Tidewater

“ In the Ouse the tide rises and falls, so it is necessary to stop the mouths of the great drains going into it, which is done by a structure of timber or brick-work like the gates of a dock, which close at high tides to keep out the sea-water, and open at low tides to let out the land water. Either from insufficient workmanship or bad locality, or unusual pressure, or from burrowing animals, the land water, or sea water, or both, made a flank movement, and burst up the whole sluice, so that the tide, instead of being confined to the river, obtained free way up the drain also. ”

“ It seems as if the whole of the great sea was forever slowly rising or falling, up and down, with a slow and solemn motion.
Any boy who lives by the shore knows that this is the tide. He knows that all his fun depends on this regular rising and falling of the tide. At high tide the fishing is good. At low tide the flats are bare, and the boys can dig clams or watch the long-legged plovers wading about in the shallow water. This curious rising and falling of the tide is caused by the attraction of the moon. The sun also helps, but in a lesser degree. ”

“ The great aim, on the contrary, of all tidal river improvement should be to facilitate to the utmost the flow of the flood-tide up a river, to remove all obstructions from the channel so as to render the scouring efficiency of the flood and ebb tides as great as possible, and by making the tidal flow extend as far up the river as possible to reduce to a minimum the period of slack tide when deposit takes place. ”

“ A bore indicates defects in the tidal condition and the navigable channel, which can only be reduced by lowering the obstructions and by the regulation of the river. No tidal river of even moderate length is ever completely filled by tidal water; for the tide begins to fall at its mouth before the flood-tide has produced high water at the tidal limit, as most clearly shown in the case of a long tidal river by the Hugli tidal diagram. ”

“ Sue followed her brother Bunny up on the deck of the Fairy. They were quite a distance out from the dock now, and were drifting farther and farther each minute, for the tide was running out. Sandport Bay connected with the ocean, and twice every day there is a great movement of the water in the ocean, called the tide. The tides make the water high twice each twenty-four hours, and then the tides get low, or run out. The moon and sun are thought to cause the tides, as you will learn when you get a little older and have to study about such things. ”

“ Now when the tide of the ocean is at its ebb, the waters of the Lake rush over these banks with so furious a current that no vessel can either go down or come up. If they attempted to go down, they would be swamped by the meeting of the waves; if they attempted to come up, the strongest gale that blows could not force them against the stream. As the tide gradually returns, however, the level of the ocean rises to the level of the Lake, the outward flow of water ceases, and there is even a partial inward flow of the tide which, at its highest, reaches to the Red Rocks. ”

“ The momentum of the tide running up the centre of the river is in excess of that along the banks, so that the current changes near the shore before it does in the middle, and, as the sea water is of greater specific gravity than the fresh, weighing 64 lb per cubic foot against 62-1/2 lb, it flows up the bed of the river at the commencement of the tide, while the fresh water on the surface is running in the opposite direction. ”

“ The tidal information becomes important and must be considered in navigation or in anchoring in waters where the available depth at low water approximates the draft of the vessel. In the general use of coast charts it is also important to observe the effect of the stage of tide on the appearance of many features. Rocks rising some feet above low water may be entirely submerged at high water. In some areas the aspect may be radically changed between high and low water by the baring of extensive shoals or reefs. ”

“ It is never high water at all points simultaneously. To show the actual state of affairs at various stages of the tide, series of lines must be drawn as in fig. 67, where the firm lines show the flood, and the dotted lines the ebb tide.
The flow in the tidal reach of a river is the same as if the water was alternately headed up by a movable weir and then allowed to flow freely and be drawn down. If the water carries silt, the tendency for deposit to occur is (Chap. V., Art. 2) no greater than if there was no heading up or drawing down. ”

“ When the tide is in, the breakers dash against these rocks even in calm weather with a force that sends the spray very many feet high, and any one then attempting to get round the point does so at the imminent peril of his life; the river also becomes swollen by the tidal inflow, and although a ferryman lives on the opposite bank, he wisely forbears from venturing to cross in his canoe until the tide has well run out again. ”

“ Progress of the Tide-wave over the Ocean and in the British Seas.—Sufficient tidal data would give the state of the tide at every part of the world at the same instant of time, and if the tide wave is a progressive one, like such wave as we may observe travelling along a canal, we should be able to picture mentally the motion of the tide-wave over the ocean and the successive changes in the height of water at any one place. ”

“ At low tide for miles out one sees only a vast plain, moist, strewn with shells, and intersected here and there with deep hollows and shifting sandbanks; but when the tide changes, and long before the waters appear in sight, are heard tremendous sounds, crash after crash, thunder after thunder, of the advancing tide, which comes in leaping like a huge monster, thirty to forty feet high, and breaks with terrific violence against the shore, carrying everything before it. ”

“ Estuary and Shore Deposits.
Rivers which discharge themselves into the ocean, where tides and currents break with a certain regularity the quiet of its waters, exhibit always at their mouths, and often along the lower part of their channels, another set of phenomena.
Where the tide enters a river's mouth, and periodically combats the freshes, these are "backed" to certain distances, their motion is nearly destroyed for a time, and the sediment, which was only suspended by the agitation of the water, is dropped in the interval of quiescence. ”

“ It is high-water in the stream, on the days of the new and full moon, between two and three o'clock; and the tide rises, upon a perpendicular, between three and four fathoms. The reason of the tide's being greater here than at other parts of this coast, is easily accounted for. The mouth of the river being situated in a corner of the coast, the flood that comes from the ocean is forced into it by both shores, and by that means swells the tide to a great height. ”

