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Introducing Flow.

“Flow has made our hydraulic design processes much easier thanks to its use of the modified rational method for sizing conveyance systems and deploying the SWMM engine for hydraulically analysing drainage systems.”

Donna Metcalf, Managing Director at Flood Risk Consultancy

Find out more
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Flow Drainage Design

The complete set of easy-to-use and powerful software, vital to carry out an optimal and adaptable end-to-end drainage design.

Flow is a hydraulic modelling package for the design and analysis of an optimal, compliant and cost effective storm or foul water drainage networks. Ideal for customers who are looking to purchase a robust, intuitive and affordable alternative to what the market already offers.

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Performance gains for you and your team

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Optimise the resources you have

Provide the team with the licences they require to work as efficiently as possible without breaking the bank.

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All of the tools your team needs

Access all of the tools your team is likely to need, including network analysis, storage and SuDS design, simulation, CAD integration and BIM.

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BIM compliance

Deliver the BIM outputs clients require.

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No need to wait for an available license

All engineers can have access to licences on demand.

PDS modules

Access all of the modules you need

The new subscription bundles mean that the extra packages you would have liked but could not justify could now be available as standard in one of our bundles.

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BIM outputs without changing your workflow

BIM tools allow you to design as usual, but deliver BIM outputs as required.


Network licencing as a standard

Gain a licence manager hosted by Causeway. All licences are wide area networked and ensure optimisation.

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CAD agnostic

Use SmartDrainage to integrate Flow with AutoCAD. Alternatively, integration with PDS will allow you to read and write DWG files as standard, therefore if you run AutoCAD LT it will still work for you.

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Rationalise your supply chain

If you currently have legacy software, Flow will provide your engineers with the latest tools. This will allow you to cut the annual maintenance you pay to other suppliers, saving money on your overall annual spend.

Flow Drainage Design Bundles

Flow Drainage Design software provides powerful tools to handle any drainage design.


For those needing straightforward hydraulic design capability
  • Flow
  • Flow+
  • Drainage Layout and Annotation (SmartDrainage and PDS Drainage)
  • Flow and MicroDrainage Integration
  • BIM Design


For those needing to deliver BIM outputs
  • Flow
  • Flow+
  • Drainage Layout and Annotation (SmartDrainage and PDS Drainage)
  • Flow and MicroDrainage Integration
  • BIM Design
Training courses

At Causeway, we are committed to providing ongoing support for our products. We have a range of training courses, where you can learn about all the latest techniques and tips that will allow you to use Flow Drainage Design more effectively.


View courses

Not sure which Bundle is right for you?

Gain access to Flow Drainage Design by getting in touch with us.
We would be happy to discuss the best Bundle for you.



Flow is a complete drainage design and modelling software built on the Modified rational method for sizing any conveyance system and the state-of-the-art 1D SWMM engine for hydraulically analysing any storm drainage system. Flow empowers engineers, consultants, developers and approving authorities to deliver an optimal and compliant design at the micro or macro catchment level.

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Whether working on a greenfield site or on a brownfield re-development project, Flow will empower you with advanced software to deliver an optimal preliminary or detailed drainage design. Design storm water networks using the Modified Rational Method, and design foul networks in accordance with the requirements of BS EN 752:2008. Flow enables designers to combine new design with existing networks seamlessly to conduct integrated hydraulic analysis, including negative falls or backdrops, throttle pipes and bifurcations.


Automated calculation of falls to give minimum velocity. Pipe diameters selected from a pre-defined set of pipe sizes, manhole sizes calculated in accordance to Sewers for adoption or user definable conduits. Automated backdrop removal and design for capacity to give optimum cover depth or to meet known outfall level.

SuDS Design

SuDS can be designed and modelled to satisfy the latest guidance (SuDS Manual C753) via templates, then cascaded with flow-back to upstream structures in the event that downstream structures fail. SuDS can also be designed at the detailed design stage independently or combined with traditional storm water drainage network, to help manage quantity, quality, amenity and biodiversity to comply with latest guidance.


Define a network as a set of nodes and links, making the design multiple links possible, with the added spinoff of not needing dendritic numbering system.

Pre-development Calculation

Calculate pre-development runoff rates and volumes to show equity or betterment to post-development runoff rates and volumes. For SuDS feasibility analysis, quickly estimate storage sizes to begin designing infiltrating structures in detail.


Define or import rainfall data by specifying FSR or FEH rainfall data or directly specify rainfall profiles and add a climate change factor. Automatically generate time varying rainfall using UK 50 percent summer profile from 15 minutes to 7 day duration. Analyse one or multiple storm durations in single run with result collated and critical durations automatically identified at every node.

Hydraulic Simulation

Simulate the design using cutting-edge 1d dynamic wave routing over multiple storm durations for a range of return periods and profiles. Hydraulically analyse drainage systems to identify and solve issues with any design swiftly and effortlessly. Dynamic wave routing takes account of node and link storage, backwater effects, entrance and exit losses, flow reversal, and pressurised flow.


Model open manhole, sealed manhole and junctions. Design Flow controls composite inline controls, overflow and multiple controls to set a range of discharge rates. Model storage and infiltration structures as on online or offline arrangements, loops and additional losses, to control flooding. Drain down time can be adjusted to check the feasibility of each SuDS option.

