Shedding Water

We wanted to make the amount of water that is shed by a parking lot visible. We chose a small subwatershed next to a loading dock.

The orange lines are contour lines at 6" intervals from a low point at the storm drain grate up to the sub-watershed divide marked in green.

Using a template, with holes spaced at the center of each square foot, we made one mark per square foot with chalk.

Then, each of the chalk marks was painted bright blue with non-toxic tempera paint.



We chose to use recycled soda cans as a unit of water.

These cans usually hold 12 ounces of liquid.

12 ounces per square foot is a very light rain of about 0.15 inch (0.15 is a little more than 1/8 inch of rain).

So, we would need  >3 cans per square foot to represent a 1/2" rain event.

To be honest, after nearly half of the cans had been set out, we had to start over and fill each can with water, because a slight breeze kept tipping the cans over.


Once everything was set up, many pictures were taken.


And the U. Akron Field Station's research blimp arrived!

Here is Maggie Duff, walking the blimp into the observation position.



Connie volunteered to hold the blimp in place while Heath Garris ran the radio equipment that caused the camera to take pictures.

A blimp's eye view of the set up of cans and contours.  Note the green band marking the divide between adjacent sub-watersheds.

Brooms helped us release the water from the cans and get everything moving down hill

At a count of three, the water began to move.

Note the sheen of water moving down the slope.

The Blimp's eye view of the events initial sweeps.

You can count the area that has been cleared by count one square foot for each blue dot.

It only took a couple of minutes before water started moving to the storm drain.

In the center of this image, you can see small tracks of water moving diagonally across the pavement.  This tells you that the pavement toward the top of the picture is a little lower than at the bottom of the picture. 

This image shows the storm drain and the pattern of water drainimg down the pavement.

By the time this picture was taken, the cans had been moved downward by 2.5 of the 4 feet elevation change.

You can see that the center of the drive, just above the storm drain is a little higher than the sides of the drive by noticing the dry area near the storm drain.

It took almost fifteen minutes to get all the cans and water down the slope.



We couldn't make a piles of cans on top of the storm drain, as I had hoped.

So the can were pushed into the corner, where they attained a reasonable angle of repose.

In the end, the pile was over 3' high.