On reporting to the Director of the Geological Survey I received verbal instructions from him to make all reasonable investigations that would tend to develop the feasibility of my project and the following written instructions:

DEPARTMENT OF THE INTERIOR,

UNITED STATES GEOLOGICAL SURVEY.

Washington, D. C., April 19, 1889. SIR: I have the honor to acknowledge the receipt of your letter of 15th instant, transmitting a copy of Special Orders, No. 85, current series, from the commanding general of the Army, authorizing you to extend your services in every proper way when they may be requested by the officers of the Interior Department in charge of the Geological Survey and its action with reference to improvements of the Rio Grande River near El Paso.

In reply thereto I hereby request that you will act as the advisory agent of this bureau in respect to matters connected with improvements of the Rio Grande River, near El Paso, and relation to the use of its waters for purposes of irrigation. You are requested to keep this bureau informed of all projects looking to such purposes, and to communicate to it your opinions and advice thereon. In view of the fact that any works affecting the flow of the Rio Grande River must be matters of equal solicitude to the people of the United States and of Mexico and to their respective Governments, you are especially requested to acquaint yourself, so far as may be, with the views of the Mexican officials and people in relation to such matters, maintaining in your intercourse with them a most friendly attitude, and representing to them a sincere and earnest desire of this office to treat all matters relating to the use of the waters of the Rio Grande for purposes of irrigation with a due regard for their rights. It is the purpose of this bureau to establish at El Paso a station for gauging the annual flow of the river, for measuring the evaporation, and for other purposes, and I should be pleased if you would exercise a supervision over this work of the employees, who will be instructed to report to you, and I further request that you will assist them in securing facilities for their work.

Very respectfully, sir,

Maj. ANSON MILLS,

J. W. POWELL, Director.

Tenth Cavalry, U. S. A., Worcester, Mass.

I arrived here May 4, and in company with the Mexican consul, Mr. Escobar, crossed the river and presented these instructions to Mr. Garfias, Federal engineer; Colonel Candano, jefe politico of the Canton del Bravo, and other local officials, to whom I explained in detail the projected enterprise, which they one and all received in the most encouraging manner, giving me permission to establish one end of my cable for the gauging station on Mexican soil and proffering to assist me in any reasonable manner. I then invited Mr. Garfias, the engineer, to cooperate with me to any extent he might see proper by accompanying me in my investigations, surveys, and

measurements, to the end that his Government might have official knowledge of all preliminary work in the matter from the beginning. After receiving the necessary authority from the minister of public works in the City of Mexico, he has kept himself advised concerning all our investigations to this date, and 1 purpose furnishing him with a copy of all maps and reports relating thereto, with a view to inducing the Mexican Congress (now in session) before their adjournment in January to pass a joint resolution authorizing their President to join the United States in the construction of the dam proper, and appropriating $150,000 for that purpose should our Government make a like appropriation; this for the purpose of gaining a year's time in the commencement of the work.

MEASUREMENT OF EVAPORATION

May 6 Messrs. Williams and Dyar reported to me.

Measurements for evaporation began May 10 and were continued until the present date with the following results:

A total of 46.64 inches for 143 days, or a mean of 0.32 of an inch per day. As these 143 days embraced the season of greatest aridity, it is probable that the annual evaporation will be about 6 feet.1

MEASUREMENT OF FLOW.

May 20 our gauging station was established, the first measurement taken that day showing 4,300 cubic feet per second; the last, taken July 30, showing 30 cubic feet. On August 5 the river ceased to flow, and has not carried any water to this date, though some small pools of water are still to be found in the pass, sufficient to float the evaporation pans. During the measurements of flow the fall of the river was very continuous and gradual and other conditions favorable to the projection of curve for the measurement of highest flood as shown by drift marks, but, unfortunately, about the middle of our observations the crest of the Mexican dam, only 300 yards below the station, was raised about 12 inches, distorting the projection of the curve so that no reliance could be placed upon it. The river probably carries about 9,000 cubic feet at highest flood, and perhaps an annual average of about 1,200 cubic feet per second.

1 For subsequent investigations on this subject see p. 411, Thirteenth Annual Report Geological Survey, Pt. III.

MEASUREMENT OF SILT.

Between June 10 and July 28, 118 samples of water were taken from different parts of the river's current and the sediment of each carefully measured, with the following result: The average of the per cent of the volume of water carried, according to the assumption that a cubic foot of dry sediment weighs 85 pounds, is 0.345 of 1 per cent. The results varied from one-fourth to one-half of 1 per cent of the water carried, save in one case of local rain, the flood of which lasted some 12 hours, wherein the per cent rose to 1.

Assuming this to be correct and that it will take one year's time for the river to fill the lake with water, it will take about 300 years for the lake to fill with sediment. This, however, is making no allowance for evaporation, which is very great (possibly on the surface of the lake one-fourth the annual flow), or for the moving quicksand in the river's bottom, or the detritus to be thrown into the lake by storms from the gulches and ravines from its mountainous sides.

