中海干拓防潮水門の水理模型実験(I) : 淡水におけるdu Buat公式の流量係数μの値の検討

In the Nakaumi Sea Reclamation Planning the discharge through tide-gates has been calculated by du Buat's formula, but it is a question whether the value of discharge coefficient given in the formula is entirely applicable to this case. It was to clarify this question positively that a number of hydraulic model experiments were carried out to investigate how the discharge coefficient is influenced by the fresh and the fresh-salt water.
In the case of fresh water the expected results were obtained as follows :
1 . The results obtained under the condition of entirely opened gates indicate that the value of the discharge coefficient μ of du Buat's formula ranges from 0.91 to 1.09. The value of μ hitherto recognized generally changes from 0.6 to 0.95, but judging from these results it seems too small. Especially in the case of larger discharge, it may be estimated to be as large as about 1.0 extending over a wide difference of water level between inside and outside.
2 . The value of the discharge coefficient C of du Buat's formula is not constant in case of partly opened gates in the fresh water, changing according to the amount of water discharge or the difference of water level. Generally it is more than 0.63 on the condition of a submerged weir.
As for the projected hydraulic model study in the fresh-salt water, it is necessary to continue more minute experiments. That will be dealt with in the following report.