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[[File:Riser.gif|thumb|A two stage riser with low flow controlled with an orifice and high flow controlled with a weir.]]
[[File:Riser.gif|thumb|A two stage riser with low flow controlled with an orifice and high flow controlled with a weir.]]
+
+There are many configurations for multistage risers according to the flow control requirements.
+It is easiest to begin downstream and design with the the highest return period required in mind.
+e.g. start by specifying the pipe/culvert component to control the 100 year flow.
+Then to work backwards to size the lip or weir at the top of the structure to meet the next return period flow.
+
+The riser is then designed with flow through one or more orifices.
<math>
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\end{matrix}\right.
\end{matrix}\right.
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+
+{{Plainlist|1=Where:
+*''Z'' = the depth of ponded water in m,
+*''Z<sub>0</sub>'' = the elevation of the bottom of the orifice in m,
+*''H<sub>0</sub>'' = the height of the orifice in m,
+*''Z<sub>1</sub>'' = the elevation of the weir in m,
+*''C<sub>w</sub>'' = the weir coefficient,
+*''L<sub>w</sub>'' = the length of the weir in m,
+*''C<sub>d</sub>'' = the discharge coefficient of the orifice (often defaulted to 0.6 for a sharp edged orifice),
+*''A<sub>0</sub>'' = the cross-sectional area of the orifice in m<sup>2</sup>,
+*}}