The K-Zone: Garden railway mark III: the waterfall

I'm sure if you're a seasoned pond builder you probably have a knack for constructing a waterfall that gives just the right length of fall, avoids water loss around the fall, and blends naturally into the surround area. I, on the other hand, do not.

The waterfall taking shape. Water runs down the large, flat-topped slates, and then falls into a culvert underneath the bottom slate. This fall of water gives the characteristic waterfall sound

Instead it took many, many frustrating hours of heaving rocks around, getting soaked, and cursing before I was able to get anything like a decent effect. The problem was that, having decided I was going to have a waterfall on the railway, I was jolly well going to have one, come what may. What's more, I was determined that it would be built with real rocks, not the pre-formed resin or concrete things you can buy from garden centres.
      The problem is that we don't have a lot of space to play with. In order to maximize the run, the track follows the very edge of the railway area all the way around. Consequently, the pond is fully surrounded by track. Because of these restrictions, the edges of the pond are never more than 18 inches from the track, which means that the waterfall can't be more than 18 inches from front to back. What's more, in practice this short distance means that the waterfall has to start on top of a tunnel. Now, a tunnel can't be longer than a few feet, unless you make access hatches in the top to get to the track (which would be impracticable as the hatches would be under the top of the waterfall). So, not only can the waterfall be no more than 18 inches front-to-back, it can't be more than a few feet side-to-side either. What's more, it can't be more than about 18 inches high without completely dominating this small layout.
      So that's the size constraints. Another constraint is that, somewhere, running water has to fall into standing water. If that doesn't happen, you don't get the characteristic waterfall sound, which is an essential part of the plan. Finally, we had to ensure that all the water that gets pumped to the top of the waterfall eventually finds its way back into the pond, not into the soil around the pond. Otherwise the waterfall would eventually drain the pond and turn the railway into a soggy mess.
      Normal practice is to use a large, flat stone as the base of the waterfall, and arrange it to overhang the pond. Water then runs down the fall onto the flat stone, and trickles into the pond. The problem with this approach on our railway is that (a) it looks stupid, as the pond isn't that big, and (b) the fall of water is not high enough to make a proper splash. What's more, it was difficult to prevent water from seeping off the sides of the base stone and running into the soil. Of course, if we'd had more room, we could have arranged the pond liner to slope gently towards the pond under the base stone; but there's no room for gentle slopes anywhere on our layout.
      In the end, I hit on a solution to these problems almost by accident. I was constructing a culvert to carry water to the pond from some other (as yet unspecified) water feature. The culvert liner was continuous with the pond liner, but the culvert liner was slightly higher at the end furthest from the pond. It occured to me that I could arrange the waterfall stones over the culvert, rather than directly over the pond. There are several advantages in doing this. First, the water of the waterfall runs partly parallel with the railway track rather than entirely perpendicular with it. There is more space to make a slope in this direction on our layout. Second, the water level in the culvert (measured from the top of the edging stones) is lower than in the pond. This means that there is increased length of drop for the water that falls over the waterfall stones. Most important of all, the edging stones around the culvert capture the water that runs from the falls and channels it into the pond. Very little water ends up in the surrounding soil.
      The final effect isn't bad, I think. At the pond end of the culvert is a large stone, whose job is to dam up the water in the culvert. By adjusting the position of the stone, we can adjust the height of water in the culvert, to get the best splash effect from the falling water.
      Here are a few other things we learned from the waterfall construction experience...

A submersible pump with its various flow control attachments is quite large. Unless your pond is more than two feet deep, you're going to be able to see the pump. In a large pond it might not be too obtrusive, but in a small pond you need to find a way to conceal it under something
In general, the pump will expect to pump out through a 12.5 mm or 16 mm hose. This seems a very thick hose to carry a trickle of water up a few feet to the top of the waterfall, and you might be tempted to fit a thinner hose. However, thicker hose is far more resistant to crushing, which is important if it's likely to have a pile of rocks on top of it. It's also less likely to kink when it goes around obstacles
It's surprisingly difficult to get low-voltage pond pumps. Mains-operated pumps are much cheaper, and shouldn't represent a safety hazard if they're connected to an electrical outlet with RCD protection. However, I have overall RCD protection for the whole house; so if I do stab a trowel through the pump's mains cable, although I may not get a shock, it will shut down the supply to the whole house. As all the other wiring on the railway is low voltage, I though it was worth the additional expense of getting a low-voltage pond pump.
It takes a lot of trial and error to get the waterfall rocks in the right place. Hours and hours.

The waterfall and pond at night. The paving slab to the left of the photo is, for the time being, concealing the submersible pump