Start with an aluminum 9X13 pan and make a river bed out of the aluminum foil to fit down the middle of the pan.
Using modeling clay, not play doh that will dissolve, roll out the river. The modeling clay is stiff and it took a lot of heavy rolling to get the clay the size of the river bed. The clay needs to cover both the sides and the end of the river bed so that the water doesn't all run out the ends.
On each side of the river fill the pan with potting soil. Lay the clay in the river bed so that it extends out over the edges and ends to keep the water contained in the river.
On top of the potting soil put a thin layer of sand, grass seed and other deserty things. Spark made a pyramid, a palm tree and add few rocks so far.
Start pouring water into the river.
Keep pouring until the water over flows the river and floods the rich delta soil.
The delta is completely flooded. Now we wait a few days to see what sprouts.