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Hydropower

Environmental Engineering · FE Reference Handbook section

Environmental Engineering
4 formulas
10 exam-style examples
~53 min
All Environmental Engineering lectures

Core formulas for this FE topic

Definitions, applicability, units, assumptions and worked examples for each relation.

Worked exam-style examples

The four ways this section is written on the real exam — thoughts first, then equations, then substitution.

Example 1
Hydropower — solve for hydropower output — Hydropower

hydropower generation output for a dam with a given head and flow Given turbine efficiency (eta) = 0.7000; water density (rho) = 995.0 kg/m^3; gravitational acceleration (g) = 9.8100 m/s^2; flow rate through turbine (Q) = 95.0000 m^3/s; hydraulic head (H) = 29.0000 m, determine the hydropower output (P) in W.

Given

  • turbineefficiency(eta)=0.7000turbine efficiency (eta) = 0.7000
  • waterdensity(rho)=995.0kg/m3water density (rho) = 995.0 kg/m^3
  • gravitationalacceleration(g)=9.8100m/s2gravitational acceleration (g) = 9.8100 m/s^2
  • flowratethroughturbine(Q)=95.0000m3/sflow rate through turbine (Q) = 95.0000 m^3/s
  • hydraulichead(H)=29.0000mhydraulic head (H) = 29.0000 m

Find

hydropower output (P), in W

Start with the thinking

  • The governing relation printed in this handbook section is Hydropower.
  • Everything except P is given, so isolate P symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • Hydropower output from a dam or run-of-river plant depends on turbine efficiency, flow rate, and hydraulic head.

Step-by-step solution

  1. Step 1 — State the governing relation:

    P=ηρgQHP = \eta \rho g Q H
  2. Step 2 — Rearrange symbolically for P:

    P=ηρgQHP = \eta\rho g Q H
  3. Step 3 — List the givens: turbine efficiency (eta) = 0.7000, water density (rho) = 995.0 kg/m^3, gravitational acceleration (g) = 9.8100 m/s^2, flow rate through turbine (Q) = 95.0000 m^3/s, hydraulic head (H) = 29.0000 m.

  4. Step 4 — Substitute the given values:

    P=0.7000995.09.810095.000029.0000P = 0.7000995.0 9.8100 95.0000 29.0000
  5. Step 5 — Evaluate:

    P=18823992 WP = 18823992\ \text{W}
  6. Step 6 — Check: returning P = 18,823,992 W to

    P=ηρgQHP = \eta \rho g Q H

    reproduces the given quantities, and both sides carry the same units.

Answer:
P=18823992 WP = 18823992\ \text{W}

Why the other options are there

  • 37,647,984 — kept a factor of two that cancels in the correct rearrangement.
  • 9,411,996 — dropped that same factor in the other direction.
  • 20,706,391 — rounded an intermediate value before the final step.

Reference: FE Handbook — Hydropower

Example 2
Hydropower — solve for flow rate through turbine — Hydropower (2)

hydropower plant power output calculation from turbine efficiency Given turbine efficiency (eta) = 0.7200; water density (rho) = 997.0 kg/m^3; gravitational acceleration (g) = 9.8100 m/s^2; hydraulic head (H) = 178.0 m; hydropower output (P) = 42,721,900 W, determine the flow rate through turbine (Q) in m^3/s.

Given

  • turbineefficiency(eta)=0.7200turbine efficiency (eta) = 0.7200
  • waterdensity(rho)=997.0kg/m3water density (rho) = 997.0 kg/m^3
  • gravitationalacceleration(g)=9.8100m/s2gravitational acceleration (g) = 9.8100 m/s^2
  • hydraulichead(H)=178.0mhydraulic head (H) = 178.0 m
  • hydropoweroutput(P)=42,721,900Whydropower output (P) = 42,721,900 W

Find

flow rate through turbine (Q), in m^3/s

Start with the thinking

  • The governing relation printed in this handbook section is Hydropower.
  • Everything except Q is given, so isolate Q symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • Hydropower output from a dam or run-of-river plant depends on turbine efficiency, flow rate, and hydraulic head.

