Double-Averaging Concept for Rough-Bed Open-Channel and Overland Flows: Theoretical Background

Vladimir Ivanovich Nikora, Ian Kenneth McEwan, Stephen McLean, Stephen Coleman, Dubravka Pokrajac, Roy Walters

Research output: Contribution to journalArticlepeer-review

310 Citations (Scopus)


The goal of this paper is to discuss the spatial averaging concept in environmental hydraulics and develop it further by considering transport equations for fluid momentum, passive substances, and suspended sediments. The averaging theorems, the double-averaged (in time and in space) fluid momentum equation, and advection-diffusion equations for a passive substance and suspended sediments are introduced and their limitations and applications for modeling rough-bed flows, experimental design, and data interpretation are discussed. The suggested equations differ from those considered in terrestrial canopy aerodynamics and porous media hydrodynamics by accounting for roughness mobility, change in roughness density in space and time, and particle settling effects for the case of suspended sediments. We show that the form of the double-averaged equations may depend on the type of decomposition of flow variables and that this difference may have important implications for modeling. We also show that the suggested methodology offers better definitions for hydraulic characteristics, variables, and parameters such as flow uniformity, flow two dimensionality, and bed shear stress.

Original languageEnglish
Pages (from-to)873-882
Number of pages10
JournalJournal of Hydraulic Engineering
Issue number8
Publication statusPublished - Aug 2007


  • turbulent kinetic-energy
  • porous-media
  • velocity distribution
  • incompressible-flow
  • momentum-transfer
  • canopy flows
  • mean flow
  • model
  • vegetation
  • closure


Dive into the research topics of 'Double-Averaging Concept for Rough-Bed Open-Channel and Overland Flows: Theoretical Background'. Together they form a unique fingerprint.

Cite this