What is a Hydraulic simulation

Hydraulic simulation is a computer-based analytical process used to model and predict the behaviour of water within a drainage, sewerage, or surface water system in response to external influences such as rainfall events, tidal surges, system failures, or development pressure. This technique allows engineers, planners, and authorities to understand how a system performs both under normal conditions and in extreme scenarios, such as intense storms, high river levels, or system surcharging.

At its core, hydraulic simulation combines fluid dynamics principles with real-world data inputs to produce a virtual representation of water movement through physical infrastructure. This process is essential for designing effective water management systems, assessing risk, and planning infrastructure upgrades or new developments.

Purpose and Importance of Hydraulic Simulation

Hydraulic simulation serves a range of purposes across the planning, design, and operational lifecycle of a drainage or sewer network. It allows engineers to test and optimise system performance without the cost or risk of real-world experimentation. Using simulation, professionals can assess how water will behave under a variety of conditions and identify areas of vulnerability, such as flood-prone manholes, undersized pipes, or inadequate attenuation features.

In modern urban environments, where climate change is leading to more frequent and severe rainfall events, hydraulic simulation plays a critical role in ensuring the resilience and adaptability of drainage infrastructure. It is also essential for demonstrating regulatory compliance, especially when submitting designs for approval or responding to environmental assessments.

How Hydraulic Simulation Works

Hydraulic simulation is typically performed using specialist software designed to model one-dimensional (1D), two-dimensional (2D), or combined 1D/2D hydraulic systems. These tools simulate how water enters, flows through, and exits a system over time. Key stages of the simulation process include:

  1. Data Input and Network Building
    Engineers input detailed information about the system, including pipe sizes, gradients, manhole locations, catchment areas, flow controls, and outfall characteristics. GIS data, topographic surveys, and asset records often inform this step.
  2. Boundary Conditions and Rainfall Scenarios
    External influences such as rainfall intensity and duration (based on IDF curves or FEH data), tidal conditions, or inflows from other networks are added. These conditions drive the simulation.
  3. Model Calibration and Validation
    If monitoring data (e.g. flow surveys or level logging) is available, the model is calibrated to match observed behaviour, improving accuracy. Validation ensures the model behaves reliably under varied conditions.
  4. Running Simulations
    The system is tested under different scenarios — for example, a 1-in-30 year storm, a pump failure, or future climate conditions. The software computes water levels, flow velocities, surcharging points, and flood extents over time.
  5. Analysis of Results
    Outputs include time-series graphs, flood maps, surcharge tables, and hydraulic grade lines. These are interpreted to identify bottlenecks, overflow risks, and areas needing intervention.

Commonly Used Software Tools

There are several industry-standard tools used for hydraulic simulation, each suited to specific contexts:

  • InfoWorks ICM – A comprehensive platform used for modelling complex sewer and surface water networks, including integrated 1D/2D flooding.
  • MicroDrainage (now Causeway Flow) – Widely used in the UK for the design and simulation of drainage systems on development sites.
  • EPA SWMM (Storm Water Management Model) – An open-source tool for urban runoff and combined sewer modelling.
  • HEC-RAS – Used for river hydraulics and channel flow, often in floodplain modelling.
  • MIKE URBAN and MIKE FLOOD – Advanced tools for simulating urban drainage, coastal flooding, and surface water interactions.

These platforms support scenario planning, climate resilience assessments, and permit applications, and are often integrated with GIS and BIM systems.

Applications of Hydraulic Simulation

Hydraulic simulation is employed across a wide range of applications in water engineering:

  • Drainage design for residential, commercial, and industrial developments
  • Flood risk assessment and mitigation planning for local authorities
  • Verification of SuDS components, including ponds, swales, and attenuation tanks
  • Planning upgrades to ageing or underperforming sewer infrastructure
  • Assessment of combined sewer overflow (CSO) frequency and volume
  • Climate change impact modelling and future-proofing of infrastructure
  • Pollution control modelling to predict contaminant pathways and dilution

It also plays a role in asset management, allowing water utilities to evaluate how their networks respond to increasing demand, infiltration, or blockages.

Advantages of Hydraulic Simulation

The key benefits of hydraulic simulation include:

  • Risk reduction through proactive system testing and design verification
  • Cost-effectiveness by identifying problems early in the design phase
  • Enhanced decision-making by presenting complex system dynamics visually
  • Scenario testing to understand system responses to rare or extreme events
  • Regulatory compliance with planning and environmental guidelines

Perhaps most importantly, simulation allows engineers to make evidence-based decisions, giving stakeholders greater confidence in drainage performance under both current and future conditions.

Conclusion

Hydraulic simulation is a powerful and essential tool for understanding, designing, and managing water infrastructure in both urban and rural settings. By accurately modelling how drainage and sewer systems behave in response to rainfall, tide, and operational changes, it enables engineers to predict risks, optimise designs, and ensure long-term system performance. In an era of climate uncertainty and urban expansion, hydraulic simulation is more than just a design tool — it is a foundation for sustainable and resilient water management.