• InfoDrainage

Introducing pipe design

Identify the rainfall theory appropriate for your storm water drainage project so that you can correctly size and place the pipe.


00:03

for drainage designs to be valid in the U. K.

00:06

They generally have to comply with the methodology

00:08

set out in the design and construction guidance

00:11

cG

00:12

formerly known as sewers for adoption.

00:16

That means they have to meet two criteria.

00:18

No surcharge and no flood

00:22

pipes have to be sized adequately and effective storage solutions need to be built

00:27

to do that.

00:28

It is vital to understand and accurately

00:30

represent the inflows entering a drainage network.

00:34

This makes it very important to use the right rainfall

00:37

methodology for each site that you are working on.

00:40

Get this wrong and it could spell disaster.

00:43

Your model could predict no flooding but the

00:46

reality might be a completely different story.

00:49

Remember

00:50

different rainfall theories will predict different rainfall levels,

00:54

which rainfall theory you use is completely dependent

00:57

on your project location and approving authorities.

01:01

This example is representative of a location in the

01:04

UK where there are two established rainfall theories.

01:08

Fs are flood studies report and F E H flood estimation, handbook

01:14

info, drainage, has these theories embedded

01:18

th is the more modern and is generally recommended but it does

01:22

need input parameters to be purchased via the th web service.

01:27

Fs our rainfall is therefore often used for

01:30

training purposes because there is no extra cost.

01:34

There are two separate stages to the design process.

01:38

Stage one is to design for a no surcharge criteria

01:41

in which the pipes must not become more than full

01:44

and there is always a free surface within the pipe

01:46

because the pipe capacity is greater than the flow rate.

01:50

This is tested by a steady state calculation for a one in one year storm,

01:54

or at most a one in five year storm.

01:58

Stage two is conducted for a higher return period storm,

02:01

typically one in 30 years

02:04

at this stage, a fully dynamic volumetric simulation is required.

02:08

The pipes can surcharge, but the manholes must not flood.

02:13

Ultimately,

02:14

the goal is to produce a system that passes both the stage one and stage two tests.

Video transcript

00:03

for drainage designs to be valid in the U. K.

00:06

They generally have to comply with the methodology

00:08

set out in the design and construction guidance

00:11

cG

00:12

formerly known as sewers for adoption.

00:16

That means they have to meet two criteria.

00:18

No surcharge and no flood

00:22

pipes have to be sized adequately and effective storage solutions need to be built

00:27

to do that.

00:28

It is vital to understand and accurately

00:30

represent the inflows entering a drainage network.

00:34

This makes it very important to use the right rainfall

00:37

methodology for each site that you are working on.

00:40

Get this wrong and it could spell disaster.

00:43

Your model could predict no flooding but the

00:46

reality might be a completely different story.

00:49

Remember

00:50

different rainfall theories will predict different rainfall levels,

00:54

which rainfall theory you use is completely dependent

00:57

on your project location and approving authorities.

01:01

This example is representative of a location in the

01:04

UK where there are two established rainfall theories.

01:08

Fs are flood studies report and F E H flood estimation, handbook

01:14

info, drainage, has these theories embedded

01:18

th is the more modern and is generally recommended but it does

01:22

need input parameters to be purchased via the th web service.

01:27

Fs our rainfall is therefore often used for

01:30

training purposes because there is no extra cost.

01:34

There are two separate stages to the design process.

01:38

Stage one is to design for a no surcharge criteria

01:41

in which the pipes must not become more than full

01:44

and there is always a free surface within the pipe

01:46

because the pipe capacity is greater than the flow rate.

01:50

This is tested by a steady state calculation for a one in one year storm,

01:54

or at most a one in five year storm.

01:58

Stage two is conducted for a higher return period storm,

02:01

typically one in 30 years

02:04

at this stage, a fully dynamic volumetric simulation is required.

02:08

The pipes can surcharge, but the manholes must not flood.

02:13

Ultimately,

02:14

the goal is to produce a system that passes both the stage one and stage two tests.

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.)
    The InfoDrainage interface with the Profile – Flow1 dialog box open in front of the Plan View, which shows an example profile view of a flow path.

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.
    The Plan View, with a drainage model in the background and the Network Drainage Report dialog box open in front of it, showing a table of pipe data for the model.

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.
    The Plan View, with a drainage model in the background and  the Connections Summary dialog box open in front of it, reporting that some of the pipes in the example are surcharged.
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