rubble-mound jetties, the outer ends of which are approximately 2 miles apart, and has a minimum width between the 40-foot contour lines of 8,000 feet. The channel in the Columbia River from the ocean to the mouth of the Willamette has a width of 500 feet. The annual freshets cause shoaling in some places, but the channel depths are restored by dredging. The Willamette River Channel.-The inner harbor of the port of Portland may be considered to be that section of the Willamette River from its confluence with the Columbia to the southern city boundary, a distance of approximately 16 miles. The improved ship channel extends to the northern end of Ross Island, a distance of about 14 miles from the mouth, and has a minimum width of 500 feet. A channel 1,500 feet wide has been dredged on the west side of Swan Island. The old east channel has been closed by a causeway, and the island has been improved as an airplane landing field. TIDES Owing to the marked difference between the two daily low-water heights on the Pacific coast of the United States, the mean of the lower low waters rather than the mean of all low waters has been adopted as the plane of reference for this coast. At the mouth of the Columbia River the mean range of tide is 7.5 feet and at the entrance of the Willamette River the mean range is 2 feet. Extreme tidal ranges are about 12 feet and 3 feet, respectively. Although the tidal range is small above the confluence of the Columbia and Willamette Rivers, the annual freshets cause large fluctuations in the level of both rivers. The rivers are usually highest in May, June, and July and lowest in September, October, and November. The heights above normal during the freshets generally range from zero at Astoria to 21 feet at Portland. TIDAL CURRENTS In the entrance of the Columbia River the velocity of the currents is variable. On a flood tide a velocity of 2 knots is seldom exceeded, but the velocity sometimes attains 5 knots during an ebb tide. This variation is due largely to the strength of the river discharge, the velocity of the tide alone being 2.5 knots at strength of either flood or ebb. Above the mouth of the Columbia the velocity of the current averages from 1 to 2 knots, except during the freshet period, when it is considerably increased, although not sufficiently to affect navigation seriously. ANCHORAGES City regulations provide in general that vessels arriving within the corporate limits of the city of Portland, if obliged to anchor, shall be anchored below the Broadway Bridge. The harbor master designates the location at which to anchor. The anchorages generally used are as follows: (a) From Broadway Bridge to the head of Swan Island Air Field, a distance of 8,000 feet, the anchorage ground covering an approximate area of 165 acres and having a depth of from 30 to 35 feet; (b) from the lower end of Swan Island Air Field to the lower limits of the city, a short distance below Municipal Terminal No. 4, a distance of 21,000 feet. This anchorage ground covers an area of approximately 500 acres and has a depth of from 25 to 33 feet. Vessels anchoring upon these grounds are subject to the following regulations: Such vessels shall be moored with the bower anchor forward and another bower anchor ready to drop, and a stream anchor out astern to prevent the vessel from swinging across the main ship channel and obstructing the same, and shall have a boat swung out ready for instant use at all times. Vessels moving from the docks or wharves to anchor in the river while waiting for cargo shall be moored under the same conditions as other vessels, so as to leave a clear channel for vessels coming up or going down the river. Pilots and masters of towboats bringing vessels to the harbor of the city of Portland shall see that the vessel in their charge is moored so as to comply with these regulations. Vessels must not be anchored or moored in the fairway channel or within 400 feet of any bridge or ferry line. WEATHER CONDITIONS Open season for navigation.-Both the Columbia and Willamette Rivers are navigable throughout the year. Navigation by smaller vessels and river boats may be rendered difficult for short periods in the winter when there is ice in the Columbia River. Prevailing winds. During the months from November to March, inclusive, the prevailing winds in the vicinity of Portland are from the south or southeast; for the remainder of the year northwesterly winds prevail. In the lower Columbia River Valley easterly and southeasterly winds prevail from October to March, inclusive, while during the remainder of the year the winds are from the northwest. On the coast northwest winds of high velocity, sometimes developing into gales which last several days, are not infrequent during the summer months, and during the winter months severe south gales may occur at any time. On the lower Columbia River the average hourly wind velocity for the year is high. Records kept by the United States Weather Bureau for a period of 26 years indicate that average to be 14 miles, increasing from 10 miles in July and August to 19 miles in December. In the vicinity of Portland the average velocity is only 6 miles an hour. Ice.