Large pond and cascade construction UK.

During last summer, one of our many jobs at a beautiful rural country house in Herefordshire, was to construct this large pond. Thank god we tackled this in the summer, as we have done these in the depths of winter before and it really is not advised. So I thought I’d share how we went about this construction, should any of you steemians ever fancied trying it. I’d advise a slightly smaller one than the one in this case though. So, once we had marked the pond out on the ground, we used a 7 tonne excavator to dig it out. Over 150 cubic meters of spoil was dug out to create the depth and width specified. Approximately 1/3 of this spoil was a good enough quality to re-use, whilst the subsoil and bedrock that we found was removed from site.

Once that was complete roughly 3 days later, it was time to install the underlay. This stops any sharp objects piercing the liner from underneath, and as we found a lot of bedrock, we made sure this stage was done incredibly thorough. If you ever need to do this on a windy day, just wet the underlay down to stop it moving about. You can also do this with certain weed membranes if you are ever caught out. Then it was time to lift the liner in. Usually a couple of workers can move these things about, but this one was over 250kg. So we positioned it with our excavator.

Then it was time to start the cascade. first job was to fill the pond slightly to help pull the liner down, and stop it from moving during this stage. Due to the size of this pond, the rock cascade needed to be substantial enough. The rocks we used were locally sourced Forest of Dean sandstone. This stone is very dense, and also it is not porous, which some sandstone can be. The largest of the rocks was in excess of 4 tonnes, and the cascade still seemed small in comparison to the size of the pond. We crained the rocks in with the excavator, and set them onto a bed of concrete, which was on top of a secondary layer of pond liner. In many places they needed to be stacked to get the desired height.

Once the rocks were all placed and the concrete had set, we then rendered between the rocks with a waterproof mix containing the additive SBR. This is mainly to direct the water flow over the rock rather than between the gaps. The final stage is to install the pump, and finish the circumference. We pushed a lot of the topsoil back in on the edges, and one feature we did with this one, was to build a natural stone wall into the pond, so it was possible to take the lawn right up to the waters edge.

A few tips if you plan on building a pond.

Buy decent underlay. I’ve seen people use carpet, old compost bags, weed membrane. Don’t take the risk. It can be a bigger task to replace that after an issue, than the project is from the start.

Use butyl liner. PVC liner is ok in certain applications, but just pay the extra and buy 1mm butyl. We have tested butyl in all types ways in the past (most by accident). It’s incredibly strong, almost impossible to pierce with a spade.

Pump and filter calculations.
Measure the volume in litres (average width in meters X average length in meters X average depth in meters X 1000) a general rule of thumb is to turn the entire volume of water over every 2 hours. So if you have a 5000 litre pond, you’ll need a pump and filter capable of 2500 litres per hour.