Locating pipes and drains

  1. If a pipe has collapsed or infilled, there may be increased local waterlogging, or an indication of a surface channel where the land has subsided in line with the pipe. Note however, that spring outlets often shift over time so that boggy areas do not necessarily indicate a broken pipe.
  2. Where a wet patch is caused by a broken pipe, the break is usually just uphill of the wet patch.
  3. To track a specific drain, first try to find its outlet. Sometimes drains are curved near their outlet to slow the flow of water, so go a few metres along the supposed line of the drain before attempting to locate it. Locate it again at a second point, and then line up these two points to indicate the drain’s alignment.
  4. To follow the exact line of a pipe, thrust a pointed metal pole or rod into the earth every few metres along it, until you hit the drain. Tile drains should leave a trace of red clay on the tip of the rod. If you miss, work out to either side, making sure your holes are more closely spaced than the drain’s diameter.
  5. Pipe-locating devices can be hired for tracing water pipes to which you have access at either end.

Causes of drain failure

Drains  may  fail  for  one  or  more  of  the  following reasons:

  1. A blocked outfall, indicated by seepage from under or around the sides of an outfall headwall. If the blockage cannot be removed with drain rods, it may be necessary to uncover the pipe for a few metres back from the headwall, and relay it or replace it as necessary. Use a length of rigid plastic pipe to prevent seepage undermining the headwall.
  2. A blocked entry point.
  3. Poor grading during pipelaying, resulting in dropping of silt where water flow is slowed.
  4. Settling of pipes due to poor installation or unstable soil conditions, causing siltation due to uneven flow, and ingress of material between the pipes.
  5. Erosion due to a failure to use sealed pipes in erodable soils.
  6. Surcharging where the pipe is too small or the head of water too great, causing water to back up before it can get through the pipe.
  7. Blockage by ‘ochre’, which forms when previously waterlogged soil is aerated, causing iron in the soil to oxidise. Pipes in soils prone to ochre may need frequent cleaning out.
  8. Blockage by tree roots. Avoid laying pipes near trees if possible. If not, use long lengths of rigid plastic pipe through the rooting zone.
  9. Blockage by small mammals which have entered the pipe. Install grids on outfalls and open inlets.

Clearing blocked drains

Drainage rods

Drainage rods with various metal attachments are available from builders’ merchants and agricultural suppliers. Head attachments are of two main types: corkscrews for pushing through and loosening solidly blocked drains, and scrapers for pulling material clear.

Use of drainage rods

  1. Choose a point as near to the blockage as possible to begin work. If you do not know where the blockage is, start at the outfall end and work upwards.
  2. Attach a screw head to the end rod, and insert it as far as it will go, adding sections as needed. Stand sideways-on to the drain and work the rod back and forth continually to pull loose material towards you. Once more than one section is in use, keep turning in the same direction so they stay tightly joined, which will be clockwise for a right-hand thread. ‘Lockfast’ rods stay attached whichever way you turn them.
  3. After two or three sections are in, back them out of the drain to clear loose dirt, using the same motion as when inserting them. Then work them back in and add more sections.
  4. After you have added ten or so sections the rod may become too flexible to push through a hard blockage. If this happens, remove a section of pipe at the point you have reached, and start again from this point.
  5. Once the worst of the blockage is broken up, remove the rod and replace the screw head with a scraper head. Push this past the blockage and scrape the material towards you, trying to twist the scraper head as little as possible.

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