Recently the issue of acid rain and acid snow is deeply concerned as one of the global environmental problems. Many prediction models for acid rain have been developed. However most of them are using the parameterized cloud microphysical processes so called bulk method. The size distribution of cloud droplets is important for considering the transportation and transformation of acidic species among each water phases. The size distribution of cloud droplets is calculated by detailed microphysical processes so called bin method. Therefore in this study we developed the prediction model for acid rain and acid snow by using the detailed microphysical processes. Moreover we also investigated the mechanism of acid rain and snow by using the developed model.

View full abstract

Cloud droplets grow on cloud condensation nuclei (CCN) with condensing the ambient water vapor in the atmospheric air parcel. The size of the cloud droplet in the equilibrium state is estimated usually by Köhler Equation. However, Köhler Equation is based on the assumption that the cloud droplet grows in an infinitely large reservoir of water vapor at constant pressure, i. e., at constant saturation ratio. This assumption causes some erroneous results in the estimation of real size in the air parcel, although the assumption makes the calculation easy. There are two apparent deficiencies in Köhler Equation. One is that the equilibrium size cannot be decided in case of the larger saturation ratio than the critical ratio. The other is that the variation of the size with the number density of CCN, i. e., the competitive growth, cannot be considered in the estimation of the size. In order to improve these deficiencies, the conventional Köhler Equation has been modified using the mass conservation of the water contained in the air parcel.

View full abstract

The purpose of this study is to analyze the relation between rainfall distribution and topography using three dimensional rainfall information of weather radar. By analyzing the distributions of three indexes of accumulated rainfall amount, accumulated rainfall time and average rainfall intensity, it is made clear how the mechanism of topographic effects on rainfall distributions is different between the types of rainfall, stratiform rainfall and convective rainfall. Additionally the three dimensional properties of topographic effects are quantified using Dependence Line on Topographic Elevations (DLTE), which represents dependence properties of rainfall distribution on topographic elevation.

View full abstract

It is quite difficult to predict a local severe thunderstorm formed under a pacific high pressure because of the shortage of observational systems. Recently, the technology of the estimation of precipitable water using GPS, expected for the local severe thunderstorms, has been developed. In this study, a numerical local circulation model was applied for a sea breeze circulation in order to make sure the relationship between precipitable water and water vapor in the lower layers, directly associated with atmospheric instability. These results show that an increase in precipitable water has directly responsibility to the accumulation of water vapor in the lower layers due to convergence along the sea breeze front. This makes the atmosphere above the sea breeze front more and more unstable and leads to the subsequent generation of thunderstorms. Therefore, the water vapor existed in the lower layers as well as precipitable water becomes quite significant clue for the generation of thunderstorms affected by an atmospheric local circulation in summer.

View full abstract

A Method of estimating spccio-tcmporal averaged rainfall with TRMM observations is developed A point of the method is that a dependency of rainfall distribution on topographic elevation is taken into consideration. Also both analytical and statistical evaluations of accuracy of the estimates are carried out based on stochastic specio-temporal structure of rain field and actual applications of the method into radar-observed rainfall distributions during 43 monthly periods, respectively. As results, the analytical evaluation almost agree with statistical one, and introducing the dependency of topographic elevation improves the accuracy of estimation of monthly rainfall averaged over a circle region with radius of 120km.

View full abstract

The purpose of this paper is to bridge the gap between the observations by surface rain gage and by ground based radar using TRMM/PR information, in order to extract qualitative information on surface rainfall distribution in mountainous regions as characteristics of horizontal rainfall distribution. First, TRMM/PR information was verified using a conventional radar and ground observations. Then, the horizontal distribution and the vertical profile of the radar reflectivity observed by TRMM/PR corresponded to the distributions of the ground based rainfall radar very well. Next, the vertical structural analysis of rainfall was performed using TRMM/PR. As a result, there is a linear relation to rainfall intensity and an altitude, and it was sho

View full abstract

The objective of this study is to develop an algorithm for quantitatively estimating snow hydrological parameters using a Synthetic Aperture Radar (SAR) mounted on a satellite and a numerical scattering model. Simultaneous RADARSAT SAR observations were carried out during the winter seasons of 1996 to 1998. The study area is located in the Hokuriku District, Niigata Prefecture, Japan, that is well known for having wet snow with a complicated layer structure from the beginning of the winter season. In previous studies, we sought to estimate the distributions of snow depth and surface roughness using these multi-temporal RADARSAT images. However, snow depths over 20cm were underestimated because the extinction effects at C-band microwave were too large. In this study, we develop an algorithm to estimate distributions of snow density and roughness using observation datasets with some parameterization techniques and assumptions. Furthermore, we show the possibility of inferring snow depths from combined parameters estimated with a L-band SAR image at test sites.

View full abstract

As an ideal soft-countermeasure to reduce the damage caused by debris-flow, a real-time alert system is necessary for rapid evacuation of people. This study evaluates feasibility of using effectively radar-measured rainfall data for the real-time alert system. For this purpose, two cases of debris-flow disaster in Hiroshima prefecture were selected. Data sets of AMeDAS, radar and telemetric ground rain gauge were employed to examine usability of radar data (accuracy), and propagation characteristics of heavy rain in particular their development, decayment and their interaction with topography. The orography effect is evaluated by comparing the forecasted and radar measured rain intensity by using the method of cross-correlation function.

View full abstract

Remote Sensing observations could aid in estimating the land surface temperature (LST) by providing spatially representative data for surface characteristics and fluxes. Operational technique to derive temporal variation of LST using a modified Priestly-Taylor equation, which relies primarily on remotely sensed inputs, is described. A method allows extrapolating one time of day LST estimates continuously to values during the day. Meteorological data and NOAA-14 AVHRR observations were used to modeling LST maps over the Natori river basin in 1992. Model-computed LST values were in reasonable agreement with satellite-retrieved surface temperature map, where Channel 4 of the NOAA AVHRR images was available twice a day.

View full abstract

In order to investigate the water balance, rainfall infiltration, runoff, evapo-transpiration during plants growth, hydrological observations have been carried on using weighing lysimeter under the conditions of planted crops. Soil moisture content and sap flow of plants are measured using Amplitude Domain Reflectrometry (ADR) probe and stem heat balance method (SHB), respectively. Leaf area and dry weight as the index of plant growth is measured, periodically. This paper describes the water balance and the evapo-transpiration based on these observed results and the results of vertical two-dimensional analysis of soil moisture movement considering the changes in the evapo-transpiration during the plant growth.

View full abstract

A new technique for the in-situ measurement of the transpiration from a tree was proposed in this paper. This technique is composed of the following two points:(a) application of two-sensor type evaporation meter to the transpiration measurement from leaves of tree (b) estimation of total transpiration from a tree. Transpiration from some kind of trees such as mango, rubber and mulberry could be successfully measured. Total transpiration from a mango tree was also well estimated by the technique. It was concluded that the technique can be widely used not only in Japan but also in South East Asian countries.

View full abstract

Mesoscale circulations induced by differential boundary layer heating due to surface inhomogeneities on scales of 5km and more can significantly change the average properties and the structure of the convective boundary layer (CBL) as well as trigger off temporal oscillations. The results of one of the first numerical case studies using Large-Eddy Simulation (LES) on the mesoscale suggest that mesoscale circulations exhibit a considerably larger average kinetic energy than convection under homogeneous conditions.
This case study uses the Hannover LES model PALM with prescribed 1D sinusoidal surface heat flux variations on wavelengths from 2.5 to 40km. The resulting mesoscale circulations are analyzed by means of domain-averaged cross-sections, time averaged and normalized with the boundary layer height, as well as domain-averaged time series.
The simulated mesoscale circulations were periodic. Vertical profiles and time series demonstrate mat the onset of the mesoscale circulation triggers off a temporal boundary layer oscillation, whose period and amplitude depend on the surface heat flux perturbation wavelength and amplitude and on the background wind component perpendicular to the surface inhomogeneity orientation. A hypothesis of the oscillation mechanism is briefly discussed.

View full abstract

Large-eddy simulation has been conducted for flows over real topography in stably stratified atmosphere based on the Boussinesq approximated LES equations of motion and temperature equation. The basic method is first applied to flows over ideal isolated three-dimensional hill and its capability and accuracy are examined. Reasonable agreement with experimental results is obtained with standard Smagorinsky type models for the both subgrid stress and subgrid heat flux. No explicit representation of the buoyancy effects on the subgrid stress was used. The results applied to the real topography over a mountainous region also appear plausible.

