Dewatering Pump Hour calculations

Dewatering Calculator tool

Excavation Inflow • Rainfall • Pump Selection • TDH • Sump Storage • Well-Point Screening

Civil Engineering Design-Support Tool

1. Project & Excavation Inputs

Excavation Length, L (m)

Excavation Width, B (m)

Excavation Depth, D (m)

Observed Fill Time (min) Used for preliminary observed inflow estimation.

Soil / Aquifer Condition Gravel / Very High Permeability Sand / High Permeability Silty Sand / Medium Clay / Low Permeability Fractured Rock / Variable

Required Dewatering Method Auto Screening Sump & Pump Well-Point Deep Well

2. Rainfall & Catchment Contribution

Rainfall Intensity (mm/hr)

Catchment Area (m²)

Runoff Coefficient, C

Rainfall Safety Factor

Q_rain = P × A × C / 1000
where P = rainfall intensity in mm/hr.

3. Groundwater / Seepage Inputs

Groundwater Contribution (m³/hr) Enter a hydrogeological estimate if available.

Seepage Safety Factor

Initial Water Level Above Formation (m)

Desired Sump Operating Depth (m)

4. Pump Selection & Total Dynamic Head

Pump Motor Power per Unit (HP)

Pump Efficiency (%)

Static Lift (m)

Discharge Pipe Length (m)

Pipe Internal Diameter (mm)

Minor Loss Head (m)

Friction Loss Head (m) Use pump-system calculation or pipe-loss analysis.

Required Pump Capacity Margin

TDH = Static Head + Friction Head + Minor-Loss Head

5. Duty / Standby Philosophy

Number of Duty Pumps

Number of Standby Pumps

Standby pumps are a reliability provision. Final standby requirements should follow project specifications, risk assessment and the approved dewatering method statement rather than being treated as a universal numerical codal requirement.

6. Concrete-Pour Protection

Concrete Placement Duration (hr)

Additional Protection After Pour (hr)

Required Freeboard / Water-Control Margin (m)

Temporary Storage Target (hr)

7. Well-Point Screening Inputs

Indicative Well-Point Capacity (m³/hr/point)

Well-Point System Safety Factor

Actual well-point design requires soil permeability, aquifer thickness, groundwater level, well spacing, filter characteristics, drawdown requirements and pump/vacuum characteristics. The calculation below is only a screening estimate.

8. Dewatering System Schematic

9. Design Summary

Enter the design data and calculate.

Excavation Volume

—

Estimated Inflow

—

Pump / Unit

—

Total Duty Capacity

—

10. Detailed Engineering Calculation

The detailed calculation will appear here after the design is calculated.

11. Sump Storage Check

Calculate the system to obtain sump-storage requirements.

12. Well-Point Screening

Calculate the system to obtain well-point screening.

13. Engineering Warnings & Checks

• Calculation not yet performed.

14. Dewatering Design Guidance

14.1 Basic Water Balance

Q_design = SF × (Q_groundwater + Q_rainfall + Q_other)

The dewatering system should have sufficient effective pumping capacity to control the design inflow while maintaining the required excavation water level.

14.2 Total Dynamic Head

TDH = H_static + H_friction + H_minor

Pump selection should ultimately be made from the manufacturer's pump curve at the calculated operating point, rather than from motor horsepower alone.

14.3 Pump Hydraulic Power

P = ρgQH / η

where ρ is water density, g is gravitational acceleration, Q is discharge in m³/s, H is TDH in metres and η is overall pump efficiency.

14.4 Concrete-Pour Protection

During critical concreting operations, groundwater should not be allowed to wash cement paste, disturb reinforcement, contaminate the concrete placement zone or cause instability of the excavation formation. The required pumping duration should therefore include the actual pour duration plus the specified post-pour protection period.

15. Dewatering — Do's

• Measure actual groundwater inflow wherever practical.
• Keep at least one operational backup arrangement for critical works.
• Check pump performance at the actual TDH.
• Provide adequate discharge routing and erosion protection.
• Monitor excavation stability and piping/boiling.
• Protect pumps from sediment and debris.
• Maintain emergency power where loss of pumping can affect safety.
• Monitor groundwater levels outside the excavation where settlement could be a concern.

16. Dewatering — Don'ts

• Do not select pumps solely by HP rating.
• Do not ignore friction and minor losses.
• Do not assume rainfall contribution is zero during monsoon operations.
• Do not discharge muddy water without appropriate sediment control.
• Do not place sumps where pumping can undermine foundations or slopes.
• Do not assume well points will work effectively in every soil.
• Do not rely on a single pump for critical concrete operations.
• Do not use this preliminary calculator as a substitute for detailed hydrogeological design.

SVGYogiPWD Dewatering Design Suite
Preliminary engineering design-support calculator. Final dewatering arrangement shall be verified against project specifications, site investigation, groundwater conditions, approved method statement, pump manufacturer's performance curves and applicable standards.