A mathematical runoff model of solutes from forested mountain basins is developed, based on a tank model comprising a surface tank with soilwater storage systems, and a groundwater tank. The model takes account of two elementary processes, (a) advection owing to the rainwater movement and (b) solute exchange between soil aggregate and adjacent soilwater. The proposed model is applied to observations of streamwater solute concentration (Cl^-and SO₄^2-) obtained from a forested mountain experimental basin (main species Cryptomeria japonica). The basic model structure is verified by the observation of solute concentrations in both streamwater and soilwater.

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In dealing with groundwater contamination and pollution monitoring, it is important to predict the characteristics of the various chemicals that flow in the soil-water environment. This research reviews the current state of the formulations of chemical flow in unsaturated mobile-immobile water systems and proposes a new approach towards the selection of a model basis. This includes the use of the irreducible moisture as the immobile moisture term and the use of a simple kinetic term for the soil sorption. These assumptions when tested on a simple discrete experiment for the sorption term and analytical and experimental fitting for the immobile term show an acceptable level of performance.

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This paper presents on a new lumped model for estimation of flood flow from mountainous river watershed. First, the new model is made up of the storage area with the retarding area, the stream reach and the translation reach is proposed. Then, the technique for identification of the model parameters and the procedure for estimation or prediction of flood runoff by the model is introduced. Finally, the model is applied to three mountainous river watersheds, and a validity of the concept of rainfall-runoff process in the model and an availability of the model to mountainous river watersheds are discussed.

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Athi basin is one of the five basins which form the drainage pattern of Kenya and occupies about 70, 000 km² (12% of Kenya's land area). Athi river drains approximately 65% of the basin's area with the remaining area drained by smaller independent streams. The study area lies approximately between latitudes 4° 50'S and 4° 30'S. Like most parts of Kenya, greater part of Athi basin experiences two rainfall regimes also referred to as bimodal rainfall regime, March to May (long rains), October to December (short rains). The coastal strip adjoining Indian Ocean has one long rainy season from April to July with maximum in May.
This paper describes water balance of this area and runoff model of upper Athi basin.

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Radar rainfall gauge gives a better information of rainfall distribution than the conventional Thiesen method. In the present study, a system for the prediction of rainfall-runoff is constructed. This system includes packages to obtain a channel network from the digital map, to combine the radar rainfall information with the channel network, and to calculate the runoff using the kinematic wave model.
This paper described the each package of the system. And parameters of the kinematic wave model were obtained for 20 runoff events in 1990 and 91. Application of this rainfall runoff prediction system to dam reservoiurs is possible with several minor improvements of the system.

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The water balance analyses of the five lakes of Mt. Fuji were conducted for 1981-94. It was found that
1. Lake Kawaguchi seems to leak in the order of 20 mm/d.
2. Each lake has an Influence Aquifer Zone around it, which not only supplies water to the lake but often receives water from the lake when water level increased during the dry periods.
3. Three lakes Sai, Shoji and Motosu seem connected under ground by porous volcanic rocks Their water levels are highly interdependent.
4. Among the three lakes, Shoji and Motosu are more closely connected than Sai and Shoji.

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Sensitivity of the physiographic factors of the basin such as the terrain, infiltration, river geometry and size of the mesh used in numerical analysis, which cause the drawback in modeling, is investigated employing a practical approach. This is shown using a new physically based model which estimates both the surface and the subsurface runoff. Both runoffs are coupled simultaneously through the infiltration rate in which land uses and ground elevation of the basin were obtained using numerical remote sensing and GIS data via data processing, respectively. Results of this approach are promising.

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At Unzen Volcano, debris flows have frequently occurred in the Mizunashi River and caused severe damage in the downstream by depositing large amount of sands and stones. Therefore it is great important to estimate the amount of deposits for protecting the area from the disasters. In this study, the neural networks which can learn a general rule from given examples is used to estimate the amount of deposits due to rainfall. The results of the predictions lead to the conclusion that the neural networks is applicable to estimate the amount of debris flow.

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The statistics of a daily rainfall-runoff process are theoretically derived from the characteristic function of a filtered point process. The counting process of a point process (daily rainfall) is represented by one of binomial, Poisson, and negative binomial probability distributions according to the ratio of mean to variance. Marks of the point process are magnitudes of daily rainfall. As an pulse-response function a tank model is adopted. The application of the proposed model to daily rainfall-runoff data at Motoyama in Kochi Prefecture is shown.

