Considering the high levels of rainfall in 2012 and 2013 and the associated damage caused to lands, it is not surprising that discussions and open days concerning land drainage have attracted close attention. Interest levels have grown in recent months with the strong grass growth rates and replenished fodder supplies providing many farmers with an opportunity to undertake drainage and reseeding.
This was very evident at the recent national open day held on Mike Dillane’s farm in Lixnaw, Co Kerry, with farmers travelling huge distances to witness a land reclamation job on the farm. There has also been a long line of enquiries from farmers who did not attend the event with questions on how to go about tackling a major land reclamation/drainage project.
Teagasc adviser David Trant, positioned in Listowel, Co Kerry, has gained vast experience in the area and detailed advice to consider when weighing up a land reclamation project. David uses Mike Dillane’s drainage job as an example of the factors that should be considered and general lessons to take into account, in his advice below.
Initial survey
The site was surveyed and levels taken to establish falls, low areas and surface run-off directions. Soil and geological maps were consulted to get an overview of the conditions in the area. Indicative vegetation like rushes and iris, their distribution, and drainage factors like old drains were identified and noted.
The key element was the digging of four test pits, which were similar in their makeup. They showed peat varying in depth from 30cm to 70cm overlying a substantial layer of silty/clay material. Below this, at circa 1.5m, the till was somewhat more permeable. Ground water pressure was evident and while the depth of silt/clay band was thick, the trial holes appeared less dramatic (filled to the top with water – approximately 2m depth of water) and weakened the case for shallow drainage. However, due to the evidence from the test pits (makeup of soil layers), it was decided that most drains would have to be at around 1.5m-plus depth, or alternatively at about 1m depth with sumps to a depth of 1.5m to 1.8m, located approximately every 30m.
Ground situation
A combination of the above drains were carried out and two-inch stone and bigger was used over the pipes. Drains were spaced at approximately 12m distance apart and most were used with 80mm corrugated pipe. There is the potential to install mole drainage in the future in localised spots should there be any surface drainage issues. The main outlet was deepened to improve fall and flow in the main open channel. The few low-lying hollows were filled with excess soil and when the drainage was completed, the whole area was ploughed and the land levelled to give all sections of the site an outfall.
General drainage lessons
Poor design. Spacing, depth and type of drain merit a lot of detailed investigation and contractors with local experience are good at advising on such matters. Where the drainage system fails or is substandard, this can be confirmed by observing the water table depths between the drains and also the drain flow rate.
Ideally drains should be installed in dry weather. Deposition of soil particles in a drain pipe usually takes place just after construction when the backfill is loose. Generally this material is coarse as the “fines” have been washed out. In wet weather, the problem is more acute and the chance of other problems occurring increases, ie scaling, which may cause breakage or misalignment of the pipe and non-uniform settlement of the drain itself and the backfill.
Soil particle entry into the buried pipe may occur in soils that are very fine-grained and uniform (fine sands) – this is where the soil enters the drains over time and clogs the system. However, this is not likely to be a problem in clay soils, especially where gravel is put in around the pipe.
Sedimentation or settlement out of the heavy soil particles from the drain water will tend to occur at joinings and where there is a sharp change in the fall. These should be avoided where possible. Organic wastes like slurry or milk, etc entering the system will quickly form a gel which rapidly blocks the pipes.
Ochre or Red/Iron deposit can cause severe problems and is difficult to overcome – larger diameter pipes and/or more gravel fill can help in this regard and submerging of the system has been successful.
Finally, the drain mouth outlet may become clogged by roots, weeds, silt, etc over time and can subsequently cause stagnation/sedimentation along the pipe, which compounds the initial problem.
Drain mouths should be identified and marked and cleared every so often and care should be taken when cleaning main drains that these outlets are not damaged.
Alan Dillon’s factors to consider
It is important that before anyone attempts to carry out a drainage job on their farm that they have taken care of the following:
Every drainage job is only as good as its outfall. Cleaning and upgrading of open drains acting as outlets for land is a must before any drainage commences. All open drains must be dug to as great a depth as possible.Perform a site assessment. Test pits must be dug to ascertain soil type in the area and the type of drainage system required (shallow or deep). Hire an experienced contractor to carry out the work. A contractor with good knowledge and experience of carrying out drainage works can be the difference between a successful drainage job and an unsuccessful one.Have finances in place. Drainage is expensive and can have a serious impact on farm cashflow if plans for finances are not properly in place. Farmers need to sit down with their adviser to assess if draining land is the best move for them to make.When reseeding land post-drainage, select grass mixes that are suitable to heavy land, select mixes with good ground cover and persistency. The mix used on this farm on a per-acre basis was Twymax 4kg, Drumbo 4kg, Abermagic 5kg and Timothy 2kg.