Step-by-step solution

  1. Step 1 — State the governing relation:

    P=ηρgQHP = \eta \rho g Q H
  2. Step 2 — Rearrange symbolically for Q:

    Q=PηρgHQ = \dfrac{P}{\eta\rho g H}
  3. Step 3 — List the givens: turbine efficiency (eta) = 0.7200, water density (rho) = 997.0 kg/m^3, gravitational acceleration (g) = 9.8100 m/s^2, hydraulic head (H) = 178.0 m, hydropower output (P) = 42,721,900 W.

  4. Step 4 — Substitute the given values:

    Q=427219000.7200997.09.8100178.0Q = \dfrac{42721900}{0.7200997.0 9.8100 178.0}
  5. Step 5 — Evaluate:

    Q = 34.0827\ \text{m^3/s}
  6. Step 6 — Check: returning Q = 34.0827 m^3/s to

    P=ηρgQHP = \eta \rho g Q H

    reproduces the given quantities, and both sides carry the same units.

Answer:
Q = 34.0827\ \text{m^3/s}

Why the other options are there

  • 68.1654 — kept a factor of two that cancels in the correct rearrangement.
  • 17.0413 — dropped that same factor in the other direction.
  • 37.4910 — rounded an intermediate value before the final step.

Reference: FE Handbook — Hydropower

Example 3
Hydropower — solve for hydraulic head — Hydropower (3)

run-of-river hydropower output estimate Given turbine efficiency (eta) = 0.8600; water density (rho) = 993.5 kg/m^3; gravitational acceleration (g) = 9.8100 m/s^2; flow rate through turbine (Q) = 207.0 m^3/s; hydropower output (P) = 285,047,900 W, determine the hydraulic head (H) in m.

Given

  • turbineefficiency(eta)=0.8600turbine efficiency (eta) = 0.8600
  • waterdensity(rho)=993.5kg/m3water density (rho) = 993.5 kg/m^3
  • gravitationalacceleration(g)=9.8100m/s2gravitational acceleration (g) = 9.8100 m/s^2
  • flowratethroughturbine(Q)=207.0m3/sflow rate through turbine (Q) = 207.0 m^3/s
  • hydropoweroutput(P)=285,047,900Whydropower output (P) = 285,047,900 W

Find

hydraulic head (H), in m

Start with the thinking

  • The governing relation printed in this handbook section is Hydropower.
  • Everything except H is given, so isolate H symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • Hydropower output from a dam or run-of-river plant depends on turbine efficiency, flow rate, and hydraulic head.

Step-by-step solution

  1. Step 1 — State the governing relation:

    P=ηρgQHP = \eta \rho g Q H
  2. Step 2 — Rearrange symbolically for H:

    H=PηρgQH = \dfrac{P}{\eta\rho g Q}
  3. Step 3 — List the givens: turbine efficiency (eta) = 0.8600, water density (rho) = 993.5 kg/m^3, gravitational acceleration (g) = 9.8100 m/s^2, flow rate through turbine (Q) = 207.0 m^3/s, hydropower output (P) = 285,047,900 W.

  4. Step 4 — Substitute the given values:

    H=2850479000.8600993.59.8100207.0H = \dfrac{285047900}{0.8600993.5 9.8100 207.0}
  5. Step 5 — Evaluate:

    H=164.3 mH = 164.3\ \text{m}
  6. Step 6 — Check: returning H = 164.3 m to

    P=ηρgQHP = \eta \rho g Q H

    reproduces the given quantities, and both sides carry the same units.

Answer:
H=164.3 mH = 164.3\ \text{m}

Why the other options are there

  • 328.6 — kept a factor of two that cancels in the correct rearrangement.
  • 82.1452 — dropped that same factor in the other direction.
  • 180.7 — rounded an intermediate value before the final step.

Reference: FE Handbook — Hydropower

Example 4
Hydropower — solve for hydropower output (case 2) — Hydropower (4)

hydropower generation output for a dam with a given head and flow Given turbine efficiency (eta) = 0.8500; water density (rho) = 990.5 kg/m^3; gravitational acceleration (g) = 9.8100 m/s^2; flow rate through turbine (Q) = 470.0 m^3/s; hydraulic head (H) = 40.0000 m, determine the hydropower output (P) in W.

