Document 49: Seattle Regrades

Arthur H Dimock, “Preparing the Groundwork for a City: The Regrading of Seattle, Washington,” Transactions of the American Society of Civil Engineers Paper No. 1669 (1926): 718-19, 722-23.

Return to Document Index

The general topography of the new city is shown on Fig. 1. [see map] Taking First Avenue and Yesler Way as the center in those early days, there lay to the south about 1,500 acres of tide flats, bounded on the east and west by steep slopes and intersected by the Duwamish River. The flat low-lying valley of this river, about 1 mile in width, extends southeasterly for about 8 miles, where it opens into far wider valley lands reaching to Tacoma, Wash. North of the central point are steep slopes coming directly down to the water-front, flattening in the vicinity of Pike Street to form a considerable level area about 100 ft. above high tide. Immediately north of Pike Street, and a little to the westward, lay Denny Hill, with a maximum elevation of about 240. To the east of Denny Hill was a valley extending to lake Union, also bounded on the east by steep slopes.

About 1 mile from Pike Street and less than 2 miles from Yesler Way is the south end of Lake Union, a body of water of about 800 acres, 1 mile in length due north and south, and ½ mile in width, lying about 8 ft. above high tide. It is bounded on the east and west by steep hills, but has level land at its southern end. It possessed an outlet to Puget Sound through Salmon Bay and was separated from Lake Washington by a narrow ridge. From the earliest times the pioneers dreamed of connecting these lakes with the Sound by a ship canal, which has since been accomplished. Between Elliott Bay and Lake Washington, about 20 miles long and 2 to 3 miles wide, was a series of hills and valleys. North of Lake Union was an extensive, rolling plateau.

Such, in brief, was the general character of the site selected by these pioneers for the city of their dreams. It possessed many elements corresponding to their vision. First, was the sheltered harbor with ample depth of water, which had caught the eye of McClellan [N.B. Capt. George B.], and the bays and lakes, which, when connected, were to form an internal system of water communication. Then, there were the tide lands which, when filled, were to form a manufacturing district with easy access to rail and water. The level lands in the neighborhood of Pike and Pine Streets, when extended by proper grading operations, were to become the retail business section and between the manufacturing and retail areas, on the slopes of the hillside, was ample room for buildings of the office and financial districts. On the hills, surrounded by sea and lake and encircling snow-clad mountains, were home sites of rare beauty. The instincts of the pioneer led them aright. Although not without its difficulties, the situation of Seattle is unique among the cities of the world.

The original business area was along First Avenue between Jackson and Cherry Streets. With no possibility in early days of growth southward because of the tide flats, the city was compelled to grow northward until to-day one of the large department stores is about a mile from the original center. Lying across this natural line of development was Denny Hill, a great obstacle in the path of progress. The removal of the major portion of this hill is known as the ‘Denny Hill Regrade.’…Lying east of the ridge rising from Elliott Bay, the Rainier Valley, a distance of seven miles. The lowest point in this ridge was at Jackson Street and Tenth Avenue South, where it had an elevation of 210 ft. The easiest grade over the hill from the water-front to Rainier Valley was about 15 per cent. Here, then, was a second obstacle to progress, the removal of which was accomplished by the Jackson Street and Dearborn Street regrades. Moreover the streets parallel with the water-front from Yesler Way to Pike Street, with the exception of Second Avenue, had gradients more excessive than was convenient or permissible. The earlier grading of these streets was necessarily limited, by reason of costs, to the least amount of work. Here, then, was another problem, a third obstacle to growth, which led to the regrading of Third, Forth, and Fifth Avenues.

In 1889, a large section of the business area was destroyed by fire. An unusually far-sighted Mayor and City Council seized the opportunity to widen First and Second Avenues from 66 to 84 and 90 ft., respectively, and to raise the grades of the lower part of the city. A period of rapid growth followed the fire ending in the bad year, 1893. In 1897 gold was discovered in Alaska, and another era of rapid growth began, which was checked by the panic of 1907.

It was during this period, however, that the obstacles which have been described were removed. The rapid rise in the value of real estate caused the optimism and furnished the incentive to the undertaking of great enterprises. Seattle was fortunate in this juncture in having as City Engineer, R. H. Thomson, [Member, American Society of Civil Engineers]., a man who clearly comprehended the necessities of the situation and had the courage and skill to take advantage of this favorable opportunity to carry into execution the practical plans and measures necessary to secure elbow room for the growing city. In initiating and carrying through the project for the removal of Denny Hill, the strong support of Mr. James A. Moore, a real estate operator, was invaluable.

The work of regrading began in a small way by cutting down First Avenue north of Pike Street. This street ran over a shoulder of Denny hill, which jutted out toward to water-front. This was followed by similar work on Second Avenue north from Pike Street. It was unfortunate that financial limitations and some local politics combined to prevent the securing of the most desirable grades on this street. By the time it became possible to proceed with the work on Third, Fourth, and Fifth Avenues, commonly known as the Denny Hill regrade, a considerable number of new buildings had been erected along Second Avenue. This made it practically necessary to conform the grades of the new work to that of Second Avenue and led to the creation of a hump at Second Avenue and Virginia Street, which subsequent efforts have failed to remove.

