on residable population within a basin is proposed as the index which can be used for future basin development and a future river planning. The relation between allowance population and discharge is obtained for each ratio in paddy field cover. The pollution load is estimated using the discharge obtained from runoff model and pollutant load factor, and the population is estimated as the index of water environment satisfying water quality condition.

View full abstract

The purpose of this paper is to evaluate the effect of the human activities on water resourcesand hydrological cycle. The Chao Phraya River basin was selected for this study. The Chao Phraya River basin, the largest basin in Kingdom of Thailand is located in central and northern part of Thailand. This basin has two large-scale dams named Bhumibol Dam across the Ping River and Sirikit Dam across the Nan River. This large storage dams are beneficial to the country for generatingelectricity and discharging water for the irrigation project areas and flood mitigation on both banks of the Ping, Nan and the Chao Phraya rivers.
There is no the long-term increase and decrease tendency of the precipitation. As the results of comparing the annual change of monthly runoff before and after dam construction, the minimum runoff increased and the maximum runoff degreased.
As the results of spectrum analysis using FFT, after the Bhumibol dam was constructed, the daily runoff in Nakhon Sawan had period characteristics in 3.5days and 7days and the released water from the Bhumibol dam had period characteristics in 2.5days, 3.5 days and 7days. Dam operation effected on the hydrological cycle considerably.

View full abstract

Simultaneous measurements of particle-laden flow have been investigated extensively. It is very difficult to measure such a two-phase flow when the particle concentration is relatively large. It is because the particles between the measuring volume and CCD device are the obstacles. Mean flow properties and turbulence characteristics of high particle concentration flow may be changed greatly than dilute flow. In this study, some experiments conducted in narrow open-channel flow enabled us to measure high particle-concentration flow. It was found that the flow field in the near-wall region (y/h<0.2) was not affected significantly by secondary current and that 2-D turbulent flow was obtained. Consequently, universal characteristics in the near-wall region are expected to clarify particle-fluids motions even in narrow open-channel flow.

View full abstract

Uniform flow on a relatively steep channel is known to be unstable to evolve into a wave train, which is termed roll waves. Though roll waves have long been studied, their wavelength cannot be theoretically determined. In this study, a linear stability analysis on the wavelength of fully-developed roll waves is performed. It is found that the instability of the fully-developed roll waves is maximized when the wavelength is 0.1-1, and roll waves with infinitely long or infinitesimally short wavelengths are neutrally stable. In order to study the development of roll waves and to verify the theory, numerical simulation is performed. As the distance from the inlet increase, roll waves tend to increase in the wavelength, and to approach a constant wavelength asymptotically.

View full abstract

Recently, research onto the hydraulics of stepped chutes was driven by needs for better design guidelines (OHTSU and YASUDA 1997, CHANSON and TOOMBES 2002, BOES and HAGER 2003). Although stepped channel flows are characterized by intense turbulence and strong flow aeration, most studies did not investigate the turbulence characteristics. In this study, mean velocity and turbulent intensity distributions for skimming flows have been investigated. The air-concentration ratio (void fraction), and the bubble count rate (the number of bubbles impacting the probe tip per second) have also been studied. The difference of velocity characteristics between the aerated and the non-aerated flow regions can be found. Further, the friction factor in aerated flow region can be obtained on the basis of the measurement of the air-concentration.

View full abstract

The aim of the present study is to reveal the hydrodynamic properties in open-channel flows including the rising-bubbles. Particularly, when we consider effective control techniques of aeration in actual rivers, turbulence structure of open-channel flows including bubble plumes has to be investigated. However, such a bubbly open-channel flow has very complicated phenomena, and thus there are few previous studies that have been tried by high-accurate measurements and numerical simulations.
Therefore, in this study, PIV measurements using high-speed CCD camera have been conducted, and consequently, the rising-lines of bubble plumes, primary velocity distributions and turbulence structure have been revealed experimentally.

View full abstract

A laboratory experiment was made to parameterize the gas transfer velocity of CO₂ at the surface of wind waves. The local flux of CO₂ was estimated at several fetches by fitting a logarithmic law to the vertical profile of the concentration of CO₂ in the air. The dissolved CO₂ concentration was measured by using a gas-liquid equilibrator made of hydrophobic porous tube. The local gas transfer velocity was obtained form the results of the flux and dissolved CO₂ measurements. For the parameterization, two dimensionless parameters, gx/μ*_w² and μ*_w³/gv_w were derived from a dimensional analysis, where μ*_w is the friction velocity on the water side, g the gravitational acceleration, x the fetch and V_w the kinematic viscosity for the water. On the basis of the experimental results and the dimensional analysis, we proposed a new empirical formul a for the gas transfer velocity of CO₂ in consideration of the fetch dependence.