It is, however, safe to assume that at least 150 years must elapse before its basin can be filled with solid matter. If these premises be correct, it should be remembered that each year one one-hundred-andfiftieth part of the lake's basin will be filled with solid matter, thus decreasing, year by year, its storage capacity in that proportion; but the date when any or all of these causes may destroy its efficiency is so remote as to be unworthy of consideration. This silt problem seemed to be the most formidable one confronting the enterprise. After it had been favorably determined you visited the locality, inspected the proposed sites for dam, the basin for the lake, and the location of the two railroads, from an engineer's standpoint, and decided to have preliminary surveys, plans, and estimates for the entire work made as quickly as possible, in order that the project might be presented to Congress at its coming session.1

2

Mr. W. W. Follett, the engineer employed by you for that purpose, arrived here July 8 and immediately began his work, which was completed September 18. His report, marked B, maps, plans, notebooks, etc., are forwarded herewith. Not being a practical engineer, I make no comments on its technical features, but his pride in his profession, his untiring energy, and the vast amount of work accomplished in so short a time impressed me most favorably.

1 For further continuous observations on flow of water and sediment after the date of this report, see Appendix B, embracing extract from the Eleventh Annual Report Geological Survey, Pt. II, pp. 52 to 57, inclusive, with diagram of sediment and discharge.

[Enclosure omitted.-Agent's note.]

SOUNDINGS FOR BEDROCK.

The soundings for bedrock were made under my supervision in the following manner: The rods were of octagonal cast steel, pointed as a square pyramid, one, for shallow soundings, of one-half inch steel 18 feet long, another three-fourths of an inch and 32 feet long for medium soundings, and still another double rod, jointed in two sections, of 1 inch, 26 feet long each, for the deeper soundings. A tripod 20 feet high with a ring in its apex was necessary to keep these flexible rods in a perpendicular position while being worked by four men, with two iron clamp bars arranged to adjust to any part of the rod as it passed down. The entire 3 miles of the pass were prospected for the bedrock at all points where the walls of the canyon rendered it practicable to build a dam, but only two available sites were found, the 52-foot rod failing to touch bottom at other points.

These two sites are described in detail by Mr. Follett in his report, on pages 2, 3, 16, and 17 and maps Nos. 2 and 3. It is not absolutely certain that the true bedrock exists as described in the soundings or, if it does exist, that it is free from faults or rifts or of such a quality as to support a dam of the kind designed, but every evidence possible with such soundings was obtained, being the more positive at the lower site by reason of the rock being so much nearer the surface and the friction on the rods consequently much less. The rod rang out clearly when in contact with the rock at the lower site, while at the upper it was dull and indefinite. Before any permanent work is commenced, the fact of the existence of suitable bedrock should be determined by boring out cores from it with a diamond drill.

RELATIVE MERITS OF THE TWO DAM SITES.

The upper site has but two advantages over the lower one; the first being that it is of sufficient distance from the Santa Fe depot to allow that line to be rebuilt on its ruling grade and rise above the dam, which it is impossible to do from the lower site, it being but 2 miles from the depot; the second, that the walls of the canyon will allow the dam to be built higher should it ever be desired.

The lower site has many advantages over the upper one: First, the cost will probably be one-half that of the upper, the bedrock being but 22 feet from the water level at its deepest part, and for the greater distance across the channel from 2 to 9 feet only, while the upper site is from 30 to 50 feet for the entire cross section. The old Mexican dam, which has a fall of about 12 feet, is about

1,000 yards below this site, and by breaking this and opening a channel through the sand to this site I think the water could be lowered 8 or 10 feet, so that the bedrock for the greater part of the cross section would be presented above the water. It would be necessary, of course, to do this in a season of low water, and perhaps to flume the channel with lumber. In this manner I think this dam might be completed in one year, and, if commenced at the right season, the flood waters of that year reserved. At the upper site it would take one year to build the cofferdams and get the masonry above water. I have suggested in pencil on Mr. Follett's map No. 3 a double curvilinear dam, with three heavy buttresses, which I think well adapated to that site. These buttresses could be built in the manner indicated by moving the middle one a little nearer the left bank than shown by the pencil mark, entirely out of water. Other advantages are that one end of the dam would be on Mexican soil and that 14 miles of expensive and difficult canals on either side would be avoided.

To have the benefit of these advantages, however, it is necessary to get the Santa Fe Railroad above the water in the lake. It will be observed that the Southern Pacific in its northbound course leaves the valley just before reaching the lower dam site and climbs the bluff behind the smelter, crossing two arroyas marked A and B on Mr. Follett's map No. 1, and on a down grade before reaching the bridge. It has occurred to me that the two roads might be adjusted to use a common double track from Fort Bliss, with a cut about 15 feet deep in the bluff behind the smelter and by a strong retaining wall built on the fills in the two arroyas mentioned, so that their tracks would be some 10 or 12 feet below the surface of the lake behind these walls and yet gain an altitude before reaching the third arroya near the present bridge sufficient to carry them above the waters of the lake. The problem then would be to cross the Southern Pacific over the broad river's channel by heavy and well-ballasted crib piers rising to near the surface of low water in the lake, so that all the woodwork might be well preserved by submersion, and a superstructure of such a nature as to be restored independently. If this be practicable it will solve the difficult problem of putting one end of the dam in Mexico and keeping both railroads exclusively in the United States.

The laws of Texas require joint or union depots in cities where railroads cross each other, and sooner or later the railroads in El Paso will be required to comply with them. Should the dam be built, the radical changes wrought in the two roads mentioned above will no doubt hasten other adjustments in the city, and as neither have any

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