Waterhole

“ Occasionally we found in this bare sandy channel waterholes of eighteen or twenty feet in depth, surrounded with tea trees and vegetation, and the driftwood, washed high up into these trees, sufficiently attested what rapid currents sometimes swept along the now dry channel. Even the waterholes were nearly all dried up, and in the bottom of these the natives had scooped their little wells. ”

“ Along the course of the larger streams huge chambers occur; for the ever-eddying water, bearing sand along in its course, eats out the sides of its channel, or, revolving stones in its bed, carves out the pothole by friction. Or some pendent mass of rock has its support undermined and comes crashing into the streamway, only to be broken up and carried away by the ceaseless energy of the stream, so ever enlarging the chambers upwards towards the light of day. But whilst this action is going on underground, a more potent factor is at work where the subterranean stream first sees the light. ”

“ When the search for water goes below ground, one must reckon with geology. What lies below the turf is [Pg 143] the deciding factor. If it is sand and gravel with a high water table (the level of subterranean water) , an excellent well can be had cheaply. The practice is either to bore through to the water table with a man-operated auger and then insert the pipe, or to drive the latter down with a heavy sledge hammer. In either case, water is but a few feet below ground and a shallow-well pump, which can raise water twenty-two feet by suction, will be adequate. ”

“ The Shark disregarded the interruption. “Hold on! Let me finish. There’s a plausible explanation of our fix. Our big bowl is plugged, and if it is, the plug is an ice jam. Remember how narrow the gorge is at the foot of the valley? Remember how the bridge piers clutter it up? Well, then! [295] Plain as the nose on your face! River carries down a lot of big chunks. They pile up against the bridges and wedge together. Then along comes a lot of logs and floating riffraff to fill in the cracks. That’s how you get your dam that’ll turn the valley into a big pond. ”

“ It should be remarked that when the strata is horizontal or depressed in the form of a basin, that is, when it partakes more of the character of a reservoir than a stream, the only use of tunnels is to facilitate the ingress of water into the shaft, and in such case they should radiate from the shaft in all directions. They are also of service in case of accident to the pumps, as the time they take to fill up allows of examination and repairs being made in that time to the pumps, which could not be got at if the engines stopped pumping and the water rose rapidly up the shaft. ”

“ However, with sand, or earth with much fine material, the pores are more or less clogged up and there is perhaps intimate contact of a part of the earth with the roof of the tunnel, so that the water cannot get under it to produce a lifting effect, and if such intimate contact is found along any horizontal or vertical section, of the earth on either side of the section, it is plain that the buoyant effort of the water on a cubic foot of material will be much diminished. ”

“ Above the vaulting there are 2 feet of earth and soil, grassed on top. The tops of the manholes are 6 inches above the soil to prevent rain-water from entering them. The drainage of the soil is effected by a depression of the vaulting over each pier, partially filled with gravel and sand, from which water is removed by a 2-inch tile-drain going down the centre of the pier and discharging through its side just above the top of the sand in the filter. ”

“ If it meet a flat layer of gravel lying upon clay, and having a free outlet, it will follow the course of the gravel,—laterally,—and find the outlet; if it meet water which is dammed up in the soil, and which has an outlet at a certain elevation, as at the floor of a drain, it will raise the general level of the water, and force it out through the drain; if it meet water which has no outlet, it will raise its level until the soil is filled, or until it accumulates sufficient pressure, (head,) to force its way through the adjoining lands, or until it finds an outlet at the surface. ”

“ Meantime, very likely, they have been working, more or less, on the dam on the creek below the house, and have raised the water still more, so that perhaps the tunnel is now full of water, and then, instead of using this tunnel to get out of, they’ll gnaw a hole through the sticks of the house, making a passage-way from the room they occupy down to beneath the surface of the water. They still keep working at the dam, raising it and making it level, so that the pond gets bigger and bigger all the time. ”

“ In the case of a decided drop in the elevation of a sewer, or of a tributary sewer appreciably higher than an outlet in any manhole, the sewage is allowed to drop vertically at the manhole, hence the name drop manhole. The Baltimore standard drop manhole is shown in Fig. 27. A well hole is an unusually deep drop manhole in which the force of the vertical drop of sewage is broken by a series of baffle plates, or by a sump at the bottom of the well hole. ”

“ In sand below water there are, of course, no open fissures, and even if adits could be Wells in sand. usefully employed, the cost of constructing and lining them through the loose sand would be prohibitive. The well itself must be lined; and its yield is therefore confined to such water as can be drawn through the sides or the bottom of the lining without setting up a sufficient velocity to cause any sand to flow with the water. Hence it arises that, in sand formations, only shallow wells or small boreholes are commonly found. ”

“ The chief obstacle to be contended against in so much of the river tunnel-work is the large volume of water which pours into the workings through fissures in rock or seams of gravel and sand, necessitating the constant use of most powerful pumps. In ordinary land tunnels the gradients are generally laid out to fall towards one or both entrances, and any water finding its way into the excavations may be led away to the entrances by drains or pipes. ”

“ This you see, will divide up the swamp into several drainage areas. Then each of these areas is to be surveyed to determine the line of drainage, the whole to be conformed to the main ditches that will flow to the river, and this intricate network of ditches must be kept at just the exact level of fall, so that it will flow unencumbered to the streams on either side of the swamp."
Roger whistled softly.
"That's why you've got to go over every foot of the country so carefully," he said. ”

