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TELEMAC

Introduction

The TELEMAC-MASCARET system is a set of integrated modelling tools for use in the field of free-surface flows. Telemac is built on sophisticated algorithms that use a finite-element approach to perform numerical simulation on an unstructured triangular mesh (Hervouet, 2007). This allows complex coastlines and estuaries to be represented more accurately than using regular grids.

The iCOASST project has made use of several modules of the TELEMAC system:

  • TELEMAC-2D, which solves depth-averaged Saint Venant equations to compute the water depth (or free surface elevation) and horizontal velocity components at each node of the computational mesh.
  • TOMAWAC, used to model wave propagation in coastal areas.
  • SISYPHE, a sediment transport and morphodynamic model that can compute bedload and suspended load (for either non-cohesive sand or cohesive mud) at each node of a TELEMAC mesh as a function of various flow (velocity, water depth, wave height, etc.) and sediment (grain diameter, relative density, settling velocity, etc.) parameters. Bedload is calculated using classical sediment transport formulae. The suspended load is determined by solving an additional transport equation for the depth-averaged suspended sediment concentration. The bed evolution can also be computed (via the Exner equation), using either a finite element or a finite volume formulation.

Model development

TELEMAC was originally developed by the Laboratoire National d'Hydraulique, a department of Electricité de France's Research and Development Division. The software is now available as open source code, which is maintained by the Open Telemac-Mascaret Consortium (www.opentelemac.org). This is a partnership of the following users and developers:

Electricite de France (France)
SOGREAH (France)
HR Wallingford (UK)
Centre d'tudes Techniques Maritimes et Fluviales (France)
Bundesanstalt fur Wasserbau (Germany)
Daresbury Laboratory (UK)

Application of TELEMAC within iCOASST

Telemac has been used within the iCOASST project in two key areas:

  1. By the University of Manchester to determine residual sediment pathways and fluxes across the coastal shelf. This has included implementation of nested TELEMAC 2D models at scales ranging from the UK coastal shelf (resolution from 1km at the coast to 35km offshore), to a regional model of Suffolk (resolution down to 8m in estuaries, increasing to 930m offshore). In the case of the Suffolk region, TELEMAC-2D model runs were undertaken for a representative year (2008), with wave inputs pre-computed using TOMAWAC, and direct coupling with SISYPHE to derive residual sand fluxes pathways. These provided valuable input to the Coastal and Estuarine System Mapping work package as well as identifying areas where cross-shore sediment exchanges may be important.

  2. At an estuary scale, TELEMAC-2D has also been used by UCL to provide hydrodynamic benchmarking of 1D hydrodynamic routines built into the new ESTEEM estuary simulator. ESTEEM can be used in conjunction with TELEMAC to provide more computationally-efficient evolution of estuary morphology than is possible through direct coupling of TELEMAC and SISYPHE, while retaining the robust hydrodynamics of TELEMAC (e.g. for assessment of changing flood risk under climate change, sea-level rise, and coastal morphological change).