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Classroom activity Grade 7 Science

Crumpled-Paper Watershed: Placing Monitoring Stations to Find a Leak

Grade 7 groups swap crumpled-paper watersheds, place up to three monitoring stations, and use upstream and downstream results to find a hidden leaking site.

Objectives

  1. Students will map the divide, tributaries, and confluences of a model watershed and identify which land drains past a given point on a stream.
  2. Students will design a plan of up to three monitoring stations and use upstream and downstream results to identify an unknown pollution source.
  3. Students will propose a change at the source and explain how monitoring stations could show whether the change worked.

Vocabulary

Watershed
A watershed is all the land where rain that falls will drain to the same stream, river, or lake. Everyone lives in a watershed, no matter how far from the water they live.
Tributary
A tributary is a smaller stream or river that flows into a bigger one. Many small tributaries join together to build a large river.
Confluence
A confluence is the spot where two streams or rivers flow together and become one. Many cities grew up near confluences because river routes for travel and trade meet there.

Also: divide, upstream, downstream, monitoring station

Teacher overview

This is a model-building and investigation activity for groups of three or four. Each group builds a crumpled-paper watershed, maps its stream network, and marks four possible pollution sites, only one of which is secretly drawn in washable ink that will run when wet. Groups then trade landscapes and act as a monitoring team: before any rain falls, they decide where to place up to three monitoring stations on the other group's streams, then spray "rain" and use which stations turn colored, and which stay clear, to work out which site is leaking. The activity maps directly onto how water agencies track pollution: a station can only detect what drains past it from upstream, so a well-placed set of stations narrows the search, while a station at the outlet alone shows only that something somewhere in the watershed is wrong.

Activity Directions

  1. Before class, build one test landscape following steps 3 and 4 and mist it to confirm that the washable ink runs along the creases and the permanent ink stays put. If the color barely moves, plan on more sprays per round. Gather the materials for each group, and check that each group's two markers are a close color match so the leaking dot cannot be picked out by eye.
  2. Introduction (3 minutes). Group students in threes or fours and explain what each part of the model stands for. The creased paper is the land, the low creases are stream channels, the high folds are divides, and the spray is rain. The washable dot is a site leaking a pollutant that dissolves in runoff, while the permanent dots are sites that are not leaking. A small pencil circle drawn across a channel is a monitoring station, where a team checks whether pollution is passing.
  3. Build and map (8 minutes). Each group crumples its sheet into a ball, opens it partway so it keeps clear hills and valleys, and lays it in the tray. In pencil only, groups trace a main channel to the lowest edge and label that end "Town intake." They trace at least two tributaries that flow into the main channel and mark each point where two channels join with a small "C" for confluence. Last, they draw a dashed pencil line along the divide that surrounds all the land draining to the intake.
  4. Mark the sites (5 minutes). Inside the divide, each group marks four sites labeled A (farm), B (parking lot), C (factory), and D (construction site). Each site is a filled dot about the size of a pencil eraser, placed within about 1 cm of a channel and at least 3 cm from every other site, with at least two sites on different tributaries. Groups color three dots with the permanent marker and one with the washable marker, write the letter of the washable site on a slip of paper, fold it, and give it to the teacher.
  5. Swap and plan (8 minutes). Each group passes its tray to a neighboring group. Working on Part A of the Student Handout, the new group sketches the stream network, decides where to put up to three stations, draws each as a numbered pencil circle across a channel, and records which sites lie upstream of each station. Stations must be placed before any rain, and no one may touch or wet the dots.
  6. Rain in rounds (10 minutes). Each group mists its landscape from about 20 cm above in rounds of 10 sprays, covering the whole sheet evenly. After each round, students check every station circle for color and record "yes" or "no" in the Part A results table. Groups run three rounds. If no station shows color after round 3, they run a fourth round and note it on the handout.
  7. Conclude and check (4 minutes). Each group uses its pattern of colored and clear stations to name the leaking site and writes its reasoning in Part A. The teacher then hands over the builders' folded slip so the group can check its answer. If the answer was wrong or the stations could not decide, the group writes where one more station would have settled it.
  8. Practice and debrief (12 minutes). Once every group has finished its rain rounds and checked its answer against the slip, students complete Part B (the Larkin Creek practice map) with a partner, and the class discusses Part C. For the closing debrief, ask two groups to share their station plans: one whose stations pinned down the exact site and one whose stations left two or more sites possible. Ask the class what the first plan did that the second did not, and guide them to the idea that useful stations sit between sites, so that some sites are upstream of a station and others are not.
Crumpled-Paper Watershed: Placing Monitoring Stations to Find a Leak — Grade 7 Science
Name: ____________________________ Date: ______________

Student Handout

Part A: Your monitoring plan and results

Sketch the stream network on the landscape your group received. Label the town intake, each confluence, the four sites, and your stations.

Station Where it sits (which channel, between which points) Sites upstream of this station
1
2
3

Before the rain, write what you expect: "If Station ___ shows color but Station ___ stays clear, the leaking site must be ___."

Station Color after round 1? Color after round 2? Color after round 3? Round 4 (only if needed)
1
2
3

Our conclusion: The leaking site is ___, because Station(s) ___ showed color and Station(s) ___ stayed clear.

Part B: The Larkin Creek practice map

Larkin Creek supplies water to the fictional town of Ashby. Read the description of its stream network, sketch it, and then answer questions 1 through 5.

All of the land described below drains toward the Ashby water intake at the bottom of Larkin Creek.

