Popular Science Monthly/Volume 26/November 1884/Drowning the Torrent in Vegetation
| DROWNING THE TORRENT IN VEGETATION. |
By S. W. POWELL.
THE extraordinarily disastrous floods of 1883-'84, in the Ohio River, have again called public attention to the close relation which the wooded or unwooded condition of steep hill-sides, in the areas drained by streams, bears to the volume of water flowing in them.
The State of New York, in particular, is discussing the question of making a great forest reservation in the Adirondacks, in order to avert floods, droughts, and other calamities which there is reason to fear may follow the alleged rapid destruction of the forests of that region.
In the course of this discussion many allusions have been made to the ravages of floods in the south of France, and to the success of efforts to tame those torrents, by reforesting the basins which they drained. A short account of those torrents and their origin, the ruin wrought by them, and the victory which forest science has gained over them, may interest the readers of "The Popular Science Monthly."
Professor Guyot, whose recent death is such a great loss to science, taught that variety of coast-outline, of elevation, of climate, and natural products, is necessary for the richest development of the individual and of society; and that in no part of the world were so many of these favoring conditions originally brought together as in the regions bordering the Mediterranean.
The Roman Empire, which, at the time when it was most widely extended, consisted almost entirely of the countries lying around or near this sea, had the best situation of any of the great empires that have arisen. The grouping and arrangement of the land and water masses; the diversity of elevation and of coast-outline; the rich and varied scenery; the wide range of animal, vegetable, and mineral products; the great number of populous, wealthy, and nobly built cities, with the marvelous Roman roads binding them together, and the majestic Roman law co-ordinating their civic life—all cooperated to make this region the garden of the world. The fact that the most favored part of the earth's surface should have been so nearly ruined, as it has been, by selfish and short-sighted treatment of the forest, its most precious possession, ought to have been a lesson to all future settlers of new territory. That it has not been heeded by the settlers of North America, the increasing frequency and severity of floods and droughts and the swift and menacing approach of timber-famine plainly prove.
The streams which flow through the valleys that wind back from the sea into the heart of the mountains and hills bordering the Mediterranean would, in their normal condition, be limpid and perennial. But, owing to this short-sighted cutting of timber from steep hillsides, and to the equally short-sighted over-pasturing of the cleared spaces afterward with sheep and goats, most of these streams were, in the upper part of their courses, changed into torrents, whose beds in dry weather are cheerless expanses of sand and gravel.
During heavy rain, or when snow is rapidly melted upon the mountains (and this is especially apt to occur when a warm wind, called the Fœhn, coming probably from Sahara, and saturating itself with moisture as it crosses the Mediterranean, strikes the mountains—Guyot said he had known this wind to melt six feet of snow in twenty-four hours), these torrent-channels are almost instantly filled with furious, short-lived floods, which often sweep off bridges, buildings, crops, and even animals and human beings, besides tearing up costly roads, and wash away a vast amount of precious soil from mountain-sides, where it is sorely needed, and deposit it in rivers and harbors, where it is a nuisance, and often a serious peril to navigation.
In their gullying and undermining rage, these torrents tear out stones and large rocks from the hill-sides, grind them up into gravel, and even fine sand, and ruin much fertile land upon which they spread this material.
Marsh, in his "Earth as modified by Human Action" (p. 272), gives Surell[1] as his authority for the statement that "the fury of the waters, and of the wind which accompanies them in the floods of the French Alpine torrents, is such that large blocks of stone are hurled out of the bed of the stream to the height of twelve or thirteen feet"; and remarks that "the impulse of masses driven with such force overthrows the most solid masonry, and their concussion can not fail to be accompanied by the crushing of the rocks themselves." On page 273, note, he quotes Coaz ("Die Hochwasser im 1868," p. 54): "At Rinkenberg, on the right bank of the Vorder Rhein, in the flood of 1868, a block of stone, computed to weigh nearly nine thousand cwt., was carried bodily forwards, not rolled, by a torrent, a distance of three quarters of a mile."
