Bottom slope and particle settling matter for turbidity current slumping dynamics!
Slumping regime in lock-release turbidity currents
- Introduction
natural hazards reliable predictive models?
- saline currents, horizontal bottom:
- \(u_{\rm c} \simeq 0.5 u_{0} = 0.5 \sqrt{g' h_{0}}\)
- \(t_{\rm end} \simeq 20 t_{0} = 20 L_{0}/u_{0}\)
- constant prefactors
dynamics of particle-ladden currents on slopes?
- Methods
Systematic parameter space exploration:
- 2 different set ups: \(\theta \in [0^\circ, 15^\circ]\), \(h_{0} \in {20, 30}\) cm
- 5 different particle diameters + saline water
- particle volume fraction \(\phi \in [0.5, 15]~\%\)
Bottom slope increases velocity
Settling decreases regime duration
- Results
Existence of a constant-velocity regime on a sloping bottom slope-induced acceleration occurs later (Birman et al. 2007)
Bottom slope increases this velocity
Settling decreases the constant-velocity regime duration
Current head shape (\(\sim L_{0}\) behind nose) independant of \(\phi\), \(v_{\rm s}\) and \(\theta\)
- Discussion/Perspectives
- Origin of the influence of \(\theta\) on \(\mathcal{F}r\)? (early times)
- How to include this on depth-averaged models ? (to be tested)
- Influence of lock aspect-ratio (\(h_{0}/L_{0}\)) on velocity ?
- What about steady-influx turbidity currents on slopes?
- Definitions
slumping regime: first, constant-velocity, phase of current propagation (see introduction)
\(u_{0} = \sqrt{(\delta\rho/\rho_{\rm f})\phi g h_{0}}\), characteristic slumping velocity
\(\delta\rho = \rho_{\rm p} - \rho_{\rm f}\), excess particle density
\(t_{0} = L_{0}/u_{0}\), characteristic slumping time
\(v_{\rm s}\), particle settling velocity
\(t_{\rm s} = h_{0}/v_{\rm s}\), characteristic settling time