Most of fishways constructed beside of weirs and dams in Japanese rivers belong to pool-and-weir type. Usually, a notch is placed at the weir. Ministry of Land, Infrastructure and Transport recommends that the ratio between the notch width and fishway one set to in the range between 0.17 and 0.20 without any verification. In this study, the notch ratio in a pool-and-weir fishway was changed in the range between 0.1 and 0.7 and migration rates of ayu, Plecoglossus altivelis altivelis, were obtained with the aid of two sets of digital video cameras. Further, three components velocities were measured with a 3-D electromagnetic current meter. It was found that the migration rate changes with respect to the discharge, the migration rate increases with a decrease of the notch ratio and also that the most of migration positions over the weir are located near the side-wall. Those characteristics concern with the flow velocity and orientation area. The position of the orientation area concerns with the flow velocity.

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Fish sometimes enters into an intake gate of weirs and dams, so that a lot of released larval ayu and salmon are lost. Some techniques with electricity, transmitted light and air bubbles have been developed to avoid fish from the intake gate. However, a lot of fisheries co-operative associations pointed out that most of such techniques have no effect. In this study, the color types of transmitted light are changed at both sides of a rectangular water tank and swimming area of Zacco platypus and Zacco temminckii are observed. It was found that the color types do not affect on the swimming behavior of both fish.
Generally, it is known that fish avoid the area which is included air bubbles. In this study, the air bubbles are injected from the channel bottom and trajectories of fish are observed. It was found that air bubbles do not affect on the swimming behavior of Zacco platypus and Zacco temminckii.

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Urgent measures protecting lakeshore vegetation have been carried out at eleven locations in Lake Kasumigaura since 2000. In these measures, beach nourishment was carried out to create a stable growth zone of lakeshore vegetation along the lakeshore, using wooden offshore breakwaters, submerged breakwaters and artificial berm produced by stones. Aerial photographs were compared to investigate the stabilization effect of the ground by these structures as well as the analysis of bottom sounding data. It was found that in the past restoration method of lakeshore vegetation, the consideration regarding dynamic changes of lakeshore due to wave action was insufficient. To create a stable lakeshore ground, wave action and beach changes at each location must be deeply considered.

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A restoration plan recovering sandy beaches at Tennozaki in Lake Kasumigaura was investigated. Past lakeshore changes were first investigated through the comparison of old map and aerial photographs. A stable shoreline of a pocket beach was predicted by applying a modified Hsu model (Serizawa et al., 1996). Numerical simulation using a contour-line-change model considering the change in grain size proposed by Kumada et al. (2003) was also carried out. Three-dimensional beach changes when beach nourishment was carried out were predicted by this model.

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Field observation of turbidity, chlorophyll and current velocity was conducted in the Barato River, which is the oxbow lake in the Ishikari River. In this oxbow lake resuspension of the sediment is main factor of water pollutant. In this survey, relationship among sediment resuspension, wind speed and current velocity were investigated. And the rate of sediment resuspesion was estimated by using observation results.
Clear relationship exists between wind speed and turbidity when the wind speed was larger than certain level in each survey point. We tried to estimate the rate of sediment resupension by the methods in our study. The estimated value was generally adjusted to observed results in 2005; however, considerable difference was found in 2006.

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Long term persistence of high turbidity water is one of the major water quality issues in rivers with a dam reservoir. This phenomenon is influenced by the grain size of fine sediment carried by floodwater into the reservoir. In his paper, analysis methodology of grain size distributions of fine sediment is discussed to propose the most proper method. Three analysis methods -sedimentation experiment in a tall tube, laser diffraction-dispersion method and centrifugal sedimentation method- are applied to several kinds of fine sediment sampled from river water and reservoir bed and the results are compared. From the results, laser diffraction-dispersion method with preprocess of sonication is proposed as most suitable for practical analysis of fine sediment in river water.

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Wind and wave fields are computed for the Lake Kasumigaura using numerical atmospheric and wave models. The meso-scale atmospheric model WRF is employed for predicting the wind field over the surface, while the temporal and spatial wave fields are computed by the third-generation wave model SWAN using the output of WRF. The computed results are compared with the observed wind and wave data. The compared periods are chosen during the passing of the typhoons 200704 and 200709. WRF reproduces the observed wind speed and direction quite well at two observation points inside the lake except the peak of typhoon wind. Consequently, the predicted significant wave height and period become smaller than the observed data near the wind peak. The wind field forecasting is also performed using the forecasting meteorological data (GFS). The results show the availability of the present model for forecasting the wind fields over the lake.

