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Flow hydrograph (in red) produced by the simulation module for a drain in the region of a flooding problem.

Note the reverse (negative) flow (at time equals 20 minutes) due to overloading of the drainage system downstream. The blue line represents the depth of water in the manhole. Again note that the water is predicted to rise above ground level which would in practice mean flooding would occur.

Micro Drainage Simulation Module

Hydraulic Analysis of Drainage Systems

We use XP Solution's Micro Drainage simulation software to analyse the hydraulic performance of a proposed or existing drainage system. Typically the software would be used to:

  • Confirm that a proposed surface water drainage system designed using
    the System 1 module will perform adequately under the various
    conditions outlined in Sewers for Adoption, see below.
  • Investigate the causes and design solutions to flooding problems within
    existing drainage systems.
  • Determine if there is sufficient spare capacity in an existing foul,
    combined or surface water drainage system to allow a proposed development to connect.
  • Following on from the previous point, if there is insufficient spare
    capacity in a surface water drainage systems, to design attenuation facilities to allow the proposed development to connect, if appropriate.

Capability of Software

The simulation software allows the modelling of surface water, combined and foul water drainage networks under most flow conditions. It can also represent ancillary structures commonly found in drainage systems including weirs, orifices, pumping stations and attenuation tanks and ponds. The software also allows the representation of infiltration, the modelling of 'looped systems', the use of observed rainfall together with FSR and FEH design rainfall.

Storm simulation for proposed surface water sewers

Although we design surface water drainage systems using System 1, we would then use the simulation module to check that the system operates satisfactorily for various conditions. These are, no surcharging for the 'pipe-full' design criteria, no flooding for the critical duration 1 in 30 year design storm and finally that any flooding caused by extreme rainfall does not affect properties or cause other damage. These are requirements of 'Sewers for Adoption' but we regard them as being generally good practice and so we would apply them to all surface water drainage systems.

Model of existing drainage system

Following construction of a model of an existing drainage system it is good practice to carry out some form of verification of the model. We would generally follow the Urban Drainage Group (formally WaPUG) 'Code of practice' in this respect.

As well as being used to analyse an existing drainage system's performance, for instance to investigate the causes of a flooding problem, a model can also be used to test various options to solve the problem. This is a better approach than assuming the cause of the flooding, construction a solution and then finding at a later date that the problem still remains.

Cost effective and appropriate design

The simulation module allows us to model how a proposed or existing drainage system would operate in reality. This then allows us to test various options to improve matters which results in a more cost effective and appropriate design.


Drainage for New Developments

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Flood Risk Assessments

Flood Consequence Assessments


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