But there is further mischief, which, as being more widely diffused, is less sure to be assigned to the true cause—the stripping steep land of its covering of trees:
1. There is the failure of springs, because water of precipitation, which should have been delayed upon the hill-sides by the roots, sprouts, mosses, fallen leaves, etc., which fill and cover the surface of the ground under a forest, till it could find the underground spring sources, runs off the bare slopes in a few hours. Dry springs mean parched pastures, small crops, and unprofitable husbandry.
2. The increased cost of buildings, bridges, furniture, and implements of all sorts, which are, in whole or in part, made of wood. A large item in the current expenses of railroads is the outlay for ties, which must be renewed frequently. Wood for fuel or structural uses is a prime necessity of civilized life; and, as it is bulky, its cost increases rapidly with the distance it must be carried to reach the consumer. Many countries have no stores of coal or peat, and must have wood, or be sorely stinted for fuel; that stinting is a waste of time, health, and vitality. Floods make the maintenance of roads difficult and costly, and so, of course, increase the expense of whatever must be hauled over them, especially anything so bulky as wood.[2] Further, scarcity of timber means the cessation of many lucrative industries which use wood for their raw material, and which are especially desirable as affording employment during portions of the year, when agriculture or the care of flocks does not call for all of the farmer's time.
3. There is the derangement of climate and rainfall. It is by no means certain that, at least, in some situations, more rain will not fall in a year upon a well-wooded than upon a bare region. Certainly, what does fall will not evaporate, and be carried away by the winds as quickly. Sudden changes of temperature, and the resulting violent winds are also less liable to occur where woods abound. A forest is a better barrier against wind than a stone wall of equal height, because it divides its force, and does not stop it all at once, causing eddies and rebounds which may do damage elsewhere.
In these and other ways many provinces of Southern France had been (before 1860) for several generations gradually growing poorer. By a misuse of the right of equal common pasturage upon the lands belonging to the communes, the richer proprietors who had large flocks could get the lion's share of the scanty store. To lighten taxes, sheep and goats were admitted from Provence and the Maritime Alps to summer pasturage, as at that season their own country was so dry and parched that they could find no food. Cézanne, in his supplement to the great work of Surell on the "Torrents of the High Alps," says these migratory flocks "obstruct the roads, and are the occasion of all kinds of disorder. They arrive at the pastures famished, and in a few days destroy the sprouting herb, the hope of the entire season. . . . One can follow the trail of the sheep of Provence by the disappearance of all vegetation. They necessarily migrate in flocks of one thousand or twelve hundred, and after reaching the pastures retain the habit—which they acquire upon the road—of crowding together and struggling for every spear of grass. In the flinty plains of the south they find very scanty fare, and, to satisfy hunger, are obliged to move stones with their noses and feet, and to dig the soil quite down to the roots of the plants which they devour. Upon the mountains they continue the same destructive habits, and one can understand what must be the effect upon the light soil, scarcely fixed upon the slopes, of such digging and tearing by these millions of animals" (pp. 245, 240).
The little ready money which the pasture-fee of these southern sheep brought into the impoverished communal treasuries seemed indispensable, though it was easy to see that it was bad economy to admit them. Such trampling and tearing weakened the turf so that it was every year more easily washed down-hill during heavy rain, and, when it went, the soil underneath went too. The farther down the mud and water rushed, the deeper and wider were the erosions. Upon the steeper slopes below, which should have been clothed with woods, the ravages were still greater. As like causes were operating in a similar way upon other surfaces in the same basin, after every heavy rain (especially if it fell upon deep snow) the streams suddenly rose thirty, forty, and even sixty feet, and then again, in a few hours, were at their old level.
If a bank overhanging the narrow gorge at the mouth of one of these mountain-basins was undermined and fell across the opening, a lake quickly formed behind, until the accumulating pressure burst the barrier, and then woe to the people down-stream! In one such dèbâcle the wave was one hundred feet high, and swept down the valley at the rate of fifty feet a second, or thirty-four and one eleventh miles an hour! "At one point the water was seen pushing before it a moving mountain of all kinds of débris of three hundred feet in height, from which was rising a thick cloud like the smoke of a conflagration" (Brown's "Reboisement in France," pp. 86-89).
