Introducing pipe design

Step-by-step:

It is very important to use the right rainfall methodology for each site that you are working on. Pipes have to be sized adequately, and effective storage solutions need to be built. To do that, it is vital to understand and accurately represent the inflows entering a drainage network.

For drainage designs to be valid in the UK, they must comply with Design and Construction Guidance, DCG (formerly known as Sewers for Adoption). They must meet 2 criteria: no-surcharge and no-flood.

Use the correct rainfall methodology for the site:

• Different rainfall theories will predict different rainfall levels.
• Dependent on project location and approving authorities.
• (This example uses the FSR rainfall theory.)
  

Stage 1 of the design process:

• Design for a no-surcharge criteria in which the pipes must not become more than full, and there is always a free surface within the pipe because the pipe capacity is greater than the flow rate.
• Tested by a steady state calculation for a 1 in 1-year or 1 in 5-year storm.
  

Stage 2 of the design process:

• Design for a no-flood criteria in which the pipes can surcharge, but the manholes must not flood.
• At this stage a fully dynamic, volumetric simulation is required.
• Tested by a higher return period storm, typically 1 in 30 years.