5 Common Mistakes made in Surface Water Network Modelling:

5 Common mistakes made in Surface Water Network modelling:

1) Assigning incorrect operation head to a flow control – Whilst the flow rate of a flow control within a network model may be correctly limited to the greenfield rate or an otherwise agreed rate, the wrong operational head will mean during the critical event, more or less flow than intended will pass across the flow control.

2) Ensuring correct node / manhole sizing – If the node/manhole dimensions in a pipe network are not assigned correctly, this will lead to inaccurate volume storage requirements, leading to over or under providing bespoke attenuation volume within attenuation structures.

3) Ensuring correct pipe gradients – Generally and desirably, a self-cleansing velocity of 1.0 m/s or greater should be met within surface water pipe networks. If less than this, then the pipe will become more prone to siltation buildup. If substantially greater than this, this will result in undesirable pipe depths and unnecessary costs to the client.

4) Allowing for pipe sizes when making soffit to soffit connections – Where incoming/outgoing pipe sizes differ, allowance should be made to the connecting incoming/outgoing invert levels to ensure a soffit to soffit connection is made irrespective of pipe size.

5) Not allowing for a potential surcharged outfall – A surcharged outflow can lead to internal building flooding and restricted outflow from the site, impeding the operationof the drainage system and should therefore be allowed for within modelling. Where private sewer levels are close to public sewer invert levels, safeguarding the private network against public sewer surcharging should also be present.

Surface water network modeling is beneficial for various applications, including flood forecasting and management, water supply planning, water quality analysis, and environmental impact assessments. It is important to make sure that we as engineers supply the correct information for decision makers on a project to make informed choices.

Article by Kevin Henning