Cress Help - Flow - Tidal flow - A16.1

Channel detention (storage area approach)

When assessing storage basins it is assumed that the surface of the water in the basin is flat and horizontal. The calculation rule determines the variations in water level in the basin that result from variations in sea level (for example tides). It is assumed that the variations in water level are sine shaped. The phase shift, the maximum fall over the flow opening and the maximum average velocity in the flow opening are also calculated.

Equations used:

The variations in water level of the sea in relation to the SWL are schematised as:

The variations in water level of the basin in relation to SWL is schematised as:

with:

For the phase shift:

and

The maximum hydraulic gradient/fall in level follows from:

and the maximum flow velocity follows from:

in which:

A: storage area of the basin [m2]
B: width of the flow opening [m]
c: discharge coe­fficient for an short free-flow weir/spillway (ca. 0.9 - 1.3) [-]
Hz: tidal range at sea [m]
h: average water depth in the flow opening [m]
T: wave or tidal period [s]

Reference:

[a] Dictaat B73, Lange golven deel 1, C. Verspuy, april 1987