Modeling Stratified Flow in Combined Sewer Overflow

A series of field surveys was conducted at Fresh Creek Basin, a tributary of Jamaica Bay, New York, the site of a proposed storage facility for combined sewer overflow (CSO). Data collected during storm events of various intensities indicate that stratification usually occurs during CSO discharge. During all storm events, including intense storms that may cause plug flow, salinity intrusion occurs rapidly with a rising tide. A laboratory model study reproduced the proposed prototype CSO storage facility. It was found that plug flow can be induced in a long channel by placing baffles (lateral obstructions forcing flow beneath or over them) in the flow field. A series of under baffles was found to be more effective than a single baffle; alternating under and over baffles were found to promote stratification. An existing two‐dimensional, unsteady, laterally averaged mathematical model was applied as a predictive tool.