Strategy of modelling with MARS3D and a problem statement

Transcription

1 Numerical simulation of currents driven by the main forcing mechanisms: wind, barometric pressure, timedependent marine inflow (with tide) and fresh water inflow in the Berre lagoon 15 March 2011 M2P2 Financial support:

2 Strategy of modelling with MARS3D and a problem statement MARS is a coastal hydrodynamical model developped by IFREMER (French Research Institute for the Exploitation of the Sea) Rang 3 Rang Rang 0 Ra ng Global domain of computation (Conf1) and Local zooming: beach of the Pointe of Berre (Conf2) 2 Conf 2. Conf1: main map of Berre lagoon - grid 377*356 (each 50 m), Conf 1. Conf2: zoomed map for the region of Pointe de Berre grid 242*87 (each 1 m)

3 General conditions for Conf1 Fresh water inflow: - Rivers: Arc (15 m 3 /s), Touloubre (15 m 3 /s) - EDF channel (0 m 3 /s, 50 m 3 /s, 125 m 3 /s, 250 m 3 /s) Marine water inflow at the entrance of Caronte Channel (sea level, accounting for tide, barometric pressure and wind effect on the sea) - sinusoidal law: with a max amplitude of 0.3 m, or - time-dependent data given from maregrams (Port de la Lèque; PAM) Wind forcing (N-NW, W, S-SE) Discretization: 4-16 layers Time of simulation: 1-4 days Transition time : 2 days Conf 1. - to establish permanent Bathymetry solution for non-tidal effect, or - to establish periodical solution in case of tidal effect Saving open boundary conditions for a zoomed map of Pointe of Berre

4 Conf 1.Tidal effect. No Wind, EDF inflow. xe( t) = 0.3cos(2 π( t tdeb )/44712) Dependency for tides in the open boundary: Where xe free surface level, tdeb- time of the beginning of simulation correspond to the tidal period equal to 12h 25.2 min Comments: Numerical results are coherent with observations given by RAMADE (1997): tidal effect have 4-5 times less amplitude inside the lagoon and 4-5 hours delay in comparison with data in the sea

5 Conf 1. Wind effect. No tide, EDF inflow. Three types of wind were chosen for simulation: N-NW, W, S-SE N-NW (currents in the layer near the surface) W S-SE Annual rose of winds N-NW W S-SE

6 Conf 1. EDF-channel inflow. No tide, wind. (currents in the layer near the surface) 250 m 3 /s 125 m 3 /s 50 m 3 /s

7 Conf 2. Wind effect on barotropic currents; with tide. Three types of wind: N-NW, W, S-SE ; N-NW W Rose of winds N-NW W S-SE S-SE

8 Conf 2. Tidal effect. Pointe de Berre. No wind. Dependency for tides : xe( t) = 0.3cos(2 π ( t tdeb) /44712) Where xe free surface level, tdeb- time of the beginning of simulation Barotropic currents and kinetic energy (color palette) with contour of bathymetry 4 hours 10 hours 7 hours 13 hours

9 Conf 2. Point of Berre TIDE + WIND(MISTRAL) currents in the layer near the bottom (20-40 cm from the bottom) Measured position of zostera noltii (Samuel Meulé, 2007)

10 Wave attenuation by seagrass beds r o u g h n e s in s e a g r a s s z 0 = f ( N, l, d ) C h e n e t a l, N e p f e t a l. 2 l le n g h o f s e a g r a s s, N n u m b e r p e r m, d d i a m e t e r Time evolution of x and y - components of velocity (black line 1 m before entrance in rectangle with seagrass, red line in the entrance of seagrass, green line 1 m after entrance in the seagrass, blue line 2 m after entrance in the seagrass, light blue line 3 m after entrance in the seagrass, rose line 4 m after entrance in the seagrass) x - component of velocity Analyzing pictures of bottom currents (previous slide) we clearly see the evolution of the wave attenuation. In the area of the seagrass vector decrease their value and increase it again out of this area. y - component of velocity According to graphics of x and y velocity s components we see that inside the seagrass area meter after meter velocity components decreasing their values, wave propagate in the seagrass area and 4 meters after decreases twice time the value, which was in the area without seagrass. Larger seagrass bed width in the direction of wave propagation results in higher wave attenuation and less energy on the shoreline. Wave attenuation by seagrass may have implications for shoreline protection.

11 For the open boundary we use condition with the angle of coming wave front: Wave propagation in the Point of Berre x( x, y, t) = a cos( wt - k( x - x )cos a - k( y - y )sin a) 0 0 w ( k) = gk th( kh ) ( x, y ) - initial position of the wave front s Using aerophotos we took for the wave: l = 12m k p w = T = = p 6

12 Perspective Projet fiche action contrat Herbiers M2P2,TIT(Russie), IRPHE, CEREGE, L. Saint-Venant, EDF, GIPREB Lot 1 : Construction et calage d un modèle spectral d états de mer sur l ensemble de l étang de Berre Lot 2 : Construction d un modèle local sur la Pointe de Berre, couplé hydrodynamique-vagues Lot 3 : Méthodologie pour l établissement des conditions aux limites du modèle de courantologie local Lot 4 : Mise en œuvre et validation de la chaîne complète (avec CEREGE) Lot 5 : Prise en compte de la présence de zones d herbiers dans les modèles numériques Lot 6 : Identification de seuils critiques permettant d envisager l a recolonisation par les herbiers Lot 9 Étude expérimentale exploratoire ( interaction vagues-courants-herbiers (lot 5) dans la grande soufflerie des échanges airmer de l IRPHE Lot 7 : Tests avec la chaîne de modélisation de solutions envisageables pour favoriser la recolonisation par les herbiers Lot 8 Aérophotos caractérisation de l état de surface marine locale (Pointe de Berre) Calage code ARTEMIS