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Behavior of sediment flowing into water reservoirs depends on the particle size. In addition, nitrogen and phosphorous content in sediment differ by the particle size. Therefore, sediment load has different effects on water quality of reservoirs according to the particle size. In this study, water quality and particle size distribution in runoff into Tono dam reservoir were measured, and L-Q models for estimation of pollution load of SS, nitrogen and phosphorous in each particle size group were built considering nutrient content of each particle size. Estimating sediment load using the models indicated that nutrient load with small particles such as those under 15μm increases with increase in rainfall intensity.

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Numerical simulations of uniform or mixture sized particle thermals on horizontal bed were performed using 3D numerical model. The thermal consists of fine and coarse sized particles and water. The numerical model is constructed with Simplified Marker and Cell (SMAC) method, Monotone Upstream-centered Schemes for Conservation Laws (MUSCL) technique, Smagorinsky turbulence model and treatment of several diameter sizes of a particle. The simulated results are compared with experimental data of maximum height, propagation speed and amount of particles deposition of particle thermal. It is found that this model can reproduce behavior of mixture sized particle thermals on horizontal bed.

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The natural environment in a brackish lake largely depends on the balance between the seawater intrusion and the salinity circulation. The latter has a great influence on the ecosystem there. Recently, Corbicula japonica has been decreasing in Lake Ogawara, which is, having been one of the most abundant lakes in Corbicula japonica in Japan, a brackish lake located in the southeast of Aomori Prefecture. So it is necessary to clarify the causes and to proliferate the ways for solution.
In this research, our aim is to examine the water quality in Lake Ogawara for explicating the reasons for the decrease. The data of the field works are used to consider the relationship between the water quality and the egg-laying and hatching of the Corbicula japonica. The results of the examination show that the egg-laying took place only in the north area of the lake, where the salinity flux is comparative more frequent than other areas. The larvae were diffused over the whole area through waves caused by winds in various conditions.

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Wind induced currents in Lake Ogawara is discussed being based on field experimental data obtained in autumn of 2006. In the experiment, three ADCPs were set on the bottom of the north, the center and the south water areas for two months. The data showed a periodic appearance of intense shear layer in the metalimnion that seemed to be generated by internal seiche. Measurement from three boats equipped with ADCP was conducted for three days in the same water areas under predominant wind direction of west and south. The data suggested the existence of rather stable horizontal currents in the surface mixed layer. These facts suggest that substances entrained from anaerobic hypolimnion by the shear motion are carried by the stable horizontal current in the surface layer to develop uneven condition of water environment.

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Water quality conservation for eutrophic lakes has many perspectives in terms of factors by which phytoplankton growth is affected. Change of water control such as diversion and water supply from nearby rivers seems to provide instantaneous effect on water quality of the lakes. However, these changes will lead to the change of both retention time and nutrient supply. Therefore, it is essential to predict water quality change by simulation analysis. We have conducted several water quality simulation which deals with the change of water control in Inba marsh. Since nutrient concentration of nearby rivers is high, dilution effect is cancelled by the increase of nutrient loading. Large amount of water with relatively lower nutrient concentration stored in northern part of the marsh has potential to improve water quality of western marsh without deteriorating the water quality of other water body.

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In order to optimize treatment of leachate from garbage-dumped landfill, a micro-bubble generation technique was applied to feed oxygen into an anoxic layer of the leachate reservoir. Although the impounded water was successfully aerated and dissolved oxygen recovered a great deal, nitrification of ammonia did not so extensively occurred. The limiting factor of nitrification was found to be biochemical reaction that were not activated so much due to insufficient amount of bacteria colonies under relatively low water temperature. Most of the oxygen demand in the leachate was caused by ammonia but not by organic compounds, which was a very different water quality feature from that in rivers and lakes. Additional finding was that chemical oxygen demand of the leachate was highly correlated with ammonia concentration as well as with electric conductivity.

