Grant, Gordon E. 1989. Morphology of high gradient streams at different spatial scales, western Cascades, Oregon. In: Omura, H., ed. Workshop on "Channel geomorphological change and sediment control at Devastated River"; 1988 October 13-14; Shizuoka, Japan. Shizuoka, Japan: Japanese Sabo Society: 1-12.
The channel and valley-floor morphology ofhigh-gradient streams is commonly expressed atseveral spatial scales. In this paper, a taxonomy ofchannel and valley floor features is proposed toimprove understanding of processes and landformsin steep streams and to provide a common frame-work for stream descriptions. This taxonomy isbased on field studies in two streams draining thewestern slopes of the Cascade Range in Oregon,lI r- A. At the finest scale (10– - 10° channel widths), step-pool sequences formed by large boul-der s oriented transverse to the channel axis domi-nate channel structure; these features appear toform in response to flow perturbations such as an-tidunes during bedload transport events. An impor-tant scale from the standpoint of hydraulics andsediment transport is the channel unit scale
(10° - 101 channel widths). Pool, riffle, rapid, andcascade channel units (in order of increasing bedslope) have non-overlapping slope ranges and par-ticle sizes, and can be distinguished in the fieldbased on hydraulic criteria and step structure.Channel units display non-random sequence andspacing in response to both fluvial mechanisms andexogenous controls, such as bedrock or source ar-eas for large boulders along the channel margin.Formation of channel units is poorly understood butmay be a steep stream analog to bar formation.