Open ditch a ‘hollow’ comfort on wet field

This week, I feature the second of two drainage jobs I recently viewed in Co Louth.

Paul Mooney

22 May 2013

Open ditch a ‘hollow’ comfort on wet field

Picture one This is the centre of the field, at the higher end, where it’s wettest. It wasn’t possible to harvest all of the cereal in this field in last year’s wet harvest.

In a number of places, Dessie Taaffe’s excavator left tracks like these (picture two) when moving across the stubble. Generally, the best solution for ground like this is piped drains placed three to four feet deep, with pebble cover, emptying into the nearest suitable open ditch. Given that the soil is relatively impermeable, surface drains, or opening of the soil, would help to collect rain water and channel it down to these collector drains. If ground is to be used for grazing, then sub

Picture three We’re looking down the 400m length of the field. It falls strongly down towards an open ditch at the furthest end – by about 20 feet. There are also long ditches at the left and right sides. A common approach to draining a sloping field like this is to lay pipes to one of the side ditches. This approach usually requires less metres of pipe than laying drains straight down the fall. However, when Dessie took levels with his laser and rod, it transpired that this approach wou

Picture four Here, we’re at the bottom of the field, on the left hand side, looking back up. Despite having been cleaned out, there is little flow of water in this open ditch. The wettest part of this field is around where the tractor is parked.

Picture five Here, half way up the field, the same ditch is four to five feet deep. Nonetheless, the laser showed that its floor here is just two feet below the centre of the field. That’s not enough to allow a deep drain go from here to the wet area.

Picture six If the open ditches at the side of the field are not deep enough, then the pipes must travel to the bottom ditch, seen here. We can immediately see that it is about seven feet below the surrounding ground, a good start. But more importantly, it is some 20 feet below the wet hollow that is up at the top end. The disadvantage of running a piped drain straight down a slope is that it will usually require lateral (sidewards) drains running off it to actually catch water – water will

Picture seven This opened channel is in the adjoining field. Again, the sub soil is heavy with little stone. There is no discernible pan. The ground here was not seriously waterlogged when I called. However, it was soft. What water was present struggled to get down. Dessie has placed this pipe at three feet.

Picture eight He has stoned to within about 12 inches of the top using a large chip. He will cover this stone with a small pebble to keep out soil.

This long, narrow field is unusual in that it is hollow in the middle and higher at the sides, where there are open ditches. The middle of the field is wettest.

The field is near Collon and is in tillage. The topsoil has high clay content and is typically 14 to 30 inches deep. The subsoil layers are just moderately free draining.

Where channels were opened for drainage pipes, it took a few hours for water to begin slowly seeping in from the sides. On such soils, piped drains can be expected to dry up ground but have to be at close spacing, particularly if the field is flat.

As last week, the drainage job here is being done by Dessie Taaffe of Eagle Plant Hire.