June 24 – 30, 2016Vol. 18, No. 3

Stormwater Runoff: Avoid a Disaster

by Dale Finseth

This year we have been short of rain. . . . and we certainly have NOT had one of those massive rain storms. It is unlikely to remain that way all season. Other parts of the country have not been so lucky. So . . . , be prepared by addressing problems now.

We have talked about stormwater runoff before. "Stormwater" is just that the rainfall or other precipitation that then runs across the landscape in liquid form. The ditch next to your driveway will have a lot of water in it during and soon after a rainstorm. The culvert beneath your driveway will run full. But, what's the big deal? The pond level may rise a bit and waves might lap against the shoreline. Isn't that just nature doing what nature does? Nature sometimes does more than usual, and that is the part we need to prepare for.

Like anything else in our life, if we anticipate it and make informed decisions, we can affect its impact. In the case of a rainstorm, we can design our landscape and manage our property in a manner so that the rainwater's impact on water quality is moderated. Where we put our roadways, buildings, lawns, patios and other structures affects how the water runs across the landscape.

We have all seen how the stormwater flow can generate erosion and silt as it heads towards the nearby wetland, stream or pond. Designers and engineers as well as municipal officials, road managers and the Maine DEP refer to this as "stormwater control". It may be an overstatement to assume "control", but how we place and manage our structures on the landscape can mitigate their impact on water quality.

June-August Precipitation

Let's start with some numbers. We measure rainfall as so many "inches of rain." Given that most of us measure liquids in gallons or liters, it's hard to translate what an inch of rain is.

One inch of rain on a single square foot of pavement, sidewalk or roof equals 0.6234 gallons of water. If you have a parking area or a building that is near the shoreline, all the rain falling on that surface is diverted to the lowest point and then leaves that surface into a concentrated runoff area.

How much water gets focused to that area? If you have a 25' X 40' building or parking area, you have 1,000 square feet of impervious area. A square foot is 144 square inches. One inch of rain on that surface translates into 625 gallons of water.

Now consider your property. How much impervious surface do you have? An impervious surface doesn't soak up the rain but carries it off to another location. For every inch of rain that falls on those surfaces, your property needs to deal with tens of thousands of gallons of water.

And that is only one inch of rain. What happens when you get 6-8 inches of rain? Depending upon how your structures are designed, that additional water is all being directed towards a few specific points on your property. That concentration of water can do a lot of damage.

What can a property owner do in order to mitigate the damage? Plan for it! Direct runoff into vegetated areas or rain gardens. Design drip edge areas where the runoff leaves your roof. Maintain your driveway and parking so the water sheets off the edges and into areas that will not erode when the concentrated runoff occurs. Be prepared.

Take the opportunity now to use some of those Best Management Practices. Focus on how to manage your yard and property. Control the water runoff. Look for places that have been damaged in past storms. It will happen again unless you do something. A good buffer planting if well established, does a good job of intercepting water runoff and filtering it before it gets to the lake. The objective is to filter it so it doesn't concentrate and transport soil, chemicals, or other toxics into the water.

Remember, there is a lot to do in order to protect water quality.

Conservation Too columns are written by staff at by the Kennebec County Soil and Water Conservation District in Augusta. For more information about the district and its projects, call Dale Finseth at 622-7847, X 3 or visit www.kcswd.org.