Given

  • turbineefficiency(eta)=0.8500turbine efficiency (eta) = 0.8500
  • waterdensity(rho)=990.5kg/m3water density (rho) = 990.5 kg/m^3
  • gravitationalacceleration(g)=9.8100m/s2gravitational acceleration (g) = 9.8100 m/s^2
  • flowratethroughturbine(Q)=470.0m3/sflow rate through turbine (Q) = 470.0 m^3/s
  • hydraulichead(H)=40.0000mhydraulic head (H) = 40.0000 m

Find

hydropower output (P), in W

Start with the thinking

  • The governing relation printed in this handbook section is Hydropower.
  • Everything except P is given, so isolate P symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • Hydropower output from a dam or run-of-river plant depends on turbine efficiency, flow rate, and hydraulic head.

Step-by-step solution

  1. Step 1 — State the governing relation:

    P=ηρgQHP = \eta \rho g Q H
  2. Step 2 — Rearrange symbolically for P:

    P=ηρgQHP = \eta\rho g Q H
  3. Step 3 — List the givens: turbine efficiency (eta) = 0.8500, water density (rho) = 990.5 kg/m^3, gravitational acceleration (g) = 9.8100 m/s^2, flow rate through turbine (Q) = 470.0 m^3/s, hydraulic head (H) = 40.0000 m.

  4. Step 4 — Substitute the given values:

    P=0.8500990.59.8100470.040.0000P = 0.8500990.5 9.8100 470.0 40.0000
  5. Step 5 — Evaluate:

    P=155274544 WP = 155274544\ \text{W}
  6. Step 6 — Check: returning P = 155,274,544 W to

    P=ηρgQHP = \eta \rho g Q H

    reproduces the given quantities, and both sides carry the same units.

Answer:
P=155274544 WP = 155274544\ \text{W}

Why the other options are there

  • 310,549,088 — kept a factor of two that cancels in the correct rearrangement.
  • 77,637,272 — dropped that same factor in the other direction.
  • 170,801,998 — rounded an intermediate value before the final step.

Reference: FE Handbook — Hydropower

Example 5
Hydropower — solve for flow rate through turbine (case 2) — Hydropower (5)

hydropower plant power output calculation from turbine efficiency Given turbine efficiency (eta) = 0.7500; water density (rho) = 991.5 kg/m^3; gravitational acceleration (g) = 9.8100 m/s^2; hydraulic head (H) = 192.0 m; hydropower output (P) = 82,389,700 W, determine the flow rate through turbine (Q) in m^3/s.

Given

  • turbineefficiency(eta)=0.7500turbine efficiency (eta) = 0.7500
  • waterdensity(rho)=991.5kg/m3water density (rho) = 991.5 kg/m^3
  • gravitationalacceleration(g)=9.8100m/s2gravitational acceleration (g) = 9.8100 m/s^2
  • hydraulichead(H)=192.0mhydraulic head (H) = 192.0 m
  • hydropoweroutput(P)=82,389,700Whydropower output (P) = 82,389,700 W

Find

flow rate through turbine (Q), in m^3/s

Start with the thinking

  • The governing relation printed in this handbook section is Hydropower.
  • Everything except Q is given, so isolate Q symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • Hydropower output from a dam or run-of-river plant depends on turbine efficiency, flow rate, and hydraulic head.

Step-by-step solution

  1. Step 1 — State the governing relation:

    P=ηρgQHP = \eta \rho g Q H
  2. Step 2 — Rearrange symbolically for Q:

    Q=PηρgHQ = \dfrac{P}{\eta\rho g H}
  3. Step 3 — List the givens: turbine efficiency (eta) = 0.7500, water density (rho) = 991.5 kg/m^3, gravitational acceleration (g) = 9.8100 m/s^2, hydraulic head (H) = 192.0 m, hydropower output (P) = 82,389,700 W.

  4. Step 4 — Substitute the given values:

    Q=823897000.7500991.59.8100192.0Q = \dfrac{82389700}{0.7500991.5 9.8100 192.0}
  5. Step 5 — Evaluate:

    Q = 58.8232\ \text{m^3/s}
  6. Step 6 — Check: returning Q = 58.8232 m^3/s to

    P=ηρgQHP = \eta \rho g Q H

    reproduces the given quantities, and both sides carry the same units.

Answer:
Q = 58.8232\ \text{m^3/s}

Why the other options are there

  • 117.6 — kept a factor of two that cancels in the correct rearrangement.
  • 29.4116 — dropped that same factor in the other direction.
  • 64.7055 — rounded an intermediate value before the final step.