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For analyzing and forecasting floods in urban small rivers, it is important to get precipitation in short interval and small area because of the characteristics of rapid runoff of floods. In this paper, we study spatial and temporal characteristics of short-term precipitation based on the data from the raingauges distributed densely on the urban small basins in Tokyo. We attempt to forecast the short-term rainfall by using spatial and temporal characteristics and showed the applicability of the forcasting method proposed herein.

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Stormwater runoff models using the dynamic wave method, diffusion wave method and kinematic wave method were applied to an urbanized lowland basin which was the pump drainage area of the Shinkomatsu River. The simulation was carried out for fourteen rainfall events in 1991. The results confirmed that the simulated hydrographs of the dynamic and diffusion wave method were shown to compare favorably with the observed hydrographs rather than the kinematic wave method. Further, it was found that the diffusion wave method was a proper model for an urbanized lowland basin, because of its shorter analyzing times and simple form of equations, compared with the dynamic wave method.

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An urban runoff simulation system that utilizes a GIS sewer data base has been developed and applied to a catchment in Kobe. The runoff analysis is based on the Storm Water Management Model (SWMM). The system provides an interface that allows actual sewer network data to be read from the data base and then to be transferred into the link-node format required by SWMM. In addition, the system facilitates the formulation, via computer mapping software, of SWMM-formatted data for drainage catchments which are not included in the data base. The system was applied to a drainage catchment in Kobe and acceptable results were obtained.

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It has been a great concern to minimize flood damage in the event of extreme rainfall beyond design level. In this paper, a structural method is presented with the concept that the urban drainage system must work properly to exclude stormwater in case of design rainfall events, while it should detain stormwater for a while to disperse inundation and reduce peak discharge into a receiving river in the event of extreme rainfall. To realize the concept, the hydrological effect of road detention and associated inlet structure are investigated.
The hydraulic function of the inlet, which comprises three phases of outflow depending on the water stage in front of the inlet, is modeled and numerical simulations are carried out to see its hydrological effect. The results showed that transversal road slope, length and the inlet configuration influence the efficiency of the road detention, and that it reduces outflow to 1/3 of incoming flow. The synthetic effect of road detention on runoff reduction is also computed in a small urbanized watershed using a distributed flow routing model.

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Snowmelt runoff analytical method consisting of three submodels is developed. These submodels are the model for estimation of basin-wide snow water equivalent as a function of snow covered area, the model for estimation of basin-wide snowmelt rate, and the runoff model. In each model the information on snow covered area derived from LANDSAT TM data is used. These models are applied to the Uono River Basin during the snowmelt season in 1989, 1993. The calculation are in good agreement with the observed data.

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The snowmelt runoff prediction using the fuzzy reasoning method has been developed. However, to improve the prediction accuracy, it is necessary to adjust the predicted hydrograph based on the level of prediction error.
In this paper, the fuzzy reasoning method with a function of predicted error correction is presented for the snowmelt runoff prediction. The applicability of the model is assessed and compared by making 3-hr lead time prediction of runoff in experimental basins. It is concluded forecast results by the use of proposed method have higher degree of accuracy in comparison with the snowmelt prediction model using only fuzzy reasoning method.

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This paper presents the performance of Xinanjiang rainfall-runoff model for a basin (524.9 Km²), of Yodo River catchment in Japan. The model has been modified to use the evapotranspiration values computed using the Energy Balance Method instead of the conventional pan evaporation method. This has been achieved by using the hourly precipitation and discharge observations in addition to the hourly evapotranspiration values. To compute the hourly evapotranspiration the Energy Balance method has been used which originally provides the daily values, therefore time distribution procedure for short wave radiation has been incorporated and AMeDAS data was used for the computations. The performance of Xinanjiang model was checked using hourly and daily data.

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The river flow is indispensable to the hydrologic cycle. But in the Atmospheric General Circulaton Model, the river flow is always ignored. So in this paper, we make a global river direction file for T21 grid resolution, at first, and then make a river routing model and calculate it. As input, we use runoff from the CCSR/NIES AGCM (T21 resolution). After calculation, we analyze the results of some world major basins by comaparing the results of model with observations. As a result of this paper, we reproduce seasonal changes of discharge better than before.

