The concept of a residual velocity is well known to most navigatorsas well as researchers. For example, Fig. 7.5, a sketch by Bowden andGilligan (1971), shows one flood and two ebb channels in the MerseyEstuary. " Flood," of course, means that the flood current is stronger thanthe ebb current, and "ebb" that the ebb current is stronger. In largeestuaries one cause of the residual circulation is the earth's rotation,which deflects currents to the right in the Northern hemisphere and to theleft in the Southern hemisphere. Therefore in the northern hemisphereflood tide currents are deflected towards the left bank (looking seaward)and ebb currents towards the right bank, resulting in a netcounter-clockwise circulation. As an example, this circulation is thoughtto explain why in Chesapeake Bay the salinity is on the average higher onthe eastern shore (the left bank looking seaward) than on the westernshore.