ON THE EFFECT OF CONFIGURATIONS OF THE COAST ON THE STORM SURGES IN THE ISE BAY

Contour lines of the bottom of the Ise-bay are shown in the Fig. 5-1, in which the water depth under the datum level (D.L.) is indicated in meter Considering the pattern of these contours and of wave crests shown in the refraction diagram, the axis of this bay and vertical sections orthogonal to it are determined as shown in the Fig. 5-1 with chain-lines. The moving direction of this typhoon in this area was about N25°E as shown also in the same figure.


INTRODUCTION
Wind drift is generally considered as the predominant factor of the storm surge along the sea coast.Authors noticed the fact that the duration of the wind blow of any direction is not long even at a big typhoon, while the storm surges more than 2 m are sometimes observed in the interiors of Osaka-, Ise-, and Tokyo-bay, and they have studied on another factor which might cause such water rise.
A hump of water caused by a low atomospheric pressure transmits in the manner of a long wave and is deformed under the topographical effect when it comes into a bay.Authors are intending to show that the build-up of water due to topographical effect is sometimes larger than that occurring by wind drift.
In this paper, the calculation was carried on neglecting the effect of wind drift and its result was compared with the observed value.Sectional area : A , width of the bay : B , and mean water depth : H 0 (jsAo/Be) relating to the distance from the inlet of the bay are given together in Fig. 5-2.
To make the calculation simple, we may assume H 0 to be constant (H 0 == 2.5 m) from No.These results may be interpreted as follows.In the inner part of thi bay, the configuration of the coast forms some typical wedge-shape.Due to the comparatively small surface area of this region, the wind effect may be secondary and the effect of the configuration of the coast may be so primar in this inner region that tne Green's law will be applicable.While in the outer part of the bay, the surface area is much larger than the inner part and the wind effect may be more dominant and the increase of tidal height will be larger than that predicted only by the effect of the bay configuration.

Fig. 5-1
The configuration of the Ise-bay

INTRODUCTION
In the South-Western part of the Netherlands the Delta project is being carried out consisting inter alia of k main dams closing k large inlets (fig.1).Through the four tidal inlets to be closed about 1800 million cubic metres of water run into the Delta area during flood tide and flow out again during ebb tide.This means about 7000 million cubic metres daily.
The bottom of the inlets and the sea-bottom consist of fine sand (dcQ = .100-.300 mm), which is in constant movement.During the past centuries considerable changes in the bottom contour have taken place.Yearly many millions of cubic metres of sand are moved by the water.The bottom is a very complicated system of gullies and sandbanks which has evolved down the centuries and is ever changing.It is evident that the dams under construction will out off the tidal flow into and out of the area and that this will result in a considerable change in the sand movement.
The underwater estuary extending as far as 20-25 km seawards from the dams will probably have to adapt itself rather suddenly, i.e., within a few decennia.This can be dangerous for the Western extremities of the islands.The whole combination of phenomena concerned has to be studied and watched very carefully.
Basic information concerning the sand movement and its consequences is given by soundings.
A long term of frequent and accurate soundings with very good repeatability is required for the entire coastal area of the estuary.However, the meteorological conditions for sounding are such that good conditions only obtain on about 20 days a year, because good visibility and a quiet sea must occur simultaneously.Moreover, there is a serious shortage of landmarks and at distances seawards of less than 10 km from the shore visual location is impossible.The only solution is to make the location independent of visibility.For these reasons it was decided that a system of radio-location should be devised.We were advised by an independent expert to adopt the Decca survey system.
With such a system it is possible to make frequent soundings with very good repeatability and with a reasonably low number of launches, because many more suitable days (and nights) become available.This system of radio-location is called the Delta chain.The system is also used for special purposes (velocity and sandtransportmeasurements).
TOPOGRAPHICAL DATA OF THE ISE-BAY AND OBSERVED HEIGHTS OF THE METEOROLOGICAL TIDE BY THIS TYPHOON Contour lines of the bottom of the Ise-bay are shown in the Fig. 5-1, in which the water depth under the datum level (D.L.) is indicated in meter Considering the pattern of these contours and of wave crests shown in the refraction diagram, the axis of this bay and vertical sections orthogonal to it are determined as shown in the Fig. 5-1 with chain-lines.The moving direction of this typhoon in this area was about N25°E as shown also in the same figure.
2 to No. 4 section and decrease linearly from No. 4 toward the inner.Precise observations of the height of the stoxm surge could not be co lected, but only the approximate values are shown in Fig. 5-3 at present, in which £ is the maximum deviation from the astronomical tidal stage.The deviation at Nagoya harbor (£^3.5 m) is the largest one ever recorded in Japan.BUILD TO OP A LONG WAVE DUE TO GRADUAL VARIATIONS OP SECTIONAL AREA OF THE BAY For the change of heights of a long wave in the variable section, thei is a well-known formula (Green's law).(See, for instance, Lamb : Hydrodynamics 6th ed., p. 274, for detailed derivation.)</<* «(B 2 *H,/B 2 H) 4 where <£ : the wave-height of a long wave, B : the width of the channel, H : the water depth before reaching of waves, and the subscript * refer to the value in the initial section.In our calculations, the static water depth (H) may be taken as folio* considering that the time variations of the astronomical tide are generally much slower than those of the storm surge.H s H 0 + h where H 0 : the water depth under the datum level, h : the height of the astronomical tide above the datum level.Ho and h in each station are shown in the Table 5-1, respectively.The ratio <?/<* and B*H*/Bll computed from the Fig. 5-2, 5-3 and the Table 5-1, are plotted in a log-log diagram.(Pig.5-4) In this figure, we see that the Green's law is applicable for the region between No. 5 and No. 8 section (at the inner part of tnis bay).While, between No. 2 and Ho 5 (at the inlet and middle part of the bay), ^ / £ * seems to be proportiona to (B*H*/B 2 H)^, and the increment of height in this region is greater than that predicted by the Green's formula.

Fig
Fig. 5-2Sectional area, width and mean waterdepth at each section.