Caudal fin

“ When the creek is at its normal level I don't believe any water flows into the cavern at all, and even with a four foot raise I don't think much goes through. It was the first rush of the flood that carried us into the hole. And now do you see what I am driving at? As soon as the back water from Honck's dam has spent itself—and it can't take very long—the stream in front of us will become shallow, and then all we need to do is to follow it down to the outlet. It probably cuts across some bend and re-enters the creek. ”

“ This extra flow disturbed both the colour and the temperature of the clear amber water of the pond. It lifted heavily against the ice, pressed up the tunnels to the very edge of the dry chamber of the lodge, and thrust ponderously at the outlets of the dam. Understanding the peril, the wise little dam-builders sallied forth in a flurry, and with [Pg 249] skilful tooth and claw lost no time in enlarging the outlets. They were much too intelligent to let the flood escape by a single outlet, lest the concentrated flow should become too heavy for them to control it. ”

“ The heavy rains, sometimes as much as an inch in a few hours, run off with great rapidity through the drainage channels and twenty-four hours later the sides of the mountains and the footslopes appear as if not having known a rain in six months. Here and there in the bottoms of the cañons a pocket in the rock holds a gallon or two of sweet pure water, and out upon the plain pools may linger for a few days on the clay. ”

“ In a very loose, gravelly, or sandy soil, which has a perfect outlet for water below, all but the heaviest falls of rain will sink at once, while on a heavy clay, no matter [pg 032] how well it is drained, the process of filtration will be much more slow, and if the land be steeply inclined, some of the water of ordinarily heavy rains must flow off over the surface, unless, by horizontal plowing, or catch drains on the surface, its flow be retarded until it has time to enter the soil. ”

“ If the geological deposits of the drainage area are highly impervious, the surface flow will receive and transmit the water into the mass only through the cracks and fissures in the rock. Pervious materials, such as sandstones, sands, gravels, and cracked or fissured rocks, induce seepage, retard runoff, and, if such deposits are underlaid with an impervious bed, provide underground storage which impounds water away from the conditions which permit evaporation, and hence tends to increase runoff and equalize flow. ”

“ It is more than two thousand miles long; its utmost surface-sources are scarcely six hundred feet above tide-water; its bottom, at its greater depth, is more than four hundred feet below tide-water. In all its course it receives less than two score of affluents, and only two of these, the St. Maurice and the Saugeen, bring to it any considerable quantity of water, and no flood in any of them discolors its emerald surface from shore to shore. Only fierce gales of wind bring up from its own depths the sediment that can discolor its whole face. ”

“ When the water cannot be discharged from the outfall at all times by gravitation, [440] we must enlarge the main and tributary drains, so that they may serve as reservoirs to contain the drainage water during the time that the outfall sluice is closed in consequence of the water in the river or the sea, where the outfall sluice may be placed, being higher than the level of the water in the main and interior drains. ”

“ When, too, in flood time, the hurrying current seems to respond more sensitively to the shape of the shallows and the banks beneath, there boils up from below a ceaseless succession of irregular circles as if the water there expanded from a centre, marking the verge of its outflow with bubbles and raised lines upon the surface. ”

“ When the stream is in flood and comes roaring down the rocky gorge bearing along with it a vast amount of mud, gravel, and - 169 - stones, one can easily see how the friction of the transported material must wear down the hard bed and sides of the channel, and how this process repeated month after month and year after year, must aid the decomposing forces in scooping out a deep ravine. From the cascade the ascent of the stream becomes steeper and the run of water is consequently more rapid. ”

“ In many cases the natural fall can be increased by a dam or weir thrown across the stream. The engineer will also examine to what extent the head will vary in different seasons, and whether it is necessary to sacrifice part of the fall and give a steep slope to the tail race to prevent the motor being drowned by backwater in floods. Streams fed from lakes which form natural reservoirs or fed from glaciers are less variable than streams depending directly on rainfall, and are therefore advantageous for water-power purposes. ”

“ If the earth's surface were, like iron, impervious to water, the rain-water would come in torrents down the hill-sides, and along the gentle declivities, into the streams, creating freshets and inundations in a few hours. But instead of that, the soft showers fall, often on the open, thirsty soil, and so are gradually absorbed. ”

“ In some drainage areas the ground is more or less impermeable to water, and in this case the water runs readily off, causing a sudden rise in the river; and as suddenly it reaches the low-water mark. In other drainage areas the ground is very permeable to water, so that the rain penetrates to a greater depth into the earth, where it is held, and by a slow process drains into the rivers, while much more of it is carried off by evaporation and into vegetation than is the case in the drainage district before mentioned. ”

“ Leaving the Doctor to guard the canoe from a crowd of Kaukauna urchins, who were disposed to be over-familiar with our property, I went down through a boggy field to view the situation. It is a grand sight, looking up from the bottom of the rapids. The water is low, and at every few rods masses of rock project above the seething flood, specimens of what line the channel. The torrent comes down with a mighty roar, lashing itself into a fury of spray and foam as it leaps around and over the obstructions, and takes great lunges from step to step. ”

“ By degrees some portions of the bottom come in this way to be filled up to the surface of the river, and wide flat marshy spaces are formed on either side of the main stream. During floods these spaces are overflowed with muddy water, in the same way as in the case of the valley plains just described, and a coating of mud or sand is laid down on them until they slowly rise above the ordinary level of the river, which winds about among them in endless branching streams. Vegetation springs up on these flat swampy lands; animals, too, find food and shelter there ”

