Horizontal Velocities
Environmental Engineering · FE Reference Handbook section
Handbook notes for this section
Definitions and conditions exactly as the handbook states them.
- 1. Water Treatment—horizontal velocities should not exceed 0.5 fpm
- 2. Wastewater Treatment—no specific requirements (use the same criteria as for water)
Core formulas for this FE topic
Definitions, applicability, units, assumptions and worked examples for each relation.
This section is conceptual; there are no equations to memorise.
Worked exam-style examples
The four ways this section is written on the real exam — thoughts first, then equations, then substitution.
horizontal velocities through a rectangular sedimentation basin Given flow rate (Q) = 17,830 m^3/day; basin width (W) = 2.6000 m; basin depth (H) = 5.0000 m, determine the horizontal velocity (v_h) in m/day.
Given
Find
horizontal velocity (v_h), in m/day
Start with the thinking
- The governing relation printed in this handbook section is Horizontal Velocities.
- Everything except v_h is given, so isolate v_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.
- Horizontal velocities through a sedimentation basin must remain low enough to avoid resuspension of settled particles.
Figure 1 — schematic for Horizontal Velocities — solve for horizontal velocity — Horizontal Velocities
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange symbolically for v_h:
Step 3 — List the givens: flow rate (Q) = 17,830 m^3/day, basin width (W) = 2.6000 m, basin depth (H) = 5.0000 m.
Step 4 — Substitute the given values:
Step 5 — Evaluate:
Step 6 — Check: returning v_h = 1,372 m/day to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- 2,743 — kept a factor of two that cancels in the correct rearrangement.
- 685.8 — dropped that same factor in the other direction.
- 1,509 — rounded an intermediate value before the final step.
Reference: FE Handbook — Horizontal Velocities (sedimentation)
horizontal velocities check to prevent scour in a settling tank Given flow rate (Q) = 48,430 m^3/day; basin depth (H) = 4.0000 m; horizontal velocity (v_h) = 2,793 m/day, determine the basin width (W) in m.
Given
Find
basin width (W), in m
Start with the thinking
- The governing relation printed in this handbook section is Horizontal Velocities.
- Everything except W is given, so isolate W 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.
- Horizontal velocities through a sedimentation basin must remain low enough to avoid resuspension of settled particles.
Figure 2 — schematic for Horizontal Velocities — solve for basin width — Horizontal Velocities (2)
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange symbolically for W:
Step 3 — List the givens: flow rate (Q) = 48,430 m^3/day, basin depth (H) = 4.0000 m, horizontal velocity (v_h) = 2,793 m/day.
Step 4 — Substitute the given values:
Step 5 — Evaluate:
Step 6 — Check: returning W = 4.3349 m to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- 8.6699 — kept a factor of two that cancels in the correct rearrangement.
- 2.1675 — dropped that same factor in the other direction.
- 4.7684 — rounded an intermediate value before the final step.
Reference: FE Handbook — Horizontal Velocities (sedimentation)
horizontal velocities computed from basin cross-sectional area and flow Given flow rate (Q) = 39,170 m^3/day; basin width (W) = 3.9000 m; horizontal velocity (v_h) = 4,402 m/day, determine the basin depth (H) in m.
Given
Find
basin depth (H), in m
Start with the thinking
- The governing relation printed in this handbook section is Horizontal Velocities.
- 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.
- Horizontal velocities through a sedimentation basin must remain low enough to avoid resuspension of settled particles.
Figure 3 — schematic for Horizontal Velocities — solve for basin depth — Horizontal Velocities (3)
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange symbolically for H:
Step 3 — List the givens: flow rate (Q) = 39,170 m^3/day, basin width (W) = 3.9000 m, horizontal velocity (v_h) = 4,402 m/day.
Step 4 — Substitute the given values:
Step 5 — Evaluate:
Step 6 — Check: returning H = 2.2816 m to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- 4.5632 — kept a factor of two that cancels in the correct rearrangement.
- 1.1408 — dropped that same factor in the other direction.
- 2.5098 — rounded an intermediate value before the final step.
Reference: FE Handbook — Horizontal Velocities (sedimentation)
horizontal velocities through a rectangular sedimentation basin Given flow rate (Q) = 8,180 m^3/day; basin width (W) = 12.5000 m; basin depth (H) = 4.5000 m, determine the horizontal velocity (v_h) in m/day.
