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Hoh River near Forks, Washington

The Hoh River is a gravel and cobble-bed stream also located on the Olympic Peninsula of northwestern Washington State. The river flows westward about 60 miles from the base of Mount Olympus to the Pacific Ocean near the town of Forks, Washington. The watershed has a drainage area of more than 253 mi2 a large portion of which is located within the boundaries of Olympic National Park. The river is steep, falling about 5,000 feet in 58 miles for an average slope of 0.016. The river slope is steepest in the upper watershed canyons and decreases in the downstream direction. In the downstream most 30 miles, the average slope decreases to 0.0025. The river is meandering and flows through very high glacial terraces all the way to its mouth. Bedrock outcrops have been observed in the channel at several locations along the river. The annual mean flow of the Hoh River is 2,524 ft3/s with a mean annual runoff of 135 inches. The highest peak flow recorded was 54,500 ft3/s on November 24, 1990 and the lowest mean-daily flow recorded was 252 ft3/s.

Debris Slide Imperilled Road

Debris Slides and Bank Failue on the Hoh River

There has also been a sharp decline in the numbers of salmon returning from the ocean to spawn in the Hoh River. Logging and the associated road building have affected the upstream watershed. Landslides and debris flows are common throughout the drainage. Roads are adjacent to the channel and floodplains along the downstream 30 miles of the river. In some locations, the riverbanks have been extensively armored with rip rap to stop active bank erosion. The physical processes of the Hoh River are being studied to determine the degree to which natural processes have been impacted by human development.

This study is just beginning. Data collection activities in the year 2000 have included a river channel survey along the lower 31 miles of river and preliminary comparison of current and historic aerial photographs. The river channel survey was performed from a raft using global positioning system instruments and a depth sounder. The channel survey data will be useful for hydraulic modeling and future monitoring. Installation of cameras with automatic timers is being planned to produce time-lapsed videos at areas of active bank erosion to determine how certain reaches are presently responding to engineered log jams or how they may respond in the future. The analysis of current and historic aerial photography is expected be very useful in evaluating changes in river channel location.

Time Lapse Photography Setup Historic Meanders on Aerial Photographs

Time Lapse Photography and Historic Meander Patterns on the Hoh River