Tropical Storm Irene didn’t do much in Greater Nashua (thank goodness), but it did provide one lesson: Hauling water from the rain barrel sure beats melting snow on the wood stove when you want to flush the toilet during a power outage.

Still, even though having no electricity in August is easier than having no electricity in February, why do we have to lose it at all?

Specifically, why do we put power lines way up in the air to be knocked down by ice, wind, falling trees and errant meteorites? We don’t expose public water lines that way, so why expose public power lines?

Let’s bury them!

This idea has been studied quite a lot, it turns out, by everybody from the North American Wood Pole Council – which (surprise!) thinks wires strung on telephone poles are great – to a whole bunch of state and regional utilities tired of complaining customers. Two conclusions have been reached.

The first is obvious: It’s expensive.

On average, it’s six to seven times as expensive to bury higher-voltage transmission lines than to put them on metal towers, said Dominion Power in Virginia and North Carolina, while it’s four to six times as expensive to bury the lower-voltage transmission lines that run down our street.

It’s no better in New Hampshire. A report by a firm called NEI Consulting – done for the Public Utilities Commission after the December 2008 ice storm – estimated that it would cost $40,000 per customer to bury the state’s entire power grid.

Forty thousand dollars per customer! That makes a $1,000 home generator look like a bargain.

Further, the process would “easily take over 40 years,” said the report. Since this rivals the average 50-year life of underground cabling, “construction and maintenance would become perpetual.”

The cost is so high because you can’t just dig a trench – difficult enough in this granite-ledge-filled state – and dump the wires into it. You also have to bury switches and transformers and the other stuff that steps voltage up and down. Rights of way can also be more complicated and expensive, and then there’s the question of the cable, phone and other lines strung on poles. If a new service enters town, they’d have to dig up the trench again.

You also have to protect the wires, which is where a second point arises: Underground cables aren’t as impervious as we think.

Water can leak in, just like it does in my basement. Burrowing rodents are an issue, just as they are in my yard. The ground can settle or rise, which I haven’t noticed yet but give me time, and this is more of a problem with a solid pipe than with hanging wires.

Much depends on what type of underground system is used: There are fluid-filled pipes, gas-filled pipes, pressurized pipes and plain old solid cable. The technical issues are surprisingly complicated.

Another study by the parent company of Dominion Power found that underground lines have only 50 percent fewer outages than overhead lines. (I am surprised: I would have thought they’d be more reliable.)

The real problem is that fixing an underground line takes much longer than fixing an overhead line on a pole. That Dominion study found this delay overwhelmed any advantage in reliability, actually increasing the total number of outage days over time, even though it decreased the number of outages.

The result is that power lines are usually buried only when there are aesthetic reasons, as well as cost/reliability reasons.

Aesthetics is why some folks want the proposed Northern Pass transmission line, designed to bring 1,200 megawatts of Quebec hydropower, to be buried as it passes through about 40 miles of undeveloped woods.

Cost is why Northeast Utilities and NStar, the utilities that want to build Northern Pass, haven’t done a detailed analysis of burying the lines. They say it’s too prohibitive to waste time on.

A similar power line being proposed in eastern Maine will allegedly be buried, but when I asked for details, I was told that the so-called Northeast Energy Link “is in the very early stages of development, and, as you know, is being proposed as an underground, high-voltage direct-current line, but the project isn’t yet far enough along to get into the details on trenching, etc.” I’m a little dubious.

Another big transmission line along the Hudson River valley will be buried under railroad rights of way for 73 miles, a clever way of getting around much of the cost of burying lines. But since there’s no railroad down my street, that doesn’t help me much.

Maybe I should buy that generator after all.

Granite Geek appears Mondays in the Telegraph, and online at www.granitegeek.org. David Brooks can be reached at 594-5831 or dbrooks@nashuatelegraph.com.