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Eco Talk: How roadside ditches work

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Drainage ditch

Road ditches serve several purposes at the same time. Therefore, it is important to understand how they are maintained and constructed. One principal function of a road ditch is to collect and carry surface water from the road surface. Road ditches are also designed to intercept surface water from agricultural fields or residential property before it reaches the roadbed. In doing so, ditches keep roads free from standing water that can weaken the pavement.

According to the Cornell Local Roads Program ( there are over 114,000 miles of public roads and streets in New York state. Counties, towns, cities and villages maintain approximately 85 percent of this mileage. That translates into a significant investment of taxpayer dollars.

How to handle the surface water on a particular road falls to the municipality that maintains the road. From that point, local budgets and decisions are based on various factors.

Road ditches fall into three categories of shapes: “V,” “U” (rounded) and trapezoid (flat-bottomed). Each of these shapes has advantages and disadvantages, and all three can be filled with large stone and a perforated pipe along the bottom to make them safer for traffic when there is limited room to widen the ditch.

Once the shape is designed or engineered, the slope of the sides is determined with the safety of the traveling public in mind. When deemed potentially unsafe, guardrails are installed. Some considerations for the side slopes include maintenance of the ditch. Maintenance is easier when the side slopes are flat. Ditches need to get wider as they become deeper; this becomes a problem when there is a narrow right of way and can force the ditch to be filled.

Another factor in road ditches is called fall. Ditches generally follow natural land contours. In flat areas, there may not be enough fall; the result may be standing water, or the ditch may fill with sediment and cease to function. Or the contour may have too much fall, which allows water to generate speed, causing erosion of the side slopes.

Generally, in central New York, properly maintained vegetative or manmade cover in properly designed road ditches is sufficient to slow the velocity of the water. However, when the ditch is too steep, “check dams” can be strategically placed to reduce the velocity of the water. When you know what you are looking for, one can spot these structures when driving along our scenic roads.

Now that we have a basic understanding of how road ditches handle surface water, there are some practices we as the general public can do to help municipalities maintain these important structures and potentially reduce maintenance costs. First, we need to remember that ditches are designed to move water from roads, residential areas and agricultural fields with little concern for water quality. In other words, road ditches have the capacity to impact the water bodies they outlet to.

With this information in mind, we need to think about what may find its way into a road ditch and either remove it or keep it from going into the ditch. All litter from the traveling public should be removed. Do not dispose of pet waste in the road ditch, and keep grass clippings and other yard waste, including raked fall leaves, out of the ditch.

Consider how you may be utilizing impervious surfaces on your property. An impervious surface is an area that is paved or hardened such that it does not allow water to go directly into the ground. These are easily identified during a rain event as the water moves over the surface. These can include driveways, patios, pool decks and even rooftops.

So what to do with the water coming from your property? Disconnect any collection system from roof tops to road ditches. As an alternative, consider using rain barrels or rain gardens to capture rain from the roof. While these might be overflowing this year, they will reduce the amount of water going into the ditches during peak rainfall events. For larger rural properties, consider disconnecting any ditches from streams. Create an infiltration basin or detention pond to allow for groundwater recharge (some of us might remember we called these wetlands or marshes) and enjoy wildlife that takes advantage of these more natural landscape features.

There is something each of us can do to help protect the quality of our surface waters by recognizing the role road ditches play in conveying water and the importance of their proper maintenance.

Judy Wright is a senior resource educator with Cornell Cooperative Extension of Cayuga County. For more information, visit or call (315) 255-1183.


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