The City of Seattle on November 1, 1914, completed a concrete dam which was to be used to impound water for regulating the flow of Cedar River. The total cost of the structure up to April 1, 1915, had been in excess of $1,700,000. Primarily, this water was to be used for generating power at the municipal hydroelectric plant.
About 1 1/4 miles above the present dam is the old Cedar Lake timber crib dam constructed a number of years ago, from which water was conducted to the present hydroelectric plant.
With the new dam, the head under which the plant was to operate was 583 ft. The minimum flow of Cedar River is 148 sec. ft. which was in October, 1902, and August, 1903. The estimated storage behind the new dam is appproximately 150,000 acre ft., which would allow of a sustained flow in the stream of approximately 389 sec. ft. The maximum power, therefore, that could be developed with this storage would be approximately 19,000 continuous h.p. The new dam has a top length of 795 ft. with a maximum height of 217 ft.
Up to May, 1912, the preliminary work consisted of clearing the site and preparing the foundations, which was done by day labor under the supervision of the city engineer and board of public works, although no complete and thorough examination of the dam site had ever been made, nor had any even partially-complete engineering plans of any description been prepared, nor had any borings been made or test pits sunk along the north bank, which is a gravel plateau or moraine, very pervious to water; yet approximately $700,000 had been expended on this preliminary work. It was at this time that the Emerson efficiency experts employed by the city severely criticized the extravagant methods employed and the protests from various commercial bodies and the taxpayers over the manner in which the work was being conducted resulted in a decision to call for bids for the completions of the dam and let the contract for finishing the work.
Earliar geological examinations of the moraine on the north bank developed the fact that it probably occupied the site of the old Cedar River Channel which originally emptied into the Snoqualmie River, the next drainage north.
Under such circumstances, it would have seemed particularly desireable and highly important to determine the depth of bed rock and whether water would escape through the moraine.
Owing to the protests already made and the continued protests of citizens, the city council in May, 1912, decided to employ a board of three consulting engineers, at heavy expense, to make an examination of the site and submit recommendations on a number of quesitons connected with it, one of which was-- whether there was any danger of seepage through the north or right bank of the river. This bank rises sharply from the river bed to a general elevation of 1600, being approximately 150 ft. in height at the present dam site. The general elevation of this morainal plateau extends northerly approximately one and one-half miles to the Snoqualmie River drainage, thence drops rapidly to that river at an elevation of approximately 600 ft. in 1 1/2 miles. This moraine is formed of sand and gravel of a highly porous character. No tests were made as to the rate of ground water movements by this board, due to lack of time, and no test pits or boring had been made previously. It was necessary, therefore, for them to approximate the amount of loss which would be had, but it was stated that they believed it entirely possible that the seepage losses mgiht be grater than their estimate of from 50,000 to 65,000 acre ft. per annum. They further stated "We regard the matter of such vital importance, in any event, that in our opinion, no work should be done in the way of actual dam construction until this problem 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 postion of the ground water plane between the proposed dam site and Snoqualmie River, actual measurements of the movements of ground water between these test wells and numerous mechanical analyses of the materials derived at different depths in said wells."
Geologists and engineers from the staff of the University of Washington had made investigations and their reports were to the same effect.
It had been stated by the municipal authorities that the exposed right bank of the river would seal up, under a plan of raising the water surface by slow successive annual stages. The board of engineers said, "We would say that in our opinion no such result may be reasonably expected under the conditions which prevail here" and this was supported by arguments which should have been conclusive.
In closing their report they recommended tht a series of well drill holes be put down, and that further diamond drill borings be made immediately upstream and downstream from the dam site, and closed by recommending strongly that all construction operations in connection with the building of the dam at the proposed site be suspended until such time as a thorough investigation of the possibilities suggested in their report could be demonstrated and the best plan to pursue be decided upon.
Notwithstanding the recommendations made by this board of engineers and the estimated loss of from 50,000 to 65,000 acre ft. of water per annum, the Board of Public Works of Seattle, in a letter to the mayor dated May 10, 1912, disposed of this all important question by stating that since the board of engineers believed that the loss would only amount to from 50,000 to 65,000 acre ft. per annum and that this loss would not imperil the dam or any of its appurtenances or render them in any way less efficient, and that since in a smaller way the experience of the city in building the original timber crib dam showed that the seepage at first encountered was gradually done away with, and that since every reservoir has more or less seepage at first, it was their belief that the north bank would seal itself, perhaps not entirely but practically so, and that they believed that the construction of the dam at the proposed site was justified. Mayor Geo. F. Cotteril, in transmitting this letter to the council, under date of May 11, 1912, stated "there is nothing in this seepage problem whlch necessarily suggests change of dam location" and insisted that there should be no delay in pushing construction. One member of the board of public works submitted a minority report recommending that the suggestions made by the board of engineers, be followed out, but no attention was paid to this report by the council; the work was ordered done and contract let for the dam.
