Monday, July 9, 2012

Raindrops keep fallin' on my head!

The monsoon season has arrived in Denver! It's the time of year when a long stretch of dry, dusty days are suddenly punctuated by daily downpours. This weather pattern lasts for much of the month of July.

Many of our refugee students are familiar with similar seasonal rains, but not how they translate to an urban environment. Each year, a number of Americans are injured or drown in urban flash floods. Now is a good time to explain to your student the basic physics of storm drains and the suction power they can generate.

This morning, an extremely heavy rainstorm poured a deluge of water on downtown Denver. Traffic was snarled and, because the storm drains in the streets were overwhelmed by the sheer volume of water, many streets flooded. The photo taken above was taken this morning during that storm. It's Welton Street just off of Colfax, between the Convention Center and Emily Griffith Technical College. The water was about thigh-high on an average-sized adult (as gauged by watching a woman wade across 12th St.).

The water was gone within 90 minutes. That's millions of gallons of water being sucked into storm drains very quickly. What many of the refugees don't understand is how strong that suction really is. It's important to let your students know how to manage urban flash floods:
  • If your student drives, the general rule of thumb is not to drive into water deeper than six inches
  • Do not wade into the water to cross the street. If you can't see your feet, go another way. If the water is more than shin-deep, it's dangerous and can easily cause a fall.
  • Do not walk near or through the water rushing into storm drains at the curb.
  • Keep children close. Do not allow children to play in the water or near storm drains. Some of the larger drains--in culverts, for example--can easily suck in a child (or adult) very quickly. There are many instances of Coloradans who have died this way!
  • Tread carefully. The mix of debris, oils, and plastic swept up in the water can make for slippery conditions. If you have to walk through it, rinse off your skin once you're inside.
  •  Remove shoes and give them time to dry thoroughly before wearing them again.
Monsoon storms can come up very quickly and it's easy to underestimate how much water is moving off of the streets. Several years ago, I was caught in a downpour while riding my bike home from work. I was on the Cherry Creek bike path downtown. Within a matter of minutes, the creek started rising rapidly. Soon after, I couldn't see if the bike's wheels were on the path or headed into the creek. There was no place for me to exit for several blocks so I just kept riding as fast as I could. I was unexpectedly pounded by a jet of water that nearly knocked me off of my bike. The path is below street level, and serves as a drainage point for the runoff. This water is channeled into large, circular holes in the walls along the path, and the pressure is immense. I was looking down as I was riding, so I never saw the blast of water coming out the wall that was about to hit me (and it's filthy). I was fortunate not to have fallen and been swept into the creek's current.

When I got home from that ride, I turned on the TV news to see that five people had to be rescued from the path only thirty minutes after I had ridden through. Some of those people were hanging from tree branches and others were clinging to the iron bridge supports that hold up the overpasses. The usually docile Cherry Creek was nearly ten feet deep and the current was raging! The really surprising thing was just how fast that happened.

On a related note, Colorado has the second-highest incidence of lightning in the U.S. (Florida is number one). According to the Colorado Office of Emergency Management (COEM), lightning has killed or injured more people in Colorado than any other thunderstorm hazard. Make sure your students know that when lightning is present, they must seek shelter. Describe what is and is not considered safe shelter. This is particularly important if you know your student has a field trip planned to open space or the mountains, where most lightning-caused deaths occur. For a safety checklist, click here for information. Remember, when thunder roars, go indoors! Additional information from NOAA regarding Colorado lightning safety can be found here.

 Stay safe, stay dry, and be smart!

No comments: