The terms “flushing time” and “residence time” have cropped up often in discussions about water quality and eelgrass health in the Great Bay Estuary. Flushing time and residence time are not the same thing and should not be used interchangeably. Flushing time is defined as the time it takes to replace a certain water mass in a coastal system and is most often used as a general measurement of water exchange in an estuary used to relate water exchange from one estuary to another. The most recent estimates of flushing time (2013) for the Great Bay are between 2.5 and 7 days. Residence time describes how long a parcel, starting from a specified location within a waterbody, will remain in the waterbody before exiting; residence time is more often used to understand or predict chemical and biological processes for a particular system. The most recent estimate of residence time for the Great Bay (2005) is between 5 and 20 days.
Piscataqua Region Estuaries Partnership (PREP)
Matso, Kalle, "Flushing Time Versus Residence Time for the Great Bay Estuary" (2018). PREP Reports & Publications. 413.