The city's new $1,500,000 concrete dam at the Cedar river doesn't hold water.
After a month of trial the storage impounded to a depth of more than fifty feet behind the the tremendous masonry wall continues steadily to seep away into the Snoqualmie watershed.
One city official who recently visited the dam states that the water in the basin, designed to impound 8,000,000,000 cubic feet, was dropping at a rate of between four and five inches an hour.
The situation is causing grave concern to the city engineers.
The leakage has obliged the engineers to try sealing the basin by clay puddling, a process which expert engineers advised the city would be abnormally expensive.
Upon the success of this sealing process depends the entire worth of the costly project.
The leakage occurs in the north bank of the river. In 1912 a board of three engineers of national fame warned the city that this would happen.
Mayor Cotterill, the board of public works and the council ignored this warning. R. H. Ober, then a city engineer in charge of the work at the dam, reiterated the warning. He, too, was ignored.
City Engineer Dimock yesterday declared that there was a seepage, but he said he could not give the rate of loss.
The sealing process at the cheapest means added expense and delay. R. H. Thomson, former city engineer and designer of the dam, who was in the city and consulting with City Engineer Dimock yesterday, declared it might easily be five years before the leaks were entirely closed. Mr. Dimock concurred in the estimate.
There is no danger to either water supply or power service in connection with the weakness of the dam. Neither need to be interrupted for years, though the structure never should hold water.
But the success of a project costing a large sum of money is at stake. Present indications do not encourage the idea that the dam will hold water. The city engineer declares work has already begun in an effort to stop the leaks.
Cedar Lake, the chief source of water supply, is by air twenty-seven miles from Seattle. It lies between two mountains, a norrow, deep reservoir, four miles long. The lake and the canyon of the Cedar River flowing from it closely resembles a bottle, the mouth of the bottle pointing almost due west, toward Seattle.
The present intake of water for city power only is at the point where the neck joins the top of the bottle. The new dam is a cork driven half way down the neck of the bottle, a mile and a half west of the western end of Cedar Lake.
This bottle neck, a river canyon, flows between a mountain of solid rock on the south and a wall of coarse gravel, boulders and sand and clay of highly porous nature on the north.
The northern bank of the canyon is a glacial dyke, that is, when a great glacier scoured out the Cedar and Snoqualmie river watersheds, it spread into two fingers, and between the fingers it built up a bank of coarse rubbish; the sawdust of a mighty carpenter.
It is through this sawdust the water leaks.
Snoqualmie watershed lies below the level of the impounded water. The water impounded against the great masonry wall, seeking an outlet, is flowing thorugh the coarse soil into the Snoqualmie watershed.
Construction of the great masonry dam, according to the plans originated by City Engineer Thomson, was authorized by popular election, November 8, 1910. The popular vote authorized spending $1,400,000 on the project.
Work was undertaken by the city itself in the same year. By 1912 the project was the occasion of serious question, both as to the advisability of the site selected and the practicability of the storage basin.
On March 8, 1912, the city council authorized the employment of Joseph Jacobs, E. H. Baldwin, and Glover F. Perrin, engineering experts of national reputation, at $150 a day, to investigate and report on the construction of the dam. Seven specific questions were submitted to the engineers.
Two months later, May 6, 1912, this commission made its report to the mayor and council. It had been employed a month on the work and was given to understand that no further money was available.
The gist of the commission's recommendation was that all work on the dam be stopped until thorough investigations of the advisability of the site could be made and tests could be made to determine the exact weakness of the north wall of the river bed.
The one clause in the report which was unequivocal concerned the weakness of the north bank. About the clause centered the debate ensuing in which the mayor and the board of public works sought successfully to go ahead with the project.
If the great water storage scheme proves a failure present events indicate it will be by the very means against which the experts warned.
In their report Mesrs. Perrin, Jacobs and Baldwin said of this north bank:
"We are led to believe that not less than from 50,000 to 65,000 acre feet of storage would be lost per annum, depending upon the actual stage of water maintained in reservoir. A loss of such an amount means a 20 percent depletion of the power possibilities, based upon total run off, and we conceive it to be entirely possible that the seepage loses may be greater than above estimated.
"We regard the matter of such vital importance, in any event, that in our opinion no definite work should be done in the way of actual dam construction until this matter has been satisfactorily solved by actual tests and by actual tests we mean the putting down of a series of test wells to determine the position of the ground water plane between the proposed dam site and Snoqualmie river, actual measurements of the movement of ground waters between these test walls and numerous mechanical analyses of the materials derived at different depths from said wells. Such a series of experiments would form a fairly secure basis for estimated probable seepage losses from the proposed reservoir and should by all means be made before further construction expense be incurred."
Seepage through the north bank was foreseen by Engineer Thomson when he designed the dam. His remedy and the remedy proposed those by who insisted upon putting the project through, despite the warnings of the experts, was to impregnate the gravel with a puddle of clay. The clay was to be dumped into the water above the dam and by it carried into the porous bank. In time this was to seal the entire mile and a half of the north side.
