Do Your Storm Drains Keep the Ocean Trash Free?
AbstractDid you know that there is plastic in the ocean? It probably isn't too hard to imagine that some of the plastic that litters roadways, sidewalks, and parks finds its way into the ocean. So, how much do you think is in there? Hundreds of pounds of plastic? How about thousands of pounds? No one knows for sure, but estimates, based on scientific surveys, suggest the amount is in the range of millions of pounds of plastic! Of course, the ocean is big, over 300 million square kilometers, so the concentration is relatively low—although still high enough to harm marine life. But how does the plastic get into the ocean in the first place? In this science project, you can determine if any plastic litter is entering the waterways from your community's storm drains. If it is, this project will help you work on a possible solution.
Sandra Slutz PhD, Science Buddies
ObjectiveTest models of local grated storm drain inlets to determine if they are designed in a manner that keeps plastic litter from entering your community's stormwater drainage system. If they are not, work to improve the design and prevent plastic litter from passing through the grated inlets.
Have you ever encountered any of these statements: "The Great Pacific Garbage Patch is twice the size of Texas. There are islands of trash in our oceans. Satellite images from space show heaps of plastic in the ocean."? You very well may have! These types of statements come up frequently in the mainstream media and blogs about the environment. But, as most ocean researchers will tell you, these comments are huge exaggerations. There is garbage in the ocean—and plenty of it—but it hasn't accumulated into an island, nor can it be seen from space. The garbage, sometimes referred to as marine debris, includes all sorts of trash from boats and ships, as well as trash that travels from the land into the world's waterways. Bottles, toys, plastic bags, rubber tires, and old fishing equipment like nets, buoys, and traps are just a few examples of the trash items that wash up on beaches.
Figure 1. Although large pieces of marine debris, including plastic, can sometimes be found littering beaches, the majority of trash in the oceans is small pieces of plastic, like the blue specks in the above beaker of Pacific Ocean water. (Photos courtesy of Ocean Conservancy and NOAA)
Recently, ocean researchers have been working hard to determine how much trash is in our oceans, what kind of trash it is, where it is located, where it came from, and how it affects marine organisms. Most of the answers aren't in yet, but the data is already starting to show us a couple of things. The heaviest concentrations of trash appear in ocean gyres, like the North Pacific Gyre, or other areas where the currents and physical features of the ocean bring different flows of water together. Several research expeditions, including the Seaplex, Project Kaisei, and the C-MORE expedition, have evaluated the waters in the North Pacific Gyre. What they have found is that large pieces of floating plastic are unusual, but if you troll the water with fine mesh nets, you will come up with many pieces of small plastic, most under 5 millimeters. Is this harmful? The jury is still out—but researchers are worried. This plastic is easily consumed by a number of marine organisms, including fish and birds. There are studies showing a significant number of sea birds, like albatross, which appear to have died of malnutrition with their stomachs full of plastic. Researchers are also interested in finding out if the chemicals from plastics can be found in the tissues of fish—especially fish that we eat. Other scientists have concerns about what is happening at deeper water levels. Is the plastic just on the surface, or is there more on the ocean floors? If you are interested in the latest research findings and conclusions, the websites listed in the bibliography below can help you get started.
Where does the plastic come from? It turns out that a large portion pours into the ocean from the stormwater drainage systems of towns and cities. Towns and cities have higher concentrations of roads, buildings, and sidewalks. Unlike open land, these structures don't absorb much water. When it rains, the unabsorbed water, called runoff, has nowhere to go. To avoid flooding, engineers construct stormwater drainage systems for these suburban and urban settings. The stormwater drainage systems consist of inlets, also called catch basins, along roads, sidewalk curbs, and underground pipes. When rain falls, the runoff flows down the streets and sidewalks and into the inlets. The inlets feed into the underground pipes, and the water continues to travel underground until it reaches an outfall. Outfalls are openings in the pipe system that dump the water into a natural body of water like a river or the ocean. In most communities, stormwater is untreated, meaning that all the pollution and trash that is swept into the inlets along with the runoff travels directly into the rivers and ocean. Although many of the inlets are grated, plastic litter can sometimes be swept through the gratings and end up in the ocean. Once in the ocean, litter tumbles around and can be broken into smaller pieces.
