I had noticed the rotting back-step and had attributed it to the age of the structure. Now I more-strongly suspected it was due to annual flooding.
Jay rented a mini-excavator and used the bucket to dig a channel along the edge of our property (there’s a road in the winter/dry season dividing us). The ground was still frozen, and the water was flowing fast, but he managed to get enough dug to keep the house dry.
Later in the year he had the same machine out again, and the difference between the two times couldn’t have been more marked: “It’s like butter!” Jay said when I asked him how it was going.
Aside from the normal reasons for looking forward to spring, I’m eager to see how this work will affect the run-off pattern this year.