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An atmospheric general circulation model (AGCM) was used for the study of global hydrological cycle. AGCM used was developed by a cooperative research project between Center for Climate System Research (CCSR), University of Tokyo and National Institute for Environmental Studies. The results were examined referring to the observational data. Especially in the case of river basin scale, estimates from the combined atmospheric-river basin water balance method using ECMWF objective analysis data (1989-92) and GRDC were used for the comparison of water balance components. The seasonal change of total water storage in each basin shows a good correspondence between the AGCM simulation and the water balance estimation.

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The main objective of this study is to develop an methodology for estimating the water and heat transfer in a soil at a macro-hydrologic grid. Macro-scale formulas for a soil model, which include water and heat transfer, is derived from Philip and de Vries model and contain areal average terms and covariance terms of physical quantities. The sensitivity of model parameters is analyzed and a numerical simulation was examined. The major conclusions obtained here are as follows:(1) soil temperature profile doesn't change so much but the difference will have an effect on landatmosphere interactions.(2) soil moisture profile changes significantly and it will make a land surface heat budget modified.

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To reproduce real continuous records of river discharge from discrete discharge measurements, how long should we choose time interval for discrete discharge measurement?This time interval represents the time for describing a hydrological response and it can be considered as a time scale of a hydrological response. In this study, to find out a time scale of a hydrological response and a relationship between the time scale and the catchment scale (catchment area), we analyze river discharge time series data in the Yodo River basin using the Fourier transform method and the sampling theorem. As a result, between a time scale Δt (hour) and a catchment scale A (km²), a relationship, Δt=pexp (q√A) is obtained, where p=0.6 and q=0.026.This relationship shows that Δt for a basin with 300 km² area is about 1 hour.

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Recently, Digital Elevation Models (DEMs) can be often used in the analysis of catchment topography and hydrological process. Some methods that extract drainage networks from square-grid DEMs are proposed. They make use of the flow-accumulation-value threshold for extracting drainage networks from delineated overland flow paths, but the relationship between chanel length, L, and catchment area, A, of the external link in the drainage network from DEMs is different from that of actual drainage networks. This paper proposes a new threshold, which is defined by the ratio of the width, w, to the penetrated length, l, in a contour line.As a result, it shows that this relation is improved. Furthermore, we examine the hydrologic response of both drainage networks, and represent effects of the threshold for this response.

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The objective of this study is to develop an algorithm to compute hydrologically sound, grid-based digital elevation model (DEM) from contour line data. Three commonly used methods, profiling method, bivariate interpolation and inverse distance method, are compared with respect to not only the interpolation accuracy but also occurrence of the spurious pits which make hydrological modeling difficult. From the result of this comparison, a new method is developed based on the profiling method by taking into account the position of valleys and ridges. In delineation of channel network and development the distributed hydrological models, the DEM derived by using this new method reduces the spurious pits significantly.

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A drainage basin consists of hillslopes and channels. Hillslopes are the main regions at which rainfall is converted into runoff discharge and channels are the region where the runoff discharge from subbasins is synthesized and transported to the outlet of the basin. Hydrologic response is influenced not only by hillslope response but also by channel network response. The properties of hillslopes and channel networks such as slope length, slope gradient and distance from sub-basin to the outlet are best described by statistical method. This paper aims at evaluating stochastic hydrological response by intro-ducing random differential equations.

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Regarding the runoff system as a set of dynamic elements which communicate with one another, we develop a new system for modeling the runoff system.
In our system, the basic and common operations in runoff simulation, such as initialization of states, giving the values of parameters, giving and receiving data, setting time steps, are standardized and modeled as functions of the “base model” of runoff elements. The users only have to derive their Models from the “base model” and do not need to write the codes for the basic and common operations as stated above.
Our system is so flexible that it can treat various types of communications among elements. As an example, a model for simulating the flow in a river network is shown.

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In the alluvial channel, water temperature may be analyzed as a quasi-uniform longitudinal profile. In the upper stream, water temperature must be analyzed taking into account of both time and longitudinal variation. This paper describes the formation process of stream water temperature along channel course in a upstream using the observational results. Simul-taneously, water temperature at a point in lower reach is analyzed. For the both cases, solar radiation and heat exchange between the stream bed and atream water play important roles. The differnce between maximum and minimum temperature reaches 6 °C: at lower reach in summer.

