How Can I Manufacture a Mini Dredge in my Backyard?

Are you going to flood it first, or is it already flooded?

My trite comments were to point out that suction-type dredging only works in water. The suction is usually created by an air lift - air is blown down a small pipe into (but near the bottom of) a large pipe. The air bubbles up through the large pipe, creating a current of water which can drag the silt (mud, sand and fine gravel) to a barge/separator tank at the surface, where the solids settle and the (possibly filtered) water overflows to rejoin the body of water from which it came.

It will clearly only work in water.

Why not use something like a vacuum cleaner. After all that's what the street sweeping machines are along with a couple of rotating brooms on the sides. You should study them to get a better idea.

Surely the solution is to stop the sand getting there in the fist place?
Del

Modify one of those ride-on leaf vacuums. You will need some type of filter bag to control the dust.

It would have been really cool if you had about two feet of water on the factory floor. Then you could have attached a big bag to the outlet of your jet-ski and ridden around with it sucking up the sand.

The cat has the best idea.

There are industrial vacuum cleaners that can collect and discharge the sand back onto the belt conveyor.

Example http://www.hi-vac.com/manifold.htm

Adding to Oregoon's excellent suggestion such a screws are used horizontally with one open face to collect a build up of material. Since the side is open the typical metal on metal friction does not occur allowing continuous running. The sweeps function is to move the excess material towards the main conveyor. So you'd use two augars in a configuration; one to move the excess to another which would lift the sand and deposit onto the belt...

Oregoon has an excellent suggestion. Another easy-to-build option is a chain or belt-driven bucket conveyor. By placing idler pulleys in the run, the bucket conveyor can easily be customized to a particular location with bends and angles as needed.