Weir Crest

**Figure:** Weir geometry
$\begin{figure}\epsfig{file=Weir.eps,width=10cm}\end{figure}$

The weir crest is the upstream element of a pair of boundary elements simulating a weir. The corresponding downstream element is the weir slope. Both are illustrated in Figure . The weir can occur in different forms such as broad-crested weirs (left picture in the Figure) and sharp-crested weirs (right picture in the Figure). The volumetric flow Q can be characterized by a law of the form

Q=C b (h-p)^{3/2},

(166)

where C is a constant. For instance, in the formula by Poleni C=2 C_d \sqrt{2 g}/3, where C_d is coefficient smaller than 1 to be measured experimentally [11]. The following constants have to be specified on the line beneath the *FLUID SECTION,TYPE=CHANNEL WEIR CREST card:

the width b
the height p
the constant C
not used
the number of the downstream weir slope element
the number of the upstream reference element, if any

The cross section of the weir is supposed to be rectangular. This is important, since a different form leads to a different exponent in Equation . Notice that a weir can have upstream channel elements attached to it. In that case it is mandatory to specify an upstream reference element.

Example files: channel7.