What’s your Runoff Footprint?
In other words, how much runoff is your home or business dumping into your neighborhood creeks when it rains? And why does this matter?
Urbanization and Creeks
In urban and suburban areas, like Cuyahoga County, runoff from impervious surfaces such as roads and rooftops is the primary stressor on our local creeks. It impacts creek health both by what it picks up and carries with it (think lawn fertilizer, road salt) and by the increased volume of water delivered at a much quicker rate than under natural conditions.
Let’s look back a couple hundred years at Northeast Ohio before the settling of the Western Reserve and the establishment of present-day Cleveland and its suburbs. What was here? Trees, mostly. The landscape was almost completely forested, with smaller areas of wetlands and open prairies. This is the landscape in which our local rivers and creeks formed and developed.
When it rains in the forest, most of that rain is initially intercepted by the leaves and branches of the forest canopy. As the rain continues or intensifies, it makes its way down to the lower levels of the forest, eventually reaching the forest floor, where it gradually soaks in. Here it is either taken up for use by plants, recharges the groundwater below the forest, or slowly drains through the soil to the nearest creek. Only after it’s been raining for a while, or during particularly intense storms, is any runoff generated from the forest floor.
If you’ve ever been hiking in the forest when it rains, you can relate to this, staying mostly dry even during rain showers.
And, if you’ve ever been in a parking lot when it rains, especially a large parking lot like you find at a mall or a Big Box Retail Store, then you certainly can understand the difference between how water moves through our urbanized environment compared to a forested setting. Rain falls directly to the concrete or asphalt surface of the parking lot and immediately becomes runoff. There it is directed to the nearest storm drain, which quickly moves the water to the nearest creek or ditch (or if you live in most of Cleveland or any of the inner ring suburbs served by a combined sewer system, directly to a wastewater treatment plant). Because none of this water was intercepted, and because it did not have a chance to infiltrate through the soil, more water gets to the creek than would get there in a forested setting. And it gets there faster, too.
This combination of more water getting to the creek faster wreaks havoc on a creek’s bed and banks. The relatively fine sediment generated by streambank erosion covers and fills in the spaces between the sand, gravel and cobbles that previously made up the creek bed, smothering the available habitat for aquatic macroinvertebrates (a key fish food and food web link). When the creek bed erodes, the creek channel cuts down. The farther down in cuts, the less ability the creek has to get out onto its floodplain where it can dissipate energy, store larger flood flows and filter nutrients, and so more and more of the creek’s flow and energy stays concentrated in the channel, further eroding the bed and banks.
It’s a vicious cycle, and one that’s hard to break for creeks in urbanized areas. Yes, storm water management requirements in place for the past 15 years for new development and redevelopment throughout most of Cuyahoga County have reduced – but not eliminated – the impact of newer developments. But the prior 200 years of urban and suburban development have left us with a lot of legacy concrete and rooftops.
Your Runoff Footprint
While leading a rain barrel workshop, I’ll often ask the workshop participants how much rain they think it will take to fill up a 60-gallon rain barrel. Responses vary, usually ranging from a quarter inch to an inch. The answer, of course, depends on the size of your roof. But for purposes of visualization (and easier math) let’s look at a 1000 square foot area, or about 20’ x 40’. It only takes a about a tenth of an inch of rain on a 1000 square foot roof or other hard surface to generate 60 gallons of runoff.
Now, think back to that Big Box department store, with its 200,000 square feet of roof plus, conservatively, another 300,000 square feet of parking lot. That’s 30,000 gallons of runoff, just from a tenth of an inch of rain. But a tenth of an inch of rain isn’t necessarily what’s causing streambank erosion and channel downcutting, and the subsequent reduction in habitat quality. Heavier rainstorms dropping half an inch, an inch or even more rain in a 24-hour period can dump hundreds of thousands of gallons of runoff into our neighborhood creeks from a single parking lot.
There are a couple web sites that can help you calculate your runoff footprint. One of the better, easier to use sites is myrunoff.org. It has a calculator that allows you to create a general estimate of your annual runoff footprint, based on local weather data, and allows you to calculate an estimate of how much runoff reduction you can achieve by installing rain barrels and/or rain gardens.
You can help your local creek by resolving to reducing your Runoff Footprint in 2015 by doing one or more of the following:
- Install a rain barrel (or two, or three, or…).
- Disconnect your downspouts.
- Plant a rain garden.
- Convert a portion of your lawn to a native prairie, pollinator garden, or native plant garden. The soil under many turfed areas is so compacted that it is little better than concrete for infiltrating rainwater.
Happy New Year!