Worksheet Grade 11 Science

Havenmoor Watershed Water Budget: Recharge and Drought Math

A grade 11 earth-science worksheet building a water budget for a fictional watershed, partitioning precipitation into evapotranspiration, runoff, and aquifer recharge.

Grade: Grade 11
Subject: Science
Material: Worksheet
Time: 45 min
Prep: No prep
Materials: Calculator

Standards

HS-ESS3-3 NGSS

Create a computational simulation to illustrate the relationships among the management of natural resources, the sustainability of human populations, and biodiversity.

How this material aligns: Items 1 through 8 build a simplified spreadsheet-style water budget for the Havenmoor watershed, partitioning precipitation into evapotranspiration, runoff, and recharge, the resource simulation this standard describes.

All materials for HS-ESS3-3 →

HSN-Q.A.1 Common Core Math

Use units as a way to understand problems and to guide the solution of multi-step problems; choose and interpret units consistently in formulas; choose and interpret the scale and the origin in graphs and data displays.

How this material aligns: Items 1, 5, and 6 carry inches, acre-feet, gallons, and million gallons per day through a multi-step unit conversion, the consistent-units reasoning this standard requires.

All materials for HSN-Q.A.1 →

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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 partition a watershed's annual precipitation into evapotranspiration, runoff, and recharge.
Students will convert between depth, acre-feet, and daily supply units and interpret a drought-year budget.

Vocabulary

Water budget: A water budget is a way of tracking all the water coming into an area, like rain and snowmelt, against all the water leaving it, like evaporation and streamflow. Scientists use water budgets to see whether a watershed or aquifer is gaining or losing water over time.
Evapotranspiration: Evapotranspiration is the total amount of water that leaves the land and goes into the air, both from wet surfaces and from plants. Scientists combine evaporation and transpiration into one word.
Recharge: Recharge is water soaking down through the ground to refill an aquifer, the way rain refills an underground sponge. Aquifers stay healthy only if recharge keeps up with pumping.
Acre-foot: The amount of water it takes to cover one acre of land, about the size of a football field, one foot deep. Western states use acre-feet to measure large amounts of water.

Also: runoff

Teacher overview

A water budget accounts for where a watershed's precipitation goes: some returns to the air, some runs off to streams, and some soaks down to recharge the aquifer. This worksheet uses the fictional Havenmoor watershed to have students partition a year of rainfall, convert the recharge into a daily supply figure, and then rerun the budget for a drought year. A common misconception it addresses is that recharge simply scales down with rainfall; the drought calculation shows instead that evapotranspiration takes its share first, so recharge can fall to nearly nothing in a dry year.

Havenmoor Watershed Water Budget: Recharge and Drought Math — Grade 11 Science

Name: ____________________________ Date: ______________

Student Worksheet

Use the fictional Havenmoor watershed for every item. Assume no change in storage in a normal year, so precipitation equals the sum of evapotranspiration, runoff, and recharge.

Watershed area: 12,000 acres
Average annual precipitation: 40 inches
In a normal year, 60 percent of precipitation returns to the air as evapotranspiration, 25 percent leaves as surface runoff, and 15 percent recharges the aquifer.
1 acre-foot = 325,851 gallons. To convert a depth in inches to feet, divide by 12.

Convert the 40 inches of precipitation to feet, then multiply by the watershed area to find the total annual precipitation volume in acre-feet.
Calculate the evapotranspiration volume in acre-feet.
Calculate the surface runoff volume in acre-feet.
Calculate the recharge volume in acre-feet, and check that your three parts add up to your item 1 total.
Convert the recharge volume from item 4 into gallons.
If Havenmoor pumps the aquifer at a steady rate that just matches the annual recharge, express that recharge as an average number of million gallons per day. Round to the nearest hundredth.
In a drought year, precipitation drops to 30 inches. Calculate the new total precipitation volume in acre-feet.
In that drought year, evapotranspiration still uses 24,000 acre-feet and runoff drops to 6,000 acre-feet. How many acre-feet are left for recharge? Explain what your answer means for the aquifer.
Write the water-budget relationship in words, including a change-in-storage term, and explain what a negative change in storage would mean for Havenmoor.
Using your drought result, explain in two or three sentences why a growing town that depends on this aquifer could face a supply shortfall after several dry years in a row.

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: 40,000 acre-feet.
40 inches / 12 = 3.333 feet; 3.333 feet x 12,000 acres = 40,000 acre-feet.
Answer: 24,000 acre-feet.
Evapotranspiration = 60 percent of 40,000 = 0.60 x 40,000 = 24,000 acre-feet.
Answer: 10,000 acre-feet.
Runoff = 25 percent of 40,000 = 0.25 x 40,000 = 10,000 acre-feet.
Answer: 6,000 acre-feet.
Recharge = 15 percent of 40,000 = 0.15 x 40,000 = 6,000 acre-feet. Check: 24,000 + 10,000 + 6,000 = 40,000 acre-feet, matching item 1.
Answer: 1,955,106,000 gallons.
6,000 acre-feet x 325,851 gallons per acre-foot = 1,955,106,000 gallons.
Answer: 5.36 MGD.
1,955,106,000 gallons / 365 days = 5,356,455 gallons per day, which is about 5.36 million gallons per day.
Answer: 30,000 acre-feet.
30 inches / 12 = 2.5 feet; 2.5 feet x 12,000 acres = 30,000 acre-feet.
Answer: 0 acre-feet.
30,000 - 24,000 - 6,000 = 0 acre-feet left for recharge. This means the aquifer receives essentially no new water in the drought year, so any pumping that year draws down stored groundwater rather than fresh recharge.
Answer: precipitation equals ET plus runoff plus recharge plus change in storage.
In words, precipitation = evapotranspiration + runoff + recharge + change in storage. A negative change in storage would mean Havenmoor is removing more water from the aquifer than nature is putting back, so the stored groundwater is shrinking.
Answer: repeated dry years drain stored groundwater.
Accept any answer explaining that in dry years recharge falls toward zero while demand continues, so the town must pump from storage; several such years in a row lower the water table faster than it can refill, which threatens the long-term supply.

Differentiation

Support

Provide a partially completed budget table with the item 1 total already filled in, so students only compute the three shares and the checks. Give the inches-to-feet step worked once before item 1.

Extension

Have students add a conservation scenario in which Havenmoor cuts pumping by 20 percent during drought years, and calculate how many acre-feet of stored groundwater that saves over three consecutive drought years.

ELL supports

Pre-teach water budget, evapotranspiration, runoff, and recharge with a labeled cross-section arrow diagram of a watershed. Allow items 8, 9, and 10 to be answered with the diagram plus short phrases rather than full sentences.