Troble with any dredging is when material is being transported to where the water line is, any distance you go above the water line makes the suction drop off dramatically.
With the size pump and suction line you are talking about not only would it be pretty ineffective it would be slow.
To even begin to contemplate it would need a much bigger pump and nozzle configured correctly. Getting the venturi effect requires a bit of tinkering or a premade nozzle. Be much more effective to drain the water, dig the mud, and refill.
If you are hell bent on what you want to do go a youtube search there are videos there that will explain it exactly. Ive built one for cleaning our small pool 1:1 ratio in 1 inch, even with a proper nozzle youd only move tiny amounts of mud over a very long time.
Not impossible to do but horribly ineffective.