Reference: FE Handbook — Hydropower

Example 6
Hydropower — solve for hydraulic head (case 2) — Hydropower (6)

run-of-river hydropower output estimate Given turbine efficiency (eta) = 0.8700; water density (rho) = 998.5 kg/m^3; gravitational acceleration (g) = 9.8100 m/s^2; flow rate through turbine (Q) = 271.0 m^3/s; hydropower output (P) = 51,896,400 W, determine the hydraulic head (H) in m.

Given

  • turbineefficiency(eta)=0.8700turbine efficiency (eta) = 0.8700
  • waterdensity(rho)=998.5kg/m3water density (rho) = 998.5 kg/m^3
  • gravitationalacceleration(g)=9.8100m/s2gravitational acceleration (g) = 9.8100 m/s^2
  • flowratethroughturbine(Q)=271.0m3/sflow rate through turbine (Q) = 271.0 m^3/s
  • hydropoweroutput(P)=51,896,400Whydropower output (P) = 51,896,400 W

Find

hydraulic head (H), in m

Start with the thinking

  • The governing relation printed in this handbook section is Hydropower.
  • Everything except H is given, so isolate H symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • Hydropower output from a dam or run-of-river plant depends on turbine efficiency, flow rate, and hydraulic head.

Step-by-step solution

  1. Step 1 — State the governing relation:

    P=ηρgQHP = \eta \rho g Q H
  2. Step 2 — Rearrange symbolically for H:

    H=PηρgQH = \dfrac{P}{\eta\rho g Q}
  3. Step 3 — List the givens: turbine efficiency (eta) = 0.8700, water density (rho) = 998.5 kg/m^3, gravitational acceleration (g) = 9.8100 m/s^2, flow rate through turbine (Q) = 271.0 m^3/s, hydropower output (P) = 51,896,400 W.

  4. Step 4 — Substitute the given values:

    H=518964000.8700998.59.8100271.0H = \dfrac{51896400}{0.8700998.5 9.8100 271.0}
  5. Step 5 — Evaluate:

    H=22.4715 mH = 22.4715\ \text{m}
  6. Step 6 — Check: returning H = 22.4715 m to

    P=ηρgQHP = \eta \rho g Q H

    reproduces the given quantities, and both sides carry the same units.

Answer:
H=22.4715 mH = 22.4715\ \text{m}

Why the other options are there

  • 44.9430 — kept a factor of two that cancels in the correct rearrangement.
  • 11.2357 — dropped that same factor in the other direction.
  • 24.7186 — rounded an intermediate value before the final step.

Reference: FE Handbook — Hydropower

Example 7
Hydropower — solve for hydropower output (case 3) — Hydropower (7)

hydropower generation output for a dam with a given head and flow Given turbine efficiency (eta) = 0.7700; water density (rho) = 990.5 kg/m^3; gravitational acceleration (g) = 9.8100 m/s^2; flow rate through turbine (Q) = 423.0 m^3/s; hydraulic head (H) = 154.0 m, determine the hydropower output (P) in W.

Given

  • turbineefficiency(eta)=0.7700turbine efficiency (eta) = 0.7700
  • waterdensity(rho)=990.5kg/m3water density (rho) = 990.5 kg/m^3
  • gravitationalacceleration(g)=9.8100m/s2gravitational acceleration (g) = 9.8100 m/s^2
  • flowratethroughturbine(Q)=423.0m3/sflow rate through turbine (Q) = 423.0 m^3/s
  • hydraulichead(H)=154.0mhydraulic head (H) = 154.0 m

Find

hydropower output (P), in W

Start with the thinking

  • The governing relation printed in this handbook section is Hydropower.
  • Everything except P is given, so isolate P symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • Hydropower output from a dam or run-of-river plant depends on turbine efficiency, flow rate, and hydraulic head.

Step-by-step solution

  1. Step 1 — State the governing relation:

    P=ηρgQHP = \eta \rho g Q H
  2. Step 2 — Rearrange symbolically for P:

    P=ηρgQHP = \eta\rho g Q H
  3. Step 3 — List the givens: turbine efficiency (eta) = 0.7700, water density (rho) = 990.5 kg/m^3, gravitational acceleration (g) = 9.8100 m/s^2, flow rate through turbine (Q) = 423.0 m^3/s, hydraulic head (H) = 154.0 m.

