A channel, usually an open channel constructed adjacent to an embankment, which conveys flows in excess of the design capacity of the principal spillway.

A spillway which provides for additional safety should emergencies not contemplated by normal design assumptions be encountered, i.e., inoperable outlet works, spillway gates, or spillway structure problems. The crest is usually set at maximum water surface.

A constructed channel at a dam or other structure designed to pass flood flows that exceed the design capacity of the flow through structures.

An outflow from a detention/retention facility that provides for the safe overflow of floodwaters for large storms that exceed the design capacity of the outlet or in the event of a malfunction. The emergency spillway prevents the water from overtopping the facility.

A shallow notch in the lagoon sidewall to allow lagoon overflow to spill over into a secondary containment or into a grass infiltration area in case of emergencies such as unexpectedly large rainfall event. The spillway should be designed and constucted under the supervision of a registered professional engineer or the NRCS and must be diverted away from water courses. While overflow should be avoided if at all possible, failure to provide a planned overflow in case of rainfall events that exceed design values risks berm failure that can result in a catastrophic pollution situation.