& Construction
![architecture engineering and construction collection logo](https://damassets.autodesk.net/content/dam/autodesk/www/universal-header/flyout/architecture-engineering-construction-collection-uhblack-banner-lockup-364x40.png)
Integrated BIM tools, including Revit, AutoCAD, and Civil 3D
& Manufacturing
![product design manufacturing collection logo](https://damassets.autodesk.net/content/dam/autodesk/www/universal-header/flyout/product-design-manufacturing-collection-uhblack-banner-lockup-364x40.png)
Professional CAD/CAM tools built on Inventor and AutoCAD
Integrated BIM tools, including Revit, AutoCAD, and Civil 3D
Professional CAD/CAM tools built on Inventor and AutoCAD
Transcript
00:03
When you design hydraulic drainage systems based on rainfall theory,
00:07
you will need to work with historical data that tracks the intensity, duration, and frequency of rainfall in a given area.
00:15
IDF curves are graphical tools that describe the likelihood of a range of extreme rainfall events.
00:21
This is an example of a typical IDF curve that represents a single design storm
00:27
as a relationship of intensity against time.
00:30
And just like all real rain events, it starts off from 0, builds up to a maximum,
00:36
and then fades away back down to 0.
00:39
There are three essential elements of any design storm: the return, the duration, and the shape.
00:47
These three elements are part of the storm definition,
00:50
which in this case is “1:30, 60 minute, FSR Winter storm”.
00:55
The return is how often that type of storm occurs.
00:59
This example is a 1-in-30-year storm,
01:02
so on average, this is the sort of storm that occurs once every 30 years.
01:06
And because it is an average, realize that two 30-year storms can occur within the same year.
01:13
Furthermore, due to climate change, severe storms like this are becoming more common.
01:18
So, the sort of storm that used to happen once every 30 years
01:22
is now happening maybe once every 10 years.
01:25
The duration is how long the storm lasted,
01:28
and you can see that this storm is 60 minutes long.
01:32
The shape of the IDF curve is determined by the rainfall theory.
01:36
This graph uses an obsolete theory in the UK called the Flood Studies Report Winter Profile,
01:42
but it gives us the storm's shape as a typical bell-shaped curve.
01:46
This next example shows three different storms of three different durations,
01:50
but all of them represent the same return—a 1-in-30-year storm.
01:56
What these show is that shorter storms are generally more intense than longer storms,
02:00
whereas the longer storms have a greater volume.
02:04
So, you can see that if 24 millimeters lands in 30 minutes,
02:08
that equates to an average intensity of almost 50 millimeters an hour.
02:13
The longer duration of 37 millimeters falls in two hours.
02:17
Therefore, a greater volume of rainfall over a longer period means that the average intensity is lower,
02:27
And again, this is still a 1-in-30-year storm.
02:31
So, when you are running your design analysis, it is important to represent all of these storms,
02:36
in case your drainage systems are susceptible to short, intense storms
02:40
or longer, lower-intensity storms.
02:43
To represent this variety in duration and intensity, you use an IDF table.
02:49
For example, for the 60-minute storm,
02:52
you can see that it has a depth of 31 millimeters in one hour.
02:56
And in the IDF table, this one storm represents one point on the curve at 31 millimeters and 60 minutes.
03:04
Therefore, the average intensity is 31 millimeters an hour.
03:09
Now, when you add other storms, they add other points to this curve,
03:13
until they build up to a complete curve.
03:16
Notice that, as the duration gets longer, the intensity gets lower,
03:20
and again, this is for one return of 30 years.
03:24
There are several rainfall theories built into the program that you can apply.
03:28
However, if you are working in a region of the world that is not covered by one of these existing rainfall theories,
03:34
then you will need to develop your own IDF curve.
03:38
To do that, you will need to input several return periods.
03:42
For example, these three IDF curves represent three different return periods:
03:53
It is important to understand that a higher return period is not a multiple of a lower period.
03:58
So, a 10-year storm would not be double what a 5-year storm is,
04:03
and you can see that in these returns.
04:05
As the return goes up, the storms do increase,
04:09
but they also retain the same shape.
04:12
This translates into a series of IDF curves, each for a particular return.