Easy Import/Export

Import/Export functionality supports several formats including the capability to copy and paste from any Excel spreadsheet. Supports industry file formats: .SWS .EWS and .MDX formats


Graphically visualise any drainage network in longsection and plan forms and detect crossings and clashes. Allows longsection, graph and plan graphics to all be displayed simultaneously or any combination thereof.

Compliance Audit

Conduct automatic compliance audits to check against approval authorities requirements before submission for consent. Perform up to 16-compliance test that determine whether a design is suitable for approval based on a set of user definable pre-defined criteria. This will allow you to identify, understand and resolve any problem with a drainage network automatically, speedily and effortlessly.


User-customisable reports of the design output data to formats such as Excel and PDF.

Flow +

Flow+ empowers engineers with the ability to model complex existing systems including negative falls or backdrops, throttle pipes and bifurcations. This capability allows seamless integration of existing models with new compliant design. These complex modmodels can be engineered using Flow’s tabular format or graphically via SmartDrainage.

Drainage Network Layout and Annotation

Storm and foul drainage networks are laid out, manipulated and edited with tools that will automatically sense manhole locations and apply depth rules appropriately. Catchment areas can be identified with multiple areas and different permeability factors applied, loaded and recorded for reference purposes. Drainage sections, combined road/drainage sections, manhole schedules and powerful user controllable annotation styles are all included.

Integration with MicroDrainage

The layout completed in PDS is exported to Causeway Flow for hydraulic analysis of the network. A dynamic link is established and any changes made in Flow will automatically be highlighted in PDS, giving the user the opportunity to accept the changes or investigate further. Importantly, all aspects of the Flow design are carried back to PDS, including flow controls and storage devises, which are essential for a complete design and BIM output. 3D networks are generated automatically in PDS from the hydraulic design. Support for MicroDrainage integration is also included.


SmartDrainage translates a plan view of a drainage layout, constructed from standard AutoCAD/Civil 3D graphic entities, into a network of nodes and links ready for Causeway Flow to analyse. The user has only to select the outfall node; one click of the outfall node will mean SmartDrainage automatically finding all the connected nodes and links, their cover levels and catchment areas, removing the unnecessary step to re-tracing CAD drawings. The layout may be drawn specifically for this purpose, or may be a legacy CAD drawing.

SmartDrainage in AutoCAD/Civil 3D

Draw networks of nodes and links from standard CAD entities. Click on the outfall – SmartDrainage will find the network. Design non-straight links where required. Define node and link types in your own standard library. Use any layering/naming standard to assign the node and link types. Automatically assign drawn catchment areas to the appropriate nodes. Assign impermeability factors to catchment areas. Apply multiple areas to the same node if needed. Derive levels using the SmartSurface tool, or from the CAD entities. Set numbering and annotation styles. Embed multiple networks within AutoCAD/Civil 3D file and output to Flow for design and analysis with one click.

Iterative Design Cycle

Re-import designed and analysed Flow data with one click. SmartDrainage will hold all Flow data, including ancillaries and non-graphic attributes and amend the network in CAD or in Flow as SmartDrainage will automatically synchronises both. Maintain current design as single standard dwg file per network or group of networks, suitable for all sizes of design team from one designer to joint-ventures. Manage easily on any document management system that handles dwg files. Due to all these reasons, SmartDrainage combined with Flow will significantly reduce risk of errors, saves time, money and delivers an optimal and compliant drainage design.


After analysis in Flow, update network drawing annotation, draw longsections, manhole and pipe schedules for graphical setting out, scheduling and the production of sections.

BIM Design

BIM compliance demands much more than 3D model output. All packages in the Flow & PDS Enterprise Bundle contribute to the BIM workflow with user controllable attribute data attached when generating outputs for BIM collaboration.

Network Licencing

Standardised wide-area network licencing offering our customers maximum flexibility and optimum licence utilisation for all of the functionalities of Flow Bundles. Licencing is controlled via a cloud-based licence manager hosted by Causeway, allowing access by users from any location with an internet connection. Licence borrowing is a feature that allows a licence to be borrowed from the network to a local PC for a given period of time, after which it is automatically reverted to the network pool.

Customer efficiency gains and cost savings

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Boost productivity thanks for Flow's intuitive, friendly interface

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Streamlined processes and engineer utilisation

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Save in upfront investment thanks to a subscription delivery

Partner with us

At Causeway, we pride ourselves on being more than a provider. We pride ourselves on being your partner.

We work closely with customers and listen attentively to their feedback to understand their challenges and identify the solutions that work for them. Watch how we partnered with Jacobs to develop a fully integrated solution.

Proud partners
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Get your personalised quote

Gain access to Flow Drainage Design by getting in touch with us. One of our team members will be happy to create a personalised quote for you.

Frequently asked questions

    • Flow Drainage Design is offered as a subscription service because it is a very efficient way to utilise software while minimising the impact on cash flow and providing maximum tax benefit.
    • As a customer, you are able to pick the bundle that best suits your needs and gain access to many productivity tools at a compelling price point.
    • You need to pay for the annual subscription based on the minimum term that was discussed when you purchased Flow Drainage Design Bundles.
    • No, the prices quoted for the Bundles are based on an annual invoice.
    • Yes, you can always upgrade. For example, if you pick the Professional Bundle as best meeting your immediate needs, then find customers requesting BIM outputs, you can move to the Enterprise Bundle at the difference in cost.