Sunday, 2 June 2019

Making a Garden Water Feature - Cascade

Hot on the heels of our waterwheel, we've now built another water feature to sit under the Cypress tree in the south-east corner of the rear garden.

This was an unusual project for me, in that there were no plans drawn up or even preliminary sketches - I had the idea for it one evening, made a start immediately and then everything was just built on the fly over the next few days.

We had five large stepping stones in the front garden bed, of irregular shapes, which I lifted and then hauled them around to the back.  I laid them out in a rough curve around and between some existing plants, overlapping the ends of the stones to establish the required start and finish points of the cascade.

I had some lengths of 2"x2" timber behind the shed, reclaimed from the old rabbit enclosures, and I used these plus other timber offcuts to make a simple carcass with five levels to carry the stepping stones.  I made the first drop much larger than the subsequent ones, to form a waterfall which pours onto the second stone down.   Each stone feeds the one below.  The fifth and lowest stone overflows directly into an underground sump from where it is recirculated back to the top using a pump.

The carcass tower was framed with offcuts of fence boards from our front fence build last year.  

carcass during construction

It was then off to a builder's yard to buy a few small bags of cobbles and some ready-mixed mortar.   I cleaned up the surfaces of each stepping stone with a rotary wire brush in the electric drill and made a dam of mortar all around the periphery, except at the water exit edge, and then pushed the cobble stones into the mortar bed and finished off by pointing between the gaps.

cascade sections 2, 3 & 4 curing in the shade

the lowest cascade section

On the top stone, I cast a short length of plastic pipe in the mortar between the two rearmost cobbles to make an entry point for the pump hose.

While I was waiting for the mortar to set on the stones, I dug the hole for the sump.   I was lucky that I didn't encounter any major roots from the Cypress tree, which is well-established and over 15 m tall.   

digging the hole for the sump
first trial fit-up to check the set-out positions

This hole was lined at the bottom with horticultural grit and then filled all around the sump box with pea gravel, the idea being to keep the neighbouring soil well away from the box edges so dirt doesn't fall inside the sump every time the lid is removed for access to the pump.   

The sump is simply a strong 35 litre clear plastic container with a secure lid.  The lid was drilled all around the edge to allow water to percolate, and holes were also made high-up in one side of the box through which to pass the pump hose and cable - the hose is routed inside the cascade carcass up to the discharge point in the uppermost stone.

With the sump lid in position, the area above is spanned by decking boards supported on a peripheral framework.  This is so the sump area will be safe to walk over.  A bed of loose pebbles are laid on the deck.

The original idea was to use a solar pump kit, but it's a heavily shaded area of the garden and therefore the solar panel would have needed to be sited some distance away, and so instead I decided to lay a cable from the existing 12V DC power supply unit in the big shed.

What with overground lengths of cable up, around and over the small shed, and then an underground run following the profile of the paving stones and flower border edging bricks, it took more than 30 metres of cable.  I already had a small Chinese submersible pump - they're only a few pounds on eBay anyway - and I installed it in the sump.

construction works almost completed ....

cut-out in the deck boards, and a support grid above for pebbles with
a fine aluminium mesh screen attached to stop debris entering the sump

The eagle-eyed amongst you will have noticed that the tower height has been lowered from the initial carcass build.   We had to reduce the height of the fall of water from the top stone during set-up and testing because it's just too windy here for a long drop, and the falling water was getting blown outside the catchment area of the second stone.

For the finishing touches, I bought a length of bamboo screen to cover the carcass construction.   There's also a bamboo cane dipstick provided to check the level of water in the sump without having to remove all the stones and decking.  

I also bought another 12V timer switch - we've several in use already - to automatically switch the cascade pump on and off.    I added another isolator switch on the side of the shed which saves us from having to unlock the shed door every time we want to manually switch it on and off.   

The cascade water flow still needs a little adjustment, but it's just about there.

just about finished ....

So we're quite happy with this new feature - it brightens up an otherwise dark corner of the garden.   We need to add a few more plants around, of species that don't mind dry shade.  The hellebores, sedum and viburnum davidii seem to like it there well enough, but I'm currently growing-on a few trays of heucheras from seed sown in March and which we can dot about in the autumn when they'll be ready to go in the ground.

We're in two minds whether or not to leave our small statue of Iris on the top of the cascade - we already have a tall cast iron plinth for this statue.

Iris - Greek goddess of the rainbow ....

However, I think she looks quite good on the cascade, just the right scale for the water feature, so we might buy another statue for the plinth.

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