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In order to properly determine oxygen discharge of a micro-bubble aeration system, dissolved oxygen and relating water qualities were measured in an anoxic reservoir hypolimnion. Consumption and loss amounts of the oxygen were estimated by analyzing oxygen balance. It was found that the oxygen loss rate linearly decreases with increasing dynamic stability of thermal stratification. A seasonal dependency of oxygen consumption due to biochemical activities was also obtained from the field dataset. Aeration discharge necessary for keeping the hypolimnion aerobic was estimated by summarizing the analytical results, which provides necessary information for optimizing the system operation. The proposed method for estimation of aeration discharge was expected to minimize both the energy consumption and the system capacity.

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Bubble-diffuse type destratification system is widely applied in reservoirs with problems of water bloom caused by cyanobacteria. However, the planning methodology on the installation scale of the system has not been established. In this paper, we propose a methodology by simulating and evaluating the gradient of surface water temperature, which is known to have some relationship with occurrence of water bloom. A hydrodynamic simulation model was verified in Haji Dam reservoir, where the destratification system has been equipped. By using the model, the proposed methodology was applied to the reservoir under the condition in 2001, and the current installation scale is evaluated as proper.

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Laboratory experiments were carried out on water quality purification with EcoBio-Block (EBB). EBB is a porous concrete block including Bacillus subtilis natto group. In this study, we examined experimentally denitrification effect of EBB by letting it live together with denitrification bacteria in soil. The time variations of TN, ON, DIN, NH₄-N, NO₂-N, and NO₃-N were obtained under the aerated condition by changing the weight ratio of EBB to water. On the basis of those data, the denitrification rate, the mineralization rate, and the decreasing rate of DIN were obtained. As a result, we confirmed that the processes of organic matter decomposition, nitrification, and denitification were performed effectively by the symbiosis of useful microbial group and denitrifying bacteria.

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We investigated the relationship between the abundance of cyanobacteria and stratification intensity N² in three eutrophicated reservoirs in which an artificial circulation system had been installed and the effects of the facility scale on that relationship. Cyanobacteria markedly increased when N² was above 10^-4 [s^-2] in all three reservoirs whether the artificial circulation was installed or not. A certain facility scale wais needed for the decrease of N². Sufficient decrease in N² by the facility occurred in the reservoir in which cyanobacteria was prevented. The appropriate facility scale to decrease N² was considered to be related to the internal Froude number inherent in each reservoir.

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The phytoplankton and their species were analyzed in the Otaki dam, the Sarutani dam and the Kinokawa flood gate. The Otaki dam, the Sarutani dam and the Kinokawa flood gate are stagnant condition. Ca⁺ concentrations in the Otaki dam and the Kinokawa flood gate were over 11 mg/l. Ca⁺ concentration in the Sarutani dam was equal to or less than 10 mg/l. Total nitrogen concentration in the Kinokawa flood gate was over 0.8 mg/l. Total nitrogen concentration in the Otaki dam and the Sarutani dam was equal to or less than 0.7 mg/l. In summer season blue-green algae increased in the Kinokawa flood gate but dinoflagellate did not increase. On the other hand, dinoflagellate increased in the Otaki dam. Then, blue-green algae increased, when total nitrogen concentration is over 0.8 mg/l. Dinoflagellate increased, when Ca⁺ concentration is over 11 mg/l.

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Salinity distribution was observed under the ground surface of the tidal flat formed at middle part of Ohta River Flood Control Channel, and the mechanism of salinity retention under the ground was considered. The measurement method of salinity under the ground was developed and the detail ground water quality profiles were measured. Furthermore, to clarify the supply mechanism of river water into the tideland ground, the characteristics of salinity variation and current field were discussed by using the continuous measurements of salinity and flow under the ground. It can be understood that intrusion into the ground of river water is limited under the condition that the ground water level has remained at the ground surface level, and the tideland environment depends on the ground water quality.

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The longitudinal distribution of salinity near riverbed and the measuring method of water exchange through the riverbed in a tidal river were investigated. The profile observation results proved the existence of the patch of saline water mass on riverbed. Based on laboratory experiments, the relation between the electrical conductivity of bed material and the salinity of pore water was influenced by fine fraction content and groundwater level at the riverbed. The estimation method of discharge through riverbed surface was successfully established and it was verified by the agreement of calculated salinity with the observed salinity of pore water. The calculation results provided the fact that water exchange through riverbed surface is of the order of 10^-3 cm/s. The tidal water exchange was occurred in about 30 cm depth layer from riverbed surface.