“ It is mentioned that there is no special reason for making the waterway of a regulator exactly the same as that of the stream, and that the waterway may be such as to give the maximum velocity considered desirable, and that the foundations of a bridge should be made so deep that it will be possible to add a floor, at a lower level than the bed of the stream—with the upstream and downstream pitching sloping up to the bed—so as to increase the waterway and so save pulling down the bridge in case the discharge of the channel is increased. ”

“ After the exploring party had passed the highest point in the channel to which the tide flowed from the sea, this huge river bed was perfectly dry, and looked the most mournful, deserted spot imaginable. Occasionally water-holes were found eighteen or twenty feet in depth, and it is from these alone that travellers have been enabled to satisfy their thirst in crossing over the unexplored parts of the bush, where no water could elsewhere be obtained. ”

“ The Dudlow Lane well is also oval, 12 feet by 9 feet, and is sunk to a depth of 247 feet from the surface of the ground. Headings have been driven from the bottom of the well for a total distance of 213 feet, and an 18-inch bore-hole has been sunk to a depth of 196 feet from the bottom of the well, which is chiefly in a close hard rock, with occasional white beds from which the water is mainly obtained. The yield is nearly 1,500,000 gallons a day. ”

“ IV. A proper system of drains must therefore be made upon the hill-side to gather and gently guide the waters, to lead them by channels across the formation and discharge them outside it, care being taken to protect and line the surface of the drains so that no leakage occurs or any erosion of the face. In countries where the rainfall is excessive or sudden at certain places or entirely, it may be sufficient to protect the slopes so as to allow of a flow over them, and particularly upon the valley slope of an embankment, and in a lesser degree upon the hill-slope of a cutting. ”

“ Where there is no vegetation, therefore, the climate cannot be healthy, and without water there can be no vegetation; for water is the necessary food of plants.
[106] The line of this subterranean aqueduct can also be traced by the wells descending into the specus, in the same manner as the Aqua Appia was traced in 1870, that is, by the bushes growing at the top of each of the wells, and generally enclosed by a wooden railing to prevent animals from falling into them.
[107] The rock in which the tunnel is cut is a sort of peperino, hard and rough, covered with a bed of clay. ”

“ Even now, in the principal thoroughfares, it is forbidden to throw anything into the canals: the sweepings even of the streets may not be cast into them. No measures, however, are taken to prevent the rain, which here falls in sudden and violent torrents, from carrying off the dirt, which is collected in piles at the corner of every street, and washing it into the lagunes, nay, what is still worse, into the gutters for carrying off the water, which consequently are often so completely stopped up, that the principal squares are in danger of being under water. ”

“ In this particular spot disintegration has created much havoc and the walls no longer show the marks of water erosion, while the floor is heaped with rock debris fallen from the ceiling. The passageway, however, that connects it with the surface is still intact as a sample of the power of water erosion. It is composed 16 of a series of potholes, connected one with the other by short narrow passages. The bottom of each succeeding pothole, as you recede from the entrance, is at a lower elevation, sometimes as much as ten or fifteen feet. ”

“ On the other hand, in a river tunnel the gradients generally fall away from the entrances down towards the centre of the river, and all water coming in must be pumped out and raised up to at least the level of the river. In places where the water comes streaming in from many points, any failure or stoppage of the pumps would place the lives of the miners, and the security of the work itself, in great jeopardy. ”

“ 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 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. ”

“ Could a line be graded so as to give a regular inclination from the Fountain Reservoir to one at the city, then the expense of laying iron pipes for conducting the proposed quantity of water, would be greater than for constructing a channel-way of masonry; and when laid, the pipes were thought to be less durable. Should the pipes follow the natural undulations of the ground, there would be so much resistance offered to the flow of water that the discharge would be diminished in a very great degree. ”

“ The bottoms require to be made water-tight, either by a thin layer of concrete or by a pavement upon a puddle layer. For the sides either masonry walls or embankments are used, the former saving space, but being in general more expensive in construction. Embankments must, of course, be substantially paved near the [Pg 12] water-line to withstand the action of ice, and must not be injured by rapid fluctuations in the water-levels in the filters.
Failure to make the bottoms water-tight has perhaps caused more annoyance than any other single point. ”

“ It is better to cut across the point of a hill, to the extent of increasing the depth for a few rods, than to go a long distance out of the direct course to keep in the valley, both because of the cost of the large tile used in the main, and of the loss of fall occasioned by the lengthening of the line. The main should be continued from the outlet to the point at which it is most convenient to collect the more remote sub-mains, which bring together the water of several sets of laterals. ”

“ The shock of the waves soon enlarges this to a blowhole, which one may find on the breezy upland, perhaps a hundred yards and more back from the cliff's edge. In quiet weather the blowhole is a deep well; in storm it plays a fountain as the waves drive through the long tunnel below and spout their spray high in air in successive jets. ”

“ While the work is progressing in the field above, there will be a great deal of muddy water and some sticks, grass, and other rubbish, running from the ditches above the basin, and care must be taken to prevent this drain from becoming choked. A piece of wire cloth, or basket work, placed over the outlet in the basin, will keep out the coarser matters, and the mud which would accumulate in the tile may be removed by occasional flushing. ”