How to build a waterfall or cascade - A 'Quick Fire' guide to getting it right the first time.

Updated: 09 Jul 2007
A simple waterfall made from natural stone using a flexible liner

Due to unprecedented public demand, here is the 'HOW TO' on building natural looking waterfalls and cascades with flexible liner.

BASIC PRICIPLES:

You must cut into the bank to make it look as though the water has the made the stream itself by cutting into the bank. The waterfall entrance into the pond is best at a sort of delta in the shape i.e. and outward curve.

The top of the waterfall must have a header pool. Also unless there is a clean drop to the bottom pool, it best to work in level, and at each level there is some sort of reservoir. In big cascades there is often the opportunity to add more water at these places as it cascades down to make an cumulative effect.

Always start from the bottom and work up to the top. If you see a perfect stone for a certain position, save it. 'Sill stones' and 'Waterfall facing stones' are particularly valuable. Stones that are shaped like the continents of Africa and India are very useful for in filling between larger stones.

Before you start you must ensure certain conditions apply. If they dont then you must resort to a more sophisticated method of contriving your waterfall, which will be covered at a later date. Basically it means that you just have to build a concrete block skeleton or framework to support your waterfall.

This method works if:

There is rising ground behind the water feature

The ground that the waterfall is cut into is well consolidated and disturbed.

Estimate:

For every 2metres of surface area of stream/waterfall you will need at least a tonne of stone. The more stone you have the greater choice you have, but also more waste at the end. Yo will also need some to build sideways from the waterfall face. This needs to be more substantial since it will actually be helping support the bank but it is not so densely laid, so for the rackery estimate for similar amounts. I try to save on the stone and the rockery area by making the waterfall seem like a face of rock exposed by the effects of the running water, and as you move away from the waterfall the rock face disappears under the soil/turf/groundcover.

Also estimate for every 2 metres of waterfall surface area 2 bags of cement and 6-8 bags of sand(150-200kgs). Also 4 x 25kgs or peagravel.

A smaller waterfall of less than 2metres square uses more than proportionately less materials. Say 1 metre square uses less than half the above quantities.

Liners and underlay: The length of the horizontal + (2 x the height of the head).

The width is partly governed by the standard width rolls: Width of the widest header pool + (2 x depth).

CLICK ON THE PICTURES TO EXPAND THEM

Cutting the stream/waterfallCutting the stream/waterfall

Cut in to the bank to give the impression that this waterfall has been cut by water. Allow enough room for the facing stone of the waterfal, front and sides, has room to sit and for it still to look as though it is cut into the bank.

Each level is made into a pool - one pool falling in to another within the confines of the sides of the waterfall, which will also be lined and therefore contain the water. When you have a series of pools, the water is contained, evened out and then allowed to spill in a controlled way to the next level, even at the final level.

The outlets are bowed in order that a small flow would be directed to the middle of the outlet. If you are confident of having a strong flow, level outlets are fine.

Forming the outletsForming the outlets Normally I would create this same structure with concrete blocks. Since this is for myself, it is a small project and all the ground is totally undisturbed, it should stay put. However where I want a strong level at the outlets of the stream, i have reinforced these with cement. If it was wet and soggy when i was placing stones around the sill, the level could easily be disturbed.
Consolidating the soil in the base of the pool 'header pools'.Consolidating the soil in the base of the pool 'header pools'. Here I am gently consloidating the base of each pool and making sure that any sharp stones are pressed down into the excavation. The header pools need to be clean and smooth.
Putting underlay and sand in the bed of the poolsPutting underlay and sand in the bed of the pools

I have lined the excavation with newspaper. Ideally this would be proper pool underlay because that will not rot.

On top of the underlay goes sand. It could go underneath, but in this case it helped to keep the underlay from blowing out. The sand will help as a cushion against the hard sharp stone going in ontop of the liner.
Lining the waterfall bedLining the waterfall bed

The excavation is lined with the flexible liner. It is important to get the folds right. Any creases should be gathered together around the edge and made to point upwards so that water cannot travel through them away from the flow of water or pointed so that they direct the water into the bottom pool or back into the flow of water. Even if you think that cement may stop a flow of water along the surface of the liner in an undesirable direction, this will not last forever. Eventually the grip of cement on liner gives way and capillary reaction can occur, leaching the water away in little siphons.

Ideally the liner will reach right down into the pool, but this was an old offcut of PVC that just about fitted for this demonstration.