This clay puddle is the remedy now being tried by the city engineer to prevent leakage.
The experts in their report recognized this proposal and answered it in the following language:
"We would say that, in our opinion, no such result may be reasonably expected under the conditions which prevail here. We are entirely cognizant of the fact that in canals and rivers charged with silt there is a tendency to seal up sides and bottoms of such channels, often to the complete prevention of seepage losses.
"It should be noted, however, that the head under which such sealing usually occurs is extremely small. And, furthermore, it is unlikely that any appreciable quantity of silt-bearing water would reach this particular bank, all such material having practically been precipitated in the main Cedar lake above, which acts as a large settling basin. Practically the only silt that could be picked up for such a process would be the silt contained in the bank itself, and it is not believed that the velocity which seepage water would attain in moving through this soil (perhaps thirty feet per day) would be such as to either pick up or deposit sufficient silt to form an effective seal.
"Under the high pressures which would obtain against this bank, and with the apparent steep hydraulic gradient of the water plane toward Snoqualmie river, we believe nothing short of a very thick and a very well compacted mat of clay puddle would be effective against seepage, and such provision would be abnormally expensive.
"When one considers in the construction of an earth dam, whose base width is usually five times its height, that undue seepage can be prevented only by first carefully selecting the earth materials of which the dam is built and then compacting these materials in six-inch layers under a process of heavy rolling, the fallacy of the notion of sealing up this bnak under heads at full reservoir varying from eight to 150 feet by a mere surface coating of silt becomes apparent."
It was the opinion of the members of the commission that no adequate survey of the project had been made. From the report it was apparent that expert engineers believed the city was going into a costly undertaking without taking congnizance of the difficulties it would encounter.
When the report was submitted to the mayor and council the engineer's department prepared a carefully thought out answer to the arguments. The board of public works agreed to this refutation and so did Mayor Cotterill who, in his capacity of a civil engineer, assured the council that the city should proceed with the work at once. Mr. Ober, in charge of the work at the watershed, submittted a minority report, urging delay and longer investigation.
City Engineer R. H. Thomson, now in the employ of the British Columbia government, was with Mr. Dimock yesterday. He took a reassuring view of the leakage of the dam.
"The only thing which would surprise me," said Mr. Thomson, "would be to learn that the dam did not leak. I expected the north bank to leak. I provided a hydraulic outfit to sluice down dirt and clay to seal the gravel. I would be surprised to learn that that outfit was not needed.
"It would not surprise me if the city would lose the Cedar river for three months at the dam. No harm would be done if the river did disappear, for it would flow back lower down.
"To completely seal the basin may require five years. My idea, now being followed, was to dump in loads of clay as the water is slowly raised, make a big mud puddle out of the basin in fact. This clay will be gradually drawn into the porous bank. In addition, the water passing through the gravel has a tendency to settle the material and gradually seal it.
"As a last resort I had planned on drilling holes along the bank and grouting the gravel by forcing cement under hydraulic pressure into the soil. This would form a rough sort of concrete wall along the north side."
Following the submission of the report of the board of three engineers, Mayor Cotterill called the board of public works together in special session and met with its members for five days, discussing the report. In the end the mayor and the board, with the exception of R. H. Ober, superintendent of buildings, determined to recommend to the council a continuation of the work at the dam, declaring that the site at Camp No. 2 was the best suited because of bed rock foundation for the construction of the dam.
Supt. Ober submitted a minority report, agreeing in the main with Messrs. Jacobs, Baldwin and Perrin, the board of engineers, that further investigation was desireable.
"Ordinary prudence will suggest, and sound engineering principles will require that a thorough preliminary investigation be made before constructive work is begun," he said. "In a proposition of this kind, involving the expenditure of a very large amount of money and the failure of which will involved the destruction of lives and of property of enormous value, it is absolutely necessary to take every precaution in deciding upon the location of this masonry dam."
Mayor Cotterill and the majority members of the board declared that they could not agree in a plan of delay. The pointed out that the board of engineers had stated in the report submitted to them that "a stable and secure dam can be built at the site proposed even to a height proposed by the city engineer" (1,605 feet water elevation).
They expressed the belief that the north bank would seal although not expecting it to become entirely water tight.
Mayor Cotterill, on May 11, 1912, five days after the report of the three outside engineers had been submitted, sent a communication to the council urging that the work at the dam proceed without delay.
"Both from the standpoint of an engineer, and with the added responsibility of the public interest as mayor," he said, "I am convinced that the facts of the situation, even as stated and reviewed in the report of the board of engineers, do not justify its closing, and the most important recommendation (No. 8), 'that constructive operations in connection with the building of a dam at camp 2 be suspended, etc.' On the contrary, I believe that great financial loss will ensue, unnecessary expense be involved and deep and lasting injury be inflicted upon the public interest in our city lighting plant, unless constructive operations be promptly and vigorously pressed along safe lines on the present dam site."
