Popular Science Monthly/Volume 16/November 1879/Why Do Springs and Wells Overflow? I
|WHY DO SPRINGS AND WELLS OVERFLOW?|
By NELSON W. GREEN.
SINCE water tends to find a level, we infer that flowing water is acting in harmony with this natural law, unless it be put in motion by some equivalent force. The overflowing of wells and springs has hitherto been accounted for by scientists only upon the supposed existence of hydrostatic pressure. But a more careful investigation seems to justify the conclusion that, while in exceptional cases this may occur, yet as a proposition it is fallacious, and it will be the aim of the following discussion to expose the fallacy.
In 1844 Rev. William Buckland, Professor of Geology at Oxford, England, was invited, on account of his learning and character, to give an address, in which he made the following statements: "Wells Slink to a greater depth through stratified rocks often afford large supplies, but rarely rise to the surface; and in cases where they do so they are called artesian wells, from the circumstance of such artificial flowing wells being common in Artois (France). In all these cases [among which the Professor included the flowing wells at Grenelle, near Paris] the water was forced up by hydrostatic pressure to various distances from the surface. At Brentford, England, there were many wells that continually overflowed their orifice, which is a few feet only above the Thames. In the London wells the water rises to a less level than in those at Brentford."
By hydrostatic pressure, the Professor, of course, means a head, i. e., that the water flowed to these wells from a higher point. If this rise were due to hydrostatic pressure, why did the water rise to a lower level at London than at Brentford among the hills? Professor Buckland continues: "In November, 1840, notice was given of an application to Parliament to obtain a new supply of water for London from wells and water-works to be made at Wetford in the chalk-hills. A company had been proposed to effect this object, which would probably have been carried out, had not Mr. Clutterbuck demonstrated, by a long-continued series of measurements of the water in the chalk-hills of Hertfordshire, near Wetford, that every drop of water taken from that neighborhood would have been abstracted from the summer and autumn supplies of the river Coln and would have robbed the proprietors of more than thirty mills upon this river and its tributaries, and the owners of adjacent water-meadows, of rights they had had from time immemorial. One intelligent manufacturer, Mr. Dickinson, had, during many years, found arithmetical evidence that the quantity of summer water in the river Coln varied with the rain in the preceding winter. He could always tell, at the end of February or March, what water there would be in the following eight or nine months; and he regulated the contracts he made in every spring, for paper to be delivered in the summer and autumn, by the quantity of water in his winter rain-gauge. This rain-gauge, the invention of Dalton, being buried three feet below the surface, showed that except in December, January, and February, rain-water rarely descended more than three feet below the soil, so as to add anything to the supply that sinks into the earth to issue during summer, and from springs and rivers; and, whenever Mr. Dickinson found by this instrument that but little rain had fallen in the three months of winter, he proportionally limited his contracts for the following summer and autumn, thus proving the practical advantage of inductions from philosophy."
The following abstract from Professor Buckland's speech may also be in order: "As persons who have no experience in these subjects may be surprised at the knowledge geologists profess to have acquired respecting the internal structure of the earth, he (the Professor) would endeavor to confirm the above theoretical explanation of the origin and supply of springs by appealing to practical proofs in the proceedings of water companies and well-diggers, and in the pounds, shillings, and pence in the ledgers of manufacturers." It certainly must be a matter of "surprise" to most people that, while the rain-water rarely sank deeper than three feet into the soil, it could yet influence the water-supply to be drawn from deep wells in the earth, so much as to draw upon the water-supply of the river Coin, which like that of all rivers is more or less dependent upon surface influences in addition to overflowing springs. Wells to supply London, the Professor thinks, must not be utilized to draw water from a depth of thirty or forty feet because it would cut off the supply due to the rains which do not sink deeper than three feet! It should have been the easiest possible thing to supply London without in any way drawing upon the supply of the river Coin, since the river and the wells draw from different sources. The learned Professor had no idea of the existence of any force in the premises other than hydrostatic pressure, and yet he proceeds in the next paragraph to give important evidence of some other force:
"In Germany, Mr. Buckmann, of Heilbronn, published in 1835 an octavo volume on artesian wells in the valley of the Keeker, from which it appeared that there were manufactures in Wurtemberg near Constadt where the mills were kept in work during the severest cold of winter by means of the warm water from artesian wells which overflowed into the mill-ponds and prevented them from freezing. And at Heilbronn, also, there were persons who saved the expense of fuel by conducting artesian warm water in pipes through their houses and greenhouses. . . . Let those who doubt go to Grenelle and see the majestic column of warm water from the philosophically discovered fountain rising thirty feet above the surface, at the exact temperature foretold by Arago, and learn the correctness and value of practical deductions from geology applied to the useful purposes of life."