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In general, the sea and land breezes are said to have a much effect on the heat island convection. The characteristics of sea and land breeze, however, depend much on daily larger scale conditions, such as the mesoscale pressure distribution. Thus it is needed to tolerate the local heat island phenomena. This study is, therfore, aimed firstly at investigating the existing sea and land breeze effect on the heat island phenomena in this area, and then at evaluating the effect of geostrophic wind on the convection.

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In this paper, we investigate the effects of land-use scale on regional mean heat fluxes and the validity of the heat flux pa-rameterization by using fractional area. We use SiBUC for the land surface processes and LCM for the atmospheric circulation. As the simulation domain, we choose the periodic pattern of two land-use conditions (forest-urban, urban-water, and forest-water).
As a result, the scale effects appear differently depending on the combination of the land-uses. And the heat flux parame-terization based on fractional area is not valid when the domain includes water body and urban area.

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This paper investigates the behavior of the sensible heat exchange between the top of the canyon and outside atmosphere using a numerical model together with available field measurement data in a mid-latitude city. It was found that the heating characteristic of the urban canyon has close relationship with the narrowness index and outside wind velocity. The increase of the narrowness index and consequently, reduction of the sky-view factor leads to the reduction of sensible heat exchange between urban canyon and outside atmosphere. The increase of outside wind velocity makes the sensible heat exchange between the street canyon and outside atmosphere larger, and consequently cooler the urban canyon. A parameterization scheme was established which permits the evaluation of the sensible heat exchange between urban canyon and outside atmosphere based on the narrowness index, outside wind velocity and latitude of the city.

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The moisture and heat transfer in the SPAC' are studied by establishing a coupled full-interacting physical SPAC model. A vegetation model which preserves the essential mechanisms is employed to describe the vegetation as simply as possible. The required input data in atmosphere are limited to only four, being net radiation, wind speed, vapor pressure, and air temperature, so that the present method can be easily applied in practical problems. Finally, the present model is verified by a field observation.

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A cold air flow which is called a “Land Breeze” often appears within Ishikari Bay in winter seasons. The flow goes down from the cold mountain area to creep into the com-paratively warm surrounding atmosphere. It is known that Sapporo has a heavy snowfall when a cold flow generates to develop snow cloud within Ishikari Bay. The present study attempts to analize the stretch and the vertical shape of a cold air flow by using the one dimensional two layer model. Stability for the cold air layer is also discussed.
As a result, it is found that the stable frequency domain becomes wider when the inner Froud number becomes greater and the ground slope becomes smaller. And by considering the thermal effect, a stretch length and a vertical shape of the cold air layer could be derived; they agreed qualitatively with the observed data obtained with Doppler Radar.

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The heat and moisture transfer between bridge road surface and atmosphere is explored from indoor experiments and survey on a real bridge road, in order to prevent bridge road freezing. It is observed that the surface temperature of the real bridge road is mainly affected by the sky radiation, the road surface long-wave radiation and the pavement heat conduction, when the wind is weak.
Finally, the reason, why a steel bridge road is apt to freeze com-pared to a concrete bridge road, is discussed from the time change of the heat energy budget and of the internal energy of the bridge floors.

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Atmospheric environment and related thermal comfort on beaches in summer are significant factors for coastal space design to provide desirable amenity environments. Through a micrometeorological field observation conducted in summer on Makuhari Beach facing Tokyo Bay, we found that;(1) an internal boundary layer of see breeze was clearly formed on the beach, (2) the beach surface with dry sand has appreciable effects of heating and drying on the surrounding air body, and (3) three physical comfort indices DI, SET^* and HS calculated with the observed data show that the sandy beach and its surroundings provide a highly contrasted spatial structure in thermal comfort.

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The purpose of this study is to estimate evapotranspiration in a wide area using a correlation relationship between NDVI and evapotranspiration. Factors which control evapotranspiration can be considered that these are reflected by the vegetation condition.In order to grasps the vegetation condition at some point, NDVI calculated from NOAA-AVHRR data is utilized. A land cover classification is performed in Korean peninsula using a seasonal variation of the NDVI, and the relationship between NDVI and evapotranspiration is estimated for every land cover category. Then, the dis.tribution of evapotranspiration can be estimated in Korean peninsula including North Korea where meteorological data are unavailable.

