Morphodynamic modeling of aeolian sediment landscapes with regard to the stabilization of shifting sands

Transcription

1 Morphodynamic modeling of aeolian sediment landscapes with regard to the stabilization of shifting sands Eric J. R. Parteli 1, Orencio Durán 2, Hans Herrmann 3, Haim Tsoar 4 1. Institute for Multiscale Simulation, University of Erlangen-Nuremberg, Germany, Eric.Parteli@fau.de 2. MARUM, Bremen, Germany; 3. ETH Zürich, Switzerland; 4. Ben-Gurion University, Beer Sheva, Israel Nouakchott Brazil NASA UK NASA Kenneth Pye

2 Morphodynamic model for aeolian sediment landscapes Model description Well-established mathematical model by Jackson and Hunt (1975) 1) Turbulent wind field over the topography The hill modifies the shear stress over the flat ground, t 0. The resulting shear stress reads, wind shear stress flow separation z 0 = aerodynamic roughness; 2L = hill s width at half height. 2) aeolian sediment flux 3) Profile update & avalanches; final surface 2 Free download: 1. Kroy, Sauermann, Herrmann, Phys. Rev. Lett. 88, (2002) 2. Durán, Parteli, Herrmann, Earth Surf. Proc. Landforms 35, 1591 (2010) Depression before and after the hill Asymmetry: upwind shift of the maximum P. S. Jackson and J. C. R. Hunt, Q. J. R. Meteorol. Soc. 101, 929 (1975)

3 Morphodynamic model for aeolian sediment landscapes Model description Flow separation occurs at sharp brinks 1) Turbulent wind field over the topography 1. smoke release 2. CFD simulation wind shear stress flow separation 2) aeolian sediment flux Haim Tsoar Univ. of the Negev Gerd Sauermann Univ. Stuttgart 3. subaqueous dune (exp.) Ingo Rehberg Univ. Bayreuth 3) Profile update & avalanches; final surface Shear stress calculated over the envelope comprising sand topography & separation streamline: Free download: wind Flow separation streamline 3 1. Kroy, Sauermann, Herrmann, Phys. Rev. Lett. 88, (2002) 2. Durán, Parteli, Herrmann, Earth Surf. Proc. Landforms 35, 1591 (2010)

4 Morphodynamic model for aeolian sediment landscapes Model description Saltation 1) Turbulent wind field over the topography Movie: Eric Parteli wind shear stress flow separation 2) aeolian sediment flux 3) Profile update & avalanches; final surface Transport occurs only if the wind shear stress t(x) exceeds the minimal threshold t th The particle mass flux (q) changes downwind according to the logistic equation of population growth: 4 Free download: 1. Kroy, Sauermann, Herrmann, Phys. Rev. Lett. 88, (2002) 2. Durán, Parteli, Herrmann, Earth Surf. Proc. Landforms 35, 1591 (2010) (saturation length) (saturated flux)

5 Morphodynamic model for aeolian sediment landscapes Model description 1) Turbulent wind field over the topography a) Local height evolves in time following the Exner equation wind shear stress flow separation ìï í îï Erosion Deposition üï ý þï wherever the mass flux q ìï í îï increases decreases üï ý þï downwind. 2) aeolian sediment flux 3) Profile update & avalanches; final surface b) If the local slope exceeds q r 34, then the surface relaxes through avalanches in the direction of the steepest descent. Free download: Kroy, Sauermann, Herrmann, Phys. Rev. Lett. 88, (2002) 2. Durán, Parteli, Herrmann, Earth Surf. Proc. Landforms 35, 1591 (2010)

6 Morphodynamic model for aeolian sediment landscapes Model description 1) Turbulent wind field over the topography a) Local height evolves in time following the Exner equation wind shear stress flow separation ìï í îï Erosion Deposition üï ý þï wherever the mass flux q ìï í îï increases decreases üï ý þï downwind. 2) aeolian sediment flux 3) Profile update & avalanches; final surface b) If the local slope exceeds q r 34, then the surface relaxes through avalanches in the direction of the steepest descent. Free download: Kroy, Sauermann, Herrmann, Phys. Rev. Lett. 88, (2002) 2. Durán, Parteli, Herrmann, Earth Surf. Proc. Landforms 35, 1591 (2010)

