Hydraulic Modelling
The use of computational software to simulate water flow in rivers, floodplains, drainage networks, and coastal zones, producing flood extent, depth, velocity, and hazard outputs.
Hydraulic modelling is the application of computational fluid dynamics software to simulate the behaviour of water in natural and engineered systems. In flood risk practice, hydraulic models are used to predict flood extents, depths, velocities, and hazard ratings for design storm events, providing the quantitative evidence base for Flood Risk Assessments and flood defence design.
There are two main categories of hydraulic model:
- 1D models: Simulate flow along a single dimension (typically the channel centreline and cross-sections). Examples include HEC-RAS and Flood Modeller. These are efficient for well-defined channels but less accurate in wide, complex floodplains.
- 2D models: Simulate flow across a two-dimensional grid or mesh, capturing the full floodplain dynamics including multiple flow paths, ponding, and velocity variations. TUFLOW is the industry-leading 2D modelling package. Direct rainfall modelling is a 2D technique.
- Linked 1D-2D models: Combine a 1D channel model with a 2D floodplain model, offering both efficiency and accuracy. This is the standard approach for most river flood studies.
Hydraulic models require high-quality input data, including:
- Topographic survey and LiDAR for ground levels
- Channel cross-sections and structure dimensions
- Hydrological boundary conditions (design flows and rainfall)
- Roughness coefficients for land use types
The Environment Agency and SEPA maintain detailed hydraulic models for many rivers, which can be requested for site-specific studies. Where no model exists, or where the existing model is insufficiently detailed, a bespoke model must be built.
Aegaea operates an in-house flood modelling team using TUFLOW, HEC-RAS, and Flood Modeller, delivering modelling outputs that are accepted by the Environment Agency and LLFAs.