Green Daily

I realize the world has moved onto forest fires but I'm still thinking about floods.

In the Midwest today it is again threatening rain, which has me thinking about terms. Levees tend to look like grass berms. They're actually made of clay and sand, an impermeable mixture that is built several feet above the normal crest of a river. The width of the levee usually depends on the force and width of the river amongst other things. Soil is piled on top of the clay and grass is planted, perhaps a flood wall is added. Typically the U.S. Army Corps of Engineers build the levees which they sometimes also manage. When engineers talk about a break in the levee it could mean that the clay and sand have eroded, leaving a gully, or it could mean that the water has breeched the berm.

The goal of a levee is to keep a river from spreading. But as Professor Chris Paola at St. Anthony Falls Laboratory pointed out, a river is a living thing. It moves, breathes and changes. Putting levees in place is akin to turning a river into a culvert. An extension of that metaphor is the absent Los Angeles River. So many agricultural and urban levees exist it logically follows that during heavy rain water will drain into a river that serves as a funnel. Eventually the pressure in that funnel will explode in someone's town.

So it's no wonder that when rain falls in a series of controlled channels and has no place to go it will break its levees. I think of the fairytale in which a sleeping dragon is tied in place with the sturdiest rope the villagers could find. As soon as the dragon awakens and tosses his head, all of the strings break.