Deprived by their own improvidence, or that of their parents, of their forest wealth, the mountaineers thought that they must starve, or else use every available acre for pasturage. Planting trees and waiting for them to grow required knowledge and capital, and they had little of either. The damage done by torrents was more severe farther down, although it all began in the uplands, whose turf was loosened by the starved sheep of the south. Lack of the timber which should have enriched and protected the zones just below these pastures made the mountaineers feel so poor that they felt constrained to take every sheep and goat which the lowlanders would bring. It was clear that they could not restrict the number of these "summer boarders" and at the same time reforest the steeper lower zones to the extent which was demanded by their own welfare, and still more by that of the people living farther down-stream.
This made it necessary for the state to step in. Under the feudal system it was held that a seignior, and especially a king, must possess one or more forests. In France, those belonging to the crown have become the property of the state, and, for the care of these there have gradually been trained a special class of officers. When the reboisement law of 1860 was passed, many of these were men of great attainments. Surell, born in the Département des Hautes-Alpes, was one of the most eminent among them. As an engineer he had long been familiar with the numerous and costly—and yet inadequate—mechanical expedients which had been tried by the authorities for the purpose of preventing the ravages of torrents. He kept dinning it into their ears that, since excessive and unscientific clearings, and unregulated pasturage of the cleared spaces afterward, were the causes of the torrents, so the remedy must be to clothe the steeper zones below the pastures with trees or bushes, and to exclude sheep and goats from the pastures above until they were again covered with a stable turf.
He was not, indeed, the first to protest against the destruction of the woods, and to insist upon their restoration. The famous inventor, engineer, and artist, Bernard Palissy (born about 1509), had discovered the influence of forests upon springs, and raised an unheeded cry to warn men against the calamities which lack of fuel and timber would occasion. The chief nobles, and especially the ecclesiastics, were clearing at a great rate and taking no thought of those who would come after them. In the time of Henry IV and Louis XIV a sharp check was given to the plundering of the crown forests by these ecclesiastics and court favorites. In 1669, three years after the famous announcement of Louis XIV that he had been long enough in leading-strings, and that he proposed from that time to be master of himself and of France, the great ordinance was passed upon which most of the subsequent forest legislation of Europe has been based. Under it, in connection with the crown forests, the science of arboriculture was studied, and a thoroughly organized corps of officials trained.
Before we come to Surell, a passing mention should be made of Fabre and Dugied. Fabre published in 1797 his "Essai sur la Théorie des Torrents et des Rivières," which may be called a prophetic work. It outlines quite distinctly the main principles which were followed in the works of restoration under the reboisement law of 1860. He said sheep and goats must be kept away from young trees, and that no clearing should be permitted except in horizontal strips not more than thirty feet in width where the acclivity of a slope is more than one foot in three, and these strips may be made wider according as the slopes are less steep. No clearings without authorization of competent officials, and on plans made by them. Where there was little earth left, he recommended gazonnement[3] and buissement.
Dugied, who had been a prefect in the Lower Alps, published a project for reforesting the Basses-Alpes. He said that more than half that department was dry and unproductive soil, and that torrents caused by cutting and grubbing woodland brought débris and added to the barren areas. For remedies he recommended: 1. Enforcement of the old law of 1667, which imposed a fine of three thousand francs for grubbing steep land; land already grubbed to be turned into artificial meadows. 2. He made careful estimates of the cost of reforesting the one hundred and fifty thousand hectares in the department which needed it, and recommended that, besides remitting taxes for ten years on reforested land, and distributing seeds gratis, the state should pay three quarters and the department one quarter of the cost. lie showed that the increased revenue from taxes, after the ten years of exemption, would repay the advance in eighty-six years.
Almost every one ridiculed the proposal; it was compared to the "Arabian Nights"; and, as a reward for making it, he was deposed. But, at the same time the state was expending one hundred and twenty million francs each year for roads and bridges, and a large part of this outlay—vastly more than reforesting cost when at last wiser counsels prevailed—was made necessary by torrents which every year grew worse, but which reforesting cured.
