15. SSO Overflow Pipe

This 10-in sewer is equipped with an 8-in overflow pipe located in the downstream manhole.  During a rain event, this sewer experiences backwater and surcharged conditions that limit flow to about 37% of the estimated full-pipe capacity.  The SSO is activated once the flow depth reaches the invert elevation of the 8-in overflow pipe.

The rate of overflow through the overflow pipe can be estimated using iso-Qs, as shown in the previous example.  This SSO lasted for over 10 hours and discharged 165,000 gallons of untreated wastewater to the environment.