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One-story, single-family house raised on concrete columns, Oregon City, Oregon This residential structure was built in 1971 along the Clackamas River in Oregon. It sits 13 feet above a grade slab on 1 O-inch-diameter concrete columns (Figure A6). The house rests on timber beams that are secured to the top of the columns by steel straps embedded in and projecting from the columns. An inclosed "core area" at ground level connects with the upper main floor. It contains an access stairway and water and sewer connections. The house itself is of wood frame construction and contains approximately 1300 square feet of space. The owner estimates that the cost of raising the house was $5000. Under the floodway concept adopted by Clackamas County subsequent to construction of this dwelling, the "core area" would likely not be permitted, particularly since the wider dimension of the core area is oriented perpendicular to flow. Clackamas County also requires a I-foot freeboard above the 100-year flood; however, this structure has approximately a 3-foot freeboard. The last significant flood was in January 1972. It peaked at 70,800 cfs and was considered approximately a 20-year flood. The owner states that water was on three sides of the concrete ground slab but did not cover the parking area. The 100-year flood discharge is 110,000 cfs and its duration is about 6 days. A verage overbank velocity is about 5 feet per second. The December 1964 flood peak was about 120,000 cfs. Of particular interest is the emergency exit provided by aerial cable tram (basket shown in the third photograph). In the event of major flooding, this provides access from the living level to nearby higher ground at the county road. Vie \.1.,' from street, Clackamas River on other side. Figure A6. One-stor}' house raised on concrete columns 24