URGENCY OF FLOOD CONTROL

In its present state of partial development, however, the river is a menace no less than it is a benefit. Each spring the snows accumulated on the mountain slopes of the upper basin melt with the advancing season until by the end of May the lower river has become a raging torrent. This flood usually reaches its peak in May or June, after which it ordinarily subsides; the floods have been known to continue into August. Flashy floods from torrential rains on the lower tributaries may occur almost any month of the year; those from the Gila have been known to reach a peak as high as any recorded from the main stream itself.

Annually the river carries past Yuma an average of 200,000,000 tons of silt. When the river is not in flood, this silt burden is largely carried to the Gulf, but in times of flood when the river spreads beyond its banks, it drops its load of silt not only at its mouth but wherever along its course the velocity of the water is checked. Especially does this deposition of material occur along and near the banks of its low water channel. These banks are thus built up by successive floods until they hold the waters to such an elevation that the main current of the stream eventually breaks through and finds a new channel in lower ground.

In the delta region below Yuma, being less restricted by natural lateral barriers, this tendency finds widest scope. Here the river has built a conical fan-shaped ridge cutting off what formerly was the upper end of the Gulf of California. Along the crest of this flat delta ridge runs the river; one slope toward the south terminates at sea level at the present head of the Gulf of California. the other extending northerly on a much steeper slope reaches a depression 250 feet below sea level at the rim of the Salton Sea. The portion of the ancient gulf thus cut off constitutes the Salton Basin, the irrigated area of which, lying largely below sea level along the northward delta slope, is known as Imperial Valley.

In ages past, the river has swung back and forth across this delta, discharging now into the gulf and now into the Salton Basin. Indian tradition would indicate that this has occurred even since the basin has been inhabited. Preceding the coming of the white man, however, the river had flowed uninterruptedly into the gulf for such a period that the Salton Sea had become reduced through evaporation to a mere remnant, and the fertile acres of its former bed invited the construction of a canal from the river for their irrigation.

In 1905 the river took possession of a temporary intake that had been cut for this canal in the river's bank and during 18 months discharged its full flow into the valley. Turned toward the gulf again after months of effort, the river found its old channel inadequate and soon abandoned it, seeking an outlet westward toward Volcano Lake and the Salton Sea. The overflow waters, being prevented from reaching Imperial Valley by an extensive levee system, rapidly filled the Volcano Lake depression with silt.

Each annually recurring flood, raising the overflowed portion of the delta higher by the amount of its deposited silt, required the levee each season to be raised and strengthened to keep pace with the ever rising flood levels. Finally, at a cost of over $400,000 the Imperial irrigation district constructed the Pescadero cut-off from the river toward a lower lying region to the south. and thus gained a temporary respite from its assaults. Within a few years at the most the silt deposits will raise the elevation of this latter area to a point where the main current of the floods will again be thrown to the west and north at which time the assaults of the river on the Volcano Lake levee will be renewed with assurance that sooner or later another break into the valley will occur.

The menace in case of such a break is not limited as at Yuma and above to the loss of crops and improvements, and the cutting away of a few or many acres of valuable land, serious as that menace is. Besides all this, the greater danger here is that the levee once breached and the river at flood turned into Salton Sea, the steep gradient of its course will induce the cutting through the soft alluvial soil of a gorge in which the flow may not be checked until a large part of the valley has become submerged beneath the waters of an inland sea.

IRRIGATION NEEDS

Next to the protection of the areas now irrigated from the flood menace, the matter of securing an adequate water supply for lands now irrigated and for those susceptible of irrigation but not now irrigated is of importance. Practically everywhere within the basin irrigation is necessary for successful farming operations. Less than one-fourth of the area that is feasible of irrigation in the lower basin now receives water and this area at times absorbs the entire low water flow. If, however, the floods should be conserved and the entire runoff of the stream utilized the regulated flow would be sufficient to supply all the lands in the lower basin that can feasibly be irrigated from the river.

