“Stormwater”—the water that originates during precipitation events—has received increasing emphasis from the EPA and state regulatory agencies. This article provides some basic insight as to why we have stormwater problems and a perspective on using “green infrastructure” to deal with those problems.
Let’s face it … did the term “stormwater” really even exist in the lexicon of the average American even a decade ago? Think also of “wastewater” in general and the significant and substantial changes that our country has experienced in terms of how we deal with our residential, commercial and industrial sewage, especially in the post-World War II era. We tackled the need to treat our wastewater/sewage instead of simply dumping it into our lakes and rivers and letting “dilution” take care of the issue. Now we are taking on “stormwater”—the water that originates during precipitation events.
Out on the family farm in 1960s and 1970s rural Nebraska, the use of the word “stormwater” would have elicited confused looks and blank stares, amidst mutterings of “…you’re not from around here are you?” We did, however, have what we in the industry refer to today as “stormwater runoff”—the precipitation that fell and then, for one reason or another, didn’t soak into the soil but rather “ran off.” As we are now painfully aware … this “runoff” contained much more than just water. The soil that eroded away was pretty evident, but there was not a lot of thought as to what else was tagging along for the ride, attached to sediment or dissolved in the water and destined for a drainage ditch, then perhaps a small creek, then a river … and so on.
While I’ve used my personal farm example here, stormwater runoff comes from a variety of places, many of them urban. From a water pollution standpoint the U.S. has been working to reduce “point source” pollution (pollution from an identifiable source) from industries and wastewater treatment plants, for example, since the 1970s under the provisions of the Clean Water Act. The National Pollutant Discharge Elimination System (NPDES) permit program of the Clean Water Act seeks to keep harmful pollutants out of our nation’s waters. The NPDES program has made great progress in controlling pollution from industrial and municipal sources. Over the past 20 years or so a primary focus of that program has been on stormwater from urban areas, which is still a significant source of water pollution.
The Hydrologic Cycle Disruption
To get a sense of why stormwater runoff is such an issue, let’s step back and look at the root cause: the disruption of the basic hydrologic cycle. It’s the water cycle that you first learned in elementary school. It rains, the rain falls on the soil and soaks in, recharging the groundwater, which then supplies water to the creeks and rivers that then flow into lakes and the oceans. Evaporation from those waters along with water transpired by trees and other plants forms the water vapor in the air that eventually falls back to earth as rain, completing the cycle. A key component in the hydrologic cycle was the presence of relatively undisturbed soil and ground covers like native grasses and trees that intercepted the rainfall, holding it and allowing it to soak into the soil.
Conditions changed with the advent of modern agricultural practices that removed large expanses of prairies and tree cover and the ever-increasing expansion of towns and cities. The removal of the grasses and trees meant that the precipitation “holding” mechanism was greatly reduced, and it was much easier for rainfall that fell, especially during heavy rainstorms, to run off instead of soak in. In towns and cities we created hard-surfaced streets and parking lots, houses and commercial buildings with acres of rooftops, all of which shed the rainfall. Of course then we needed to ensure that the rainfall was dispersed away from our buildings so we would not have soggy basements and threats to the structural integrity of foundations. So … we developed curbs and gutters that directed the rainfall runoff to storm drains, which necessitated the building of underground pipes to take the runoff away. And direct it we did … right into the nearest creek or river in many cases.
Our altered hydrologic cycle simply eliminated most of the “soak-into-the-ground” phase, putting the water directly into the surface waters. In doing so, many creeks and rivers have less “base flow”—water that comes from groundwater. Instead, more water enters the streams from the surface, causing more erosion, bank instability and incision of the channel itself. Can you imagine the covered wagons of 150-plus years ago attempting to cross many of our creeks and rivers today? Also, and very importantly, development and channelization have reduced or simply eliminated many of our natural floodplains, which used to function in times of heavy precipitation to disperse floodwaters and enriching the soil in those floodplains in the process. How times have changed.
Green Infrastructure Relief?
Currently, we are faced with daunting federal unfunded mandates to deal with this stormwater runoff. Many entities are turning to various forms of what is commonly referred to as “green infrastructure” to help meet these water-quality improvement mandates. Green infrastructure seeks to mimic natural hydrologic processes by capturing stormwater close to where it falls as precipitation (i.e., dealing with it before it really becomes “runoff” in the first place). While various green infrastructure practices like green roofs, vegetated swales, bioretention gardens and constructed wetlands can deal effectively with stormwater runoff, the best “green infrastructure” tool in the box is simply better site design. By utilizing good site design we can minimize the amount of runoff generated in the first place and thus not be reliant upon the aforementioned bioretention gardens and other techniques to capture and deal with the runoff. By minimizing street widths, for example, we reduce the amount of impervious surfaces that generate stormwater runoff. Using vegetated swales along our roadways instead of the traditional curb and gutter provides not only an infiltration mechanism but also reduces the capital cost of underground storm sewer pipe, infrastructure that requires ongoing maintenance and replacement.
Yes, green infrastructure also requires ongoing maintenance—it’s not a free ride—but it also does one other critical thing that the underground pipe can’t … it provides a visible link to the process, one that everyday citizens can see in action and that, I believe, is a very positive educational tool—one that helps to “reconnect” us to a natural process that for hundreds of years took care of all that stormwater. Quite frankly, it’s a welcome connection, and one that we will need to build upon as we seek to meet all those federal mandates and, most importantly, improve water quality.