Senator KENDRICK. Do you mind if I interrupt you to ask a question there?

Mr. DAVIS. Not at all.

Senator KENDRICK. Your study of the river had to do with the flow of the river, did it not, with the amount of water?

Mr. DAVIS. Yes, sir; that was one of the principal features, but not all.

Senator KENDRICK. Were you able to determine as to whether or not there was a greater flow of the river where it traveled through the canyon than down below in the country in which the diversion dams are to be constructed?

Mr. DAVIS. Yes, sir.

Senator KENDRICK. In other words, there is a loss in the canyon region?

Mr. DAVIS. No, sir; through the canyon region there is a gain. When we get below that, there are large losses by evaporation from the river and its tributary valleys from the time the river leaves the deep canyon region and becomes more sluggish, and the loss in volume and the loss in grade lead it to gradually deposit a large amount of earthy material that it erodes in the canyons of the upper basin. The principal branch of the Colorado River usually called the Grand River, rises in Colorado. The one next in importance, Green River, rises in Wyoming, and those two States furnish by far the greater part of the waters tributary to the Colorado River. Utah and New Mexico each furnish some. Arizona furnishes some, and California and New Mexico furnish smaller quantities. Mexico furnishes practically nothing.

The basin of the Colorado River comprises about 224,000 square miles, the topography and the agricultural conditions dividing it naturally into three very different regions. The first is the mountain region lying in the States, in order of their area, of Colorado, Wyoming, Utah, and New Mexico, which furnish large quantities of water to the river. All of them are largely mountainous, the high mountains furnishing a large amount of melted snow throughout the melting of snow season, and they also have valleys along the tributary streams many of which are irrigated and some of which are still to be irrigated.

Along the western boundary of Colorado and the southern boundary of Wyoming, roughly speaking, the river enters canyons. They are not entirely continuous, opening out a little in Utah, but the region below the boundary lines of Colorado and Wyoming is mostly the canyon region. There is some very rough country along in there. They are very deep canyons, including the Grand Canyon and the Marble Canyon and many other canyons on the Colorado River, some of which are steeper and more abrupt than are the mountains of Colorado itself.

That canyon region is largely of the most barren character. Some of it carries timber. Very little agricultural land is found there, the amount being negligible; the exception to that being where the canyons of the Green River open out in the State of Utah, there some agricultural land existing.

However, in general the mountain region has some mountain valleys and lower valleys mergeing into the canyon region, and

throughout both those regions the erosion is great, particularly in the canyon region. The river gathers an almost incredible amount of eroded material, and it thus happens that when the river emerges from the canyon region it is carrying a very heavy load of sediment. It loads itself up with the sediment from the canyons that it is getting and it is carrying down and has been for many centuries and when it emerges from the canyon region two things

occur.

The first is that the grade of the river greatly decreases so that its carrying power decreases; and second, the hot climate that occurs down there and the open valleys that are there lose a great deal of water through evaporation. So that the quantity of water greatly decreases from the time the river leaves the canyon region.

Roughly speaking, at the end of the canyon region are Boulder Canyon and Black Canyon, which are one continuous canyon, at the northwest corner of Arizona, and a short distance below that it becomes the boundary line between Arizona and California; but the point where it is proposed to build this high dam is on the boundary line between Arizona and Nevada and is the lowest point on the river where it is practicable to build a high dam and a reservoir large enough to control the entire flow of the river.

Senator KENDRICK. I wanted to ask you a question about the erosion. Is it not your opinion that the control of this flow by reservoirs will largely reduce the amount of erosion in the Colorado River, by controlling the volume of the stream?

Mr. DAVIS. It will reduce it to a considerable extent. The control by reservoirs will not very much reduce it if the quantity of water were not reduced. It will make the water run more equally and, to a slight extent, reduce it by reducing the erosive power at high water, but it will increase the erosive power at low water; and by reducing the quantity of water, as will occur to some extent by use, the quantity of sediment will be materially reduced.

Senator KENDRICK. Because the flow will be uniform and not disturb the banks on either side?

