Water balance in lysimeters with bare surface was studied under the condition of artificially controlled room temperature and humidity and soil temperature. Evaporation was found to dominate the water balance there. The evapora-tion was investigated by the use of an “evaporation” pan and from a viewpoint of heat balance. The reasonable evaporation rates were evaluated by the heat balance method. The evaporation process in the lysimeters was categorized as the constant-rate stage for each experimental condition. The sensible heat flux was found to almost always enhance evaporation in this series of experiment.

View full abstract

A theoretical study of combined steady thermal energy and vapor diffusion equations has been performed to estimate temperature and evaporation in an unsaturated porous media under temperature gradient due to the radiation. The results calculated were compared with experimental results and the availability of the present model was confirmed. For a simulation of drying process an application of the present model to the successive steady method was tried, and could produce a couple of attractive results, that is, Q ∝ t^a (Q: cumulative evaporation, t: time, a ≈ 0.5) and D ∝ t^b (D: thickness of dry layer, b ≈ 0.4).

View full abstract

This study aimes at modelling of forest transpiration process associated with heat pulse velocity as an index of sap flow velocity. Outdoor experiments are carried out with an 8-year-old chamaecyparis obtusa (Hinoki). It is clarified that transpiration and heat pulse velocity has a nonlinear relationship and transpiration decreases with decrease of soil moisture potential. This model can explain measured transpiration very well using heat pulse velocity.

View full abstract

Basic equations of plant system (leaf-stem-root) have been developed from a view point of fluid mechanics based on the bio-meteoro-hydrological process. From these equations, the characteristics of transient response of plant for the water movement have been investigated both analytically and numerically.
1) From a mathematical analysis of the linearized plant-system equations, the lag between transpiration and water flux in stem and lag between water flux in stem and water uptake by roots shown to be governed respectively by one nondimensional parameter which is composed of physical constants of plant
2) A nonlinear numerical simulation suggests that lag between transpiration and water uptake by roots is extremely delayed when plant is under the ‘ water stress’ condition, while under ordinary condition, plant shows the response as given by the linearized analysis.

View full abstract

A new numerical model of three dimensional hydro-metorological process has been developed for investigating the initiation and development of convective clouds considering the effect of air-soil interactions. This model consists of three parts, that is, atmosphere, constant flux layer and soil. For the subgrid turbulence process, ‘ Large Eddy simulation (LES)’ model is adopted with a timedependent turbulence energy equation. Soil temperature distribution is determined time-dependently and locally to satisfy both energy and moisture balances.
Microphysical processes of cloud and rain generation are described by the Kessler parameterization.The results show that the initiation of convection is effected strongly by the soil moisture distribution and the air-soil interaction intensify the development of convective clouds.

View full abstract

Both theory and experiment in passive microwave remote sensing of snow have been studied. Synchronizing the airborne experiments using Microwave Scanning Radiometer (MSR) with the passing days of Marine Observation Satellite 1 (MOS-1), ground truth data were obtained around Asahikawa of Hokkaido during February 1988. Snow surface temperature, snow depth, and snow density were observed along the route of the aircraft from Mt. Asahidake to Biei. The distribution of snow water equivalent was identified and it was compared with brightness temperature derived from the airborne MSR. The microwave emission from snow at each observational site was calculated using the radiative transfer equation. Results of calculations considering Rayleigh scattering were in good agreement with the airborne observational data.

View full abstract

This study investigates the discrepancies of heat budgets on snow surface between in the high alpine area and in the lower-lands through field observations. The energy exchanges across the snow surface were measured at two observation sites; one located at 2950 m a. m. s. l. on the northern slope of Mt. Fuji, and the other at 300 m a. m. s. l. in Niigata prefecture. Snowmelt was calculated using snow density measured by snow sampler once every week and melting depth by camera in every six hours. Role of turbulent heat flux in the high alpine area was more important than in the lower-lands. The latent heat flux was usually negative and the large positive latent heat flux associated with the warm, humid and strong wind sometimes caused the very intense snowmelt in the high alpine area.

