Snake River Bank Stabilization

Abstract

The Snake River in Idaho and Wyoming has annual floods that approximate 20,000 cfs. Stream beds have steep gradients, are composed of clean, sandy gravels and there is heavy bedload movement during floods. Channels are braided, subject to extensive changes during floods, and threaten adjacent farmland with erosion and evulsion. Experience with Corps of Engineers levees and bank protection along approximately 37 miles of the stream during the last 20 yr shows that failures of levees and riprap are generally caused by undermining, but such failures can be avoided by extending riprap below the active depth of bedload movement and scour. Stone size of riprap, as specified in engineering manuals, is sufficiently large but small stone and dirt that prevent interlock must be avoided. Riprap slopes should not be steeper than 1 on 2. Riprap can be overtopped several feet without damage, provided levee slopes are relatively flat and are protected with coarse gravel.