The mouth of the Toutle River
Where the Toutle enters the Cowlitz River, just above the town of Castle Rock, a wide sand bar forms because of increased cross-sectional area of the stream, which leads to decreased stream velocity and hence decreased competence (the ability to carry sediment). Coarser sand and gravel particles drop out of the flow whereas finer silts and clays move on down the Cowlitz to the Columbia, eventually to enter the ocean. The result is a nice fishing spot for salmon:
Photo by James Maynard © 2011 - free use with attribution [full-size jpeg]
Toutle River sediment loads from Major - J Geophysical Research - 2004. Gaging station at Tower Bridge below the confluence of the North and South Fork. SRS refers to the construction of the sediment retention structure. Note increase in yields after 1995.
Sediment budget for the Toutle-Cowlitz system. USACE 2010
See also:
Grain-size distribution of Cowlitz River sediments
Flood frequency data for Cowlitz River
Other data sources:
http://www.nwp.usace.army.mil/docs/d_msh/Final_Cowlitz_LOP_02-04-10.pdf
http://www.nwp.usace.army.mil/docs/d_msh/Cowlitz_levees_safe_water_level2010.pdf
http://www.nwp.usace.army.mil/docs/d_msh/Toutle-Cowlitz_sediment_budget.pdf
http://www.nwp.usace.army.mil/docs/d_msh/Jun23_2010_mtg_slides.pdf