Science proves water seeks it's own level through experimentation. Two bodies of water being joined together through any form at surface or below will equalize and have the same horizontal surface and not curve at any point. If you disagree, I then challenge you to actually verify the water contained in the Suez Canal curves with a Globe Earth's circumference and is not below the grade of the curve and is not level as experimentation proves.
A surveyor by the name of Bourdaloue would disagree and verified the curvature for the Suez Canal project back in the 1850's. His predecessor, LePere, had erroneously surveyed and stated the Med was 9 meters above the Red. That stalled the project for some 50 years. Bourdaloue came along and being one of the fathers of "Orthometric Levelling", determined that the difference was actually negligible. He performed his survey from end to end.
What is Orthometric Levelling in surveyor parlance? It is defined by determining the orthometric height of a point. It is the distance H along a plumb line from the point to a reference height. When the reference height is a geoid model, orthometric height is for practical purposes "height above sea level".
In order to determine the true height of the Med versus the Red and all points in between, Orthometric Levelling surveying was performed and verified.