Takeshi Horie

Flow and particulate nutrient removal by wetland with emergent macrophyte

Coastal wetland with emergent reed has the important function of settling particles in the flow. We undertook some experiments in order to ascertain the hydraulic characteristics of shallow surface flow in reed fields. The decline of water surface and the flow resistance coefficient were measured for low velocity in an experimental channel. Particle tracers were injected into the flow and the particle removal rate was calculated from the change of the particle concentration along the flow. The one-dimensional model with water level correction fits well to the data. The wetland system with reed will be a powerful means of eliminating particulate nutrient load in coastal areas.

Numerical modelling for the prediction of sedimentary improvement by sand capping over a contaminated seabed

An ecological system dynamics model is developed for the prediction of the seabed change after the placement of a sand layer over the contaminated seabed. The model simulates the cycling of materials among seawater, seabed sediments, and marine natures such as benthos, bottom fish and oyster in the coastal seas. Special attention is paid to the modelling of the interaction between the aquatic system and the sedimentary one, such as settling and the release of nutrient salts. The computation domain is divided into ten boxes with eleven layers in the water zone and seven layers in the sediment zone. The degree of seabed improvement is evaluated with the decrease of benthonic mortality and the decrease of dissolved oxygen consumption in the bottom layer. A field experiment of seabed capping was carried out in Kure Bay, Japan. The model predicted quite well the seasonal variations of the dissolved oxygen, zooplankton, and benthos, which were observed in the field. The model developed here enables to evaluate ...

Water quality management and waterfront development of a eutrophic bay

ABSTRACT Excess nutrient loads from urban areas give rise to many problems with the water quality in shallow littoral zones. New waterfront development should be accompanied by a system of water quality improvement. A perspective of counter-measures, other than sewage treatment systems, is proposed and some case studies are given. Utilization of natural energies and coastal ecological activities is essential for economic improvement. Numerical water quality predictions are made with the assigned removal efficiency of the systems. Construction costs of treatment systems are roughly estimated for each study area.