The Problem of the Floods
FLOODS are the most relentless and universal of natural visitations, and the loss of life and property since the Ark rested upon Ararat probably far exceeds the flesh and substance destroyed in that primal catastrophe.
There is a disposition in these later times to charge man with responsibility for this seeming non-fulfillment of the covenant, — ‘And God said ... I do set my bow in the cloud, and it shall be a token of a covenant between me and the earth, that the waters shall no more become a flood to destroy all flesh,’ — and to connect it in some way with the process of replenishment. It is true that this process has placed life and property in ever-increasing volume in the pathway of the floods; but the process itself were otherwise impossible. It is also true that man’s work has modified to some extent the facility with which the flood waters return from off the earth; but whether this has increased or diminished the evil of the floods is at least an open question.
When it comes to fundamental causes, however, there is no debatable ground. With these man has nothing to do. The windows of heaven are opened and closed by an authority higher than himself. To him is left the problem of dealing with situations which are not of his making and which develop without his fore-knowledge or antecedent power of control. As the process of replenishing the earth advances, the complexity of the problem increases, until it has become perhaps the most onerous imposed upon man by the necessities of his existence. The scope of this problem, as we find it in that part of the world in which we live, and the methods, tried and untried, which are proposed for its solution, are the subject of this present study.
Omitting fortuitous causes of floods, such as dam failures, storm-waves on coasts, and earthquake waves, the most universal cause is the presence of more run-off water from the land than stream channels have capacity to carry. This excess is caused by precipitation, generally in the form of rain. ‘The rains descended and the floods came’ remains as of old a truly scientific statement of cause and effect. Sometimes the precipitation is in solid form (snow); and as it generally happens that snow melts under a later rain, the effects of two storms are thus added together. This often greatly increases the intensity of floods.
Another primary influence affecting floods is temperature. Heat and cold sometimes exercise decisive effects. Snow melting, already referred to, is an example. Another is the effect of frost in making the ground impermeable, so that rain falling upon it cannot soak in, but must run off as from a roof. Heat has exactly the opposite effect: it dries out the ground, directly or through vegetation, and leaves it in condition to absorb vast volumes of water. Thus it happens that, although the most intense rains generally occur in the summer, late spring, or early fall, the most intense floods generally occur in winter, late fall, or early spring.
These two agencies — storm and temperature — are, as we have said, entirely outside the power of man to control. Science has discovered no means of modifying them in the slightest degree. Even the prediction of storms is confined to their progress and probable results after they are well developed. In the two great controlling factors in the production of floods man is thus entirely helpless, and his own work begins only after emergency has arisen.
Let us now consider the effect of man’s occupancy of the earth — the process of replenishment — upon the destructiveness of floods. This opens up the chief controversial aspect of the problem — the alleged effect of man’s operations in hastening the run-off of storm-water to the streams and in diminishing the natural capacity of the streams to carry it away. Deforestation, drainage, and encroachment upon flood-channels are the substance of the indictment. So wide is the scope of these matters that we can here enter into no argument concerning them, but must confine ourselves to a categorical summary of what we understand to be the conclusions of the engineering profession in its practical dealings with the problem of floodcontrol.
First, as to deforestation. It is held by forestry enthusiasts that the forest soil, by virtue of its cover, is more receptive of moisture than the open country. This has never been demonstrated and is very doubtful as a fact. Cultivation of the soil, ploughing, sowing, and so forth, greatly increase capacity for absorption. On the other hand, the undisturbed condition of the forest soil through long periods, and the solid packing of the ground around the roots of large trees, tend toward impermeability of forest soils. Where the balance of these influences lies, it is impossible to say, but it is probably slight, one way or the other.
It is held that forest cover is the best protection against erosion. There is no protection superior to a well-knit sod, or a thin covering of close-standing crops or underbrush. There are situations where forest cover is probably best for this purpose, but there is no universal rule to that effect.
It is held that forests, by their cooler status, as compared with the open country, induce greater precipitation. As a factor in the flood-problem, even if this were so, it is insignificant and on the side of greater floods.
Beyond question, forests tend to intensify floods from melting snow. This is because they prevent drifting, and thus expose greater surfaces to melting influences.
The definite controlling fact in the whole matter, however, is this: that, even if there be a certain reservoir effect in forest cover, it invariably becomes exhausted in the long rains which lead up to great floods, and is altogether ineffectual when the crisis arrives.