POWER REQUIREMENT

An adequate source of power at a low cost is much needed in the southwest at the present time to supply its rapidly-growing power market and to aid in its industrial development. Coal deposits here are lacking or inaccessible. Oil fields, while producing abundantly now, are subject to such rapid exhaustion and their output is of so much greater value for other purposes that they ean not constitute a permanent source of industrial power on a large scale. The progress of hydroelectric power development in California has been remarkable in recent years and there are still a number of undeveloped power sites in that region. The more feasible sites, however, have been developed and some projects now under way there or planned for early construction are near the limit of feasibility under present conditions. The development of some additional source of power in this region at an early date is greatly needed to supply its constantly-increasing demands. Mines, railroads, and local industries in Arizona, Nevada, and southern Utah are suffering under a similar handicap.

Flood control is the urgent need of the lower basin, and irrigation is generally considered in the arid region as a use of water superior to its use for power where the two conflict. In the present instance, however, investigations by Bureau of Reclamation engineers have demonstrated that an opportunity exists above Boulder Canyon in northwestern Arizona and southeastern Nevada for the construction of a single reservoir which will combine flood control and irrigation storage and at the same time without interference with free and complete extension of irrigation in both the upper and the lower basins will permit the development of a large amount of power. This power can be made not only to repay the entire construction cost of dam and power equipment with interest but will remain thereafter a permanent asset.

LEVEES V. RESERVOIRS FOR FLOOD CONTROL

Two principal methods of flood control may be considered for the lower basin. viz, levees and reservoirs. Levees at present protect the Yuma project lands and the lands of the Imperial Valley. They are a source of continued and, as the delta rises, of constantly increasing expense. No construction short of a complete line of levees adequately maintained on both sides of the river from Laguna dam to the Gulf of California can be considered as a complete solution of the problem and such construction would impose an insupportable burden of expense.

Reduction of the maximum flow at Yuma to 40,000 second feet or less will keep the river below that point within its natural banks at most places, will make the rock-protected levees now constructed in that region safe against attack and will permanently free the Imperial Valley from the present annually repeated menace of possible submergence by the waters of the Colorado River. While levees will still have to be maintained, at least until the Gila floods are similarly controlled, their maintenance under these conditions will be a minor matter as compared with the present heavy annual maintenance expense. Gila floods while sometimes of high maximum discharge are always flashy in character and even if a flood from that source should break the levees it would subside so that repairs could be effected before the permanent course of the river should be established through such break.

Provision of 10,000.000 acre-feet storage capacity in a reservoir on the lower river operated solely for flood control will effect a reduction of all floods to the above maximum of 40,000 second-feet with the exception of such floods so

92265-24 PT 4—12

far in excess of any that have occurred within the period that records have been kept on the river that their recurrence may not be anticipated as often as once in 100 years. At the top of a larger reservoir otherwise devoted to irrigation or power storage that flood control storage capacity may be reduced to 8,000,000 acre-feet. This last named alternative is by far the lowest in cost of any effective methods of flood control for the lower valley.

WATER SUPPLY AND IRRIGATION

The irrigable lands in the Colorado Basin fall naturally into two groups. those above the canyon region on the upper reaches of the river and its tributaries, in what is known as the upper basin, and those below the canyon region in what is similarly known as the lower basin. For convenience, Lee Ferry, just below the Arizona-Utah State line has been adopted as marking the point of division between the two basins.

The upper basin is the source of by far the larger portion of the water supply of the river. While a large part of the waters arising in this region can be utilized for irrigation by diversion from natural flow and by storage on the upper tributaries, physical conditions are such that a considerable portion of this water augmented by the unutilized return flow from upper basin irrigated lands, will always remain in the river as it flows past Lee Ferry and be available for use on lands below. About Lee Ferry the total area of lands in the upper basin now irrigated and of future development as it may be predicted from present considerations is 4,187,000 acres.

Below Lee Ferry and above Laguna Dam are a number of valleys aggregating some 469,000 acres of irrigable lands which can be irrigated by diversion from the river but of which only 40,000 acres are now being irrigated. Such levees as have been built along these reaches of the river has been repeatedly breached and flood control as well as irrigation storage is essential if any considerable area of these lands is ever to be reclaimed.

Laguna Dam is the point of diversion of the Yuma project of the Bureau of Reclamation. Below Yuma lies the Colorado River delta, the northward slope of which lying largely in California and extending to the Salton Sea, 250 feet below sea level is known as the Imperial Valley. Below Laguna Dam 659.000 acres are new under irrigation and estimated future developments for which water is estimated to be available with complete utilization of the river brings the total for the lower basin below Laguna Dam to 1,699,000 acres for which water supply is sufficient.

