Tidal water

“ 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. ”

“ In such cases, however, where the rivers flow into tidal seas, it is important to place the jetties sufficiently apart to avoid any loss of tidal influx, since the tidal flow assists the fresh-water discharge in keeping the outlet open; whereas, with rivers flowing into tideless seas, a moderate restriction of the width between the jetties increases the scour. ”

“ 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. ”

“ We now turn to another class of waves which are of even more importance than those of the tides—to the undulations which are produced by the action of the wind on the surface of the water. While the tide waves are limited to the open ocean, and to the seas and bays which afford them free entrance, wind waves are produced everywhere where water is subjected to the friction of air which flows over it. While tidal waves come upon the shores but twice each day, the wind waves of ordinary size which roll in from the ocean deliver their blows at intervals of from three to ten seconds. ”

“ Tide is the vertical rise and fall of the water, and tidal current is the horizontal flow. The tide rises and falls, the tidal current floods and ebbs. The navigator is concerned with the amount and time of the tide, as it affects access to shallow ports. The navigator is concerned with the time, speed, and direction of the tidal current, as it will affect his ship’s position, speed, and course. ”

“ Again, when the tidal swelling is increased in height by the convergence of the shores between which it moves, it is no longer a mere oscillation or pulsation of the great ocean, but the water acquires a true motion of translation, and rushes past headlands and through narrow channels with tremendous force and speed—a phenomenon well known along the west coasts of Scotland and Scandinavia. In some cases the advancing tide on entering a narrow inlet or estuary gathers itself into one or more large waves, and rushes up between the converging shores. ”

“ The front side of this great wave takes an almost vertical position, resembling an advancing wall of water, and works great havoc with boats and shipping which have had the misfortune to be left in its path. To understand more completely how a “bore” is formed, the reader must be reminded of the cause of all tidal phenomena. Any one who lives by the sea or an estuary knows well that the sea-level rises and falls twice every 24 hours, and that the average interval of time between high water and high water is nearly 121⁄2 hours. ”

“ Lying funnel-shaped toward the great tidal movement from east to west it gathers from the incoming tide a great deal of water that does not belong to it, and then gradually compressing it between narrowing shores, piles it up in places sixty feet in height, and this gives rise to many peculiarities. ”

“ The range of the tide at times of new moon and full moon 'is greater than the average,' as 'high water then rises higher and low water falls lower than usual.' The tides at such times are called 'spring tides.' When the moon is in its first and third quarters, 'the tide does not rise as high nor fall as low as on the average.' At such times the tides are known as 'neap tides.' 'Tidal Datum Plane,' U.S.C.oast and Geodetic Survey, Special Publication No. ”

“ If the theory of the tides was to be the simple one so often described, then at every port noon should be the hour of high water on the day of the new moon or of the full moon, because then both tide-exciting bodies are on the meridian at the same time. Even if the friction retarded the great tidal wave uniformly, the high tide on the days of full or change should always occur at fixed hours ”

“ Stand on the bank of an estuary or river up and down which a great tidal current ebbs and flows; you [42] will see the water copiously charged with sediment which the tide is bearing along. Engineers are well aware of the potency of the tide as a vehicle for transporting stupendous quantities of sand or mud. A sand-bank impedes the navigation of a river ”

“ Whereas the size of tideless rivers depends wholly on their fresh-water discharge, the condition of tidal rivers is due to the configuration of their outlet, the rise of tide at their mouth, the distance the tide can penetrate inland, and the space available for its reception. ”

“ There are another ten thousand who show in varying degrees some tiny, almost imperceptible, superiority of standing a long spell without air under water. Raising of the land or the set of winds gives a season of abnormally low high tides. The animals just on the upper edge of the tidal belt die out for lack of their regular tidal supply of water, except some few who can, having the slight differential advantage apparent among them, stand the strain of living so long in the air. ”

“ The ocean tides are also immensely powerful, but the rise and fall of the water is so slight and so gradual in most places that an enormous plant is [175] required to obtain any appreciable amount of power. In certain regions, however, tidal power is actually in use to-day. ”

