I built a model river in my garden. Part VII

By Stephen Rodgers


Reed Bed Plan, Well Plan Detail, Well Section Detail ~14K GIFs


The Reed bed.

So now we finally get to the meat. Having described my engineering in the same order as I committed it, it may seem that that I was concentrating on stream beds, waterfalls and wildlife more than on the re-cycling, reed-bed aspect of the project. This is not so, in fact, as the scheme progressed, the need to recycle water became ever more urgent. For one thing, Spring was turning into Summer which meant that the rain had largely stopped and evaporation had increased. For another thing I had had a few disasterous water losses, and for yet another I had LEAKS.

I confess that it had never really occured to me that I might develop leaks, but in fact with a system of this complexity, with this many junctions and seals, and built by a complete novice, they are inevitable. They are also incredibly difficult to locate and fix. The only solution is to always aim to be 100% water tight and keep a good mental model of what you have built, and where your weak spots are. The fact is that the average household jettisons so much water that you should never really go short.

That being said, any leak is bad news, and a persistant leak near the foundations of your (or your neighbours) house could seriously affect the properties value (it might fall down!).

So, following my 'big projects tip' I had periodically been darting up to the top of the garden and digging. At this time I had no knowledge of what sort of area was required, nor what depth - the TV programme had never really shown us Kirsty's installation, so I had to let other other factors make my decision. The garden is about 4 metres wide, I wanted a path, and I figured that 40 cms ought to be deep enough. The final width decider was that the roll of polythene was 4 metres wide, so the bed had to be between 2.5 and 3 metres wide. I had left enough room for it to be up to 6 metres long - but I had not left enough room in the garden for a shed, I had not got much polythene left (and no way was I going to buy another roll), and I had no more enthusiasm for digging. Final dimensions of reed bed : 3 x 3 x 3, this gives nine square metres, which is space enough for about 80 plants.

I wanted to be able to control the height of the water within the growing medium. This was because I didn't know what was the optimum height for the plants, and if water gets low in the sump I can now lower the height to allow more water down. The method of regulating the height that I settled upon was to build a well within the the reed bed, using different length pipes to control the height.

The garden also had a natural slope down to one corner which I considered to be beneficial, I can drain just about every drop from the reed bed if need be.

I cut a trench to arrive in the bed right on the corner. I then laid two, 1 metre lengths of 50mm pipe into this trench and protruding into the bed. They were joined with a 45 degree coupling in the middle and a 90 degree 'swept bend' pointing skywards at the well end. With a temporary pipe stuck in this hole I laid a circular concrete pad about 30 cms in radius, I did not use any waterproofing additive in the mix. This pad completely contained the pipe, and most of the swept bend, I also concentrated on making its surface as flat and smooth as possible, because I was about to be very brave and deliberately make a hole in my last piece of polythene - right below the water line.

The next step was to partially bury the drainage pipe (to rebuild the edge at the corner), and to throw enough soil back into the hole to bring it up to the height of the pad. I carefully flattened the surface, removing sharp stones etc. and ensured that the pad was still the lowest point in the bed. All my 'gash' polythene, and another load of newspaper, was then put down, and finally the liner. Almost an entire tube of bathroom sealer was then squirted and smeared all over the pad, a 48mm diameter hole cut in the liner and the liner then slid over the protruding pipe connector.

Bathroom sealer tip #1.

There is no 'bathroom sealer tip'. If anyone knows a method of smearing this stuff around without getting completely covered in it, and leaving smooth surface, please let me know.

There now followed a cement mixing frenzy. I wanted to be sure that the roots of the water plants (reeds, iris etc.) could not puncture the polythene so I applied a 40mm layer of fairly coarse concrete all over the floor of the bed, and as much up the sides as possible. However, I stayed away from the well pad and polythene to a radius of 40cms or so.

Cement mixer tip #1

All the mortar and cement had, thus far, been mixed in a wheelbarrow. One barrow at a time is O.K., but I needed to produce about 1/3 of a cubic metre, so I hired a electric mixer. Ten or so loads were produced in 2 hours for far less effort, and about twelve pounds. A more organised river engineer could probably arrange to hire it for one day and mix up just about all the concrete needed for the whole project.

I now put an upturned empty tuna fish tin (rod caught, natch!) over the end of the pipe, to protect it, and loosely arranged the land drainage pipe in the bottom of the hole, on top of the very fresh concrete. I then hefted a good 40mm layer of waterproofed mortar onto the polythene, all round the pipe (but the tuna tin still in place), and up to the edge of the coarse concrete. I wanted the sheer weight of the mortar and brick to press the polythene onto the sealant, and NO LEAKS!

The diameter of the drainage pipe was about the same as the width of a brick, so I laid five courses of bricks on their sides, in a square, with the end of the drainage pipe set firmly into the bottom course.

Over the next two days, the garden suddenly got a lot tidier. The drainage pipe was out of the way, laid in an evenly spaced spiral on the floor of the reed bed. It is extremely springy, so all the stones and aborted concrete structures that I had collected over the weeks went between the coils to hold them in place. Then I threw most of my remaining gravel and sand onto the the top, and finally the enormous pile of topsoil that I had stored on an unused part of the vegetable patch was shovelled back into the hole.

For some time I had been pumping the river's flow into the wildlife pond through two lengths of garden hose, one coming from the top end and the other from the middle watering point. The pump was set 'flat out', and the waterfall was disapointing - more 'a dripping, wet wall'. So I had invested in another pump, connected in parallel, to boost the flow. The reed bed was filled on a Wednesday, so I left it until the Saturday with the two hoses dumping water on top of the soil, at the highest point, with a long pipe in the well (I wanted to get the bed entirely full, and the soil well soaked).

Saturday morning dawned and I dived up to 'the pipe shop' for supplies and, sawing off the tap at the top watering point, I installed a 'T' piece. It has a tap on one side and a 30mm valve on the other which leads to a three-outlet delivery system around the top corner of the bed. I opened up the valve and waited...disaster!!

With a sinking heart I watched the level of the surface water climb until it was lapping at the edge of the lowest point of the polythene, in fact it was spilling over the edge. My plans for the rest of the day flew out of the window as I started a series of experiments with valve openings and height settings.

After two days, and the loss of over 1000 litres, I had learned three main things:-

I left everything to settle down for a week or so, to see if anything would change radicaly. It didn't, so I ordered another 0.8 cubic metres of gravel, rolled up my sleeves, picked up my faithful spade (I am sick of the sight of that tool!), and set about incorporating the gravel into the soil.

I had finally made contact with others in the field of APTS, and learned that they grow their reeds in gravel and sand only - no soil at all - however they are using their beds to process raw sewage as well, I am not (yet) that ambitious, so some soil seemed neccessary.

Having finally used up the gravel, and levelled the bed, I switched on and lo! - it drained beautifully! It remained only to gather and plant 80 or so aquatic plants and the river was functionally complete.

I gathered the reeds, and some purple loostrife, from a local pond (with permission, I hasten to add). Really it was the wrong time of year for transplanting (they were all 2 metres tall, and flowering), but I trusted to the natural vigour of wild plants, and cut them back to about 30cms. Within 2 weeks they had established themselves, some sending out three new leaves. A week after that I plumbed in my washing machine, and kitchen sink.

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