The records of stream-flow where longest kept do not indicate an increase in the intensity or frequency of floods as a result of deforestation, or a contrary effect where reforestation has been long in progress.
Finally, whatever merit there may be in the conventional forest theory, it is impossible of general application because of the necessities of human existence. On the average, not more than one fourth of the land area can be given over to forests in a thickly settled country. That is less than the existing areas of virgin forest and regrowth in all the territory east of the Mississippi.
It is necessary to lay emphasis on the foregoing facts in order to disabuse the public mind of an illusory theory which amounts almost to an obsession. So long as the public believes that it can protect itself from floods by planting trees, so long will the cause of effective flood-control suffer. How great is the need of enlightenment on this subject may be appreciated when so prominent a man as the late United States Senator Newland, of Nevada, who claimed to have special acquaintance with these subjects and was influential in legislation concerning them, was capable of an utterance like the following: —
‘Why, we have been destroying our forests, those great natural reservoirs of moisture into which the waters fall from the heavens, and where they are stored in the leaves and the loose soil, and drunk up by the thirsty roots of the trees and vegetation, and thence the surplus gradually makes its way to the creeks and the tributaries of our rivers. We have destroyed our forests, and the water which used to be absorbed by these forests is now hurried on into the creeks and the rivers.’
Secondly, as to drainage. It seems obvious enough that drainage works — pavements, sewers, road-ditches, tile and open drainage on farms — must hasten storm-water to the streams. That may at once be accepted as a fact. But in this, as in forestry, there are powerful compensations which never occur to one on first thought. This, in particular, is the case with the drainage of lands naturally wet and marshy. In a state of nature these lands are thoroughly saturated in their normal condition. But drainage takes this water out, and creates enormous space for ground-storage where none existed before. So it happens that the drainage itself, which may hasten the flow of water when once in the ditches, is ever operating to create ground-storage which shall delay the rapid filling of the ditches. We do not know where the balance lies, but our progressive friends, the French, lay especial stress on the restraining influence just pointed out.
Thirdly, as to channel encroachment. In this connection two kinds of channels are to be considered — one, the normal channel between banks in which the ordinary flow of the stream is confined; the other, the overflow channel through the bottoms between the uplands on either side, which comes into use only in time of high water. These bottom lands are universally subject to encroachment and occupancy because they are the most valuable of all lands. This forces an extra burden upon normal channels in time of flood. As to these channels, it seems to be a fact (contrary to the accepted view) that man’s work tends to increase rather than diminish their capacity. There are, of course, exceptions, some of them very pronounced; but the rule seems to be as just stated. A most striking example is furnished by the recent studies of the great Miami River flood-problem. The channel capacity through those of the chief towns on that stream where there have been radical modifications by human action, was found to be from two to eight times as great as in the country districts above and below, where man’s interference has been slight. Such a condition cannot, of course, be merely an accident.
We may here observe that one of the most capricious and uncertain things in nature is the channel capacity of streams. It is subject to no uniform rule. On the same stream it may vary all the way from the magnitude of the greatest flood to perhaps not one per cent of it; and so it results that the problem of flood-control, even on the same stream, may be entirely different on the different sections.
The conclusion of this whole question of the influence of man’s occupancy of the earth upon the intensity and destructiveness of floods may be stated thus: —
So far as deforestation, drainage, and so forth, are concerned, the compensating influences of cultivation are so many and important that we cannot tell where the balance lies. There is no reason to suppose that in great and prolonged floods it falls decisively on one side or the other. Whatever it may amount to, it is more apparent near the sources of streams than on the lower courses of great rivers, where it is subject to certain other influences to which we shall refer in discussing the subject of reservoirs.
The great and controlling effect of man’s work in causing flood destruction arises from his occupancy of natural overflow channels (bottom lands), thus blockading Nature’s chief highway for conducting her flood waters to the sea. It is here that man dwells in greatest numbers; it is here that wealth accumulates in greatest abundance. It is a situation in which man is in part responsible for his own misfortunes, and on him rests the burden of adequate provision for escape from them. What such provision should be, is our next inquiry.
This subject we may consider under three headings — warnings, prevention, protection.
