River flood simulations

Context

In response to increasing flood risks driven by climate change and extreme weather events, government agencies and engineering consultancies are increasingly keen to model river dynamics and floodplain behavior. OpenTelemac enables detailed simulations of flood propagation, helping to assess the effectiveness of mitigation measures such as levees, retention basins, and early warning systems.

Workflow overview

Step 1: Data collection

• Topographic data from LiDAR or satellite imagery
• Hydrographic network (riverbeds, tributaries)
• Soil infiltration and land use data
• Meteorological input (rainfall events, climate forecasts)
• Historical flood records (for calibration)

Step 2: Model setup in OpenTelemac

• TELEMAC-2D or TELEMAC-3D is used to simulate hydrodynamics.
• The model domain is created using BlueKenue or similar mesh generation tools.
• Boundary conditions are defined: inflow from upstream, rainfall input, and downstream water levels.
• Calibration and validation are done using historical flood events.

Step 3: Scenario simulation

• Simulate historical extreme rainfall events to validate the model.
• Simulate future extreme weather scenarios (e.g., 100-year flood).
• Analyze the extent, depth, and duration of floodwaters.

Step 4: Flood prediction

• Integrate real-time data from weather forecasts and upstream gauges.
• Use OpenTelemac in a real-time forecasting chain, possibly linked with tools like Python for automation.
• Simulate the likely flood spread several hours to days in advance.

Step 5: Prevention and mitigation

• Identify vulnerable areas (urban zones, farmlands, infrastructure).
• Test mitigation strategies:
• • Building levees and retention basins
  • Modifying land use or zoning
  • Emergency evacuation routes
• Run "what-if" scenarios for structural or policy changes.

Outputs and impact

Key outputs

• Flood extent maps
• Water depth and flow velocity at each time step
• Time of arrival of flood wave
• Risk maps and damage estimations

Decision support

• Early warning for emergency responders
• Urban planning and zoning regulations
• Cost-benefit analysis of mitigation measures
• Community awareness tools (e.g., public-facing flood risk portals)

Example projects

• Rhône River (France): TeleMac used to simulate extreme floods and inform dike construction.
• Seine River Basin: Real-time flood forecasting system integrated with OpenTelemac.
• Bangladesh Flood Forecasting: OpenTelemac part of integrated systems assessing monsoon flood risks.

Advantages of using OpenTelemac

• Customizable for specific basin characteristics
• High-accuracy solvers for shallow water equations
• Supports 2D and 3D modeling
• Integrates easily with GIS and external data sources
• Scalable for local to regional floodplain management