Water levels are often influenced significantly by weirs within the watercourse. The General Weir is a general purpose unit for modelling a broad crested weir with a rectangular throat. By amending the input coefficients, it is also possible to model weirs with a parabolic or triangular control section. The unit models the weir in free or drowned mode with forward or reversed flow.
To add a 1D General Weir:
In the 1D River Network table, confirm you have a River Section at both the upstream and downstream toe of the weir.
If only one River Section exists, select the River Section in the 1D River Network, Right-click and select Copy. Right-click again and select Paste. Rename the duplicated River Section with an appropriate node label.
Set the Distance to next value as zero within the upstream River Section.
From the 1D River Build tab, select the Weirs dropdown menu and select General Weir. Manually place the General Weir unit between the upstream and downstream River Sections.
Copy the node labels of the upstream and downstream River Sections into the upstream and downstream labels of the General Weir unit.
Define the geometry of the weir by specifying the Elevation of Crest. Note that the weir upstand does not need to be explicitly entered into the General Weir unit.
Define the Breadth of Crest. This is the breadth of crest perpendicular to flow. For non-rectangular control sections the breadth should be set to 1.0 and the Velocity Coefficient input as normal.
Specify the Discharge Coefficient and Velocity Coefficient as required. Note that these coefficients are multipliers applied to the broad-crested weir equation. See Weir for details on the equations used.
Specify the Modular Limit and Exponent as required. Note that the default Exponent of 1.5 is for modelling a rectangular control section. For parabolic or triangular control sections the exponent should be changed to 2.0 and 2.5 respectively.
Your General Weir is now added to your river reach. Make sure to save the adjusted river network!
Download the sample data used in the video to try it yourself: