✔ Why do drainage systems stopperforming?

✔ How can I ensure future ease ofmaintenance?

✔ How are open drains maintained?

✔ What methods unblock drains?

✔ What time of year should field andopen drains be maintained?www.teagasc.ie/heavysoils

Useful Publications

Land Drainage BookletA freely downloadable practical guidebook toland drainage is available via the Teagascwebsite, www.teagasc.ie/publications Search“Land Drainage”.

Land Drainage ManualThe Teagasc Manual on Drainage and SoilManagement is available from Teagasc offices orcan be ordered via the Teagasc website,www.teagasc.ie/publications Search “TeagascManual on Drainage and Soil Management”.

What methods unblock drains?

• Jetting (above) – is an efficient way of cleaningpiped drains. A hose, fed through the pipewashes and flushes sediment, iron ochre anddebris from its internal walls, perforations andadjacent stone fill. Some models can extend to300 m up the pipe.

• Rodding – is a more labour intensive and lesseffective alternative.

What time of year should in-field and opendrains (ditches) be maintained?

• To protect fish eggs and small salmonids,maintenance of open drains likely to containthese species should be carried out betweenmid-May and mid-September.

• Hedgerows adjacent to drains should not be cutbetween 1st of March and 31st of August.

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Land Drainage:MAINTENANCEQ&A

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Animal &Grassland Research & InnovationProgramme

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Introduction

• A maintenance plan should be adoptedfollowing the installation of any drainagesystem.

• Maintenance vastly improves the capacity andthe lifespan of the drainage system.

• A regular maintenance programme shouldinclude assessment of the whole network,focusing in particular on likely areas forblockages (Figure 1) and adequate upkeep.

What causes drains to block?

• Fine soil particles: silt and clay particles aremany times smaller than aggregate or pipeslits, they can enter pipes and settle in low flowconditions.

• Iron ochre deposits: these are predominantly‘rust’ and occur naturally in certain soil types.

• Plants and their roots: can thrive in openchannels, at the pipe outlet and deep within thesystem.

• Collapse/sedimentation of open drains, due toflow conditions, undercutting of banks orlivestock damage.

How can I ensure future ease of maintenance?

• Clean and upgrade open drains before fielddrain installation to ensure good outfalls andconsistent flows.

• Use simple layouts with few junctions, usemanholes as access points. The upstream endof field drain pipes can be brought to the fieldsurface and capped to allow access.

• Mark the locations of field drain outlets andmanholes in the field and on maps to helplocating them afterwards.

• Always use pipes to allow for maximum waterflow and maintenance by jetting/rodding.

• Ensure the aggregate used above the pipe iswashed and 10-40 mm in size. At present thereis no evidence to suggest membranes on top ofaggregate or around pipes help.

How are open drains maintained?

• Open drains should conduct surface waterduring rainfall, be deeper than in-field drainsand also where possible drain groundwater allyear round.

• Open drains should be clean and as deep aspossible with a graded profile (Figure 2).

• The bank slopes of open drains need to beappropriately graded to prevent collapse (SeeTable).

• If such grades cannot be achieved then pipingof new open drains may be necessary.

• When cleaning open drains, care must betaken to protect field drain outlets fromdamage.

• Spoil from such works can be spread onadjoining land but must not impede water.

Figure 1: Examples of where blockages may arise.

Why do drains stop performing?

• The performance of drainage systems willdeteriorate over time, due to a variety ofblockages.

Figure 2: Maintenance of open drains changes the shape ofthe drain and makes them more efficient for water transport.

Channel Channel Max waterSoil <1.3m >1.3m velocity

deep deep m/secHorizontal:Vertical

Heavy 0.5:1 1:1 1.5ClayClay or 1:1 1.5:1 1.0Silt Loam

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