The next step in the table is to build up an area on the river to have the water flow from. I find this is usually better than letting the fake water spill over the side by mistake (there are ways to avoid this, which I will be showing later on). For now though, consider this an artistic choice.
I built up the culvert using foamcore, and then hid it using some polystyrene foam insulation. More detail will be carved in here once the glue is set. I've driven some toothpicks into the structure to give additional stability.