From which quotations it appears that the Professor is in a remarkable position. At Wetford these wells could not be utilized because the river-supply of the Coln would be exhausted; but in Germany they were a new and important source of supply to the rivers themselves. Imagine the "majestic column" at Grenelle rising thirty feet high and the overflow in the other cases being due to hydrostatic pressure—i. e., due to the fact that all these immense floods were the result of a flow from some other higher bodies of water. Why did it not occur to Professor Buckland that, however high and abundant the source, such drains must of necessity have sooner or later exhausted the supply, if no equivalent streams were flowing into that also? But suppose this to be so, whence could come the higher head to flow into and supply that in turn? Carry this on until a flow is secured from the highest land on the earth, and then whence comes the flow to supply that? The mere statement of the case proves the existence of some force in nature other than hydrostatic pressure by which these vast bodies of water are driven to the surface. This hydrostatic pressure Professor Buckland thus illustrates and explains: "The portions of a water-logged, porous bed between two beds of clay may be illustrated by a tea-saucer placed within another tea-saucer, and having the narrow space between filled with sand and water. If a hole were drilled through the bottom of the upper saucer and a quill or small pipe fixed vertically in the hole, water would rise in the pipe to the level at which it stands within the margin of the lower saucer, its rise being caused by the same hydrostatic pressure that raised the water in the well at Southampton, coming from subterranean sheets of the fluid which exists in the fissured chalk-beds of the Hampshire basin, as they do also in the chalk under the basin of London."
Should these exceptional and assumed conditions occur in nature, the result would be substantially as indicated; but, as will be seen at a glance, the flow from a well sunk under such circumstances would be limited to the amount of water between the two saucers, and this will be limited to the quantity of rainfall. Since flowing wells and springs are seldom if ever thus limited, we infer that the case supposed does not occur. But whether it does or not is of no importance, since it in no sense satisfies the conditions of the "majestic column at Grenelle, and other cases where the flow is perpetual. We must, therefore, look for some other force to explain this class of phenomena. Professor Faraday followed Professor Buckland's lead six years later. M. Garnier, the celebrated French engineer, whose essay in 1822 upon this subject took the governmental prize, also takes this position; as does Dr. Halley. This theory we combat not merely from speculative motives, but in the interest of public health.
Various other theories have been advanced besides hydrostatic pressure. Aristotle and Seneca suggested the central heat of the earth. This theory has been more fully and scientifically stated by E, S. Chapin, in his work on gravity. But this is not the force that we seek. It is inadequate, as the following simple experiment shows: If a moderately flowing spring is surrounded by an air-tight inclosure which shall contract, and terminate in a tube, and this tube be allowed to have a discharge some distance below the surface of the water in the spring before its inclosure, it will be found that the water-flow from the spring has been greatly increased, though no change of temperature has occurred. Again, it has been suggested that the overflow of springs was due to capillary action; but this can hardly need a serious consideration in view of the amount and character of those overflows.