“ At length the tide began to flow, the ship began to bury forward; down she went, till the water was coming into the hawse-holes, the cable sung, and the tar began to stand in drops on it with the strain, when all at once the anchor let go with a surge that threw every man from his feet. The tide was very convenient then; if it had not been for it, we must have gone ashore, got a grappling, and grappled to the fluke of the anchor, or left it. Again the tide is very convenient for a timepiece; if you keep the run of the tide, you have the time of day. ”

“ The time of greatest flow of an artesian well will occur at low tide in the ocean. This might be accounted for from the fact that when the tide is at its height the moon is also pulling upon the crust of the earth, which would tend to take the pressure off the sand rock which lies one or two thousand feet below the surface and through which the flow of water comes, and thus slacken the flow. When the moon is in position for low tide, the crust of the earth would settle back and thus produce a greater pressure upon the water-bearing rock. ”

“ I don't know how the tides are, but if it is high tide now, the top of the opening would be eighteen inches out of water at low tide, for, as you know, the tide only rises about two feet on this coast. In that case a boat would be able to come in and out at low tide, but of course a man wanting to come in or go out could easily dive under at any time. Well, that settles that point for the present. It was a clever plan; any amount of water could flow out in flood time, and yet no one who took the trouble to come behind that ledge of rocks we saw would have any idea that there was an opening. ”

“ Tide′-gauge, an instrument for registering the state of the tide continuously.—adj. Tide′less, having no tides.—ns. Tide′-lock, a lock placed between an entrance-basin and a harbour, canal, or river, and furnished with double gates, so that vessels can pass either out or in at all times of the tide; Tide′mill, a mill moved by tide-water: a mill for clearing lands of tide-water; Tides′-man, Tide′-wait′er, an officer who waits the arrival of vessels, to secure the payment of the duties: one who watches public opinion before declaring his own ”

“ The argument on which we are to base our researches is really founded on a very familiar phenomenon. There is no one who has ever visited the sea-side who is not familiar with that rise and fall of the sea which we call the tide. Twice every twenty-four hours the sea advances on the beach to produce high tide; twice every day the sea again retreats to produce low tide. These tides are not merely confined to the coasts; they penetrate for miles up the courses of rivers; they periodically inundate great estuaries. In a maritime country the tides are of the most profound practical importance ”

“ A tidal wave that propagates up a relatively shallow and sloping estuary or river in a solitary wave. The leading edge presents an abrupt rise in level, frequently with continuous breaking and often immediately followed by several large undulations. An uncommon phenomenon, the tidal bore is usually associated with very large ranges in tide as well as wedge-shaped and rapidly shoaling entrances. ”

“ For the regular order the flood-tides observe, and the notoriety of the extent of the country subject to inundation by them, could never have given occasion for such absurd actions. For the tide flowing twice every day, how could any one think for an instant that it was not a natural and harmless phenomenon, and that it occurs not only on their coasts, but on all others bordering on the ocean? ”

“ The result will be that the particles will travel a little farther out from the shore each time it is swung to and fro in the alternating movement of the tide.
The effect of tidal movement in nurturing marine life is very great. It aids the animals fixed on the bottoms of the deep seas to obtain their provision of food and their share of oxygen by drawing the water by their bodies. All regions which are visited by strong tides commonly have in the shallows near the shores a thick growth of seaweed which furnishes an ample provision of food for the fishes and other forms of animal life. ”

“ You must understand, then, that all tide takes its rise in the free and open ocean under the action of the moon. No ordinary-sized sea like the North Sea, or even the Mediterranean, is big enough for more than a just appreciable tide to be generated in it. The Pacific, the Atlantic, and the Southern Oceans are the great tidal reservoirs, and in them the tides of the earth are generated as low flat humps of gigantic area, though only a few feet high, oscillating up and down in the period of approximately twelve hours. ”

“ Also made my ninth canvas ballast bag all French seamed and Bristol Fashion. At 5 p.m. tide slacked, and we made our next creek and anchored soon after for the night. We can make neither head nor tail of these creek tides and just have to go when they serve and drop over hook when they don’t. Sometimes one sound will dominate the tide in a connecting stream, sometimes the other, and the time of change cannot be judged by change in either sound, but depends upon size of water body drained by that special stream. Local knowledge alone can solve the problem. ”

“ Out in mid-ocean, for instance, an island like St. Helena is washed by a tide only about three feet in range; an enclosed sea like the Caspian is subject to no appreciable tides whatever, while the Mediterranean, notwithstanding its connection with the Atlantic, is still only subject to very inconsiderable tides, varying from one foot to a few feet. The statement that water always finds its own level must be received, like many another proposition in nature, with a considerable degree of qualification. ”

“ To get a very large tide, the place ought to be directly accessible by a long sweep of a channel to the open ocean, and if it is situate on a gradually converging opening, the ebb and flow may be enormous. The Severn is the best example of this on the British Isles; but the largest tides in the world are found, I believe, in the Bay of Fundy, on the coast of North America, where they sometimes rise one hundred and twenty feet. Excessive or extra tides may be produced occasionally in any place by the propelling force of a high wind driving the water towards the shore ”

“ Jetties at Lagoon Outlets.—A small tidal rise spreading tidal water over a large expanse of lagoon or inland back-water causes the influx and efflux of the tide to maintain a deep channel through a narrow outlet; but the issuing current on emerging from the outlet, being no longer confined by a bank on each side, becomes dispersed, and owing to the reduction of its scouring force, is no longer able at a moderate distance from the shore effectually to resist the action of the waves and littoral currents tending to form a continuous beach in front of the outlet. ”