04:17
A rainfall event's shape is defined by the rainfall theory applied.
04:21
There are several different theories built into the program that impact the drainage design,
04:26
such as the Desbordes, NOAA, SCS or Conservation Service, and Chinese design.
04:34
Notice that the Chinese design is a constant intensity throughout the storm;
04:38
therefore, it does not have a curved shape.
04:41
These are represented using a dimensionless profile,
04:45
which is graphed as the dimensionless duration against the dimensionless cumulative depth.
04:50
This allows for the representation of storms of any return and any duration,
04:55
yet they still retain the same shape in the curve.
04:58
This example is one that is used in Germany and could be applied to other countries in the vicinity, such as Poland.
05:05
Alternatively, you can develop your own curve,
05:08
such as this one that was generated from the first bell-shaped curve shown in this tutorial.
05:13
So, you essentially take both the return and the duration out of it.
05:18
In summary, if you need to represent storms outside of one of the available existing theories,
05:23
you need two elements.
05:25
You need the IDF curve,
05:27
which defines the return and the duration,
05:30
and you need the cumulative depth percentage against the time percentage,
05:34
which is dimensionless, and defines the shape of those events.
Video transcript
00:03
When you design hydraulic drainage systems based on rainfall theory,
00:07
you will need to work with historical data that tracks the intensity, duration, and frequency of rainfall in a given area.
00:15
IDF curves are graphical tools that describe the likelihood of a range of extreme rainfall events.
00:21
This is an example of a typical IDF curve that represents a single design storm
00:27
as a relationship of intensity against time.
00:30
And just like all real rain events, it starts off from 0, builds up to a maximum,
00:36
and then fades away back down to 0.
00:39
There are three essential elements of any design storm: the return, the duration, and the shape.
00:47
These three elements are part of the storm definition,
00:50
which in this case is “1:30, 60 minute, FSR Winter storm”.
00:55
The return is how often that type of storm occurs.
00:59
This example is a 1-in-30-year storm,
01:02
so on average, this is the sort of storm that occurs once every 30 years.
01:06
And because it is an average, realize that two 30-year storms can occur within the same year.
01:13
Furthermore, due to climate change, severe storms like this are becoming more common.
01:18
So, the sort of storm that used to happen once every 30 years
01:22
is now happening maybe once every 10 years.
01:25
The duration is how long the storm lasted,
01:28
and you can see that this storm is 60 minutes long.
01:32
The shape of the IDF curve is determined by the rainfall theory.
01:36
This graph uses an obsolete theory in the UK called the Flood Studies Report Winter Profile,
01:42
but it gives us the storm's shape as a typical bell-shaped curve.
01:46
This next example shows three different storms of three different durations,
01:50
but all of them represent the same return—a 1-in-30-year storm.
01:56
What these show is that shorter storms are generally more intense than longer storms,
02:00
whereas the longer storms have a greater volume.
02:04
So, you can see that if 24 millimeters lands in 30 minutes,
02:08
that equates to an average intensity of almost 50 millimeters an hour.
02:13
The longer duration of 37 millimeters falls in two hours.
02:17
Therefore, a greater volume of rainfall over a longer period means that the average intensity is lower,
02:27
And again, this is still a 1-in-30-year storm.
02:31
So, when you are running your design analysis, it is important to represent all of these storms,
02:36
in case your drainage systems are susceptible to short, intense storms
02:40
or longer, lower-intensity storms.
02:43
To represent this variety in duration and intensity, you use an IDF table.
02:49
For example, for the 60-minute storm,
02:52
you can see that it has a depth of 31 millimeters in one hour.
02:56
And in the IDF table, this one storm represents one point on the curve at 31 millimeters and 60 minutes.
03:04
Therefore, the average intensity is 31 millimeters an hour.
03:09
Now, when you add other storms, they add other points to this curve,
03:13
until they build up to a complete curve.
03:16
Notice that, as the duration gets longer, the intensity gets lower,
03:20
and again, this is for one return of 30 years.
03:24
There are several rainfall theories built into the program that you can apply.
03:28
However, if you are working in a region of the world that is not covered by one of these existing rainfall theories,
03:34
then you will need to develop your own IDF curve.
03:38
To do that, you will need to input several return periods.
