A stochastic analysis is presented of the probability of overtopping of a dam. The discussion is based on the case of a dam for a small water storage reservoir which has recently been constructed in the Saar district in the FRG. The problem is first solved by means of a simulation method. However, it is possible to describe the result of the simulation method by means of a much simpler model which is based on a solution of the failure integral of Freudenthal for uncorrelated resistances and loads. It is shown that the actual safety of this dam against overtopping is extremely sensitive to both the operation rule for the reservoir, and the freeboard allowance. Some general conclusions are derived from this study for assisting in the ongoing discussion of dam safety.

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The erosional process of soft muds is studied experimentally and theoretically. Mud erosion is classified to three types according to water content of them. These characteristics are distinguished by the range of the slump value. The erosion tests of soft muds show that the critical shear stress of erosion τ_ce is expressed as a function of solid fraction of muds at the surface layer and the initial erosional flux as a function of non-dimensional bed shear stress τ/τ_ce-1. The erosional fluxes at constant shear stresses decrease in an hour after the start of experiment because of the hardening of muds by the shear deformation which accompanies the reorientation of mud particles.
On the basis of these experimental results, a model for the behaviour of muds is developed to simulate the erosional process. This model well describes the changes of suspended solids concentration and vertical distributions of solid fraction in uneroded remaining muds.

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Opposing currents affect the breaking processes of shoaling waves on uniform slopes. The wave breaking conditions depend on the normalized discharge per unit width of the opposing current as well as on the deep water wave steepness and uniform slope. Experiments were conducted to examine these effects on the breaker depth (or height) in the presence of the opposing current, as compare to the breaker depth (or height) in the absence of the current. A new empirical parameter was proposed to express the ratio of the breaker depth (or height) with and without the opposing current. The proposed new parameter accounts for the combined effects of the opposing current, deepwater wave steepness and uniform slope. The measured ratios of the breaker depth (or height) were shown to be expressed as a function of the proposed parameter.

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Mass transfer mechanism in porous riverbed was investigated using chloride tracer method and a hotfilm anemometer in two experimental open channels which have porous media composed of 1.9cm and 4.08cm diameter ceramic ball respectively. Water depth to particle diameter ratio was about 1.7 and surface flow mean velocity was 3.9cm/s-42cm/s.
Flow over porous riverbed was found to have very high turbulent intensity near porous boundary, which was about 20% of surface flow mean velocity in all hydraulic conditions. Values of vertical-direction diffusion coefficient in porous media increased with increasing surface flow mean velocity, and were found to have the distribution pattern in porous media which shows linear decrease with depth. Observed values of diffusion coefficient near porous boundary satisfied the theoretical relationship between diffusion coefficient and turbulent intensity.

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Fall velocity of spherical particles in vertically oscillating fluid is studied experimentally and theoretically. The dimensionless mean fall velocity u is found to be governed by dimensionless parameters of Reynolds' number R_e0, frequency of oscillation af and velocity amplitude of oscillation α/a. In the range of small α/a, where relative fall velocity to fluid velocity is positive throughout the period of oscillation, the equation of particle motion is solved in terms of perturbation technique taking account of variation of drag coefficient. The result shows that the increase of R_e0, af and α/a decreases u. In the range of large α/a, an approximate numerical analysis is presented. The combination of these two theories performs well for laboratory tests made by the authors and Ho for widely varying conditions of R_e0, af and α/a.

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To simulate the mixing process induced by the combined action of mechanical and thermal stirring, a numerical analysis is carried out by using a multi-equations approach of turbulence closure. The mixing properties, such as entrainment rate, thickness of the interfacial transition layer, fluctuation of thermal field and so on, are analytically reproduced by the present model, which shows a fairly good agreement with our experimental results. Additionally, the present analysis also succeeds in describing the turbulent field, e. g., turbulence intensity, turbulent energy flux balance, etc., which are much difficult to measure in laboratory and field observations. Combining the analytical work presented here with experimental and field informations, we should be able to profoundly understand the mixing mechanism in such a situation.

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The existence of dead time and delay time is recognized in one-component input-output system response. These two effects should not be regarded as identical. Various reports have been given on delay time over a long time as an important concept to explain the mechanism of rainfall-runoff process, that is, concentration time of flood. However, the studies on dead time have not been sufficiently conducted yet. The present paper proposes new methods of runoff analysis introducing the concept of dead time, and of runoff component separations by means of the frequency response method. The proposed method is of practical use to clarify the runoff properties. The effectiveness of the model is verified using simulated data as well as actual flood events.

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The structure of the vertical circulations caused by the combined effect of the bottom oscillatory boundary layer (Stokes layer) and bottom inclination in on-offshore directions have been analyzed theoretically. In the first-order theory, the maximum amplitude of water surface appears at the shallowest water depth of the reflection boundary in coastal region, and the major axes of hodograph deflect towards shallower water region. The generating terms of residual current in tidal currents with different distributions have been discussed. It has turned out that second-order vertical circulations show 2-layer structure. The results obtained through the discussion may give useful suggestions to investigate the generating mechanism of the tide induced residual currents in the coastal region.

