BEGINNER'S GUIDE TO BUILDING STREAMS AND WATERFALLS: PART 4 Making a professional job.

Using a framework or skeleton to make your stream or waterfall a permanent feature

This is a technique to be used in made up, or unstable ground, or loose sandy soil. You will be using all the techniques in the BEGINNER'S GUIDE To BUILDING STREAMS: PART 3 ,  but you will be stabilizing the rockwork and holding it in permanent position by using a blockwork skeleton.
Start from the bottom, working up. Imagine, as you are excavating into the bank down which you wish this cascade to run, the water coming down in a series of drops. Even if the there is only one drop and it is vertical or the scheme is near horizontal and it looks simply like a stream, regard it as a series of pools flowing from one into another for the initial skeletal construction.
This project is intended to be permanent and there will be a considerable amount of stone involved with some individual pieces quite heavy, then it is best to create a construction that will hold everything in place with the liner at the right level and the water being contained where necessary, even if there wasn’t any stone there.
For the series of waterfalls, leave enough room to lay a skeleton of  ‘4 inch’ concrete blocks. These effectively face the soil with a hard framework that supports the liner and the stone facing that covers the liner. You’ve got the picture already.

Excavate a series of 'pools' with outlets on the proposed waterfall face level with the top of the next pool down: Start from the bottom, cutting the outlet of the final 'pool' level with the framework of the main pool.

Lay a concrete block framework for each 'pool' with each framework unit level.: The outlet to the level of the next pool is bricked up so that it is 10-15cm lower than the rest of the unit. Dont forget the hose from the submersible pump up to the top pool.

Lay underlay through the waterway, especially over the blockwork. On top of this lay a good quality liner.: Fold and tuck this into place ensuring all folds help to contain the flowing water and the tops of the folds are well above the level of the water.

This stream will have a series of waterfalls cascading down at some speed. Already there is a blockwork pool at the bottom. A line of bricks will raise the face of the other two drops to contain the water. When they are filling with water the lower front edge will allow water to cascade from one pool into another.
Blockwork in place for a complete pond and waterfall.: I hope you can see the 'armchair' effect from hereCompleted pond and waterfall

Close up of the completed waterfall of project on the left.: Using the 'blockwork skeleton' method

The stream for the project left and right in close up.: Underneath the stone work is a 'blockwork skeleton'

The blocks must be laid level, apart from the outlet at the front, which will be at least 10cm (4ins) lower. This is where the water flows into the next section and has to be low enough to allow for the thickness of a 'sill' stone cemented into place on top of it. These pools I often describe as 'armchairs' where the 'arms' of the 'chair' contain the water within the chair as it flows over the 'seat' until it reaches the water in the next pool. Make sure the face of the waterfall is well back behind the end of the side blocks at that level i.e. the face of the 'seat of the armchair' is well behind the 'arms'. In this way the block work projecting out beyond the sill and the fall whilst supporting the liner up the sides of the waterfall contains any sideways seepages.

The stream liner is laid on sand and some sort of protective membrane: In this case the landscaper has built a 'staircase' as foundation to his waterfall. The sides are not built up to contain the water. He endaevoured to do that later on. Neither did he create a series of pools running from one to the other.

The stream liner should come over the waterfall face and well into the pond.: Maybe not quite far enough here. The client had some very choice water worn stone that he wanted to use and looked perfect for the project. Unfortunately it was in quite large pieces.

The landscaper's experience in building waterfall really begins to pay off at this point.: Any potentially wayward rivulets must be guided back to the main flow even when the cement joins begin to fail in future years.

The stonework begins to take shape.: There is now support for the side edges of the liner that will work to contain the water. Also there is a final pool before the main pond. This will act as a settlement chamber for debris coming down the stream.It will even out the flow of the stream to create a nice wide fall into the pond.

The pond and stream one year on.: The stream looked perfect in the end although it would remove a fair amount of water to get going. This being because it did not retain any water except at the bottom. The temptation would then be to top up with tap water and endure a subsequent algae bloom.

