Modeling of the interactions of the cohesive sediments with the Mangrove Sylvain Guillou University of Caen Normandy Applied sciences laboratory of Cherbourg, LUSAC, EA4253 50130 Cherbourg-Octeville, France LMDCZ Workshop, April 2017

Mangrove slows down the flow inside Modeling of the interaction of the cohesive sediments with the Mangrove Mangrove is in mud areas Mangrove slows down the flow inside Mangrove are on the edge of the area are more exposed to the attack of the waves and the flow 2

Fluid mud Soft mud Compact mud Introduction Transport Flocculation Cohesive sediment: Physical phenomenon Transport Flocculation Deposition Erosion Entraînement arrachement de copeaux Fluid mud Soft mud Compact mud Transport Exchanges Evolutions 3

SPM transportation Surface : bottom : Cohesive sediment: reservoir Flocculation Deposition Erosion Transport bottom Non erodible bed : components of the fluid velocity : vertical and horizontal diffusivity : Concentration in SPM C u,v,w : settling velocity Ws KMC, AMC : Erosion and deposition fluxes Fe, Fd Surface : bottom : 4

Falling velocity for cohesive sediments SPM transportation Cohesive sediment: reservoir Flocculation Deposition Erosion Transport Falling velocity for cohesive sediments bottom Non erodible bed Deposition flux : Deposit critical shear stress cd ce : Erosion critical shear stress b : Bed shear stress Krone(1962) Erosion flux Partheniades (1962) 5

Consolidation Cohesive sediment: 𝜏 𝑐𝑒 6

Multi-layer model Consolidation Teisson (1993) Cohesive sediment: 7 mud Flocculation Deposition Erosion Transport bottom non erodible bed Multi-layer model C1 C2 C3 C4 C5 C6 e1 e2 e3 e4 e5 e6 t1 t2 t3 t4 t5 t6 C1 C2 C3 C4 C5 C6 Teisson (1993) 7

Multi-layer model Consolidation Teisson (1993) Teisson (1993) Cohesive sediment: Model based on the time residence C1 C2 C3 C4 C5 C6 e1 e2 e3 e4 e5 e6 t1 t2 t3 t4 t5 t6 C1 C2 C3 C4 C5 C6 mud Flocculation Deposition Erosion Transport bottom non erodible bed Teisson (1993) Teisson (1993) 8

Consolidation Cohesive sediment: Model based on the time residence 9

Expulsion of the interstitial water (permeability) Consolidation Cohesive sediment: Model coming from soil mechanics Théorie de Kynch, Gibson, Tan, ... Gibson’s equation : Expulsion of the interstitial water (permeability) Structuration of the mud (effective stresses) 10

Calculation of the flux between two layers Consolidation Cohesive sediment: Multilayer based on the Gibson equation Thickness of a layer : Calculation of the flux between two layers Particles’ velocity : Darcy’s law, Postulat of Terzaghi, Continuity Hypothesis : There exists one transitional concentration Ct between sedimentation and consolidation (Thiebôt and guillou, 2006) 11

Consolidation Cohesive sediment: Multilayer based on the Gibson equation Thiébôt and Guillou, 2006. 12

Consolidation Experimental mass concentration profiles (blue line, from Bartholomeeusen et al., 2002 ) and simulated sediment mass concentration profiles (stepped profiles in green from Thiébot, Guillou, Brun-Cottan, CSR, 2011). 13

Consolidation Cohesive sediment: Intercomparison of models Phd of Lan Anh Van (Numerical modelling of sand-mud mixtures settling and transport processes : Application to morphodynamic of the Gironde estuary (France), LHSV, LNHE Model 1 : Faster Development of a process to calculate the transfer coefficient Model 2 (Gibson eq.): more physic: Effective stress, permeability Need the determination of the effective stress and the permeability 14

Cohesif/non cohesive Sediment in TELEMAC Cohesive sediment: The two models have been implemented in SISYPHE and are available in the open source code Mixture can be considered: two modes: non cohesive sediment of mean diameter Dns and a cohesive sediment of diameter less than 60 m Coupling of hydrodynamic, waves and Sediments evolutions (TELEMAC, TOMAWAC, SISYPHE) Mixture Sisyphe user’s manual 15

Interactions with the Manvrove Mangrove is a vegetation with small diameter regarding the size of the area It could be considered as a resistant force a porous media S. Guillou@ Laboratoire de Construction Hydraulique, EPFL 16

Interactions with the Mangrove Mangrove is a vegetation with small diameter regarding the size of the area It could be considered as a resistant force to the flow a porous media Laboratoire de Construction Hydraulique, EPFL 17

Interactions with the Mangrove Mangrove is a vegetation with small diameter regarding the size of the area It could be considered as a resistant force to the flow a porous media Porosity J. Lhomme, S. Soares-frazão, V. Guinot, Y. Zech, Large scale modelling of urban floods and 2D shallow-water model with porosity, LHB, 2007. 18

Interactions with the Mangrove Mangrove is a vegetation with small diameter regarding the size of the area It could be considered as a resistant force to the flow a porous media J. Lhomme, S. Soares-frazão, V. Guinot, Y. Zech, Large scale modelling of urban floods and 2D shallow-water model with porosity, LHB, 2007. 19

Simulate the impact of the waves on the mud (TOMAWAC) Modeling of the interactions of the cohesive sediments with the Mangrove Cohesive sediment with sedimentation-consolidation process (SISYPHE): Model 1 Modelling the impact of the vegetation on the flow in the mangrove with a porous approach (TELEMAC) Simulate the impact of the waves on the mud (TOMAWAC) 20

Modeling of the interaction of the cohesive sediments with the Mangrove Modelling could be like that: Mesh produced by Thong Definition of: Mud bed composition per zone Consolidation model: Ci, Ai, Ti, Tauci SPM model: Settling velocity Zones of Mangrove and porosity Tidal flat area 21

Thank you for your attention To be continued LMDCZ Workshop, April 2017