There are three classes of water to be taken into account in this discussion: 1. The surface waters mainly influenced by rainfalls; 2. Subterranean waters, seldom, if ever influenced by rains; 3. A class of waters coming from both of these sources. This discussion relates mainly to the second class. But what are the facts as to the flow of water in this class? Arago says of the well at Grenelle, 1,800 feet deep, "The water to supply it may have come from 40, 80, or 100 miles." There is a "large and important spring called Pales's Hole which issues permanently in quantities sufficient to run a mill at Otterbourne (England). … Springs of fresh water often rise even from fissures at the bottom of the sea, and one near Chittagong was 100 miles distant from the land." "The artesian well at Tours rose with a jet that sustained a cannon." "Chautauqua Lake rests like a jewel in the crown of a high mountain-ridge. The basin is shallow, with not more than 80 feet of water at the deepest points, and an average depth of about 20 feet. The surrounding hills are low, 100 to 150 feet higher than the water. Viewed from the hills near Jamestown, four miles distant, the lake has the appearance of being lifted up above its shores; you seem to be looking up to a 'hanging lake,' and you wonder the whole concern does not fall over into some of the valleys close around it. It is a wonder to the unpracticed observer where the water-supply of Chautauqua Lake comes from. The lake nearly fills its own valley. There is not a live stream emptying into it, save one, and that would run through a six-inch pipe. Of course, it is supported like a weary sleeper by the springs in its bed. These must be innumerable to maintain a body of water 20 miles long and two miles wide. Where the water is shallow you can plainly see these springs bubbling up from the bottom of the lake. Their warmth cuts the ice out in large spots in winter at points where they are most numerous. You see floating in the lake tufts of water-grass, which have been uprooted from the bottom by these under-currents."—("New York Semi-Weekly Tribune," August 2, 1878.)
This lake is on the highest land in the State, west of the Catskill Mountains, and yet it is but a vast overflowing spring from which issues a large mill-stream. To account for this large flow from the top of this elevated region by supposing it to fall from some other higher elevation is absurd, since there is no such higher ground from which it could flow without being exhausted. The whole mountain-region of northern Pennsylvania may be referred to as another good illustration of high springs. At every step the traveler notices abundant streams of the purest water, gushing sometimes from the very tops of mountains, and it is in these thickly clustering springs that the great rivers of that wild labyrinth of high ridges and deep valleys find their abundant sources. Within sight of the main road which crosses the summit dividing the waters of the Alleghany River from those running into the Genesee is to be seen a cluster of abundant streams which unite and cross the highway—a noisy torrent—rejoicing in being among the head-waters of the latter river, and the brightest product of overflowing springs. No possible head to this overflow could exist; and, in general, this class of springs flowing out of the mountain-tops can not be materially influenced by the rainfall. There is no land above them from which such torrents could flow in such constant abundance. The White and Adirondack Mountains are also full of similar cases.
"Scribner's Monthly" (vol. xi., p. 784) has a very interesting article by Martin A. Howell, Jr., entitled "Is there a Subterranean Outlet to the Upper Lake Region?" While we are sorry to quarrel with Mr. Howell as to his conclusions, we are very happy to accept his facts. He speculates upon the premise that, because "an area of some 400,000 square miles is drained by the tributaries of Lake Winnipeg alone," a certain amount of this accumulation of waters which do not find an exit "toward the Polar Sea and through the Mississippi Valley" may pass by subterranean channels into Lakes Superior and Huron; and he says that "while Lakes Superior and Huron are supplied largely through such subterranean channels on the one hand, they suffer severely through losses by similar channels at some point in their vast expanse." He shows by a map the track of this supposed underground current to be down the valley of the Illinois from Lake Superior to the valley of the Mississippi. The facts he gives tend strongly to support his novel theory of underground flow southward from the lakes, however it may be as to the amount of it. He gives no evidence that it comes from the direction of Lake Winnipeg, but, on the contrary, the balance of his evidence goes to prove that the Northern lakes are nothing more or less than great, overflowing springs. "That there exist channels of communication with some of these lakes," Mr. Howell says, "has long been believed and admitted by many"; and then, having shown that Lake Superior at its surface is 600 feet above the Atlantic and at its bottom 573, and Ontario to be 235 feet above, with the same depth as Superior, he proceeds to make the following significant statement, which is not at all conclusive as to the intercommunication between the lakes, but is unanswerable as proof that these lakes are overflowing springs:
