Tidal Bores

The interaction of the tide with the outgoing current from a river can sometimes produce an unusual solitary wave that proceeds up the river from its mouth. Called a "tidal bore", this wave illustrates the depth dependance of the wave velocity of waves from the ocean.

潮水与河流出海口的水流相互作用有时会产生一种不寻常的孤立波，该波从河口向上游传播。这种波被称为'潮汐涌浪'，它展示了波速与波深的依赖关系。

The precondition for the creation of a tidal bore is the existence of an outflow current speed from the mouth of a river that exceeds the incoming speed of waves from the ocean associated with the incoming tide. The wavelength of tidal waves is longer than the depth of the shallow water near the shore, so they move shoreward with a velocity that depends upon the water depth. The limiting case expressions for the "celerity" or wave velocity with respect to the water are

潮汐涌浪形成的前提条件是，河流河口处的出流速度必须超过与入潮相关的海洋波的入射速度。由于潮汐波的波长比近岸浅水区的水深大，因此它们以取决于水深的速度向岸边移动。关于“波速”或波相对于水的速度的极限情况表达式为

From the shallow water velocity expression, you can see that the wave slows down as it approaches the shore in progressively shallower water. As it slows, the waves become steeper in the fashion of general ocean waves. In a shallow estuary, it is possible for the wave velocity to be slower than the outflow velocity from the river. This can effectively create a block of the incoming tide at the depth where the incoming wave velocity is equal to the river's outflow velocity. But the rising tide deepens the water and increases the wave velocity until it exceeds the river's outflow velocity. "Once this condition has been reached, the tidal crest sweeps into the estuary as a conspicuous wave or even as a frothy front - the tidal bore - following the passage of which the water levels inside and outside of the estuary remain more nearly equal." (von Arx)

The most famous of the tidal bores is that in the Tsientang Kiang estuary in China. "Here junks tie up securely against the rush of the bore, which on ocasion may be as much as 25 feet high, and schedule their trips to ride upstream on the current that follows."(von Arx) Tidal bores are more prevalent under the conditions of spring tides when the gravitational pulls of the Sun and Moon are in phase. They also occur in some straits such as Messina, the passage between Scylla and Charybdis. Tidal bores occur in the Amazon River, the Severn River in England, the Petitcodiac River at the head of the Bay of Fundy, and the Seine, Orne and Gironde Rivers of France.

最著名的潮汐涌浪之一是在中国汀塘江河口出现的。‘在这里，船只可以安全地停泊，以抵御涌浪的冲击，有时涌浪的高度可达25英尺，船商则安排行程，乘着随后而来的水流逆流而上。’（von Arx）当太阳和月亮的引力作用处于同相位时，潮汐涌浪更为常见。它们也出现在一些狭窄水道中，如斯库拉与卡吕普索之间的墨西拿海峡。潮汐涌浪也出现在亚马逊河、英格兰的塞文河、新不伦瑞克河（位于芬迪湾入口处）以及法国的塞纳河、奥恩河和吉伦特河中。

从浅水速度表达式可以看出，当波浪进入越来越浅的水域时，其速度会减慢。随着速度减慢，波浪会变得越来越陡，这与一般的海浪特征一致。在浅海湾中，有可能出现波浪速度小于河流的出流速度的情况。这种情况下，可以有效地在波浪速度等于河流出流速度的深度处形成一个阻塞，阻止潮水进入。然而，涨潮时水深增加，波浪速度也随之增加，直到超过河流的出流速度。'一旦这一条件得到满足，潮汐波就会作为明显的波浪或甚至泡沫前沿进入海湾，即潮汐涌浪——即潮汐波——在进入海湾后，海湾内外的水位将更加接近。'（von Arx）