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Describe the considerations when connecting a 1D sewer network to a river model.
Transcript
00:03
Connecting a 1D sewer network to a river model is a relatively simple operation,
00:10
requiring you to attach links to common nodes so that their calculations are linked.
00:16
It is important to note that outfalls do not provide connectivity.
00:20
So, if you have an outfall node that is located within a river reach, this will not transfer flows at that location.
00:28
A break node—and cross section—is required at any point where you connect a conduit to a river.
00:35
It is a good idea to plan the locations first, to ensure that break nodes exist at these locations.
00:42
This is especially true if the models are being built independently.
00:46
Ideally, you do not want to build all these locations into your river model retrospectively.
00:53
The connection itself can be made by either changing the conduit downstream node into a break node,
00:59
or by adding a flap valve or culvert outlet link in between, as appropriate.
01:05
If you are connecting existing models, there can be problems with misalignment of levels.
01:11
This is usually a problem at outfall locations, where levels are not always available and are often assumed.
01:19
For integrated models, the level is fundamental to understanding the hydraulic impact that the systems have on each other.
01:27
Therefore, it is quite common to have to undertake additional outfall surveys when doing this work.
01:34
Depending on the extent of the assumed data, you may need to realign sewer networks that were assumed or inferred.
01:42
An appropriate headloss also needs to be set at the conduit end.
01:47
This may simply be NONE for an outfall discharging at a high level.
01:51
Note that the NORMAL headloss type for conduits is intended to represent the headloss due to manholes
01:59
and should not be used for this purpose.
02:02
A multi-system model is going to have different peak timings.
02:06
The challenge is trying to marry together several different systems
02:10
and their interactions in a way that gives you the required output in the most efficient manner.
02:17
The response time of the watercourse to rainfall is critical when considering interactions.
02:23
If the below-ground system and above-ground system have similar concentration times,
02:29
there is a strong case to integrate the models of the two systems.
02:33
If the above-ground system has a significantly greater time of concentration,
02:38
a case can be made for the two systems to be treated independently.
02:43
For instance, a level file is often applied to represent large rivers in sewer models.
02:50
The justification is that the peak timing and duration of the river is a magnitude above that of the sewer system,
02:58
so you are representing a worst-case scenario.
03:02
However, the fact that the level is driven by a different system
03:06
means that the chance of such an occurrence is much lower than with the rainfall probability alone.
03:12
Nonetheless, the use of a level file does significantly simplify the modelling.
03:19
When you have an urban watercourse, it may be a combination of rural and urban runoff that creates the peaks,
03:26
or it may be that the peak timings are significantly different from the sewer, due to the nature of the systems—piped vs natural.
03:35
This is when a fully integrated model is likely required.
03:40
You may even need to adjust your input files so that you can align the peaks from both systems,
03:45
if you want to consider the consequence of that occurring.
00:03
Connecting a 1D sewer network to a river model is a relatively simple operation,
00:10
requiring you to attach links to common nodes so that their calculations are linked.
00:16
It is important to note that outfalls do not provide connectivity.
00:20
So, if you have an outfall node that is located within a river reach, this will not transfer flows at that location.
00:28
A break node—and cross section—is required at any point where you connect a conduit to a river.
00:35
It is a good idea to plan the locations first, to ensure that break nodes exist at these locations.
00:42
This is especially true if the models are being built independently.
00:46
Ideally, you do not want to build all these locations into your river model retrospectively.
00:53
The connection itself can be made by either changing the conduit downstream node into a break node,
00:59
or by adding a flap valve or culvert outlet link in between, as appropriate.
01:05
If you are connecting existing models, there can be problems with misalignment of levels.
01:11
This is usually a problem at outfall locations, where levels are not always available and are often assumed.
01:19
For integrated models, the level is fundamental to understanding the hydraulic impact that the systems have on each other.
01:27
Therefore, it is quite common to have to undertake additional outfall surveys when doing this work.
01:34
Depending on the extent of the assumed data, you may need to realign sewer networks that were assumed or inferred.
01:42
An appropriate headloss also needs to be set at the conduit end.
01:47
This may simply be NONE for an outfall discharging at a high level.
01:51
Note that the NORMAL headloss type for conduits is intended to represent the headloss due to manholes
01:59
and should not be used for this purpose.
02:02
A multi-system model is going to have different peak timings.
02:06
The challenge is trying to marry together several different systems
02:10
and their interactions in a way that gives you the required output in the most efficient manner.
02:17
The response time of the watercourse to rainfall is critical when considering interactions.
02:23
If the below-ground system and above-ground system have similar concentration times,
02:29
there is a strong case to integrate the models of the two systems.
02:33
If the above-ground system has a significantly greater time of concentration,
02:38
a case can be made for the two systems to be treated independently.
02:43
For instance, a level file is often applied to represent large rivers in sewer models.
02:50
The justification is that the peak timing and duration of the river is a magnitude above that of the sewer system,
02:58
so you are representing a worst-case scenario.
03:02
However, the fact that the level is driven by a different system
03:06
means that the chance of such an occurrence is much lower than with the rainfall probability alone.
03:12
Nonetheless, the use of a level file does significantly simplify the modelling.
03:19
When you have an urban watercourse, it may be a combination of rural and urban runoff that creates the peaks,
03:26
or it may be that the peak timings are significantly different from the sewer, due to the nature of the systems—piped vs natural.
03:35
This is when a fully integrated model is likely required.
03:40
You may even need to adjust your input files so that you can align the peaks from both systems,
03:45
if you want to consider the consequence of that occurring.
Connecting a 1D sewer network to a river model is a relatively simple operation, requiring you to attach links to common nodes so that their calculations are linked.
It is important to note that outfalls do not provide connectivity. So, if you have an outfall node that is located within a river reach, this will not transfer flows at that location. A break node—and cross section—is required at any point where you connect a conduit to a river.
IMPORTANT: If you are connecting existing models, there can be problems with misalignment of levels. This is usually a problem at outfall locations, where levels are not always available and are often assumed. For integrated models, the level is fundamental to understanding the hydraulic impact that the systems have on each other. Therefore, it is quite common to have to undertake additional outfall surveys when doing this work.
A multi-system model is going to have different peak timings. The challenge is trying to marry together several different systems and their interactions in a way that gives you the required output in the most efficient manner.
A level file is often applied to represent large rivers in sewer models. The justification is that the peak timing and duration of the river is a magnitude above that of the sewer system, so you are representing a worst-case scenario. However, the fact that the level is driven by a different system means that the chance of such an occurrence is much lower than with the rainfall probability alone.
Note: When you have an urban watercourse, it may be a combination of rural and urban runoff that creates the peaks, or it may be that the peak timings are significantly different from the sewer, due to the nature of the systems—piped vs natural. This is when a fully integrated model is likely required.