I settled on simply using acrylic gloss medium - in this case "Modge Podge" - having seen some youtube videos that showed it gave the sort of result I was after without looking too difficult (or time consuming, or expensive). I used an offcut of foam-core as a test piece, and found:
- It is thick and sticky - it won't run off the edge of the board so no need to "seal" the area, nor wick up the banks.
- But it also won't settle smooth, it will show brush strokes (so use a fine brush) and is hard to lay flat and smooth (see the left end of the test piece - I wonder if diluting it would help it settle more smooth?)
- Ripples are really easy to make by dabbling with a brush - but the size of the ripples depended on the size of the brush
- It could be applied quite thick - a good couple of millimetres - and sets clear within 24 hours, further coats can be added to thicken it. I didn't try pouring it.
- It was easy to do and looked very effective!
The base of the river is simply the MDF board, which I painted to look like deep river water. My first attempt was too green, so a tried a muddy brown. That looked too like mud, so went to a dark almost black with a hint of greeny brown, but blended this into the muddy brown towards the bank and quayside as though the water was getting deeper. Happy with that result, I worked out where to place the sunken barge and wildlife.
Next to apply the Modge Podge, thickly with a largish brush then dabbed into ripples with a smaller brush, working it carefully up to the banks. This is just before the barge and birds were placed into the wet Modge Podge. The foil you see at the bottom was arched over the "water" while it was drying to prevent anything landing on it.
I am very happy with the finish, I think it looks just like I was hoping it would and wasn't as difficult as I had feared. The light glares off it a bit in this picture, but it definitely looks "wet"! I've only used one coat and I don't think it needs another, but I guess I could add a thin coat if it ever lost it's shine.