Washougal Bridge Project February 8, 1999 University of Washington Forest Engineering 444

UW Forest Engineering 1999 Senior Class

In this project, we designed for two crossings in the Washougal planning area. The conclusions based on our analyses of these crossings are discussed below.

Mine Creek Crossing

Based on the USGS method, it was found that the 100 year flood level at our crossing of Mine Creek is 64.3 cfs. A 60 inch culvert would be required to pass this flow with a velocity of 13.8 ft/sec. The culvert is at a 13% slope. A pipe arch at the same location would have dimensions of 65 inches by 40 inches. The road crosses Mine Creek in the middle of a switchback. The curve widening required here is 14 feet, resulting in a 28 foot running surface. 20 feet of fill is needed at this location. With a 1:1 fill slope, this results in a 68 foot long culvert or pipe arch.

Little Washougal Crossing

Based on a Log Pearson Type III Distribution, the 100 year flood level was found to be 2,025 cfs. This flow will reach a height of 10 feet above the river bottom. There is a lot of flexibility in the approach to the crossing, so any curve widening required can be implemented. The crossing requires a span of 80 feet. Four bridge types were investigated: Log Stringer, Glulam, Portable, and Pre-Stressed Concrete. Log Stringer bridges are unsatisfactory due to the lack of availability of very large logs. The other three bridge types are satisfactory. Glulam bridges were explored in more depth. The specifications for a satisfactory glulam bridge are as follows:

Back to outline