  • Mill Run starts in the west hills and flows past a dairy farm (Site A).
  • Pine Run starts in the north hills and flows past a parking lot (Site B).
  • Mill Run and Pine Run join at Confluence 1 to form the North Branch.
  • The South Branch starts in the east hills. It flows past a factory (Site C) and then, farther downstream, past a construction site (Site D).
  • The North Branch and the South Branch join at Confluence 2 to form Larkin Creek, which flows to the Ashby intake.
  • A gravel pit (Site E) sits on the far side of the ridge east of the South Branch. Rain that falls there drains east into a different stream, Bell Brook.

Ashby's monitoring team has three stations:

  • Station 1 is on Larkin Creek, just above the Ashby intake.
  • Station 2 is on the North Branch, just below Confluence 1.
  • Station 3 is on the South Branch, below the factory and above the construction site.

After a rainstorm, the team tests the water at each station. The pollutant is detected at Station 1. It is not detected at Station 2 or Station 3.

  1. List the sites that are upstream of each station: Station 1, Station 2, and Station 3.
  2. Which site is the source of the pollutant? Explain how each station's result helped you decide.
  3. Suppose instead that the pollutant had been detected at Station 1 and Station 2, but not at Station 3. Which sites could be the source? Where would you place one more station to tell them apart, and how would you read its result?
  4. A town council member suggests saving money by keeping only Station 1. Explain why Station 1 by itself could never identify which site is the source.
  5. Could the gravel pit (Site E) explain the result at Station 1? Use the word "divide" in your answer.

Part C: Debrief

  1. In your own model, which station showed color first, and in which round? Explain why stations closer to the leaking site, and directly downstream of it, tend to show color sooner than stations farther away.
  2. Choose the leaking site you found, either in your model or at Larkin Creek. Propose one change at that site that would reduce the pollution reaching the stream, and explain how you would use monitoring stations to check whether the change worked.

From Water for Schools (waterforschools.org). This material is in the public domain (CC0) and may be copied, edited, and shared freely.

Answer Key

Part A results depend on each landscape, so check that each group's conclusion is consistent with its own results table and station list: a colored station means the source is among the sites upstream of it, and a clear station rules out every site upstream of it.

  1. Answer: Station 1 has all four Larkin Creek sites upstream of it (A, B, C, and D). Station 2 has Sites A and B upstream, because Mill Run and Pine Run both feed the North Branch above it. Station 3 has only Site C upstream, because the construction site is below it. Site E is upstream of none of them.
  2. Answer: Site D, the construction site. Station 1 detected the pollutant, so the source drains to Larkin Creek somewhere above the intake. Station 2 was clear, which rules out Sites A and B. Station 3 was clear, which rules out Site C. Site D is the only remaining site, and it drains to the South Branch below Station 3 and above Confluence 2, which matches every result.
  3. Answer: The source could be Site A or Site B. Place one more station on Mill Run between the dairy farm and Confluence 1. If it detects the pollutant, the source is Site A; if it stays clear, the source is Site B. A station on Pine Run between the parking lot and Confluence 1 also works, read the opposite way.
  4. Answer: Every site in the watershed is upstream of Station 1, so a detection there would look the same no matter which site was leaking. Station 1 can show that pollution is entering the creek somewhere, but only stations placed between sites can show where.
  5. Answer: No. The gravel pit is on the other side of the divide, the ridge that separates the Larkin Creek watershed from the Bell Brook watershed. Runoff from the pit flows downhill away from Larkin Creek, so it cannot reach Station 1.
  6. Answer: Answers depend on the model. A complete answer names the station and round from the group's table and explains that the colored water must travel downhill along the channel from the leaking site, so it reaches the nearest downstream station first and arrives later at stations farther along the channel. A station on a different tributary from the leaking site should not show color at all.
  7. Answer: Accept a reasonable change matched to the site, such as silt fences and covering bare soil at a construction site, a fenced strip of grass or trees between a farm field and the stream, or catch basins and regular sweeping at a parking lot. The monitoring plan should compare the results before and after the change at a station just downstream of the site, ideally alongside a station just upstream of it, so that any drop in pollution can be traced to that site rather than to a different source.

Differentiation

Support

Give the group a landscape with the main channel, tributaries, and divide already traced, so the group can focus on placing sites and stations. Allow these groups to mark three sites instead of four and to place two stations, and arrange the swap so that they receive another three-site landscape; two well-placed stations are enough to tell three sites apart. Provide the sentence frame "Station ___ showed color, so the source is upstream of it. Station ___ stayed clear, so Site ___ is not the source."

Extension

Ask students to find the fewest stations that could identify any one of the four Larkin Creek sites (A through D) after a single storm, assuming exactly one site is leaking and stations can go anywhere on the streams. The answer is three. Two stations cannot do it, because on a branching stream network the sets of sites upstream of two stations are either nested (one set inside the other) or share no sites at all, and neither arrangement gives four different result patterns. One working plan of three stations is one on Mill Run below Site A, one on the North Branch below Confluence 1, and one on the South Branch below Site C and above Site D, which gives a different set of results for each site. Students who finish can then plan for the harder case of two sites leaking at once.

ELL supports

Pre-teach "upstream" and "downstream" with a hand moving down a drawn channel, and "tributary" and "confluence" with two fingers joining into one. Label the column headings of the Part A tables with small pictures (a circle on a line for a station, a raindrop for each round). Allow students to give their conclusion by pointing to the stations on their model and completing the sentence frame from Support.