Mr. DAVIS. Not so much for that reason. The canyon region has no banks except the high walls—that is, very few-and the regulation of the river alone would not, in my opinion, very materially, if at all, decrease the erosion. It would decrease erosion at high-water seasons, because less water would go down, and it would increase it at low water, because more water would be going down; but, so far as the river is depleted, then the erosion will necessarily decrease, because there will be less power expended upon rocks to wear them out.

The depositing effect of the river increases as it reaches the valleys in the southern part of the basin, causing it to build up its bed and banks, because it has a heavier load of sediment than it can carry, although it still carries all it can to the sea and deposits it there. This tends to place the mouth of the river farther out into the Gulf and make the river longer. That has a tendency, by increasing the length, to decrease the grade, because the fall is distributed over a greater length and causes a gradual rise for that region, and the river, as its velocity decreases, has a greater tendency to deposit its sediment. The river as it fills up its bed has a tendency to overflow its channel and deposit the sediment upon its own valleys, mostly at

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the river bank, so that the river is constantly rising, and it does not take very long for the river to get into a very unstable condition.

The filling of its bed, causing it to overflow its banks, has a tendency to divert the water somewhere else, and at last the river finds a channel where it can get a better fall and leave its own channel. In that way wide valleys are built up, and in that way the river has built up an immense delta at its mouth, largely known as the Imperial Valley, and by pushing this delta farther and farther into the Gulf as the centuries went by it cut off the head of the Gulf, leaving a basin there below sea level. The northern end of the Gulf of California, which is an arm of the Pacific Ocean, was thus cut off from communication with the ocean, and the land between the Gulf of California and what was formerly the head of the Gulf of California is 40 or 50 feet higher than sea level, and the land cut off constitutes the Imperial Valley and is mainly below sea level.

There are adjacent lands slightly above sea level, and there is a large lake called the Salton Sea, which has gradually dried up and been depleted to its present state on account of the high evaporation of that country and the small amount of inflow.

Senator JONES of Washington. Is the Salton Sea a part of what was formerly the Gulf of California?

Mr. DAVIS. Yes, sir. The process is still going on. The Colorado River is carrying this load of sediment, slightly depleted but still an immense quantity, nearly as much on the average every year as the American commission excavated from the Panama Canal in its construction. That does not include what was excavated by the French. Roughly speaking, those quantities are nearly equal, and this means something like 100,000 acre-feet of sediment per annum being carried down.

That means that any storage in the lower basin must have a very large capacity or it will be soon filled with sediment. The reservoir proposed here, if receiving all the waters of the Colorado River and taking therefrom the sediment it carries, would receive that sediment before it filled for a period of about 300 years. It would be abour 100 years before the storage function of the reservoir would be materially injured or depleted by the filling.

The CHAIRMAN. Does the greater amount of erosion occur below the proposed site of the dam?

Mr. DAVIS. The deposition occurs below, the erosion occurring in the upper stream, mainly in the canyon region. These rivers fall rapidly and cut these mountains rapidly, and that constitutes, roughly speaking, the canyon.

The CHAIRMAN. I would think, if that be true-and I do not want. to place my opinion above yours-that the erosion was above the impounded water and that when it struck the still water the deposits would be made and fill up very rapidly.

Mr. DAVIS. The reservoir will fill rapidly, but it is so large that it takes it 300 years to entirely fill. I am assuming that the waters. will still continue to erode the canyon region and will deposit all the resulting sediment in a constructed reservoir. Of course, clear water will have a greater carrying power than muddy water and will have some tendency to pick up the sediment from the river below; but the grade of that lower stream is so low that the river

will not have a cutting velocity, except to a limited extent, and the coarse material it receives from the side tributaries will be distributed on down the river and the coarser left on the bed of the river and the finer carried along. So there will be a gradual process under those conditions of paving the bed of the river with coarse material which it will have no power to cut.

Senator JONES of Washington. Do you mean to say it will be about 100 years before there will be any appreciable filling up of that reservoir?

Mr. DAVIS. Not appreciable; I do not mean that, but injurious. For example, the dam that is proposed will be a high dam. We may take it that when completed it will be about 550 feet high and that it will have a storage capacity of something like 25,000,000 acre-feet.

Senator JONES of Washington. That is on the theory of the water coming how high-to the top?

