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Planning Construction

Well we have gotten this far without to much difficulty, but now's the time for some searching questions.  At this point most people are still planning on doing the work themselves, assuming incorrectly that its only a matter of buying a decent spade and a good wheelbarrow.  I only completed my latest pond a few years ago so I still remember the details clearly. Let me lay some real-world facts and figures on you.

My pond is 7.2M long x 6M wide x 1.2M deep, lined with triple-ply pond liner and fitted with 2 bottom drains. For stability the pond is constructed inside a 400mm x 400mm concrete collar. The filter is housed in a dedicated shed about 10M from the pond and interconnected by 3 x 100mm solvent-welded PVC pipes. The primary settlement chamber is a 1200L food-grade underground storage tank encased in a brick surround which supports the filter house above.  It is accessible via a trapdoor in the floor of the filter house. Another 100mm underground pipe connects this chamber to the public mains sewage system.   Inside the filter house the main filtration is handled by a EA Nexus system, aided and abetted by a few other devices which I will discuss in detail later.

So first thing to be dug is the trench for the concrete collar around the pond, that's 26.4M x 0.4M x0.4M = 4.22 Cu Metre.  Apart from the effort required to dig the trench even in normal garden soil, the excavated soil weights in at 1.52 tonne per cubic metre, so that's almost 6.5 tonne.  I don't remember how many wheelbarrow loads there is to the tonne, but by the time you have filled the first of your builders skips you won't really care, you'll just want to sleep for a week.

Next stage is to fill the trench with concrete to a height of 25mm above the planned water level of the finished pond. If you thought the soil was heavy then you are in for a shock now.  Standard grade ready-mixed concrete weights 2.4 tonne per cubic metre. So after digging the soil out, you now have to tip in 10.1 tonne of wet sloppy concrete.  What's more, you won't have all weekend to do it.!  The ready-mix truck will hang around for perhaps 30-40 minutes, before tipping the whole load onto the driveway and heading back to the depot.

A week later, assuming you have been released from hospital, you can start to dig the pond inside the collar.  Referring back to my pond, that's a hole 7.2M x 6M x 1.2M = 51.84 Cu Metre, and with a spoil weight of over 78 tonne.  In my case I paid a local contractor around £500 to come along with his JCB and dig it out in one day. Luckily enough he also wanted the soil for a little job that he had going so he took it all away at no extra charge.  The points that I am highlighting here are the effort required, and the costs involved. Its true that I am no longer a strapping young lad, but the volume and weights involved here are possibly beyond the capabilities of any normal bloke.  If skips are to be used to dispose of the soil then you have to reckon on about 6 - 7 tonne per skip.  For me that would have been about 12 skips at £50 - £60 each, plus £500 for JCB Man, say around £1,100 - £1,200 just to get the hole dug.

Sorry, forgot about the ready-mixed concrete.  Can't remember the exact cost but I don't recall getting much change out of £200.

Next came the underground pipes connecting the whole thing together.  By the time I had finished I had dug 50M of 1.5M deep trench and installed 90M of 100mm pipe,  (remember, 3 pipes between pond and filter)  The cost of the pipe, the bends and couplings, the control valves, the tank connectors and the bottom drains is not insignificant, but 50M of deep trench is another 57 tonne of soil.  True, I didn't have to dispose of it, but I had to shovel it twice, once to dig it out, and again to fill it back in..!

So what's my point I hear you ask.  Well I did raise these issues a few pages back.  Are going to be doing this work yourself? are you even capable of doing this work yourself?   For most of us the answer is NO, not without some serious help.  That being the case you need to factor in the costs of sub-contracting out the heavy work and enticing a few reliable friends to lend a helping hand.  Timing is also important. A few days of heavy rain can bring the whole project to a very sticky end.   A devastated garden and weeks of muddy footprints through the house is not going to earn you any 'brownie points'

Just one last point on the planning, where are you going to get all the bits?  For small ponds you can usually buy all the bits as a kit. Preformed pond or pre-packed liner and a small pump are all that's needed.  Most medium sized ponds are also catered for in a similar manner.  Liner is usually available pre-cut up to about 8M x 10M, if you need bigger you can get it off-the-roll in 6M, 8M or 10M widths.  Filters and UV's rated up to 10,000 - 30,000 litre, or even more, are not uncommon stock items. Most dealers will also stock pumps with similar ratings, together with all the necessary hosing, clips, connectors etc.

The same does not hold true for large Koi ponds however.  There are few, if any, stores which will carry all the necessary bit-and-pieces in stock.  This complicates things somewhat.  How can you be certain that the valve which you bough on the Internet from shop A will fit the pipe from local shop C and the tank connector from mail order shop C?  There is even two different types of underground piping, each with its own specific solvent for welding the sections together.  Don't leave these details to the last moment.  Get everything that you need at the start or you'll end up waiting weeks on some vital component while your half-finished pond slowly fills with rainwater.

Koi and Goldfish in a Garden Pond