Weir property sheet
This special weir object or component can be used with the Full unsteady hydraulic model to provide multiple outlets from detention basins, which can be subject to tailwater influence. It operates like the orifice object that has the same purpose.
The inputs to the property sheet for the weir consist of the name (of up to 10 characters) and various weir characteristics, as shown below. For the rectangular (transverse) and rectangular (side spill weir) weir types, it is necessary to enter a discharge coefficient, a crest elevation and length.
The transverse weir applies the usual equation in which flowrate is proportional to h1.5, where h is the depth of the flow, while the side spill weir assumes that flowrate is proportional to h1.67. Side spill weirs may be located in some pits.
The V-notch and trapezoidal weirs require side slopes to be specified at the edges of the weir.
The weir object can be bent in the middle, by dragging and dropping the 'W' at the centre. This facilitates the specification of several weirs located between the same end points, as shown below.