06.24.11Kelly Duke

Root Cause Analysis

Thick and fleshy roots filled the zone around the pipe and valveThick and fleshy roots formed thick bundles around the valve and pipes creating lateral pressure that cracked the tee fittingGot Roots?A small portion of the roots removed from the 30 cubic foot volume of soil excavated for the repair

I suffer from that particular malediction that requires me to take on most, if not all, home improvement, maintenance, and repair projects around our house.  Normally I would say that this is a positive thing but there are times when I overestimate my skills or underestimate the task.

Two weeks ago I noticed that the ground was overly damp in a section of our side yard.  Looking in a nearby sprinkler valve box I found standing water and knew I had a leak in the main line system.  As lord of the manor and as the installing technician of record, I felt duty-bound to carry out the repairs.

I shut the mainline off to allow the ground a week to dry out.  When I started in, the ground was moist but not muddy and digging was initially very easy.

Then things got ugly; really ugly.

The entire area in and around the valve, the mainline, the lateral lines, and an adjacent drain line were a sold mass of big, fleshy roots.  The roots came from an adjacent Giant Bird of Paradise (Strelitzia nicholii).  For those unfamiliar with this plant its roots  have an outer cortex that has look and consistency of a raw fingerling potatos surrounding a central core that is similar to a twine of hemp rope.  They are easy enough to cut but deceptively strong in terms of the lateral force they can exert on buried pipe and fittings.

This mass of roots had, over time, exerted sufficient lateral pressure on the mainline to crack the tee fitting that supplied one of the remote-control valves.  My analysis suggested that the repair could go one of two ways:

Option 1: Cut out the tee and install a new tee using a compression repair coupling

Option 2: Cut out the tee and complete the assembly with solvent weld fittings

I tend to shy away from compression couplings so I took Option 2.  This was a bit more complicated as there was no really good way to bow the mainline enough to allow the gluing and insertion of the fittings.  I solved the problem by off-setting the tee with elbows.  As I have a looped mainline I was not concerned that these added elbows would diminish flow or pressure.

There are many trees that I consider to have aggressive and invasive root systems (Elms and Poplars come to mind).  Strelitzia was never on that list.  Tree roots are not malicious by nature.  They are in fact lazy in that they take the path of least resistance preferring any place where pore space grants them entry and moisture lets then thrive.  They can be relentless however once they get that first toe hold.  Most of the roots encountered in my ordeal were clustered within the trench lines of the original installation where the soil was more easily penetrated and where the piping likely created a cooler micro-environment that help the soil to retain moisture.

I titled this installment “Root Cause Analysis” for a reason.  Forgetting the obvious and intentional play on words, the root cause of the problem was in fact, the roots. This led me to the following guidelines that one should consider when designing future irrigation systems:

  • Locate critical main line fittings and assemblies away from trees if at all possible.  A likely safe zone would be at or beyond the drip line.
  • If you cannot avoid installing the valve near a tree, then consider installing some form of root diversion technology (example: Bio-barrier®) around any endangered valve boxes at the time of installation.
  • Compact all trench backfill thoroughly to make it a little less advantageouse for any roots stumbling upon the trench lines as a target of root growth opportunity.

I do not know how long this cracked fitting had been leaking.  I can tell you that the floor of the hole I had dug became progressively muddier as accumulated ground water migrated to the opened pit.  In any case, the situation represented a waste of water and an expense of time and effort for its repair.  Better design may help reduce this as a problem in the future.

Perhaps you have encountered this situation at your properties or projects and have found additional or better ways of dealing with it.  I welcome your feedback and suggestions.

K. F. Duke

Kelly Duke

Not many people can say that they have dedicated their life to the landscape industry. Kelly Duke can. His diverse background ranging from maintenance to estimating, to design, along with a passionate commitment to his trade has given Kelly a lifecycle perspective to landscaping. As the leader of the ValleyCrest’s Pre-Construction Services team, he analyzes early conceptual designs to determine whether or not and how they can be built within budget while meeting long-term design and maintenance goals. Many of the projects that come across Kelly’s desk require he examine the cost and savings of baseline water use in comparison to high efficiency alternatives.



  1. Friday, 1:51 Alan Harris

    Kudos to you for noticing a tell tale sign of an irrigation leak. Too often these signs go unnoticed for a long time and as you noted the amount of water leaking may be small, but the continuous nature of the leak adds up over time.

    BTW – having been trained in Six Sigma where we are taught to conduct Root Cause Analysis on problems, I found your title to be quite intriguing and accurate both literally and figuratively

  2. Sunday, 9:10 Dana Seelig

    Kelly, I can’t agree more, I have a Liquidambar Street Tree that is about 3′ from my Water Meter. It and its roots have taken me down the same path on more than one occasion.
    As long as you are going there, let’s make sure that shrubs are not planted (even though they are “shown that way on the plans”) where they will block spray from the irrigation heads and cause similar issues down the road.

  3. Thursday, 12:31 jeff clark

    Good analysis and you are absolutely right that a proper design can help avoid these type of issues in the first place.

    One comment about the site, can you increase the font size? On high resolution monitors, like mine, I have to zoom in or squint.

  4. Friday, 5:11 Frank D. Gorman P.E.

    I agree with using option 2. You indicated a looped system which is always is a plus. If you have enough pressure the minor hydraulic friction losses with the bends should not be a problem. A compression coupling will deteriorate over time and you will be back in the same spot you started. Fixing a leak. Just remember to compact the soil around the pipe as to minimize pipe movement due to water hammering. I suggest at least 90% of maximum density.

  5. Tuesday, 8:24 Kelly Duke

    I have been out in the yard digging some more on unrelated matters. When one lives in a ninety year old house one must expect some problems. I need to reline the cast iron sewer lateral that runs from my house to the main trunk line in the street. While digging an access pit for the lining contractor, I found roots from that same Giant Bird of Paradise noted above some twenty feet away from the main tree. The rule of thumb that the roots diminish at the drip line apparently does not apply to Strelitzia nicholii. KFD

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