"And that a great subterranean influx into the upper lakes exists there is little doubt, as a comparison of the discharge through the mighty St. Lawrence with the limited supply from the country bordering on the upper lakes clearly demonstrates, leaving the problem to be settled in the mind as to where this volume does come from in its course to the ocean. Again, the discharge through the St. Lawrence is equal to double the volume poured into Ontario through the Niagara, or into Erie through the St. Clair; suggesting that from the shallowness of Lake Erie and the great depth of Superior and Huron a subterranean channel may connect Superior and Huron with Ontario, giving to the latter, through this source, to be discharged by the St. Lawrence, a greater volume than is given through St. Clair. It is also a well-demonstrated fact that the volume of water escaping from the lakes through the mighty St. Lawrence is far greater than the amount discharged from the upper lakes into Ontario by the proper channels—the St. Clair and Niagara; and it is also well settled that the supply of Lake Erie from St. Clair is about equaled by its discharge through the Niagara; showing that it receives from no subterranean source any perceptible surplus of water. And this is generally attributed to its comparative shallowness as compared to the greater depth of Superior, Huron, and Ontario"—from which it follows that the immense difference between the outflow and the inflow of Ontario is due to its greater depth, thus making it a possible deep spring; and that this applies also to the other deep lakes; and that Superior, Huron, and Ontario, and possibly Michigan, are overflowing springs of subterranean water. The conclusion is therefore inevitable that this great overflow must be accounted for upon some other hypothesis than that of hydraulic pressure, since there is no higher land which could furnish an adequate supply. Indeed, if we suppose all the land on the continent which is higher than Lake Superior to be but shells tilled with water, the difference between the outflow and inflow of Ontario would exhaust the supply in a short time. But the subterranean supply is known to be constant, and has always been so. But Mr. Howell supposes this vast surplus in Ontario to come through a subterranean channel, connecting it with Superior. And here, again, we must thank Mr. Howell for his facts. The surface of Superior is, he says, 600 feet above the sea, and Ontario but 235 above. Therefore, the difference of level between the two is 365 feet. If this channel exists as supposed, the surfaces of these lakes would find a common level, instead of a difference of 365 feet!
Mr. Howell, in presenting the proof that there is a great underflow from Superior southward under the valley of the Illinois River, says: "And here on this bank of the old Illinois, opposite the junction of the Fox River, are the celebrated Mineral Springs. . . . These waters are somewhat similar to the waters of Saratoga County, New York," which certainly proves that they do not come from Superior, the waters of which are not of this class. The editor of "Scribner's Monthly" naively adds this note: "Whether the Great Lakes are the true reservoirs from which our Northern wells, springs, and subterranean streams receive their constant supply of water, is a question of sufficient interest and significance to merit a thoughtful consideration. The data upon which the advocates of this theory found their conclusions are manifold and forcible, and, though there may be breaks in the line of evidence, the facts as now established would seem to favor the views which the author of this paper now proposes to define and defend." While Mr. Howell presents strong evidence of a possible underflow from Superior southward, he has hardly claimed that the general supply of the "Northern wells, springs, and subterranean streams," all comes from the Northern lakes. A hundred facts are at hand which prove the contrary, even in the vicinity of the lakes. Among these are the magnetic wells at Three Rivers and other places in Michigan and other States. Certainly, Chautauqua, in New York, which has been shown to be but a large overflowing spring, does not draw its supply from these lakes, as its surface is many feet above even that of Superior, the highest of the four Northern lakes.
At different times irregular tidal influences have been observed on these lakes, an example of which is given in this news-note printed in the "Springfield Republican," June 26, 1876: "The water in the canal at Sault Ste.-Marie, Michigan, began rising about ten o'clock Friday morning without any apparent cause, and reached a greater height than has been known for many years. Its variation was four feet nine inches in one hour and twenty minutes," All this without apparent cause. Continuous western winds would have been an "apparent cause," but this did not exist. This and other irregular tidal influences on these lakes are in harmony with the supposed internal force for which we seek.
