What we do
Herrington Consulting employs a wide range of numerical modelling software, which helps to set us aside from our competitors. Our experienced modellers are capable of representing fluvial, coastal and pluvial flooding events, as well as being able to construct drainage models and 3D architectural models used in our bespoke daylight and sunlight assessments.
As any Master Tradesman knows, the key to success is selecting the "right tool for the job", and the same principle applies to numerical modelling. Some projects can benefit significantly from the detailed understanding of risk and other environmental factors provided by numerical modelling. In most cases, the imporved understanding of risk gained using numerical modelling techniques increases the confidence in any proposed mitigation. This increased understanding of risk provides the Environment Agency/SEPA and the Planning Authority with the level of confidence required to approve new development in flood risk areas.
Accurately predicting the depth and extent of flooding can also free-up more developable area within a site, or reduce the amount of floor raising required. Robust flood prediction can in some cases also enable more vulnerable uses to be located on the ground floor of a development, whereas without it, possibly only commercial uses would be acceptable. All of these benefits significantly outweigh the additional costs associated with numerical modelling.
Click on the examples tab above to see the array of modelling capabilities Herrington Consulting currently have to offer.
Many flood risk assessments can be carried out using the flood level data from studies already commissioned by the Environment Agency or other operating authorities. However, for the appraisal of watercourses that have not been subject to detailed modelling, the quality of extreme water level data may not be appropriate for quantifying flood risks for new developments. Consequently, numerical modelling enables the risk of flooding for a subject site to be accurately determined and quantified.
The value of undertaking numerical modelling as part of a Flood Risk Assessment (FRA) is that the model provides detailed site-specific information and this is used to more accurately inform the Flood Risk Assessment (FRA). It often shows that the risk of flooding to a site is less than depicted by the Environment Agency’s/SEPA’s flood risk maps and this often requires the developer to meet less onerous conditions.
There is, however, always the chance that the modelling will show that the site is still at risk of flooding, albeit the risk maybe lower than first perceived. Consequently, mitigation measures may be required to be incorporated within the development, although these can be refined at an early stage of the design based on the outputs from the modelling, ensuring the cost of any measures can be factored into the project.
Below are some examples of the types of detailed modelling that Herrington Consulting use to aid their clients with their projects.
- Hydrological modelling
- Hydraulic modelling
- Hydrodynamic modelling
- Wave modelling
- Daylight/Shadow modelling
Herrington Consulting is a dynamic consulting practice specialising in both Coastal and Flood Risk Management across the UK. We use a range of numerical models to provide our clients with the most suitable solution for their site, big or small. So regardless of site or budget, contact us today for a friendly and competitive quotation.
What is hydrological modelling?
Hydrological modelling is used to make predictions of peak river flowresulting from a rainfall event, for any given return period, over a specified catchment. Several software packages can be used to make these predictions including; FEH, WINFAP and ReFEH. The peak river flows can then be used to estimate flood depths at a given location.
What is a hydraulic & hydrodynamic modelling, and what is the difference?
To determine flood extents, depths and flowpaths it is necessary to undertake a hydraulic model of the watercourse. This is generally referred to as a 1D model and ascertains whether the water flowing in the watercourse under different return period events will remain within the channel. In order to simulate the effects of extreme flood flows in this watercourse we will apply rainfall catchment data and flow data to a 1D hydraulic model (ESTRY/HEC-RAS). This will identify whether any water leaves the watercourse, and at which point it does so.
In order to show any propagation of floodwater across a development site, hydrodynamic 2D modelling is required. This uses topographic data in the flood area to create a digital terrain model (DTM), which includes man-made features such as buildings, roads and walls. Herrington Consulting has developed the use of TUFLOW hydrodynamic modelling software for use in predicting the impact of breach, overtopping and overflow scenarios in both urban and rural areas.
Why is hydraulic/hydrodynamic modelling required?
Generally the starting point of the FRA process is the Environment Agency's/SEPA’s Flood Zone maps, which give an indication to the extent of flooding. However, this mapping does not take in to consideration the presence of any flood defence infrastructure. Therefore, in cases where flood defences do exist, a true representation of flood risk is not given and as such development potential is often curtailed.
TUFLOW provides the ability to overcome this by simulating the propagation of floodwater across a detailed model terrain that can include a range of features that influence the flow of water such as buildings, underpasses, bridges etc. This allows a more realistic representation of flood risk as well as enabling a range of flood flow simulations to be developed.
- flooding from rivers
- complex overland and piped urban flows
- breaching of tidal and fluvial defences
- wave overtopping of estuarine and coastal defences
- inundation from storm tides
- direct rainfall runoff
To enable the risk of flooding to be quantified, both within a wider study area and at a site-specific scale, the TUFLOW model can be interrogated at selected points to provide detailed flood depth and velocity information. In addition, data such as water level, unit flow vectors, energy level, flood hazard and Froude numbers can also be extracted.
Having established the extents, depths, flow paths, velocities and duration of the design flood event, we will assess the potential impact of flooding on the proposed development and make recommendations for mitigation. We also analyse the hazards associated with access and egress from the site under flood conditions.
