A number of parameters define the culvert characteristics:
· Upstream Invert
Invert level to the left of the cross section for a short culvert and at the start line for a long culvert.
· Downstream Invert
Invert level to the right of the cross section for a short culvert and at the end line for a long culvert.
NOTE: Upstream and downstream location is not necessarily the inlet and outlet location, respectively.
· Length
Length of the culvert.
· Manning's n
Manning's bed resistance number along the culvert (for friction loss contribution). n = 1/M (Manning number)
· No. of Culverts
'No. of Culverts' is a number identifying how many culverts exist at the specific culvert location with identical geometrical definition.
An example; Five identical shaped draining pipes are placed just next to each other in an earth dam, and in order not to make 5 individual culvert definitions - one for each pipe - the 'No. of Culverts' in this case can be defined as 5 and the simulation engine will recognize that 5 culverts of identical shape and size are located here and flow calculations will take this into account accordingly.
· Alpha zero
When the water level gradient across a structure is small the corresponding gradient of the discharge with respect to the water levels is large. This in turn may result in a very rapid flow response to minor changes in the water level upstream and downstream. Alpha zero is the water level difference at which the discharge calculation is described by a linear variation. If the water level difference is below this value the discharge gradients are suppressed. The default setting is 0.01 meter. If a structure shows oscillatory behavior it is recommended to increase this value slightly.