Permeability is the degree to which water or other liquids are able to flow through a material. Different substances such as soil, gravel, sand, and asphalt have varying levels of permeability. The porosity of the material enables permeability. Material with high permeability has pore spaces that are connected to one another, which allows water to flow through the material easily. However, if there is low permeability then the pore spaces are isolated, or fit together tightly, and water will not flow as easily or may even get trapped within them.
As the population of the Earth has increased and as more development and urbanization has occurred, more of the Earth’s surface has been replaced by impervious or non-permeable surfaces that include roads, houses, parking lots, and buildings. The cumulative effect is a reduction in the seepage of water into the ground and an acceleration of runoff into ditches, streams, and detention basins.
When rain falls to the ground it can do one of two things: flow into the ground and join the groundwater, or flow on top of the ground and become runoff. As water flows into the ground the soil acts as a filter, catching and holding onto most anything that the rain brought with it. This filtration traps most of the pollutants before they can enter the groundwater. However, when water has no way to enter the ground, like when it falls onto a parking lot, it will keep traveling above ground until it reaches the nearest creek, river, lake, or sea (this type of runoff is referred to as stormwater). Since this water has no opportunity to deposit whatever it grabbed along the way, it deposits that matter into the body of water it flows into, where it can have a negative effect on the ecosystem.
Unfortunately, our roads, buildings, and all sorts of other things we humans have built, prevents much of the stormwater from entering the soil at all. When water reaches the pavement it will either run over it until it reaches a body of water or enter our sewer system, which is eventually diverted via pipe into our rivers and lakes. This stormwater runoff carries with it many pollutants such as motor oil and antifreeze.
Thankfully, stormwater runoff is a problem that scientists have been researching for decades. Engineers and city planners have created exciting new initiatives and strategies for curbing some of the negative effects of stormwater runoff. The rest area that you are in has examples of some of these strategies.
You are standing on a sidewalk constructed with permeable concrete pavers. This drainage system is composed of several layers of material. The top layer consists of the permeable concrete pavers separated by joints filled with crushed aggregate. Water is able to infiltrate through the joints into transitional layers beneath. These transitional layers are comprised of increasingly larger stone beds leading to the native soil. These transitional layers start the filtration of the water before it reenters the soil and ultimately the ground water.
Additionally, rainwater is captured off the rooftops of the building here and is stored in an underground cistern. This water is then used to irrigate the surrounding lawns and plant life. The nearby landscaping is also designed to help control runoff and assist in returning the reclaimed water to the ground water.
Using the information in the description and the listed resources, email me your answers to the following questions:
1. Based on the reading and your observations, what would be the possible impact to this area if non-permeable materials were utilized?
2. From where you are standing, what are two things you see that could result in stormwater runoff if not for the strategies put in place here?
3. Based on the reading and you observations, what are two benefits of having permeable pavers?
4. What are the layers between the pavers and the native soil called?
Landscaping is another means of slowing down stormwater runoff.
5. Post a photo of yourself, or a personal item, wit a nearby landscaping feature that you believe helps with runoff.
Resources:
Permeability: https://en.wikipedia.org/wiki/Permeability_(earth_sciences)
Stormwater: http://www.greenvillesoilandwater.com/what-is-stormwate/
Permeable Pavers: https://www.nitterhousemasonry.com/pavers/how-do-permeable-pavers-work/
