« PreviousContinue »
The knowledge of this possibility prevents the investment of money needed for development and also prevents many people of the valley from making comfortable, permanent homes and improvements that they otherwise would. The 450,000 acres of irrigated land in Imperial Valley has a market value of at least $100 per acre less than it would with the flood menace removed, which in itself is $15,000,000.
The total cost of flood protection of the valley has been at least $7,000,000. The known damages to the valley has been at least $33,000,000, and the unknown, undetermined damages many millions more, making a total of more than $50,000,000.
In other words, flood-protection costs and flood damages sustained to date are considerably in excess of the estimated cost of the proposed Boulder Dam.
The ('HAIRMAX. Does any member of the committee desire to question Mr. Pound? If not, the committee thanks you for your statement.
Mr. W. J. Dowd, general superintendent of the Imperial irrigation district, will discuss the silt problem resulting from the Colorado River; also water drainage in the Imperial Valley.
STATEMENT OF W. J. DOWD, GENERAL SUPERINTENDENT OF THE
IMPERIAL IRRIGATION DISTRICT
Mr. Dowd. Mr. Chairman and gentlemen of the committee, in order that I may comply with your request and get through on time, I will have to read mine, too. One of the many problems with which we are confronted in Imperial Valley is that of silt disposal, and although it is not the most serious it is nevertheless causing the expenditure of large sums of money each year and fast reaching a critical stage with no relief in sight without storage works on the Colorado River.
The watershed of the Colorado River covers 244,000 square miles, and the various streams draining this area each contribute a large volume of sediment to the main river, with the result that the latter is virtually a “river of mud” by the time it reaches Yuma. It is not generally known, I believe, that the Colorado Rivir has a silt content three times that of the Ganges, ten times that of the Nile, and, with the possible exception of the Tigris, greater than that of any other river in the world.
Observations of the silt content of the Colorado River at Yuma, carried out over a long series of years, show an average annual amount by volume of 113,000 acre-feet, or over 182,000,000 cubic yards, which is equivalent to a cube of 1,700 feet on a side; put in other words, it is over three-fourths of the total yardage moved in the construction of the Panama Canal.
As an illustration of what this silt amounts to: Some few years ago a flood coming down the Colorado and overflowing into the Volcano Lake region so completely buried with sediment 14 wagons of a contractor's equipment, which had been left behind, that their platform tops, 4 feet above the bottom of the wheels, were just visible abore the new general ground surface after the flood water had receded.
Not far below Yuma is the diversion gate for our irrigation system, the last point of diversion on the river and the one through which must pass the river water with its maximum load of silt. In an effort to keep the silt out of the canal system, the diversion gate—“Rockwood was constructed as an overpour structure or skimming weir, having 74 openings, each 6 feet and 6 inches wide, the diversion being controlled by use of flashboards inserted into the openings. However, from tests made of the silt content of the water in our canal, it has been found that the percentage is the same as exists in the river itself at Yuma, indicating that the diversion gate does not reduce the silt content and that the amount which enters our canal system is in proportion to the amount of water diverted.
On this basis the following table has been prepared, showing the total annual acre-feet of silt which entered our canal system for the years 1912 to 1924, inclusive: Acre-feet of silt diverted into Alamo Canal at Rockwood Gate:
8, 438 1913
9, 658 1914
11, 850 1915
11, 385 1916
18, 575 1917.
8, 478 1918
11, 006 1919.
19, 244 13-year average, 14,126 acre-feet.
Acre-feet 15, 139 12, 738 17, 093 24, 928 15, 113
The maximum shows to be 24,928 acre-feet in 1923, the minimum 8,438 acre-feet in 1912, and the average 14,126 acre-feet or 22,790,000 cubic yards, the latter being equivalent to a cube of a little over 850 feet on a side and about one-eighth the total silt flow of the river. A better idea of what this volume of silt amounts to is gained when I say that it is equivalent to 1,139,500 carloads which, at 40 cars per train, would mean 28,485 trains annually, or 78 trains daily, of sist being dumped into our canal below the intake.
