As part of Great Lakes and Fresh Water Week, we hope you enjoy this special blog entry from Southeast Michigan’s One Water campaign.
Rain is a natural occurrence right? Why should we care what happens to it once it falls? Well, I’m here to tell you why you should care. To tell the story of what happens to rain when it reaches the ground, let me introduce you to the star of our story. Meet Walter Dripp, the water drop.
We all learned about the water cycle in grade school science class, but let’s review just for fun. We’re going to walk through what Walter would do in a few of the scenarios illustrated below.
So Walter plummets out of the sky (he’s an adrenaline junkie, so this doesn’t faze him) and hits the ground. He can do one of two things – infiltrate or runoff. If he takes the infiltration path, here’s what would happen.
Infiltration
To infiltrate into the ground, Walter had to land in an area that is not paved, like a park or someone’s yard. The easiest way for Walt to get into the ground is to follow the roots of a plant that stretched deep into the ground. Usually plants that are native to an area have long, deep roots, and make it easy for water like Walter to infiltrate. For us humans, this is the best case scenario. The water feeds our plants, is naturally filtered through the ground, and SLOWLY makes its way back to a water body.
But…with more and more development – think parking lots, pavement, and rooftops – it’s harder for water to take this route. And some more bad news: even in grassy lawns, water can’t get deep into the ground quickly. Regular turf grass doesn’t have deep roots, so as soon as it gets a little wet, it reacts like pavement and the water has nowhere to go. So what happens when it rains on one of these surfaces? Walter takes the runoff route.
Runoff
If Walter is unlucky enough to land on an impervious surface – such as a road, parking lot, or roof – he has no choice but to flow off of it. There are no pores for him to slide into and it’s really hard for him to get back into the ground. Since there is no easy path for Walt or any of his friends, they all have to band together and take the easiest slope off that surface. Think of a parking lot. It’s usually sloped so that water doesn’t pool, but what happens when we get a heavy rain? The water rushes through the paved surface to the nearest outlet.
But what is an outlet and where does it go? In our nice, natural water cycle image above, runoff just means that water follows the natural slope of a grassy knoll and gently lands in the nearest river. But most of us don’t live in areas comprised mostly of grassy knolls. We live in Southeast Michigan, which is densely populated and highly developed. Our water cycle tends to involve a lot more pipes, pavement, and other kinds of impervious surfaces.
For a majority of Southeast Michigan, there are two types of sewer systems: combined sewer systems and separated systems. In a combined system, Walter would flow into a sewer pipe that also collects wastewater from your home (wastewater is anything and everything that goes down the drain – bath water, laundry water, flushed toilet water, or even food scraps that make their way from your dishwasher drain. In a separate system, the wastewater is collected in one set of pipes, and Walter and his rain friends go into another.
When Walter and his friends band together to find the best way to get off of the impervious surface, they will find the shortest path they can to get underground. In some cases, like in a driveway, water might rush off the pavement and land in a lawn or rain garden. From there it can happily make its way back underground. In a city, it may follow the slope of a road or parking lot and find a catch basin. A catch basin is a structure that allows the water to flow directly into the sewer pipes. From the sewer, it will either go through the pipes to the Water Resource Recovery Facility where it’s treated and sent back out to the river – this happens in a combined sewer system. The other option – if it’s a separate system – is that it will go directly to a pond or natural body of water. Both of these solutions can be problematic, and here’s why.
If we get a really heavy rainfall with several inches of Walter and his friends coming down in a short period of time, the sewer pipes may not be able to handle all that water. Our sewer pipes were often designed and installed 50-plus years ago, when there just were not as many heavy rain events. So as sewer pipes get overloaded and the water is pushed back up to the street, we have flooded streets and yards. In combined sewer systems, that water can be pushed back up into basements, causing flooding inside of homes. In these cases, there is also an emergency situation called a combined sewer overflow, where the combined flow can follow an emergency release route and flow directly into a natural water body. This allows untreated wastewater -though diluted from the heavy rain – into our natural system. If Walter and all of his friends had the opportunity to slowly infiltrate into the ground, these problems could potentially be avoided. This is why we advocate for green spaces, not just with grass, but with native plants that have those long root structures.
In a separate sewer system, if Walter and his pals (the heavy rainfall) don’t infiltrate, they collect in a storm sewer and flow directly into a natural water body like a pond, river, or lake. This seems like it might be a good idea. But the issue here is that this Walter isn’t going through the natural filtering process of the ground or native plants across the surface. He’s picking up everything he flows across. Imagine a parking lot – oil leaks, gas droplets, pesticides, windshield washer fluid, plastic bags, cigarette butts, empty water bottles – anything you can think of can make its way into a parking lot. When Walter flows over that, he picks up those chemicals, contaminants, and physical trash. He brings that with him into the sewer, and when he hits that outlet pipe, he brings it directly into our natural water bodies. The same water we then have to work hard to treat before we can drink. The same water that is a clean habitat for our fish and wildlife. We want to prevent the contamination.
The lesson here: If we can work to create less impervious surface in our communities, coupled with an opportunity to collect rainwater like in rain gardens with native plants, we’ll be helping our natural systems, our piping systems, and benefiting personally.
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