First steps in the implementation of a sediment transport model in the Ebro Delta Continental Shelf (Catalan Sea) UPC - LIM - Juan Fernandez, Manuel Espino, Vicenç Gracia, Gabriel Jordà, Agustin Sanchez-Arcilla

Objectives of the Presentation   S7.3.1 Data: Inventory of needs and availability – Ebro Delta Continental Shelf   S7.3.2 Sedimentary modelling - Ebro Delta Continental Shelf   Description of work carried out   Data gathering process   First model implementations   Future work   Revision of State of the Art Formulation for Sediment Transport Modelling outside the Surf Zone (D ). Input from several partners. Almost completed.

Field Site Area  Ebro Delta Continental Shelf  West Mediterranean Sea  135 km south of Barcelona  Ebro shelf in transition zone Figure 1 – Ebro Delta location (Durand et al. 2002)

Oceanographic Characteristics - Driving terms   Ebro Continental shelf is becoming more wave dominated   Water level increase can shift this. Figure 2 - Delta classification as a function of dominant dynamical processes (Sanchez-Arcilla and Jimenez, 1997)

Oceanographic Characteristics - Driving terms   Ebro River – –Highest water discharge rates and biggest hydrological catchment in the Iberian peninsula – –Highly regulated watercourse (dams) Figure 3 – Ebro Daily Discharge at Tortosa (FANS project)

Oceanographic Characteristics - Driving terms   Waves – –Most energetic forcing agent acting in the coastal zone – –‘Energetic’ period, from October till March – –Most persistent waves are from eastern (25%) and southeastern (20%) directions. – –Wave periods range between 2 and 10 s and heights are lower than 4.0m for 98% of the time. – –Storm waves - significant wave height exceeds 1.5 m Figure 4 – Directional distribution of waves at Cap Tortosa (Jiménez, 1996).

Oceanographic Characteristics - Driving terms   Tides – Mean water level – –Semidiurnal micro-tide area – –Maximum tidal range of around 0.25m – –Water level changes due to meteorological effects can be in excess of 0.5m. – –Meteorological tide is relatively frequent in the study area. – –These events can occur simultaneously

Oceanographic Characteristics - Driving terms   Currents – –Wind main physical forcing – –Southerly and south-westerly wind prevail during summer and northwest winds during winter – –Northern current

Bottom Sediment Characterisation   Inner zone (from the beach to 7m), medium and small size sands, diameter no greater than 125 µm.   Mid-zone (7m to 10-15m) smaller sands diameters from 63 to 125 µm.   Mud belt.   Offshore, surface sediment consists of relict transgressive sand Figure 5 – Distribution of sediment types (Diaz et al, 1990)

Bottom Sediment Characterisation Figure 6 – Ebro Delta Continental Shelf bathymetry and grain size   A grain size distribution map is being constructed for the following grain classes and their corresponding D50: – –I clay: 2µm – –II silt: 15µm – –III fine sands: 75µm – –IV coarser sands:125µm – –V cohesive sediments: 140µm

Grain size Distribution   Several sources have already been consulted: – –Core survey information from several locations (Guillén et al. 2005). – –Percentage maps for sands, silts and clays (Callis et al. 1988) – –Percentage maps for particles greater than 40µm (Callis et al. 1988) – –Mean grain size maps for the whole Ebro continental shelf. Figure 7 – Spatial percentage distribution for Clay (Callis et al. 1988) Figure 9 – Spatial percentage distribution for particles greater than 40µm (Callis et al. 1988) Figure 8 – Cross-shore profile and mean grain size of bottom sediment (Guillén et al. 2005)

Symphonie   Developed in the Pole d’Oceanographie Cotiere in Toulouse (France)   3D primitive equation model of the coastal ocean.   Hybrid vertical coordinates sigma-z   Full air-sea interactions   Implemented and validated in different coastal and ROFI areas symphonie/symphonie.htm

  STRADA (Simulations du TRAnsport par Diffusion Advection).   Settling velocity: (after Ulses et al. (2007)) the Stoke’s Law or Zanke formula for non-cohesive and Agrawal and Pottsmith for aggregates – –Stoke’s Law – –Zanke (1977) – –Agrawal and Pottsmith (2000) Formulation

  Bottom shear stress. Current and waves. After Soulsby et al. (1993). – –Current – –Waves   Possibility of bed armouring: following Harris and Wiberg (2001).Thickness of active layer: – –Sandy beds (bed-form) – –Silty beds Formulation

  Erosion non-cohesive formulation: Flux – F=fw s C(z 1 )ρ; for C(z 1 ), choice of – –Smith and McLean (1977): semi-empirical relation for the bed concentration. Rouse profilefor, or for whereand with a reference height of – –Zysermann and Fredsoe (1994): empirical model with a reference height of   Erosion cohesive formulation: choice of following – –Mehta: – –Partheniades:, for and otherwise. Formulation

Available information   A whole inventory of the available data necessary for the modelling stage for the Ebro Continental Shelf was carried out. – –EU-MAST III – Project FANS. MAS3-CT ( ) – –TRASEDVE projects (1999 – National project) – –Previous PhD reports (Gracia and Jordà)

FANS – –Spatial superficial suspended sediment concentration measures were taken around the Ebro River Plume. – –Two instrumented bottom boundary layer tripods were placed at 8.5m and 12.0m measuring suspended sediment concentration at three different depths – –Two RCM07 meters coupled with transmissometers were placed at 60m and 100m depth to measure suspended sediment transport at 5m above the seabed at the mid and outer shelf.  Sediment transport measures were carried out using three different approaches in three areas Figure 10 – EU-MAST-III Project FANS instrumented locations

FANS   Data from the mentioned locations were examined Figure 12 – EU-MAST-III Project FANS sediment transport measures location Figure 11 – Tripods location

Event selection strategy   Events were selected depending on: – –Data availability – –Driving terms   River influence   Waves   Wind – –Significant sediment transport measured

Event description   River Plume example case: – –6-7 February 1997: supercritical river plume conditions with a high river discharge and varying wind conditions. Figure 13 – Wind and discharge conditions during February Figure 14 – Wind rose for the February event Constant discharges of 880m 3 /s

Event description   Inner shelf area example case: 26 December 1996 – 3 January 1997: High discharge from the Ebro River and high wave energy. Figure 16 – Driving terms for the first tripod eventFigure 15 – SSC for the three OBS sensors during the first tripod event

Event description   Mid and outer shelf area example case: 3-9 November 1996: significant transportation and low wave energy period Figure 17 – Driving terms for the RCM07 events

First results – Plume Events   The sediment transport model has been initially implemented around the Ebro river mouth.   POC Pole d’Oceanographie Cotiere in Toulouse collaboration.   Four plume events have been modelled and analysed.   Results have been compared to measured concentration and to satellite images (qualitative).

  6-7 February 1997 simulation Flow rates around 880m 3 /s Varying wind conditions Figure 21 – Modelling results and satellite image Landsat-TM (Channel 2, visible green) for the February simulation First results – Plume Events Figure 20 – Wind conditions for the February event

  6-16 July 1997 simulation Flow rates from 220 to 120m 3 /s Constant wind conditions Figure 23 – Modelling results and satellite image Landsat-TM (Channel 2, visible green) for the July simulation First results – Plume Events Figure 22 – Wind conditions for the July event

Next steps   Sediment transport modelling (V0) for the tripods and RCM07 areas   Sediment transport modelling (V0) of the whole Ebro Delta Continental Shelf   Results analysis   Improvement of the sediment transport module (V1)   Target Operational Period (TOP) model