Flood warnings. Although science cannot predict the occurrence or intensity of a storm with the least degree of certainty, it can forecast something of its progress after it has begun, and it can do a great deal to warn the public of its probable effects in run-off. The Flood Service, as this branch of public activity is called, thus becomes a matter of great importance, and in France and Germany it is developed to a high state of perfection. By its forecasts it can avert practically all loss of life and, to a large extent, loss of property. It is a highly useful department of the public service, and should be made as efficient as possible.
Flood-prevention. This feature of flood-control has to do with retarding the run-off so that, it will not pass downstream as rapidly as it would naturally. It is altogether a matter of reservoir action — catching the water in great basins as it runs from the land, holding it until the storm is past, and letting it out gradually afterward. The method is so logical in theory that the enthusiast never stops to inquire what may be the limitations of its universal application; but, as a matter of fact, these are many and important. The subject itself, like that of forestry, is so extensive in its scope that argument pro and con is impossible in a paper of this length, and it is necessary therefore to stop with a detailed statement of the conclusions generally accepted by the engineering profession.
In their purpose and functioning, reservoirs are of two classes: storage reservoirs, in which the water is held for some later use, such as power, municipal supply, irrigation, and the like, flood-control being rather an incidental than a main purpose; and detention, or retarding, reservoirs, with outlets always open, so that the water detained during a storm is promptly released afterward, flood-control being in this case the sole consideration. In the storage reservoir the land occupied is permanently lost to other use. In the detention reservoir it remains available for agricultural use.
With the storage reservoir there is generally a conflict of purpose between flood-control and other uses. Inasmuch as the quantity of rainfall in the wet season, when water is being collected, can never be foretold, it becomes important, for storage purposes, to fill the reservoirs as soon as possible, so as to be sure of a supply; while, for flood-control, it is important to reserve ample space until the season of storms is safely past. The conflict can best be harmonized by building the reservoir so large that it can safely store a maximum run-off; but this may greatly increase the cost and may often be impracticable for lack of site. In the majority of cases, both purposes cannot be completely satisfied.
The influence of reservoirs upon flood-control is, of course, greatest on those sections of the streams which lie immediately below the dams. The protection there afforded may be absolute. But the effect diminishes rapidly downstream as additional tributaries come in, and in large part disappears on the lower courses of great rivers like those of the Mississippi basin. This is due in part to the impracticability of building reservoirs on all the tributaries, but mainly to the impossibility of so manipulating outflow as to make it diminish floods on the main stream. Such floods are the result of combinations of floods from many tributaries. Reservoirs, particularly of the detention type, might release their stored waters at the wrong time, so far as the combination below is concerned. There can be no doubt that this would often be the case, and for that reason any system of reservoirs which could not hold back the flood water above them until the season of floods was safely past would be of doubtful value. The enormous development of the system necessary to make it at all effectual, and the difficulty of so manipulating it as to reduce tributary combination, cause engineers to look with misgiving upon the scheme as a means of controlling the floods on the lower courses of great rivers like the Mississippi.
It seems clear that the reservoir principle of flood-control is bound to have wider and wider application; but it is doubtful whether this will take the form of detention basins for flood-control exclusively, so much as of storage reservoirs with flood-control as one consideration only.
Flood-protection. This is distinguished from flood-prevention in that it does not seek to hold back the runoff, but rather to expedite its progress to the sea, and to make the channels carry it without overflow. The whole purpose is to increase channel capacity. This is accomplished by one of the following measures or by a combination of two or more of them: —
(a) By cutting off bends, thus shortening the channel and increasing its slope, streams may be made to carry more water for the same dimensions. Cut-offs are a very important resource on small streams, and even on some large rivers, like those of the Hungarian plain. Official sentiment is strong against them in the case of the Mississippi, but for other reasons than those of flood-control.
(b) Enlargement of the channel itself may be effected by widening (which is least desirable because it costs more for right-of-way, requires much excavation, and restricts the area of bottom land available for occupancy); or by deepening, which involves expensive excavation and is likely to have to be repeated more than once; or, finally, by enlarging the channel upward through the building of dikes along the banks. This is the levee system — the cheapest, most effective, and most universally used of all methods of channel enlargement. It has been resorted to in all ages and on all sorts of streams, and the property protected by it is beyond possibility of estimate. In nearly all situations it is at least an auxiliary aid; in some few cases of great importance, — like the Mississippi and the Po, — it is the only method of practical value.
