15 May 2014
Dr. Michael Dietz
Stormwater and Low Impact Design
Recently, our class was fortunate to have guest speaker Dr. Michael Dietz come to our class to share his knowledge on Stormwater and Low Impact Design. Michael works for the Connecticut Nonpoint Education for Municipal Officials (NEMO) and the Center for Land Use Education and Research. Michael has a vast knowledge of stormwater impacts and Low Impact Design, or LID. This ties in with new development standards, as new buildings are trying to meet ‘Green’ building codes.
Michael explained that since the implementation of the Clean Water Act in the 1970’s, our waterways have become many times cleaner than they used to be. In the past, the number one pollution source was from point sources such as discharges from industries that would need to get rid of process waters, or from sewage treatment facilities that would discharge directly to the rivers. These days, Michael explained that the biggest point of pollution is actually from stormwater. Stormwater pollution is a non-point source pollution because its pollutants come from various sources, like cars, septic systems and even from the fertilizers that people put on their lawns. As stormwater runs over various impervious areas, it also picks up these pollutants before it eventually gets to our rivers and streams. The traditional method of dealing with stormwater was to collect it into stormwater systems, and then dump it out into the rivers.
This is where stormwater LID’s come into place; they differ primarily on the way that they deal with stormwater because they do everything that they can to treat the water on-site, and keep it from getting into the traditional stormwater systems. The whole idea is that if we can keep water from getting into our traditional stormwater systems, it will increase the stormwater quality by essentially treating the stormwater on-site. This can be done by essentially letting nature do what it does best. In a natural stormwater system, the water soaks into the ground and is filtered by the soil. This is almost the complete opposite of what we see today because all of our roads, buildings and other impervious spaces do not allow the water to do this. Impervious surfaces also create other water quality issues other than just the pollutants that they collect when it rains. For example, imagine a parking lot on a hot day; a summer rain comes by and all of the water is running over the steaming hot parking lot and then discharging into a nearby river. What happens in this scenario is that the temperature of the rainwater increases greatly then it would have naturally, eventually going to a water system and raising the temperature of the water for the poor inhabitants on the receiving end.
Another way that impervious surfaces can cause pollution is from the sheer amount of volume, and the timing of the volume that is discharged. Instead of having the water infiltrate into the ground, the water collects and runs off quickly, causing the streams to receive more water in a short amount of time then they would have naturally. Natural streams receive water slowly from groundwater, and a much smaller amount of surface water actually runs off into them directly. Another harmful effect of having increased water volumes discharge into our waterways is that when the rivers and streams receive this water, they often increase in speed and volume as well, causing erosion problems as the water rises up the banks of the streams.
The common denominator here is impervious surfaces. Michael as well as other stormwater experts recognize this fact. Michael actually said that he worked on a study to try and correlate water quality and impervious areas. The findings were astounding; areas that had greater than 12% impervious cover almost always had failing stream systems when compared against pre-determined standards for water courseways. It is a simple enough concept; the more we disrupt the natural hydrologic cycle, the less organisms will be able to live in the areas that are directly affected. The great part is that throughout study, an actual number has been discovered that can be used to guide new developments into developing less harmful systems.
So, as you can imagine, we can avoid the large volumes of polluted water with all of its detrimental affects by simply letting nature take its course and act like it would naturally. Michael explained that there are a variety of techniques that can help accomplish this goal. One technique is to use a rain garden. Rain gardens collect water from a rooftops or parking lots and let the water infiltrate into a detention basin. The detention basin holds the water and lets it infiltrate into the groundwater, and in some cases if it is designed to do so it can release the excess water if the volume is too much for the system to handle.
Another LID technology that can be used is to build a detention basin. These are built so that they collect a certain volume of water into a pond like area, and keep it from discharging directly into a river or stream. If we think back to the parking lot example in the middle of the summer, having one of these systems allows the water to collect so that the large volume doesn’t just discharge right away into the stream. This allows the volume and time of concentration to be reduced, and also allows the temperature of the water to cool off in the process. Lastly, exposing the water to sunlight can help degrade many of the pollutants that are in the system.
Another major way that the LID technology for stormwater is pervious pavement. This technology allows stormwater to infiltrate right through the pavement and into the soil. This is a great technology, however it requires some upkeep, such as cleaning it with a specialized suction sweeper to get any sand out of the ‘pores’ of the pavement. If too much sand accumulates, it will clog the pores and the pavement will lose its pervious ability.
Overall, I think that Michaels presentation was great because it really depicted where we are heading in the developing industries. Its good to know that there is hope for our society to become developed and at the same time co-exist with the environment. I find it ironic that we ultimately have gone into treating stormwater the same way that nature does, when if we just paid a little more attention in the beginning we would have got it right the first time. I think that we don’t give nature enough credit; it has been here and withstood the test of time, and has come up with the most economic of systems in which nothing goes to waste and everything serves a purpose. I guess the moral of the story is that we need to stop trying to outwit nature, and try harder to listen to the wisdom that she speaks.