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Long-duration observations of salinity distribution were conducted at 4.8 km upstream from the mouth of the Ohtagawa diversion channel where flow and density conditions change significantly. In addition, measurements of tidal current and suspended particulate matter (SPM) were carried out, using an acoustic Doppler current profiler. The long deployment periods allowed us to examine the effect of a flood incident, wind, mean depth, and both semi-diurnal and neap/spring aspects of tides. The influences of the river discharge, wind, tidal range, and mean depth on the transport of saltwater and SPM were examined by the regression analysis. The direction of the mean SPM transportation was toward upstream for the restricted freshwater discharge. The upstream SPM flux increased with the increasing tidal range. Conversely, the intrusion of salt water was suppressed by the tide.

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Recently, the frequency of occurrence of red tide in the Ariake Bay tends to increase. The nutrients-rich fresh water from rivers is pointed out as a reason for the red tide in the Ariake Bay. Therefore, information on behavior of the fresh water in the sea area is very important to discuss the aquatic environment in the Ariake Bay. In this study, four field observations on surface currents were carried out by using drifters under the stratified condition in order to clarify the Lagrangian flow patterns of fresh water from the Chikugo River. As a result of this study, it is clarified that the westward excursion distance of the fresh water under calm conditions is considerably influenced by the river inflow rate, because the velocity at the mouth of the Chikugo River governs the magnitude of the Colioris force. On the other hand, the motion in meridional direction mainly depends on the tidal range. Findings of the present study imply that the fresh water from the Chikugo River can reach the Isahaya Bay within a tidal period under circumstances that the inflow rate is larger than that in this study.

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Simulation model for bottom topography changes in tidal land are applied to field data. A formulation for settling velocity in cohesive sediment transport model is described through a flocculation model that includes the effect of turbulence-induced aggregation and floc breakup. Firstly, wet-dry scheme is applied into the simulation model to incorporate the effect of tidal flat to make clear the tidal circulation properties in North Ariake Sea. Secondly, bottom topography change model is applied to bottom topography changes in navigation channel and tidal flat. These simulation results show that the simulation model in this study is effective to predict bottom topography changes due to only tidal-induced current in tidal flat.

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Intensive field measurements of the turbidity maximum movement were undertaken in the Chikugogawa River mouth estuary and tidal flat. The estuary has two channels - the main channel and a subchannel called Hayatsuegawa. The vertical profiles of the suspended sediment concentration (SSC) and salinity were measured at 20 stations along the Chikugogawa River course. The current profile was monitored by ADCP at six stations. The SSC and salinity are highly correlated; the SSC growup in front of the salt-wedge maximum concentration. A significant relationship is observed between the SSC and bottom shear stress at the upstream stations, but there is no correlation at the downstream stations along the main channel. The suspended sediment loads on the tidal flat and in the upstream channel are much higher during flood tides; on the other hand, the main channel discharges the suspended sediments into the sea. These facts suggest that the turbidity maximum occurs on the tidal flat, and the suspended particles intrude into the Hayatseugawa channel. Further, since these intrusions run up to the upstream channel, the suspended particles settle on the upstream bed as well.

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Water quality and primary production in an enclosed bay are dependent on inflow loads from rivers and outer ocean, and nutrients released from sea bottom. A nutrient load by rainfall also has an important role in the primary production. We here focused on the influence of the precipitation on the water quality and primary production in the Osaka Bay, and then conducted water quality analyses of rainwater and river water.
The rainwater had high concentration of dissolved inorganic nitrogen, and the ratio of rainfall load to Yodo River load was about 20% on average for observation period. This result suggests that the precipitation make phytoplankton biomass increase in the surface layer with nitrogen limitation. Furthermore we examined the changes of water quality and primary production using a system dynamics model to make a quantitatively evaluation of precipitation effect.

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Wave hindcasting at each of 5 points located in Tokyo Bay area is conducted consecutively over a year period of 26 years from 1979 to 2004 using a backward ray tracing model on a nested grid with very high space resolution. Hourly wind distribution is provided with the ECMWF analysis/reanalysis surface winds-based data set in the open sea and the measurement winds-based data set in the nearshore area including Tokyo Bay. Comparison between hindcasts and measurements is made for both time variation of waves and wave climatic parameters. The main conclusions are that the model gives reasonable estimates for the wave height conditions in the inner bay area and that the model demands an input wind data with an improved time resolution in the open ocean for a better evaluation of wave conditions in the outer bay area.

