Cress Help - Scour - Scour by jets - B28.11

Two dimensional jets

In this part of the calculation rule the erosion process cause by descending and horizontal in-flowing jets is handled. Some simple equations are presented that calculate the maximum erosion depth. The figures below show a number of erosion situations associated with various hydraulic structures.

 

Usually a current/jet picks up particles from the bed/bottom and transports them downstream of the impact area. The impact area is transformed into an energy dissipater, as a result of which an erosion hollow is formed.

Two dimensional inflow jets

The two-dimensional inflow current is found, for example, with partially opened gates. The split has an infinite breadth (or is sufficiently wide). Different types of current can arise, see the figure below. The following equation can be used to determine the maximum erosion depth:

    equation 1

with

    equation 2

and

    equation 3

In which :

This equation is only valid if the water depth directly behind the inflow opening is approximately equal to the undisturbed downstream water depth (downstream of the hydraulic jump).

There is still some uncertainty about the value of c2H.