Stewarding the Earth’s Natural Resources – A Storm Drain Runoff Demonstration
My family recently spent a week camping just outside Madison, Wisconsin. We were there visiting with some other worldschooling families and checking out some of the amazing things to do in the Madison area. It was a great time that kept our schedule pretty full, but when a demonstration visited our campgrounds, we made sure to find room in our schedule!
What was it?
The United States Geological Society – Madison (USGS-Madison) visited our campground with a scientific demonstration showing the effects of some different kinds of surface types on water run-off into the storm drains, and, eventually, into local lakes.
Storm drain run-off can be a big problem for larger cities for a variety of reasons, and those problems can be exacerbated by the choices that cities and citizens make about the design and upkeep of the city. While many of the problems caused by run-off could be fixed through structural changes to our cities, those solutions can be costly, or carry consequences of their own. Fortunately, if everyday people are willing to make small changes in the way they take care of their property, much of the damage can be stopped!
The Problems
Storm drains aren’t something that most people pay attention to. They’re designed to blend into sidewalks and roads, and, unless something is going wrong, they’re just not something people notice. However, with cities being as large as they are, storm drains move a massive amount of water. All that water, and everything in it, ends up contributing to a wide variety of problems that is noticeable, and that have some pretty significant impacts on our environment.
Sediments
Whenever a large amount of water moves anywhere, erosion is inevitable. And storm drain runoff is an absolutely massive amount of water.
That’s because the storm drains are taking in all the water runoff from that would have been soaking into the ground before we paved our cities. Water from our roads, parking lots, and construction sites are all being funneled into nearby water systems.
As it flows, that water picks up the dirt and dust that it flows over and carries it all along with it. That doesn’t seem like it would be a huge problem until you consider the scale of these flows.
According to a study by the Wisconsin Department of Natural Resources, erosion from construction sites without erosion control methods in place can create 30 tons of sediment per acre. That’s a lot of dirt!
All of that dirt ends up getting dropped into waterways and can cause a ton (or 30) of damage. It clouds the water, making it look dirty and it can fill in entire streams, destroying ecosystems in the process.
Phosphates
The same water can also carry chemicals known as phosphates.
Phosphates are naturally occurring chemicals that can actually be really helpful for plant growth. Because of this, they are used in many different chemical fertilizers to help crop yields. In nature, they often end up getting stored in the leaves of trees or smaller plants, and they’re generally helpful to those plants.
The problem is, once again, one of scale. As the rain flows through gardens where people have used chemical fertilizers or piles of leaves in the street, that water picks up massive amounts of phosphates that end up helping a different group of plants to thrive.
Algae.
Algal blooms occur when chemicals in the water allow algae to grow at an accelerated pace, and they cause all sorts of problems, from clogging waterways with the bad-smelling algae to killing off other water plants and animals.
Salt
Salt isn’t as much of a problem in places with mild winters, but in Wisconsin, it can be a pretty big deal. That’s because salt is often laid down on roadways and sidewalks to help melt snow and ice and keep them clear for the people who use them.
That salt has to go somewhere, and, as with sediments and phosphates, that place is typically a local waterway.
Those waterways are not supposed to be saltwater, and having large amounts of salt dumped into it causes some pretty big problems. Excess salt can kill local plants and animals, and throw the local ecosystem off balance.
The Demonstration
It’s fairly obvious that the large quantities of water flowing through our storm drains is a problem. One solution to that problem is to decrease the amount of water that flows into the storm drains themselves.
When it rains, that water has to go somewhere, and there are generally only two places for it to go. It either flows above the surface of the ground until it finds a body of surface water to join as runoff or it soaks into the ground itself and becomes part of the groundwater that plants use for hydration, and which feeds our natural springs.
Plants in the soil and the soil itself both filter the water and slow down its flow so when it eventually does reach larger bodies of water it is purer and less likely to carry pollutants or sediments.
The demonstration that we attended was designed to show how much of a difference surface type can make on whether rainfall becomes surface water or groundwater. Here’s how it was set up:
There were a number of slanted containers filled with different surface types. A bin underneath each surface represented the groundwater that would filter through, while a second bin would catch whatever water ran off.
The surface types ranged from typical non-porous pavement all the way to sod from a natural prairie land.
- Non-porous pavement (asphalt)
- Permeable Pavement (pavement designed to allow water to pass into the soil)
- Covered Construction site (Dirt with mulch)
- Tilled garden/construction (Bare dirt)
- Sparse, compacted lawn (sod with some grass)
- Dense lawn with compost (sod with thick grass)
- Natural Prairie land (sod with native prairie grasses)
Water was poured into a strainer above each surface to create a slower dripping that would simulate rainfall.
The Results
It was amazing to see the difference in how much water became runoff in each section!
Traditional pavements like asphalt and compact dirt surfaces like in construction sites allowed almost all of the water to become runoff. On the other hand, permeable pavements and natural prairie lands allowed almost all the water to become groundwater only allowing a very tiny amount of runoff.
The difference was stark, and clearly favored soil with native plants!
Why is that Important?
The experiment showed how important it is for cities to create spaces that help to recharge groundwater resources, either through the use of permeable pavements or by creating large spaces where native plants can take root and help prevent runoff. It also showed the importance of keeping bare soil areas covered to slow down the water flow and to prevent sediments in any runoff that does occur.
While families can make these sorts of decisions for properties that they own, a lot of it comes down to decisions made by the city. Still, if everyone does their own small part, there could be a big overall effect.
What you can do
So, practically speaking, how can you do your part? You probably aren’t in charge of what kinds of pavement are used in your neighborhood, but there is still a lot that you can do to help!
Grow native-plant Rain Gardens
Native-plant gardens have a ton of positive effects on the environment! They provide shelter and food for local animals and pollinators, need less maintenance and upkeep, and help to reduce air pollution.
And they are one of the best ways you can help reduce storm drain runoff!
The Wisconsin Department of Natural Resources has a beautifully detailed manual for how to build and plant your own rain garden to help reduce the amount of runoff from your property. But, if you live outside of Wisconsin, doing a quick search for ways to grow native plant gardens in your area can be helpful to ensure you are making the best use of your space.
Keep leaves off the street
A recent study of the amount of phosphates in runoff water has shown that water from streets without fallen leaves has up to 80% fewer phosphates than water from streets covered in leaf litter. That’s because decaying leaves are a huge source of phosphates.
In nature, that’s great, because those leaves would allow their phosphates to pass back into the soil where they fall and encourage more plant growth, but if those leaves stay on the pavement their nutrients end up in runoff instead.
Taking the time to clear the street of fallen leaves before storms can drastically lower the levels of phosphates in surface water and help prevent the algal blooms that damage lake ecosystems.
Bonus: All those leaves can be mulched back into the yard as a free source of fertilizer!
Use less salt for de-icing, or switch to sand
Areas with heavy snowfall have been using salt to keep roadways and sidewalks clear of ice for years, but as cities have grown so has the amount of salt found in runoff water.
It doesn’t take a lot of salt to keep paths clear, so making sure to only use a small amount can be an effective way to reduce your impact. But if you’re willing to go above and beyond, switching to sand can lower salinity even more!
Sand doesn’t help with melting the ice, but it does create a rough surface on top of the ice to prevent slipping. Your freshwater reservoirs will thank you.
Try the Demonstration at home!
This PDF from the Midwestern Regional Climate Center gives a great overview of how to do a similar demonstration at home! Try it with different surface types to see how different materials affect runoff quantities!
