Worksheet Grade 11 Science

Coldstream Well 4: Drawdown, Total Dynamic Head, and Pump Power

A grade 11 hydraulics worksheet where students compute drawdown, specific capacity, total dynamic head, and pump horsepower for a fictional municipal well.

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

Standards

HS-ETS1-2 NGSS

Design a solution to a complex real-world problem by breaking it down into smaller, more manageable problems that can be solved through engineering.

How this material aligns: Items 3 through 7 break the pump-sizing problem into separate lift, discharge-head, friction, and efficiency stages, so students reach the motor horsepower through the smaller engineering sub-problems this standard names.

All materials for HS-ETS1-2 →

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 3 through 7 carry pressure, head, flow, and power units through the total-dynamic-head and horsepower chain, the consistent multi-step unit reasoning this standard targets.

All materials for HSN-Q.A.1 →

HSN-Q.A.3 Common Core Math

Choose a level of accuracy appropriate to limitations on measurement when reporting quantities.

How this material aligns: Item 7 asks students to report motor horsepower to a sensible precision given the estimated pump and motor efficiencies, matching reported accuracy to the inputs' limits as this standard requires.

All materials for HSN-Q.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 well drawdown and specific capacity from static and pumping water levels.
Students will build total dynamic head and convert it into water, brake, and motor horsepower.

Vocabulary

Drawdown: Drawdown is how far the water level in a well drops when a pump pulls water out. The harder and longer you pump, the bigger the drawdown gets.
Total dynamic head (TDH): Total dynamic head is the total amount of lift a pump has to provide to move water where it needs to go, adding up the height it must lift the water, the friction it must overcome in the pipes, and the pressure needed at the far end. Engineers calculate it to pick a pump that is powerful enough for the job.

Also: static water level, specific capacity, water horsepower, brake horsepower

Teacher overview

A well pump does more than lift water; it works against the depth to the water, the pressure the system must hold, and friction in the pipe at the same time. This worksheet walks students through the quantities an operator reads off a well every week, from drawdown and specific capacity down to the horsepower the motor actually has to supply. The recurring point is that the motor always works harder than the water alone, because no pump or motor is perfectly efficient.

Coldstream Well 4: Drawdown, Total Dynamic Head, and Pump Power — Grade 11 Science

Name: ____________________________ Date: ______________

Student Worksheet

Coldstream Well 4 is a fictional municipal well. Use these stated values. When the pump is off, the static water level sits 80 feet below the ground. When the pump runs at 600 gpm, the pumping water level drops to 140 feet below the ground. The pump discharges into a system held at 65 psi. Friction losses in the discharge piping are 25 feet. One psi equals 2.31 feet of head. Show your work and round sensibly.

Find the well's drawdown (pumping water level minus static water level), in feet.
Find the well's specific capacity (pumping rate divided by drawdown), in gpm per foot of drawdown.
Convert the 65 psi discharge pressure into feet of head, using 1 psi = 2.31 feet.
Build the total dynamic head (TDH) by adding the lift (the 140-foot pumping water level), the discharge head from item 3, and the 25 feet of friction losses. Give the TDH in feet.
Find the water horsepower using WHP = (flow in gpm x TDH in feet) / 3960.
The pump is 75 percent efficient. Find the brake horsepower the pump shaft needs: brake horsepower = water horsepower / 0.75.
The motor is 90 percent efficient. Find the motor input horsepower: motor horsepower = brake horsepower / 0.90. Report it to a sensible precision.
If the pump runs at 600 gpm for 18 hours in one day, how many gallons does the well deliver that day?
Over several years the well screen clogs, so drawdown grows while the pumping rate stays at 600 gpm. Explain what happens to the specific capacity and what that tells the operator.
Explain why the motor input horsepower in item 7 is larger than the water horsepower in item 5.

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: 60 ft. Drawdown = pumping water level - static water level = 140 - 80 = 60 feet.
Answer: 10 gpm per ft. Specific capacity = pumping rate / drawdown = 600 / 60 = 10 gallons per minute per foot of drawdown.
Answer: about 150 ft. 65 psi x 2.31 feet per psi = 150.15 feet, about 150 feet of head.
Answer: 315 ft. TDH = 140 (lift) + 150 (discharge head) + 25 (friction) = 315 feet.
Answer: about 47.7 hp. WHP = (600 x 315) / 3960 = 189,000 / 3960 = 47.73, about 47.7 water horsepower.
Answer: about 63.6 hp. Brake horsepower = 47.73 / 0.75 = 63.64, about 63.6 horsepower.
Answer: about 71 hp. Motor horsepower = 63.64 / 0.90 = 70.71, about 71 horsepower. The efficiencies are known to only two figures, so a two-figure answer matches the precision of the inputs.
Answer: 648,000 gal. 600 gallons per minute x 60 minutes per hour x 18 hours = 648,000 gallons.
Answer: Specific capacity falls, because the same 600 gpm now costs more drawdown. A dropping specific capacity is a warning that the well or its screen is losing efficiency and may need rehabilitation.
Answer: Some energy is lost to friction and turbulence inside the pump, and more is lost as heat in the motor. Because neither is perfectly efficient, the motor must draw more horsepower than the water horsepower that actually moves the water.

Differentiation

Support

Give students a labeled cross-section of the well showing the static level, the pumping level, and the drawdown gap, and provide the four horsepower and head formulas on a reference strip. Let them fill drawdown and specific capacity first before tackling the head and power chain.

Extension

Have students convert the motor horsepower in item 7 into kilowatts (1 horsepower is about 0.746 kilowatt), then estimate a daily energy figure for the 18-hour run and explain how a clogged well from item 9 would raise that energy use.

ELL supports

Pre-teach "static," "drawdown," "head," "friction," and "efficiency" with the labeled well cross-section and simple arrows showing water being lifted and pushed. Allow items 9 and 10 to be answered with a short sentence built from a provided sentence frame.