Why can icings block culverts and overflow onto roads?

Icings, also known as Aufeis or naleds, form in smaller streams when the water flow freezes completely during cold periods. When subsequent groundwater—which remains relatively warm—continues to flow into the stream, it is forced over the surface of the existing ice, where it then freezes.1

This process can repeat, causing the ice to build up to significant thicknesses. These accumulations can become large enough to completely block culverts, which prevents water from passing through its intended drainage path and forces it to overflow onto adjacent roads.1