(c) On some rivers it seems impossible ever to confine the greatest floods to the main channel. In such cases auxiliary flood channels, or bi-passes, have to be provided. The Sacramento is the most prominent example. It is considered desirable to avoid this method whenever it is possible to do so, and it has been definitely rejected on the Mississippi, although it has always had its advocates there.
(d) A bi-pass, strictly speaking, returns to the main stream. An outlet differs from it in leading to the sea by its own channel. All deltaic rivers have outlets near their mouths. From the point of view of navigation, they are looked upon with disfavor because they tend to dissipate the energy of the current and lead to the deterioration of the main channel. On the lower Mississippi one such natural outlet, the Atchafalaya, has been maintained; all the others have been closed. Surveys have been made for another in the vicinity of New Orleans, but official sentiment is generally against them for that stream.
It is manifest, from this very cursory survey, that the flood-problem is one of great complexity, not to be worked out by any definite rule, but to be studied from every angle in order to determine the method or combination suited to the particular case. It is, perhaps, fortunate, in spite of the losses suffered, that there has been delay in solving the problem on most streams, because technical knowledge on the subject has greatly increased in recent years, and the engineering profession is far better prepared than it was twenty, or even ten, years ago to deal with it effectively.
If we were to attempt to formulate any broad conclusion as to the application of these various measures of floodcontrol, it would be this: as a rule, reservoirs will find their greatest usefulness near the headwaters of streams; levees will be the main resource on the lower courses of great rivers; cut-offs will generally be confined to the smaller streams; and excavation will be resorted to only in special situations, where less expensive methods fail to accomplish the purpose.
There is the satisfying fact about the general problem of flood-control that it is capable of definite solution. Some of the railroads have so far provided against such disasters that they no longer fear them. Every thoroughgoing treatment places so much of the problem behind us. The total cost, moreover, may not prove so great as we are apt to think. In casually reviewing some of our more important problems, it is difficult to see how the aggregate for this country, in addition to that portion which will be defrayed on other accounts (through works for industrial use, and the like), can equal that of the Panama Canal. Spread over a quarter of a century, the burden will be light and the resulting benefits will virtually cancel it as we go along.
Perhaps the most perplexing question confronting the engineer who is called upon to formulate a scheme of flood-control in any particular case is to determine what degree of control to advise. He invariably becomes convinced that there is nothing in the conditions of the case which can furnish assurance that no greater flood will ever occur than those which he knows to have occurred. He feels that, to be safe, he must make a large allowance — factor of safety — over the greatest, known flood. At the same time, he knows that such floods occur only at very rare intervals, and this further question is forced upon him for decision: is it wise to provide for those extreme visitations which may occur only once in a generation or so? Would it not be better to stop with provision for high floods, accepting the very rare deluges with such emergency measures as may be practicable at the time, and then foot the bill of damages? This is, in fact, the general policy of railroads, which are perhaps the greatest sufferers from floods; and it would be easy to demonstrate, on the basis of financial profit and loss, that the same course would apply to many of the great flood problems of the country.
There are, however, considerations other than mere profit and loss, which assume an importance in some problems that justifies a policy of absolute protection.
A serious hindrance to effective measures of flood-control arises from the quick recovery of the public mind from the shock of disaster. This is a universal experience. Iroquois theatre tragedies, Cleveland school holocausts, stir the public mind to frenzy and lead to the most strenuous measures of protection. But the lesson is quickly forgotten, and severity of regulation correspondingly relaxes.
So in the case of floods. Situations like that in the lower Mississippi, where flood disasters occur every few years, furnish their own impelling force for remedial measures. Other situations, like those in the State of Ohio in the terrible flood of March, 1913, do not arise often, and it requires a forceful, self-denying, and determined public spirit to carry through truly comprehensive measures.
Perhaps the most urgent need of the flood problem to-day is a broad-gauge, enlightened, and energetic public policy in regard to it. There is no occasion for further delay in formulating such a policy, and this fact seems to have found recognition in Congress in the recent creation of a new committee in the House of Representatives for the exclusive consideration of the subject of flood-control. While the powers of this committee do not at present extend to the bringing in of appropriation bills, they certainly do permit the formulation for submission to Congress of a definite national policy; and in the expectation that it will live up to its opportunities, we shall examine some of the features which such a policy should embrace.
