If you've ever been curious about what flash flooding looks like

[Fatalifeaten]

The remnants of Hurricane Lorena are passing through Phoenix today. it wasn't a big storm as hurricanes go, and those of you used to them will probably view this is a minor storm. For us though, it's been a pretty hectic morning. My part of town has seen 2.6" of rain so far, and the forecast is "iffy" on whether we're done or not.

We're set up to handle monsoon rains with up to a half inch pretty well with our storm sewers and retention basins, but once you go over that, all bets are off. Volume vs duration is also an issue. We can handle an inch in 24 hours, for example, but an inch an hour is a completely different story. That's what leads to flash flooding and messes around here.

This is some local runoff in my neighborhood.

1.) that's an 8 foot baseball backstop out there, water's maybe 4 foot deep in this master catchment.


2. Panoramic of the same basin. At the far end it's about 8 foot deep and water is overflowing onto the main street causing hatred to traffic.


3. That underpass is 5 foot deep, and the water is MOVING. Hopefully the kids who cross there on the way to school don't get any bright ideas, that current is a killer.

4. Other side.


5. This looks kinda tranquil, but it's 6 foot deep and moving fast.

 

[MerlintheMad]

The remnants of Hurricane Lorena are passing through Phoenix today. it wasn't a big storm as hurricanes go, and those of you used to them will probably view this is a minor storm. For us though, it's been a pretty hectic morning. My part of town has seen 2.6" of rain so far, and the forecast is "iffy" on whether we're done or not.

We're set up to handle monsoon rains with up to a half inch pretty well with our storm sewers and retention basins, but once you go over that, all bets are off. Volume vs duration is also an issue. We can handle an inch in 24 hours, for example, but an inch an hour is a completely different story. That's what leads to flash flooding and messes around here.

This is some local runoff in my neighborhood.

1.) that's an 8 foot baseball backstop out there, water's maybe 4 foot deep in this master catchment.
View attachment 31583

2. Panoramic of the same basin. At the far end it's about 8 foot deep and water is overflowing onto the main street causing hatred to traffic.
View attachment 31584

3. That underpass is 5 foot deep, and the water is MOVING. Hopefully the kids who cross there on the way to school don't get any bright ideas, that current is a killer.View attachment 31586

4. Other side.
View attachment 31582

5. This looks kinda tranquil, but it's 6 foot deep and moving fast.
View attachment 31585

Yeah! My son used to live in Tucson, with the same kind of runoff channels and catch basins. I tried to imagine what those looked like when full. Now I know.

Locally (well, speaking of the State as a whole), the Virgin River gorge in S. Utah is a killer. 99% of the time it's this feeble trickle of murky water winding this way and that in a wide river bed. But when flash flooding expands the volume, the depth can go up to thirty feet! At times like that, the barrow pits on the freeway turn into rivers as well; and recently, bridges under the freeway were washed out.

I saw a video taken through the rear window of a stalled vehicle, showing a minivan managing to get driven into the "river" running down the middle of the barrow pit: floating and bobbing along until it plunged out of sight over a "waterfall", where the "river" dropped into the channel below, which was a road that crossed under the freeway. You can only imagine what that felt like inside the minivan, or what the fate of the passenger(s) might be. There were several fatalities that year from that flooding.

Then, I saw another video out of Aus: taken from the second or third floor of an office building, showing a "river" of junk, trees, other detritus, CARS, all being rushed along below, as the water level rose and snagged other vehicles out of the parking lot. One guy appeared below, splashing to his vehicle and getting in, backing out in deepening water and successfully driving away!? "No, Dude! Don't deeyou it!" said a voice in the video (one of the office onlookers). But he did. He was lucky. Later, the video was finished up downtown, where the vehicles ended up, after the water level had subsided: and cars were piled three deep. Amazing sight.

 

[CKeeler]

Wow. Didn’t know there was that much rain passing through Phoenix. I’ll have to check up on my cousin and his family