LAST week I featured drainage contractor Dessie Taaffe of Eagle Plant Hire opening up a wet field to install a nine-inch drainage pipe with side branches coming off it. I returned to see him laying the pipe.
The field is close to 14 acres, square in shape and has an open ditch on one side. The pipe will be placed in the middle of the field and will run from the open ditch most of the way across to the other side.
Therefore, it's a long run of pipe - some 160m.
This long run was one of the reasons why Dessie opted for a big, nine-inch pipe. A longer run requires a larger diameter pipe than a short run. The other main reason was the sheer volume of water here.
The open ditches here are six to eight feet deep and provide a good outlet. The River Boyne is less than 1km away and some 2.5m (eight feet) lower than this field.
The nine-inch main drain will be laid at 1m depth and its outlet will be about 1m above the floor of the ditch.
However, some sections of ditch between here and the river are silted up and need cleaning out. Unless these sections are cleaned out, then in times of heavy rain water will tend to back up temporarily in the ditch.
The pipe is laid almost on the level. It will rise 10cm (four inches) in the 160m run.
Dessie is well practised on the excavator and can follow a slope with his eye, but he also has a laser unit on a tripod and it's a useful back-up where a pipe is laid on the level.
The field has 10 to 12 inches of topsoil. On most of the field, lying underneath is a deep layer of very sandy, permeable soil. Parts of it have a more dense, gritty subsoil which is less permeable but not impermeable.
A nine-inch pipe requires a wide channel and bucket. Dessie is using this trapezoidal bucket which opens a channel 15 inches wide at the bottom and 60 inches at the top.
Across most of the field, as soon as the channel is opened water begins seeping out; this despite the lengthy dry weather.
The pipe comes in 20-foot lengths which are fitted together using joiners. When the channel is as wide as this, laying these pipes is straightforward.
Shane Taaffe rolls a length into the opened channel and throws in a joiner. He jumps in, slides the joiner onto the previous pipe and pushes the next pipe into the other end of the joiner. With no rocks here the trapezoidal bucket leaves a smooth floor on the channel, which is good to work on.
The men install a branch drain every 20m. In part of the field Dessie is using a plastic 80mm pipe in the branches; in others just a 24-inch depth of pebble.
The branch drains are placed about three inches above the main drain. The pebble used here is 75mm. A cover of eight inches is being placed over the main drain.
Draining this field will cost about €10,000. This includes 13 rolls of 80mm pipe at €57 each; 160m of nine-inch at €33 per 20 foot length; 300t of stone at €8/t and machinery hire at €5,000, all plus VAT.
As a guide it works out at approximately €14 and €4.70, plus VAT, per metre for nine-inch and 80mm pipe, respectively, backfilled.