In order completely to realize the irrigation possibilities of the lower basin with full development above will require provision of storage capacity to the extent of 25,000,000 acre-feet besides an additional allowance for silt storage and for flood storage to the extent deemed necessary. Part of this storage capacity could be provided by the construction of reservoirs on the main branches of the river in the upper basin and such storage would provide for the irrigation needs alone of the lower basin for a number of years. Indeed, a flood-control reservoir of 10,000,000 acre-feet capacity on the lower river could be so operated by closing down the gates as the annual floods subside each year as to provide an adequate water supply during most years for the present irrigated acreage in the lower valley and even for some extension thereof. The limitations on either of these plans are such, however, that the provision of storage in the lower basin completely to control the river at one point is by far the most feasible proposition.

POWER MARKET

Power development on the Colorado at the present time is in its infancy. Distance from centers of population, the presence of enormous coal deposits in the upper basin, and the absence of large industrial demand have combined to render such development to date of minor importance. Eventually dams at Flaming Gorge, Dewey, Kremmling, and other sites on the upper river, together with the construction of a great series of dams in the canyon region. dropping the water step by step clear to Bulls Head rock may provide between three and six million horsepower without invading the boundaries of the Grand Canyon National Park.

Market for development to any such an extent is of course lacking now, and economic power development can not far precede the development of an assured market. In southern California, however, the growth of the power load is

rapidly exhausting the available hydroelectric resources of the State and competent authorities have stated that by 1935 California must look outside the State for a supply of power to keep pace with the increasing demand.

Recent advances in electrical engineering have so far extended the feasible limits of transmission of electrical energy that any power site on the Colorado River below Grand Canyon National Park is now within feasible transmission distance of the southern California market, although the cost of the delivered energy rises rapidly with increasing distance.

A consideration of water supply and irrigation demand on the Colorado River demonstrates conclusively that at the Boulder Canyon reservoir site in connection with a reservoir providing flood and irrigation control of the entire flow of the river. there is opportunity for the development of 667,000 horsepower of electrical energy at 100 per cent load factor, justifying the construction of a power plant with an installed capacity of 1,200,000 horsepower operated at 55 per cent load factor, which is the condition under which comparable plants in this region are found to operate.

Mr. SINNOTT. What does that mean-load factor?

Mr. WEYMOUTH. That is the amount of power that is used. You see, you do not put out the same amount of power continuously throughout the 24 hours a day, or through the month; so that you generally have a lot more power stored than you put out.

Mr. RAKER. Just read that sentence again, about the horsepower? Mr. WEYMOUTH. There is opportunity for the development of 667,000 horsepower of electrical energy at 100 per cent load factor. justifying the construction of a power plant with an installed capacity of 1,200,000 horsepower operated at 55 per cent load factor, which is the condition under which comparable plants in this region are found to operate.

This power can be made to pay the entire cost of complete flood and irrigation control at Boulder Canyon both dam and power installation, including a fair rate of interest on the investment. Careful studies of the growth of the power load in this region indicate if work should be authorized immediately that by the time the dam can be completed and the power plant ready to deliver energy the growth of the southern California power market will require the installation of three of the twelve 100,000 horsepower generating units, after which the installation of an additional unit every nine months will be required to keep pace with the growing load.

BOULDER CANYON RESERVOIR SITE

Field surveys, geological examinations, diamond drill borings of the foundations, exhaustive studies of dam design, of costs and of construction layout having been made for the Boulder Canyon site, its feasibility as an individual development has been thoroughly established. There then remained to be determined the place of this project in the orderly development of the resources of the river. The points considered in that inquiry were the possibility of some combination of reservoirs or power dams on the lower river furnishing equivalent control with lower cost of power, possibility of conflict of the Boulder Canyon development as planned with other power opportunities and finally, other questions having been resolved, the actual height of dam and resultant reservoir capacity which is justified at this site.

