Koreyoshi Yamasaki

Modeling of fluid mud flow on an inclined bed

Characteristics of fluid mud flow on an inclined bed were investigated in the quiescent state in an experimental flume. The slope of the inclined bed was adjustable from 0 to 1:473. Suspension concentration in the experiments ranged from 3.2 to 64 kg m −3 . With an increase in the initial concentration, the maximum velocity of fluid mud decreased but the highest concentration increased. Apparent viscosity in the fluid mud was three orders of magnitude larger than that of water. Based on these experimental results the constitutive equation, the rate of deposition and the dispersion coefficient in fluid mud were obtained. Using these equations discretized by the SIMPLE method, simulation of fluid mud flow on the bed was performed. The simulation results in the quiescent state agreed well with the experimental results, and accurately reproduced fluid mud flow on the inclined bed.

A New Fish Biological Health Index for Assessing River Health Environment in the Muromi River Japan

This research was carried out to develop and apply a new fish-based biological health index (FBHI) to assess the river health and to diagnose the current state of the Muromi River basin in Japan. The research system was the Muromi River (33°34’ 46.38”N, 130° 20’ 8.7” E) class B river which flows past the city of Fukuoka prefecture, Japan and confluence destination the Hakata Bay. Data on fish assemblages collected via fishing net. We used the scientific literature and expertise from regional fish researcher to provide a comprehensive functional description of the FBHI, than we screened 14 candidate metrics from inter-regional variation in metric utility which has five main sources, all of which are illustrated in this research: the origin fish community, life history type, swimming layer, suitable flowing type and spawning ecology type. We can quickly calculate the assessment result of an FBHI score using fish data collected from a river section. Hashimoto Bridge was in much better condition than the other four locations, as the area around it exhibited a diversity of habitat types. Hamaide Weir, Hanadate Weir and Tochigawara Weir were all in poor condition, meanwhile Otoide Weir were in moderate condition. According to these results, we suggest some detail design planning to the each site referring to the lacking habitat: to construct floodplain, to make a variety of flow velocity using, and to install some spawning vegetation.

A Study on the Behavior of Hypoxic Water in the Offshore Hollows near Muromi River Mouth in Hakata Bay

The behavior of the hypoxic water in the offshore hollows which were dug from 1982-1986 near Muromi River mouth in Hakata Bay, is studied.In these three years, 17 years after the construction of these hollows, the hypoxic condition of the bottom water of these hollows has been observed to be gradually worsening.Rapid formation of the hypoxic condition in June and rapid extinction in October were seen at the bottoms of the hollows in 2006.Piling up of the density layers in the sea water was thought to be the formation mechanism of hypoxic condition in June.The DO flux caused by the vertical mixing of the sea water or inflow of the sea water of high DO and high density from outside was thought to extinguish the hypoxic condition in October.

Field study and modelling on the characteristics of bed mud formation processes at the Rokkaku River

Field observations of bed mud formation prosesses were continuously carried out at a site 11km upstream from the river mouth of the Rokkaku River in Japan from November 28, 1994 to February 4, 1995. A large experimental reservoir was constructed along a mudbank in the midstream of the Rokkaku River. From the observations, the maximum sedimentation rate on the flats per one tide cycle reached about 0.01m at spring tide. Based on the observations, modelling the bed mud formation process in the reservoir was performed. The process of the bed mud formation consists of three stages: deposition-consolidation, sweep-out and evaporation processes. The simulation results explain the formation process of the bed mud layers in the reservoir very well, so that, the process in tidal rivers can be explained in terms of this method by composing shear stress in the bed itself and that generated by the flow.

Variation of Chemical Properties of Ground Water in Farm Land

Effect of the fertilizer on chemical properties of ground water was investigated from March to November in a farm land of West of Fukuoka City. The variation of dissolved oxygen (DO) and nitrate (NO3-N) concentrations in ground waters with time was greatly different by the surface conditions of the land: paddy field or vegetable field. In the case of the former, the DO and NO3-N concentrations decreased gradually from May and showed a minimum at the end of August. While, in the case of the latter, the concentrations were highly constant. Despite that the large amount of phosphate was manured, its concentration in ground waters was low.