Unsaturated sand column experiments were carried out to evaluate the effects of water content (θ) on the sorption-desorption reaction of cobalt by sand. Uniform water content in the unsaturated sand column was obtained by passing air into the column. Water content was controlled by the solution feed rate, the air suction and the height of sand column. The distribution coefficient (Kd) of cobalt estimated from chloride and cobalt breakthrough curves was minimum at about volumetric water content (θ)=0.17. And saturated Kd was about five times larger than minimum Kd(at θ=0.17). The relationship between θ and Kd was expressed by the concave curve. Therefore, in the case of evaluating the movement of sorptive materials in the unsaturated soil layer, it is important to perform unsaturated soil column experiments and estimate the unsaturated Kd values.

View full abstract

We propose analytical methods using satellite data to regress effluent axis with the weighted least squares method, and estimate the influence of river effluent on the ambient sea through the distance along the axis in arange between the river mouth and the downstream boundary of diffusion area. As examples the effluents from the Shingu river are analysed and show that the diffusion area estimated through water temperature may differ from that through water turbidity, especially when the discharge rate at the mouth is small. It is considered that turbidity distribution is under the influence of suspended soil particles washed out at the sand bar or beach near the mouth. The salinity is also one of indispensible parameters demonstrating the behaviors of density currents such as the river effluent, and we estimate it through the ratio of TM-band 1 to band 3.

View full abstract

To improve a water quality in the stagnant reaches of urbun rivers, the “airlift” apparatus can be efficiently introduced. Hydraulic behavior of the airlift was discussed by laboratory experiments. The discharge lifted and the suitable aspect ratio of the channel cross-section for the effective circulation of flow induced by the airlift can be determined by the aid of theoretical analysis. Field tests were also conducted in order to investigate the applicability of the airlift. The information on the characteristics of DO and SS behaviors caused by the airlift was also obtained.

View full abstract

The disintegration phenomena of nonlinear wave train passing over a submerged dike have been investigated by a previously developed numerical model. The model, based on the time dependent boundary element method, employs an effective non reflective open boundary treatment and can be applied to arbitrary nonlinear wave processes. The computed wave profiles at various locations agree favorably with experimental observations. The numerical results indicate that the higher harmonics generated during the passage over the dike are transformed into prominent free waves in the trailing side of the dike, demonstrating the essential mechanism of the observed disintegration phenomenon. It is found that the amplitude of each higher frequency component is spatially modulated with the beat λ over the dike, and that the corresponding amplitude of transmitted wave becomes remarkably large when the width of the dike is nearly one half of λ. Furthermore, in the case of large incident waves, significant decomposition is found to occur even when the dike is deeply submerged.

View full abstract

To investigate the mechanism of beach erosion in a storm, a daily survey of beach profile and the measurement of infragravity waves near the shoreline have been carried out in a field during two and half years. Evidences of berm erosion and berm formation have been abstracted, being 58 cases and 219 cases respectively. Analyses of these data reveal that the infragravity waves and the level rising of water table play a important role in the berm erosion in a storm. The infragravity waves run up beyond the berm crest to the backshore. The swashed water permeates into the beach, which contributes to a high water table. The permeated water rises to the surface of foreshore, where the beach is eroded by the backwash of infraravity waves.

View full abstract

The flocculent activated sludge is adhered and bound with high molecular compounds which is produced by microorganisms. We developed the biological waste water treatment process by using this original characteristic of activated sludge. The majar advantage of this process is to stimulate the solids-liquid separation by increasing density of activated sludge floccule with taking in blast furnace granulated slag powders. We investigated a mechanism of taking blast furnace granulated slag powders in activated sludge and the sludge convection in the fludizied-bed reactor for the purpose of making clear the characteristics of the process.

View full abstract

Based on the results of field observation in a tidal river, modeling of sediment transport processes is performed and long term transport is simulated with newly developed procedure, in which a Lagrangian reference frame is used to reduce numerical dispersion. Suspended sediments transport in the tidal river is calculated with erosion and deposition of sediment, consolidation of fluid mud to cohesive bed mud, and transport by turbidity current of fluid mud. Sediment transport processes concerned with the formation and maintenance of turbidity maxima are sufficiently simulated for a fortnightly cycle with a Lagrangian sediment transport model.

View full abstract

Field observations were carried out at several times for one semi-diurnal cycle and for one fortnightly cycle in the well-mixed estuary, the Rokkaku River, in order to investigate the mechanism of suspended sediment transport and water quality variation. In the estuary, a turbidity maximum is formed and moves toward up- and down-stream with erosion and deposition of sediment according to tidal action for the semi-diurnal cycle. For the fortnightly cycle, salt intrusion varies with tidal stage and variations of suspended solids concentration have such a tendency that the concentration becomes lower during neap tide and higher during spring tide. Water quality on dissolved matters is easily characterized with water volume accumulated from the head of the estuary.

View full abstract

Changes of marine epilithic organisms are examined to the surface of the concrete with continuous voids (NFC) which may be effective in the prompt establishment of biologically favorable environments. When NFC is immersed in the seawater, its continuous interior voids as well as its rough surface are fully exposed to the water and rapidly neutralized. This then leads to the attachment and growth of marine microbes and eventually to the formation of a layer of biotic membranes. As a result, decomposition and mineralization of the marine organic matters and the growth of algae, attached bacteria and animals are accelerated. Thus, this type of concrete may be useful in the establishment of well-balanced biological environment.

View full abstract

Leachate from waste disposal site often contains refractory organic compound and/or high concentrations of nitrogen and salts. In this paper, the leachate application experiments were performed to investigate the availability of soil-turf filter system for advanced treatment, and the effects of the leachate irrigation on the growth of turfgrass (Zoysia matrella Merr.) was studied. As the application rate increased from 3 to 20mm/day, the biomass yield of Z. matrella increased. It was concluded that Z. matrella possessed superior salt tolarance. However, the nitrogen uptake of Z. matrella was inhibited when the chloride (Cl^-) concentration was over 5000mg/l, and when Cl^- concentration was beyond 10000mg/l, the growth rate decreased to half of the no chloride addition experimental run.

View full abstract