There are eight possible dam sites at which power may be developed below Grand Canyon; namely, Parker, Mohave Valley, Bulls Head, Boulder Canyon, Devils Slide, Spencer Canyon, Bridge Canyon, and Diamond Creek, studies of each of which sites have been made by our engineers. Estimates have been made for power developments involving different combinations of the above sites both with and without Glen Canyon Reservoir (above Lee Ferry) as a 'regulating reservoir, always, as a prerequisite, including adequate provision for flood control and priority for irrigation demand over power. The final results of these studies demonstrate conclusively that for power development as for flood control and irrigation storage the most feasible development on the lower river under existing conditions is the construction of a single large reservoir at Boulder Canyon.

Additional studies the results of which are embodied in table 23, page 148, show how the unit cost of power development at Boulder Canyon becomes less as the height of the dam is increased, and also show the periods within which with the greater heights of dam the returns from sale of power may be counted upon to repay with interest the entire cost of the dam and of the power installation.

Details of the investigations outlined in the preceding pages are contained in the general discussion which follows: For convenience the final results of the investigations are summarized in the conclusions, a statement of which precedes the general discussion.

CONCLUSIONS

1. There is immediate need of flood protection for river bottom lands in the Lower Colorado Basin and the Imperial Valley. The Colorado River flows along a narrow ridge adjacent to this valley which lies many feet below, most of it below sea level. There is imminent danger during each flood period that the river will break into the valley and destroy it.

2. There is a shortage of water in the Imperial Valley now each low water year, there being only 3,500 second-feet or less of water available for the entire valley during periods of such low years.

3. The area in cultivation in the Imperial Valley is increasing slowly in the United States and rapidly in Mexico. There are approximately 415,000 acres of land now in cultivation in the United States and 190,000 acres in Mexico. but the Imperial Valley Canal commands over 500,000 acres of Mexican land. 4. Under a Mexican concession, approved June, 1904, by the Congress of Mexico, the right to divert 10.000 second-feet of the water of the Colorado River was granted subject, however, to the condition that one-half of it be used on Mexican land. The right was also granted to receive this water from a canal heading in California north of the boundary line and to convey the same in canals or in natural channels through Mexico. The physical conditions are such that one-half of the water from the main or Imperial Valley Canal in Mexican territory as granted in this concession can be diverted to lands in Mexico. Consequently, the water shortage for American lands in low years will rapidly become more serious unless storage is provided, causing a heavy loss of crops on American farms, for in such low years the American lands would have for periods only about 1,750 second-feet of water (and at times even less) for over 415,000 acres of land in cultivation, or only about one-half of the water needed during such period. Therefore, the water supply for lands in the Imperial Valley in the United States already in cultivation is in jeopardy regardless of upper river development. Under such conditions further development can not wisely be made without storage.

5. The area now in cultivation below Boulder Canyon is estimated at 700,000 acres. If storage can be provided, it is estimated that an additional 1,470,000 acres can in time be reclaimed, making a total area below Boulder Canyon of 2,170,000 acres.

acres.

6. The area now in cultivation above Boulder Canyon is estimated at 1,500,000 It is estimated that an additional area of 2,825,000 acres may in time be reclaimed, making a total area of 4,325,000 acres above Boulder Canyon. 7. If a larger reservoir is constructed at Boulder Canyon with a capacity of 34.000.000 acre-feet it will so equalize the flow of the Colorado River as to permit the entire area below the reservoir, as shown above, to be reclaimed without in any way interfering with the development of the 4,325,000 acres of land located above the reservoir; provided the Federal bill authorizing construction of the reservoir directs that all rights granted thereunder to individuals, canal companies, districts, corporations or municipalities, should he subject to the provisions of the Colorado River compact negotiated at Santa Fe, N. Mex., and dated November 24, 1922. A reservoir of this capacity will also control the floods and take care of the silt problem for 200 years or more. 8. The Colorado River brings down each year over 100,000 acre-feet of silt and deposits it in the delta region, building higher and higher the delta area over which the river flows between the levees adjacent to the Imperial Valley." making it progressively more expensive to protect the valley by levees.

9. There has been spent since 1906 on levees below Yuma $7 500.000 (exclusive of cost of closing the 1905-6 break by the Southern Pacific Railroad Co.) for inadequate protection. The delta will gradually increase in elevation so