-Ice forms occasionally in the two rivers but it is seldom heavy enough seriously to affect navigation. Fogs. Although fogs are most frequent on the outside coast of Oregon during the months of July, August, and September, they may occur at any time. They are at times dense, extend many miles seaward, and frequently, during the months of greatest prevalence, continue for extended periods. The following table, prepared from records of the Bureau of Lighthouses, indicates the number of hours annually, for a period of 17 years, during which fog signals have been sounded by official stations at various points between the ocean and Portland: Aver Station 1913 1914 1915 1916 1917 1918 1919 1920 1921 1922 1923 1924 1925 1926 1927 1928 1929 age for period Columbia River 869 530 481 899 789 811 554 595 586 643 530 527 471 449 198 595 697 596 232 396 264 While fogs are more prevalent during the summer months on the outside coast, this condition does not prevail on the Columbia River as is shown from the following table compiled from official records kept for a period of 10 years, including 1929, indicating for that period the average number of hours per month of operation of fog signals: Jan. Feb. Mar. Apr. May June July Aug. Sept. Oct. Nov. Dec. The following statement shows the number of days per year, for the last 17 years, during which dense fogs, that is, fogs which obscure objects at a distance of 1,000 feet, prevailed at Portland: Precipitation. The North Pacific coast experiences a rainy and a dry season, the former occuring during the months October to May, inclusive, and the latter during the remaining months of the year. The average annual amount of precipitation at Portland is 43.88 inches. Snow does not fall in substantial amounts in the regions drained by the lower Columbia and the lower Willamette Rivers. The average monthly and annual snowfall in inches at Portland is indicated in the following table: Length of Place Jan. Feb. Mar. Apr. May June July Aug. Sept. Oct. Nov. Dec. Annual Temperature. The mean annual temperature, estimated for a period of 45 years, is 52.8°. There is a very considerable range between maximum and minimum temperatures in this vicinity. While the mean maximum temperature, estimated for a period of 42 years, is 61°, and the mean minimum is 44.9°, the annual range between summer and winter temperatures may be illustrated by the fact that the highest temperature registered in Portland during the year 1930 was 97° on September 2, and the lowest was 13° on January 17. The mean average for the year was 53.2°. The following table of meteorological data has been prepared from the records of the Weather Bureau, United States Department of Agriculture: Length of Meteorological data [United States Department of Agriculture, Washington, D. C.] Place Jan. Feb. Mar. Apr. May June July Aug. Sept. Oct. Nov. Dec. An nual Portland... Portland... Mean temperature, degrees Fahrenheit 45 39.0 41.9 47.2 51.7 57.3 61.8 66.9 66.4 61.2 54.2 46.1 41.4 52.8 Mean maximum temperature, degrees Fahrenheit 42 44.0 48.0 54.7 61.0 66.6 71.4 77.8 77.5 71.1 62.1 52.1 46.2 61.0 Miles above mouth BRIDGES The Columbia River is crossed by a highway toll bridge at Longview, Wash., 66.2 miles above the mouth. This bridge, owned by the Longview-Columbia River Bridge Co., is a high level, fixed bridge, with channel span of 1,085 feet and a vertical clearance of 196 feet above mean low water and 180 feet above high water. The Willamette is crossed by nine bridges, a description of which is contained in the following tables: Bridge regulations. The following is part of the regulations prescribed by the Secretary of War governing the opening of bridges across the Willamette River at Portland: 1. Call signal shall be as prescribed for each bridge in paragraph 2 of these regulations. It is given by vessels as notice to bridge operators to open the draw, or in case the draw is already open, that they intend to pass through. A call signal given twice in rapid succession indicates that vessel has authority to pass bridges during closed periods (see par. 12). Acknowledging signal shall be the same as the call signal for each bridge. Its purpose is to acknowledge the call signal of a vessel and to indicate that the operator intends to open the draw as soon as practicable, or that he will hold it open. Danger signal shall consist of a series of short blasts, at least four, given in rapid succession, and repeated if necessary. Its purpose is to answer the call signal of Right M. L. W. H. W. |