On Abnormally High Water in the Oosaka Bay

Abstract

The problem entit_??_ed is an important matter concerning with the prevention of flooding disaster in the city of Oosaka. In this paper, the present authors have investigated the problem of high waters at Oosaka and Kobe using the data obtained at the several typhoons.
First of all the high water at Oosaka was treated at the typhoon of September 1936. The treatment showed that the differnce between the predicted height of the tide and the observed height, namely the abnormal high water H caused by the violent wind and the low pressure can be expressed as follows:
or
Here V (cm/sec) is the component of wind velocity taken in the direction of the major axis of Oosaka Bay, p the observed atmospheric pressure in Hg-cm., p_??_ the normal pressure, a the appropreate constant, and c=13.2+c', p₀=76.0+p_??_', 76.0-p=P, b the wind factor, and c the pressure factor.
The numerical values of wind factor b and pressure factor c are calculated as follows:
b=0.21 and c=17.15.
The theoretical value of the wind factor obtained by Dr. Colding for the case concerned is 0.17 and smaller than the value obtained above. It is probably due to the complexity of the form and depth of the bay, here overlooked.
The high water at Kobe was discussed for a severe typhoon which passed through the Oosaka bay in August 1935. Calculating as before we get;
b=0.056 c=25.4
A probable reason for the large value of c thus obtained will be the following. A kind of drift current produced, by severe wind within the typhoon area causes an abnormal high water in the ocean, and it flows into Oosaka bay and makes, the water there high.
If we assume that the inflow is constant during the time concerned, the accumulating mass should be proportional to the inflow, and a following equation may be obtained: (a+13.2p₀')+bV²+c'P+dT=H-13.2P
Where T is the time concerned, d the accumlation factor. Calculating from this formula, we get b=0.015, c=19.25, d=0.57.
The pressure factor c is yet too large though it is smaller than that obtained in the previous case. But it seems to be impossible to separate the pressure effect from the accumlating mass by the drift flow, because the pressure falls almost proportionally to the time.
Assuming c=13.2 as a theoretical value, we get d=0.86, b=0.011 and again assuming the pressure factor of the same value as above, and considering the term of T², the previous equation becomes
(a+13.2p₀')+bV²+d+dT2=H-13.2P
Here we get the wind factor 0.031 and accumlation factor 0.72. This value of the wind factor coincides very well with that obtained by Colding's formula for Kobe.
Besides, assuming that the accumlation factor is 0.7, we calculated the maximum velocity of flow passing through the Kitan straits and obtained 2m/sec for velocity of flow. Though we have no data to affirm the result at present, the above velocity of inflow seems not to cause serious error as the current there.