An argument often encountered in FE literature is the putative fact that engineers ignore earth's supposed curvature when designing/building bridges, railroads, tall buildings, and canals. I think the issue has been argued to a standstill regarding bridges and tall buildings. I'm not sure about railroads. It depends upon how much extra track and ties are truly needed. If the discrepancy is significant, cost factors could be affected, and cushy engineering jobs lost.
However I haven't looked much at canals yet. For a short canal, yes, one can say that simply digging a bit deeper here or there might suffice. But here is a case that we should look at, namely, the 100-mile
Suez canal connecting the Mediterranean and the Red Sea. From
Earth--Monthly Magazine Numbers 47-48, I find these pictures.
First, the full two-page spread of the canal:
Next, the image portion from the left-hand page:
Next, the image portion from the right-hand page:
Here is a brief discussion given in the article:
Is this a convincing case that encourages the opinion that the earth is flat? Or is it merely the case that the earth happens to be flattish in that area?