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In this paper. results of the application of the new method for estimating regional evapotranspiration rate using NOAA-AVHRR data to the areas of central Japan are presented. The method has the following advantages; 1) the estimation procedure is reasonably simple - based on a pixel of an area, 2) surface soil parameters and aerodynamic parameters need not be assumed, and 3) daily averaged values of evapotranspiration can be calculated from a pair of instantaneous, remotely sensed images. The results of the application at the areas show that the method has good potential but need more precise local meteorological data.

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The Richards equation is adopted as a fundamental equation for the solution of unsaturated infiltration flow. At the first stage, a new boundary condition has been introduced and its accuracy has been cross checked with experiments. At the second stage, on the lumping process of non-dimensional form of Richards equation, a compensation factor has been proposed to equalize the semi-lumped equations. Finally, the relation between storage and discharge has been achieved by fully lumped equations.

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The hydrochemistry of the Tsukuba experimental forest (67.5ha) has been observed since 1985, including rainfall, throughfall, stemflow, soilwater, groundwater and streamwater. The annual water input by rainfall and output by streamwater averaged during 7-year water cycles were estimated to be 1656mm and 849.7mm, which gives the rainwater runoff rate to be 51.3%.
As to the streamsolute, the nitrate concentration tended to be raised with increasing streamwater discharge and temperature in summer season every year, and such coincidence in the rise of concentration and discharge produces a large amount of runoff loading in summer. Contrary to this, the dissolved silicate of streamwater reduced the concentration in summer. The difference between both streamsolute behaviors is reasoned to be driven by the runoff of soilwater, which keeps the nitrate. concentration higher and the silicate lower near surface due to the element cycle in the forest ecosystem.

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Runoff and contribution of dissolved organic matter to stream chemistry were examined in Motoki Brook draining small forested watershed in Sendai.Dissolved organic carbon and the absorbance at 260nm raised their concentrations in the brook during episodic events.It was considered that leaching components from the litter layer mainly influenced to it as a source of organic matters.From results of calculation about ion-balance, it was assumed that dissolved organic matter had a role of organic anion in the brook.Chemical aluminum fractionation indicated that dissolved organic matter directly contributed to the runoff monomeric aluminum to work as organic ligand.

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The objectives of this study are to simulate pollutant runoff from a small river basin in an urban area by using Water Quality Tank-Model, which can simulate it from a large river basin correctly, and to evaluate its accuracy for an urban river. As a result of the simulation, it was proved that Water Quality Tank-Model has a certain accuracy on solid pollutant in an urban area, but has less accuracy on soluble pollutant especially on soluble nitrogen. However, it was also proved that Water Quality Tank-Model could calculate integrated runoff pollutant load during a storm event, which was very significant especially in an urban river. In the result, it was cleared that a little more improvement made Water Quality Tank-Model more available to apply for the analysis of pollutant runoff from a small river basin in an urban area.

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This paper discusses field observation and model results for temperature and salinity in Myojin-ike, a group of saline lake. Myojin-ike is itself composed of three smaller interconnected basins, the largest of which is connected to the sea of Japan. Water temperature and salinity observed 0.5m and 3.0m below water surface showed abrupt variations like a step function during November to December 1985. This phenomenon is investigated in relation to the water movement in the lake.

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The flow in the brackish lake with nearly closed basin was measured by the use of an Acoustic Doppler Current Profiler (ADCP). The circul atory flow inherent to this basin which has not been observed so far was measured by ADCP.
The numerical model was developed to explain well the flow field in the brackish lake, except for the circulatory flow.

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A field experiment was planned and carried out in the catchment area of Shichigashuku Reservoir in order to study the transport of fine suspended materials (wash load) contained in flood water. In data processing, focus is made on the difference of behavior between relatively coarse component and finer one: A careful check is made on the conservation of each component by time integration of its flux across the measuring stations so that sorting process at the upstream end of the reservoir is clarified. The most interesting output of this study is that a percentage of relatively coarse component has a peak with a time lag of few hours after the peak of flood discharge.

