Why depth matters for drainage
Water standing in a shallow buried line freezes solid. A frozen line does not drain, so the next thaw backs discharge up the pipe and out at the foundation — precisely where you buried the line to avoid. Depth is not about protecting the pipe from cracking so much as keeping the water inside it moving.
What that means in practice
Full frost-line depth is not always achievable or necessary for a downspout line. What matters more is continuous fall: a line that slopes consistently to daylight or to a pop-up emitter drains completely between rains, so there is no standing water left to freeze. A perfectly deep line with a belly in it will still freeze at the low point.
Where we can get depth we take it, particularly on long runs and on the north side of a house where ground stays frozen longest. Where we cannot, we prioritise slope and a clean outlet.
Frost heave
The other consequence of freezing ground is movement. Soil expands as the water in it freezes, and that heave shifts anything sitting in or on it — splash blocks, surface extensions, pop-up emitters, and shallow pipe. It is a large part of why surface drainage solutions drift out of position over a few Kansas City winters while properly buried ones stay put.
Clay makes it worse
The dense clay under most of the metro holds water rather than draining it, so there is more water in the soil to freeze and more heave when it does. That combination — wet clay plus a real freeze depth — is why drainage that would be fine in a sandier climate underperforms here.