Flood Modelling

Development Project HEC-RAS Flood Models

Whenever land needs to be prepared for development schemes, it’s rare that standard broad-brush charts will be enough to satisfy regulators.

Instead, getting planning approval for complex schemes across the UK usually needs detailed hydraulic modelling to assess flood risk accurately on the ground.

National mapping helps as a starting point, but it cannot capture site-specific nuances or show how water interacts with individual building plots.

Using digital simulations, design teams, drainage engineers and regulators can clearly see how prospective water movement will play out.

The technical evidence from flood modelling supports local schemes with water damage concerns and only strengthens the likelihood of successful planning applications.

How Does Flood Modelling Work?

Through hydraulic calculations, multiple environmental datasets are combined to reconstruct real-world water activity on a digital canvas.

To generate flood risk information, specialists compile rainfall scenarios, catchment details and historical records. The evidence is paired with high-resolution topographic data, utility network layouts and fresh survey data from the site.

By gathering inputs from the ground scans alongside other sources like nearby culverts and bridges, specialists can create a digital framework showing true flood behaviour.

The combined hydrological and hydraulic modelling method evaluates how changing weather will influence development potential and water flow across channels and surfaces.

Instead of resorting to guessing, engineers simulate conditions in real-time digital environments, creating a baseline that can assist broader flood forecasting operations.

When is Flood Modelling Needed?

A standard desk study or a simple flood risk assessment (FRA) could be enough for straightforward plots of land, but with high-risk locations, more technical backing is needed.

If a development site sits close to an ordinary watercourse, main river or coastline, local authorities and statutory bodies will ask for verified evidence.

More specifically, detailed modelling would be needed if:

• The Environment Agency (EA), lead local flood authorities (LLFAs) or another regulator asks for further proof
• The planning officer needs detailed information regarding exact flood levels
• The plot lies within a designated flood zone (such as Zone 2 or 3)
• The site needs to account for heavier rainfall or altered predicted river flows driven by climate change
• You need to show that your proposed development will not increase flood risk for neighbouring properties
• You’re testing to see if your drainage setup and SuDS designs offer adequate capacity to manage the overall risk of flooding

Types of Flood Models

Every development scheme presents distinct constraints, topography and water sources.

Choosing the most appropriate approach depends on your plot layout, data availability and the specific water issues you need to resolve.

Specialists review such factors to decide between different modelling approaches, often combining 1D and 2D methods to simulate channel flow and overbank spill in one connected exercise.

1D Flood Modelling

One-dimensional analysis calculates fluid movement along a single direction, making it ideal for in-bank river courses, enclosed pipes and simple culvert networks.

Building a one-dimensional baseline model calculates the exact discharge rates, channel capacities and water levels at defined cross-sections.

Engineers also evaluate flow conditions at key points and downstream boundaries to see how water exits the local drainage system.

2D Flood Modelling

Two-dimensional analysis simulates how shallow sheets of water travel across open ground surfaces in multiple directions.

By plotting elevation grids, the method tracks how water spreads across flat floodplains, roads and slopes.

It’s actually the preferred method for assessing surface water flooding in dense urban areas, as it pinpoints localised velocity patterns and maps out precise flood extents.

3D Flood Modelling

Three-dimensional analysis models complex, multi-directional and turbulent currents in intricate detail.

As calculating fluid dynamics in three spatial dimensions involves immense computing power, it’s rarely necessary for standard housing schemes.

It does, however, deliver a high level of insight for complex engineering structures like large bridge piers, dams and outfall structures.

Flood Modelling Techniques

Specialists use a range of proven techniques to simulate water behaviour.

A mix of a hydrological assessment and 2D overland flow grids allows teams to construct detailed flood models that reflect real physical conditions.

All techniques work to encourage clear visual assets, including depth maps, velocity plots and a site-specific flood map showing safe development envelopes.

The Process for Flood Risk Modelling

For the results from flood modelling to be complete and defensible, a staged process needs to be followed:

1. Scoping

Defining the goals of the planning project, highlighting local site constraints, and clarifying local council expectations.

2. Data Gathering

Collecting ground heights and LiDAR grids, and commissioning a new survey if the existing information is outdated.

3. Model Build

Assembling the digital hydraulic network and setting boundary conditions during the model build stage.

4. Scenario Simulation

Setting up multiple model scenarios to test rare and high-intensity flood events and confirm how the design responds to them.

5. Quality Review

Applying robust quality assurance protocols, including an internal peer review to check mathematical stability.

6. Reporting

Reviewing the model results to identify all potential flood impacts before creating a clear model report suitable for local council submission.

Flood Modelling Software

As a way of guaranteeing accuracy, all calculations need to be retrieved from platforms and programmes that meet strict industry standards.

Common software packages used for flood modelling include:

• Flood Modeller: Jacobs’ dedicated software suite for river catchment analysis.
• HEC-RAS: Widely used across the UK for simulating channel flow and overland networks.
• InfoWorks ICM: A catchment management package for drainage and sewer systems.
• TUFLOW: A leading simulation engine for 2D overland flow, surface runoff and pipe networks.

Experts in Flood Modelling

For you to secure planning approval for developments in sensitive drainage areas, you need technical precision and robust data.

Specialist hydraulic engineers build detailed flood models that reflect real ground conditions and satisfy regulatory expectations.

By working with an experienced flood modeller, you can test drainage strategies, account for climate change, and demonstrate effective flood risk management to local planning authorities.

The team at 24Housing don’t conduct flood modelling first-hand, but we can refer clients to environmental and hydraulic engineering specialists from our network of trusted service providers.

Talk to 24Housing for a Referral

If your development site sits in a designated flood zone, or if the Environment Agency (EA) has requested further technical backing for planning applications, our partner network can deliver the technical support you need.

You can ask for a free quote by simply completing a quote form on our website, emailing us or calling us. We will then send your information across to our flood risk, water and drainage partner, leading to an accurate quote for your site and the opportunity to book an assessment.