Linking Theory and Practice for Restoration of Step-Pool Streams

Abstract

Step-pools sequences are increasingly used to restore stream channels. This increase corresponds to significant advances in theory for step-pools in recent years. The need for step-pools in stream restoration arises as urban development encroaches into steep terrain in response to population pressures, as stream channels in lower-gradient areas require stabilization due to hydrological alterations associated with land-use changes, and as step-pools are recognized for their potential to enhance stream habitats. Despite an increasingly voluminous literature and great demand for restoration using step-pool sequences, however, the link between theory and practice is limited. In this article, we present four unique cases of stream restoration using step-pools, including the evolution of the approaches, the project designs, and adjustments in the system following restoration. Baxter Creek in El Cerrito, California demonstrates an early application of artificial step-pools in which natural adjustments occurred toward geomorphic stability and ecological improvement. Restoration of East Alamo Creek in a large residential development near San Ramon, California illustrates an example of step-pools increasingly used in locations where such a channel form would not naturally occur. Construction of a step-pool channel in Karnowsky Creek within the Siuslaw National Forest, Oregon overcame constraints posed by access and the type and availability of materials; the placement of logs allowed natural scouring below steps. Dry Canyon Creek on the property of the Mountains Restoration Trust in Calabasas, California afforded a somewhat experimental approach to designing step-pools, allowing observation and learning in the future. These cases demonstrate how theories and relationships developed for step-pool sequences over the past two decades have been applied in real-world settings. The lessons from these examples enable us to develop considerations useful for deriving an appropriate course of design, approval, and construction of artificial step-pool systems. They also raise additional fundamental questions concerning appropriate strategies for restoration of step-pool streams. Outstanding challenges are highlighted as opportunities for continuing theoretical work.

A conceptual model of check dam hydraulics for gully control: efficiency, optimal spacing and relation with step-pools

“…Their morphological features have inspired the design criteria for artificial check dam sequences in high-gradient streams stabilization (Lenzi, 2002;Wang and Yu, 2007;Chin et al, 2009;Wohl et al in Conesa-García and Lenzi, 2010). Furthermore, several studies (Abrahams et al, 1995;Zimmermann and Church, 2001; Lee and Ferguson, 2002) have shown that step-pool morphologies tend to maximize flow resistance, leading to minimum velocity and shear stress, which is the final cause of its stability.…”

“…This is the common interval of gradient found in check dam interventions (Heede, 1978;Nameghi et al, 2008), flume experiments (Abrahams et al, 1995;Comiti et al, 2009) and step-pool systems (e.g. Zimmerman and Church, 2001;Chartrand et al, 2011); c. check dam effective height z between 0.5-1.5 m, typical of control structures in agricultural areas (Heede, 1978;Nyssen et al, 2004;Nameghi et al, 2008); d. channel roughness ranging from 0.03 to 0.06, from clean and straight to weedy winding channels (Chow et al, 1994).…”

Delineating incised stream sediment sources within a San Francisco Bay tributary basin

“…Where appropriate, sediment storage from incised streams could also be promoted with check dams (Geyik, 1986) and stone weirs (Shields et al, 1995), or more natural analogs using large wood (Shields et al, 2003), beaver dams (Pollack et al, 2014), and Native American techniques (Norton et al, 2002). In the Arroyo Mocho watershed, initial strategies to reduce erosion from incised channels include construction of a step pool channel (Chin et al, 2009), sediment retention ponds, and earthen check dams that also serve as cattle ponds (Bigelow et al, 2012a). In addition to sediment supply and sediment storage potential, practitioners should also consider the causes, current evolutionary stage, and history of channel incision within the watershed when determining the location of restoration projects to promote sediment storage (Schumm, 1999).…”

On kinematics and flow velocity prediction in step‐pool channels

“…These morphological units are able to almost maximize the energy losses due to the high flow resistance they generate [Whittaker and Jaeggi, 1982;Abrahams et al, 1995]. The analogies between step-pool/rapid sequences and engineered structures [e.g., consolidation check dams, bed sills, grade control structures, and ramps] have motivated investigations of naturally steep channels [Chin et al, 2009]. Steps contribute to the reduction of the mean energy slope mainly through the vertical flow drop that promotes a tumbling flow regime [Peterson and Mohanty, 1960] with a critical or supercritical jet flow over the step lip and subcritical dissipative flow in the pool [Zimmermann and Church, 2001;Wohl and Thompson, 2000].…”