Two-dimensional morphological simulation in transcritical flow RCEM 2005 Urbana, October 5, José A. Vásquez (UBC) Robert G. Millar (UBC) Peter M. Steffler (UoA) University of British Columbia (UBC), Vancouver, Canada University of Alberta (UoA), Edmonton, Canada

Previous applications:Previous applications: –Bed aggradation and degradation –Meander scour and deposition. –Alternate bars in straight channels. –Dam-break. Knickpoint migration:Knickpoint migration: –Importance –Results of the model 2D FE morphodynamic model

www. River2D.ca 2D Hydrodynamic model. Computes u, v and h. Developed by U of Alberta. Finite Elements. Sub- and supercritical flows. Steady and unsteady flows. Freely available. Very robust and stable. Handles partially wet areas. FIXED BED.

The Exner Equation (bedload sediment continuity) porosity porosity z b bed elevation (m) q s sediment transport rate (m 2 /s) For a 1D reach of length  x in a time interval  t: Aggradation (deposition) Degradation (erosion)

Bed aggradation due to sediment over- loading (Soni et al. 1980) Bed Degradation by shut-off of sediment supply

Bend scour

The Waal River (The Netherlands) Deposition Erosion Deposition

Initiation of Alternate Bars in a straight flume B/H = 34 Fr = 0.69 S = 0.452%

Dam break 1 m 0.4 m DAM Q = 1 m 3 /s 0.40 m 0.12 m INITIALLY WETINITIALLY DRY Leal et al. 2003

Point of sudden change in the bed slope. Examples:Point of sudden change in the bed slope. Examples: –Meander cut-offs –Dam removal –Bed dredging Knickpoints Cantelli et al Cui and Wilcock, in press

Knickpoint migration in tidal flat (Vancouver, Canada)

Experiment of Nickpoint Migration (Brush and Wolman 1960) S o = 10% S o = 0.125% Hydraulic Jump Knickpoint WSE bed

Experiment of Nickpoint Migration (First 6 minutes...) S o = 10% S o = 0.125% Hydraulic Jump Knickpoint WSE bed

Experiment of Nickpoint Migration (Measurements at 160 minutes) Knickpoint WSE bed

Qualitative dyke-breach test (Unsteady flow) WSE bed

River2D-MORphology is a 2D model based on triangular FE with capabilities for transcritical flow morphology.River2D-MORphology is a 2D model based on triangular FE with capabilities for transcritical flow morphology. The potential of the model in this field are:The potential of the model in this field are: –Dam removal –Dam-break –Dyke breach The model also have capabilities for secondary flow in bends and transversal bed correction.The model also have capabilities for secondary flow in bends and transversal bed correction. In summary

In some problems of transcritical morphology 2D effects such as sand bars, meandering, channel widening might be important (e.g tidal flat, dam removal in meandering river) that do not warrant the application of a 1D model.In some problems of transcritical morphology 2D effects such as sand bars, meandering, channel widening might be important (e.g tidal flat, dam removal in meandering river) that do not warrant the application of a 1D model. Present limitations:Present limitations: –Uniform bed material sediment. –Lack of numerical upwinding (not good for sediment waves)....in summary