View full abstract

Using the data of the continuous field observation at residential site in Tokyo from March 2001, following results are obtained; 1) The existence of constant-flux layers for momentum, sensible-heat and latent-heat flux above the urban area are confirmed. 2) The probabilities of constant-flux layer achievement (C. F.-rate) are 32.5%, 51.1%, 43.9% and 17.0%, for momentum, sensible-heat, latentheat and carbon dioxide flux, respectively. The C. F.-rate for all fluxes simultaneously is only 0.9%. 3) In this observation site, the C. F.-rate is less affected by the wind direction but slightly related to the atmospheric stability. 4) When a large-scale turbulence or front passes through a sensor, the sensible-heat flux ratio of 29m to 21m is diverted from 1.

View full abstract

The relation between the urban structures and radiation processes within 3D canopy layers has been investigated through the experiment by using small-scale models. Concrete blocks (15cm×15cm×15cm) were regularly arranged and the built-up densities were systematically controlled. As a consequence, the following results were obtained;
(1) Canopy albedo are significantly influenced by urban structures and seasons. There exists an urban density which gives a minimum values of canopy albedo in each season.(2) The four kinds of representative urban temperature, that is, complete temperature, radiation temperature, satellite temperature and aero-dynamic temperature are compared, and their dependency on canopy densities are discussed.(3) The contribution of heat transfer of each surface is shown.

View full abstract

Land-surface parameters of urbanized terrain are evaluated based on the field measurement data. Following results are obtained;(1) The value of momentum roughness length (Z₀) is 1.56m and it is greater than the heat roughness length (z_T) and water vapor roughness length (Z_q). The ratios kB_T^-1=ln (Z₀/Z_T) and kB_q^-1=ln (Z₀/Z_q) are 8.0 and 20.5 respectively.(2) The value of evaporation efficiency (β) is 0.05-0.2. After precipitation β is significantly decreasing with time for a few weeks. Evaporations from vegetation and concrete material are estimated respectively. Vegetation has a potential to emit latent heat as much as net radiation due to the oasis effect. Concrete material has a potential to cover the β variation range over residential area. When horizontal wind velocity is large, β is decreased.(3) The averaged value of albedo is about 0.13. When there is rainfall, albedo is decreased. But the value is back to about 0.13 within 2-3 days.

View full abstract

The spatial representativeness of turbulent fluxes on the basis of point measurements has been investigated through a theoretical approach and numerical experiments using Large Eddy Simulation (LES) Model. These investigations have been done for the daytime atmospheric boundary layers heated uniformly over the flat surface with no synoptic vertical motion under several geostrophic winds from 1 to 4 (ms^-1). The following results were obtained;
(1) The spatial representativeness of turbulent fluxes based on the time-series analysis are shown to be problematic: Their horizontally averaged value has a negative imbalance irrespective of the density of measurements points, and their spatial variability increases, in accordance with averaging time, or under lower horizontal wind.
(2) The imbalance intensities are closely related to turbulent organized structure (TOS). The points over the updraft regions are likely to have positive imbalance due to highly activated thermal plumes. The temporal and spatial change of TOS pattern cause low-frequency trends in time-series data, which can account for the large horizontal scatter of flux estimates.
(3) High-pass filter excluding the temperature trend is theoretically useful to improve the representativeness of point measurements, although the filter choice actually needs a great care not to damage the turbulent components.

View full abstract

Southern Oscillation (SO) is an atmospheric see-saw phenomenon in tropical Pacific sea level pressure between the eastern and western hemispheres associated with the El Niño and La Niña oceanographic features. The oscillation can be characterized by Southern Oscillation Index (SOI) which is derived from values of the monthly mean sea level pressure difference between Tahiti and Darwin, Australia. The impacts of SO on climate are widespread and extend far beyond the tropical Pacific, a phenomenon known as teleconnection.
In this study, long-term fluctuation characteristics of SO are presented as guidance when using SOI for other analyses. The results show SO intensity (i. e., cross-correlation of Tahiti and Darwin pres sure deviations) is increasing almost constantly since around 1900. The reasons of increase of SO intensity are also investigated statistically in detail.

View full abstract

Interannual variability and potential predictability of seasonal mean water resources is investigated based on the SST-forced ensemble seasonal atmospheric forecast using Japan Meteorological Agency global model. The ensemble consists of four model integrations with different atmospheric initial conditions with the same sea surface temperature. The interannual variability of water resources (residual of Precipitation to Evapration: P-E) are not simulated well especially for the rainy season over the selected four regions of Asia. Howere, the ensemble mean of the seasonal atmospheric forecast could contribute to the seasonal water resources at some regions. The potential predictability of P-E is largely low at the land areas in from mid-to high-latitude. It is lower than that of precipitation in North Africa and central Eurasia continents.

