Transient Hydrodynamic Dispersion in Rough Open Channels: Theoretical Analysis of Bed-Form Effects

by Marilena Pannone, Aggregate Professor; Dept. of Environmental Physics and Engineering, Univ. of Basilicata, Viale dell'Ateneo Lucano, 10, Potenza 85100, Italy.,,

Serial Information: Issue 3, Pg. 155-164

Document Type: Journal Paper

Abstract: A stochastic Lagrangian approach is proposed to describe dispersion in a two-dimensional low-regime river flow past random bed undulations characterized by the superposition of periodical and stationary exponential correlations, through a suitable time-dependent coefficient. The resulting dimensionless expression depends on the overall resistance factor, which is proportional to the average Peclet number of the process. A graphical analysis shows that the oscillatory transient originating from the periodic component of the bottom elevation pattern is enhanced by reduced global flow resistance, while relatively more intense tracer spreading is associated with wavelike profiles affected by persistent trendless random noise, which also determines the characteristic time needed by the plume to achieve the asymptotic domain. Numerical simulations, validating the first-order analytical approach in a wide range of heterogeneous bed geometries, are also discussed. A semianalytical procedure is finally suggested for the study of depth-averaged transport processes in real three-dimensional streams, based on the use of the derived dispersion coefficient.

Subject Headings: Hydrodynamics | Bed forms | Stochastic processes | Open channels | Transient response | Flow resistance | Numerical analysis | Transient flow | Load and resistance factor design | Probe instruments | Two-dimensional flow | Flow duration |

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