What goes with the flow?

14 years ago

    It has been raining a lot this fall, but do we ever stop and wonder where all of that rainwater goes after it falls from the sky? Most people don’t give it a second thought, but the rain has to go somewhere, and that means ending up in our lakes, rivers, streams, bays and groundwater.
    The average annual precipitation in Maine is 42 inches. According to the Maine Geological Survey (MGS), that is the equivalent of 24 trillion gallons of water falling from the sky onto the surface of Maine every year. And do you know how much precipitation turns directly into runoff? The MGS estimates approximately 50% or 12 trillion gallons of water runs off into Maine’s surface waters; some of the other half is taken up by plants, and the majority soaks into the ground to become groundwater.
    As it washes over our yards, driveways, parking lots, and roads the surface water runoff picks up hitchhikers – pollutants such as fertilizer, weed and bug killers, pet waste, oils and gas, as well as eroding soil. These hitchhikers travel with the runoff to the ditches, storm drains, streams and right into the waters we use for swimming, fishing, boating, even drinking.
    We can’t stop storm water runoff, but we can reduce the amount that picks up pollutants and then flows into Maine’s surface waters. The rate that water soaks into the ground depends on many factors, slope, soil type, and type of surface (pavement, lawns, fields, and forests to name a few). Roads, buildings, and parking lots let very little water sink in- they are impervious to water, so most precipitation flows over them to become runoff. There are technologies towns and businesses can use to decrease the amount of impervious surface such as types of pavement that allow water to soak through and “green rooves” that slow and cool runoff.
    But what can we do to reduce runoff in our own yards? In a heavy rainstorm, our lawns shed 40-60% of the precipitation. Planting more trees, shrubs and groundcover helps slow down the rainwater and gives it time to soak into the ground.
    We can also reduce the hitchhiking pollutants. One simple way is to regularly remove pet waste from our yards. We can also reduce the amount of fertilizers and pesticides we use. Other ways of preventing storm water pollution are to direct runoff from our driveways into vegetated areas or plant a rain garden to absorb and filter the rain. Remember, water diverted by roadside storm drain systems usually bypasses water treatment facilities altogether and empties, untreated, into our lakes, rivers, streams, and oceans.
    Do one or all of these preventative measures on your property and you will be helping your local waters to stay clean and clear. To learn more, visit www.thinkbluemaine.org.
    This column was submitted by Geoffrey Ng, an AmeriCorps intern with the DEP’s Bureau of Land and Water Quality. In Our Back Yard is a regular column of the Maine Department of Environmental Protection. E-mail your environmental questions to infodep@maine.gov or send them to In Our Back Yard, Maine DEP, 17 State House Station, Augusta, ME 04333.