poster - International Conference of Agricultural Engineering

Wind-Induced Flow in a Closed Water Body with Floating Culture
System
Abstrat
Kunihiko Hamagami 1 *, Masayuki Fujihara 2 , Ken Mori 3 , Hidekazu Yoshioka 4
1 Faculty of Agriculture, Iwate University, 3-18-8 Ueda Morioka, 020-8550 JAPAN
2 Faculty of Agriculture, Ehime University, Matsuyama city, Ehime, JAPAN
3 Former Professor of Kyushu University, Fukuoka city, Fukuoka, JAPAN
4 Faculty of Agriculture, Kyoto University, Sakyo-ku, Kyoto, JAPAN
*Corresponding author. E-mail: ham@iwate-u.ac.jp
Hydraulic experiment by using a test tank and the construction of water flow prediction model
were conducted to take into account the effect of the floating culture system on wind-induce
flow. As the result of hydraulic experiment, it was revealed that a surface wave development
was significantly inhibited due to the coverage. When the coverage is set up transversally at
water surface, two wind-driven circulations are formed at the up- and down-wind portions of
the coverage. The water flow prediction model employing CIP-CUP (CIP-Combined Unified
Procedure) method and introducing air-water interaction of two-phase flow model well
reproduce the development of surface wave and the pattern of internal circulation obtained
by the hydraulic experiment.
Key words: wind wave, internal circulation, C-CUP method
1. Introduction
Water quality degradation due to eutrophication is a serious problem in stratified closed
water bodies in Japan. When there is no disturbance in closed water bodies with little inflow
and outflow, they are easily stratified according to their density, and then vertical mixing
becomes weak. The stratification also causes oxygen depletion in waters. Therefore,
biological purification, which largely depends on the oxygen concentration, is scarce in
closed waters compared to natural rivers. So, the water in closed waters is easily
eutrophicated or polluted. Recently, due to the increasing environmental concerns, the
heavily eutrophicated closed waters have been studied in various fields of research.
In recent studies, water purification by plant nutrient absorption attracts great attention as a
solution to the water quality problem. The floating culture system, which was originally
developed to produce crops on the water surface of lakes and rivers in China (Song et al.
1991), seems a possible option. In Japan, this has been introduced as the method for water
purification in closed waters by taking out nutrients using plants grown in a floating board
without soil (Miyazaki et al. 2000; Agata et al. 2000). Nutrients are removed from the water
while the plants grow; hence, the water is purified. Although previous studies discussed the
nutrient absorption ability of plants and considered the aspects of actual operation and
management, those had hardly considered the physical dimension of the system, i.e. the
relationship between the existence of coverage and the flow in the water.
The main driving forces of water movement in closed waters with little inflow are the wind on
the water surface and the water density distribution. The flow generally depends on the
characteristics of the water body, like its shape or depth; hence, it is necessary to estimate
the effect of the floating culture system on the flow at each water body. In the closed waters
with the floating culture system, the floats shorten the fetch, and then weaken the
entrainment at the density interface. Ozaki et al., (2003) reported that when floats are set on
the water surface of a closed water body, the entrainment velocity decreases as the area of
coverage increases. This is because the existence of the floats decreases the amount of