View full abstract

In this paper, the authors made a fundamental experiment to investigate the effect of atmospheric factors influencing snowmelt runoff, that is, wind speed, solar radiation, air temperature and terrestrial heat.
The amounts of snowmelt runoff was measured by the experiment under the condition concidered solar radiation, air temprature and terrestrial heat which were controled and under the condition considered above mentioned factors in addition to wind speed.

View full abstract

Calculation of snow-melt runoff to Shijyu-shida, Gosyo and Yuda dam reservoirs was performed. This numerical model requires only daily air temperature and precipitation at a representative point in the basin as input data. 8 parameters in the model were chosen from past meteorological and hydrological data, and calculated hydrographs show a good coincidence with observed runoff at these dams. Improvement of methods to determine these parameters is left for the future research.

View full abstract

Combined snowmelt and rainfall runoff during active snowmelt season is predicted by using tank model and the model parameters are optimized by applying Powell's conjugate direction method. The parameters optimization is conducted for the data of water year 1988. The obtained set of optimized model parameters is used to predict the runoff of water year 1989. The input data for the model are snowcover area evaluated from remote sensing data, daily precipitation, daily mean air temperature and daily observed runoff.

View full abstract

This paper firstly presents the temporal and spatial characteristics of short-term urban-scale rainfall. The studies are based on measurements of rainfall made on a network of 12 gauges situated in the city of Lund, Sweden. Three-year series of one-minute rainfall records from each gauge are used for the analyses such as areal intensity-duration-frequency relationships. Secondly, a method for real-time prediction in time and space of urban-scale rainfall under the assumption that the rainfall process is governed by the stochastic convective-dispersion equation. The method is applied to the shortterm rainstorm prediction in the city of Lund.

View full abstract

Recently the Tokyo urbanized area becomes more vulnerable to thunderstorm-like heavy rain rather than the rain acompanied with typhoon (Tamashima et al.1990). Hence in the present study an attempt has been made to analyze the characteristics of the generation and evolutional process of cloud cells in the Tokyo metropolitan area by using of a 3D radar system. The results of the analyses for typical three cases of 31 July 1987, 13 August 1988, and 17 August 1988 suggest that in addition to the heat island effect due to the urbanized area, the existence of Tokyo Bay as a cool island and a source of water vapor also affects the evolutional process of cloud cells.

View full abstract

To make a distributed rainfall-runoff model, it is very important to build a model of topographic surface of a basin which takes account of the direction of water flow.
The objective of this work is to represent the landscapes numerically using Triangular Irregular Network Degital Elevation Model data structure. Landscapes are modelled as a set of contiguous non-overlapping triangular facets whose vertices are made up by points on regular grids and points on river segments. Those triangular facets are subdivided, if needed, so that each of them has only one edge through which water flows out.

View full abstract

Morphological characteristics of the urban sewer system at Higashinada District in Kobe City are investigated in terms of Horton's Law, Hack's Law, Melton's Law and Fractal dimension. Results of calculation for 25 main sewers show that the maximum order of the sewer system is 1-3 and the Fractal dimension is 1.00-1.33 (ave. 1.10). Horton's Law, Hack's Law and Melton's Law are almost proved with some exceptions. Modified Hack's Law using Fractal dimension gives higher correlation between main sewer length and drainage area compared with the original Hack's Law.

View full abstract

For rainfall interception process in forests, four types of tank models are examined using field observations of gross rainfall, throughfall, and stemflow of a Sugi stand in forests. The models are single tank models and double tank models with different constants and coefficients during a rainfall event from those after the cessation of the rainfall. Parameters in the models are identified by minimizing the square sum of residuals of stemflows. The double tank models obtain better results.