The following is also well authenticated: "Silver Springs, one of Florida's curiosities, is a subterranean river bubbling up into a basin nearly 100 feet deep and an acre in extent, which sends out a stream 60 to 100 feet wide to the Ocklawaha River six miles distant. To this natural inland port run three streams from St. John's, and in the basin the fish and everything on the bottom can be seen through the crystal waters." Here is a case for which no adequate cause recognized by scientists can with certainty account. A singular case occurs on the shore of the Gulf of Mexico, opposite the town of Alvarado. A ridge of sand has formed on the beach by the action of the wind. It is within memory that, before this ridge formation, "a fresh-water spring was known to exist at its northern extremity, which was then but a few feet in height. The spring is there still, though the ridge is twenty feet in height, the water rising to the top of the ridge."
But instances need not be multiplied. The ordinary observer will recall the common fact that the highest land is universally best supplied with flowing springs, and that these overflows can not be accounted for on the supposition of the fall of waters from higher grounds, since such higher grounds do not adequately exist. "The cataract issuing from the Himalayas, or as it is sometimes called Roodroo, is the source of the river Jumna—a rapid and large river; and in fact, many of the largest rivers of the world proceed immediately from mountains and lakes that are formed from cataracts." Thus the Ganges, Nile, Indus, Senegal, Rhine, Rhône, Vistula, Elbe, Loire, Guadiana, Po, Adige, Swale, Tay, Severn, Don, Monongahela, Platte, Missouri, and numerous others have their sources directly in mountains, and many of these "receive no increase from tributary streams, but issue with such astonishing abundance from rocks as to overflow and fertilize the countries through which they pass." This has been more than confirmed by the discoveries of Dr. Livingstone and Mr. Stanley in the heart of Africa, where some of the greatest rivers of the world flow out of the highest part of the African Continent. And in this connection the important element of the rainfall is not ignored. These countries are subject to long and weary droughts. But, while the volume of these great rivers is sensibly affected by the rain and the want of it, they continue to flow within their banks, subject to loss by absorption and evaporation—great and navigable rivers, throughout the longest dry season; and the Nile has no tributaries for five hundred miles of its course.
And, lastly, from the highest mountains in the world—the Himalayas—out of their highest points, great cataracts and streams have poured and still do pour, with an abundance that not only is astonishing, but that would exhaust any possible reservoirs at their extreme tops. Since this is the highest land of the world, no such higher source is possible. Hence the conclusion is inevitable that some force not yet identified exists to which these great overflows are due. It should be remembered that up to this time it is generally held, to use the words of M. Garnier, that "unless there be a reservoir higher than the surface whence we intend to bore, we can not hope to obtain an overflowing fountain." And, as if conscious that there might be some mistake about this theory, he says further that gases may force water up, by which he means to suggest a cause other than hydrostatic pressure. But the experiment which may be seen any day at the gas-works will show that gases do force water down when both are inclosed by a common receiver. There is no conceivable situation in which gases could be expected to force subterranean water in a direction opposed to gravity in such quantities as to satisfy the conditions.
Is it possible, then, to point out any other force in nature which not only may, but which positively must, force waters out of springs at high elevations?
Let a, a, a, be a great circle of the earth attained by passing a plane through the earth's center C, perpendicular to its axis, and b, b, b, the circle cut by the same plane through the inner surface of the earth's supposed crust. In order to obtain room in the figure for illustration, this section is exaggerated. Let the line A B represent the force of gravity, and A E the centrifugal force, at the point A, which will operate in the direction of the tangent A G. These two forces, for the purposes of this discussion, may be assumed to be equal, as the question of their relative intensities does not enter into the problem. Erect upon the line A B the square A B D E, and draw the diagonal A D produced to F. By a well-known law we shall have A D representing the resultant of the forces A B and A E—that is, the line A D will represent the direction A F, and the intensity of the resultant of the force of gravity and the centrifugal force, acting at the point A.
It will be observed that since the diagonal either of a square or of a parallelogram is longer than either of its sides, the resultant, A D, will have a greater intensity than gravity represented by A B. Now, suppose the point A' to be some point inside the earth's crust, and some
distance from the surface, and suppose also that it is a particle of water in a body of water imprisoned by surrounding rocks. This particle will be acted upon by a continual impulse to move in the direction A' F', with an intensity represented by A' D'. This will be true of every other water-particle in the imprisoned body of water.