Dugied's ideas were, in the main, those finally adopted, except that he left out the essential idea of compulsion. An entire torrent-basin must be taken in hand at the same time, and one uniform process be carried on over the whole of it. As Surell said, success should not be imperiled by the first stupid or stubborn peasant who would not do his part. The state must not only bear the expense, but also assume the direction. Expropriation or confiscation must be resorted to, as is done in taking land for roads, etc.
In May, 1856, when heavy rains fell all over France, floods in the valleys of the Loire and the Rhone did incalculable damage. This so re-enforced the appeals which had been made by specialists like Fabre, Dugied, and Surell, that the Corps Législatif consented to make a trial of the new way of fighting floods. The old way—erecting barriers, etc.—had been altogether defensive; the new was almost wholly offensive. The method, as an expert expressed it, was "to drown the torrent in vegetation"—that is, to turf the higher and more level pastures, and then to retard the flow of water down the steeper slopes below the pastures by trees, bushes, fallen leaves, and mosses, so that much of it would have time to soak into the ground and reach the spring-reservoirs, and another large portion be absorbed by the fallen leaves, etc., and held as by a sponge, or be taken up by the growing vegetation; and to hold back the remainder by millions of small obstacles so that it would reach the stream no faster than a full channel could carry it away; and, finally, that, flowing at no point over bare soil, it might reach the stream-bed as limpid as when it started down-hill.
Difficulties.—The hindrances to the success of the work were both moral and physical, but the moral were the greater. They were:
1. The unwillingness of an ignorant peasantry to try any new thing;
2. Reluctance on the part of the Corps Législatif and of local authorities to interfere with private rights as much as the success of the work demanded; and, 3. The doubt whether such torrents would not wash away the plantations as fast as they could be made.
The first two difficulties demanded great patience and kindness in making clear to the peasants the necessities and advantages of reforesting, and in convincing them that the work would be done so honestly and cheaply that they might reasonably expect to be able to repay the cost of the work and get back their land, which would soon begin to yield some income, and in the course of twenty years would, as a rule, be more profitable than pasture-land. A sort of science primer, "Les Études de Maître Pierre sur l'Agriculture et les Forêts," was prepared and circulated among them with excellent results. It consists of eight dialogues between a government teacher and a peasant, Mâitre Pierre, in which the latter is converted from a stubborn opposition to the reboisement law (which he said would ruin him because, in obedience to it, his landlord was about to withdraw a certain pasture from his moutons) to a quite intelligent advocacy of it. The main reasons for and methods of forest propagation, conservation, cutting, thinning, etc., are gradually instilled into the peasant's not very bright mind. The book is a fine model of Socratic teaching.
The velvet glove was always kept upon the iron hand in carrying out the law. As far as possible the co-operation of those whose land was taken was secured; and none was taken except after full opportunity for every one to learn just what the government meant to do and to present objections. Local magistrates and land-owners must be united with the state officials upon the boards which decided where to run the lines which included lands to be reforested.
The third difficulty—doubt as to the possibility of success—was overcome by the prudently bold policy of attacking some of the worst torrents first. Of course, victory over these insured success with less violent ones.
The conflicts with physical obstacles may be classified as preparatory and final. The first thing was to exclude sheep and goats from the pastures above the forest zone. The next was to divide the whole area by horizontal walls into two or more zones, and in the lateral ravines to build as many dams as the case might require, so as to check the downward flow of water and compel deposit of earth above the walls and dams. In the deeper ravines whole trees were thrown with tops down-hill, fascines, etc., being packed among the limbs. Then, with explosives, the sides of the ravines were thrown down upon these trees so as to afford a deep and somewhat level soil that could be planted at once. Horizontal mule-paths about a metre wide were made where, later on, roads for working the forest would be needed. These paths, in passing ravines, ran upon the dams, etc., and by them laborer and material could reach the points where they were needed in the preliminary works. Besides these paths there were made, at distances twelve or fourteen feet apart, narrow terraces, supported on their lower edges by pebble walls, and having their upper surfaces slightly sloping in toward the mountain, so that water would be checked, and, as far as possible, made to soak in and find the spring-reservoirs.