View full abstract

The present study describes an experimental relationship between turbulence structures in water layer and the water-surface fluctuations in wind-driven open-channel flows by using both a laser Doppler Anemometer (LDA) and a wave gauge simultaneously. The purpose of this study is to make clear the characteristics of surface fluctuations on water dynamics in air-sheared open-channel flows, and to evaluate the effects of surface fluctuations on vertical momentum transport in the water layer. As the results of experiments, it is shown by spectral analysis that the velocity fluctuations near the interface in both only open-channel flow and wind-driven open-channel flow are significantly affected by the water surface in every range of frequency, and that there exists a high correlation between turbulence near the air-water interface and the surface fluctuations in a predominant frequency due to high-sheared wind flow. Moreover, it is recognized by wavelet analysis that the turbulence structures in weak wind-driven open-channel flows are governed by both wall shear and wind-induced flows.

View full abstract

This paper presentsa new innovativem ethod for measuringt wo-dimensionawl aterl evel variations.T his method uses a pair of images captured by a stereo arrangement of CCD cameras. With this method it is possible to measure the instantaneous water surface form non-intrusively. At first, we explain the measurement principal and the experimental procedure for obtaining stereo images. Second, we exam measurement accuracy by applying our technique to waves and surface ripples generated by a falling drop, and find that we can resolve waves as small as 1mm. Third, we measure periodic surface fluctuation produced in an asymmetry cavity with a reasonable accuracy. Finally, we describe the problems of this technique and future research plans.

View full abstract

Severald ischargef ormulae, w hich can predict the dischargep er unit width in open-channefl lows with a sideweir, have been suggesteda s yet. The dischargec oefficientsi n such formulaew ereo btainede mpirically.I nthis study, the velocitym easurements in subcriticalo pen-channel flows were conducted with an electromagnetic current meter and also the flow depth measurements were conducted with a point gauge, with changing the inlet Frouden umber and the ratio between the inlet flow depth and the length of the side-weir. It was found that the direction of the velocity on the side-weir is almost constant in the vertical direction, but those changes in the streamwise direction. The relationship between the direction of such velocity and the inlet Frouden umber and the ratio between inlet flow depth and the length of the side-weirw as made clear. As a result, a new dischargef ormulao f side-weiri n subcritical open-channel flows with zero height was suggested.

View full abstract

In compound open-channel flows, there are some large-scale horizontal vortices with a vertical axis. Such coherent vortices influence significantly the transverse transport of scalar variables like suspended sediment between the main-channel and floodplains. So, it is very important in hydraulic engineering and river environment to investigate hydrodynamic characteristics of coherent horizontal vortices in compound open-channel flows and thus there are a lot of experimental and numerical studies on these topics. From recent measurements, it isinferred that the horizontal eddies have a 3-D structure of vortex tubes.
However, 3-D structure of horizontal vortices has not yet been revealed in detail. Therefore, in the present study, a new PIV system using dual-layer laser light sheets was developed and instantaneous velocity fields on two laser sheets were measured simultaneously. As a result, 3-D coherent properties of horizontal vortices and their convection mechanism have been investigated experimentally.

View full abstract

Measurements of instantaneous flow fields and the dye concentration in and around side cavity that was set around the permeable wall, were conducted. Measurements of flow properties were conducted by PIV. On the other hand, DV-camera was used for measurements of dye concentration. Permeable flow from the side wall of the side cavity was divided into 4 kinds of patterns. From the upstream wall, side wall, downstream or upstream and side wall. The permeable flow rate was set to 3 patterns. The 3%, 5% and 8% of the main-channel flow rate were changed. The aspect ratio (the streamwise length of the side cavity/the lateral length of the side cavity) was set to 2.
Flow patterns were changed. In the case of the permeable flow from upstream wall, side wall and upstrea and side wall, the center point of circulation flow moved to the downstream. On the other hand, in the caseof permeable flow from the downstream wall, the center point changed to the upstream. Dye concentration distribution in all cases was that high concentration area was observed at the upstream in the side cavity.In and around the circulation flow, there was low concentration. In the case of permeable flow from the upstream and side wall, the influences on flow fields or concentration fields were the greatest.

View full abstract

The effects of several kinds of permeable spur dike on 3-D flow structures and river bed evolution were investigated in curved open channels experimentally and numerically. In this study, three-dimensional mean flow structures were measured in a curved open channel with spur dikes arranged along the outer bank. Experiments were conducted in movable beds and the effects of spur dikes on the local scour were examined. The secondary flow cell was generated in the same manner as the uniform rod roughness cases. Outer-bank arrangements of permeable spur dikes can reduce the outer-bank scour, but additional scour is generated in different regions. A traditional hydraulic structure, “Seigyu” has the similar effects on flow structures as the pile dikes. A 2-D numerical simulation model can be applied to these spur dike cases with the same assumption for the secondary flow dispersion terms.

