Why should I care: Stormwater

InTrans / Dec 17, 2014

Go! Magazine

posted on December 17, 2014

Have you ever wondered where rain goes after it lands on a parking lot? Stormwater systems work to move water away from streets, buildings, and land by transporting water straight to local waterways. It’s important because these systems keep potential flooding problems under control. Two important reasons for this discussion of stormwater systems include increased urbanization and more dramatic weather effects due to climate change.

With increased weather events coupled with an increase in population to urban areas, there is a need for improvements in how we manage stormwater. By 2050, it is said that 86 percent of the population in developed countries and 64 percent in developing countries will live in urban areas.

So what does this mean for stormwater drainage?

The purpose of stormwater drainage is to control flooding and erosion. One of the contributing factors of flooding is due to the amount of impervious pavement in urban areas, which is pavement that does not let water infiltrate (think of concrete or asphalt). As the amount of impervious pavement increases, the volume of water running over surfaces combines and increases (rather than seeping into the once soil or grass), causing stormwater drains to back up quickly.

To learn more about what can be done to reduce the impact of urbanization and stormwater management, I interviewed Associate Professor in Landscape Architecture, Carl Rogers.

A Conversation with Iowa State University’s Associate Professor in Landscape Architecture, Carl Rogers

What issues do you see with stormwater drainage?

The biggest issue with stormwater is water quality. In Iowa, we are already battling poor water quality from agricultural fields due to runoff of nutrients and fertilizers. In urban areas, we are adding to the state’s poor water quality with stormwater runoff. In urban areas, rainwater falls over paved areas and carries sedimentation and pollutants (e.g., oil, antifreeze) straight to the waterways through stormwater drains.

The second issue is flooding. If rain falls on a site, like a parking lot, all the water on that surface that can’t infiltrate increases in velocity and speed, which also causes erosion. If pavement does not allow water to infiltrate right where it falls, it makes the volume increase somewhere else, which causes flooding.

Can you describe some of the green alternatives you have suggested to help manage stormwater in urban areas?

One important alternative is material change. We need to be making parking lots with permeable material, such as porous asphalt, which allows water to infiltrate into the lot and make it to the water table.* Another improvement could be to collect water in parking areas using infiltration areas such as bioswales or small depressions. If you can collect water in those areas with native grasses, then you can help slow down the water runoff and help absorb the water where it lands. Native plants have deeper roots, allowing water to infiltrate deeper into the ground. This method would require parking lots to have more room for this type of infrastructure.

Planting trees in parking lots is also a great way to allow water to infiltrate from above. Also, trees help moderate temperatures and reduce what is called the “heat island effect.”?* If we have smaller compact urban spaces in terms of stormwater management, then we can put in cisterns, or underground basins, to collect water. This water could then be used for things like irrigation, which makes up 30-60 percent of urban fresh water usage. What are the advantages to having green infrastructure? We have an opportunity to reduce flooding, reduce erosion, and improve water quality with green infrastructure. If we implemented greener vegetation into our urban areas, I believe we could make better places. Do you see this happening already in Des Moines, Iowa? It is starting to happen more places in Des Moines. It is happening on smaller sites currently. The City of Des Moines is becoming more aware of these practices and are beginning to understand the benefits. The city is slowly updating their policy for green infrastructure. What would you tell someone interested in doing this type of work in the future? What skills would they need, and how do they get started? I would encourage them to study landscape architecture. Landscape architects decide how to design and implement environmental improvements to make cities more livable spaces. Landscape Architecture is unique because it transforms scientific ideas into artful pieces of design.

Did you know?

* The “water table”? is the line at which the unsaturated ground meets the saturated ground. Have you ever dug the sand on the beach near the water? If so, you probably found water soon after digging. If you dig far enough in any area, you will find the water table. Of course, the water table will be much shallower in areas closer to sea level. The water table follows the general topography, or shape, of the land. If you’ve ever seen a hot spring, this is a great example of where the water table meets land.

* The “heat island effect”? describes areas that are hotter than other nearby rural areas. This effect is caused by an increase of impermeable pavement that replaces open land. During a warm summer day, the sun hits pavement and other urban infrastructure that holds heat. By the end of the day, heat is released from the pavement and heats the evening air. In some instances, temperature changes can be as high as 22 degrees Fahrenheit between the city and nearby rural areas!

InTrans

Institute for Transportation