Underground power lines and trees
Trevor_Lambert
| Posted in General Questions on
This one’s a bit odd, but my internet search yielded confounding results, so I thought I’d try here. We have about 6 acres of land, with underground lines from the road to a shed, and from the shed to our house. My wife has now decided to plant 1400 trees in areas that encompass both lines. What’s the minimum distance I should mark off from the lines where to avoid planting? The trees are maple (red and sugar), cherry, and oak (red and white). One line set is inside DB2 conduit, the other is direct buried.
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I would leave room so that if you ever have to replace the lines you won't kill the trees. The rule I've heard is it's best not to dig within the drip line of the canopy.
There isn't a requirement that you keep any particular area clear, but you might want to keep some area clear just in case you have to do any future maintenance work. I'd try to keep at least a two foot wide path clear, but that's pretty narrow to try to do any work in. 8-10 feet is better. Utility rights of way are typically 10 or more feet wide, just as an example, but you can do whatever you want with your own private system.
DC is right about the trees though. There is more risk to the trees than there is to the conduits. For that, outside the drip line of the tree is a plus, but you're probably reasonably safe if you can keep 5-10 feet or so distance between the trunk and the conduit depending on the size of the tree.
Bill
If you have space for 1400 trees, you have space to keep a clear area 30' wide (15' on either side) at the buried power line.
Think about needing to access the line in 20 years when some of the trees have 15" diameter - you won't want to dig within 5' of the centerline of the trunk...In 40 years you will want even more clearance from the trees...and by that time there may be recompense costs associated with the removal of each tree such as there currently are in urban areas...it is about $3k per mature tree in my area + planting 2 new trees (you have to find a place to plant them which also has costs).
30 feet is really excessive here. It's not that bad digging within 15 feet of a tree to presumably just repair damage to the conduit run, and the chances of needing to make such a repair is very remote anyway. If you really want that conduit system to last, use HDPE pipe instead of the more common PVC stuff -- the HDPE stuff will be one piece, no couplers, and very robust.
If I was planting something like oaks or maples that would be spaced out, then I'd run the conduit well away from all the trees since there would be plenty of space to do so. If these are smaller landscaping trees, then it's probably not practical to leave such a wide swath of clear area around the underground facilities.
Bill
The cables are already there, so I don't have the option of selecting different conduit. The longest run is direct buried.
Trevor,
I would look at this as an opportunity, allowing the lines to inform the landscaping. Arrange the trees in copses with clearings, making them seem more natural that evenly spaced ones. Use the lines as paths, and position features along them.
The details I'm staying out of, that's the job for my wife and the conservation agency. I'm assuming they know what they're doing. I just have to mark where they can't plant.
My primary concern is with the roots damaging the insulation of the buried line. I've read suggestions ranging from 2-4 feet being far enough, up to 30 feet+. I tried getting advice from the local utility, and their response was literally, "we don't care, because we won't be responsible for fixing it if it goes wrong".
That's very unusual, and the roots are going to go where they want to go over time anyway. The best protection is to run cables in conduit, but you've indicated that you have some direct bury cable already in place. I would follow Malcolm's suggestion of using the cable run to form a general line of landscaping, maybe putting in a garden path over the cable route, or meandering generally over the cable route. This makes the route blend in, and provides a plant-free area above the cable if you ever need to dig. You don't want a perfectly straight path because that will look weird (like the replanted forests with all the trees in perfect rows, so that you can periodically "see through the forest" as you drive past).
In my nearing 30 years now working with utilities, I have yet to see tree roots damage underground cables just by growing. I have seen roots get into sewer pipes (usually they get in at the seams between sections of old terra cotta pipe), I have seen trees pull up gas lines when the tree blows over and the roots get ripped up (hurricane damage in that case, and very unusual -- I saw pictures of it ONCE), and trees sometimes direct lightning and the wires are damaged underground by the lightning.
The natural enemy of underground cables is the backhoe, not the tree. I don't think you have much to worry about here.
Bill
"The natural enemy of underground cables is the backhoe, not the tree." Wise words!
Other wise words heard spoke at times:
"Wow, those wires are mighty colorful!"
That means the errant backhoe just dug up telecom cables, which use lots more colors than the power guys use. We telecom guys will then visit the errant backhoe operator, seeking much green to compensate us for our restoration efforts...
To paraphrase the "most interesting man alive" guy, "Keep calling Miss Dig, my friends" :-)
Bill
The plan is already to have a path along where the line runs. There already is a path there with hay on either side, but it's only about 5 feet wide. The only detail I'm trying to sort out is how much room to leave. I'd like to err on the side of caution, without going overboard. I'm thinking at least 10' to either side is reasonable.
I think you'll be fine with that much clearance. Don't worry about it.
Bill
The backhoe is also the enemy of mature trees. Trenching a line through the roots can kill a tree. I would avoid planting trees where you think you might have to trench in the future.
So 10' to either side is going to be a 20' clear area.
Think about a mature tree - find one on your property that is 30 or so years old. Now think about trenching a line 10' from the center of the trunk. Are you going to be able to stay out of the root zone? Your equipment itself is going to be about 4-6' wide, so now you have the weight of equipment on the roots 7' from the center of trunk. Seems far too close to me.
Obviously the wider area you leave the safer you are. I'd go at least 30' (15' to each side) or wider if possible..
If there is a need to replace the run in the future with lots of now-mature trees, just put it in by directional drilling and go UNDER the trees. I have done this a number of times in wooded areas going under ~2 foot diameter mature red and white oak trees, and had no problems. It's not a problem for a directional drilling crew to put things down 8+ feet if needed, even 20+ isn't a problem.
The simple reality here is that the potential to need to work on the underground lines in the future is very small, since the risk of failure is very low. If the need ever does arise, there are ways to deal with it that minimize the risk to any of the trees.
This really isn't a big deal that needs a lot of worry and planning.
Bill