Given
Find
horizontal velocity (v_h), in m/day
Start with the thinking
- The governing relation printed in this handbook section is Horizontal Velocities.
- Everything except v_h is given, so isolate v_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.
- Horizontal velocities through a sedimentation basin must remain low enough to avoid resuspension of settled particles.
Figure 4 — schematic for Horizontal Velocities — solve for horizontal velocity (case 2) — Horizontal Velocities (4)
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange symbolically for v_h:
Step 3 — List the givens: flow rate (Q) = 8,180 m^3/day, basin width (W) = 12.5000 m, basin depth (H) = 4.5000 m.
Step 4 — Substitute the given values:
Step 5 — Evaluate:
Step 6 — Check: returning v_h = 145.4 m/day to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- 290.8 — kept a factor of two that cancels in the correct rearrangement.
- 72.7111 — dropped that same factor in the other direction.
- 160.0 — rounded an intermediate value before the final step.
Reference: FE Handbook — Horizontal Velocities (sedimentation)
horizontal velocities check to prevent scour in a settling tank Given flow rate (Q) = 38,000 m^3/day; basin depth (H) = 2.6000 m; horizontal velocity (v_h) = 3,628 m/day, determine the basin width (W) in m.
Given
Find
basin width (W), in m
Start with the thinking
- The governing relation printed in this handbook section is Horizontal Velocities.
- Everything except W is given, so isolate W 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.
- Horizontal velocities through a sedimentation basin must remain low enough to avoid resuspension of settled particles.
Figure 5 — schematic for Horizontal Velocities — solve for basin width (case 2) — Horizontal Velocities (5)
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange symbolically for W:
Step 3 — List the givens: flow rate (Q) = 38,000 m^3/day, basin depth (H) = 2.6000 m, horizontal velocity (v_h) = 3,628 m/day.
Step 4 — Substitute the given values:
Step 5 — Evaluate:
Step 6 — Check: returning W = 4.0285 m to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- 8.0570 — kept a factor of two that cancels in the correct rearrangement.
- 2.0142 — dropped that same factor in the other direction.
- 4.4313 — rounded an intermediate value before the final step.
Reference: FE Handbook — Horizontal Velocities (sedimentation)
horizontal velocities computed from basin cross-sectional area and flow Given flow rate (Q) = 36,250 m^3/day; basin width (W) = 8.0000 m; horizontal velocity (v_h) = 1,401 m/day, determine the basin depth (H) in m.
Given
Find
basin depth (H), in m
Start with the thinking
- The governing relation printed in this handbook section is Horizontal Velocities.
- 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.
- Horizontal velocities through a sedimentation basin must remain low enough to avoid resuspension of settled particles.
Figure 6 — schematic for Horizontal Velocities — solve for basin depth (case 2) — Horizontal Velocities (6)
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange symbolically for H:
Step 3 — List the givens: flow rate (Q) = 36,250 m^3/day, basin width (W) = 8.0000 m, horizontal velocity (v_h) = 1,401 m/day.
Step 4 — Substitute the given values:
Step 5 — Evaluate:
Step 6 — Check: returning H = 3.2343 m to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- 6.4686 — kept a factor of two that cancels in the correct rearrangement.
- 1.6171 — dropped that same factor in the other direction.
- 3.5577 — rounded an intermediate value before the final step.
Reference: FE Handbook — Horizontal Velocities (sedimentation)
horizontal velocities through a rectangular sedimentation basin Given flow rate (Q) = 10,660 m^3/day; basin width (W) = 9.2000 m; basin depth (H) = 3.0000 m, determine the horizontal velocity (v_h) in m/day.
Given
Find
horizontal velocity (v_h), in m/day
Start with the thinking
- The governing relation printed in this handbook section is Horizontal Velocities.
- Everything except v_h is given, so isolate v_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.
- Horizontal velocities through a sedimentation basin must remain low enough to avoid resuspension of settled particles.
Figure 7 — schematic for Horizontal Velocities — solve for horizontal velocity (case 3) — Horizontal Velocities (7)
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange symbolically for v_h:
Step 3 — List the givens: flow rate (Q) = 10,660 m^3/day, basin width (W) = 9.2000 m, basin depth (H) = 3.0000 m.