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The effect of updraft to precipitation processes is investigated numerically. We use the numerical simulation model which has detailed cloud microphysics and represents cold rain processes. We recognize that the relationship between updraft and rainfall amount is not monotonous. This relationship is explained by referring the results of simulation that the hail occasion is important for heavy rainfall. We supporse that there is suitable updraft strength to cause heavy rainfall and that heavier updraft does not cause heavier rainfall. This supposiotion is qualitatively confirmed through comparison with rain gage data at Gozaisho-yama, Shiga Prefecture.

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Rainfall mesurements uisng weather radars have becoming very popular in these days. However, there are several problems in the procedure of transforming observed radar reflection factor into rinfall intensity. Especially, the identification of radar constants B and β, which represent the relationship between radar reflection factor and rainfall intensity (Z-R relation), is very important.
The radar constants B and β are generally determined using the correlation between radar reflection factor and observed surface rainfall. B and β are influenced by various factors such as weather condition, topographical effect, spatial scale of observation and so on.
In this paper, a new method to identify the optimum radar constants B and β based on the runoff analysis using discharge data, is proposed. The surface rainfall is mesured at only one site. But the discharge is a integration of all the rainfall in a basin. Therefore it is convenient to identify the radar constants taking account of runoff data.

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Macro-scale hydrological models have been investigated for the purpose of introducing the effect of land surface heterogeneity to the GCM. The shortwave radiation budget, which is one of the most important components, is influenced by the topography as well as the surface albedo. Generally speaking the topographical effect on incident solar radiation is expressed by using inclination and aspect of a slope. This paper evaluates the difference between the insolation receiving rate using only averaged inclination and aspect on the grid scale of a GCM and one by using the variance and co-variance as well as mean values. The difference is related to a area-wise parameter to give the effect of topographical heterogeneity on shortwave radiation budget.

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When we deal with the unsaturared flow problems from a microscopic standpoint, the evaluation of the soil fabric becomes important as well as the determimation of particle size distribution. In this paper, we derive the distribution of the porosity of soil. Moreover, the distribution of coordination number was determined by using this distribution. This method is based on the ideal soil of homogeneous sphere.

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The effects of wind on the heat exchange between sand surface and atmosphere are examined by using a wind tunnel fixed sand column. The water vapor flux generated by the evaporation in the sand column subjected to the wind is expressed as the sum of the molecular diffusion flux and the mechanical dispersion flux. A change of the heat balance at the sand surface is caused by the wind velocity adjusted and is mainly affected by the sensible heat, the latent heat due to the evaporation and the soil heat conduction.

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To evaluate the water budgets of sand dunes, soil water content was observed at Desert in China. A bare and vegetated dune area were selected for observation. Soil water content of the vegetated field was lower than that of the bare field because of water uptake by plant roots. Because of lateral flow along the slope, soil water content at the bottom of the dunes increased a few days after rainfall, especially for bare surface. The Eulerian correlations were calculated and the results indicated the lateral water movement along the slope.

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The authors developed a formulation and solution for discharge of each aquifer in a multi-layered aquifer-aquitard system including the resistance of a well casing and leakage between each aquifer. Numerical solutions for two field pumping tests are carried out. One is unsteady flow caused by pumping up from a two-layered confined aquifer system. Another is an unsteady flow caused by pumping up from a well in a peddy field area considering leakage through an aquitard.
The observed drawdown in a well and seepage rate into a well from each aquifer determined by vertical velocity measurement in a well are in good agreement with predicted results.

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A mumber of rock caverns due to the water-seal system have been constructed to store a large amount of fuels like oils and liquified propane gas (LPG). The water-seal system is one of the most powerful techniques for piling the fuels through groundwater barrier. This paper studies key points of water-seal hydraulics theoretically and experimentally. This is focused on:(1) mechanism of water-seal system, and (2) gas penetration process after gas leakage. According to the results of the present study, it is suggested that the design depth of caverns is specified not only by hydrostatic pressure but also by capillary pressure and threshold pressure of gas penetration in wetted rocks.

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The experiment on leakage through concrete crack was carried out to grasp the leakage characteristics. In this paper, a turblent infiltration theory to estimate the leakage discharge through concrete crack was developed from several experimental results. The characteristics of the experiment was in good agreement with the calculated results by the present model when the crack width was more than 0.1mm and the Reynolds number was more than 50-60.

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