View full abstract

Long-term runoff analysis by a tank model incorporated with rainfall interception and SPAC (Soil-Plant-Atomosphere Continuum) is performed using observations of rainfall interception and daily atmospheric temperature besides rainfall and runoff. Parameters representing evaporation rates by rainfall interception and from ground water runoff and the transpiration rate of soil moisture through vegetation are identified by minimizing the square sum of residuals of runoff discharge.

View full abstract

The separation of flows using the geochemical tracer SC (specific conductance) has been utilized as a first step to determine the flow characteristics of a study basin. Through the utilization of a non-steady state equation of mass balance, the incorporation of the relative contributions of surface and sub-surface flows to the total flow, and the effect of long and SC varying rainfall, a physically based function of new rainwater was determined. Experiments were made to this effect and an actual rainfall event was used in separation of new and old rainwater. The result, of the separation yielded contradictory results as compared to those using a non-chemical tracer.

View full abstract

The soilwater and streamwater chemistries in the Tsukuba experimental forest were examined using data sets gained during four years since 1985. The concentrations of nitrate nitrogen and potassium etc., the major essential elements for forest plant growth, rose in surface soilwater in summer season due to decomposing organic substances accumulated in surface soil. Furthermore, the soilwater leaching during successive storm events increased those concentrations in streamwater through summer season. Such coincidence of the time-varied pattern between solute concentration and flowrate brought in the rise of the annual streamsolute concentration like nitrate nitrogen and potassium with increasing the annual streamwater amount.

View full abstract

Water path flow was examined using the unsaturated medium consisted with glass-beads of uniform diameter.
Experimental results showed that the ratio of width of water path to that of the total layer decreased as the glass-bead diameter increased and that the mobile water content was smaller than the total water content in the water path.
These results could be explained more comprehensibly by the capillary model presented by Tamai et al.(1987) than by the conventional method using the hydraulic conductivity.

View full abstract

Water holding substances mixed in soils affect the infiltration characteristics of soils, thus rainfall-runoff process changes. Therefore, the headwaters conservation and the flood-prevention may be controlled.
The laboratory experiments with the artificial rainfall, have been made by a lysimeter with diameter φ 200.
The effect of mixture ratio of soil and water absorbent high polymer was examined. The soil parameters of each mixture case are identificated by the analysis of hydrograph data.

View full abstract

This study aims to make clear relationship between infiltration capacity and topography, soil type, and land use in urban areas. Infiltration capacities in urban areas are measured with a rainfall simulator. Topography of objective areas are upland, low land, and hilly land. Soil types of objective areas are sand, loam, and alluvial soil. Land uses are sports ground, bare land of temple or shrine, and garden of houses. Number of plots of infiltration test are 27. Nine plots are taken for each topography. The statistical analysis of final infiltration rates of 24 plots was done by Hayashi's quantification theiory 1.

View full abstract

Flood concetration time equations are derived from fractal theory for urban rivers and sewer network. To know the effect of urbanization on flood controll, flood observation had been started in Tama New Town for the past fourteen years and its data were analyzed hydrologically. The major results are as follows; on the process of urbanization, concentration time has been shortened since impervious area, river improvement and sewer network increased in a watershed. However, the peak runoff coefficient only increased with impervious area and sewer network. These mechanism can be explained very clearly by the concentration time equations expressed by fractal.

View full abstract

The authors have developed an automatic data processing system for analysis of geomorphologic features of river basins and channel networks, using digital terrain maps (DTM) such as the Digital National Land Information released by the Geological Surveying Institute, the Ministry of Construction. This paper describes the fractal dimension of rivers obtained by using the system and the DTM of ten river basins in Japan with the area of several hundred square kilometers. The relationships are also investigated between the fractal dimension and some characteristic values of channel network used in conventional analyses.

View full abstract

The objective of the present study is to clarify the processes of the formation of hydrograph and its characteristics in actual basins. From the field observation and numerical analysis, the followings are concluded.(1) The linearity between the discharge in a river and the catchment area is assured in the basin with the catchment area less than 4000km².(2) The effects of Manning's coefficient for the deformation of hydrograph is smaller than the magnitude of the discharge from large tributaries and its timing.