Mr. DAVIS. Yes; I am speaking of the entire capacity of the reservoir, and a zone at the top will be kept as nearly empty as possible by discharging water when it comes into it, for flood control, and then the other portion will be used, if it is properly handled, for the regulation of the river and making the waters useful by the development of power and irrigation. Then a lower part not needed for either of those other two purposes will constitute, in addition to the other two, a head upon which power can be developed and in which we can store sediment without encroaching upon the two parts that are reserved for the two purposes needed-flood control and water storage.

Now, until the lower part, say 10,000,000 acre-feet, is filled with sediment, which will take about 100 years; it does not interfere at all with the storage capacity for anything else and does not interfere with the head for power. It furnishes a working head which is the same when filled as empty. Now, this is important, for the reason that the rapid depletion of the reservoir capacity by being filled with sediment means that we must not destroy any useful reservoirs on that river. We must utilize the natural conditions and add to the storage capacity when it is practicable to do it, and it also means that a reservoir of small capacity will have a short life of usefulness and that only a large reservoir is justified. It happens, fortunately, that the larger we build that reservoir, up to about thirty-five or forty million acre-feet capacity, the cheaper is its output of power, because, as you know, the unit cost decreases as we increase the height of that dam to the extent I have indicated.

Senator JONES of Washington. You have not been able to devise any way yet by which you can get that silt out of the dam?

Mr. DAVIS. It can be washed out, but the expense is very much greater than the construction of new capacity. In other words, if we take the very lowest bids for sluicing out such materials, so far as I can judge it might cost somewhere in the neighborhood of 5 or 6 cents a cubic yard. If it would cost that, it would amount to nearly $100 an acre foot of storage capacity. Storage capacity can be built by building this same dam higher for about $1 per cubic foot.

Now, of course, the sluicing out can only be carried on in one reservoir in order to throw the silt down to the ocean and you can never be sluicing one out and putting it in the other.

Senator KENDRICK. What is the maximum possible height of the dam?

Mr. DAVIS. At that point?

Senator KENDRICK. Yes.

Mr. DAVIS. Well, I do not know that that has been determined. It is very much higher than it is proposed to build this one. I think it would be entirely feasible, although I have not gone into it sufficiently to give a final opinion, to make this dam 1,200 or 1,300 feet above the river bed.

Senator JONES of Washington. Well, the wise thing for you to do, if you want to do that, would be to start out with a foundation that is sufficient, would it not?

Mr. DAVIS. Well, if we were deliberately to go that high within a short time, that would be wise. It is not necessary, however, because it would be impossible to excavate the foundation below the dam.

Senator JOHNSON of California. Would it not be wise to build this with a foundation sufficient to bear the raising of this dam in 100 or 200 years?

Mr. DAVIS. That is not in contemplation in this bill, although that detail is not excluded, for the Secretary would have power, in my judgment, to take some such course.

Senator JOHNSON of California. Don't you think that really ought to be done? Of course, a hundred years in your life or mine is a long time, but a hundred years is not very long in a matter of this

sort.

Mr. DAVIS. That is true; but if we were defeating the construction of this dam to a higher level by not putting in that foundation, of course you are right; but we are not doing that. We can excavate the foundation a hundred years hence.

Senator JOHNSON of California. In other words, in your judgment it is not necessary in order to get a higher dam in the future to build a foundation now of the size that might be necessary?

Mr. DAVIS. No, sir; that is my opinion.

Senator JOHNSON of California. You may add to that by simply adding the foundation later on?

Mr. DAVIS. Yes. My advice, however, is not to build another dam above this final point where the large reservoir is possible. That would interfere with the construction of such a dam in the future. In other words, we should so plan the general development of the river that a very large reservoir of something like 35,000,000 or 40,000,000 acre-feet capacity can some day be built, and it is very much cheaper now to build it to a capacity of 25,000,000 or 30,000,000 acre-feet, because it develops more power for each dollar expended. The CHAIRMAN. What is the height of the walls of the river there? Mr. DAVIS. What might be called the walls is not very definite, but at a height of 1,300 feet above the river the canyon has a width of about 1,300 feet. It widens a little more rapidly above that point. I should say that a conservative estimate of the height of those canyon walls along there would be over 2,000 feet, and in places reach probably 3,000 feet. I do not suppose, however, it would be feasible to build a dam any higher than 1,500 or 1,600 feet.