If, now, in an hermetically sealed vessel of water a set-screw is turned and pressed upon the water inside until the resistance to it is equal to one pound, that one-pound pressure will be duplicated upon every other equal space of the vessel: and thus, if the end of the screw has one square inch of surface, every square inch of the inside of the vessel will feel a pressure of one pound. Exactly this will occur in the case of the water imprisoned in the rocks. The resultant of the two natural forces, centripetal and centrifugal, will be duplicated upon every point of the inside surface of the supposed rock-prison. The intensity of this resultant will be represented by the aggregation of all the resultants of all the particles of water. Now, suppose a small opening to be made in this rock-prison. Immediately, the water will be forced out with a velocity equal to the influence of these aggregated resultants modified by the laws of friction, and this velocity will not be at all influenced by the direction of the original impulses given to the water-particles. Although the direction of the resultant itself is say 45° from the direction of the force of gravity, its transmitted force will be unimpaired should the opening lead in a direction opposed to gravity, or in fact in any direction, since the tendency of water expansion or reaction under pressure is uniform in all directions. Moreover, since the resultant has been shown to be greater under all circumstances than gravity, certainly the vast aggregations must also be greater than the aggregated gravity, and will be able to overcome it under the conditions stated.
Hence, if fissures exist in rocks that lead to imprisoned waters it would happen that through these outlets the waters must certainly flow; and, if by any artificial means, as by boring, an opening should be made between a body of confined water and the surface of the earth, a flowing well would result.
But, of course, it must be understood that this would not happen if the body of water supposed were an isolated one and completely unconnected with other bodies of water through channels and intercommunications known to exist in the various ramifications of the earth's surface. The subterranean water circulation which interpenetrates the crust of the earth is clearly caused by the centripetal and centrifugal forces of nature, reënforced no doubt often by differences in temperature and other minor causes. And it also might and probably does occur that the overflowing of a well or spring is due to the fact that the water flows from a higher to a lower level, but this will be found to be too rare to form a rule.
The intensity of the centrifugal force will increase with the distance from the center of the earth, while gravity will decrease; the resultant will also increase. Thus, we find the strongest and most abundant overflows at the tops of mountains or on high plateaus. But suppose it had been fully proved that a particular overflowing spring was caused by hydrostatic pressure, it would still remain to be accounted for how the water got to that higher point. This can best be done by the force demonstrated, which is always acting upon the partially confined water-beds and water-channels forming the internal water-structure of the earth's crust. The conditions necessary to the realization of the best results are that these water-deposits shall be more or less imprisoned and the outlets comparatively limited. The overflow will be continued and upward until the resultant is overcome by friction. The lengthening of the channel of overflow, as in the spring at Alvarado, furnishes a corroborating instance of how this law of overflow operates. The spring was originally on the level of the shore until the sand drifted by degrees and formed a ridge twenty feet high, but the water appeared at the top of the ridge.
This law can be utilized in increasing the flow of water. As above mentioned, it was found that, by inclosing an overflowing spring tightly and allowing the inclosure to be terminated by a tube with an opening carried to a level below the fountain, the flow was increased because the channel was increased, and the resultant of the natural forces with it.
If an artificial connection be made with a stratum of water or water-bed, as by a tube tightly set in the earth or a series of tubes, and the suction-tube of a pump be attached thereto, we shall have the best conditions for a utilization of this newly discovered force in obtaining water for domestic purposes. The natural channels will thus be continued to the pump, and when this is operated (the air being lifted off) the new force acts as a handmaid in lifting the water. Many experiments fully prove this. As the water-deposits drawn upon are subterranean they are ample for all practical purposes; and, if these facts had been within the knowledge of Professor Buckland and the proposed company to which he has given such prominence, London could have been supplied with pure water without the least occasion for anxiety that the manufactories on the banks of the river Coln would be robbed of their portion.
The force, then, which we have demonstrated may be thus formulated: The resultant of the earth's centripetal and centrifugal forces acts impulsively upon the subterranean water-deposits, and tends to force them into and through the natural channels of the earth's crust.
- Copied into vol. iii., p. 70, of "Littell's Living Age," from the "Edinburgh Journal."