Classroom activity Grade 6 Engineering & Design
Camp Marloch Constructed Wetland Design Activity
A grade 6 engineering station rotation where teams score competing constructed-wetland design options on a rubric, then combine the best features into one class design.
Objectives
- Students will score competing constructed-wetland design options on a shared rubric.
- Students will combine the best-scoring features from several designs into one wetland plan.
Vocabulary
- Greywater
- Gently used water from showers, bathtubs, bathroom sinks, and washing machines. With the right setup, it can be reused to water plants instead of going down the drain.
Also: constructed wetland, design rubric, trade-off
Teacher overview
This is a station rotation for teams of three or four students. Camp Marloch, a fictional summer camp, wants a constructed wetland to clean the greywater from its wash station before it soaks back into the ground. A constructed wetland is a shallow, plant-filled bed of gravel where roots and the tiny living things on them break down waste as water moves through. Four stations each hold one design decision, and the format follows how engineers choose among options: teams score competing choices on a shared rubric, then the class combines the best-scoring features into one design.
The session runs about 5 minutes for the introduction, 28 minutes for the rotation (7 minutes at each of four stations), and 12 minutes for building the class design and the debrief. All card text, the design brief, and the score sheet are in the Student Handout below; prep consists of printing and cutting apart the cards.
Activity Directions
- Before class, print the Station Cards from the Student Handout, cut them apart, and set up four stations around the room. Each station holds the three cards for one decision: Station 1 is bed material (cards 1A to 1C), Station 2 is plant choice (2A to 2C), Station 3 is water depth (3A to 3C), and Station 4 is flow path (4A to 4C). Each card names one option and lists its pros and cons. If the class has more than four teams, put two sets of cards at each station so two teams can work there at the same time. Print one design brief and one score sheet for each team.
- Give each team the design brief and score sheet, and assign each team a starting station. Read the design brief aloud and explain the shared rubric: every option is scored 1 to 3 on cleaning power, cost, and upkeep, where 3 is always best for the camp. A 3 for cost means the cheapest to build, and a 3 for upkeep means the least work to keep running. Point out that cleaning power is the camp's main goal (the criterion), while cost and upkeep are the limits the camp must work within (the constraints).
- At each station, the team reads all three option cards, discusses the pros and cons, and writes a rubric score for each option on its own row of the score sheet. The team adds the three scores to get a total out of 9 and circles the option with the highest total for that decision. If two options tie, the team circles the one with the higher cleaning power score, because cleaning the water is the camp's main goal.
- After 7 minutes, call time and have teams rotate to the next station. Repeat until every team has scored all four stations.
- Bring the class together. For each station in turn, ask each team to report the option it circled and that option's rubric scores, and tally the reports on chart paper. The option circled by the most teams becomes the class choice for that decision. If two options are circled by the same number of teams, choose the one the teams scored higher on cleaning power, for the same reason as in step 3.
- Assemble the four winning options into one combined "Camp Marloch wetland" design on the chart paper, with a simple side-view sketch showing the bed material, the plants, the water depth, and the flow path. This combined design is the class solution built from the best feature at each station.
- End the activity when the combined design is complete and posted. Close with these debrief questions so teams connect the rubric choices back to how a wetland cleans water: "How does a constructed wetland actually clean the greywater?" "Why did we score each option on three measures instead of just cleaning power?" "Why can combining the best feature from each station give a better design than any single team's plan?" "Do any two of our winning options work against each other?"
Student Handout
Design brief: the Camp Marloch wetland
Camp Marloch has an outdoor wash station where campers wash dishes and hands. The used water, called greywater, carries soap, bits of food, and grease. It first flows into a settling tank that catches the heavier solids, and then it will flow into a new constructed wetland behind the wash station.
The wetland must clean the greywater well before it soaks into the ground. That is the criterion, and it is scored as cleaning power. The camp also has limits, called constraints:
- The camp has a small budget for building the wetland, which is scored as cost.
- Two maintenance workers can spend only about an hour a week on the wetland during camp season, which is scored as upkeep.
- The wetland must fit in one fixed plot of ground, so every option uses the same area.
- The water must stay a few inches below the top of the gravel, so there is no open standing water for mosquitoes and no smell.
Scoring rule: give every option a score from 1 to 3 on each measure, where 3 is always best for the camp. Cleaning power 3 means it cleans the most. Cost 3 means it is the cheapest to build. Upkeep 3 means it takes the least work to keep running.
Station Cards
Print each station's three cards and place them at that station.
