Angela's Tools · Chapter 18 · The Water Cycle
Worksheet 5 of 10
Snowpack Down, Creek Up: Two Datasets on Energy and Moving Water
Learning target: I can graph and calculate from data to show how a melting snowpack feeds a creek with a delay, and how the rate of evaporation depends on temperature even far below boiling.
Data and graphingAbout 45 minIndividual
MS-ESS2-4 · practice
data analysisindependent practice
NameDatePeriod
Directions
Both datasets are teaching datasets: the numbers were invented to be realistic, not measured at a real station. Part A follows a Sierra creek through one year. Part B follows an evaporation pan. Graph with a ruler, show every calculation with units, and write answers in complete sentences.
You will need: This worksheet, Pencil, Ruler, Calculator, Two colored pencils
Part A: A snowpack and the creek below it
A snow station on a mountain meadow reports the snow water equivalent (SWE) on the first day of each month: the depth of liquid water the snowpack would make if it all melted at once. A gauge on the creek 3 km downhill reports the creek's average flow for the month that follows, in cubic meters per second (m³/s). No rain fell between April 15 and September 1.
Snow water equivalent and creek flow at Granite Meadow (teaching dataset)
Simulated teaching dataset: the numbers are invented to be realistic, not measured.
| Date | SWE on that date (cm) | Average creek flow in the following month (m³/s) |
|---|
| Jan 1 | 40 | 1.2 |
| Feb 1 | 62 | 1.4 |
| Mar 1 | 85 | 2.0 |
| Apr 1 | 98 | 4.5 |
| May 1 | 70 | 11.0 |
| Jun 1 | 28 | 9.5 |
| Jul 1 | 0 | 3.0 |
| Aug 1 | 0 | 1.0 |
Simulated data for teaching. The pattern (snow peaking in early April, creek peaking about a month later, creek still flowing after the snow is gone) matches real Sierra Nevada stations.
1.On which date was the snowpack largest, and what was its SWE? How many centimeters of SWE were lost between that date and July 1? Show the subtraction.
2.Calculate the average melt rate in cm of SWE per day for April (April 1 to May 1, 30 days) and for May (May 1 to June 1, 31 days). Round to the nearest hundredth. Which month melted faster, and what about the sun explains the difference?
3.Describe the shape of your creek-flow graph in two sentences: when it rises, when it peaks, and how it falls.
4.The snowpack peaked on April 1, but the creek's biggest month began on May 1. Explain this one-month delay using at least two processes from the lesson and the two drivers (the sun's energy and gravity).
5.On July 1 the SWE was 0 cm and no rain had fallen since mid-April, yet the creek averaged 3.0 m³/s in July. Where was that water coming from? Name the most likely pathway and explain why it is slow.
6.Not every centimeter of melted snow reached the creek. Name two pathways by which meltwater could leave the meadow without ever flowing past the creek gauge.
Part B: How fast does water evaporate?
An evaporation pan is a wide, shallow metal pan of water left outdoors. Each morning a technician measures how much the water level dropped and refills it. No rain fell during these weeks, and the water never got anywhere close to boiling. The table gives the average daily loss for weeks with different average air temperatures.
Evaporation pan losses at different average air temperatures (teaching dataset)
Simulated teaching dataset: the numbers are invented to be realistic, not measured.
| Average air temperature (°C) | Average water lost per day (mm) |
|---|
| 10 | 1.5 |
| 15 | 2.4 |
| 20 | 3.5 |
| 25 | 4.9 |
| 30 | 6.6 |
Simulated data for teaching; realistic for a standard pan in calm, dry air. All temperatures are far below the 100 °C boiling point of water.
7.Describe the shape of your Part B graph. Does each extra 5 °C add the same amount of evaporation, or more each time? Use two differences from the table as evidence.
8.Suppose a small farm pond has a surface area of 200 m² and the average temperature for a 30-day month is 25 °C. Using the table, calculate (a) the depth of water lost in the month in mm and in cm, and (b) the volume lost in liters. (1 mm of depth over 1 m² is 1 liter.)
9.A classmate claims water only evaporates when it boils. Use two rows of the Part B table as evidence against this claim, and explain in terms of water molecules why evaporation can happen at 10 °C.
10.Put the two parts together. Part A shows that the sun's energy releases stored snow and gravity carries it downhill. Part B shows that the sun's warmth also sends water back into the air faster as the summer heats up. Using numbers from both datasets, explain why the creek's flow in August (1.0 m³/s) is so much lower than in May, even though the valley is warmer in August.
Rates are differences divided by time
A rate tells how much something changes per unit of time. For q2: subtract the later SWE from the earlier SWE to get the change in centimeters, then divide by the number of days between the two dates. Write the subtraction on one line and the division on the next: for example (made-up numbers) 50 cm − 20 cm = 30 cm; 30 cm ÷ 10 days = 3.0 cm per day. The unit of your answer is centimeters per day.
Fill the creek with the snow
Suppose the snow station represents a basin of 100 square kilometers (100,000,000 m²) that all drains past the creek gauge, and that the whole basin lost the same 98 cm of SWE between April 1 and July 1. Convert that SWE into a volume of water in cubic meters. Then estimate the volume that actually flowed past the gauge in April, May and June using the average flows (multiply each month's m³/s by the number of seconds in a month, about 2.6 million). Compare the two volumes, calculate what percent of the melt reached the gauge, and explain, with the pathways from q6, where the missing water most likely went.