Energy Profiles Across Constructed Riffles

Riffle reconstruction has become an important river rehabilitation technique in disturbed channels. However, design has often lacked sufficient hydraulic analysis to adequately assess the potential effects on flow resistance and flood levels. This paper describes the results of a hydraulic field study of four steep gravel–cobble bed rivers where it was found that the energy loss across natural and constructed riffle–pool sequences varied between 50 and 100% of the total energy loss over a range of high discharges up to, and including bankfull. This demonstrates that riffle reconstruction can influence postrehabilitation flood elevations, and that the additional flow resistance should be an important consideration in design. Importantly, the observed riffle energy loss is found to vary between 0.5 and 1 times the riffle amplitude, and it is proposed that this relationship can be used to account for the additional hydraulic resistance imparted by constructed riffles in the design and analysis of riffle–pool rehabilitation initiatives in steep gravel–cobble bed rivers.