Figure 2. Stormwater runoff travels down city streets and sidewalks into grated inlets, like the one above on the left, through underground pipes, and out into rivers and oceans through outfalls. Plastic litter can sometimes get swept through the grated inlets and end up in the ocean too. (Photos courtesy of Nashville, and NOAA/NOS/Monterey Bay National Marine Sanctuary.)
Is plastic litter a problem in your community? How well do your community's grated inlets keep plastic litter out of the ocean? In this science project, you can explore the answers to these questions. First, you'll take a survey of the local grated inlets and types of plastic litter. Using that information, you'll make a model of one of the grated inlets and test how efficient it is at keeping out the exact types of plastic litter you found in your town. If the grated inlet does well in your tests, you can be relieved that your community isn't contributing to the problem, and if it doesn't, you can test what modifications would be necessary to the inlets in order to keep plastic out!
Terms and Concepts
- Marine debris
- Stormwater drainage system
- Why do urban and suburban communities have storm drains?
- What kinds of pollution are known to end up in stormwater?
- How does plastic end up in the ocean?
- Do scientists know whether or not there are consequences to having plastic in the ocean? If so, explain their conclusions. If not, what are they doing to find out?
- What is photodegradation and how does it apply to plastics in the ocean?
These websites are a good place to start gathering information about marine debris and the North Pacific Gyre:
- Goldstein, Miriam. (2011, January 10). Does the "Great Pacific Garbage Patch" Exist?. Retrieved January 23, 2011.
- NOAA. (2010, March 25). Information on Marine Debris. Retrieved January 23, 2011.
- Ocean Voyages Institute. (n.d.) Project Kaisei. Retrieved January 23, 2011.
The following resources have additional information about stormwater pollution and the stormwater drainage system.
- Australian Marine Environment Protection Association. (n.d.) Marine Stormwater Pollution How does it happen?. Retrieved January 23, 2011.
- City of Los Angeles Stormwater Program. (n.d.) About the Los Angeles Storm Drain System. Retrieved January 23, 2011.
- City of Oceanside. (n.d.) Clean Water Program: Just For Kids. Retrieved January 23, 2011.
Materials and Equipment
- Measuring tape
- Camera (optional)
- Lab notebook
- Polymer based clay, like Sculpey®, that can be baked in the oven (need approximately 2 lbs). Can be purchased at craft stores or online at Amazon.com
- Plastic rectangular flying carpet sled, or any other large flexible plastic sheeting. Can be purchased online at Amazon.com
- Utility knife, also called X-Acto® knife or box cutter
- 5-gallon buckets (2)
- Basin or plastic storage box; this should be rectangular in shape and hold a minimum of 18 liters
- Saw horse (2); these can be purchased at a hardware store. You may have something else at home you can substitute, read the Experimental Procedure and look at figure 3 below to help decide.
- Duct tape
- Measuring cup; quart size (4 cups) works best, but any size will do
- Permanent marker
- Plastic litter; see the Experimental Procedure below for more details
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Measuring Local Storm Drains
Find three local grated storm drain inlets in your community. You will probably be able to find these during a simple walk around either the downtown area or several residential blocks. In most communities, the Department of Public Works maintains the local stormwater drainage system; contact them for help if you have trouble locating grated inlets.
- You may find that your community has only one type of inlet, or that it has several different types.
For each of the storm drains you find:
- Make a sketch of the grated inlet in your lab notebook.
Using the tape measure, measure all the dimensions of the inlet including length, width, and spacing between the gratings. Record this information in a data table in your lab notebook.
- If the grating pattern is complex or difficult to measure, you may also find it useful to make a crayon or pencil rubbing of a sample area of it. This will give you an accurate template to refer back to later when you are creating your model.
- You may want to take photographs for future reference, and for your project display board if you plan to present your findings at a science fair.
- Also make notes about any litter, particularly plastic litter, you find surrounding the storm drain inlets (see Determining What Litter to Use below).
Determining What Litter to Use
The goal is to determine what types of litter are around your community and may be entering the local stormwater drainage system. You'll use this information to test the grated storm drain inlets models you make.
- For the purposes of this procedure, we'll focus on plastic litter as it is one of the major problems in the Great Pacific Garbage Patch. But, you can decide to focus on another aspect of litter, or include all types of litter, in your own science project, if you prefer.
