Flow in the local ditches slows down in winter. What water remains freezes low in the trough. But groundwater seeps that daylight along the ditch margins keep flowing at 50 degrees year round. This pushes thin sheets of water out over the ditch ice, raising its elevation day by day. Eventually, the ice surface overtops the ditchline and begins to creep out over the road surface. Maintenance crews periodically come by with their melt hoses and steam guns to create channels through the ice to drop the seeping water down below road level. It works for about 2 weeks. Then the channels ice in and the crewmen come back.
The steam-filled hose cuts its canyon down through the ice to the bottom of the ditch.