“ The lengthening of their new canal completed, their foraging grew easier. Trees fell every night, and the brush pile reached a size that guaranteed them immunity from hunger till spring. By the time the dam had been strengthened to withstand the late floods, there had been some sharp snow-flurries, and the pond was half frozen over. Then, in haste, the beavers brought up a quantity of mud and grass roots, and plastered the domes of their houses thickly till they no longer looked like heaps of sticks, but rather resembled huge ant-hills. ”

“ Any works in the river must be strong enough to withstand the enormous body of water of the flood stage. The locks in the chutes or side channels within the highwater levees will be inundated. The movement of the water must cause scour; and weirs, locks and abutments leading thereto would be threatened with imminent destruction.
The ratio of sediment carried by the river to the stream discharge is large. Much of this sediment is rolled along the bed of the river in waves transverse to the direction of stream flow. ”

“ If this water fell upon a flat surface of soil, with an impervious subsoil of rock or clay, we should have some sixteen inches of water in the course of the year more than evaporates from the land. If a given field be dish-shaped, so as to retain it all, it must become a pond, and so remain, except in Summer, [70] when greater evaporation from a water surface may reduce it to a swamp or marsh.
With 16 or 18 inches more water falling annually on all our cultivated fields than goes off by evaporation, is it not wise to inquire by what process of Nature or art this vast surplus shall escape? ”

“ The rapidity of the increase is accounted for by the fact that every field it passes whose surface inclines towards it is a watershed from which an unseen but considerable drainage takes place. When no brook passes through the fields the water stands and soaks downwards, or evaporates slowly: directly a ditch is opened it fills, and the effect of a stream is not only to collect water till then unseen, but to preserve it from evaporation or disappearance into the subsoil. ”

“ Strong gales are prevalent in these latitudes, and these loosen the roots, so that, if the storms are accompanied by flood, large masses of the plants are set free, and begin drifting over the lagoons. Quantities of earth remain clinging to their drifting roots, and thus they are driven backwards and forwards by the wind. The storms come generally just before the flood, and thus there is plenty of water for the reeds to float in. Eventually they are driven, whole acres at a time, into the channel of the river, and are carried down the stream. ”

“ Even the beds of sluggish rivers flowing over porous strata generally become so impermeable that excavations made in their neighbourhood, though freely collecting the subsoil water, receive no river water whatever. Thus natural or artificial surfaces which are completely permeable to rainfall may become almost impermeable when protected by surface water from drought and frost, and from earth-worms, vegetation and artificial disturbance. The cause of this choking of the pores is precisely the same as that described below in the case of sand filters. ”

“ After the height of the flood the stream clears itself by the flowing away of the turbid water much more rapidly than the water clears itself by sedimentation in the reservoir. That is to say, if at the time of maximum turbidity we take a certain quantity of water from the stream and put it aside to settle, at no time will the improvement by settling equal the improvement which has taken place in the stream from natural causes. ”

“ When there is a gradual rise lasting for a considerable time—and this is most likely to cause a high flood—there is no rise of the flood-level downstream of the embanked reach, except such as is due to the increase in the discharge of the stream consequent on the absorption and evaporation being less than before, owing to the reduced area of flooding in the embanked reach. ”

“ With such opportunities to become acquainted with the changes of the stream they could not fail to know the quantity of water flowing at periods of the highest freshets, and knowing it, to adapt an overfall of sufficient capacity for its discharge. For this purpose it was thought ample provision was made; yet at the time when the work was nearly completed such a flood occurred as could not have been anticipated from previous knowledge of the River; the water filling the entire passage at the overfall, flowed over the top of the embankment where it was not supposed it could ever reach. ”

“ Upon every water-shed which is drained into the sea, the precipitation, for the whole extent of the shed so drained, may be considered as greater than the evaporation, by the amount of water which runs off through the rivers into the sea. In this view% all rivers may be regarded as immense rain-gauges, and the volume of water annually discharged by any one, may be taken as an expression of the quantity which is annually evaporated from the sea, carried back by the winds, and precipitated throughout the whole extent of the valley that is drained by it. ”

“ Very often a larger supply from a spring may be obtained by collecting into one basin a number of separate and smaller springs. A swampy or boggy piece of ground is often the result of the existence of a number of springs, and if drains are laid to some convenient corner of the field, and a well dug there, into which the drains will discharge, not only will the swamp be drained, but an ample supply of water in this way be obtained. ”

“ When the basset-edge of the strata is covered with gravel or sand, any body or stream of water will readily percolate downwards through it, and fill up the porous interstices between the coal-measures, till arrested by the face of a slip, which acts as a valve or flood-gate, and confines the water to one compartment of the basin, which may, however, be of considerable area, and require a great power of drainage. ”

“ So, in the saturated earth in a flower-pot, the earth, merely moist at the surface, is wet mud just above the water-table. So, in drained land, the capillary force which retained the water in the soil to the height of a few inches, is no longer able to sustain it, when the height is increased to feet, and a portion descends into the drain, leaving the surface comparatively dry. ”

“ After a time the salt water becomes diffused in the fresh, so that the density of the water in a river decreases as the distance from the sea increases. The disposal of sewage discharged into a river is due primarily to the mixing action which is taking place; inasmuch as the tidal current which is the transporting agent rarely flows more rapidly than from two to four miles per hour, or, say, twelve to fifteen miles per tide. ”