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A basic experiment for mappingof eelgrass distribution using the balloon with the simple spectralcamera in this researchwas conducted. The field survey stationwas selected to the Yoshina Tidal Flat in Takehara, Hiroshima Prefecture. Asa result, the followingmatters were clarified. 1) The characteristic for the spectral reflectance of the eelgrass appears in the wavelength at 450nm, 500nm, 650nm, and 700nm<. 2) A strongcorrelation was observedthe relationship betweenthe reflectance ratio (533nmand 440nm; 533nm and 620nm; 620nm and 720nm) and the area ratio (index of the density) . 3) The width of theobservation and the spatial resolutionof the balloonwereprovisionally calculated as 17m and 13mm. 4) Strengthof the balloon rope used was measured with about1000N. 5) The infrared composite color imageof the eelgrasstaken with the simple spectrum camera was clearer than the natural color composite image.

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The acquisition ratio of observational data by ocean radar presents a cyclic variation synchronized with tidal motion and an abrupt decreasing due to the meteorological conditions. Information relevant to the property of variation of the data acquisition and the impact factors on its variation is important for practical uses of ocean radar observation systems. The authors investigated the impact factors to the data acquisition ratio of the DBF (Digital Beam Forming) ocean radar with VHF band, central frequency 41.9MHz through long-term observation in Ariake Bay. As a result, the appearance of tidal flat along the coast off Arao mainly affected the cyclic variation of the data acquisition due to the transmission loss of radio waves. Besides, the flood from Chikugo River accompanied by heavy rainfalls and the decrease of conductivity at sea surface caused the abrupt decline of the acquisition ratio. At the term of weak wind less than 1m/s, the data acquisition also decreased by way of suppression of surface resonant wave.

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The purpose of this research is to study the estimation of surface chlorophyll-a concentrations (Chl-a) using the ALOS/AVNIR-2 data. The southern part of Hiroshima Bay was chosen as a test site. The Chl-a estimation was tried using the AVNIR-2/in-situ Chl-a data set of two days. As a result, a strong negative correlation was observed in the relationship between the AVNIR-2 Band 1 and Chl-a. Moreover, to treat the data at different time with the same data range, the correction of the pointing angle is the most effective. The AVNIR is certified as an effective tool to the Chl-a estimation in the closed gulf such as Hiroshima Bay through this research.

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A grain size distribution of suspended solids or sediment in a closed basin is closely related to habitat suitability of aquatic benthic animals such as coral or a shellfish. However, it is very difficult to get correct information about an equilibrium grain size distribution because it always changes spatially and temporally. We investigated a method to estimate grain size distributions both of bed load material and suspended one by using bottom friction velocities which were calculated by wave analysis based on statistical wave data. And then, we assume that the equilibrium grain size distribution of sediment can be approximated with the mean value of bed load material and suspended load material. We applied this method to estimate the grain size distributions of sediment in the Takegashima Marine Park which is located the southern end of Tokushima and the estimated grain size distributions coincide with the field data.

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[in Japanese]

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In order to understand current conditions of water environment and investigate improvement methods for water quality in an estuary, it is important to clarify characteristics of flow field and circulation of nutrients. Maizuru Bay has complex shape that the northern part with bay mouth (North bay) is quite narrow, and the southern part is separated into West and East bays. Toshima is located at the separation zone. Due to this complex structure, the tidal exchange with the Japan Sea is not always enough, and a deterioration of the water quality in the bay has been concerned. In this study, we investigate characteristics of tidal current and distributions of nutrients (COD, DO, nitrogen and phosphorus) in Maizuru Bay through the numerical analysis based on the baroclinic model and the ecosystem model. The flow field of tidal current and the distributions of temperature, salinity and nutrients are simulated in the case of the summer with density stratification.

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We investigated the real-time forecast system of a storm surge to reduce its disaster. Typhoon properties such as central atmospheric pressure were forecasted before several hours by two methods. The one is forecasting by using neural network technique based on the past typhoon data and the other is utilization of typhoon forecast information by the Meteorological Agency. As a result of the comparison of both methods, it was found that the latter gave more correct forecast of typhoon properties. Based on the forecasting values of typhoon, we carried out the real-time forecasting of a storm surge and examined the practical utility of this system.

