Classroom activity Grade 4 Math
Marlbeck Ridge Runoff Trays: Measuring How Far Water Travels
A grade 4 activity where teams build a foil ridge in a tray, pour water down both slopes, and measure the runoff distance in centimeters and millimeters.
Objectives
- Students will measure a runoff distance in centimeters and record the same distance in millimeters.
- Students will compare two measured distances and find the difference in centimeters.
- Students will convert a pouring time from minutes to seconds.
Vocabulary
Key words: runoff, slope, ridge, centimeter, millimeter
Teacher overview
This is a hands-on measurement activity for teams of three or four students, built around a fictional hill called Marlbeck Ridge. Each team crumples aluminum foil over a propped book inside a shallow tray to make a ridge with two slopes, one steeper than the other, then pours water from the top and measures with a ruler how far the water runs down each side before it stops or pools. The activity teaches the concept directly, because the ridge is a watershed divide in miniature and the two measured distances show how the steepness of a slope changes how far runoff travels before it pools or soaks in. Every measured number belongs to the team that measured it, so the recorded results will differ from group to group and no single set of distances is the correct one.
Activity Directions
Before class, set out one tray, one sheet of foil, one hardcover book, two plastic cups, one ruler, and a small stack of paper towels for each team. Fill a pitcher with water and keep it at a central table.
Take 5 minutes to group students into teams of three or four and assign roles: a builder who shapes the foil, a pourer who fills and empties the cup, a measurer who handles the ruler, and a recorder who fills in the handout. If a team has three students, the pourer also records.
Give teams 10 minutes to build. The builder lays the book inside one end of the tray so it makes a low hill, drapes the foil over the book and presses it down, then props one side of the book higher than the other so Side A is clearly steeper than Side B. Teams should press the foil flat where it meets the tray floor so water is not trapped at the edge.
Open the 15-minute pouring block by demonstrating one pour for the whole class, marking on your own tray where the water stopped so students can see what "how far the water ran" means.
Teams then use the rest of that block to run their pours. The pourer fills a cup with about half a cup of water, holds it just above the top of the ridge, and pours slowly onto Side A. The measurer waits until the water stops moving, then measures from the top of the ridge to the far edge of the wet mark, in centimeters. The recorder writes the number on the handout.
Teams repeat the pour on Side B, the gentler slope, and record that distance the same way. Teams blot the tray with paper towels between pours so an old wet mark is not measured twice.
While one pour is running, the builder counts the seconds until the water reaches the bottom edge of the tray on Side A, and the recorder writes that number of seconds on the handout.
Give teams 10 minutes to finish the handout questions using their own recorded numbers. Teams that finish early may run one more pour on Side B and see whether the distance changes.
Close with a 5-minute debrief. Ask two teams to read their Side A and Side B distances aloud, then ask the class one question: the same amount of water was poured on both sides, so why did the steeper side carry water farther? Take three answers, then ask where a town built on a hill like this would need to plan for the fastest runoff.
Student Handout
Write your team's own measurements. Your numbers will not match other teams, and that is expected.
Complete the last row of this table.
Centimeters Millimeters 1 10 5 50 12 120 30 Pour water on Side A, the steeper side. Measure how far the water ran, in centimeters. Write the number.
Write your Side A distance from question 2 in millimeters.
Pour water on Side B, the gentler side. Measure how far the water ran, in centimeters. Write the number.
Write your Side B distance from question 4 in millimeters.
Which side did the water run farther on, Side A or Side B?
How many centimeters farther did the water run on that side?
How many seconds did the water take to reach the bottom edge of the tray on Side A?
Your team pours water for 2 minutes in all today. How many seconds is 2 minutes?
A town wants to slow the water that runs off a hill like Marlbeck Ridge. Where on the hill would you plant a rain garden, and why?
From Water for Schools (waterforschools.org). This material is in the public domain (CC0) and may be copied, edited, and shared freely.
Answer Key
Answer: 300 millimeters.
One centimeter equals 10 millimeters, so 30 centimeters equals 30 times 10, or 300 millimeters. The table's earlier rows show the same pattern.Answer: Accept any measured distance in centimeters.
The number depends on the team's tray, slope, and pour. Check that the student wrote a whole number of centimeters and labeled the unit, and that the measurement started at the top of the ridge.Answer: Accept the question 2 distance multiplied by 10.
A team that wrote 18 centimeters should write 180 millimeters. Check the conversion rather than the size of the number.Answer: Accept any measured distance in centimeters.
As in question 2, the value belongs to the team. Side B is usually shorter than Side A, but a team whose foil trapped water may get a different result, which is worth discussing rather than correcting.Answer: Accept the question 4 distance multiplied by 10.
Check that the student used the same conversion as in question 3.Answer: Accept either side, matching the team's own numbers.
Most teams will name Side A, the steeper slope. A team that names Side B should be asked to point to where the water stopped on each side.Answer: Accept the difference between the question 2 and question 4 distances.
The answer must equal the larger distance minus the smaller one, in centimeters. A team with 18 centimeters and 11 centimeters should write 7 centimeters.Answer: Accept any timed number of seconds.
Check that the student recorded a whole number of seconds and did not write a distance here by mistake.Answer: 120 seconds.
One minute is 60 seconds, so 2 minutes is 2 times 60, or 120 seconds.Answer: Accept any reasonable placement with a reason.
Strong answers place the rain garden near the bottom of the steeper slope, where the water arrives fastest and in the greatest amount, and explain that plants and loose soil there give the runoff somewhere to soak in before it reaches the street.
Differentiation
Support (below grade level)
Pre-build the foil ridge for these teams so all of their time goes to pouring and measuring. Give them a ruler with only centimeters marked in bold and a printed strip showing 1 centimeter next to 10 millimeters. Provide a recording sheet with the unit labels already written after each blank so students only supply the number. Pair each student with a partner who reads the ruler aloud while they write.
Extension (above grade level)
Ask these teams to run three pours on each side and record all six distances, then find the largest and smallest distance on each side and describe the range in centimeters. They can also change one variable on purpose, such as propping the book with a second book or covering half the foil with a paper towel to stand for grass, and write a short conclusion about what that change did to the runoff distance.
ELL supports
Pre-teach "slope," "runoff," and "ridge" using a simple side-view drawing of a hill with two different slopes and arrows showing water running down. Label the drawing with the same words used on the handout and post it where every team can see it. Provide sentence frames for questions 6 and 10: "The water ran farther on Side ___," and "I would put a rain garden ___ because ___." Allow oral answers for question 10 before writing.
Extensions
Teams can rebuild Marlbeck Ridge with a paved side, made by taping a strip of wax paper or plastic over the foil, and a planted side, made by pressing a thin layer of damp paper towel onto the foil. Measuring runoff distance on both sides gives students a second comparison and connects the classroom tray to the reason towns require green space alongside new parking lots.