A Unit-Scale Framework for Designing Step-Pool Sequences

Artificial step-pool sequences have long been used in river restoration projects worldwide for channel stabilization and ecological improvement. However, previously used design methods for artificial step-pools are problematic in that the designed sequences may not fulfil restoration objectives and fail. We propose a new design framework consisting of five modules based on the morphological evolution, energy dissipation, hydraulics, and stability of step-pools. This new framework focuses on individual units instead of a reach or subreaches as done in previous approaches, allowing for greater design flexibility. A detailed description of the new unit-scale design framework is presented in this paper with step-by-step procedures and recommended criteria for design evaluation. The new framework is then applied to three mountain streams to evaluate existing artificial and natural step-pool sequences. Finally, advantages and limitations of the framework and insights for restoration of mountain streams are reviewed.