Austin, TX Ice Storm 2

[dpc]

Just wondering if anyone knows what utilities in this part of Texas use as a maximum radial ice loading for design of their OH lines and service drops? And how much ice they actually got. The news reports I've seen are pretty useless.

 

[Gr8blu]

dpc: As to how much ice accumulated - it really depends on the location. Areas less than 15 km (10 miles) apart recorded massive differences, ranging from a low of about 6 mm (0.25 inch) through 18 mm (0.70 inch). On average, I'd have to say that the city of Austin TX saw something like 15-18 mm (0.6-0.7 in) while the surrounding communities saw much less (6-10 mm or 0.25-0.4 in).

As a past resident of the Austin area, the real issue is that the vegetation (trees) in the area typically overgrow the right-of-way for overhead conductors, particularly in residential areas. The trees also tend to be fairly dry at this time of year, thus more susceptible to wind and weather damage (e.g. dropped limbs). The combined tangle of debris makes the cleanup difficult - since the Austin teams aren't really geared up for that kind of thing on such a large scale. To be fair - they do a pretty good job on the "normal" hazards like a hail storm or a high wind event.

Other Texas communities (Dallas, San Antonio, and smaller cities) see much the same problem - the severity is primarily related to how much vegetation is involved. For example - Taylor TX (pop 16700) is an agricultural community roughly 30 km (20 miles) outside Austin. It has far fewer trees overhanging the overhead conductors - and saw 25 people go without power as a result of the storm. Their ice accumulation total from this past storm was in the 12 mm (0.5 in) range.

Converting energy to motion for more than half a century

 

[stevenal]

NESC says half inch, based on ASCE 7-10.

 

[dpc]

So it may have more to do with tree limbs than with actual ice weight on the lines. 1/2" doesn't seem like much. In the midwest we used to consider 1-1/2" of radial ice, IIRC.