  4. Step 4 — Substitute the given values:

    P=0.7700990.59.8100423.0154.0P = 0.7700990.5 9.8100 423.0 154.0
  5. Step 5 — Evaluate:

    P=487388526 WP = 487388526\ \text{W}
  6. Step 6 — Check: returning P = 487,388,526 W to

    P=ηρgQHP = \eta \rho g Q H

    reproduces the given quantities, and both sides carry the same units.

Answer:
P=487388526 WP = 487388526\ \text{W}

Why the other options are there

  • 974,777,051 — kept a factor of two that cancels in the correct rearrangement.
  • 243,694,263 — dropped that same factor in the other direction.
  • 536,127,378 — rounded an intermediate value before the final step.

Reference: FE Handbook — Hydropower

Example 8
Hydropower — solve for flow rate through turbine (case 3) — Hydropower (8)

hydropower plant power output calculation from turbine efficiency Given turbine efficiency (eta) = 0.8500; water density (rho) = 996.5 kg/m^3; gravitational acceleration (g) = 9.8100 m/s^2; hydraulic head (H) = 43.0000 m; hydropower output (P) = 177,163,800 W, determine the flow rate through turbine (Q) in m^3/s.

Given

  • turbineefficiency(eta)=0.8500turbine efficiency (eta) = 0.8500
  • waterdensity(rho)=996.5kg/m3water density (rho) = 996.5 kg/m^3
  • gravitationalacceleration(g)=9.8100m/s2gravitational acceleration (g) = 9.8100 m/s^2
  • hydraulichead(H)=43.0000mhydraulic head (H) = 43.0000 m
  • hydropoweroutput(P)=177,163,800Whydropower output (P) = 177,163,800 W

Find

flow rate through turbine (Q), in m^3/s

Start with the thinking

  • The governing relation printed in this handbook section is Hydropower.
  • Everything except Q is given, so isolate Q symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • Hydropower output from a dam or run-of-river plant depends on turbine efficiency, flow rate, and hydraulic head.

Step-by-step solution

  1. Step 1 — State the governing relation:

    P=ηρgQHP = \eta \rho g Q H
  2. Step 2 — Rearrange symbolically for Q:

    Q=PηρgHQ = \dfrac{P}{\eta\rho g H}
  3. Step 3 — List the givens: turbine efficiency (eta) = 0.8500, water density (rho) = 996.5 kg/m^3, gravitational acceleration (g) = 9.8100 m/s^2, hydraulic head (H) = 43.0000 m, hydropower output (P) = 177,163,800 W.

  4. Step 4 — Substitute the given values:

    Q=1771638000.8500996.59.810043.0000Q = \dfrac{177163800}{0.8500996.5 9.8100 43.0000}
  5. Step 5 — Evaluate:

    Q = 495.8\ \text{m^3/s}
  6. Step 6 — Check: returning Q = 495.8 m^3/s to

    P=ηρgQHP = \eta \rho g Q H

    reproduces the given quantities, and both sides carry the same units.

Answer:
Q = 495.8\ \text{m^3/s}

Why the other options are there

  • 991.7 — kept a factor of two that cancels in the correct rearrangement.
  • 247.9 — dropped that same factor in the other direction.
  • 545.4 — rounded an intermediate value before the final step.

Reference: FE Handbook — Hydropower

Example 9
Hydropower — solve for hydraulic head (case 3) — Hydropower (9)

run-of-river hydropower output estimate Given turbine efficiency (eta) = 0.8000; water density (rho) = 991.5 kg/m^3; gravitational acceleration (g) = 9.8100 m/s^2; flow rate through turbine (Q) = 400.0 m^3/s; hydropower output (P) = 97,180,700 W, determine the hydraulic head (H) in m.