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It has been considered that a new statistical parameter estimation method using probability weighted moments (PWM) is difficult to be applied for the distributions that cannot be expressed in an inverse form, i. e., x=x(F). The authors show in this paper that it has been successfully applied and that the analytical PWM solutions were obtained for the representative distributions of non-inverse type, that is, Normal, 3-parameter Lognormal and 3-parameter Pearson-III distributions. The PWM estimate of the standard deviation of the Normal distribution turned out to be unbiased and having a form of a linear combination of samples.

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Following the successful derivation of PWM solutions for Normal and 3-parameter Lognormal distributions by the authors, this paper presents their relative accuracy in comparison with other parameter estimation procedures such as Moment, Maximum-likelihood, Quantile and Sextile methods through Monte Carlo simulation experiments.
Simulation results revealed that PWM estimates of quantiles are unbiased for Normal distribution and less biased than those of Moment method for Lognormal distribution with a large coefficient of skewness. It was also revealed that rmse of PWM estimates of quantiles is as small as that of Moment method for Normal distribution but larger for Lognormal distribution.

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In this study, a mathematical model of axisymmetrical oil spread on calm water is developed. Two basic equations are used to express the characteristics of oil slick: one is the conservation of volume and the other is the r-component of the equation of motion. By using the kinematic wave theory, those equations are transformed into characteristic equations along the characteristic curve. These simultaneous equations are solved to give the spreading rate of the oil front. This model describes the motion of the oil slick ranging from the gravity-inertial to the gravity-viscous spread. The theory is examined by comparing it with the experiments for the spread of continuously spilled oil from a small outlet onto open calm water.

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A theoretical and experimental study is performed to determine the characteristics of the drag coefficient for a vertical circular cylinder in waves. Theoretically, the laminar boundary layer solution on the cylinder is obtained by applying the perturbation method to the Navier-Stokes equation. By using this solution, the separation point is determined and the point vortices to model the wake are shed from the separation point. The drag force is calculated by applying the momentum equation to the wave field including the shedding vortices. In the case of non-separation flow, the momentum defect in the boundary layer causes a drag force which greatly exceeds the surface friction force around a cylinder. The experimental values of the drag coefficient versus the Keulegan-Carpenters' number are compared with the theoretical. They agree quite well, which verifies the presented theory.

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Coherent structures in the inner layer of turbulent channel flow are investigated using the technique of simultaneous flow visualization/LDV measurement. The flow visualization were done in the streamwise view using fluorescent dye illuminated by a sheet of halogen light. Some new aspects of the correlation between characteristic velocity signals of U, V and the structures of streamwise vortices are inffered from this present experiment. The velocity signals associated with bursting event are formed when the pairs of counterrotating streamwise vortices pass through, which generate near the viscous sublayer and develop away from the wall in the inner layer of turbulent channel flow. Further an evaluation of effectiveness of the VITA technique is done by making direct comparisons with the flow visualization.

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This paper reports the results of the field study which has been carried out in the Aso basin belong to Quaternary volcanic rocks zone, and it has been continued to for the purposes of investigating the flowing route and mechanism of rain-water in the drainage basin. Then this paper shows that the Aso basin consists of the following two zones, recharging zone and discharging zone. Next, two types of field for the observation of hydrological events have been set. After the consideration of the results of observation, hydrological budget is evaluated for drainage basin divided by ridge line on the basis of water balance. Under the evidence presented above, characteristics in hydrologic cycle of volcanic drainage basin is clarified.

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This paper proposes a new framework for evaluating probability distribution models used in hydrologic frequency analysis. In the framework, the variance (standard deviation) in estimation of T-year events (quantiles) obtained by the model is incorporated as an evaluation criterion as well as some goodness-of-fit criteria; resampling methods such as the jackknife and the bootstrap are also incorporated to quantify the variance. Using the existing extreme data (annual maxima of κ-day precipitation, κ=1, 2, 3), the authors reveal the insufficiency of the conventional model evaluation which is based on only the goodness of fit. The proposed framework evaluates ten distributions with two or three parameters. Additionally, the relation between the amount of data and the variance (estimation accuracy) is investigated through bootstrap-type resampling.

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We developed several colour graphic screens which can visually represent both the distribution of echo intensity and the shape of the three dimensionally spread precipitation field, in order to investigate how fine resolution the radar information has.
By the use of VCAPPI (Various Constant Altitude Plan Positions Indicator), which we developed from CAPPI, we can visually investigate three dimensional characteristics of the precipitation phenomena in meso-β scale. Furthermore, by the use of FVCAPPI (VCAPPI for an arbitrary specified domain) and RRHI (in the form of the arrangement of fifteen RHIs), we can visually investigate characteristics in meso-γ scale.
In the case of very heavy rainfall which arose along Baiu front on the 21 July in 1986, from FVCAPPI and RRHI we can find a convective echo consists of several echo cells in various life stages. This means the convective echo is from a multi-cell storm. This fact can be also verified from RHTI (Range Height Time Indicator), which can visually represent the time series of an echo pattern in an arbitrary vertical section, by setting the vertical section along the storm moving direction.