The dam was completed late in 1914. The north end of it is approximately 25 ft. above the surface of the surrounding country. In order to reach the same elevation as the crest of the dam, it is necessary to go at approximately right angles to it a distance of about one-half mile to reach high ground upstream, which is part of the gravel plateau. The intention was to construct an earth bank or dam on top of this plateau to an elevation corresponding with the top of the dam, and it was thought quite probable that it might be necessary to put in a concrete core wall-- this, however, without having made any sounding in this plateau to determine the depth to which such core wall would need to go. Upon the completion of the dam, Nov. 1, 1914, and the backing up of water in the reservoir, numerous springs and streams developed at points down stream both in the Cedar River and Snoqualmie watersheds, indicating a heavy loss of water, so great in fact that is was believed impossible and dangerous to raise the water to even the temporary spillway elevation, which was some 45 ft. below the crest of the dam. The water leaked out rapidly, in fact the outflow was greater than the inflow. Investigations were immediately begun by the city as to the possibility of silting. No clay being available in that vicinity (and it was not believed there is any within miles of the dam site) it was decided to sluice in the top layer of soil from the area immediately above the dam site in an endeavor to to stop the leaks. The top layer of soil consists of humus, sand and some loam, the latter being very light and forming a small percentage of the layer. After some time and money had been spent in this eadeavor, it become questionable in the minds of city officials whether such a procedure can be followed satisfactorily. Various estimates have been made as to the cost of doing this work, and while it is acknowledged that it is in the nature of an experiment, these estimates range from $250,000 to $1,000,000 and upwards. Competent engineers acquainted with the situation do not believe it is possible to seal under the conditions here existing. More recent investigations have developed the fact that the water when allowed to back up still escapes as rapidly as before, and in some instances a greater flow is had in the new streams. It is now proposed to build either a concrete core wall or practically a new dam across this moraine. Soundings have now been made in this morain to a depth of 300 ft. without encountering bed rock. If such is the case, any engineer can readily appreciate the impracticability of attempting to construct a concrete wall in a hole of this depth. Further it can be readily realized what the cost of a wall under such conditions would be.
The city engineer as recommended that a commission of engineers of national reputation be appointed to thoroughly investigate and report upon the situation--that test holes be driven to determine foundations, if any exist, for curtain wall. He further states that at least 400 acres of the sides and bottom of the basin will have to be silted and that in his opinion this would be a doubtful experiment while entailing an enormous expense. Councilman Erickson stated in the council chambers that the voters would turn down a bond issue for a curtain wall which would cost at least $1,500,000 and he was opposed to making such a request of the taxpayers because municipal ownership would get a black eye in Seattle.
Needless to say, with a board composed of members who were on it when the mistake was made, no stone will be left unturned to attempt to utilize the present dam. Had they taken the advice of men competent to give it, the present situation would not have been had. Ordinary business prudence would have suggested that caution be used in proceeding with a work of such magnitude before definite knowledge was had relating to the bank in question, but due to the fact that there was an insane desire on the part of city officials to increase the capacity of their power plant, no reasonable recommendations would be recognized by them since the did not want any further delay.
As the situation stands today, the city of Seattle has expended $2,959,454 for their municipal hydroelectric plant, transmission lines and the city substation, and with a total investment in plant January 1, 1915, of $6,225,867, are able to generate only 10,400 kw., and this can be obtained only about nine months in the year, it being necessary to supplement if this amount is obtained with steam auxiliary plant. This makes a total cost for a water power plant of $285 per kw. If $1,000,000 will seal the reservoir, and $1,100,00 additional is required for the hydraulic and electrical work and transmission lines, the total consturction cost of the water power plant would amount to $5,000,000 and with 19,000 h.p. available, the cost would be $357 per kw. or $268 per horsepower.
Press reports state that the city officials are considering abandonment of this dam, with the large amount of money invested in it, and the acquisition of a power site on another stream to supplement the city's supply of power.