Workshop May 2015, Toulouse

Transcription

1 Workshop May 2015, Toulouse Salle Lyot, LEGOS Observatoire Midi Pyrénées COASTVAR (ANR) COMODO WAVES (LEFE) Multi scale and multi method study of Coast al Var iability in West Africa and Vietnam The main objectives of COASTVAR is to advance our understanding of tropical nearshore hydro morphodynamic processes, from event to interannual scales, and improve operational tools. Emphasis is given to extreme events and their long term effect, and to swash surf shelf exchanges. The study sites are West Africa and Vietnam. Innovative observational tools (video imagery and drone) will be used in addition to conventional instruments. Forecasting will be based on the ECORS beach evolution predictor, which will be applied for the first time to tropical coastal systems. Another part of the modeling effort is focused on surf shelf processes and exchanges and is on common grounds with the COMODO WAVES LEFE project. In the latter, a test bed is proposed for comparing various modeling approaches: 3D or 2D models, structured or unstructured grid methods, wave averaged or phase resolving models, simplified or full non hydrostatic equations. The primary goal of the COASTVAR/COMODO WAVES kick off meeting is to present the context of the projects, have the participants introduce their planned contribution to some of the topics, and prepare field observations and modeling test cases. Grand Popo 2014 experiment, aerial pict. P. Grandjean (Univ Lyon) LEFE/EC2CO Venue: mip.fr/presentation/acces

2 SCHEDULE Thursday 28th Morning A.M. Introduction 10 11h COASTVAR project (R. Almar) Nha Trang (Thuan/Viet) Saint Louis (M. Sall visio) COMODO WAVES (P. Marchesiello) 11h LEGOS lab seminar: Coastal Processes Research at Water Resources Engineering, Lund University Magnus Larson Lunch 12:00 Thursday 28th Afternoon 1:30 6 P.M. Session 1: Multi scale observation of the nearshore system. pre project outcomes (GPP1&2, NT1&2): Surf zone circulation, swash zone hydro morphodynamics (energy dissipation/reflection and beach equilibrium) Long term forcing and evolution Session 2: Modeling of beach evolution using the ECORS simulator Application to Saint Louis and Nha Trang beaches Impact of extreme events (e.g. typhoon Haiyan 2013) and beach recovery Dinner/Restaurant 20:30: La Braisère, 42 rue Pharaon, TOULOUSE, Friday 29th Morning 9 12 A.M. Session 3: Regional to beach scale 3D ocean wave modeling (COMODO WAVES) 3D/2D models, structured/unstructured grid methods wave averaged/phase resolving models, full non hydrostatic equations. Intrinsic/extrinsic variability Surf shelf exchanges Lunch 13:00 Friday 29th Afternoon 2 4 P.M. Discussion on planned numerical test cases/developments Discussion on planned field observations and specific scientific points

3 DETAILED SCHEDULE OF THE SESSIONS Session Haiyan typhoon impact at Nha Trang beach and recovery under intermediate conditions (results from MOST1, NT1&2 experiments) D.B. Thuan Longshore drift cells on the human impacted Bight of Benin coast, West Africa: Articulations with beach sediment budgets, beach morphodynamics and coastal management E. Anthony Application of remote sensing techniques to measure swash zone dynamics L.P. Almeida Pre COASTVAR main results, an overview R. Almar Experimental investigation of the swash zone at the wave time scale L. Lacaze pause (15h15 15h30) Shoreline evolution on the timescales from hours to decades : complex process based vs simple behaviour orienting modelling B. Castelle Modeling coastal evolution in Vietnam at long and short time scales M. Larson Modeling long term shoreline evolutions and coastal erosion (Tran Hai Yen PhD thesis) E. Barthelemy pause (16h30 16h45) Session 2 Sediment transfers off Grand Popo beach: origin and variability F. Floc h The ECORS beach evolution predictor, application to beaches of Nha Trang and Saint Louis

4 T. Garlan Modeling sediment dynamics around breakwaters in the Hammam Lif littoral (Tunisia) C. Chevalier ROMS AGRIF status for nearshore modeling and morphodynamics, preliminary results on TrucVert experiment R. Benshila Session 3 3D nearshore modeling within COMODO WAVES P. Marchesiello Modelling wave current interactions in tidal inlets X. Bertin Latest news from the COAWST modeling system O. Olabarrieta On the 3D modelling of wave currents interactions A.C Bennis pause An efficient phase resolving approach for wave modelling in the coastal zone P. Bonneton A full 3D non hydrostatic and non boussinesq model F. Auclair Discussion

