BORE or Tidal wave.
The dee loll, . . BUM. Bana, . . . MALAY.
Eagre, . . . . CHIN. Bar, PERS. Ball, Bora, . . . HIND.
The bore occurs in Southern and Eastern Asia on several rivers, in the Gulf of Cambay, the Ganges, the Irawadi, and the Sitang, and on some rivers in China,. Arrian (Exped. Alex. vi. 19) mentions how this phenomenon astonished the soldiers of Alexander, who had been accustomed to the tideless waters of the Mediterranean. The bore is a tidal wave which comes rolling in from the sea. In the Hoogly this is called Bora or Bore ; in China it is known as Eagre ; in the mouth of the united Tigris and Euphrates it is called Bar ; in the Dordogne in France, it is called Mascaret ; in the Maranon it bears the name of the Rollers ; but by the American Indians it is called Pororca. This phenomenon is con nected with the tides, as it always occurs at the springs.
The crest of the tidal wave in the Bay of Bengal, to the south of the bay, is almost a straight line running N.W. and S.E. between the south coast of Ceylon and the southern coast of Java. As it proceeds up the bay, it becomes convex towards the shore, and near the estuary of the Megna encounters at an obtuse angle vast quantities of fresh water coming down the three channels. When the tide is more than usually strong, as at full moon or under the influence of a strong S.W. wind, or when the river is heavily flooded, the opposing masses of water accumulate more rapidly, and the bore is produced. But when this occurs there are always two bores, one of salt water up the Sundip channel; known as the Chittagong bore ; the other, called the Dania bore, up the middle and western channels. These two bores meet to the north of Siddhi. When the bore is violent, as during the equinoxes, and also when the S.W.. wind is strong, it advances as a wall of water several feet high, stretching across the channels, and is so dangerous that native boatmen will for no consideration venture out into the river. Dr. Hooker mentions that, at the of the Megna river, the great object in the navigation is to keep afloat and to make progress towards the top of the tide and during its flood, and'to ground during the ebb in creeks where the bore (tidal wave) is not violent.
Similarly, the bore in the Hoogly is occasioned by the flood-tide, driven into the narrow river through the broad estuary, overcoming the freshes sent down by the heavy rains of the S.W. mon soon. It occurs between May and October, but is heaviest between July and September, between two days before and two days after the full moon.
It also occurs at the change, but not with such violence. The wave usually rises on the Diamond Sand, where the river suddenly contracts and comes in 12 or 15 feet perpendicular with tremendous noise, carrying everything before it, though not with equal force, on both sides of the river, as it goes from point to point in the reaches, travelling at the rate of nearly 20 miles an hour to above Calcutta. There are generally three rollers follow ing one another in quick succession, at 13 to 15 feet apart. When the S.W. monsoon has set in, the bore, for three or four days at the full and change of the moon, may be seen racing up the Hoogly river at the rate of twenty miles an hour, dashing from side to side of the river according as the bends or reaches deflect it in its course. Upon the approach of this wave a distant murmur is heard, which soon turns into the cry, Ban ! ban ! ban from the mouths of thousands of people, boatmen, sailors, and others, who are on the look-out for this much dreaded wave. This cry is the signal for all sort of small craft to push out into the centre of the river, the only spot where the wave does not curl over and break. Should any boat or small craft be caught in that portion of the wave that breaks, instant destruction is inevitable. Numerous boats from the up-country provinces are lost every year, from the crew being ignorant either of the existence of the bore, or from not knowing the correct position to take up so as to meet it. Ships at anchor in Calcutta, though not exposed to the breaking portion of the wave, frequently part their cables when struck with the wave. Standing on the shore during the rapid rushing passage of the bare, it is a curious sight to see the lower portion of the river, or that nearest to the sea, six or eight feet higher than the upper portion of the river. the tide rising that number of feet in an install+ The height of the bore in the Hoogly varies fro/ five to twelve feet ; it is exceedingly dangerou in some parts of the river, but more moderate others ; it never breaks on both sides of the rive at the same time. Deep water engulfs its force but shallow water, or a sandbank, brings out all its power and fury. The bore, in 1782, flowed as far as Nuddea in the Hoogly, but at the present day it falls short of that place by many miles, not ascending much beyond Sooksagor. It reaches Dacca on the Buree Guuga, and Castee on the Horinghatta branch.