Step 4 — Substitute the given values:
Step 5 — Evaluate:
Step 6 — Check: returning v_h = 386.2 m/day to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- 772.5 — kept a factor of two that cancels in the correct rearrangement.
- 193.1 — dropped that same factor in the other direction.
- 424.9 — rounded an intermediate value before the final step.
Reference: FE Handbook — Horizontal Velocities (sedimentation)
horizontal velocities check to prevent scour in a settling tank Given flow rate (Q) = 30,670 m^3/day; basin depth (H) = 4.9000 m; horizontal velocity (v_h) = 4,423 m/day, determine the basin width (W) in m.
Given
Find
basin width (W), in m
Start with the thinking
- The governing relation printed in this handbook section is Horizontal Velocities.
- Everything except W is given, so isolate W 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.
- Horizontal velocities through a sedimentation basin must remain low enough to avoid resuspension of settled particles.
Figure 8 — schematic for Horizontal Velocities — solve for basin width (case 3) — Horizontal Velocities (8)
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange symbolically for W:
Step 3 — List the givens: flow rate (Q) = 30,670 m^3/day, basin depth (H) = 4.9000 m, horizontal velocity (v_h) = 4,423 m/day.
Step 4 — Substitute the given values:
Step 5 — Evaluate:
Step 6 — Check: returning W = 1.4151 m to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- 2.8303 — kept a factor of two that cancels in the correct rearrangement.
- 0.7076 — dropped that same factor in the other direction.
- 1.5567 — rounded an intermediate value before the final step.
Reference: FE Handbook — Horizontal Velocities (sedimentation)
horizontal velocities computed from basin cross-sectional area and flow Given flow rate (Q) = 12,450 m^3/day; basin width (W) = 19.5000 m; horizontal velocity (v_h) = 1,310 m/day, determine the basin depth (H) in m.
Given
Find
basin depth (H), in m
Start with the thinking
- The governing relation printed in this handbook section is Horizontal Velocities.
- 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.
- Horizontal velocities through a sedimentation basin must remain low enough to avoid resuspension of settled particles.
Figure 9 — schematic for Horizontal Velocities — solve for basin depth (case 3) — Horizontal Velocities (9)
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange symbolically for H:
Step 3 — List the givens: flow rate (Q) = 12,450 m^3/day, basin width (W) = 19.5000 m, horizontal velocity (v_h) = 1,310 m/day.
Step 4 — Substitute the given values:
Step 5 — Evaluate:
Step 6 — Check: returning H = 0.4874 m to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- 0.9748 — kept a factor of two that cancels in the correct rearrangement.
- 0.2437 — dropped that same factor in the other direction.
- 0.5361 — rounded an intermediate value before the final step.
Reference: FE Handbook — Horizontal Velocities (sedimentation)
horizontal velocities through a rectangular sedimentation basin Given flow rate (Q) = 32,330 m^3/day; basin width (W) = 19.6000 m; basin depth (H) = 4.4000 m, determine the horizontal velocity (v_h) in m/day.
Given
Find
horizontal velocity (v_h), in m/day
Start with the thinking
- The governing relation printed in this handbook section is Horizontal Velocities.
- Everything except v_h is given, so isolate v_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.
- Horizontal velocities through a sedimentation basin must remain low enough to avoid resuspension of settled particles.
Figure 10 — schematic for Horizontal Velocities — solve for horizontal velocity (case 4) — Horizontal Velocities (10)
Step-by-step solution
Step 1 — State the governing relation:
Step 2 — Rearrange symbolically for v_h:
Step 3 — List the givens: flow rate (Q) = 32,330 m^3/day, basin width (W) = 19.6000 m, basin depth (H) = 4.4000 m.
Step 4 — Substitute the given values:
Step 5 — Evaluate:
Step 6 — Check: returning v_h = 374.9 m/day to
reproduces the given quantities, and both sides carry the same units.
Why the other options are there
- 749.8 — kept a factor of two that cancels in the correct rearrangement.
- 187.4 — dropped that same factor in the other direction.
- 412.4 — rounded an intermediate value before the final step.
Reference: FE Handbook — Horizontal Velocities (sedimentation)