Q. What is stormwater runoff? How can it be minimized?

A.This is going to be a two-issue response as the questions of what stormwater runoff is and how it can be minimized require an extensive use of space. In this installment, I will cover what stormwater runoff is and how it impacts an urban community. The next installment will cover several methods which are currently being used to minimize stormwater runoff.

Stormwater runoff is essentially rainfall or snowmelt that runs off the ground, primarily impervious surfaces such as rooftops of buildings, roads, and parking lots and drains into natural or manmade drainage systems. These drainage systems include streams, rivers, creeks, and oceans. However, in urban areas, water may run into manmade “storm sewers” (not to be confused with urbanized sewer systems which handle waste disposal). These “storm sewers” differ from the typical sewer disposal systems as the water is not treated before being discharged. Consequently, this may cause problems down the road as this stormwater runoff may contain contaminants which would normally be filtered out by conventional sewage treatment plants. Stormwater runoff has its greatest impact in urbanized areas although its impact is felt everywhere.

OK, you might think that water is water, and so what is the big deal?

First, stormwater runoff is not just water. It often contains sediment, nutrients from fertilized lawns, bacterea, oil and grease from automobiles, trace metals, and road salt.

As stated in the definition, stormwater runoff creates the most potential impacts in urbanized areas where one finds more paved roads, parking lots, buildings, and driveways. The more pavement that exists decreases the amount of vegetative surfaces water can filter through. This leads to more flooding on streets, in parking lots, and basements. I am sure that most individuals have seen culverts that have backed up due to the amount of stormwater runoff.

A secondary problem is the relationship between stormwater runoff and sediment. As you may know, sediment is the greatest pollution problem in the world’s waterways. As water running off impervious material has little to impede its rate of flow, material such as sediment can be carried off through the “storm sewers” into the streams, rivers, lakes, ponds, or creeks. Sediment entering the larger waterways causes filtration problems in hydro-electric turbines which help create the electricity we need, creates an added cost in producing drinking water, and in some cases, acts as a substrate for various bacterial species which have been known to cause disease in man. As some of the sediment may be extremely small, (clay) filtering it out can be extremely expensive and removing the microscopic organisms difficult. Sediment buildup in lakes and ponds, which act as impoundments for drinking water, decreases their capacity of these impoundment to hold water. This sediment buildup also decreases the available habitat for a variety of aquatic species which require clear streams, gravel beds, and little if any sediment deposits for their survival.

Flooding is also an issue. Direct stormwater runoff can cause downstream flooding and streambank erosion. Water flooding basements, businesses, and property, including the loss of property due to erosion, could be, under certain conditions, a financial disaster for a property owner.

In an undeveloped area, approximately 10 percent of rainwater discharges directly into streams, rivers, creeks, lakes, and oceans. The remaining 90 percent either evaporates or filters into the groundwater. Again, the more impervious surfaces in an area increases the direct runoff and decreases the percentage of water re-entering the ground water supply.

The bottom line is that stormwater runoff is a problem and becoming more so as development and urbanization increases. I have outlined some of the obvious, direct impacts of stormwater runoff here, but I need to stress that there are many unrecognized or indirect problems associated with runoff which I did not mention in any detail. There are alternatives to impervious pavement materials currently being used. I will be discussing them in the next issue as I sense alternative approaches and methods to minimize this problem will be the wave of the future.

(Jamie Johnston, executive director of the Little Tennessee Watershed Association, wrote this article. He can be reached at LTWA, 5 West Main Street, Franklin, NC, 28734; or via e-mail at nbumppo@dnet.net.)

 

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