Worksheet Grade 7 Science

Sannox Ridge Snowpack: Snow Water Equivalent and Spring Runoff

Students turn snow depth and density readings from a fictional mountain basin into snow water equivalent, forecast spring runoff, and model the path to a reservoir.

Grade: Grade 7
Subject: Science
Material: Worksheet
Time: 45 min
Prep: No prep
Materials: Calculator

Standards

MS-ESS2-4 NGSS

Develop a model to describe the cycling of water through Earth's systems driven by energy from the sun and the force of gravity.

How this material aligns: Item 10 has students draw and label a model of water moving from snowpack to reservoir to tap, marking where the sun's energy and gravity act.

All materials for MS-ESS2-4 →

7.RP.A.3 Common Core Math

Use proportional relationships to solve multistep ratio and percent problems. Examples: simple interest, tax, markups and markdowns, gratuities and commissions, fees, percent increase and decrease, percent error.

How this material aligns: Items 5 and 12 express a computed runoff as a percent of the reservoir's capacity, item 6 is a percent increase from last April's 12.0 inches to this April's 14.7 inches, and item 7 works backward from depth and water content to a density expressed as a percent.

All materials for 7.RP.A.3 →

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This material is in the public domain (CC0) and may be copied, edited, and shared freely, without attribution. Updated 2026-07-23.

Objectives

Students will calculate snow water equivalent from snow depth and snow density.
Students will forecast spring runoff and compare it with a reservoir's capacity.
Students will model the path water takes from mountain snowpack to a town's tap.

Vocabulary

Snowpack: The snow that piles up in the mountains over the winter. As it melts in spring and summer, it acts like a giant water tank feeding rivers and reservoirs.

Also: snow water equivalent, snow course, density, runoff

Teacher overview

In mountain regions the winter snowpack works as a reservoir made of snow, holding water until warm weather releases it. Surveyors measure snow depth and snow density at fixed spots called snow courses, then multiply the two to get snow water equivalent, the depth of water the snow would make if it all melted at once. This worksheet uses fictional April readings from Sannox Ridge, the basin that supplies the town of Trelane. Teaching note: students often assume that deep snow always means plenty of water, so they compare depths and stop there. Two feet of dense spring snow can hold more water than three feet of dry powder, which is why density has to be part of the calculation.

Sannox Ridge Snowpack: Snow Water Equivalent and Spring Runoff — Grade 7 Science

Name: ____________________________ Date: ______________

Student Worksheet

Every April, surveyors in the town of Trelane visit two snow courses on Sannox Ridge. Snow water equivalent equals snow depth times snow density. Trelane's reservoir holds 900 acre-feet, and in our scenario each inch of average snow water equivalent across the basin melts into 50 acre-feet of runoff.

Snow course	Snow depth (inches)	Snow density
Course A	60	25 percent
Course B	48	30 percent

What is the snow water equivalent at Course A, in inches?
What is the snow water equivalent at Course B, in inches?
What is the average snow water equivalent of the two courses, in inches?
Using the average from item 3, how many acre-feet of runoff should Trelane expect this spring?
What percent of the 900 acre-foot reservoir would that runoff fill? Round to the nearest tenth of a percent.
Last April the average snow water equivalent was 12.0 inches. From last April to this April, what is the percent increase? Round to the nearest tenth of a percent.
A third site, Course C, has 50 inches of snow holding 12 inches of snow water equivalent. What is the snow density there, as a percent?
Which of the three courses has the densest snow?
Course B has 12 inches less snow than Course A, yet it holds almost as much water. Explain how snow of the same depth can hold different amounts of water.
Draw and label a model showing the path water takes from the Sannox Ridge snowpack to a tap in Trelane. Mark the place where energy from the sun acts on the water and the place where gravity moves it.
Suppose next April the basin average drops to 9.0 inches of snow water equivalent. How many acre-feet of runoff would that produce?
What percent of the 900 acre-foot reservoir would that smaller runoff fill?
Trelane uses 600 acre-feet during a summer. How many acre-feet short would the runoff in item 11 leave the town?

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: 15 inches.
60 inches of depth times 0.25 equals 15 inches of snow water equivalent.
Answer: 14.4 inches.
48 inches of depth times 0.30 equals 14.4 inches of snow water equivalent.
Answer: 14.7 inches.
15 plus 14.4 equals 29.4, and 29.4 divided by 2 equals 14.7 inches.
Answer: 735 acre-feet.
14.7 inches times 50 acre-feet per inch equals 735 acre-feet.
Answer: 81.7 percent.
735 divided by 900 equals 0.8166, which rounds to 81.7 percent.
Answer: 22.5 percent.
The change is 14.7 minus 12.0, or 2.7 inches. Then 2.7 divided by 12.0 equals 0.225, which is a 22.5 percent increase.
Answer: 24 percent.
12 inches of water divided by 50 inches of snow equals 0.24, or 24 percent density.
Answer: Course B.
Course B is 30 percent dense, compared with 25 percent at Course A and 24 percent at Course C.
Answer: The snow differs in density.
Dense snow has more ice and less air in the same depth, so it holds more water. Light, airy snow of the same depth melts into much less water.
Answer: Accept a labeled model with the stages in order.
A complete model shows snow on Sannox Ridge, melting, runoff flowing down the slope into a stream, the stream filling the reservoir, and treated water reaching a tap in Trelane. The sun's energy should be marked at the melting stage, and gravity should be marked where water flows downhill.
Answer: 450 acre-feet.
9.0 inches times 50 acre-feet per inch equals 450 acre-feet.
Answer: 50 percent.
450 divided by 900 equals 0.50, which is 50 percent of the reservoir.
Answer: 150 acre-feet.
600 acre-feet of summer use minus 450 acre-feet of runoff leaves the town 150 acre-feet short.

Differentiation

Support

Give students a worked example using a fourth snow course, such as 40 inches of snow at 20 percent density, before they begin item 1. Provide a filled-in row of the Trelane table showing depth, density, and snow water equivalent so the structure of the calculation is visible.

Extension

Have students find the snow density that would let a 48-inch snowpack at Course B match Course A's snow water equivalent, then explain what weather during the winter would produce snow that dense on Sannox Ridge.

ELL supports

Provide a picture card showing a ruler in snow labeled depth and a beaker of melted snow labeled snow water equivalent. Allow students to answer item 9 with a labeled drawing of two snow samples from the town of Trelane rather than a written paragraph.

Extensions

Students can track April snowpack reports published by a state or federal snow survey for a real basin, then use the Trelane method to estimate how a similar percent change in snow water equivalent would affect that basin's summer supply.