Why would it need to be 1.2 miles deep? at that point, the floor no longer 26 feet below sea level, but 1.2 miles below.
The builders may not account for the curve, but if they are digging relative to sea level., then they never have to. If throughout the whole stretch of the canal the depth is 26 feet, then the base of it actually is curved without them even intending it to be.
water will always act due to the forces of gravity, not necessarily stay "level." It's why when you have instances of zero gravity (such as in the infamous "vomit comet" plane ride used to train astronauts), you'll see water float.
Sea level is relative to the center of the earth though, not the surface of the land. So sea level actually does have a curve
Why would it need to be 1.2 miles deep? at that point, the floor no longer 26 feet below sea level, but 1.2 miles below.
The builders may not account for the curve, but if they are digging relative to sea level., then they never have to. If throughout the whole stretch of the canal the depth is 26 feet, then the base of it actually is curved without them even intending it to be.
water will always act due to the forces of gravity, not necessarily stay "level." It's why when you have instances of zero gravity (such as in the infamous "vomit comet" plane ride used to train astronauts), you'll see water float.