From the viewpoint of preservation of the ecosystem of rivers, expectations are on the rise for various fishways for fish migration. Stream type fishways with cobble stones and boulders as roughness elements create a good natural landscape. These type of fishways offera wide variety of flows with different depths and appear as murmuring little streams or as high-speed rapids. This research aims to develop a new type of fishway which can reduce the costs and time and look like as a natural stream. We analyzed the hydraulic characteristics of a fishway built with concrete blocks that was developed with the earlier mentioned objectives using hydraulic testing. Based on it, a design method was proposed. Further, we conducted ascending tests for many kinds of fish and the results confirmed that this type of fishway is well used by all the tested fish under various flow conditions

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The objective of this research was to conduct quantitative evaluation of the possibility of fresh water fish to live, based on “PHABSIM”, a US-proven physical environment evaluation model that is increasingly gaining attention in Japan. In this research, the Mac Cormack method, that had earned a reputation for mixed flow (ordinary and shooting flow) simulation, was applied to an actual river.
As a result of investigation conducted on the data of 1999 and 1998 about Mochigase points of the Sendai River, we found that the weighted usable area of sufficiently large size is preserved for L (Tribolondon) halconensis in every growth stage between the dry and rainy seasons, but that of Rhinogobius flumineus is extremely insufficient through the year.

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Dispersion mechanism of hatchlings of horseshoe crab Tachypleus tridentatus at tidal flat off the Yasaka Rivermouth in Moriye Bay in Oita Prefecture was investigated by field observations of tidal currents and numerical simulation. Hatchlings of horseshoe crab creep out of the sea bottom of the spawning site between two hours before and after the high tide. Field observation of tidal currents on and off the tidal flat and Lagrangian analysis of neutral floats modeled hatchlings show that hatchlings can reach tidal flat, where larva horseshoe crabs live, by the dispersion effect of tidal currents in spite of their low swimming capability. This well explained observed results.

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The sediment trapped by a sabo dam during a flood should be back to the downstream reach if the sediment trapping causes the sediment imbalance in the river system. The sediment flushing must, however, give a great impact on river environment. In this study we have investigated sediment movement in mountain rivers after sediment flushing and its impact on the habitats of fishes and aquati insects with some experiments on sediment flushing in a field. In the experiments, the released sediment passed the observation section completely covering the armor coat and filling up a series of pools. Such a sediment movement took the habitats from fishes and aquatic insects. The deposition volume in the pools and the deposition depth on the armor coat were taken as the indexes of the influence on fishes and aquatic insects. A method for estimating the indexes was presented with a numerical bed variation model. The method can be used for establishing the criterion for sediment flushing.

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Riparian woodland on waterfronts is indispensable, for it functions as buffer space and helps in maintaining ecosystem. On the other hand, when trees grow in river channels, there are many disadvantages in the flow capacity of channel. It is very important subjects that the maintenance method of riparian woodland is established. Field observations on the growth characteristic of pruned riparian woodland were conducted at the Toyohira River. Observations were made of the growth rate of trees, thenumber of sprouts and shape of trees. The following become clear as a result of the investigations. The growth capacity of willow is very high and recovered in one season depending on circumstances. The quantity of twig growth becomes less when the trees submerged in current. The quantity of twig growth becomes less when pruning method that remains trunk is conducted.

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Surface flow velocity distributions of flood flows are measured by using a conventional video camera. Surface flow patterns visualized by water surface ripples, foam, drifting wood, or local differences in color of water are analyzed by a specific PIV (Particle Image Velocimetry) technique developedby one of the authors that can treat oblique angled video images. The point of this paper is to check the accuracy of discharge measurements with PIV by comparing it with those obtained by the other velocity measurement techniques such as the float method, the method that uses aerial photographs andthe Manning's formula. In addition, velocity resolution by the PIV measurement is examined in detailas functions of viewing angle and distance from the video camera.
The result shows that estimated discharges by the presented PIV technique are comparable to those obtained by the float method. The PIV technique is a promising method that can farther be extended to an automatic measurement preparingfor the coming optical fiber cable network system.

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From river management point of view, it is important to forecast morphological behavior after river modification work such as straightening, widening and excavation. However, little is known about theinfluence of artificial impact on channel processes, especially in small rivers, because of lack of data. Therefore, in order to supply the information mentioned above, we investigated morphological changes after river channel improvement work in an actual river. In this paper, we deal with temporalchanges of bed configuration after excavation of the meandering low-flow channel which was carried out in the Yamamori River. By field survey, we examined the plan form variation of low-flow channel, the bed profile in the longitudinal direction and the grain-size distribution of bed materials. The significant difference of discharge, which is one of the main features of floods in small rivers, leads to considerably different morphological behaviors. This channel morphology was analyzed by the numerical model, and channel processes in the Yamamori River were explained on the basis of the numerical results.

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The motion of 2-D buoyant clouds formed by releasing fine particles into quiescentwaters with finitedepth is numerically studied. In the numerical model, particle phase is modeled by the dispersion model and turbulence is calculated by the large eddy simulation. The governing equations, including the filtered 2-D Navier-Stokes equations and mass transport equation, are solved based on the operator-splitting algorithm and an implicit cubic spline interpolation scheme. The eddy viscosity is evaluated by the modified Smagorinsky model including the buoyancy term. Comparisons of main flow characteristics, including shape, size, average buoyancy, moving speed and the amount of particles depositedon the bed, between experimental and computational results show that the numerical model well predicts the motion of the buoyant clouds in the whole process, from the falling to spreading stage. The effects of silt-fence on the motion of particle clouds are also investigated through numerical experiments.

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Motion of turbidity clouds propagating along the bottom boundary, that produced by instantaneous release of turbid water from water surface into a stagnant water, is investigated experimentally. A series of laboratory experiments is conducted by varying inflow condition as well as ambient water depth. The motion of turbidity clouds is found to be distinguishied into two flow regions: the transition and gravity current region. The effects of inflow condition and ambient water depth on the motionof the clouds, and the relationships of the flow characteristics before and after impingement are investigated.

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This paper is associated with the computer simulation and the field observations of salinity to analyze the freshening process in the Yongam lake, which is a standard freshening reservoir. The freshening process was predicted by salinity equivalent model based on three kinds of hydraulic mechanisms comprising the convection, the vertical diffusion and the mixing of salinity. The model was applied to the conditions of two different times, which were decided by the introducing time of desalt fresh water and the operation of desalinization facilities. As the results, the observed salinity was greatly reduced with the lapse of time and varied according to the season, river discharge, and tidal phenomena. The spring layer of salinity related to hydraulic stability was found 15-16meters below the water surface. In the desalinization process, the computed salinity was 1, 000-1, 700ppm and 2, 000-4, 000ppm separately, in case of the introduction and without of desalt fresh water.

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River water temperature has a great influence on the distribution of aquatic animal and plant, and it is a fundamental measurement item in water quality test. The theoretical analysis of the river water temperature has not been carried out sufficiently in Japan. In this paper one-dimensional generalized heat balance equation was introduced, by considering river bed conduction, viscous dissipation, advection heat, and chemical reaction heat of submerged material as well as surface heat balance. The effects of heat exchange coefficient, equilibrium temperature and river discharge on the river water temperature were clarified through numerical calculation. Some nomographs for obtaining the heat exchange coefficient and the equilibrium temperature from each meteorological element were constructed. Finally, the sensitivity equations of the river water temperature on hydraulic and meteorological elements were formulated, and some numerical calculation results were shown.

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