How Many Gallons?!

Over the past few days as we ring in the new year, Iowa City has received somewhere in the neighborhood of a foot of snow blanketing our yards, streets, and parks. We know the drill: enjoy the fluffy flakes falling gently, then head out to shovel the sidewalks, and repeat as needed. 

We watch the birds swarming backyard feeders as the snow blocks access to some of their regular seeds, and follow the tracks of neighborhood dogs, cats, rabbits, and others where the white powder is soft enough to hold prints.

Then, as the days warm, the snow melts. And melts. Where does that foot of snow go?

Just like rainfall and other precipitation, snow melt would typically infiltrate into the ground, where it can help replenish recharge our groundwater supplies, or find its way to wetlands or other areas that can accommodate fluctuating levels of water. 

Our cities and suburbs, however, often interfere with this process. All our paved areas--streets, driveways, parking lots...backyard basketball courts--can prevent water from infiltrating into the ground where it lands and instead diverts it into municipal stormwater systems. These are typically underground tubes that channel water to existing creeks and rivers or specially-constructed basins to collect the water. In these systems, not only the water but everything else on those surfaces finds its way into those waterways: chemicals from treated lawns, oil and trash from streets. Heavy rains can swamp the  rivers and ponds they drain into and cause flooding. It's an imperfect solution to a created problem.

The Sycamore Greenway is an example of an alternative to that imperfect system. Instead of channeling water directly into our rivers and streams, rain and snowmelt from the neighborhoods around the Greenway are instead channeled into dozens of one-acre cells that allow it to infiltrate the ground. From north to south, the cells are stepped down so that excess  water flows down into the outlet basins near Kickers Soccer Park, The entire system can store up to 1.21 million cubic feet of water after a heavy rain.

Bear with me while I do a little sloppy math:

• Ten inches of snow yields around 2715 gallons of water per acre*, so estimating a foot of snow we would get 3258 gallons per acre. 
• My own little suburban yard is around 1/6 an acre, so my property will contribute around 543 gallons to our stormwater system from the recent snows.
• Converting the Greenway's capacity to gallons we get a little over 9 million gallons (estimating 7.48 gallons/cubic foot = 9,050,800)
• Using my yard as an example, the Greenway could accommodate the snow from 16,668 similar properties! 

Obviously these numbers just give a general idea of the services the Greenway provides in removing all this water from our neighborhoods. Because we have transformed the landscape so drastically, we have been forced to construct infrastructure to take care of things that would normally be handled by a functioning natural system. The Sycamore Greenway takes care of the South District in so many ways, not least of which is handling all the rain and snow that falls on us throughout the year.

*Source: USGS Water Science School