Walk around your community and examine the different types of plastic litter you see on the sidewalks, near the storm drain inlets, and along the roadsides.
- In your lab notebook, make a table showing the types of litter you see and how frequently you see each type.
- Types of plastic litter you might see include, but aren't limited to, bottle caps, disposable pens, plastic bags, plastic bottles, containers or plastic wrap from takeout food, and fishing line.
- You may also find smaller bits of plastic from unidentifiable sources. Log these as unidentifiable plastic bits in different ranges of sizes. For example, plastic bits 1-2 centimeters wide vs. plastic bits 2-3 centimeters wide.
- You may also want to collect the plastic litter, especially the unidentifiable plastic bits, for testing your storm drain inlet designs later (see step 12 in Building and Testing Storm Drain Inlets, below).
Building and Testing Storm Drain Inlets
- Once you've gathered your data about local storm drain inlets and plastic litter, you are ready to build and test your own storm drain inlet models.
Use the polymer clay to build a replica of one of the grated storm drain inlets you found in your community.
- Use the tape measure and notes you took about the storm drain inlets to shape your clay copy into as close a replica as possible.
- If the storm drain inlets you measured were too large to comfortably fit in the middle of the plastic sled (or in your oven since you'll have to bake the model to harden it!), then make a model where the distance between the gratings is preserved, but the overall size of the inlet is smaller. For example, a 2 foot by 2 foot inlet with horizontal bar gratings 2 inches apart would be too large. Instead, you could create a 1 foot by 1 foot replica where the horizontal bars are still set 2 inches apart.
- Tip: Make the edges of the inlet beveled (meaning the top side will be just a little bit wider than the bottom side) to make it easier to fit the grating securely into your testing rig.
- After being shaped, the polymer clay replica will need to be baked in an oven so that it is hard, durable, and waterproof. Follow the manufacturer's instructions on how to work with and bake the clay.
Once the storm drain inlet model has been built, you are ready to assemble the rest of your testing rig.
- Tip: The instructions provided here on how to test your storm drain inlet models can be modified to fit your needs. You may find that you have materials at home that will work just as well without going out and buying buckets, a plastic sled, or saw horses. Feel free to modify the instructions to fit the materials you already have at home.
- Using a utility knife, cut a hole out of the center of the plastic sled. The hole should be the same size as the bottom side of your grated inlet model.
Place the grated inlet model in the hole in the sled. Use duct tape to secure the grated inlet model in the hole.
- Tip: If you've accidentally cut the hole too large you'll have to problem solve how to securely fit the grated inlet there; a putty adhesive may be helpful in this situation.
- Position two saw horses, or other supports, so that their distance apart is approximately six inches less than the length of the sled.
- With the help of two volunteers, place the sled on the two saw horses. A volunteer should stand at each end of the sled holding the edges of the sled so that they curl slightly to form a channel. See Figure 3, below, for a visual reference. The weight of the sled and grated inlet model should be supported on the saw horse.
Figure 3. This diagram shows one way you can test your grated inlet models. The model is set in a hole inside a plastic sled (pink semicircle tube), with a basin beneath it. Buckets are used to poor water into the channel created by the sled and collect any water at the end which fails to flow through the inlet.
- Position one bucket at the far end of the sled-channel. This bucket will catch any water that passes over the grated inlet (as opposed to going through the inlet).
- Place the basin directly beneath the hole in the sled with the grated inlet model. This basin will catch the water that flows into the stormwater drainage system through the inlet.
Next, you'll need to experiment with the testing setup to make sure things are working well.
Start by filling one 5 gallon bucket half way. Dump all of the water (approximately 2.5 gallons) into the top of the channel, all at the same time.
- What happens to the water? Does it flow down the channel and through the inlet? It is fine if some of the water also flows through the channel into the bucket at the far end of the channel. But, if the water pools in the channel and does not enter the inlet, you'll need to put the channel at a slight angle. Do this by placing a plank of wood, bricks, a thin box, or any such water-resistant item (in case it gets wet!) underneath the saw horse where you are dumping the bucket of water in.
Once you have it working with half a bucket of water, try it with more water.
- Decide how much water would make the best test-scenario.