Station 1: Bed material. Every option fills the same lined pit. Tiny living things called microbes live on the surface of the bed material and break down waste in the water.
| Card | Option | Pros | Cons |
|---|---|---|---|
| 1A | Pea gravel: small, rounded stones about the size of a pea | Water spreads evenly through the small gaps and touches a lot of stone surface where microbes live. Plant roots grow through it easily. | Costs more than crushed stone because it is washed and sorted to one size. Over several years, grease and solids slowly fill the gaps near the inlet, and that section must be dug out and replaced. |
| 1B | Coarse sand | The very small gaps strain out fine particles, and the large surface area gives microbes many places to live, so it cleans very well while it stays open. | Costs about the same as pea gravel. The gaps are so small that greywater solids and grease clog it quickly. When it clogs, water pools on top, bringing smell and mosquitoes, and the sand must be dug out and replaced, sometimes more than once a season. |
| 1C | Crushed stone: sharp stones about the size of a golf ball | The cheapest of the three to buy. The big gaps almost never clog. | Water rushes through the big gaps and touches less stone surface, so microbes have less chance to clean it. Young plants root poorly between the large, sharp stones, and some may need to be replanted. |
Station 2: Plant choice. The roots carry air down into the bed, take up nutrients from the water, and give microbes a place to live. The root depths below come from the planting notes of the camp's local plant nursery and are measured down from the water level in the bed.
| Card | Option | Pros | Cons |
|---|---|---|---|
| 2A | Cattails | Grow fast and fill the bed in the first summer. Thick roots take up a lot of nutrients. The nursery sells them for the lowest price of the three. | Spread quickly, including out of the bed. Tall dead leaves must be cut and removed every fall so they do not rot back into the water. Roots reach only about 12 inches below the water level. |
| 2B | Bulrushes | Roots grow deeper than the other two plants, reaching about 18 inches below the water level and carrying air to deeper water. Spread more slowly, so they stay inside the bed. | Cost the most of the three at the nursery. Slow to fill in, so cleaning is weaker during the first season. Need some thinning every couple of years. |
| 2C | Sedges | Low-growing native plants that stay in neat clumps and rarely need cutting. Handle the bed drying out a little between uses. | Roots reach only about 6 inches below the water level. Take up fewer nutrients than the taller plants. The nursery price is between the other two. |
Station 3: Water depth. This is the depth of water kept inside the gravel. All three options use the same plot, so a deeper bed holds more water, and each batch of greywater stays in the wetland longer before it leaves.
| Card | Option | Pros | Cons |
|---|---|---|---|
| 3A | 6 inches | The least digging and the least gravel, so it costs the least. The roots of all three plant choices reach all of the water. | Holds the least water, so greywater passes through fastest and has the least time to be cleaned. In hot weather the bed can dry out, and the workers may need to water the plants. |
| 3B | 12 inches | Water stays about twice as long as in the 6-inch bed. Cattail and bulrush roots reach through the whole depth of water. | Twice the digging and gravel of the 6-inch bed, so it costs more. Sedge roots reach only the top half of the water. |
| 3C | 18 inches | Holds the most water, so water stays about three times as long as in the 6-inch bed. The bed is unlikely to dry out. | The most digging and gravel, so it costs the most. Only bulrush roots reach the bottom. Water near the bottom, below most roots, gets little air and is cleaned more slowly. A clogged section is the hardest to dig out. |
Station 4: Flow path. This is the route the water takes from the inlet pipe to the outlet pipe.
| Card | Option | Pros | Cons |
|---|---|---|---|
| 4A | Straight path: inlet at one end, outlet at the other | The simplest and cheapest to build. Nothing inside the bed needs to be checked. | Water tends to find a few fast routes through the gravel and skip other parts of the bed, so some gravel and roots do little cleaning. |
| 4B | Zigzag baffles: plastic walls inside the bed make the water snake back and forth | The longer path spreads water across more of the gravel and roots, so fewer parts of the bed are skipped. | The walls add cost and building time. Solids collect at the turns, which need a quick check each week. |
| 4C | Two cells in series: the plot is split into two smaller beds, and water flows through the first bed and then through a pipe into the second | The first cell catches most of the leftover solids and grease, so the second cell stays clean longer and gives the water a second round of cleaning. If the first cell clogs, the workers dig out only that smaller bed. | The most expensive of the three, because it needs a dividing wall, an extra pipe, and a second outlet. There are two inlets and two outlets to check each week. |
Team score sheet
For each option, write a score from 1 to 3 on cleaning power, cost, and upkeep (3 is always best for the camp). Add the three scores for the total, then circle the option with the highest total at each station. If two options tie, circle the one with the higher cleaning power score.
| Station (decision) | Option scored | Cleaning power | Cost | Upkeep | Total (out of 9) |
|---|---|---|---|---|---|
| 1 Bed material | 1A Pea gravel | ||||
| 1 Bed material | 1B Coarse sand | ||||
| 1 Bed material | 1C Crushed stone | ||||
| 2 Plant choice | 2A Cattails | ||||
| 2 Plant choice | 2B Bulrushes | ||||
| 2 Plant choice | 2C Sedges | ||||
| 3 Water depth | 3A 6 inches | ||||
| 3 Water depth | 3B 12 inches | ||||
| 3 Water depth | 3C 18 inches | ||||
| 4 Flow path | 4A Straight path | ||||
| 4 Flow path | 4B Zigzag baffles | ||||
| 4 Flow path | 4C Two cells in series |
Recording prompts:
- Which single decision led to the biggest disagreement in your team, and why?
