When all this snow finally melts (obviously not all at once), how much flooding will there be? If it had been rain, it would have begun running off while still coming down, rather than just sitting on the ground as snow.
Snowfall of 6 inches is the water equivalent of a half inch or rain, and they get those every week or so. The precipitation they got is what they got, and freezing/thawing it doesnt change that.
Houston gets 50 inches if rain every yer, So a 6-inch snowfall would be only 1% of that.
Post-snow flooding is a thing though. There are things like cascade effect to be considered - snow that fell in lower lying places is speeded in its melting by the flow of meltwater from higher places.
For comparison: When I lived in Montana, every major road had drainage ditches alongside it, big enough to lose a couple of cars in them. 51 weeks of the year, they’d be basically empty. But for a week every spring, they were filled clear to the brim.
Does Texas have similar ditches? I doubt it.
Post-snow flooding is a thing, occasionally, in places where the ground freezes solid in the winter, which inhibits absorption into ground water channels. Did the south also have a hard freeze?
We’ve had such a wet year here, the ground just can’t absorb any more. Fortunately, we haven’t gotten a whole lot of snow, but the creeks and runs are all pretty high anyway. If we should get major snow before the winter is over, it will be a mess in southern Merrylande.
Post-snow flooding is a thing, occasionally, in places where the ground freezes solid in the winter, which inhibits absorption into ground water channels, and where the snowfall accumulates to great depth over the entire winter. It’s made worse when there’s a sustained heat wave: random days that dither just above freezing are OK, but a sudden stretch of sunny days with highs around 50F is more likely to be a problem.
It’s the melt and freeze that’s a problem.
Northern Illinois is just one giant flood plain anyway so we’ve already established places for the water to run off and go (channels, detention ponds, etc). But I did notice some road crews out this morning scooping up the huge built-up snow piles from plowing and loading dump trucks so it could go melt somewhere else next week and not flood the intersections. Can’t trust the storm sewers to not be clogged with ice and debris (or under 10’ of plowed snow)
Actually they do. Texas has a massive system of ditches to drain away water. It’s generally intended for hurricanes and other big rainfalls but I assume it will work for snow melt.
Snowmelt from a single storm, especially one this small isn’t typically a problem anywhere. As mentioned, it’s the equivalent of only a small rain storm. Snowmelt from a winter’s snowpack is the major problem in areas with a lot of snow, and that’s not happening in the deep south.
Indeed so. Flooding hasn’t been a problem in Texas so far in the aftermath and not likely to become one. We didn’t get much snow/ice to begin with. Partial melt and re-freeze has been more of an issue on roads, especially as we don’t have many sand trucks.
The systems we have in place are not always sufficient, as Harvey showed, though I don’t think there are any systems that can brush off 40-50 inches of rain in less than a week. And even then, most of the area came through that better than expected.
Snowmelt flooding is generally on a smaller local scale. As mentioned, even with deep snowpack the water content is equivalent to only a few inches of rain, and it isn’t going to melt instantly. Anyone who has hiked in or near snow-covered mountains knows that streams and rivers become swollen and can be uncrossable during the snowmelt. But warm air can hold a much greater quantity of water, so snowmelt flooding is never on the catastrophic scale that can result from sustained heavy rain as with hurricanes or even just sustained regular convective thunderstorms.
Yes, but this is true for rainfall as well, of course.
It is gonna be a mess up here in Chicago. Anyone w/ a dog is familiar w/ “mud season!” As far as flooding, I’m awaiting the first spring rains, when the ground is still frozen…
Ignore my comment on this above, I did not read what you wrote carefully enough.
I’m not sure if this is true, though. Snowmelt from above flows into narrow channels, streams and rivers, it does not wash across broad snow-covered areas. It will cut back the snow-covered banks somewhat as streams become swollen, but I’m not sure that the snowmelt flowing from higher ground is itself going to melt a significant amount of snow below.
I’ve seen it do that; water washing across the surface breadth of an entire field or flooding a plain, eventually finding a channel, but in the meantime, wetting a large area - and if that area has snow on it, that’s additional water that was just sitting there, not draining away
From this map of snow depths across the U.S., it seems like major amounts are mostly confined to northern New England.
The possibility and extent of spring floods depends on how much more snow we get, the time course of thawing and extent and timing of spring rains. Texas weather is highly variable, and even in the flood-prone areas of southeast Texas where I lived, the relatively miniscule snow and ice on the ground is an insignificantly tiny fraction of the precipitation that normally (and abnormally) falls on the region. I can remember springs where le deluge was semi-apocalyptic without the help of any melting frozen stuff.
When you look at a map and see a North/South river, you probably think it flows from north to south. The Mississippi, the Hudson, and the Delaware all do. A major excepetion is the Mackenzie river in Manitoba. What a difference that makes. It empties into the arctic with the result that the sources thaw long before the mouth does and there is major flooding every years as a result.
About 5 years ago I was in the Houston bus station and there were families stranded there for days, when heavy summer rains had I-10 under water. Main roads there are often under a foot of water for a couple of hours after a heavy rain, but it drains off quickly.
Here’s a lecture on the history of flooding down in Texas (Prof. S.R Vaughan)