- Keep experimenting with the amount of water you are using and the angle of the channel until most of the water flows through the inlet and just a little (between 0.5 gallons and none) of the water makes it down the channel into the last bucket.
Once you have the right test setup, take careful notes about it in your lab notebook so that you can easily replicate the conditions.
- Use a permanent marker to mark the bucket at the right water-level height so that you can reliably fill the bucket with the same amount of water each time.
- Start by filling one 5 gallon bucket half way. Dump all of the water (approximately 2.5 gallons) into the top of the channel, all at the same time.
Once you have settled on your testing setup, collect your baseline data. This data will show how well the storm drain inlet performs without the addition of plastic litter.
- Fill the bucket of water to the level you determined in step 10.
- Pour the water, all at once, into the channel.
- Once the water has finished draining, use the measuring cup to measure the amount of water in both the basin and the bucket. Write in your lab notebook the total amount of water that went into the storm drain system (the basin underneath the storm drain inlet), and the total amount of water that overflowed the inlet (the bucket at the far end of the channel).
- Repeat a-c four more times, for a total of five trials. Average the data for your five trials to calculate the baseline performance of the grated inlet.
Gather together your plastic litter items for testing.
- All of the plastic litter items should be ones you saw (see Determining What Litter to Use, above) in or near the storm drain inlets in your community. They can be similar items that you have at home (for example, a plastic water bottle) or the actual items you saw and collected during your survey.
- You will need approximately 10-20 items total. Use your judgment to decide exactly how many.
- For smaller items, you may want to use multiple of the same item.
Now you are ready to test how well the grated inlet allows stormwater to flow into the storm drain system while keeping the litter out.
- Repeat steps 11a-11c, this time adding the plastic litter items to the bucket of water. Tip: Remember to add water first and plastic second. Otherwise, you may have too little water in your bucket.
- In addition to measuring the water that is in each container, write down in your lab notebook which pieces of plastic litter entered the storm drain system (i.e., were washed into the basin underneath the storm drain inlet) and which ones were kept out (i.e., stayed in the water channel and/or landed in the bucket at the far end of the channel).
Repeat steps a-b four more times, for a total of five trials.
- Average the water measurements for the five trials and compare them to your baseline data. Did the plastic litter change the performance of your storm drain inlet?
- Make a table, bar graphs, or pie charts showing what litter entered the storm drain for each trial. Is there a trend across the five trials? What type(s) of plastic litter is your community's grated inlet good at keeping out of the stormwater system? What types of litter does it let through?
Improving Your Local Storm Drain Inlets
- Did your testing show that your local storm drain inlets are letting plastic litter into the stormwater system? If not, that's a cheerful result. But if they are, you may be able to improve on the grated inlet design to prevent that.
Look at your data and information you have gathered about storm drains and think of a grated inlet design that might catch more water.
- You can design a completely different grated inlet, or you can add to the design of the existing one to improve it. This second option is called retrofitting, and it is sometimes cheaper than buying or making all new versions.
- Keep in mind that grated storm drain inlets have two purposes: to prevent flooding by making sure the water gets into the storm drain system and to keep litter out. Your design should not drastically diminish the inlet's ability to have water flow through it as that would result in flooding.
- Once you have a design idea you are happy with, create your new inlet model out of the polymer clay and whatever other supplies you need.
- Repeat the testing as in steps 10-13 of the Building and Testing Storm Drain Inlets section.
- Compare the baseline performance (without any plastic litter) of the two inlet models, as well as the performance when litter is present. Was your re-designed version an improvement? Why or why not?
- Feel free to keep improving on your design until you have what you think is the best possible grated storm drain inlet for your community!
Ask an Expert
- If you find grated storm drain inlets with different designs in your community, build models to test each one. Is one design better at catching litter than the other? Do they have similar or different flow-through rates? Choose the best design, based on your testing, and try to improve on it.
- Plastic is just one type of litter that people are concerned about entering the stormwater drainage system and polluting waterways. Motor oil and other chemicals are other major areas of concern. Can you devise a way of improving storm drain inlets to prevent oil and other chemicals from being swept into the drainage system? Tips: You may want to do some research on storm drain inlet filters. Also, for safety reasons, use cooking oil in your tests instead of motor oil.
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