Research group
River and delta morphodynamics
Tjalling de Haas and Maarten G. Kleinhans
tjallingdehaas@gmail.com
Stability of river bifurcations from bedload to suspended load dominated conditions
Introduction
• Bifurcations unstable?
• Difference between gravel- and sand-bed rivers?
• see posters Marra et al. EP31C-0749 Wednesday 8:00 am, Lavooi et al. EP51C- 0560 Friday 8:00 am, talk Gupta et al. EP24B-06 Tuesday 4:00 pm
Model
•1D network model with Y-shaped bifurcation:
•Gradually varied flow, bedload transport and morphological change
•Width: f(Q), mass conserved
•Flow and sediment division: transverse slope effect and spiral flow effect caused by bend
Results
References
Bertoldi, W., Tubino, M., 2007. River bifurcations: Experimental observation on equilibrium configurations.
Water Resources Research 43, W10437
De Haas, T., 2010. Network dynamics and origin of anastomosis, upper Columbia River, British Columbia, Canada. Msc Thesis, Utrecht University
Edmonds, D.A., Slingerland, R.L., 2008. Stability of delta distributary networks and their bifurcations. Water resources research 44, W09426
Kleinhans, M.G., Jagers, H.R.A., Mosselman, E., Sloff, C.J., 2008. Bifurcation dynamics and avulsion duration in meandering rivers by one-dimensional and three-dimensional models. Water resources research 44, W08454
Problem definition
•Opposite trend gravel- and sand-bed rivers
•Hypothesis: connected by optimum?
Model scenarios
• Bifurcations unbalanced:
1.Bend at bifurcation 2.Gradient advantage
• Mobility increased:
a.Discharge
b.Channel gradient c.Particle size
• Sediment transport
___ Including threshold for sediment motion
_ _ Excluding threshold for sediment motion
Anastomosing River (Columbia River) River delta (Cumberland Marshes) Braided River (Tagliamento River) Meandering River (Rhine River)
Optimum
Acknowledgements
•Netherlands Organisation of Scientific Research (NWO) (grant ALW-Vidi-864.08.007 to Dr. Maarten G. Kleinhans)
•Molengraaff Funding
•Thanks to E. Lavooi, Dr. B. Makaske, prof. D.G. Smith and W.M. van Dijk for their help during the fieldwork
transverse slope effect
spiral
flow effect backwater
effect
Q
H
ks D i
W
H
backwater effect
Shear stress
vector flow
vector
Width = discharge
channel
channel
Conclusions
•Threshold for motion Optimum
•Gravel-bed rivers Shields stress lower than optimum
•Sand-bed rivers Shields stress higher than optimum
•Opposite trend explained!
0 0,2 0,4 0,6 0,8 1
0 0,5 1 1,5 2 2,5
Shields stress
discharge/area ratio
Experimental braided rivers (Bertoldi and Tubino, 2007) Upper Columbia River (De Haas, 2010)
Cumberland Marches (De Haas, 2010)
Delft3D modeled bifurcations (Edmonds and Slingerland, 2008)
Symmetric
Asymmetric
Gravel-bed Sand-bed