Considering the high levels of rainfall in 2012 and 2013 and the associated damage caused to lands, it is not surprising that discussions and open days concerning land drainage have attracted close attention. Interest levels have grown in recent months with the strong grass growth rates and replenished fodder supplies providing many farmers with an opportunity to undertake drainage and reseeding.
This was very evident at the recent national open day held on Mike Dillane’s farm in Lixnaw, Co Kerry, with farmers travelling huge distances to witness a land reclamation job on the farm. There has also been a long line of enquiries from farmers who did not attend the event with questions on how to go about tackling a major land reclamation/drainage project.
Teagasc adviser David Trant, positioned in Listowel, Co Kerry, has gained vast experience in the area and detailed advice to consider when weighing up a land reclamation project. David uses Mike Dillane’s drainage job as an example of the factors that should be considered and general lessons to take into account, in his advice below.
Initial survey
The site was surveyed and levels taken to establish falls, low areas and surface run-off directions. Soil and geological maps were consulted to get an overview of the conditions in the area. Indicative vegetation like rushes and iris, their distribution, and drainage factors like old drains were identified and noted.
The key element was the digging of four test pits, which were similar in their makeup. They showed peat varying in depth from 30cm to 70cm overlying a substantial layer of silty/clay material. Below this, at circa 1.5m, the till was somewhat more permeable. Ground water pressure was evident and while the depth of silt/clay band was thick, the trial holes appeared less dramatic (filled to the top with water – approximately 2m depth of water) and weakened the case for shallow drainage. However, due to the evidence from the test pits (makeup of soil layers), it was decided that most drains would have to be at around 1.5m-plus depth, or alternatively at about 1m depth with sumps to a depth of 1.5m to 1.8m, located approximately every 30m.
Ground situation
A combination of the above drains were carried out and two-inch stone and bigger was used over the pipes. Drains were spaced at approximately 12m distance apart and most were used with 80mm corrugated pipe. There is the potential to install mole drainage in the future in localised spots should there be any surface drainage issues. The main outlet was deepened to improve fall and flow in the main open channel. The few low-lying hollows were filled with excess soil and when the drainage was completed, the whole area was ploughed and the land levelled to give all sections of the site an outfall.
General drainage lessons
Poor design. Spacing, depth and type of drain merit a lot of detailed investigation and contractors with local experience are good at advising on such matters. Where the drainage system fails or is substandard, this can be confirmed by observing the water table depths between the drains and also the drain flow rate.
Ideally drains should be installed in dry weather. Deposition of soil particles in a drain pipe usually takes place just after construction when the backfill is loose. Generally this material is coarse as the “fines” have been washed out. In wet weather, the problem is more acute and the chance of other problems occurring increases, ie scaling, which may cause breakage or misalignment of the pipe and non-uniform settlement of the drain itself and the backfill.
Soil particle entry into the buried pipe may occur in soils that are very fine-grained and uniform (fine sands) – this is where the soil enters the drains over time and clogs the system. However, this is not likely to be a problem in clay soils, especially where gravel is put in around the pipe.
Sedimentation or settlement out of the heavy soil particles from the drain water will tend to occur at joinings and where there is a sharp change in the fall. These should be avoided where possible. Organic wastes like slurry or milk, etc entering the system will quickly form a gel which rapidly blocks the pipes.
Ochre or Red/Iron deposit can cause severe problems and is difficult to overcome – larger diameter pipes and/or more gravel fill can help in this regard and submerging of the system has been successful.
Finally, the drain mouth outlet may become clogged by roots, weeds, silt, etc over time and can subsequently cause stagnation/sedimentation along the pipe, which compounds the initial problem.
Drain mouths should be identified and marked and cleared every so often and care should be taken when cleaning main drains that these outlets are not damaged.
Alan Dillon’s factors to consider
It is important that before anyone attempts to carry out a drainage job on their farm that they have taken care of the following:
Every drainage job is only as good as its outfall. Cleaning and upgrading of open drains acting as outlets for land is a must before any drainage commences. All open drains must be dug to as great a depth as possible.Perform a site assessment. Test pits must be dug to ascertain soil type in the area and the type of drainage system required (shallow or deep). Hire an experienced contractor to carry out the work. A contractor with good knowledge and experience of carrying out drainage works can be the difference between a successful drainage job and an unsuccessful one.Have finances in place. Drainage is expensive and can have a serious impact on farm cashflow if plans for finances are not properly in place. Farmers need to sit down with their adviser to assess if draining land is the best move for them to make.When reseeding land post-drainage, select grass mixes that are suitable to heavy land, select mixes with good ground cover and persistency. The mix used on this farm on a per-acre basis was Twymax 4kg, Drumbo 4kg, Abermagic 5kg and Timothy 2kg. 
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