- Name one option that cleans well but costs a lot to build. Which two scores on your sheet show that trade-off?
From Water for Schools (waterforschools.org). This material is in the public domain (CC0) and may be copied, edited, and shared freely.
Answer Key
Scores will vary by team, since the rubric asks for judgments. The sample below is one reasonable set of scores that follows the card text, and it shows how the tie rule in step 3 works. Use it to check that teams are reading the cards, not to mark a team's scores wrong.
| Option | Cleaning power | Cost | Upkeep | Total |
|---|---|---|---|---|
| 1A Pea gravel | 3 | 2 | 2 | 7 |
| 1B Coarse sand | 3 | 2 | 1 | 6 |
| 1C Crushed stone | 1 | 3 | 2 | 6 |
| 2A Cattails | 3 | 3 | 1 | 7 |
| 2B Bulrushes | 3 | 1 | 2 | 6 |
| 2C Sedges | 1 | 2 | 3 | 6 |
| 3A 6 inches | 1 | 3 | 2 | 6 |
| 3B 12 inches | 3 | 2 | 2 | 7 |
| 3C 18 inches | 2 | 1 | 2 | 5 |
| 4A Straight path | 1 | 3 | 3 | 7 |
| 4B Zigzag baffles | 3 | 2 | 2 | 7 |
| 4C Two cells in series | 3 | 1 | 2 | 6 |
With these scores, the combined design is a pea-gravel bed planted with cattails, holding 12 inches of water, with zigzag baffles. At Station 4 the straight path and the zigzag baffles tie at 7, and the tie rule picks the baffles because they score higher on cleaning power. The 12-inch depth also suits cattails, whose roots reach about 12 inches below the water level.
Signs that a team has misread a card:
- Coarse sand scored 3 on upkeep. Card 1B says it clogs quickly and may need replacing more than once a season.
- Crushed stone or the straight path scored 3 on cleaning power. Both cards say water moves through fast or skips parts of the bed.
- The 6-inch depth scored 1 on cost. Card 3A says it is the cheapest depth to build, so it should score 3.
Recording prompts:
- Answers will vary. A strong response names the decision and the measure the team disagreed on, for example, "Plant choice, because cattails clean well and cost little but need cutting every fall."
- Either bulrushes (2B) or two cells in series (4C) fits, with a cleaning power score of 3 and a cost score of 1. The 18-inch depth (3C) also fits if a team scored it high on cleaning power.
Debrief questions from step 7:
- Debrief question: "How does a constructed wetland actually clean the greywater?" Answer: Water moves slowly through gravel and plant roots, where microbes living on the stones and roots break down waste and the roots take up nutrients, so the water that leaves is cleaner than the water that entered. The longer the water stays and the more gravel and root surface it touches, the more cleaning happens, which is why depth and flow path matter.
- Debrief question: "Why did we score each option on three measures instead of just cleaning power?" Answer: A design that cleans well but costs too much or needs constant upkeep may not be the best real choice, so cost and upkeep are constraints that matter alongside cleaning power, which is the main criterion.
- Debrief question: "Why can combining the best feature from each station give a better design than any single team's plan?" Answer: Each team's plan is strong in some decisions and weak in others, so taking the highest-scoring option at every station builds one design that carries the best feature from each, which is how engineers optimize a solution.
- Debrief question: "Do any two of our winning options work against each other?" Answer: Answers depend on the class design. A strong response checks the plant against the depth, for example, sedges with a 12-inch or 18-inch depth would leave much of the water below the roots, and cattails with an 18-inch depth would leave the bottom 6 inches below the roots.
Differentiation
Support
Remove the coarse sand, sedges, 18-inch, and two-cells cards so each station has two options instead of three (teams leave those rows of the score sheet blank), and highlight one pro and one con on each remaining card so teams can focus on scoring rather than reading. Pair students who need support with a strong reader at each station.
Extension
Ask a team to identify one place where two winning options conflict, for example a plant whose roots do not reach the bottom of the chosen depth, and propose a change that resolves the conflict while keeping the design's cleaning power high. As a further step, the team can argue whether cleaning power should count double in the total and show whether that change would alter any of the class's winning options.
ELL supports
Add picture icons to each station card, such as gravel, sand, and large stones at Station 1, a cattail, a bulrush, and a sedge at Station 2, a water-depth ruler at Station 3, and arrow diagrams at Station 4, so the options are clear without heavy reading. Give a sentence frame for the recording prompts: "We picked ___ because it scored high on ___."