How is overflow above the top of a LID control accounted for?
To model overflow from a LID control, enter the maximum height of the berm in the property called "Surface Storage Depth" in the properties of the Low Impact Development Control.
"When confining walls or berms are present this is the maximum depth to which water can pond above the surface of the unit before overflow occurs (in inches or mm). For Rooftop Disconnection it is the roof’s depression storage depth and for Vegetative Swales it is the height of the trapezoidal cross section"
When the depth rises above the surface storage depth, overflow passes to the Outflow Node of the LID element's parent catchment, using the following equations:
–Overland flow using Manning’s formula
–Overflow using the weir equation
Low Impact Development (LID)