Under modern conditions, however, the necessity for easy gradients has diminished. These gradients were determined formerly by considering the load a team of horses could pull, and those pavements were selected which afforded the best footing. The motor vehicle has made old theories seem very ancient indeed. It is still true that easy grades are better than steep ones, but the limits have been greatly widened. There is one street in Seattle which was paved with asphalt on a maximum grade of 12%, on the theory that it would never be used anyway; but it has become the main access to the First Hill District. It requires a sprinkling of sand under certain weather conditions, but the capitalized cost of this expense would go a very small way toward paying the cost of securing a better gradient. The ease and comfort of the lowly pedestrian is a more potent factor than motor traffic in limiting the growth a business district and in determining limiting gradients. Traffic will now avoid detours and seek the steep short-cut wherever possible. In order to obtain a 5% gradient on one of the parkways, a series of hair-pin turns, reminiscent of stage coach days on mountain roads, was used. Today, these turns are a source of inconvenience and even danger. A more direct route with a 12% gradient would be preferable.

The writer has recommended the use of escalators on the steep cross streets of the business district of Seattle. The practical effect of these escalators would be equivalent to the flattening out of these grades to pedestrians. Some day, owners of the property on these steep streets will awaken to the value of this mechanical means of overcoming the disadvantages of their situation. When the first street is properly equipped with this means of easy access, owners on the remaining streets will hasten to follow their lead.

Fortunately, these hills were composed of sand, gravel, clay, and hardpan. They were the product of glaciers which, in the Pleistocene Age, covered the site of Seattle to a depth of several thousand feet. Geologists state that there were two such ice sheets, each originating in the Cordilleran center and coming down from the north. They were separated in time by a considerable inter-glacial period. Little of the deposits of the first sheet are exposed, but the handiwork of the second constitutes the foreground of much of the scenery of Puget Sound. The glacier extended to a point about 70 miles south of Seattle. It dammed the natural outlet of the Sound through the Straits of Juan de Fuca. When it began to recede and melt, the water, denied its normal outlet through the Straits, formed a lake or lakes into which flowed many of the rivers of the Sound Basin. The outlet for this water was over a low divide to the south and down the Chehalis River to the Pacific Ocean.

The outwash from the glacier formed extensive gravel plains south of Tacoma which now yield a large part of the sand and gravel required for building and engineering construction in Seattle, Tacoma, and other Puget Sound cities. As only the very best and hardest of the rocks survived the action of the glacial mill, the quality of this material is exceptionally high. The retreating glacier also deposited a layer of material called Vashon Till by geologists and commonly known as hardpan. Its thickness varies from 2 or 3 to 20 ft. or more. Beneath are sand and gravel and extensive deposits of a hard blue clay, laid down in the glacial lakes from materials encountered by the first glacier. It constitutes the foundation of much of the construction work. Rocks occurs only in a very few places in the city and not at all in the business district. This, the, was the material to be moved, and as the cost of handling the large volume of excavation by orthodox methods would have been prohibitive, a new and cheaper method had to be discovered.

On the Denny Hill work, city water was not available. The supply was from two sources. On the water-front a 4-state pump with a 850-h.p. motor delivered 5,000,000 gal. per day. A second plant of three units was constructed on Lake Union about 1 mile from the work. Two units consisted of two 10-in., 4-stage turbines each, with a 650-h.p. motor. The other unit was a 15-in. 4-stage pump, with a 650-h.p. motor. The total capacity was 12,000,000 gal. per day. Here, also, wood stave pipe conveyed the water to the giants.

The quantity of spoil carried by the water varied within wide limits, depending on the gradients of the discharge pipes and the character of the material. On Jackson Street the average was 6.75% of the volume of water. With a water supply of 20,000,000 gal. per day, this would mean 10,000 cu. Yd. Of material moved. A large allowance, however, on such work must be made for changing pipe lines, moving giants, clogging of discharge pipes, and all the innumerable petty delays incident to such work. On Jackson Street the quantity moved averaged about 4,000 cu. yd. per calendar day.

In the Jackson Street regrade all the material was used to fill in the adjacent tide lands. The grades of some of this area were raised about 40 ft. In this, as in the Denny Hill project, provision was made in the specifications for the removal of earth from private property at the same price as that paid by the City, the contractor being required to accept a lien on the property payable in ten annual installments, as in the case of the assessment for the street work. This provision applied also tot he fills. The result was a substantially unanimous acceptance of this provision by the property owners, there being, however, a few exceptions.

It will be noted that the dreams of the original pioneer settles for a great city, which they visualized, perhaps, somewhat hazily and indistinctly, required for their initial realization the development of pioneer engineering methods. Hydraulic sluicing, the hydraulic giant, wood-stave water pipe, wood-stave pipe lined with blocks for carrying spoil, and the shear-board method of building up embankments, are all the product of Western conditions.

The dumping grounds were just south of the territory and comprised of several hundred of the 1,200 acres of the Seattle tide flats, which were brought to grade at 2 ft. above extreme high tide. This filling was done by the writer with two 20-in. hydraulic dredges, and the 12,000,000 cu. yd. so placed, formed an essential part of the regrade work of Seattle, making useable the land from the foot of Queen Anne Hill to the southern end of Elliott Bay. The portion of the tide flats near the Jackson Street regrade was filled with the dirt sluiced down in doing this work. This, together with the material removed from Denny Hill regrade, constitutes the greatest sluicing operation ever carried out, and it redounds to the credit of those who did the work, as well as to the City of Seattle, the possibilities of which were dependent on the great works described.

Center for the Study of the Pacific Northwest