What Happens When You Pave Paradise

– By Douglas  McKean –

Back in 1887, my great-grandfather invented a formula that if followed might have saved Rye residents from the devastating effects of the flooding last year.  Over 120 years ago, Robert McMath, a civil engineer, invented the formula Q=ACI to calculate the sizing of storm water systems in the developing suburban St. Louis landscape.

Q = The quantity of runoff from a given area
A = Area of the area being analyzed
C = Coefficient of runoff (lower for woodlands and lawns and higher for paving or roofs)
I = Intensity of the rainfall.

For Rye, the key to this formula is “C” - the coefficient of runoff – which has degraded greatly in Westchester County as the watershed area that drains into Blind Brook has been developed over time. Every new house, driveway, parking lot, and bluestone terrace in Rye, and especially upstream, speeds runoff to Blind Brook.  The Joni Mitchell lyrics “They paved paradise and put up a parking lot” – says so much about which has had a negative impact on Rye.  Simply, the more each of us pave — changing any of the Rye watershed from native woodlands to suburban ‘dreamland’  — the more flooding will occur.

After the devastation from Hurricane Katrina you may have received the email showing the sophisticated flood control systems from London, Venice and the Netherlands.  By comparison, the e-mail also contained photos of the New Orleans 9th Ward levees – which were little more than Jersey barriers set atop peat moss mounds. Our solutions to flooding in the past have been dams, levees and channelizing water, all to constrict the flow. Then, after a tragedy, we ask what happened.

So why was Rye heavily impacted by flooding last spring? Because we haven’t
been paying attention to information developed over 100 years ago. The Blind Brook watershed (the “A” of Q= ACI) is the same as it was 100 years ago and the storms are roughly the same intensity as they were 100 years ago, so the only factor that is constantly changing for the worse is “C” – the coefficient of runoff.

What are some alternative sustainable strategies to correct the damage we have done? Restore our former wetland areas – as originally proposed on the old Rye Nursery property. Modifying the Bowman Avenue Dam and re-widening the flooding plain are more expensive options, but ones we should consider.

A radical but very exciting project would be to install a tree-lined central median the entire length of Midland Avenue from Apawamis to Playland Parkway. This overly wide road can easily accommodate the planting and still handle vehicular traffic.  It would transform a sea of pavement to a glorious boulevard.  The plan would reduce floodwaters from rushing down the pavement and into Blind Brook.  Instead, rainwater would be directed to the plantings which could be a wonderful combination of trees, ornamental grasses and seasonal flowers. We could make a positive change from a flooding perspective and improve our community’s appearance!

Inexpensively, we could start tomorrow and make fast and long lasting progress to mitigate flood damage to our community, save many neighbors money from flood damage, reduce anxiety, lower insurance costs, improve biodiversity of the local ecology, and restore habitat for migratory birds. On the list of low cost solutions, holding thestormwater on each of our properties for the longest amount of time is the least expensive way to reduce flooding. Two easy solutions are rainwater gardens, which use the collected water from the downspouts off our roofs and driveways, and removing unnecessary paving.  My two-block-long street, Halstead Place, has sidewalks on both sides of one of the two blocks and none on the second block.  It has far less traffic and is far wider than Rye Beach Avenue, which has a sidewalk on only one side, yet has thousands of square feet of unnecessary paving, which speeds water to the storm sewers, instead of being absorbed by lawn or planting areas.

The perils to our future are very real but surmountable.  The fact remains that the faster runoff gets to Blind Brook the more damage it will do.  This photo, right, shows the impact of the swiftly moving water as it went under 1-95 and the Metro-North Railroad culvert – the speed of the water gushing through the narrow pipe was like a water cannon and took out the retaining wall along Theodore Fremd.  Over a year after the floods of 2007, we haven’t recovered from the damage to our community.  The scars remain as evidence of our past indiscretions.

Today, everyone is becoming aware of the importance of sustainability and being responsible to each other — thinking globally and acting locally.  Solving our flooding problems can be accomplished both personally on our own property and as a community on public property. In the words of the Great Law of the Iroquois Confederacy, “In our every deliberation we must consider the impacts of our decision-making on the next seven generations.”