To obtain the best result from your drainage programme it is essential there is good planning, correct installation and recording.

To Plan Drainage:

• Springs and seepages are pegged in winter to identify drain positions.
• For moleable soils, mole design determines drain position.
• For slopes steeper than 1:15, mole direction should be designed with a level.  Pipe size is designed after checking grades.
• For flat drain grades, 1:300 or less, a laser-aligned trencher is preferable.
• Drain lines should be pegged and grades fixed before digging starts.
• Junctions with main drains should be Y junctions and should have extra fall.

To Install Drainage:

• The pipe should have a minimum cover of 0.75 meter backfill.
• Tiles should be laid with no more than a 5mm gap between them.
• Tiles should be laid in a trinket or blinded to ensure good alignment.
• Only dry backfill is replaced.
• Mole drains are pulled when soil conditions are suitable.

The depth of drains will vary with each set of local conditions.   In clay soils and silts the depth is determined by the following factors:

• Depth to an impervious layer - the drains should be immediately above this.
• Depth to avoid damage from stock and implements - 1m or preferably 1.2m is needed.
• Depth below which mole ploughs operate this is generally 500mm below the surface.
• Depth below the main root growth.
• Grades must be maintained to achieve design flows and avoid silting in the pipes.  A minimum 1:1000 is suggested in fine soils where there is little risk of silting but this should be increased to 1:200 where sands occur.
• The tile are laid butted and the water seeps into the drain through the joint between the tiles.

To Record Drainage:

• Pegs allow easy finding for maintenance
• An aerial photograph after installation is an accurate way of recording drain positions or marking details on your farm plan is a simple alternative.
• Another option is to use GPS and or your computer system for recording.