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Resultant forces for standing and breaking waves on a wave dissipating caisson with double vertically slotted walls are investigated in this paper. First, theoretical results obtained using an integral equation derived for an unknown horizontal velocity component are presented to show the effects of structural configurations upon the total horizontal and vertical forces due to standing waves. The numerical predictions are then compared with the experimental results for accuracy. Secondly, a model experiment is conducted for breaking weves using only those configurations which were found to be effective for standing waves. The optimum structural configuration which minimizes the resultant wave forces and displays strong stability against sliding is found from these results. Finaly, this paper discusses the difference between a double walled structure and a single slotted caisson.

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Possibility of quantitative forecasting of local tsunamis sufficiently before their arrivals, by use of a super computer, is examined. Provided that the initial tsunami profile can be determined within a few minutes after an earthquake by such a method as proposed by lzutani and Hirasawa, the tsunami numerical simulation based upon the linear long wave theory can be finished within two minutes and give practically accurate tsunami heights at every 200m along the castline of the Sanriku district extending from 41°30′N. to 36°20′N.

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The Lagrangian coordinate system has a notable advantage in the description of surface conditions which essentially prescribe the dynamics of water waves, although some difficulties are involved in numerical solution of equations. In this context, two alternative schemes (velocity and pressure formulations) are presented for analyzing two-dimensional transformation of water waves. Their usefulness is examined through application to the resonant behavior of sloshing waves as well as to the breaking of a solitary wave.

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Seasonal fluctuation of collected amount of municipal solid waste in Sapporo is studied. In order to make characteristics of fluctuation pattern clear, collected amounts are normalized giving special consideration to national holidays and their next collection days on which amounts of waste sharply change. Correlation coefficients, moving averages and autocorrelation function are calculated to give quantitative information on the fluctuation pattern and to make comparison among different districts or years. In addition detailed investigations are carried out on the increase of waste in the periods of December to January and March to May. Strong relationship between snow-thawing and people's behavior of waste production is confirmed.

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Laboratory tests on biological treatment process applying suspended biological flocs with glass beads media which has 0.1mm and 0.05mm each in diameter have been carried out to investigate both the critical diameter of biomass flocs and the optimum input rate of media in a reactor.
It was confirmed from the tests that the critical diameter was proportional to rms velocity gradient (at a range of 10 to 2500s^-1) to the minus one-half power. An estimation of the optimum input rate was also found to be possible by setting up the VSS concentration in reactor.

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This paper presents a measurement technique for the analysis of solid-liquid two-phase flow with a laser-Doppler velocimeter. Setting up an optimum threshold value between amplitudes of Doppler signals from fluid and those from particle makes it possible to discriminate the particle from the fluid signals. The present two-photomultiplier system, which is composed of an optical arrangement with two reference beam modes, is effective for reducing the ambiguity noise in the spectrum of the fluctuating fluid velocities. It is also shown that the particle concentration can be calculated from the measured particle velocity, particle arrival rate, and the cross-section, where the amplitude of Doppler signal is greater than the threshold value, within the measurement volume.

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Turbulent characteristics in open channel flows are estimated by means of the stress flux model proposed by Launder, Reece and Rodi. Vertical distributions of the components of Reynolds stress tensor and turbulent energy dissipation rate are derived numerically. Numerical results are compared with the previous experimental studies by Nezu and Asano. Then the constants appeared in Launder's formula concerning the turbulent diffusion coefficients are estimated using the numerical results in this study and the experimental studies of the turbulent diffusion coefficients in open channel flows.

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It is very important in the river-works design to estimate maximum hydrological quantities occurrence, such as the heavy rainfall and the flood. In this paper, assuming that the annual maximum values follow the log-normal distribution, we consider the distribution of the maximum values which occur within the lifetime of structure for river-works. And analyzing the data from four stations (Kanazawa, Toyama, Fukui and Nanao), we find that the hydrological variable in accordance with large return period is nearly equal to the value which is the mode of the annual maximum values distribution that can occur within the lifetime of the structure. Furthermore we suggest the statistical method to evaluate the occurrence times and magnitude when severe hydrological events occurred repeatedly in a fixed interval.

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It has been found experimentally that a row of two-dimensional vortices forms in an offshore zone when surface waves climb up a sloping flat bed. The vortices occur near the separation point of the Stokes layer, i. e., near the breaking point, and are transported in the offshore direction. Performing the vortex pairing, the vortices increase their length scales offshorewards. They are nearly equal to the local depth of water. In the case when the slope of the bed from the horizontal is 2.44°, the row of vortices appears when h_b/L_b≤0.096. Here, h_b and L_b are the mean water depth and the wavelength at the breaking point, respectively.

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