In discussing the recommendation that the seepage flow should be investigated, Mayor Cotterill said:
"Referring to the problem of north bank seepage, while giving full weight and recognition to its discussion and the recommendations of tests to ascertain its extent, as made by the board of engineers, there is nothing in this seepage problem that suggests change of dam location. The test recommended should be made but their results affect storage capacity and advantageous height of dam, and not location. I recommend that tests which may be necessary to thoroughly ascertain the seepage situation be carried forward before the dam is raised to any greater height than 1,555 feet, an elevation which is conceded by all will not introduce any possible difficulties by reason of seepage."
The recommendation to the council of the majority of the board of public works, made on May 11, is similar to that of Mayor Cotterill.
"Granting that the loss of water from the basin due to this cause may reach 50,000 or 65,000 acre feet per annum," said this report, "we still belive that the construction of the dam at camp 2 is justified in view of the showing made in the report of the board of engineers that, even with this loss, the cost of power to be generated by the proposed plant will be reasonable."
Supt. Ober in his minority report submitted to the council said, in part:
"In my judgment, in a proposition of this kind, involving the expenditure of a very large amount of money in the construction of a masonry dam which must be built in such manner that it will endure for all time, and the failure of which will involved the destruction of lives and of property of enormous value, it is absolutely necessary to take every precaution in deciding upon the location and in the actual work of construction of this masonry dam at Camp 2.
"Ordinary prudence will suggest, and sound engineering principles will require that a thorough preliminary investigation be made before construction work is begun.
"In my opinion, the work required in the construction of this dam should be divided into three stages:
"First, the preliminary investigation, such as the making of all surveys required, the drilling of test holes in the rock, and the testing of rock under hydraulic and pneumatic pressure, the sinking of well holes and test pits in the gravel formation along the entire north bank, and the making of experiments to determine the rate of flow and seepage through this material, and collection of all data necessry for the consideration of the entire project.
"Second, having obtained full information, to prepare plans and estimates of cost at each practicable location, and from comparative estimates of the plans to determine the best, safest and cheapest location for the structure. Then to prepare the plans complete in every detail, and from these plans to prepare a careful estimate of the entire cost of the whole project.
"Third, when the plans are complete, and not before, begin the actual construction of the dam and carry it through to completion wiith all possible speed.
"As far as my information goes the work relating to all three stages--viz, of preliminary investigation, the preparation of plans and actual construction--is now being carried on.
"Complete plans and estimates have never been presented to the board of public works, and the proper location of the dam itself has never been accurately determined.
"In my judgment, therefore, the only safe course to pursue is to suspend all constructive operations, if any such are now going on, until the completion of the complete plans of the dam.
"Seepage occurred at the time the crib dam was constructed at Cedar river," said City Engineer Dimock yesterday, "and our experience with that induces us to believe that the north bank, aftter it has been saturated with water, will eventually close up its pores. When the timber dam was first constructed and the water raised behind it, springs appeared below in the south bank. These springs dried up and finally stopped. Later the crib dam was raised an additional five feet. Springs appeared again in the south bank and finally ceased flowing.
"Machinery is at hand at the dam so that the north bank can be coated with silt and fine material to fill up the places where water escapes. A coating of clay might be applied if necessary. We are prepared to take care of seepage if any considerable amount of water flows into the bank."
"City Engineer Dimock told me three or four days ago in the course of a conversation about the dam that seepage had been discovered," said Mayor Gill yesteray. "This was expected, and was a surprise to no one. We anticipate that the north bank will fill itself after the water has been back of the dam for a time through the flow of silt into the crevices."
"The board of public works always expected there would be seepage, but can not estimate the amount until the water is in the dam for a considerable length of time," said J. D. Ross, superintendent of city lighting. "It may be a year beore we can say that this runoff though the plateau is an amount sufficient to noticeably reduce the water available. The city is now usng about a third of its available supply. It can afford to lose water until the north bank has closed itself, and can depend on the Lake Union steam plant as an auxillary if the water is low."
"The height of the water in the dam will not rise above 1,555 feet until the population of Seattle becomes such that the present outlet in the dam is closed and the water allowd to rise to the 1,590-foot level," said L. B. Youngs, superintendent of water. "The opinion among engineers is practically unanimous that there can be no severe loss of water through the porosity of the north bank until the water rises above 1,555 feet elevation at the most, and it is not likely then that the bank will absorb any great amount."
"The principal reason, I take it, that the board of engineers advocated delay was so that the plan of constructing an earth or rock-filled dam on sand and gravel foundation might be investigated," said former Mayor Cotterill yesterday. "The seepage in the end will be found to be negligible. When the crib dam was put in, seepage occurred, and after a short time the ground filled up and the flow stopped. This, engineers believe, will be the history of the new dam site."