5 ABSTRACTS Seminar Coastal Processes Research at Water Resources Engineering, Lund University Magnus Larson Since the early 1970s research has been conducted on coastal processes at Water Resources Engineering (WRE), Lund University. From the very beginning, there has been a strong emphasis in this research on mathematical modeling with focus on developing models of direct use to the engineering community. Developed models include the simulation of shoreline evolution, beach profile response, bathymetric change, and long term coastal evolution. The presentation will give a brief overview of the ongoing coastal processes research at WRE, both with regard to mathematical model development and to more detailed studies on physical processes needed for the model development, calibration, and validation Session Haiyan typhoon impact at Nha Trang beach and recovery under intermediate conditions (results from MOST1, NT1&2 experiments) D.B. Thuan Presentation of preliminary results on video based seasonal scale observation of Nha Trang beach and first modeling steps. An emphasis will be given to the 2013 Typhoon (cat 5) Haiyan impact and rapid recovery. Longshore drift cells on the human impacted Bight of Benin coast, West Africa: Articulations with beach sediment budgets, beach morphodynamics and coastal management E. Anthony The Bight of Benin coast is a major sand barrier and lagoon system locked between two major West african river deltas, the Volta and the Niger. Longshore drift cells and their development patterns in the course of the Holocene, derived from the barrier system, provide a template for understanding the current problems of massive erosion or accretion that affect the bight coast. These patterns have interesting implications for original research on the links between medium (order of years) to long term term (order of decades) cell sediment budgets, longshore sand transport, beach morphodynamics, and coastal management. Application of remote sensing techniques to measure swash zone morphodynamics P. Almeida During my PhD (Plymouth University, UK) I worked on the development of a new remote sensing technique (2D laser scanner) to measure swash zone on gravel beaches during extreme conditions. Now I'm in Toulouse (LEGOS) working as a post doc with Rafael Almar on COASTVAR project. The aim of my post doc is to apply remote sensing techniques (video and

6 laser) on the project study sites (e.g., Nha Trang Vietnam) and use these novel datasets to investigate the swash zone morphodynamics during calm and stormy conditions Pre COASTVAR main results, an overview R. Almar Main achievements of preliminary projects MOST1 ( ) at Nha Trang, Vietnam and INSU EC2CO/LEFE ( ) will be presented to provide some insights on the key scientific points, goals and challenges for COASTVAR. 4 intensive experiments were conducted, long term video monitoring and hindcast of wave forcing, longshore sediment transport and shoreline changes Experimental investigation of the swash zone at the wave time scale L. Lacaze A stereoscopic technique has been deployed in a large scale wave flume to measure the sand bed evolution in the swash zone. The waves regimes considered are a random Jonswap spectrum and various bichromatic wave forcing. The present work focuses on the bed evolution at a high temporal and spatial resolution to investigate single wave to wave group time scales Shoreline evolution on the timescales from hours to decades : complex process based vs simple behaviour orienting modelling B. Castelle Shoreline evolution on the timescales from hours to decades : complex process based vs simple behaviour orienting modelling". Abstract: Over the last decade, it has been shown that simple empirically based behaviour oriented models can lead to more reliable long term evolution than do parameterizations of much smaller scale processes in process based models. We will discuss the pros and cons of the 2 modelling strategies with field and laboratory applications. Modeling coastal evolution in Vietnam at long and short time scales M. Larson Water Resources Engineering at Lund University has be involved in research on the coastal evolution in Vietnam and its management for more than 15 years. Initially, work was performed in the Red River Delta focusing on simulating the erosion experienced along certain stretches of the Delta, including both the response during severe storms acting over a few days and the long term coastal evolution related to gradients in the longshore transport affecting the evolution over decades. Subsequently, studies have been carried out on the coastal evolution around Hue, including the interaction between lagoon water exchange and coastal sediment transport. Recently, work has been initiated around Nha Trang with the aim of quantifying the large scale sediment transport patterns at Nha Trang Beach and their effects on the coastal evolution Modeling long term shoreline evolutions and coastal erosion (Tran Hai Yen PhD thesis) E. Barthelemy