7 Simulation vs measurements simulation real dune Model parameters: grain mean diameter and density wind velocity (time series, direction) surface roughness (as well as gravity, air density and viscosity) For a review: Durán, Parteli, Herrmann, Earth Surf. Proc. Landforms 35, 1591 (2010) along-wind profile cross-wind profile 7 wind velocity profile sand flux profile

8 Topography and bedform interactions collisions between dunes of different sizes simulation image Movie by Orencio Durán topography simulation 8 Parteli, Durán, Bourke, Tsoar, Pöschel, Herrmann, Aeolian Research 12, 121 (2014) image simulation

9 Genesis of an aeolian sediment landscape Lençóis Maranhenses, Brazil 9 Parteli, Schwämmle, Herrmann, Monteiro, Maia, Geomorphology 81, 29 (2006)

10 Genesis of an aeolian sediment landscape 10 Durán, Parteli, Hermann, Earth Surf. Proc. Landforms 35, 1591 (2010) Parteli, Andrade, Herrmann, Physical Review Letters 107, (2011) Movie by Orencio Durán

11 Dynamic wind regimes changing wind intensity Dune advance in presence of an exposed water table Lençóis Maranhenses, Brazil barchanoids October simulation March 11 Local rainfall and wind velocity image simulation Luna, Parteli, Hermann, Geomorphology 159/160, (2012)

12 Dynamic wind regimes changing wind direction Seif dunes images simulations simulation Nouakchott image Sinai 12 Parteli et al., PNAS 106, (2009) Parteli et al., Aeolian Res. 12, 121 (2014)

13 Stabilization of shifting sands Crude oil Bulldozing dune sand in Morocco Transition from a mobile barchan to a stabilized dome dune after spreading crude oil on the dune surface Sketch by Kerr and Nigra, Am. Assoc. Pet. Geol. Bull. 36, 1541 (1952) simulation 13 Schatz, Tsoar, Edgett, Parteli, Herrmann, J. Geophys. Res. 111, E04006 (2006)

14 Stabilization of shifting sands - vegetation Model simulation images 1. vegetation growth 2. shear stress partition RAUPACH et al. J. Geo. Res.96 (1993) Q = 3.5 Brazil Q = 0.47 Brazil Dune stabilization if Q < 0.5 White Sands, USA Q = 0.16 White Sands Broughton Islands Simulation of barchan-parabolic transition, Q = 0.22 Q = Durán, Herrmann, PRL 97, (2006) Luna, Parteli, Durán, Herrmann, Geomorphology 129, 215 (2011)

15 Dune du Pilat, France Response to wind and climate changes Collaboration with Gonéri Le Cozannet & Héloise Müller 15 Gabarrou, Le Cozannet, Parteli, Pedreros, Oliveros, Mallet (2014, submitted)

16 Stabilization of shifting sands biogenic crusts dune surface Amir et al. (2014) DFG (2004) drylandresearch.de Linear dunes at Nizzana, Negev desert, Israel sand, vegetation and biogenic crust Model ingredients: biogenic crust cover growth rate threshold wind velocity in presence of the crust vegetation biogenic crust interaction rainfall, evapotranspiration Collaboration with Haim Tsoar Yosef Ashkenazy Gershon Hanoch 16 (outlook)

17 Stabilization of shifting sands sand fences CFD calculation of the wind shear stress over a landscape with fences Morphodynamic evolution of the sand landscape Brushwood fence, Formby, Merseyside, UK Photo credit: Kenneth Pye Project s goals: Predict fence s effect on the long-term terrain evolution Optimize fence design, porosity, height, number and spacing according to wind and vegetation conditions Collaboration with Ascânio Araújo, Uni Fortaleza, Brazil Hans Herrmann, ETH Zürich, Switzerland 17 (ongoing research)

18 Thank you for your attention! 18