View full abstract

Meteorological radars have covered almost the Japanese archipelago. The information from these radar systems consists of mesh data. The size of each mesh is approximately 3km*3km. It is very important to estimate the runoff from these small basins to use the information from radar system. In this paper, the effects of variations of channel network structure on flood peak magnitude are investigated using simulated stream networks for the small basins. Numerical experiments are carried out to explore the relationship between the hydrograph and the channel network structure. It is concluded that the duration of rainfall input plays an important role.

View full abstract

A drainage basin consists of slopes and channels. Slopes are the main fields at which rainfall input is converted into discharge. Stream-channels are the main fields at which the discharge from the subbasins in synthesized and transported to down-stream. The channel network geometry plays very important role in the above transportation process. This paper forcuses on its process based on channel network geomorphology. Author presents new findings on the relationship between runoff characteristics and network magnitude.

View full abstract

The objectives of this paper are (1) to show longitudinal variation of channel geometry and flow resistance of mountain rivers, (2) to incorporate this variation into distributed rainfall-runoff model already developed and (3) to apply this model to predict flood hydrographs. In two experimental basins, 28 cross-sections are surveyed for channel geometry, slope and discharge at that time. From this data, Manning's n is computed. Both channel width and Manning's n show a longitudinal variation, and are related to drainage area used as longitudinal index in this study. By taking this variation into account, the model reproduces the measured hydrographs with a good correspondance both in experimental basins and in large basins.

View full abstract

Layer-averaged equations describing the characteristics of a two dimensional unsteady inclined starting plume, which consists of two parts, i. e. a front and a following, are derived. A numerical model is formulated on the basis of an explicit scheme of the characteristic method for the following flow and the fourth order Runge-Kutta method for the front flow. The model incorporates the major physical principles involved. For a wide range of practical applications the present model is capable of predicting characteristics of the flow such as velocity, thickness, and density.

View full abstract

A System for the analysis of river effluents using satellite data is developed. Effluents from the Shingu River are analyzed as an example to study the difference in diffusion areas detected by water temperature and water turbidity. When the effluent discharge is small, the turbidity distribution off the river mouth may be affected by the floating substances released from neighboring other rivers. But the water temperarure is not affected significantly by the neighboring rivers. Thus the water temperature distribution is more proper parameter, in comparison with the turbidity distribution, to be employed in field surveys of the effluent diffusion.

View full abstract

A one-dimensional mathematical model is proposed to describe thermal stratification in lakes. The vertical diffusion coefficient is formulated in terms of wind velocity and the gradient Richardson number. Heat exchange through the air-water interface can be calculated from the observed daily averaged meteorological data. This model is validated for simulation of temperature field observed in Lake Chuzenji. Calculated results of the thermal structure of the lake showed good agreement with the observed data. Effect of wind velocity on the thermocline formation is also evaluated.

View full abstract

Mixing processes in shear flows with temperature and salinity stratifications depend on the composite effect of double diffusion and turbulence. Diffusion characteristics in such flows are studied both experimentally and numerically. Experiments are carried out on two types of double diffusive flows (diffusive and finger types). In each type of diffusion, the eddy viscosity and eddy diffusivities of heat and salt are estimated in relation with the Richardson number. A two-dimensional numerical model is applied to simulate the double diffusive shear flows. The performance of the model is evaluated by the comparison of numerical results and measurements.

View full abstract

An empirical model is developed and calibrated for the estimation of salt intrusion into Lake Ogawara. The model is based on one-dimensional kinematics of the salt water front in a divergent channel of the lake to the ocean. An assumption is made that the longitudinal profile of salinity concentration around the front is kept constant, and the profile is empirically evaluated.
The model successfully reproduces the time series of flow rate and salinity concentration at a measurement station in the channel. The time-integration of estimated salinity flux agree fairly well with the increment of total salinity in the lake.