Given

  • turbineefficiency(eta)=0.8000turbine efficiency (eta) = 0.8000
  • waterdensity(rho)=991.5kg/m3water density (rho) = 991.5 kg/m^3
  • gravitationalacceleration(g)=9.8100m/s2gravitational acceleration (g) = 9.8100 m/s^2
  • flowratethroughturbine(Q)=400.0m3/sflow rate through turbine (Q) = 400.0 m^3/s
  • hydropoweroutput(P)=97,180,700Whydropower output (P) = 97,180,700 W

Find

hydraulic head (H), in m

Start with the thinking

  • The governing relation printed in this handbook section is Hydropower.
  • Everything except H is given, so isolate H symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • Hydropower output from a dam or run-of-river plant depends on turbine efficiency, flow rate, and hydraulic head.

Step-by-step solution

  1. Step 1 — State the governing relation:

    P=ηρgQHP = \eta \rho g Q H
  2. Step 2 — Rearrange symbolically for H:

    H=PηρgQH = \dfrac{P}{\eta\rho g Q}
  3. Step 3 — List the givens: turbine efficiency (eta) = 0.8000, water density (rho) = 991.5 kg/m^3, gravitational acceleration (g) = 9.8100 m/s^2, flow rate through turbine (Q) = 400.0 m^3/s, hydropower output (P) = 97,180,700 W.

  4. Step 4 — Substitute the given values:

    H=971807000.8000991.59.8100400.0H = \dfrac{97180700}{0.8000991.5 9.8100 400.0}
  5. Step 5 — Evaluate:

    H=31.2225 mH = 31.2225\ \text{m}
  6. Step 6 — Check: returning H = 31.2225 m to

    P=ηρgQHP = \eta \rho g Q H

    reproduces the given quantities, and both sides carry the same units.

Answer:
H=31.2225 mH = 31.2225\ \text{m}

Why the other options are there

  • 62.4451 — kept a factor of two that cancels in the correct rearrangement.
  • 15.6113 — dropped that same factor in the other direction.
  • 34.3448 — rounded an intermediate value before the final step.

Reference: FE Handbook — Hydropower

Example 10
Hydropower — solve for hydropower output (case 4) — Hydropower (10)

hydropower generation output for a dam with a given head and flow Given turbine efficiency (eta) = 0.8800; water density (rho) = 996.5 kg/m^3; gravitational acceleration (g) = 9.8100 m/s^2; flow rate through turbine (Q) = 9.0000 m^3/s; hydraulic head (H) = 87.0000 m, determine the hydropower output (P) in W.

Given

  • turbineefficiency(eta)=0.8800turbine efficiency (eta) = 0.8800
  • waterdensity(rho)=996.5kg/m3water density (rho) = 996.5 kg/m^3
  • gravitationalacceleration(g)=9.8100m/s2gravitational acceleration (g) = 9.8100 m/s^2
  • flowratethroughturbine(Q)=9.0000m3/sflow rate through turbine (Q) = 9.0000 m^3/s
  • hydraulichead(H)=87.0000mhydraulic head (H) = 87.0000 m

Find

hydropower output (P), in W

Start with the thinking

  • The governing relation printed in this handbook section is Hydropower.
  • Everything except P is given, so isolate P symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • Hydropower output from a dam or run-of-river plant depends on turbine efficiency, flow rate, and hydraulic head.

Step-by-step solution

  1. Step 1 — State the governing relation:

    P=ηρgQHP = \eta \rho g Q H
  2. Step 2 — Rearrange symbolically for P:

    P=ηρgQHP = \eta\rho g Q H
  3. Step 3 — List the givens: turbine efficiency (eta) = 0.8800, water density (rho) = 996.5 kg/m^3, gravitational acceleration (g) = 9.8100 m/s^2, flow rate through turbine (Q) = 9.0000 m^3/s, hydraulic head (H) = 87.0000 m.

  4. Step 4 — Substitute the given values:

    P=0.8800996.59.81009.000087.0000P = 0.8800996.5 9.8100 9.0000 87.0000
  5. Step 5 — Evaluate:

    P=6735824 WP = 6735824\ \text{W}
  6. Step 6 — Check: returning P = 6,735,824 W to

    P=ηρgQHP = \eta \rho g Q H

    reproduces the given quantities, and both sides carry the same units.

Answer:
P=6735824 WP = 6735824\ \text{W}

Why the other options are there

  • 13,471,648 — kept a factor of two that cancels in the correct rearrangement.
  • 3,367,912 — dropped that same factor in the other direction.
  • 7,409,407 — rounded an intermediate value before the final step.

Reference: FE Handbook — Hydropower

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