| Muddy River | |
| Map Size: | 300 |
| Pushpin Map: | Washington#USA |
| Pushpin Map Size: | 300 |
| Pushpin Map Caption: | Location of the mouth of Muddy River in Washington |
| Subdivision Type1: | Country |
| Subdivision Name1: | United States |
| Subdivision Type2: | State |
| Subdivision Name2: | Washington |
| Subdivision Type4: | County |
| Subdivision Name4: | Skamania |
| Length: | 29.8miles[1] |
| Discharge1 Location: | 0.5miles from the mouth[2] |
| Discharge1 Min: | 153cuft/s |
| Discharge1 Avg: | 865cuft/s[3] |
| Discharge1 Max: | 25000cuft/s |
| Source1: | southeast flank of Mount St. Helens |
| Source1 Location: | between East Dome and Shoestring Glacier, Gifford Pinchot National Forest |
| Source1 Coordinates: | 46.19°N -122.1564°W[4] |
| Source1 Elevation: | 5023feet[5] |
| Mouth: | Lewis River |
| Mouth Location: | slightly upstream of Swift Reservoir |
| Mouth Coordinates: | 46.0697°N -122.0069°W |
| Mouth Elevation: | 1040feet |
| Basin Size: | 351sqmi |
The Muddy River is a stream, about 29miles long, southeast of Mount St. Helens in the U.S. state of Washington.[1] The Muddy River flows south - southeast and joins the Lewis River just above the Swift Reservoir. The Lewis River flows west and is a tributary to the Columbia River. The east flank of Mount St. Helens is within the watershed of Muddy Creek.[6]
During the 1980 eruption of Mount St. Helens, lahars (volcanically-induced mud and debris flows) swept through its channel.[7] About 135miles of stream channels around the volcano were affected by lahars.[7]
The United States Forest Service maintains the Muddy River Picnic Site, next to the river and to Forest Road 25 in the Gifford Pinchot National Forest.[8] Trails cross the river on its upper reaches.
Muddy River originates at about the 5000feet level on the southeast side of Mount St. Helens in the Cascade Range. The river source is within Mount St. Helens National Volcanic Monument and Gifford Pinchot National Forest. Shoestring Glacier is to the right and East Dome is to the left. Flowing southeast down steep slopes, the river curves sharply to the northeast just beyond the 3000feet level of the volcano. Here the river crosses Forest Road 83 and passes the Ape Canyon Trailhead and the Lava Canyon Interpretive Site, both on the left,[9] before entering Muddy River Gorge.[10]
Flowing northeast through the gorge, the stream plunges over three waterfalls before emerging from the narrows and curving sharply again to the southeast.[10] Here Crane Lake is on the left, Smith Creek enters from the left, and Smith Creek Trailhead is on the right.[10] Slightly downstream of the trailhead, the river leaves the national volcanic monument but remains in the national forest.[10] At about the 1700feet level, Clearwater Creek enters from the left.[10] Turning south, the river descends less rapidly, passing under Forest Road 25 and then receiving Clear Creek from the left about 5miles from the mouth.[10] At the road crossing, Muddy Creek Picnic Site is on the left.[8]
Below the confluence with Clear Creek, the river meanders through Cedar Flats, leaves the national forest slightly more than a mile from the mouth,[10] and passes a United States Geological Survey (USGS) stream gauge, on the left 0.5miles from the mouth.[2] Muddy River enters the Lewis River about 60miles from the larger stream's mouth on the Columbia River.[10]
The USGS monitors the flow of Muddy River at a station 0.5miles upstream of the confluence with the Lewis River. The average flow of the river during 54 water years, including 1984 - 2011, is 865cuft/s.[2] The maximum flow recorded was 25000cuft/s on February 8, 1996, and the minimum flow was 94cuft/s on December 5 - 7, 1929.[2] The high flow in 1996 was associated with general flooding in the Pacific Northwest during the Willamette Valley Flood of 1996.[11]
A flood destroyed an earlier version of the gauge in January 1974. The existing gauge began recording data in October 1983. The mudflow flood related to the eruption of Mount St. Helens in 1980 occurred outside the period of record for either gauge.[2]