I built a model river in my garden. Part I

By Stephen Rodgers


Before and After pictures and Dimensions ~11K GIFs


I first viewed the house where I now live in June, 1991. The summer heat (and drought) was just beginning to take hold and, seemingly unrelated at the time, I had just constructed a small pond in the garden of my London flat. I had also seen a television programme, presented by Kirsty McColl (the singer and gardener), all about the absurdities of waste water treatment in this country, and the use of reeds and other aquatic plants to purify water - both large scale (for third world towns and villages) and small (her garden).

The house is one in a conventional terrace, with a long thin back garden 'laid to lawn' which sloped smoothly down to the small patio in front of the kitchen. The house viewed, and an offer made, I promptly cleared off on holiday. During the long drive to Spain I worried about my pond drying out, the fish dying, and the lawn going all brown yet again. A plan (a day dream really) started formulating - with a long thin sloping garden and a reed bed, why couldn't I build a model river system? I could recycle all my grey water, keep fish, and water the garden ALL YEAR LONG.

The vagaries of the housing market, cliché ridden phone calls to solicitors and mad Hungarian flat buyers all conspired to delay our move until January 1992. This delay had given me another six months daydreaming, so after screwing enough shelves to walls and inserting enough light bulbs, I left the house to sort itself out and wandered up the garden with a spade and a puzzled look. Six months later, I have 7,000 litres of water moving in concert through my garden, with three watering points spread through its length. Any time I like I can simply open on one of the taps and drench the lawn or vegetables with crystal clear, drinking quality water. I am longing for a confrontation with an irate water warden!

In this booklet I shall endeavour to describe the steps, techniques, materials and problems encountered during the construction of my model river. I shall go into quite a lot of detail so that anyone who feels inclined could follow my lead, and perhaps save some of the heartache. I wanted a river so that I could keep fish but a simple domestic waste water re-cycling scheme would not have to be so complicated, consisting of just two bodies of water. Somebody constructing such a smaller system will (I hope) still benefit from reading this.

A domestic waste water re-cycling scheme basically consists of a closed loop of water kept in motion by a pump. Fresh (but 'dirty') water arrives every time the bath is emptied, the washing/dishwashing machine is used, or the children clean their teeth. Water leaves the loop when it is drawn off for irrigation or (if the system is full) an equal volume of water is allowed out into the conventional drains. My system is arranged so that any water that does leave through this route has been through the system at least once, and is therefore extremely clean.

The water is purified by passing through a bed of reeds growing in 3 cubic metres of sand, gravel and garden soil, this causes both a mechanical filtration and a biological one. Reeds and other aquatic plants have adapted to live in soil that is being constantly leached of nutrient and minerals, their roots therefore seem to have adopted the policy of absorbing everything from the passing flow 'just in case'.

The water in a reed bed is not instantly available for irrigation purposes, nor could many plants survive the scalding hot soapy effluent of the 'boil wash'. So the other element required is a storage 'sump', this serves to both cool and dilute incoming effluent. It could probably be engineered to have both of these elements in the same waterproof container - provided that the levels were arranged so that water had to travel through the reed bed on its loop.

The river I set out to build is rather more grandiose.

The patio in my new house was always going to be too small for our purposes, so I resolved from the outset that the sump was to be underneath an extended patio. This was the ideal site as it was close to the house for the plumbing and electricity, and gravity suggested that a sump should be at the bottom of the circuit. In fact a sump (perhaps renamed 'storage tank') could be at the top of a system if your garden so dictated, however, storing a lot of water high up has certain risks (disastrous tidal waves!).

With the sump at the bottom of the garden, nearest the house, it followed that the reed bed should be at the furthest end, and highest point. At this stage I was not expecting the reed bed to be particularly attractive - more of a sort of plant factory and perhaps unsightly. In fact I have discovered that the range of suitable plants is quite large enough to produce a very attractive, and of course functional, bog-garden/pond.

I then planned three bodies of water, connected by a gravel stream. The first, highest, was to be a wildlife pond, analogous to a spring or source. Then quite a long run of stream, quite narrow, along the side of a family lawn, was to deliver the water into a wider, quieter, stretch of water arranged at sixty degrees to the lie of the garden. The analogy being a slower, mature river.

Finally the water was to fall over a dramatic waterfall into a large, deep pond, analogous to a freshwater lake. The overflow from the lake was then to return quietly to the sump. Throughout this whole project ideas conceived on paper have rarely turned out exactly the same on the ground, but I can honestly say that 'that is what I wanted, and that is what I got'.

A word about materials.

It is very easy to spend a fortune on water gardening. I believe that this is because growing interest in this field has attracted some serious profiteers. Frankly we are being ripped off. I have paid (because I had to) over eighty pounds for a 15W Ultra Violet unit to control algae. A glance at the materials used, and the low level of technology embraced, reveals this exploitation.

Throughout the project I have looked at an engineering problem, worked out what was needed, and then consciously explored alternative materials with which to make the construction. Full understanding of the properties of the materials you are using is essential.

The pond I had constructed in my previous garden had been lined with 1000 gauge 'builders damp course membrane' - heavy polyethylene sheet. All the gardening books warn against this material, suggesting instead PVC or butyl liners. I had paid £10 for my sheet of polyethylene where an equivalent 'approved' liner would have been £80 or £90. Polyethylene does have its problems of course. It becomes brittle if exposed to the UV light in sunshine (after about two years), it seems to be impossible to patch in the case of a puncture, it can be unsightly (unless you like blue), and it has very little stretch, so 'crinkles' are unavoidable.

To use butyl or PVC to line an entire model river would have made the project too expensive (for me), moreover I discovered that builders merchants sell polyethylene in 25 metre rolls for around £25. In total I used 100 metres of the stuff, of which my errors, miscalculations and children caused me to waste about 2/3. The only area that I have left exposed to sunshine is the big 'lake' which has been designed to be replaceable without too much effort. In fact, due to a shaky hand with razor blade I have already had to replace it once, perhaps next time I shall use the preferred material.

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