Situation in June, 1906 (whole river going into Salton Sink)
Active work began on the 6th of August, 1906, when the summer flood had fallen enough to reduce the flow through the crevasse to about 24,000 cubic feet per second. By that time the receding water had left exposed extensive sand-bars on both sides of the river, which narrowed the channel to 600 or 700 feet, and President Randolph’s plan was to dam this channel sufficiently to throw all or most of the water through the by-pass and the Rockwood head-gate, and then permanently to close the break. As it was deemed essential to blanket the bed of the river with a woven brush-mattress, to prevent bottom erosion and to make a foundation for the rock, two shifts of men were set at this work. In twenty days and nights, they constructed, with baling-wire, steel cable and two thousand cords of brush, about 13,000 square feet of mattress, which was enough to cover the bed of the river from shore to shore with a double thickness of blanketing about one hundred feet in width. When this covering had been completed and sunk, a railway trestle ten feet wide was built across the crevasse, and on the 14th of September work-trains of “battleships” began running across it and dumping rock on to the mattress at the bottom of the stream. Meanwhile, the by-pass to the Rockwood head-gate was completed and enlarged, and in less than two weeks the dam was high enough to close the crevasse in part and thus divert water through the by-pass and gate. On the 10th of October, nearly 13,000 cubic feet of water per second was passing through the gate, while only one-tenth of that amount was flowing over the dam. The gate, however, under the pressure to which it was subjected, both by the water and by great masses of accumulated driftwood, began to show signs of weakness, and at two o’clock on the following day two-thirds of it gave way, went out, and floated down stream. The by-pass then became the main river, while the top of the diversion dam was left practically dry. Thus ended, in almost complete failure, the fifth attempt to control the Colorado. The river had been barred in one channel, but it burst through another, carrying with it a 200-foot head-gate which represented four months of labor and an expenditure of $122,000.
Mr. Harriman and the Southern Pacific engineers were disappointed but not disheartened. The steel-and-concrete head-gate at Andrade had been ready for use since June, and powerful dredges were set at work clearing out and enlarging the four miles of silted-up canal south of it, so that water might be furnished to the Imperial Valley by that route while another attempt was being made to close completely both the Rockwood by-pass and the original intake.
An inspection of the rock-fill dam, which had been left exposed by the diversion of the river, showed that the objections made to a structure of this kind were not well founded. The brush-mattress had not been broken by the weight of the rocks; the rocks themselves had not sunk out of sight in the soft silt of the bottom, and the dam had not been breached or seriously injured. It leaked a little, but its good condition in other respects suggested the possibility of quickly closing the by-pass and the intake with rock barriers of this type. Additional trestles were built across both waterways; ten trains of flat cars and “battleships” were set at work bringing rock from three or four different quarries, and the laboring force was increased to about a thousand men with seven hundred horses and mules. Operations were pushed night and day, and in a little more than three weeks, high rock-fill dams were built across both intake and by-pass, and were connected by massive levees so as to make a continuous barrier about half a mile in length. Leakage through the dams was stopped by facing them with gravel and clay, forced into the interstices and puddled with streams of water from powerful pumps, and the levees at both ends were connected with those that had previously been built up and down the river by the California Development Company. In the course of the work there were used, first and last, about three thousand carloads of rock, gravel and clay, while 400,000 cubic yards of earth were moved by dredges and teams.
First Closure of Crevasse, Nov. 4, 1906
On the 4th of November, a little more than two years after the cutting of the lower Mexican intake, the crevasse into which it had grown was closed, and the river was forced back into its ancient bed. The danger had apparently been averted and the Imperial Valley was safe; but where a treacherous river like the Colorado is concerned, danger is never over and safety can be secured only by incessant watchfulness and continual labor. On the 7th of December, another sudden flood came down the Gila and increased the discharge of the Colorado from 9000 to about 45,000 cubic feet per second. The rock-fill dam of the Southern Pacific engineers stood fast; but, about midnight, a reconstructed earthen levee of the California Development Company, twelve or fifteen hundred feet further south, was undermined, began to leak, and finally gave way. The breach at first was small; but it was so rapidly deepened and widened by erosion and caving that it soon became a crevasse, and in less than three days the whole river was pouring through a break a thousand feet wide and again rushing down the slope of the basin to the Salton Sea.
This new crevasse, taken in connection with the history and the experience of the two preceding years, showed conclusively: 1, that the tendency of the Colorado to flow into the Salton Sink was increasing rather than diminishing; 2, that floods of from 180,000,000 to 360,000,000 cubic feet of water per hour were liable to occur at almost any season of the year; 3, that the defensive dikes of the California Development Company were everywhere inadequate or untrustworthy; and 4, that in order to afford certain protection to the Imperial Valley, it would be necessary not only to close the new break, but to build a stronger, higher and more massive levee along the west bank of the river for a distance of at least twenty miles.
These considerations raised of course the question whether it was worth while for the Southern Pacific Company to continue this work, upon which it had already spent about $1,500,000. The interests chiefly imperilled were those of the national Government. It owned all the irrigable land along the lower Colorado, including even that upon which the Imperial Valley settlers had filed.[12] It was then constructing an immense dam at Potholes, twelve miles above Yuma, upon which it had already expended about $1,000,000 (the Laguna dam) and with the water to be impounded thereby it expected to irrigate and reclaim about 90,000 acres of fertile land in Arizona and Southern California. If the uncontrolled river should continue to “cut back,” by means of its receding waterfalls, it not only would destroy the Laguna dam, and the irrigation works upon which the Imperial Valley depended for its very existence, but would eventually turn the whole bed of the lower Colorado into a gorge, out of which water for irrigation purposes could never be taken. This would make valueless more than two thousand square miles of potentially fertile land, which, if intensively cultivated, would support a quarter of a million people.