The flood...

So what is the one thing you don’t expect when moving to the desert? 

Correct.  A flood. 

It was really the last thing on our minds, even when we woke up one morning last week to a steady downpour.  No wind, no storm, just rain pouring out of the sky in a steady constant deluge.

We thought it was strange that it was raining so hard in the desert and we were right.  This is not the sort of thing that happens out here very often.  It started in the middle of the night and it just kept coming, non-stop for more than 12 hours.

You would think rain in the desert is a good thing – that the dry parched soil would just soak it up, drink it in.  The bunnies and other desert creatures would come out of their holes and dance and sing and frolic in the puddles.  My endless hours of watching Planet Earth told me that the cactus would fatten up and and pretty flowers would come out carpeting the ground in pinks and yellows.  False.  The soil here has virtually no capacity to absorb water at all.  So when it rains, it all just starts pouring across the ground in sheets, channelling together into a torrent and then heading downhill.  Quickly.

Flash floods are a terrifying reality in the canyons that carve out the landscape here.  You don’t want to be in one if there is any chance of it raining anywhere in a 100 mile radius.   They say the first thing you hear is a roar from up canyon, like a freight train coming through a tunnel.  The first thing you see is a wall of debris, trees, rocks, and mud, maybe 10 feet high at the leading edge coming towards you.  If you aren’t already on high ground by this point, they say your best chance is to get behind a big rock to break the initial force of the impact.   Truth is, they are just being nice.  At that point you should have just aboout enough time to cower into a ball, put your head between your legs and kiss your butt goodbye.

Cities in wet climates (like say Charlotte...) know how to deal with water.  They have drainage ponds, and storm drains, and very detailed (and cautiously oversized) rain water management systems.  Cities in the desert (like say Santa Clara...), understandably, spend a lot less time and energy on the subject.   Most of the time they simply make a note not to build things in natural drainage channels.  Most of the time.

At some point in the past, maybe half a mile (fortunately straight downstream) from our neighborhood, someone chose to ignored this simple concept, and slapped up a whole bunch of houses, businesses (and other buildings not designed for use underwater) right in the middle of a natural “wash” - that is, a dry stream bed that is only a stream when it rains.  At some later date, it rained, (though clearly not all that much) and they suddenly realized their error.  So what to do about it?

What if, immediately upstream of this neighborhood, we built a giant dike out of dirt and sand?  We just dam off the stream bed, creating a big pond, so the water can’t get to us?  All that water will just sit there, and eventually evaporate away!  Great idea!

The point they missed of course, is that this only works as long as it doesn’t rain enough or often enough to completely fill the pond to overflowing… which of course, is exactly what happened.

The most interesting part of this story , I think, is that the city knew it was coming.  They had done the math and knew that there was a specific amount of rain that would overwhelm the dike, and when it happened there would be nothing they could do about it.  They talked about redesigning it, making it bigger, maybe adding some cement to it, but nothing was ever done.  No provisions were ever made to redirect any excess water away from the homes should it overflow.  No provisions were ever made to at least reinforce the dam and avoid a total collapse when that happened.

And so at noon, when the rain still hadn’t stopped, they sent some engineers in raincoats with walkie-talkies down to the dike to watch it happen.

At 1:30 pm the water started pouring over the top.  By 1:50 the dike had completely disintegrated dumping the entire contents of the pond into the neighborhood downstream.

All in all about 30 homes and a dozen businesses were evacuated.  All suffered pretty extensive damage.  At least nobody was hurt.

I happen to be driving by and got a quick view of the area while the pond was still emptying.  Police were politely redirecting traffic away from a roaring river of mud that tore across one of the main streets in town and into the neighborhood below.

Up next… Hidden Canyon (Flash flood not included.)

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