The crown jewel in both form and function of any water feature is the waterfall, doing it correctly takes a lot of experience. It is very easy to spot a pond built by a contractor who has little to no training or experience. We call them "dump truck ponds", they appear as if a hole was dug and a pile of cobblestone was dumped in. Another common mistake is the "pearl necklace". This is a consistent ring around the water made of small cobblestone. I've included several simple rules below to prevent these unfortunate outcomes.
Scale is Everything
Beware the dreaded volcano falls. The waterfall should blend into the surroundings seamlessly. If you aren't building into an existing slope, for every foot up you go, you should be at least 2 times that in width on each side of the falls. For example, if we are building a two-foot high waterfall we step the grade down slowly and extend 4' or more on all three sides. This means your total footprint is a minimum of 10' in width. Rarely are we setting the biofall or wetland filter directly in the middle of this area. Typically, the side furthest from the viewing areas will step down faster but will extend out further. This way we can counter mature plant heights with the finished grade allowing space for a taller upright plantings in the backdrop.Bigger is Better
Using larger boulders takes more time and even more heavy equipment. These boulders must be strapped and placed individually. It is the first and most obvious difference you will see when comparing a seasoned professional pond builder to a novice. Think about what happens in natural environments, where are the small cobblestones? The water has washed them all downstream! Large boulders should always be used on the waterfall in particular. These are called the framing rocks. How you want the water to flow will determine placement. Are you building rapids or sheet falls?
Less is More
We use considerably more total tonnage than a novice builder, but the difference is how that weight is distributed across boulder sizes. Unfortunately, most contractors are primarily going to use cobblestone with the largest boulders being maybe 16". This means they have to stack small boulders on top of each other in order to get the height they need. Use fewer, but larger boulders on the falls and vary your sizes on the edge treatments. There should be less than 2 framing rocks around the initial falls. At least one of them should be set so the tops are above the waterfall weir. While we are using more tons, we are still using fewer boulders.Groups of Variety
Whether setting outcroppings on a slope or large boulders around a water feature you should be paying attention to groupings and the horizon view. Most of the boulders should be placed at different heights but on a parallel plane (level head). Rock layers are typically stratified so if you are using a dimensional stone you should be setting a minimum of a third of the boulders with a "level head". When grouping, these should alternate with each group containing an odd number of boulders possibly with one vertical boulder. The history of this placement goes all the way back to early Zen gardening and is called classic triad rock composition. The arrangements original design was to represent Buddha and his two attendants. This follows the same design philosophy as plantings. When installing an upright, oval shrub or small tree (focal point) you will offset a shrub about half the height to one side and then underplant the canopy of the focal point. The underplanting is typically on the viewing or "business side" with a ground cover. The same premise applies to boulder placement. That doesn't mean you shouldn't group three boulders at a similar height or the same direction. Doing this takes some practice and a good eye for negative space. It is usually accomplished by horizontal slate stacking between the grouped boulders. Even number groupings can also be successful, but are reserved for combinations such as a tall vertical and a reclining boulder or a short vertical and a flat rock. More on this below.
When asked about the placement of specific boulders most pro's will tell you the boulder told them where to put it. It might sound funny, but it's true. While we do pick out specific boulders and driftwood at the supplier for specific locations, we also walk around the boulder pile on site for a considerable amount of time before we even start digging. Certain boulders will jump out as to where they should be set and which side is up. We can then set them aside and excavate specifically for that boulder. Inexperienced builders are excavating the same concentric rings at a set depth and then trying to fit random boulders in. An experienced builder have excavated the soil so once the liner and boulder pads are in, a specific boulder will set perfectly into place. "Listening" to the boulders takes some experience and background knowledge. Japanese gardening contains very specific rules that are still generally followed in today's landscape practices. Boulders are classified as tall, vertical, low vertical, arching, reclining, or flat. Each category and subcategory have a set of rules on how the setting should be accomplished. For example, a leaning stone should never be placed without a supporting stone. One of my favorites is called the nameless boulder. This is reserved for a boulder that normally would have been cast off as a reject. It differs from a focal point or "specimen" in that the boulder itself has little beauty. It is a seemingly random placement in the landscape that is both unexpected, yet feels balanced. It forces contemplation by the viewer as you wonder why it is there, but also feel it is necessary and should not be removed.
Go with the Flow
Flowing water is not just for the aesthetic value. It plays an important role in the acoustics, filtration and oxygen levels of the water feature. The height, flow rate and splash zone of the falls will determine the both the aesthetic and acoustic value. If the client requested a babbling brook, you are probably going to make up for a lack of aeration and flow with a combination of aerators and subsurface jets. Aesthetically, you don't want to go below around 2,000gph per foot of waterfall. This has to be balanced with the turn-over you require. Smaller ponds require the water to be turned over more frequently. As long as you have enough plants and aren't overstocked with fish, the more volume you have, the less turn-over you will require. You can create echo chambers in the splash zone to create more sound or a pooling area to dampen it. Use waterfall foam to keep the water flowing over the rocks and not between the voids. You also want debris to go with the flow and flush down to the skimmer or intake bay, not get lost in the voids. Speaking of going with the flow, water takes the path of least resistance which is rarely a straight line. Be sure to twist and turn the waterfall and streams. My best advice is to get out to some natural streams and waterfalls and watch them with a new-found appreciation. Where does the water turn? Most likely it's where it hit a large rock and eroded its way around it. Mimic this in your stream construction. the outside of a turn should have an anchor boulder that appears to have forced the water to turn. The inside of the turn is more likely to be a great place for smaller boulders or stone with a ground cover to soften the edge.
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