View full abstract

Daily weather records of old diaries are useful for investigating hydrological environment in historical days. In this paper, we collected daily weather records from 8 old diaries of 18-20^th centuries in Lake Biwa area and attempted to use them for evaluating the intensity of historical droughts in Lake Biwa area. Annual maximum duration of continuous no-rainy days and annual minimum PI (Precipitation Index) for 30, 60, 90 days, which is calculated by summing up the number of rainy days for 30, 60, 90 days with the weights of ‘small rain:rain:heavy rain=1:2:5, ’ were calculated for each diary, and the intensity of some serious drought were quantitatively evaluated.

View full abstract

The possible trend and jump in hydrologic time series, due to climatic change, is investigated in this paper. The detection is accomplished by using both parametric and nonparameiric statistical tests. The analysis is made to two regionalized datasets: 115-year annual temperature over 6 climatologic stations and 103-year annual precipitation over 46 rain gauges in Japan. Both long-term trend and jump temperature data are detected, and the results indicate that the annual temperature increases 1.33-Celsius degree due to climatic change in Japan over the past century. Although it still needs further study on the variability of precipitation te series, both two kinds of above variations in annual precipitation seem also exist. The relationship between the current length of hydrologic time series and the possible length of time series required for detecting jump is investigated. These conclusions may provide some useful insights into the issues related to the hydrologic frequency analysis.

View full abstract

Although both temporal and spatial scales of heavy rainfall and flood disasters are different from drought's, it is same for these disasters that spatial distribution of precipitation is more useful than point precipitation that is observed at each observation point. This means that clarifying the special correlation structure of precipitation is required regardless of the scales for investigating these disasters. The authors obtained results as follows; 1) correlation coefficient of precipitation during more than one day increases when a period of accumulation increases; 2) starting point from which cumulative precipitation is calculated often affects strongly to the correlation. Moreover, results for the cumulative precipitation whose time scale is less than 24 hours are as follows; 3) the correlation weakens if a criterion of heavy rainfall increases; 4) when the duration is relatively long and the criterion is large, there is a possibility that heavy rainfall or flood disaster occur due not only to the precipitation depth itself, but also to the strong correlation.

View full abstract

A rainfall spatial variation scale to be considered in a runoff simulation will be investigated using meshtype rainfall data and a distributed runoff model. At first, a runoff simulation is conducted by using a mesh-type rainfall data as it is, and the result is regarded as a standard result. As the next step, the rainfall data is averaged in some area and a runoff simulation is conducted by using this averaged rainfall data. If we have little difference between the standard result and the result obtained by using the averaged data, we do not have to explicitly consider the rainfall spatial variability in the area where the data is averaged, and we have only to use the average rainfall data as an input data of the simulation. Conversely, if the difference is large, we have to consider the rainfall variability in the averaging area when conducting a runoff simulation. These numerical experiments indicate that it is important to find out the rainfall spatial variability which affects the results of runoff simulations and the scale changes with basin size.

View full abstract

Macro scale distributed hydrological models simulate river discharge with better accuracy but it depends upon the grid resolution of input data. Effects of different input resolutions are studied here. Three different grid resolution input data obtained from HUBEX-IOP EEWB data and GAME Re-analysis data are used to simulate river discharge and compared against the observed one. GAME Re-analysis 1.25-degree resolution data are found quite satisfactory in larger basins, while HUBEX-IOP EEWB 10-minute resolution data are better for small catchments. GAME Re-analysis 2.5-degree resolution data did not give good result. Simulated results by using spatially interpolated data are rather worse than using original data. The Huaihe River basin (132350km²) is taken as the case of study.

View full abstract

An application of Equivalent Frequency Transfer Function (EFTF) was applied in this study. This EFTF has originally been used among control engineers to analyze non-linear elements; for example threshold and saturation elements. Previous study by the authors had successfully derived the EFTF between rainfall input and discharge for real catchment area based on kinematic wave model. This study developed application of EFIT by using diffusion wave model with zero gradient of depth downstream boundary condition. Gain, time lag characteristics and vector locus are proposed in order to investigate efficiency and effectiveness of EFTF. It is also able to extend this technique to multi element basin.