“ The evidences of the powerful wearing action of tidal currents is seen in their extremely rugged and precipitous coasts, and deep channels. Sharp pointed peaks three to four thousand feet above the sea, rise nearly perpendicularly out of the water. ”

“ The semi-synchronous oscillation of the Southern Ocean raises the magnitude of oceanic tides somewhat above these directly generated values.
Oceanic tides are true waves, not currents. Coast tides are currents. The momentum of the water, when the tidal wave breaks upon a continent and rushes up channels, raises coast tides to a much greater height—in some places up to 50 or 60 feet, or even more. ”

“ 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. ”

“ And it is probable the time is yet future when we shall have any theory that will fully account for all the phenomena of the tides. On account of the shallowness of some seas, and the narrowness of the straits in others, there arises a great diversity in the phenomena, only to be accounted for by an exact knowledge of the place. For instance, in the English channel and the German ocean, the tide is found to flow strongest in those places that are narrowest, the same quantity of water being, in this case, driven through a smaller passage. ”

“ If, however, the ball is hanging by a long string we can play at battledore and shuttlecock with it, and it always meets our blows. The latter is the analogue of the tides, for a free wave in our shallow canal Tides Inverted. goes slowly, whilst the moon's tide-generating action goes quickly. Hence when the system is left to settle into steady oscillation it is low-water under and opposite to the moon, whilst the forces are such as to tend to make high-water at those times. ”

“ But the tide was still rising, and very soon the biggest waves began to come quite over the rocks, rolling the big beasts over and even washing them off, and it angered them when the waves struck them, and they roared aloud, and by and by they began to go away, some disappearing beneath the water, others with heads above the surface swimming away out into the open sea, until all were gone. ”

“ 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. ”

“ In considering the effect of the natural forces still in operation during the many thousands of years during which they have been at work, it is necessary to bear in mind that the level of the sea has all along remained the same, except so far as it is varied by the rise and fall of the tide, and by the exceptional exaggerations of tidal movement caused by the wind. ”

“ For instance, it will happen sometimes that when both the sun and moon are acting conjointly they will both be at their nearest point to the earth, and when this is the case the spring tide will be much higher than usual.
For many years the writer has observed that artesian wells, made by deep borings of small diameter into the earth to a water supply, have a daily period of ebb and flow, as well as a neap and spring tide, the same as the tides of the ocean, except that the process is reversed. ”

“ It is well known that where there are deep Inlets, large Creeks, etc., into low lands, that it is not occasioned by fresh water Rivers; there is a very great indraught of the Flood Tide, the direction of which will be determin'd according to the possition or direction of the Coast which forms the Entrance into such Inlets; and this direction the Tide must follow, let it be ever so contrary to their general Course out at Sea, and where the Tides are weak, as they are in general upon this Coast, a large Inlet will, if I may so call it, attract the Flood tide for many Leagues. ”

“ 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. ”

“ The tidal movement of the ocean, deep-sea currents, and the agitation of inland waters by the wind, lift up the sands strewn over the bottom by diluvial streams or sent down by mountain torrents, and throw them up on dry land, or deposit them in sheltered bays and nooks of the coast—for the flowing is stronger than the ebbing tide, the affluent than the refluent wave. ”

“ The air soft, and truly balmy, not like real air at all. It somehow fails to satisfy. Doesn’t seem to fill the lungs. By noon to St. Simon’s Sound, where we struck the fiercest of ebb tides. Nobody ever told me about these tides. There is a rise and fall of 7 feet and with kicker going strong and braced to a light air, we could not gain and over yank in deep water where we had to give 15 fath. scope. The tide was running better than 4 knots and that’s some tide. A beautiful afternoon and I boiled and roasted half a ham besides a duck which H. got yesterday on the wing with the rifle. ”

“ 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. ”

“ 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 ”

“ 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. ”

“ 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. ”