The blocks are laid on cement on a well-consolidated soil base. A footing would be ideal but not always practical.
After the cement is dry the blocks are backfilled with soil. The bases of the pools are smoothed out and consolidated gently.

A 1" layer of sand can be laid throughout the system with an underlay over the blocks.

Dougie Knight is one for breaking these rules and getting away with it!Waterfall by Paul Dyers Very Interesting Water Feature and Landscaping Company at Tatton Park Flower Show 2008Lay the hose from the pump along the most sensible route. Excavate a trench for it but save the back filling for when you are finishing off the rockery.

Lay the liner over the blockwork and underlay with a large overlap right down into the pool (with the stream liner on top of the pool liner!  - Believe me people do get it wrong.)
Carefully push and fold the liner into place, gathering as many creases together as possible whilst fitting it right into the contours of the block work.
Thoughtfully trim off some of the excess liner where it obviously wont be required, but leave plenty spare at the top until the last possible moment.

The side and base of the pools and stream can be lined with pool underlay to lend the liner a bit of protection from the stone you will face the inside of the pools with. Be careful not to have this underlay folding over the top of the blocks, either at the sides or down through the stream or series of waterfall. It will work as a wick and siphon the water out of the stream pools into the surrounding soil or down into the bottom pool, which may cause it to overflow. Remember, you want the waterfall/stream pools to stay as full as possible, even when the stream is not running so that when you turn the stream pump on, there is a minimal amount of water taken from the main pool at the bottom to get the stream flowing again.

Fill the individual 'pools' with plenty of peashingle. This
will act as a cushion and support for stone facing the inside of the
'pools'. 
Line the pools and stream with stonework. Start from the bottom and work up, laying base stone on a thick layer of mortar. Whilst saving the best flat stones for the sills, concentrate on the face of each waterfall and work outwards and slightly forwards into the rockery or wall retaining the soil at the side of the waterfall. Always think in terms of how the water will be retained in the stream within the liner as the water comes over the sill and falls down the face.
Cutaway view of stream construction - side viewDiagram of the waterfall face
For a large part, particularly around the sides of the stream and waterfall, try to lay the stone with its strata as it would have laid naturally in the ground, i.e. following the general strata of the rockery if there is one. However this is a rule to be broken, because as you will see in nature, very often a waterway cutting is strewn with rocks and boulders heaved up and cast aside in more geologically or meteorologically violent times.

Pull out the liner between the side facing stones (not so much that it cannot be disguised), enough to prevent water travelling out sideways behind the stone.
In order to use the minimum amount of mortar, the best technique for the long term is to make the stonework as self-supporting as possible and only use mortar around and behind the outlet, the sill stones and usually the facing stones on a large fall. Using cement mortar gives you a really solid finished feature, but it will add lime to the water, so a water-proofing agent in the mortar mix may help.  Fill in the gaps and backfill behind the stone with smooth pea gravel. You will use a lot but it is much more healthy for the pool environment than cement and often doubles up as a biological filter bed if the stream or waterfall is in operation for long periods.

There is no point in trying to seal the stone to the liner with cement. In the longer reach of time water will find its way between the liner and the cement and seep down, sideways and with the pressure of a flowing water from behind, can seep upwards thus creating a hidden seepage you had hope to deter by using cement. The pea gravel behind the stone works as a gentle cushion, a growth medium, filter medium and holds the water static. Moving water, the stuff that we see, flows over it.

When placing the sill stone on a bed of cement it is very often best to project it over the lower facing stone unless the facing stone is very rough and patterned. The result otherwise is that the water sticks to the facing stone surface and the effect of the fall is lost.
Stones cemented into place on top of the sides of the sill stone contain the water as it flows over. They can be on the stone if it is wide and reaches right across the width of the outlet, or they can be cemented to the side of it with the gap between sill and side stone pointed up with cement and dressed with pebbles or gravel.