How to add Spills to Bridges
- 10 Jul 2023
- 2 Minutes to read
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How to add Spills to Bridges
- Updated on 10 Jul 2023
- 2 Minutes to read
- Print
- DarkLight
Article Summary
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Extreme flood events can often overtop bridges and culverts. If a spill is not included then water can artificially back up causing an unrealistically high water level upstream of the structure and an unrealistically low water level downstream.
A spill unit can be used to allow flow to bypass the structure via the deck of the bridge or culvert and return to the channel downstream.
Note:
The spill unit should be used where the user expects the flow to return to channel downstream and be conveyed elsewhere once overtopping the structure.
Steps
Starting with an existing Bridge unit (Arch, USBPR or Pier-Loss) connected to upstream and downstream River Sections, open the Bridge unit and update the upstream and downstream node labels to become unique labels (i.e. different to the labels of the upstream and downstream River Sections). E.g. i
Tip:
If your upstream River Section label is XS01, your bridge upstream label might be XS01b, for instance.
In the 1D River Network table, select the River Section upstream of the bridge unit.
From the 1D River Build tab, navigate to the Connectors menu and from the Junctions dropdown menu, select an Open Junction. Manually place the Open Junction unit between the upstream River Section and the bridge unit. Copy the upstream River Section label and the bridge unit upstream label into the Open Junction unit. Repeat this to add a second Open Junction unit downstream of the bridge.
Within the bridge unit, copy the upstream and downstream River Section labels into the Upstream Remote and Downstream Remote label fields. The bridge unit should now be linked to the upstream and downstream River Sections via Open Junction units.
From the 1D River Build tab, select a Spill unit. Manually place the spill unit on the deck of the structure adjacent to the bridge unit. Within the Spill unit, specify the upstream and downstream node labels. E.g. if your upstream River Section label is XS01, your spill upstream label might be XS01spu. Copy the upstream and downstream Spill unit labels into the upstream and downstream Open Junction unit labels respectively.
Populate the Spill Section Data of the Spill unit with the cross-section data for the structure deck, noting that the width of the spill section should be consistent with that of the upstream and downstream River Sections. Consider an appropriate weir coefficient (Cd) for calculating discharge over the deck of the structure.
Note:
Your spill unit has now been added to your existing bridge. Make sure you save the adjusted river network!
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