View full abstract

As the bed shape depends on the distribution of the bed shear stress, it is important to evaluate the accurate that. However, the bed shear stress in a compound meandering channel has not been cleared yet. In order to clarify the characteristic of flow turbulence structure and bed shear stress, a measurement device is developed by meansof LDV. In this paper, the measured three-dimensional flow turbulence and shear stress are explained in detail and flow structure are cleared. A three-dimensional numerical analysis is performed to reproduced flow and shear stress, and numerical results are compared with experimental results. It was shown that measured bed shear stress distribution is different from that in numerical results though the time averaged flow in numerical results can explain that in experiments.

View full abstract

Hydraulic experiments are carried out to clarify fundamental characteristics of fluid force on a large structure due to an inundated flow caused by a tsunami. Impulsive force at an early stage, and drag force, buoyancy and uplift pressure at a quasi-steady stage after the early stage are taken up as the fluid force. Dependency of drag coefficient on hydraulic quantities and opening ratio of structures is also examined.

View full abstract

Damage by flood inundation has often occurred in recent years even in urban areas, where water management systems are controlled properly. Advance provision of useful information such as hazard map and evacuation routes to the peripheral people is considered to be necessary in order to prevent and minimize the damage. Development of inundation flow numerical model is, therefore, required to predict flood inundation areas precisely.
In the present study, a depth-averaged flood inundation flow model in the Cartesian coordinate system is developed using a CIP method and a SMAC method. The validity of the model was verified by comparing the computed results with existing numerical and experimental ones in the one-dimensional and horizontally two-dimensional fields. As a result, the model was confirmed to be consistent with the existing numerical schemes and be able to reproduce the laboratory experiment with high accuracy.

View full abstract

Hydraulic physical model experiments concerning the inundation by river water in Kyoto City are carried out to clarify the characteristics of the behavior of flooding water on a complicated city area. The physical model scale is 1/100 and it is a non-distorted model. The model can make allowance for the intrusion of flooding water into underground space. Flooding processes were simulated by using a numerical model that incorporated the finite volume method and unstructured meshes. The flooded area and depth of water in case of no intrusion of flooded water into underground space were reasonably well evaluated by this method, while in case of intrusion of water into underground space calculated results were not well evaluated. The reason is that the drop flow equation was used to estimate the discharge into underground space and that the entrances into underground space were not taken into account reasonably. The suitable equation for evaluating the discharge into underground space must be developed and also the unstructured mesh of entrances must be constituted reasonably.

View full abstract

A two-dimensional numerical model for uraban flooding is developed. The model is based on a numerical model with Finite volume method on Unstrucuted grid using Flux-difference splitting technique for 2D Flood flows (FUF-2DF model). The treatments of complicated flood plain geometries with sumberged/ emerged topgraphy, stuructures, road networks, flood retarding plantation etc. are incorporated into the model. In experiment, flow depths, velocities and hydrodynamic forces acting on structers in flood plain with complicated geometries were observed. The model is verified comprehensively against the experimental data, and it shows that the model can reproduce the complex behavior of the flow and hydrodynamic forces with reasonable accuracy.

View full abstract

A hydraulic model test is conducted by use of the undistorted hydraulic model with 1/30 scale. The studied underground space is the complex one comprising the shopping mall, the parking lot and the subway station. Inundation process there is studied in detail and evacuation possibility is examined based on the depth and velocity of inundation flow. It is found that if the inundation flow invades the studied underground space, the inundation area expands rapidly and the water depth rises very quickly. The studied space also becomes very dangerous by the difficulty of evacuation.

View full abstract

To make the detailed inundation flow analysis in urban area, a sewer model has an important role. In this study, the slot model is used in the sewer network model, and the sewer pipes whose diameter is over 300mm are treated. As for the inundation flow in the ground, the 2-D inundation flow model by unstructured meshes is used. The inundation water exchange between the ground and the sewer system is treated in detail. The above combined model was applied to Tsurumachi drainage basin in Osaka city. Through the analysis, it was found that drainage process is expressed in more detail than it was, and branch sewer pipes have a large effect on drainage.

View full abstract

Flood inundation due to dike-break or overtopping is a serious problem to cause great damages and losses to human beings, and thus threats the sustainable development in the suffered regions. In addition, flooding flows usually company with sediment transportations and yields. The sediment not only can worsen the damages, but also can change the elevations of floodplains. Now, flood inundation can be simulated successfully by 2-D shallow water equations (SWEs). The 2-D SWEs can also be coupled to transport equations to simulate the sediment transportation. However, problems of mass conservation and numerical instability may arise if the numerical schemes of simulation models are not chosen with cares when the sediment transport and variations of floodplains are coupled with the inundation model. For the purpose of overcome these problems, the Koren upwind scheme of third order accuracy is employed to discretize the advection terms of the sediment transportation equations. A case study was conducted in a small area of the lower Yellow River in China. Results of the case study demonstrate that the Koren scheme is robust and accurate for the coupled 2D SWEs and sediment transportation equations so that a precise estimation of floodplain variations can be made.

View full abstract