In addition there is a large quantity of very heavy silt, or “ bed sand” we term it, that travels along or near the bottom of the river out of reach of the silt-sampling apparatus as used at Yuma and in our canal and which, therefore, is not included in the figures of silt content for either point. Just what this quantity amounts to can not be stated, as very little is known about bed sand but, although we feel that the Rockwood diversion gate reduces somewhat the amount of this type of silt entering our canal, we have found that it is the major cause of trouble in our main canals, and also comprises the material excavated from the canal bottom by the suction dredges, which we operate in the Alamo Canal just below Rockwood Gate.
What becomes of the silt that enters the canal system? We have but one wasteway, known as Tortuoso Waste, that empties back into the river, and this has not silted in to the point where it will be out of use in another year. With this exception the silt must either deposit in the canal system on the land or be carried to Salton Sea; in other words we must keep practically all the silt we receive, and how and what to do with it constitutes our problem.
During the year 1914 tests were made of the percentage of silt in suspension in our canal system at Andrade below Rockwood Gate, at Allison heading which is on the East Side Main Canal about 45 miles from Andrade, and at No. 5 heading which is located about 8 miles downstream on the East Side Main Canal below Allison heading or 53 miles from Andrade. The object was to observe whether there was any loss in suspended silt content as the water traveled through the main canal system. The tests showed conclusively that there was little if any difference between the percentage at the three points, allowing one day's difference for travel of the water between Andrade and the other two stations. This fact is borne out by our experience in that, although berms are forming continuously along the banks of the main canals and have to be periodically removed, the yardage involved is very small, the main problem being the filling in of the bottom with bed sand which, as has been stated, travels along or near the bottom out of reach of the silt-sampling apparatus.
Thus, it is seen that the suspended silt does not deposit in the main canals but passes on to the wasteways and smaller canals which must carry in addition to the above, especially over the central and southern end of the valley, a large volume of bed sand.
In order that some idea may be had of the quantities of silt deposited in the various places, conditions as existed in 1923 have been taken as an example.
That year 24,928 acre-feet, or 40,217,000 cubic yards, of silt entered the canal system. We excavated, in cleaning our canals, but not including the dredging at the intake, about 2,940,000 cubic yards by dredging, shoveling, and “V-ing.” Assuming that the water wasted back to the river and to Salton Sea and delivered in Mexico carried its quota of silt—which is a fair assumption--at Tortuoso wasteway, 1,847,000 cubic yards of silt was returned to the Colorado River, users in Mexico received 5,405,000 and Salton Sea 8,531,000 cubic yards.
There is thus accounted for 18,723,000 cubic yards, or 11,610 acrefeet, leaving 21,494,000 cubic yards, or 13,300 acre-feet, of silt which was, therefore, carried onto the irrigated lands in the United States.
These figures are, of course, only approximate and do not include the bed sand, of which a large amount gets onto the land, but they do show that silt disposal is a big problem, which is found to be increasing year by year.
The CHAIRMAX. It has reached the hour when the Senate committee must adjourn for luncheon, and we will now recess until 1.30.
(Whereupon a recess was taken until 1.30 o'clock p. m. of the same day.)
The committee reconvened at 1.30 p. m., pursuant to the taking of recess at 12 o'clock noon.
The CHAIRMAN. The committee will proceed with the afternoon program. Mr. Dowd, you may continue your statement.
Mr. Dowd. Before considering the cost of handling the silt, I would like to discuss briefly some of the troubles it causes and with which the irrigation district and the farmers have to contend.
The bed sand entering Rockwood gate, being very heavy, has a tendency to deposit at that point, filling in the bottom and then gradually working downstream, spreading into the various main canals, then to the laterals and onto the land. We have found it necessary to operate the big suction dredges in the canal at the headgate for from four to six months each year for three reasons: First, we can excavate the bed sand with these dredges for about one-half what it costs to remove it from the canals below by dragline and Ruth dredges; second, the water surface of a number of our main canals is raising year by year-in one stretch of the Alamo Canal called “Alamo Mocho cut-off” the water surface has raised an average of one-half foot a year for the past three years—due to the bottom filling in with bed sand—and it is necessary to reduce this raising to a minimum, not only because it is very costly to raise the banks, but also on account of the increased danger from breaks which results as the water surface in the canal gets higher above the natural ground surface; and, third, if the bottom of the canal is allowed to raise at the intake, it would be impossible to divert our supply of water during the low flow of the river, even with the temporary weir which has to be placed across the latter each year. .