Trying first stones in positionTrying first stones in position Try any stones in position before cementing them in place. The waterfall facing stones are particularly important to get right since the help form a (a visual) dam to the water. In fact they operate mainly as facing stone to the final dam before the final fall into the pool. Ideally they will face the last hump in the waterfall/stream up to the top of the hump. They can be higher at the sides if there is room for the 'sill stone' to sit between them.
Cementing in placeCementing in place Lay down a good solid cushion of mortar right back to the last hump of the final waterfall. Although this wont form a permanent seal to the wate, it needs to 'dissuade' it as effective as possible, so make sure it sinks down into all the creases. Note that I am not using underlay to cushion the liner. I will only do this where there are particularly sharp or heavy stones. At the face of a waterfall, underlay can act as a wick sucking water out between the liner and the cement or stones.
Filling all the gapsFilling all the gaps Lay the stone and backfill behind it to the level of the stone and to the level of the last hump.
Mortar bed for the 'sill stone'Mortar bed for the 'sill stone' Lay an even bed of mortar for the sill stone. It is important to have this to hand and also some suitable flanking stones. Also ensure that it is going to sit level without too much mortar.
'Sill Stone' in position'Sill Stone' in position The sill stone is laid in position with flanking stones that will guide the bulk of water over it. A slight fall (bubble on the line of the spirit level) towards the bottom pool on the level of the sill stone is desirable to throw the water away from the face of the waterfall.
'Bedding in' support for face stone to the next waterfall.'Bedding in' support for face stone to the next waterfall. Bedding in the base stone for the next waterfall on a bed of mortar. This may be obscured by the water level when the waterfall is running.
Facing stone and another sill stone in placeFacing stone and another sill stone in place Working up the waterfall. A neat facing stone for a waterfall saves a lot of effort. Other techniques of creating something more interesting, like white water, will be covered in later articles.
Dont forget the hose.Dont forget the hose.

Dont forget the hose. It should cut deeply into the bank coming out of the bottom pool at a convenience and obscure point.

You can see that where I have found a useful stone for a particular position, I have used it. A cushion of peagravel in the base of the header pool can make the excess use of cement unecessary and also help as a bio-filter when the stream is in operation.

Building the face of the flanks that contain the water over the sill stonesBuilding the face of the flanks that contain the water over the sill stones As you fill out the inside of the waterfall and gradually work out with facing stones, make sure the liner is held up behind the stone to contain water.....
Making sure the liner is well supported to contain the water.Making sure the liner is well supported to contain the water. ...by jamming it upright between stones. Any excess can be trimmed off later.
Building up and away from the stream itselfBuilding up and away from the stream itself Build away from the waterfall with rockery stone. From a 'worm's-eye view' this must look like a solid rock face. Each level of the water fall is a stratum to the rockface. If you take strata away from the various levels, as you move away from the waterfall, planting areas can be made between the strata. So backfill behind the rockery facing stones with soil, bringing them proud of the waterfall face.  
Fine adjustments neededFine adjustments needed

Building a stream or waterfall can be a bit like a jigsaw puzzle of fitting stones together. Some stones however may need some minor adjustment to get them to fit. A stoe hammer or even a lump hammer can be pretty essential, particularly in the latter stages.

The hose disappears behind a facing stone in the top header pool. Make sure it does not lie below water level as it will siphon the contents of the pool down to the bottom when the pump is turned off.

Make sure the top level surround of the tp header pool supports the liner well above the water level. It may be necessary to lay a fillet of mortar under it in order to keep it well above the water level in the top pond - water bcks up unexpectedly high in this pool.

At the bottom, where the liner goes into the bottom pool, if there is a marginal shelf, try facing the surface of the liner with flat stones built up from the shelf.

If this is not possible the liner becomes obscured with time especially if both materials are black as they tend to be nowadays.

 

 

 
The final testThe final test

Fit a submersible pond pump to the bottom of the hose. This should be as far away from the watefall as possible in summer. Subsequent to this a 'veggie' filter system was installed at the top of the waterfall, which made being able to circulate all the water in the pond to the filter doubly more important.

The size of the pump is dictated by the height of the waterfall above water level and the width of water required. Very approximately, allow 60 gallons per inch of flow, or 100litres per centimetre up to the desired height. It is better to get too strong a pump than to compromise. You can always turn a pump down with a gate valve at the top of the waterfall.

Try not to circulate more than the total volume of the pond every hour. This will damage the eco-system. Once every 2 hours is more desirable. If you have a desperate need to impress the neighbours when they come round, you can always have 2 pumps, with only one operating all the time, leaving the 'full bore' option for special occasions.

For those of you out there that just want the waterfall and no pond - I know you are out there- you will need a big hidden sump and make sure there is an hours worth of water there in the sump. The pump must have a float switch turn it off when the level drops below a certain level.

You can get away with a small sump, if you have two sumps..........hang on. This is another story for another day!

But back to this....When you first turn it on and the flow doesn't sem quite right, all is not lost. There is an amazing amount you can do to adjust the flow or the throw from a waterfall by placing small stone to the side of the sill stone. Sometimes a combination or a little handful of peagravel may be necessary.

The scudgeon on the back of your stone hammer is useful for cutting small amounts off the surface of a stone like the sill stone if it just needs the level lowering a millimetre or so. You can very carefully do this whilst it is running so yu can see an instant effect. A stone file is a more gentle adjusting tool - but not an easy tool to find at a moments notice.