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page 2858

Publication Date
  • Serial Set 3080


2858 ILEPOBT OF THE CHIEF OF ENGINEERS, U. S. ARMV. are encouraged to build up, the desired object will undoubtedly be at- tained. Mention lias before been made of the fact that a large portion of this water is lost at Snag Island, where it escapes to the northward. I would recommend that this opening be closed by suitably constructed dikes or dams, and in order to facilitate its passage and give it direc- tion over the shoal below that a channel 22 feet deep and 150 feet wide be dredged through this. The erosive action of the water would con- tinually enlarge this dredged channel until it had gained a normal sec- tion commensurate in size with its own requirements. While this is being done there will be a tendency to an increase of flow through the two openings in this locality leading southward into what is known as Prairie Channel. This might cause an enlargement of these, which would retard, if not altogether prevent, the opening of the channel through the shoal. These openings should therefore be closed at the same time that the escape of the water to the northward is prevented. I have indicated on the tracing herewith the location of these dams and of the cut that it is proposed to make through the shoal. The aggre- gate length of the diking at present necessary in this locality is 15,000 feet. The estimated amount of material to be dredged in order to ob- tain a 22-foot channel here is 400,000 cubic yards, and to obtain a chan- nel 25 feet in depth the removal of 540,000 cubic yards will be necessary. Where this channel joins the present ship channel about 1 mile north of Tongue Point there is a distance of 1,000 yards where the present depth is less than 25 feet. The indications now are that this is cutting out, and it is possible that before the permanent works proposed can be constructed we may find 25 feet of water here. In its present condition it will require the dredging of 55,000 cubic yards of. material to provide a 22-foot channel and 90,000 yards to provide the 25-foot channel. At the shoal place before mentioned, which is in front of Upper Astoria, there will be 20,000 cubic yards of material to be dredged in order to obtain a 22-foot channel, and 75,000 cubic yards to obtain the 25-foot channel. From here to the sea, a distance of 15 miles, there is a good channel having a depth of 25 feet or more. In this locality the average rise of tide is 7 feet. It is not deemed necessary or advisable at the present time to locate any permanent works with the view to controlling the water below Tongue Point. When those that are herein proposed for procuring and maintaining the 25-foot channel above this point have produced their effect a resurvey of the river in this locality will indicate the X)oints where permanent works can be placed to the best advantage, if any be found to be necessary, in order to maintain the deep water to the sea. It may always be expected that in a wide expanse of river such as is found here, where sands are continually drifted about by the waves and current, that points of shoals will occasionally get into the deep chan- nel and may change its course or temporarily impair its depth, to the disadvantage of commerce. To provide for emergencies of this kind one or more good dredging machines should be constantly on hand, with funds for operating them as may be required. This can not be avoided at the present time by permanent works unless at an expense for original construction and maintenance that would far exceed the expense of the occasional dredging. Everything should be done to encourage the building up of these shoals so that they may be similar to those on the south side of Cath- lainet l>ay, near Prairie Channel, where we find them at a height nearly

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