I can offer that back to you and it once again becomes teet for tat.
You can try but you'd make a teet of yourself.
Show me the facts I'm disregarding in favour of fantasy.
Don't lead with water level, there are facts but not in your favour.
oh and you seem to have missed this....
Here's a simple device you could make for yourself if you wished, templates are available online.
I never knew that central spindle was called a gnomon so maybe this is all an appeal to authority and no longer works but...
If you point it North and set the angle to your own latitude, or put another way, parallel to Earths axis of rotation, two things will happen which you will find difficult (and by difficult I mean impossible) to explain on any version of a flat or orange squeezer Earth, especially one with a carbon arc projector in the middle.
Firstly you will notice that for half of the year, one side of the disk is in shadow, while for the other half of the year the other side is in shade.
Secondly you might notice, weather permitting, that at the equinox both sides are in shade as the Sun will be shining directly along the edge.
Set up correctly this will work anywhere on Earth, so long as it's a globe, tilted, spinning and in orbit around the Sun.
On a related note, put a stick in the ground, or make use of a convenient fence post or something similar. Given a sunny day, you could mark at regular intervals the position of the tip of the sticks shadow. Do this as often as you like and you'll find the shadows tip marks out an arc, except for around the equinox where the shadow tip will mark out a straight line.
Both of these make perfect sense if you are on a slightly tilted and spinning globe in orbit around the sun. They are not possible otherwise.