Relief Sewer : A sewer built to carry the flows in excess of the capacity of an existing sewer; also, a sewer intended to carry a portion of the flow from a district in which the existing sewers are of insufficient capacity
NFPA 820 Standard for Fire Protection in Wastewater Treatment and Collection Facilities, 2008 ed. http://www.nfpa.org/codes-and-standards/document-i nformation-pages?mode=code&code=820, (Std: Fr Prac in Wastewater Treatment and Collection Fcilty - Amer) {351 NFC}