View full abstract

The storage-routing approach has been successfully applied to the rainfall-runoff processes in subbasins as well as flood propagations in channels. We additionally propose the new approach, which can take into account the surfacesubsurface runoff as well as groundwater runoff in the subbasin runoff modeling, using the two-cascade storage routing model. The two runoff components can be separated via use of the numerical filter so that the optimal parameters of each component can be independently identified. Especially, the parameters of groundwater runoff component can be automatically determined by the known parameters and hence computational burdens can be significantly reduced. We show that the proposed approach can remarkably improve the reproduction of flood hydrographs, when the flood flows are routed through both of subbasin and channel phases.

View full abstract

Two-dimensional runoff analysis with rect-linear finite differential scheme or one-dimensional runoff analysis with more complex finite differential scheme has been studied. We propose triangle scheme that covers ground surface to make a numerical model of the ground surface topography and strata structure. The ground surface is covered by point-polygon system and the vertexes of a polygon are defined at the gravity centers of triangles surrounding the point. The topography and strata structure are explained by the elevation of ground surface and boundary of each stratum. The depth is defined at the point and the flux is defined at the gravity center of the triangle. Based on the arrangement of variables, two-dimensional runoff analysis can be done. We apply kinematic wave theory to the triangle scheme and show an example of calculation.

View full abstract

A mountainous drainage basin with forested soil is considered as a lowpass filter. Unsaturated flow equation is frequently substituted for runoff system in a mountain slope. This substitution is based on the analysis of actual rainfall-runoff phenomena there. This paper adopts a two-dimensional unsaturated flow equation as runoff system and theoretically derives its equivalent frequency transfer function. The validity of the proposed function is cross-checked by a simulation method. By using this function, it is possible to estimate a gain characteristic of substituted runoff system. The analytical result using frequency response method by the gain characteristic shows the response characteristic of this system for arbitrary rainfall input.

View full abstract

In this study, the accuracy and stability of a subsurface flow model previously reported by the authors was examined. The model is based on splitting the flow continuity equation into vertical and horizontal components. Vertical flow is computed by Richard's equation in the unsaturated zone, and lateral flow is computed by Darcy's law, assuming that most of the lateral flow occurs in the saturated zone. In joining these two parts of the continuity equation, a systematic error occurs, but this can be reduced by introducing a correction factor to the height of the vertical flow results. Use of this factor also improves the stability of the model, which is stable for most natural groundwater conditions.

View full abstract

Resistance on DNAPL droplets settling in a saturated porous medium and DNAPL migration behavior through a saturated pore is experimentally investigated in this paper. Motion of a settling droplet is described by an equation, which is similar to that for a rigid solid sphere settling in an infinite liquid medium. A correlation between droplet Reynolds number (Re) and comprehensive resistance coefficient (C_R) is established for each droplet size. The results indicate that a settling droplet wobbles throughout its motion in a porous medium. Equivalent DNAPL thickness (h) in a saturated pore just before and after snap-off is correlated to pore neck area in rectangular and triangular pores. It is found that the power and linear relations hold well in the former and latter cases respectively within the data range of this study. Three different stages in DNAPL migration through a saturated pore are observed. The results indicate that the migration behavior depends on both pore geometry and DNAPL physical properties.

View full abstract

In order to protect sandy beaches from erosion caused by waves, a Beach Management System (BMS) is planned in some areas along the Japanese coast. In order to predict the flow in the extended unsaturated zone due to increased drainage, numerical simulations were carried out for a laboratory aquifer and the cross section at a test site in Chiba Prefecture, Japan. The numerical simulations revealed that the unsaturated zone extends below the sandy beach and that salt and fresh water mixed around the drainpipes.

View full abstract

Land development often leads to adverse environmental effects. It is therefore important to assess the potential change in regional hydrologic cycle due to surface alteration in advance. A rainwater recharge model, that is to be combined with the quasi-threed imensionaul nconfinedg roundwater flow, is proposed in the presentp aper.
The water balance in the catchment of the planned campus of Kyushu University is evaluated by the present schemew hiche nables to simultaneously calculate both the surface runoff and groundwater flow. The resultso btained in the present paper indicate that the calculated monthly and annual runoff agree well with the observed discharge.
Besides, it is also shownt hat the variation of the groundwatetra ble can be accuratelyc alculated.
On the other hand, however, it is revealedt hat the calculatede vapotranspiratiorne mainsu ncertainb ecause of the lack in the information of accurate potentiale vapotranspiration. Some attempts are presented in order to improve the calculation of the evapotranspiration.