In the first place, it should extend to all streams, and not be limited to navigable streams. Such technical limitation has been the chief barrier hitherto to any comprehensive flood legislation. It has always seemed to the writer a most illogical barrier. The constitutional authority of Congress to act in these matters is not in terms restricted to navigable rivers, nor indeed to rivers at all. It is difficult to understand why Congress may appropriate money to remove a river-bar or other obstruction to navigation, and may not appropriate money to control floods on streams where such floods interrupt interstate commerce, delay the mails, and otherwise interfere with the general welfare. In spite of the fact that Congress has thus far religiously clung to the theory that it can appropriate no money affecting stream-control unless it be in aid of navigation, the grounds upon which this policy rests must be challenged, and we believe that the creation of this new committee is premonitory evidence of its early abandonment.
In the second place, we may observe that there should be close coördination between flood-prevention or protection and other purposes of stream-control, in order that there may be no serious conflict of purpose or undue waste in the cost of development. This is perhaps the most difficult feature of the flood-problem—more difficult than the physical problem in itself. At the outset arises the perplexing question, how to deal with private development upon our streams. We ought not, on the one hand, to prevent or seriously discourage private capital in the development of power; on the other hand, we must not permit such development to become an obstacle to adequate flood-control. A particular feature of private development which might, and generally would, so interfere, is the construction of storage reservoirs. The sites occupied may be the only ones suitable to flood-control, and development for industrial use only might permanently bar the other purpose. It would seem that all such development should first receive the approval of some public body, both as a guaranty of safety and as a means of control.
It is right here that public aid might well be given. Suppose that a reservoir of certain capacity at a particular site will answer all the purposes of industrial development, while one of greater capacity will serve also the purpose of flood-control. If, in addition to the cost justly chargeable to private development, the public could add enough to secure the larger work, manifestly two important ends would be gained.
Some such policy would seem to be exceedingly desirable, because waterpower, domestic supply, and irrigation are destined to undergo wide development; and it seldom happens that the particular industrial use concerned requires a dam great enough, or perhaps of the right type, to serve with highest efficiency the purposes of flood-control.
In the third place, there will be situations, as in the Great Miami Valley, where reservoirs will be built for floodcontrol only, without any possible return from future use of the stored water. What will be an equitable system of apportioning the cost in such a case? Flood-control clearly benefits two distinct interests — public and private. A great flood destroys means of communication, obstructs interstate commerce, delays the mails, may affect navigation adversely, while its effects may extend to other states than that in which the stream lies. The Federal government certainly has a material interest at stake in all such occurrences. Likewise cities on river-banks subject to the direct onslaught of floods, are interested vitally in their public capacity. But great as these interests are, private interests affected generally far exceed them, and it is right that they should be called upon to bear the burden of works of protection. The problem is to devise a system which shall apportion the cost of flood-control in each particular case equitably, on the basis of the interests involved, and shall have the power to compel unwilling interests to contribute their proper share. Local communities, and even private interests, may prefer to handle their own problems at their own expense, as in the present case of the Miami Conservancy District. There can be, of course, no objection to this, provided the work satisfies the necessary conditions of effectiveness and safety. But isolated examples of this kind do not affect in any way the duty of public coöperation and aid wherever it is needed.
A strong consideration in favor of a national policy for handling this question is the necessity of eliminating conflicts of jurisdiction. Public agencies of various sorts, — such as towns, counties, and assessment districts, — exist, or are called into being, for particular purposes; but only two — the general government and the states — have the attributes of sovereignty. As between state and nation, if the streams of a state were confined to its own territory, instead, as is generally the case, of crossing the boundaries into other states, there would be some argument for state as against Federal control. But as matters stand, state control can never be made sufficiently comprehensive, and it is far better that the jurisdiction should rest in that authority which embraces the streams from their sources to their outlets. Even with this jurisdiction, international boundaries may interfere; and they do, in fact, sometimes give rise to grave complications, as in the case of the Colorado River, where a situation of such gravity exists that nothing short of a cession of a small tract of territory will ever solve the problem satisfactorily.