View full abstract

Steady state spread of oil slick formed when the oil is continuously poured on the surface of uniform water stream is dealt with. Theory is developed by means of the twolayers model which takes into account the lateral spread of oil slick whose velocity is assumed proportional to the advancing velocity of the density front. Governing equaions of the average thickness, average velocity and the width of oil slick are derived. Calculations of width of oil slick is compared with experimental data.

View full abstract

This paper deals with the numerical simulation study of eutrophication phenomena coupled with hydraulic behaviours of stored waters in a stratified reservoir by means of plane multi-layered model. This model is deduced from the hydrodynamic principles by making use of curvilinear orthogonal coordinate systems according to the geometrical features in the flow field. The case study in Muroh Reservoir is made and the results obtained through the simulations are discussed with successful verifications of the proposed procedures.

View full abstract

Aeration/Circulation is a method to reduce algae abundance by generating vertical circulation. It is said that this countermeasure is performed by limiting light, supplying dissolved oxygen to hypolimnion, lowering of pH of epilimnion, and so on.
In this study, results of field measurement are shown and following consequences are obtained.
1. When blue-green algae is dominant, pH of the epilimnion is high.
2. After treatment, pH of the epilimnion has been lowered and dominance of blue-green algae in summer has disappeared in this reservoir.

View full abstract

The salmon is the main marine product of Iwate prefecture and salmon culture projects are very active: therefore it is very important to prevent the mouth of a salmon culture river from being blocked by sand deposit. However civil engineers had not been concerned with fluctuations of such small rivers. In this study, field observations were carried out at 41 river mouths in Iwate to comprehend the situations of small rivers. Observations show that at 75% of river mouths both water depth and river width are not enough for salmon returning, and that the time scale of river mouth fluctuations depends on topographic features of coast line near the river mouth.

View full abstract

The purpose of this paper was the investigation of a numerical calculation method for a diffusion of pollution in a network of tidal rivers. Using the split-operator approach, an advective transport process was calculated by the two-point fourth-order Holly-Preissmann scheme and a dispersion process was calculated by the Crank-Nicholson scheme. The method of applying these schemes to the confluence and branching of a river were investigated. The calculated results for the Shinmachi River system were consistent with the observed ones.

View full abstract

The Barato River basin, located in the northern part of Sapporo City, is characterized by low-lying areas. The prevention and mitigation of flood damages in this basin are mainly controlled by the two gates; the gate of Shibi canal plays an important role in shutting off the backwater effect of the Ishikari River, while the gate of Ishikari Floodway draining out the inflow volumes from three upstream tributaries of the Barato River as fast as possible.
The current gate operations in the Barato River system are heavily relied on intuition of the experienced engineers, mainly because decision-makings should be done on complicated predictions of inflows to the Barato River, water levels of Ishikari and Barato Rivers and the tide in a river mouth.
The present study describes the basic concept of a Fuzzy support system applied to gate operations of the Barato River basin and some simulation results.

View full abstract

This paper discusses the characteristics of soil reflectance under many different soil moisture ratios and vegetation cover rates, and the influence of vegetation vitality on its reflectance. A very close correlation between soil reflectance at a wavelength of 650nm and that at a wavelength of 800nm is revealed. The vegetation cover rate is formulated in terms of soil and vegetation reflectance at wavelengths of 650nm and 800nm. The vegetation reflectance is strongly influenced by its vitality, which is related to the moisture content and chlorophyll-a concentration in the vegetation.

View full abstract

In this paper, the results of the field observation of precipitation by the present authors are shown and the results of altitude or direction of the slopes in a mountainous area on rainfall are discussed. In order to investigate the characteristics of precipitation processes, numerical simulation of rainfall by using Kessler's and Hobbs' parameterization are carried out. Finally comprehensive comparison with the numerical solutions obtained from the two models and the field data are performed.

