RIO GRANDE DIVISION.

The project of greatest interest in this division is that of the proposed reservoir above El Paso, Texas, named by Maj. Mills Lake Constance.

The general results of the engineering and hydrographic work at this point were stated in the first annual report, and details were given in the report of the Select Committee of the Senate, as well as in various official publications bearing upon the international features of the problem presented. It is thereforefficient at this time to state briefly the conclusions. A masonry dam at the pass 65 feet above the river bottom will create a lake 144 miles long by 4 miles in maximum width, with a surface area of about 26,000 acres, an average depth of 23.6 feet, and a cubical content of 537,000 acre-feet. Of the two possible ssible sites, which are 13 miles apart, the upper one was considered to be the more favorable. The estimated cost of a at this place is a little over $300,000, to which must be the cost of removing the railroads, about $590,000, and the cost of the land overflowed, which is very nearly $69,000, making a total, including incidentals, of about $1,060,000. This cost, while large in itself, is small when taken in consideraWith the probable returns, as at least 200,000 acre-feet of per annum would be available.

dam

addel

tion

water

Ha

dent

sio11,

ing completed the survey, maps, and calculations incito this great project, Mr. Follett, the engineer of this diviwas for a time transferred to the Arkansas division, but

subsequently returned to make a reconnaissance of the headwaters of the Rio Grande for the purpose of discovering reservoir sites and obtaining other information regarding water storage.and irrigable lands, preliminary to the surveys of the

succeeding field season.

Th e

principal localities examined were in and adjacent to the

Mesilla, Albuquerque, Española, Taos, Puerco, San José, Chama, and

Besides these, several great mesas containing many thousand acres of good land were traversed and the probabilities of sup

11 GEOL., PT. 2—10

valleys and mesas there is a large percentage of the territory examined which is worthless for agricultural or pastoral purposes, hardly producing enough vegetation to support one sheep to 50 acres, the rainfall and snowfall being scanty over the whole of this area, except in the northern portion near the Colorado line.

The result of this examination brings out more strongly than ever before not only the great need of storing the flood waters of the Rio Grande, but also the many natural facilities which this basin possesses for this purpose.

For example, the following approximate estimate of the water needed will give some definite conception of the demand for water. In the San Luis Valley are five large canals with a combined carrying capacity of 8,000 second-feet. Probably none of them are now carrying over half their maximum flow, but even then 4,000 second-feet are being used in this valley. Of course, much of this water will find its way back into the river at or above the canyon, as irrigation is now conducted.

Between Embudo and San Marcial about 1,000 second-feet are used or needed. In the Mesilla Valley from Rincon to El Paso 900 second-feet are needed. The new El Paso ditch, which owns all the water rights of the old ditches below on the United States side, has a capacity of about 400 second-feet and the Mexican ditches have a capacity of about 800 second-feet.

Thus there are needed below Embudo 3,100 second-feet to supply the demand. Of course, seepage will cause some water to be used two or three times over, but even then there will be a shortage of water except in years of maximum flow.

The country which suffers first, the Mesilla and Ysleta Valleys, is that the products of which are far more valuable per acre than those of the land on which the water has been used. With storage the Territory of New Mexico can support a much larger population in the Rio Grande Valley than at present; without it her progress will be slow.

It is to be noted that water is needed not only for land not yet under cultivation, but even for a large portion of the land which for years has been farmed, so that apparently New Mexico, or rather so much of it as depends upon the water of the Rio

Grande, can not grow or even hold its own until storage has been provided. That there are many natural advantages for this is shown by the fact that in New Mexico alone over fifty reservoir sites were discovered, besides ten in Colorado. For discussion the New Mexico sites are classified as A, B, C, D, and E. A tabulated statement of the capacity in acre feet of

the reservoirs of these different classes is also given, with brief to reason of assignment of all sites included in D

notes

and E

The relative merits of these five classes are about as follows: A-Sites with abundant water supply, good dam site, good foundations, material handy for dam construction, and large Capacity in proportion to size of the dam. These sites ery valuable.

storage are all

B-Sites not quite so good in one or more respects as those classed A. Generally the storage capacity is not so great in proportion to the cost of the dam. These are all valuable sites. C.-Sites where it is difficult to get foundations, or the water is somewhat doubtful, or storage capacity is small in proportion to the size of the dam.

supply

D.

dam is

danger E.

ites where the water supply is doubtful, or where the large and the foundation difficult, or where there is of the reservoir filling with sand.

Small sites of little value, listed to show that they have been examined.

Of these different classes the number and storage capacity

are as

follows:

Rejecting class E and two-thirds of D, it is safe to say that there has been found storage capacity for 2.000.000 acre-feet of water, and that there is in all probability a sufficient water supply

available.