An Uncontrolled Outlet can be a component of a Dam, Diverted Outlet, or Outlet Group. An uncontrolled outlet can represent an ungated overflow spillway or any opening in the dam through which water can pass without impediment by a movable gate or panel.
Two options for specifying the capacity of an uncontrolled outlet are provided — a weir equation or an Elevation vs Outflow capacity table. If the outlet is a standard overflow weir, you can use the weir equation to compute the flow over the spillway using a Weir Coefficient and a spillway Length that you must provide. You can use the capacity table for all types of uncontrolled outlets whose capacity can be defined by a simple rating curve (elevation vs outflow relationship.
Weir Coefficient—typically in the range 2.6-4.0 depending on the shape of the spillway crest. This value determines flow over the spillway in the weir equation.
Length—spillway length.
Elevation vs. Outflow Table—enter data into the table in increasing order of elevation. You can either copy-and-paste the data from a spreadsheet application or type it in manually.
Figure: Reservoir Editor - Physical Data - Uncontrolled Outlet
Whether you use the weir equation or the Elevation vs Outflow table, you must specify an Outlet Elevation. The Outlet Elevation serves as a trigger to determine when this outlet starts "flowing."
Outlet Elevation—The minimum elevation at which the outlet will begin to release water. This elevation is usually the "sill" or bottom of the outlet opening. .