View full abstract

For the large-scale 2D and quasi-3D groundwater flow numerical simulation based on FEM, spatial discretization scale has significant influence on the result of simulation. A large element size may result in inappropriate local water balance, and then lead to spurious oscillation. Although Zhang et al.(2001) showed the criterion on “time step” to avoid the spurious oscillation for the fully implicit quasi-3D groundwater flow finite element scheme, the criterion of “spatial scale” against spurious oscillation in quasi-3D groundwater flow finite element solution has not been given. In this paper, the criteria to select spatial scale L for the 2D and quasi-3D groundwater finite element schemes are derived based on Zhang et al.(2001), and the effects of spatial scale on spurious oscillation solutions in the finite element solutions of 2D and quasi-3D groundwater flow models are discussed using two examples.

View full abstract

The characteristics of surface-subsurface water interaction in a river with sandbar are threedimensional. The exchange phenomena at the surface-subsurface water interface are still unknown. An investigation has been carried out by tracer experiment and vertical 2D (V2D) simulation at the interface with various bed shapes and hydraulic conditions to understand the phenomena as well as to delineate the subsurface water and groundwater components. The flow properties at the surface and subsurface zone are verified by 1D Darcy theory. A line, which separates the subsurface and ground water components, is determined for individual cases. The experiment as well as V2D simulation shows that at the interface subsurface water components are found to be about 80-90% of the total flow (subsurface plus groundwater) components. The subsurface flow is found to be two-dimensional within the surface water zone and one-dimensional at the subsurface zone, which satisfies the Dupuit's assumption.

View full abstract

Geochemical investigations of salinized groundwater in Motooka area, west of Fukuoka City, Japan were carried out. The measured tritium concentrations in the shallow groundwater system are higher than those of the deeper groundwater system. From the results of hydrogen-oxygen isotope ratio plotting on the mixing line of meteoric water and seawater, it was inferred that the deeper groundwater is affected by seawater. ¹⁴C isotope dating of a shell that was collected at the depth of approximately 2m from the core samples of B2 indicated the age of about 2000 years. Accordingly, the salinized groundwater in this area was assumed to be originally below the sea bottom. Further, it was found that the geochemical properties of salinized groundwater should be utilized as the index of the environmental isotopes as well as characterization of the water quality using Piper diagram.

View full abstract

Field measurement of groundwater level and analysis of groundwater quality were carried out quarterly to clarify the present situation of confined and unconfined groundwater in Takamatsu district. Our measured data, the groundwater data obtained by public sectors and other relevant digital data were arranged on GIS software to develop the database on hydrological cycle. It is confirmed that the contours of unconfined groundwater level run nearly parallel to those of topography and that the groundwater level has shown seasonal variation of about 1 to 2m. Nitrate nitrogen of unconfined water at several locations has exceeded the environmental standard, which may have come from the overuse of fertilizer. The level of confined groundwater has gradually increased owing to the regulation of groundwater uptake. The pH value of confined subsurface water has unchanged whereas the levels of iron and evaporation residue have decreased.

View full abstract

The time-dependent mechanisms of saline water intrusion into a coastal aquifer were investigated through systematic field observation that covers the duration of more than half of the tidal cycle. The investigation included three measurements for water table height, vertical distribution of electric conductivity at various testing wells and water levels of the tidal river at a few selected bridge points. It was found that the mixing region between the fresh-saline water bodies is fairly dynamic, and it shifts the depth corresponding to the variation of sea water level. The tide-induced variations of saline water intrusion were analyzed with relation to the variations of sea water level and groundwater level at various testing wells. The mean depths of a mixing region at testing wells appeared more shallowly than the depth predicted by the Ghyben-Herzberg's law.

View full abstract

In the Kamafusa Lake catchment, we measured water discharge and water samples once a month at twelve points and once an hour at one point. The samples were analyzed for total-phosphrus, souble-P, total-N, nitrate-nitrogen, and ammonium-nitrogen. In a flood, the increasin g of total-N is similar to water discharge, and the increasing of total-P is earlier than the increasing of water discharge. Inorganic nitrogen is almost covered with nitrate-nitrogen in this catchment. The upper-course in forest, nitrogen runoff is larger but middle-course is smaller, and downstream is large. The reason is why upper-course covered with forest land, in middle-course has smaller forest is decreasing, and downstream has urban field usually. Nitrogen flow out from urban area in this area. On the other hand, Nitrogen flow out from urban area, barron land and paddy field in flood period.

