Drew Hall: Drainage maintenance helps reduce flooding


Drew Hall - Contributing columnist



Delaware County is well known for its wet, poorly drained soils. Our soils are highly productive once the excess water is drained away.

Driving along the local roads, you may see the vast amount of drainage ditches and basins (both wet and dry) which can sometimes become home to cattails, brush, trees and saplings. While these may look beautiful and add to the scenery of the roadside, they can be a major problem. Establishments of woody vegetation can cause the drainage systems to not function as they were intended and may cause flooding to the roadway.

I personally love the beautiful trees and plants found in our forests and fields; however, they should not be growing in drainage ditches and basins. Vegetation with deep clogging roots or dense foliage brings into play a variable known as roughness.

When water is flowing through a channel, its discharge can be calculated and quantified with a tool engineers use called Manning’s equation. Variables such as slope of channel, flow area, flow rate, velocity, etc., are factors in this equation and the one that we are concerned with is Manning’s Roughness Coefficient. This coefficient is determined by the frictional forces in the channel that act upon the water. More friction translates into slower-moving water. Trees with thick, invasive roots can effectively increase channel roughness, which can slow down and back up the water. Trees in combination with cattails increases channel roughness even more.

Why should we be concerned about Manning’s Roughness coefficient and Manning’s Equation? Higher numbers indicate slower-moving water which can lead to standing water in our farm fields and severely reduced yields, flooding of basements, dangerous water levels on our roadways, creation of mosquito habitat, and other problems that can occur from poorly functioning drainage ditches and basins. Ohio in its natural state is dense forests and wetlands. The only reason our land is well-drained today is through extensive tile and artificial drainage systems that have been installed over the past century or more.

The Delaware Soil and Water Conservation District, in partnership with the Delaware County Commission and county Engineer’s Office, handles the county’s drainage maintenance program. Following state law, our staff inspects all basins and ditches annually as a minimum and — after heavy storm events — “hotspot” sites known to cause problems. When necessary, mechanical and sometimes chemical control measures are used to eliminate cattails, trees, shrubs, saplings and brush in ditches and basins to ensure water moves efficiently through those systems to the nearest body of surface water.

More information on soils and the SWCD’s drainage maintenance program can be found on our website at www.delawareswcd.org.

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Drew Hall

Contributing columnist

Drew Hall is an intern for the Delaware Soil and Water Conservative District. He is a junior at Ohio University majoring in geology and is an Olentangy High School graduate.

Drew Hall is an intern for the Delaware Soil and Water Conservative District. He is a junior at Ohio University majoring in geology and is an Olentangy High School graduate.

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