Hydraulic geometry of a small tidal estuary

A tidal channel in a marsh bordering the Potomac River near Alexandria, Va., was mapped, and current-meter measurements of discharge were made at various locations and at various stages in the tidal cycle.These measurements allowed analysis of the change of width, depth, and velocity with discharge at various cross sections and along the length of the channel.There is also presented a theoretical development of some, of these same relations based on hydraulic principles and on the assumption of a uniform distribution of energy and a minimum rate of work in the system as a whole.The change of width, depth, and velocity with discharge downstream developed from the field data checked closely with the theoretically derived values.The estuarine channel differs from a terrestrial one in that discharge at any section in an estuary varies depending on how the flow shaped the entire length of the channel between the point in question and the main body of tidal water.The result is that a tidal channel changes more rapidly in width and less rapidly in depth as discharge changes downstream than does a terrestrial channel. Bl