What are the benefits of undertaking modelling?
Modelling is not always a necessity, however, it can provide many benefits to a development. Firstly, the more accurate flood levels provided by the modelling may show that the site is not in fact affected under the design flood event. In these cases, the degree and magnitute of mitigation measures will be less onerous, which can consequently help to reduce the cost of development. Furthermore, even if a site is shown to be effected by flooding, because the depth and velocity of flooding at the site can be quantified it often results in the finished floor levels being set at a lower level than would otherwise be acceptable.
The second major benefit that numerical modelling can afford a development in terms of flood risk, is that the model results can help to delineate the most suitable, safe access/egress routes to/from the development.
How accurate is the modelling?
The accuracy of the model is dependent on the resolution of the data used. In the case of the 1D models, it will depend on the level of detail captured by the survey of the watercourse, and in particular how many cross sections were undertaken.
For a 2D model the accuracy is dependent on the resolution of the land level data, however, with the increasing availability of high-resolution LiDAR data across the UK, most of the models we provide are run using a minimum of 2m resolution data.
In either case, the use of modelling provides a significant improvement over a simple comparison of static water levels and the land levels at the site, and in the majority of cases the benefits of undertaking numerical modelling far out ways the cost to commission the model.
I thought modelling was only undertaken for large-scale developments?
Although most people associate flood modelling with large-scale developments, the flood level data provided by the Environment Agency/SEPA does not take into account existing defences. Consequently, flood risk is overestimated when the flood level is directly compared to the land levels of a site.
By constructing a numerical model that takes into account the existing flood defences, it is usually possible to show that the risk of flooding to the site is lower than first anticipated, even when a breach of the defences occurs. Furthermore, many smaller watercourses have not been modelled by the Environment Agency/SEPA and so modelling can be used to accurately quantify the risk of flooding to a site.
How long does it take to complete the modelling?
The complexity of modelling does mean that it takes sometime to build and run a model. Depending on our workload at the time it is often possible to complete the modelling within 3-4 weeks of commission. However, it may take longer especially if we are obtaining in-channel flood level data from the Environment Agency/SEPA, as they have a 20 working day response time.
What data is needed for the modelling?
In order to build a hydraulic model we may require a detailed survey of the watercourse, providing cross sections to enable the construction of the 1D element of the model. We may also require bank levels and general land levels in the surrounding area. Depending on availability, the land levels data may be obtained in the form of high resolution LiDAR data. In the case of coastal modelling, we are usually able to obtain the relevant detail required using LiDAR data.
What will the modelling show?
The modelling will show the evolution of the flood over time. In the case of a fluvial model, it will likely show the water levels in the channel increasing as the peak of the rainfall event is reached. If the levels are high enough to exceed the banks a 2D model will capture the dynamic flow of water over the landscape, providing flood depth, velocity and hazard rating.
For a coastal model, which usually depicts a breach of the sea defences or wave overtopping, the model will show the tide rising and the water levels increasing. At a given time the defences are assumed to fail and the model will show the water flowing through the breached defences, flooding the area inland of the defences. The models can also identify how quickly the floodwater recedes.
Will I be able to understand the results?
Although the modelling and underlying processes are very complex, we are able to present the results of the modelling in a way that can be interpreted by a lay-person. If flooding affects the site we are able to give flood extents, depths, flow paths, velocities and duration of the design flood event in both a numerical and visual format.
What is wave modelling?
To gain a reliable estimate of the nearshore wave climate within a study area, such as a harbour or along a specific coastline, Herrington Consulting has developed numerical wave modelling capabilities.
The prediction of wave heights in areas of complex bathymetry and coastal structures is governed by a combination of factors, including; the seabed topography, tidal currents and the presence of any coastal structures located within the area of interest. These features cause temporal and spatial changes in the wave field, and to analyse the interaction of these features within the study area an advanced nearshore wave propagation model is required to inform clients of the potential design implications
To undertake this type of analysis for their clients, Herrington Consulting coastal engineers apply a Boussinesq wave model. As a phase-resolving nonlinear wave model, it can be used in the modelling of various wave phenomena including:
- full/partial reflection and transmission through coastal structures
- bottom friction
- nonlinear wave-wave interactions
- wave breaking and dissipation
- wave run-up and overtopping of structures
- wave-current interaction
- wave-induced currents
The model is used to construct a detailed Cartesian grid, based on the bathymetry and topography of the study area. The existing coastal structures are represented within the model domain and input boundary conditions are taken from offshore wave data, which can also be derived using a separate model if required.
The wave model enables the user to simulate various conditions, including a multidirectional sea state, and by testing a range of scenarios based on extreme wave height and water level combinations, it enables the user to ascertain which set of wave conditions would have the greatest impact within the study area.
The model itself employs a time-domain solution of fully nonlinear Boussinesq-type equations, valid from deep to shallow water, representing the depth-integrated equations of conservation of mass and momentum for waves propagating in water of variable depth.
The model can also be used to simulate the reflection and transmission characteristics of marine structures existing within the model boundaries.