I've been doing some research on this equipment / technology for dredging muck and silt from our 40 yo pond. Drought has it low and the muck is getting exposed. I've found several companies that do this and here is some more information to consider.

As seen on Dirty Jobs....
Venturi system: http://www.aquacleaner.com/

No venturi, running everything through the pump...
http://waterfrontremodelers.com/index.html

Summary is that using the venturi system, you're going to be moving water with fewer solids than running everything through the pump which means more water loss per cu yd of materiel removed.

Still looking for more information and examples.

- RFL