03:42
For example, these three IDF curves represent three different return periods:
03:53
It is important to understand that a higher return period is not a multiple of a lower period.
03:58
So, a 10-year storm would not be double what a 5-year storm is,
04:03
and you can see that in these returns.
04:05
As the return goes up, the storms do increase,
04:09
but they also retain the same shape.
04:12
This translates into a series of IDF curves, each for a particular return.
04:17
A rainfall event's shape is defined by the rainfall theory applied.
04:21
There are several different theories built into the program that impact the drainage design,
04:26
such as the Desbordes, NOAA, SCS or Conservation Service, and Chinese design.
04:34
Notice that the Chinese design is a constant intensity throughout the storm;
04:38
therefore, it does not have a curved shape.
04:41
These are represented using a dimensionless profile,
04:45
which is graphed as the dimensionless duration against the dimensionless cumulative depth.
04:50
This allows for the representation of storms of any return and any duration,
04:55
yet they still retain the same shape in the curve.
04:58
This example is one that is used in Germany and could be applied to other countries in the vicinity, such as Poland.
05:05
Alternatively, you can develop your own curve,
05:08
such as this one that was generated from the first bell-shaped curve shown in this tutorial.
05:13
So, you essentially take both the return and the duration out of it.
05:18
In summary, if you need to represent storms outside of one of the available existing theories,
05:23
you need two elements.
05:25
You need the IDF curve,
05:27
which defines the return and the duration,
05:30
and you need the cumulative depth percentage against the time percentage,
05:34
which is dimensionless, and defines the shape of those events.
Designing hydraulic drainage systems based on rainfall theory involves working with historical data that tracks the intensity, duration, and frequency of rainfall in a given area.
IDF curves: graphical tools that describe likelihood of a range of extreme rainfall events.
A typical IDF curve for single design storm shows intensity over time:
Similar to real rain events, an IDF curve starts from 0, builds to maximum, then fades to 0.
Return is how often the type of storm occurs.
Duration is how long the storm lasted—here, 60 minutes long.
Shape of the IDF curve is determined by the rainfall theory applied.
Next example shows three storms of three different durations, all representing the same return—a 1-in-30-year storm.
When running design analysis, important to represent variety of storms, in case drainage systems are susceptible to short, intense storms or longer, lower-intensity storms.
Used to represent variety in rainfall duration and intensity.
Example: the 60-minute storm from the IDF curve has a depth of 31 mm in one hour. In an IDF table, that same storm represents one point on the curve at 31 mm and 60 minutes for average intensity of 31 mm/hr.
Adding storms adds more points that build up to a complete curve.
For this return of 30 years, as the duration gets longer, the intensity gets lower:
Several rainfall theories are built into InfoDrainage that can be applied.
If you are working in a world region not covered by one of these theories, an IDF curve can be developed by inputting several return periods.
For example, these three IDF curves represent return periods of 2, 30, and 100 years.
Note that a higher return period is not a multiple of a lower period. Example: a 10-year storm is not double the intensity of 5-year storm.
IMPORTANT: with increased return, storms do increase, but they also retain same shape. This translates into series of IDF curves, each for a particular return:
The shape of a rainfall event is defined by the applied rainfall theory.
Theories built into InfoDrainage that impact drainage design include: the Desbordes, NOAA, SCS or Conservation Service, and Chinese design.
Note: the Chinese design has constant intensity throughout storm; therefore, it has no curved shape.
Theories are represented using a dimensionless profile—graphed as the dimensionless duration against the dimensionless cumulative depth.
Allows representation of storms of any return and duration, yet they retain same shape in the curve.
Example below used in Germany—could be applied to countries in vicinity, such as Poland.
Alternatively, you can develop your own curve, such as this one, generated from the first bell-shaped curve shown previously. Essentially, the return and duration are not included:
In summary, to represent storms outside of available existing theories, two elements are needed:
How to buy
Privacy | Do not sell or share my personal information | Cookie preferences | Report noncompliance | Terms of use | Legal | © 2025 Autodesk Inc. All rights reserved
Sign in to start learning
Sign in for unlimited free access to all learning content.Save your progress
Take assessments
Receive personalized recommendations