I bought a house about a year ago that was built in 1952, and the original house has French drains and a sump pump which keeps the basement dry. There is an extension, however, which was added at some subsequent point, and its basement has a problem with flooding.
I noticed the flooding only happens in the winter. Snowmelt is the most common precipitator, but heavy rain at non-freezing temperatures does as well. But it is bone dry in other seasons.
There are two large neighboring fields, probably about the size of a football field, which the city floods in the winter, in order to allow it to freeze and become a public ice rink. There is a truly enormous amount of water in those fields, and my house is about 100 feet from there. My basement flooding seems to have more-or-less started when they they flooded the fields, although hard to pin down timing due to heavy rainfall/snowfall not being too frequent.
Could the hydrostatic pressure from a man-made neighboring body of water be raising the water table and causing my flooding? If so, how could I test this hypothesis?