Although the suction dredges remove a large volume of sand each year it is only a part of the total which enters the system. To illustrate this point, I would like to cite what has happened in the Carrillo Bend Canal. This canal takes out of the Alamo about 43 miles below Rockwood Intake and parallels the Alamo for about 2 miles to where a spillway empties back into the latter below East Side check. On June 1 of this year it was carrying 152 secondfeet; three days later the capacity had dropped to 60 second-feet ; and by the 7th it was possible to get but 20 second-feet through the headgate. This was due to no other cause than bed sand filling up the head end and even with a fall of over 1.5 feet per mile, which this canal has, the sand would not move through. We have spent over $10,000 a year on this canal alone, or about $5,000 a mile, and although it is one of the hardest canals we have to maintain, we are nevertheless faced with the same conditions, to a lesser extent, in a number of our canals.
As has been stated, the suspended silt does not deposit to any extent in the main canals, but passes through to the smaller ones and the laterals; here the formation of berms is very rapid and, due to our excessively long and hot summers, the growth of vegetation is astounding along the berms and even in the bottoms of the laterals. This growth retards the flow of water, increasing the rate of silt deposit, and we find it necessary to dredge or shovel practically all of the lateral system at least once, and in many cases two and three times, each year.
Dumping of the dredged silt on the canal banks continually raises them at a rapid rate, making it necessary to do a large amount of grading down with “V's” and graders, with the result that there are hundreds of miles of small canals and laterals which now take up a width of as much as 40 and 50 feet, where in other projects, that do not have the silt to contend with, the same ditch would not require more than 15 or 20 feet.
We are constantly faced with the necessity of obtaining more and more right of way, which is becoming harder to obtain; the county officials are constantly and most strenuously objecting to the encroachment of our ever-increasing width of ditch banks on the highways, and it appears in some locations that the only thing to do with the dredged silt is to ship it back to the upper States where it came from.
Unless one has actually seen it, it is hard to realize how fast a lateral can silt in, especially during August and September when the silt content is greatest. It is not an uncommon occurrence for a lateral to lose two-thirds of its capacity in 10 days' time, and what may be a fine looking canal one month may be a grass and silt filled ditch the next.
It should be borne in mind that in Imperial Valley crops are grown the year round, there being hardly a month during the year in which some crop is not being planted and another harvested; in view of this situation, we must operate and maintain 12 months in the year instead of from 6 to 9 months, as on most other projects, and during the past few years there has been a large increase in the acreage of winter grown crops, making it more difficult to cut the water out of the canals to lessen the cost of cleaning them.
The outlets of the Alamo and New Rivers into Salton Sea are an ever increasing problem. When the water in the rivers enters the still water of the sea, the silt in the former is immediately deposited and deltas are formed, which, as they build up and spread, block the flow, causing the water to back up and overflow the banks, changing the river's course and flooding adjacent land.
During 1923 New River changed its course in this manner, and lands which had been dry and in crop for several years were flooded. Plans were then made for cutting a new channel to the sea and during the next year, 1924, this was accomplished by excavating for a distance of three and a half miles, for the first two of which it was possible to use a Bucyrus drag-line dredge. The other mile and a half was wet excavation and had to be made with a floating dredge, for which purpose a half-yard floating-dipper dredge was specially constructed at a cost of over $25,000. During the present year this dredge has operated a major portion of the time and will have to be continued for an indefinite period in order to keep the channel open.
The Alamo River outlet presents a similar problem which will have to be met in the near future.
The silt in suspension causes the farmers all over the project ar immense amount of trouble, and the bed sand bothers mostly over the central and southern end. The irrigation district delivers water to the high corner of each 160 acres, from which point the farmer must take it at his own expense onto his land. The amount and frequency of the cleaning of his supply and head ditches, which a farmer must do, varies with the location and elevation of the farm. There are many cases where the farmer must clean his supply ditch after each irrigation and his head ditches three or four times a year; in a considerable number of other cases the supply ditch has to be cleaned from one to three times a year and the head ditches a similar number of times.