Irrigation

Once the first two raised beds were in place (with more to come) we had to think how we were going to water them.  There is an outside tap but it is some way from the beds and given our worries about the well running dry, it didn’t seem like very good idea to use well water for watering the vegetables.

The obvious solution was to use water from the stream, however, the flow is at times very low and almost dries up in the summer.  We therefore decided that a small dam would be a good idea to at least try and store water when flow was low and to provide a bit of pressure.

About halfway up the field, the stream runs through a gully that looked like an ideal location for a small dam.  My Sister and family, Clare, Chris, Stefan and Zosia were coming to stay for the May Day Bank Holiday and Chris wanted a project.

The plan was to build a small earth dam with clay dug from a borrow pit at the top at the top of the field and lay a water pipe down to the vegetable garden.  The pipe would feed a tap and an old watering trough I found in a hedge.  The pipe and fittings were ordered from Screwfix.

The first problem faced was the lack of clay.  The borrow pit hit hard ground at about 300mm that turned out to be coal mixed in with the shale!  Thereafter the borrow pit was dug with a pickaxe (again!) with Stefan and I taking turns.  In fact the clay was too wet to work with when placed in the bed of the gully and the more granular excavated shale/coal proved ideal.  This was supplemented by a stockpile of arisings from a land drainage trench that I had not got around to screening.  The real work was shifting all the muck around in a wheelbarrow and took almost 2 days.

Despite out best efforts the dam does leak slightly, however, this will keep a small flow in the stream.  I made a spillway with a few bits of slate lying around and some larger stone, however, the flow in the stream has not been has high enough so far to test this bit of the works.  It may not get tested now until the winter.

Chris decided to lay the water pipe from the dam to the vegetable garden which was no mean feat in itself.  Rather than attempt to dig a trench, the 70m of pipe was pushed into a slit cut sa deep as it would go with a spade.  A valve was installed on the pipe immediately downstream of the dam and a washout at the vegetable garden to allow the pipe to be drained if a heavy frost is forecast as the pipe is not buried deep enough to guarantee that it would not freeze and split.

After a few leaks at the compression joints when backfilling the pipe I found you really do need to tighten the compression joints well and in the end used an adjustable wrench pliers rather than relying on hand tightening.

In hindsight, it might have been better to put a larger pipe in as the pressure at the tap is quite low and when connected to a 20m hose only a gentle trickle come out of the end.  However, I did form chamber of sorts at the inlet of the pipe behind the dam to stop it getting blocked using a section of slotted pipe wrapped in geotextile and this may be reducing the pressure at the outlet.

The water trough works well for filling the watering can or bucket but it takes ages watering the two beds we have now and we might need a more industrial strength solution when we have another 6 beds and a polytunnel!

The stream has now reduced to an imperceptible trickle and yet there is enough water collected behind the dam to enable us to water once a day.  It is unlikely that the spillway will be tested until the winter

Thanks to Chris, Stefan and Zosia for all their hard work over the weekend and to Clare who was official photographer for the project.