Finally, it is strongly urged by many that some one in authority, such as a national Board of Public Works, should have control of all the uses to which our streams may be put. The idea appeals to the mind as logical and plausible, but closer analysis fails to justify it as in any sense necessary. Irrigation work, for example, can very well be carried on by the Reclamation Service as it is now constituted, and works in aid of navigation by the Corps of Engineers. The functions of these two organizations might properly be expanded to include flood-control, so far as it relates to their particular work; and a Department of Flood-Control might be created, to deal with those features of the problem lying outside the two fields just mentioned. We do not advance this suggestion as an argument against the central board idea, except to counsel caution in adopting a system which may prove unworkable by its very ponderosity. There is no reason why separate management of matters which are really quite distinct cannot be accomplished, not only without serious conflict of authority, but rather with intelligent coöperation wherever their respective spheres come into contact.
There is no reason either why such a system may not be just as effectual and economical, while there is even less liability to abuses of the ‘pork’ variety. ‘ Pork ’ is a state of mind, and we shall never get rid of it by any change in departmental methods, but only by a change in the mental attitude of the people.
Let those who imagine that relief in this matter is in sight in the proposed new scheme of centralized control now before Congress consider the following estimate for the next ten years, taken from Senator Newlands’s speech cited above. According to the programme there outlined, the sum of $600,000,000 is to be expended in ten annual installments of $60,000,000 each for streamcontrol work of all sorts, ‘apportioning this vast sum fairly [sic] between the different watersheds of the country,’ on the following basis of annual expenditure: —
|Atlantic Coast streams||$10,000,000|
|Gulf streams exclusive of the Mississipi||5,000,000|
|Ohio and its tributaries||5,000,000|
|Colorado and its tributaries||5,000,000|
|Upper Mississippi and its tributaries||5,000,000|
|Missouri and its tributaries||5,000,000|
|Sacramento, San Joaquin, and their tributaries||5,000,000|
|Snake and Columbia and their tributaries||5,000,000|
|Some watershed evidently overlooked||5,000,000|
|Total annually for ten years||$60,000,000|
This is ‘pork’ — not by the barrel, subject to the approval of a disinterested and scrupulous body of engineers, but by the hogshead, without any engineering scrutiny, yet ‘apportioned fairly,’ and absolutely guaranteed from the outset. The great American public should think twice before it takes a plunge like this which, so far as the ‘pork’ evil is concerned, may prove a veritable jumping out of the fryingpan into the fire.
Limit of space in this paper precludes consideration of special cases, with one exception — that of our greatest flood-problem, perhaps the greatest in the world: the problem of the lower Mississippi. Controversy has raged about it for at least two generations. Great floods have come along and have broken through the levees, carrying destruction to the neighboring bottoms, and the public has forthwith united in pronouncing the levee system a failure. Solutions of the problem have been proposed, ranging from the most visionary schemes to those which have real merit; but the outcome of it all is that ‘ levees only ’ is practically accepted by the engineering profession as the true solution. Not only is this the case, but there have been collected sufficient data upon which to base a complete scheme of control.
There is no reason, from an engineering point of view, why the problem should not be taken up forthwith and carried to completion in the course of a few years. And there is every reason why such a course is imperative. The situation on some portions of the riveris in what we may call a critical stage — one in which the work so far done actually aggravates the evil that it is intended to eliminate. This is because, on the one hand, the partial protection so far achieved has induced increased occupancy of the bottom lands, so that there is more property to destroy; and, on the other, because the levees have raised the flood-surface of the river, as levees always do, so that, when a break does occur, it produces more destructive currents than when the overflow was spread in a thin sheet all along the bank. It is of the highest importance to bridge this gap between partial and complete protection with the utmost possible dispatch.
The difficult and uncertain feature of this problem, as it appears to the writer, relates entirely to the method of financing it. This should not be done with Federal funds alone. There must be some proper division of cost between the Federal government and local beneficiaries. The proportion will doubtless vary on different portions of the river, and there will be necessary adjustments with existing levee districts. The direct benefits to the valley taken as a whole certainly justify local aid of fifty per cent.
How this coöperation is to be brought about so as to be dependable and effective is the real problem. It will require most careful consideration, and, beyond doubt, a great deal of time. But a plan once settled upon, there would seem to be no excuse for not hastening it to completion within the next few years. The interests at stake have now become so vast, and their growth so rapid, that efficient and positive measures are imperative.