7 Cross shore profiles (terrace, barred...) determine how wave nonlinearities develop and therefore how the sediment is stirred by the waves then transported by the longshore drift. In the thesis we aim at combining the scale event changes of the cross shore profiles with one or two line type models that are long shore drift dependent in order to describe long term evolutions Session 2 Sediment transfers off Grand Popo beach: origin and variability F. Floc h The aim of this study is to investigate the hydrodynamic conditions and the sedimentary fluxes at the boundary of the nearshore zone at GrandPopo. During the 2014 field measurements, the wave and tide climates has shown a large variability. An analysis using the ADCP backscatter signal, calibrated according to a colocated turbidimeter, gives us first highlights on the main processes leading to sediment suspension. The ECORS beach evolution predictor, application to beaches of Nha Trang and Saint Louis T. Garlan The ECORS coastal forecasting simulator includes two levels of models and a set of Data Bases of tidal parameters, bathymetrical soundings, sedimentary and climatology of waves. The first step of models is composed of simple formulas to obtain a rapid characterization of some beach parameters and of the 1D beach profile. The second level is a system of models including : SWAN, MARMONDE, TRANSPOR2004, 1DBeach and XBEACH to calculate waves, currents, turbidity and morphological evolutions. We present the system and the works which will be done with it during COASTVAR On 3D modelling of sediment transport and morphological evolution: a case study at Truc Vert, SW France R. Benshila Modeling sediment dynamics around breakwaters in the Hammam Lif littoral (Tunisia) C. Chevalier In the eighties, eight detached breakwaters have been built in front of the Hammam Lif Beach. Since this construction, tombolos have appeared causing beach disappearance and water confinement between tombolos. The MedCot project has been developed to study breakwaters impact by coupling modeling and in situ measurement. Our aim is to perform a numerical model of hydrodynamics and sediment dynamics in order to suggest solutions to this problem. In this presentation, we will present the MedCot project and the developed strategy to understand the sediment dynamics around detached breakwaters Session 3 3D nearshore modeling within COMODO WAVES P. Marchesiello

8 Robust 3D formalisms of wave current interactions in ocean models have only emerged in the last decade. These advances are providing new opportunities for nearshore and offshore research communities to work together on challenging problems, e.g., surf shelf exchanges. Fundamental methodological and scientific questions also emerge in the process: What is the role of the vertical structure of currents and 3D processes? How do compare wave resolved and wave averaged models for representing the flow variability? How do compare the various approaches of grid refinement to optimize model cost and performances? Some answers will hopefully be given within COMODO WAVES. Modelling wave current interactions in tidal inlets X. Bertin Wave current interactions are the main driver of the intense hydro sedimentary dynamics that took place in tidal inlets. This study presents the development of a 3D, unstructured grid, fully coupled wave and currents modelling system and its application to the mouth of the Gironde Estuary. This application reveals that the model is capable of reproducing both wave induced currents and strong wave transformations induced by tidal currents Latest news from the COAWST modeling system M. Olabarrieta This talk will presentation the latest developments of the coupled ocean atmosphere wave sediment transport (COAWST) modeling system On the 3D modelling of wave currents interactions A.C Bennis First, we present our modelling platform (MARS WW3) as well as the recent updates and improvements. Second, we talk about two recent studies dealing with the impact of bottom friction and turbulence modelling on wave current interactions. Lastly, we discuss about our first results concerning the morphodynamic evolution of a rip system An efficient phase resolving approach for wave modelling in the coastal zone P. Bonneton We will analyse the spatial and temporal variability of wave propagating in the coastal zone, focusing our attention on hydrodynamic processes in the zone affected by wave breaking (surf and swash zones and the neighbouring non breaking zone). From this physical analysis we propose an efficient and mathematically well posed strategy for wave modelling in the coastal zone A full 3D non hydrostatic and non boussinesq model F. Auclair

9 DISCUSSIONS 1. Experiments Vietnam 2015 experiments specific objectives deployment plan participants NT 3: seasonal deployment, June 2015 deploy 2 cameras in the north and renew of one of the 2 cameras in the south; ADCP; LIDAR (5 Hz); sediment characterization and fluxes; monthly sea and beach surveys (bathymetry) until December; bi monthly download video data check Long Beach to prepare December exp NT 4: 23 november 6 december (10 days), including Long Beach 2 3 days rip exp, depending on tides NT 4: rent a boat; sediment measurements; pressure sensors and ADV from France; Long Beach: dye release; ADCP offshore (EPOC); bathymetry with echosounder; ADV in the rip? drifters? Profil en tete de rip (AWAC EPOC; AQUAPRO?); stratification (CTD?); video; drone; GPS Saint Louis 2016 experiment: preparation in December? specific objectives deployment plan participants 2. Numerical test cases Xavier Bertin presented the possibility to design a field experiment on the Oleron island (St Trojan beach) that would suit the model intercomparison project in a first phase. The Oleron site offers ideal characteristics of a 2DV plane beach setup. The measurements of vertical flow profiles will provide data available for the whole community to test and validate our models. We will test structure functions used in models for wave breaking, wave induced turbulence, and bottom flow... Xavier will coordinate the experiment and

10 provide instruments. Measurements of bottom currents may require new acquisition of an instrument (15k ). For financial support and advertisement of the field experiment, we will submit a proposal to EC2CO or CNRS (call for Littoral projects) Model intercomparison on a more complex 3D rip current system (Biscarosse) is postponed to next year.