View full abstract

This report is delivered on run-off of residential area with infiltration facilities. The rainfall datas were classified into three cases. The results were as follows:(1) if it was even slightly rainfall, the ratio of run-off was 0.1 or less.(2) If it was peak shaped rainfall, the ratio of run-off was about 0.2 in cace of 20 mm/hr.(3) It was found that infiltration capacity of the facilities had not changed since field observation was begun.

View full abstract

In spring of 1987, a large ice movement and ice ride-ups on the shore of Lake Ogawara in Aomori Prefecture were observed. About 15 cm thick ice cover invaded inland 23 m deep and piled up 1 m high. Calculation of wind shear stress as an ice driving force resulted in 600 tons. As a conclusion, ice formation and its movements could cause considerable loads on hydraulic structures, and it is strongly recommended to pay enough attension for possible damages of structures by ice.

View full abstract

The purposes of this study is to clear the relationship between bank erosion mechanics and river channel charactors, and to know the place where bank erosion is up to occur. Field survey, especially the Hinuma river, has been done for this purposes. From this survey the shapes and mechanics of bank erosion have been found to be different from each river channel charactors

View full abstract

Field survey of sediment deposit on high water channel (flood plain) of the Hinuma river has been done to understand the deposit condition of sediment, which is suspended in low water channel at flood time, on high water channel.
Through the study, the place where sediment deposit occurs is able to be estimated by using the ratio of frictional velocity to fall velocity of sand for both both high and low water channels.

View full abstract

Field measurements have been carried out at the mouth of the Nanakita River which flows into the Pacific Ocean. Since 1988, the river mouth was closed twice, owing to high seas. The wave incident direction was important as well as the wave height and period. The onshore sediment transport was more effective than the longshore sediment transport. The sand spit at the mouth was also flushed twice by floods. At the initial stage of floods, river water overflows with a depth of several ten centimeters, and the flushing was completed within 3 to 4 hours.

View full abstract

The upstream motion of saltwater fronts in tidal upper reach of the Hiji river has been observationally studied. The measurements were obtained at two fixed stations and several temporary sites apart from 200 m each other by boat. The profiles of density fronts were figured by lines at each mix-ture specified in percent and the velocities of their head during ebb and flood were evaluateded. The study shows that, the upstream velocities of flood water in well mixed are about 1, 000 times as great as that of tidal water rising. The un-stable state in interfacial transition layer through ebb are scrutinized by local Richardson number (Ri<1) at each layer in 10cm.

View full abstract

The turbulent fluctuations of velocity have been measured actual rivers in the field where the relative water depth to roughness height is small, using ultrasonic flowmeter. The turbulent structures of river flows where roughness is relatively small, are similar to those in laboratory channels with the smooth bed. For the rivers where the roughness is relatively large, the turbulent structures in the river bed region are very complex and significantly different from those in laboratory channels with the smooth bed.

View full abstract

The accuracy of the correlation method is examined by simulating particle movements under uniform parallel flows and uniform shear flows. Particle images are produced by decomposing each pixel into 9x9 sub-pixels and shifting particle patterns in a sub-pixel unit. This method is also applied to the aerial photographs taken during floods. The results show a reasonable velocity distribution reflecting the river bed configuration and a large scale structure of the flow along theedge of the lower bank.

View full abstract

Resistance of the overbank flow is decomposed into surface resistance and form resistance. Form resistance caused by tall vegetation in the floodplain is explicitly formulated by the form drag of trunks and momentum loss due to macroturbulence generated by a branch-leaf complex. Hydrodynamic parameters in a formula aredetermined by the critical review of existing knowledge on coherent structures in turbulent open channel flows. An application of the proposed formula to the overbank flow through floodways gives good agreement with observed discharge without any tuning of coefficients.

View full abstract

Purification of water in the slack water reach of rivers and lakes is one of important problems. The purification by means of airlift may be most favorable, andin order to apply such apparatus for practical use, the intensive laboratory tests and hydraulic analysis are made. Based on the results of the fundamental study, the dimensions of the apparatus are decided and field tests are made. The results obtained in the field are acceptable.

View full abstract