Impervious Surface

February 1, 2013

by Tim Burris, Mariton Preserve Manager

Mariton received 2.41 inches from the recent storm.  We ended the month with 4.01 inches of precipitation, which is about half an inch above average.  We are starting the year with a slight precipitation surplus.  That is a good thing, since we ended 2012 with a deficit. 

Dan’s photos of Crow’s Nest Preserve after the storm are stunning.  We had all that rain, but the ground was frozen solid, so it had nowhere to go except overland.  That morning, there were a number of road closures due to flooded streets.  In this circumstance, even protected open spaces like Mariton and Crow’s Nest couldn’t absorb the copious rain.  Fortunately, many preserves were able to store some of the run off in low areas, reducing flooding, however this event provided a clear illustration of what happens when you pave over the region. 

When we detour around flooded streets, we don’t spend much time thinking about the root cause.  We are worrying about getting to work on time, and which route will be open.  This is exactly the time when we should be looking at the reason for flooding.  Society’s impervious footprint grows more rapidly than we can protect open space, or people can install rain gardens.  Unfortunately, most fixes are about diverting the flood waters somewhere else, instead of addressing the flood’s origin.

When I first started at Mariton, I was usually out on the trails in a rain suit during rain storms.  I studied how water affected the trails and tried different methods to reduce erosion on the trails.  I learned very quickly to always head upstream and address the water before it got on the trails.  Sometimes that is easier said than done, but it has taught me a lot about how water moves on the preserve.  Sometimes I think Urban Engineers need to spend more time with their boots and rain slickers, and a little less time with their computer models.