Hydraulic design of riffles in gravel‐cobble bed Rivers

Abstract

The reintroduction of riffle‐pool sequences has increasingly been promoted as an appropriate rehabilitation alternative for the re‐naturalization of modified gravel‐bed channels. However, in the absence of hydraulic design guidelines, enhancement efforts often fail to evaluate the subsequent impacts to flood levels and sediment transport capacity. This paper describes a new hydraulic design procedure developed for the evaluation of constructed riffles in steep gravel‐cobble bed streams. The procedure addresses specific design issues such as riffle location, configuration, amplitude, stability, and the associated effects on flow resistance, sediment transport efficiency, flood capacity, and aquatic habitat. With this approach, project reach design profiles can be developed for individual catchment and reach characteristics, governing fluvial processes, and specific rehabilitation goals and objectives. Used in association with proper geomorphic, hydraulic, hydrologic and ecologic appraisal, the proposed procedure should therefore represent a valuable resource in the design and rehabilitation of riffle‐pool sequences in steep uniform, channelized or incised gravel‐cobble bed rivers.

Keywords:

• Riffle‐pool sequences
• hydraulics
• design
• flood levels
• sediment transport