After all these preliminary works were executed, the final planting began. Generally, the terraces and the more level and deep made ground in the lateral ravines were stocked from nurseries which were established here and there in the districts to be reclaimed. Where the spaces between the terraces were especially liable to washing, they were covered by thatchings of brush, retained if necessary by stones or any convenient rubbish.
In gorges and other places where the danger of erosion and the difficulty of getting out large timber would be greater than elsewhere, the kinds of trees selected were such as shoot readily from the stump, grow rapidly, and can be frequently cut with profit—in other words, those more especially suited to coppice or sprout-growth culture. A dense coppice resists the pelting of rain and fixes the soil better than larger trees. The kinds selected for such places were therefore acacias, ashes, elms, maples, willows, alders, poplars, lindens, etc.
By working with a sufficiently large force to cover an entire basin with the various preliminary works, and then to plant, promptly and simultaneously, the plantations were not washed away; on the contrary, to use the vivid words of Cézanne: "These works, so ingenious in their very simplicity, form a net-work of horizontal lines, like the alleys of a garden. The green edgings and linings develop themselves among the innumerable sinuosities of the combes [valleys], embracing, from the rocky beds of the torrents to the very summit of the mountain-crests, those ravines which were but lately inaccessible, and presented an aspect full of horror. On seeing what has been done, one immediately understands how such a combination should be effectual. Every liquid molecule, so to speak, is seized individually, the thin sheet of water flowing down is retarded in its course by a thousand thirsty little plants, by the lines of cultivated herbage, and by the hedges of shoots and trees. It is compelled to tarry a little on each terrace to slake the thirst of the ground, and when it reaches the lower end of a furrow it spreads itself out on the flattened bed there prepared for it. Stopped at every barrier, it loses its vital force on every hand, and finally, from resting-place to resting-place, and from descent to descent, it arrives, after a thousand retardations, and still limpid, in the channel which conveys it to the river. The violence of torrents is occasioned by the combination of an infinitude of elements infinitely minute; and the system of extinction consists in extinguishing each of these elements without disregarding one; it is an accumulation of infinitesimal littles. The secondary ravines are blocked up, their minute ramifications are intercepted, the lesser flanks are filled up, and finally there are spread over the soils, completely to diffuse them. the innumerable threadlets [of water], divided and subdivided like the fibers of a root."
In conclusion, it is gratifying to be able to state that all opposition to the reboisement law is in France a thing of the past. The credits voted for the first ten years were at the rate of only two hundred thousand francs a year. Now nearly twenty times as much is readily obtained by the forest administration. The total annual outlay upon the state forests is about twelve million francs, but the direct revenue derived from them is more than three times that sum, besides the vastly greater incidental advantage of building up the agriculture, commerce, manufactures, health, and general prosperity of the restored regions, to say nothing of the diminished expenditure needed to replace roads, bridges, and other structures formerly destroyed by the torrents. How much longer shall we refuse to heed what the experience of other countries teaches with regard to the treatment of forests?
In the recent Ohio floods the States which suffered most—Ohio, Indiana, and Illinois—were not those where most of the deforesting was done which caused the floods. The Hudson's head-waters are almost all in New York, and it is in the power of her Legislature to provide the needed safeguards.
- ↑ "Étude sur les Torrents des Hautes Alpes," published in 1841. This and the supplementary volume by Cézanne (1870) are of the first importance.
- ↑ Ladoucette, in his "Histoire, Topographie, Antiquités, Usages, Dialectes des Hautes Alpes," says that the peasant of Dévoluy often goes a distance of five hours, over rocks and precipices, for a single man's load of wood; and that the justice of the peace for that cantonment had, in the course of forty-three years, but once heard the voice of the nightingale. Thanks to reforesting, wood and nightingales' songs are there now in abundance.
- ↑ Reboiser, to reforest; deboiser, to deforest; gazonner, to plant with turf; buissonner, to plant with bushes, with their nouns, boisement, reboisement, deboisement, gazonnemait, buisonnement, are in constant use in French forest literature. The nouns are, in translations, often transferred to the English, and sometimes one meets, to reboise = to reforest.