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When tsunami hits a harbor, the destruction of the structures in the coastal area is caused not only by the wave force but also by driftage collision. If the structures are destroyed, the wrecks might be drifted and cause further destruction.
The main purpose of this paper is to develop the numerical analysis code for predicting the driftage behavior in tsunami run-up. The features of this method are (1) to be applied to the motion of driftage object with FAVOR method and (2) to be applied to a flow involving free surface with VOF method. The method is applied to the vertical oscillation of the driftage near the free surface and the horizontal motion of driftage with tsunami run-up. As the results, this method properly simulate the vertical oscillation and the horizontal movement of the driftage object. The obtained numerical solution of driftage horizontal velocity agrees well with the result of hydraulic experiment.

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We developed a numerical quasi-3D hydrodynamic model using CIP-FEM to evaluate the enclosed coastal environments. The model was applied to Tokyo Bay to investigate its performance and usefulness. The calculated profiles of salinity and water temperature agree well with the observed ones. These results show that the validity of the proposed model was confirmed, and the improvements of the solving method for the advection term made progress toward the accuracy of the vertical profiles in the surface layer. We discussed a relationship between wind conditions and clockwise/counterclockwise circulation in the upper and middle layer using the proposed model.

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In order to properly simulate the natural phenomena using numerical model, model parameters have to be estimated by an appropriate manner. Authors regard the model calibration as global optimization problem and have applied global optimization techniques, such as adaptive cluster covering method (ACCO), genetic algorithm, and so on, to the estimation of model parameters. Here, new approach using ACCO and artificial neural network (ANN) is proposed for the model parameter estimation. ANN works as an error estimator in this proposed model (ANN-ACCO) . From the comparison of results with ACCO and genetic algorithm (GA), it is shown that the optimization by ANN-ACCO is reasonably carried out with better accuracy and stability. Model parameter estimation was also successfully established by ANN-ACCO, then the some degree of its applicability to model calibration were shown.

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Characteristics of a flow around submerged asymmetrical structures (we call this structure the BaNK block) in an irregular wave field were experimentally investigated. Komatsu et al. (2001) proposed ‘BaNK System’ in order to cope with beach erosion and shoaling of fairways. So far, regular wave fields and oscillatory ones with constant wave periods have been treated in hydraulic model tests and numerical simulations for the BaNK system. In this study, plural half cylinders are used as the BaNK blocks which are set on the bottom of a wave channel. It was found that vertical circulating residual currents were created over a wide area encompassing the block-set area in the irregular wave field like in a regular wave one. Furthermore, the relationships among the residual currents, the turbulent energy and the Reynolds stress in the BaNK system were estimated.

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Kinematic wave flow models for simulating river basin runoff are reviewd. After the baic equations of kinematic wave flow are derived, some modified kimematic wave flows which are devised for treating surface-subsurface flow on watersheds are introduced. Then, the routing of kinematic wave flows on digital terrain models are inroduced. Finally, lumping methods of kinemtatic wave flows for watershed runoff are shown.

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The river channel process is one of conventional yet current subjects in hydraulic engineering, and sediment transport phenomena play important roles in the process. Studies on the process have been carried out from two standpoints, practical necessity of river training and intellectual curiosity or scientific interest in fluvial morphology, though the sediment transport had been investigated mainly from practical requests. As studies on river channel process have rather long history and wide variety of background, so background and development of the research in Japan are described briefly and some comments are given on current researches and near future studies.

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An integrated inundation flow model is developed which can treat both surface and underground urban inundation. We combine an inundation model on the surface with an underground inundation model. The surface inundation model is based on the horizontally two-dimensional unsteady flow model with unstructured meshes. The underground inundation model is based on the storage pond model, in which the underground mall is expressed as a combination of three-dimensional storage ponds. The drop flow formula is applied to the inflow at entrance to underground mall. This model is applied to Fukuoka City, Japan, and the inundation that occurred there in 1999 is simulated. The simulation results are in good agreement with the inundation records.

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The landslides due to heavy rainfalls have been thoroughly investigated by many researchers to mitigate the sediment disasters. However, because of the complicated mechanism of the landslide, it is difficult to predict the landslide accurately by the conventional simulation method. Of course there are many factors such as the rainfall, surface and subsurface geomorphology, and soil physical properties affecting the occurrence, but it is very significant to point out the important issues on landslides for the future research. Last five years, authors have investigated several landslides in Japan, and examined the landslide occurrence by experimental and modeling approaches. Consequently, some important issues which have a great influence on the landslide occurrence were found. In this paper, these issues are reported.

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