When runoff exceeds inlet capacity, the spread, depth and velocity of ponded water may be calculated from the geometry and hydraulic properties of the cross section.

In an XPSWMM/XPStorm model, Pavement Crossfalls may be stored in the Global Database. A Pavement Crossfall record is assigned to a hydraulics inlet node using the Inlet Capacity dialog.

As shown in the above diagram, the Pavement Crossfalls are defined as a section extending from the boundary line (representing the edge of the drainage) to the pavement centerline. It consists of three regions:

1. Verge (Shoulder) region between the boundary and the gutter
2. Gutter channel draining to drainage inlet, lowest point designated as invert
3. Pavement roadway surface extending from the lip to the centerline (or highpoint)

The terms in the dialog are defined as: 

A Verge (Shoulder) Distance (Boundary to Back of Curb) (ft, m)

B Verge (Shoulder) Slope (Boundary to Back of Curb) (%)

n-verge Verge (Shoulder) Roughness (Manning's n)

C Width of Top of Back of Curb (ft, m)

D Distance from Face of Curb to Nominal Curb Line

E Distance from Nominal Curb Line to Gutter Invert (ft, m)

F Distance from Gutter Invert to Curb Lip (ft, m)

G Depth from Back of Curb to Gutter Invert (ft, m)

H Depth from Back of Curb to Gutter/Pavement Lip (ft, m)

n-gutter Gutter Roughness n

I Pavement Width (Lip to Road Centerline) (ft, m)

J Pavement Crossfall (Lip to Road Centerline) (%)

n-pave Pavement Roughness n