View full abstract

Daily mass flow values of COD, Cl^-, T-P and NO₃^-; in the Yamatogawa basin could be calculated from daily flow rates because the mass flow values were proportionate to flow rate. Though flow rate was measured daily, the concentrations were measured once a month. Daily mass flow values of BOD and NH₄⁺ could not be estimated from daily flow rate however because the mass flow values of BOD and NH₄⁺ didn't depend on flow rate but rather on water temperature. The calculated daily mass flow value of COD per number of people was high in the high density population area. The values of Cl^-, and NO₃^-per number of people were low but abnormally high in the high density population area. The values of T-P per the number of people and per area were high in the farmland area and low in both the forest area and the housing site. The values of COD, Cl^-, and NO₃^- per area were high in the housing site.

View full abstract

BOD, NH₄⁺-N and anion surfactant concentration in the Yamato River indicated seasonal change curves with maximum values in winter and minimum values in summer. As these seasonal changes depended on water temperature, and BOD/Cl^- ratios also indicated seasonal changes and Cl^- is not decomposed in natural condition, decomposition of organic compounds was thought to cause seasonal changes. Degree of decomposition varies seasonally was thought to occur in private sewerage systems because wastewater from sewerage disposal plants and stream purification indicated no seasonal changes and BOD, NH₄⁺-N and anion surfactant was mainly derived from household wastewater. On the other hand, Cl^- was inversely proportional to flow rate and did not depend on temperature.

View full abstract

Annual mass flow values along the Kinokawa river were estimated from daily flow rate. Mass flow calculation needs both flow rate and concentrations. However BOD, Cl^-, T-P and T-N concentrations were only measured once a month although flow rate was measured everyday. As good relation between flow rate and mass flow was found, daily mass flow can be estimated from the relation and daily flow rate. Daily mass flow was integrated into annual mass flow. Annual mass flows per areas and per the number of people of BOD, Cl^- and T-N reached maximum values at the downstream of Kinokawa river where industrial activity was high. On the other hand, daily mass flows per areas and per the number of people of T-P were high at the middle stream of the Kinokawa river where the main land use were orchard area.

View full abstract

We applied a distributed model, which Yoshino et al. had developed for the Lake Kasumigaura watershed. As this model was initially developed for mountainous area, we attached a quasi-three dimensional ground water model to it. The estimated result in river discharge, ground water height and lake surface height explained observed data almost successfully. Along with this, we estimated hydrological cycle of highly urbanized area in a standard grid cell and overall watershed. Compared to the latter, the former showed well the feature of hydrological cycle in urbanized area. The result showed that a distributed model attached a quasi-three dimensional ground water model was effective to enhance watershed management.

View full abstract

In this study, a numerical simulation of inundation flow in an urban area is carried out using fine information of altitude. The numerical model is two-dimensional shallow water model. The grid size is 1m, which is fine enough to understand overland flow in an urban area. The altitude data is obtained by altitude of lid of manhole distributed randomly in the study area. The resolution of the altitude data is 1cm, which is fine enough to represent the contrast of altitude in a flat urban area. The numerical results proved that the inundation flow is sensitively affected by the geophysical features with undulation in the area.

View full abstract

The purpose of this study is to elucidate physical phenomena and hydraulic processes of urban river runoff in channe networks. We carried out field observation to investigate the runoff processes in several urban areas, and its hydrologic data was compared with the results calculated with runoff model. The following results were obtained; 1) hydrologic parameters adjusted with a single-peaked rain storm which reproduce the urban runoff processes with high accuracy fo many different types of rainfall pattern are tested. 2) especially the results of the calculation for single-peaked rainfall as we as those for constant intensity rainfall agree with the observed values, however peak discharges calculated for multi-peake rain storm found to be under estimated. 3) surface runoff analysis adopted land use distribution and pattern reproduces runof processes with high accuracy. 4) hydrological parameters adjusted by field observation reproduce flood runoff processes.

