Step pools in stream channels

Abstract

Steps and pools are the characteristic bedforms which dominate the channel morphology of steep mountain streams. However, such steps and pools have received less attention in fluvial geomorphological research than pools and riffles. In the absence of sufficient published research on step pools, there may have been a tendency to assume that they are very similar to pool riffle sequences.Step pool morphology, different from pool riffle forms, characterizes mountain areas which cover a sizable portion of the earth's surface (Graf, 1988: 175). Because mountain areas are sources for the water and sediment of large downstream basins, the enhanced understanding of step pools is critical in explaining the operation of the general fluvial system. Present literature is widely scattered and has originated from different intellectual sources. There are three major groups of studies. The first is a body of engineering literature concerned particularly with the mechanics of tumbling flow resulting from the step pool configuration. The second is a group of catchment studies that demonstrates the hydrologic significance of step pools in mountain streams. The third is a small but growing body of literature that ties together the previous two groups of studies and focuses on channel processes and step pool formation. This third group includes studies of vegetative debris and log steps.This paper synthesizes the literature on step pools, with particular reference to theory construction and explanatory models. The paper proceeds from a discussion of the fundamental aspects of step pools to a clarification of terminology. The paper then reviews the contributions made by the three groups of studies, followed by suggestions for areas of future research.

Controls on at‐a‐station hydraulic geometry in steep headwater streams, Colorado, USA

“…The resistance is mainly related to skin friction and form drag around large boulders. The major source of roughness in a step-pool reach is from energy dissipation as fl ow tumbles over each step and enters into the pool (Wilcox and Wohl, 2006;Curran and Wohl, 2003;Chin, 1989Chin, , 2003Chanson, 1996;Abrahams et al, 1995). Wood is a major component of resistance in both channel types, with the greatest amount being found incorporated into the steps (Figure 9).…”

Morfología y estabilidad de las secuencias en escalones (step pool) en los torrentes alpinos de elevada pendiente

“…Se observa que el campo de variación de la relación Ls/B (0.5-1.6) es más reducido respecto al intervalo 1-4 indicado por otros autores (Whittaker, 1987;Grant y otros, 1990;Montgomery y Buffington, 1997), y decididamente inferior respecto al campo 5-7 que caracteriza los rápidos-remansos (Leopold y otros, 1964). En la muestra analizada, en contraposición a las observaciones efectuadas por Chin (1989) Lenzi, 1998). La relación entre Z y H (Tabla 3) indica en definitiva que la pérdida efectiva de cota a lo largo de un tramo es, en términos medios, el 75% de la suma de las alturas de los step presentes en el mismo tramo.…”

“…Edificados por bloques reciproca mente embriciados formando una rampa natural corta con fuerte pendiente ; pueden incorporar durante el desarrollo longitudinal algunos escalones de bloques; • Escalones en roca. Son característicos de los tramos de cauce condicionados por afloramientos de roca ; esta unidad está condicionanada por la geología, antes que por las condiciones hidráulicas del flujo (Chin, 1989);…”

“…Una comparación de las denomina ciones y clasificaciones propuestas ha sido efectuada por algunos investigadores (Grant, 1994;Rosport, Dittrich, 1995;Montgomery, Buffing-ton, 1997) y sintetizada por D'Agostino, Lenzi (1997). Algunos autores (Judd, Peterson, 1969 ;Hayward, 1980;Heede, 1981 ;Whittaker, 1987;Chin, 1989;Grant y otros, 1990;Grant, 1994;Wohl, Grodek, 1994) observaron que la longitud media de los step (Ls) relativa a una secuencia, está ligada a la pendiente del lecho a través de una relación del tipo…”

Morphological dynamics of an englacial channel

“…Such morphological form is thought to be a char-acteristic of streams with slopes > 2 % (Chin, 1989;Grant et al, 1990;Montgomery and Buffington, 1997) and may represent a process akin to meandering in the vertical dimension (Chin, 2002;Kostrzewski and Zwoliñski, 1995). Indeed, recent work on bedrock rivers (Hayakawa and Oguchi, 2014) suggests step-pool sequences may be related to intrinsic channel hydraulics and flow perturbations rather than more commonly cited extrinsic environmental controls (Phillips et al, 2010).…”