View full abstract

The objective of this study is to improve a distributed hydrologic model using SMPT (Soil Moisture Parameter Tank) model by applying kinematic wave model to river flow routing changing time step of day to an hour. The watershed basin is divided into a grid cell of 50m. This model is composed of three structure; surfaces division, river division, and groundwater division. In surface division, evapotranspiration, infiltration, percolation, interflow, and surface outflow were computed in each cell. Kinematic wave model was applied to river flow components. Groundwater component computes the groundwater levels and the flows in the saturated zone of an unconfined aquifer, stream interactions, and groundwater seepage at the ground water surface. The model is applied to simulate water cycle in the Azuma Upper Experimental basin (1.81km²) with a time step of an hour. The model parameter is calibrated through comparison of the simulated river discharge, groundwater levels with the observed value.

View full abstract

Infiltration models are used to estimate the effective rainfall for runoff analysis, and its role is important for the accurate simulation of a runoff hydrograph. Only a few infiltration models take rainfall intensities into account. The infiltration model proposed recently by Diskin and Nazimov (1995) takes into consideration the rainfall intensity variations, and it can also be used to calculate the variation of the infiltration capacity for un steady rainfall. This infiltration model is a fairly simple conceptual model. In this paper, the Diskin-Nazimov infiltration model is applied to the actual runoff analysis, and validates the runoff model's applicability. Concretely, the lumped hourly hydrological model presented by Ando et al.(1981) is coupled with the Diskin-Nazimov infiltration model to calculate the effective rainfall. The study basin is the Kotta River basin which is located in Tama New Town, an urban development in the Tama hills, in the western suburbs of Tokyo. The results showed that the calculated hydrographs represent the observed hydrographs for long-term rainfall runoff events in the Kotta River basin.

View full abstract

The objective of this study is to develop a simulation model of water utilization such as reservoir regulation, water intake and irrigation. This model is based on a distributed hydrological model developed by the authors. In this model, the entire river basin is divided into many grid blocks, the type of water utilization of all grid blocks can be defined. In this study, these data are stored in a database in which all grid blocks are arranged in the order same with the optimal routing order. In the simulation, the runoff generation is computed by using XinAnJiang model. The sum of runoff from a grid block and upstream river channels subjects to the water use, and then be routed to adjacent downstream grid block by using the kinematic wave method. In this study, this simulation model is applied to the Brantas River basin in Indonesia. The result shows the applicability of this simulation model.

View full abstract

WEP MODEL, the physically based distributed model developed at PWRI, was applied to a watershed with mixed agriculture and urban land uses. The watershed is 166km² in total area having a population of more than 0.12 million, and feeds two main streams flowing into a downstream lake. Paddy field is a dominant type of land use along the rivers, whereas urbanized area scatters over the watershed. Some recent modifications to WEP MODEL and parameter settings were briefly described, and the application results were verified using records of river discharge and groundwater level of the unconfined aquifer. It was found that the groundwater level in the unconfined aquifer is much more sensitive to its hydraulic conductivity than the conductivity of the river bed. The irrigation of the paddy fields plays significant role in maintaing groundwater level and river flow not only during irrigation period, but also in non-irrigated seasons.

View full abstract

Reasons for the errors in runoff simulations for large-scale watersheds are discussed. BTOPMC (Block wise use of TOPMODEL with Muskingum-Cunge flow routing method) was used to simulate hydrological processes in the Mekong river basin. The Model was calibrated for the year 1987 and verifications were carried out for the years 1993 and 1994. The digital stream network was created after removing depression points in the original Digital Elevation Model (DEM). Discussion of the reasons for the differences between simulated and observed runoff values is done using daily hydrographs at five stations in the lower Mekong river basin. Not only the physical characteristics of watershed such as topography, vegetation, geology and soil but also the human activities such as paddy cultivation and reservoir operations control the hydrological processes in a watershed. BTOPMC, coupling with human activities and reservoir water operations can be used to simulate runoff in large-scale watersheds.

View full abstract

The purpose of this study is to understand the potential impact of reservoir induced water storage on the basin scale water cycle. In this study, the increase of the basin scale residence time of river water is used as the index of the effect of reservoir on water cycle, and its spatial and temporal distribution in Japan are demonstrated. The results of analysis show that the potential increase of residence time by dam reservoirs in Japan has gradually increased from 1960's and reached to 14.5 days in 1995. The actual residence time increase is also estimated in the Tone river basin where operation and seasonal variation of river discharge are taken into account. It is shown that the estimated actual residence time is much smaller than the potential, in the case of the Tone river basin, 45%.

View full abstract