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Stormwater Pump Station Design Calculator

This tool allows you to input values and calculate outputs for each step in the stormwater pump station design process. Calculations are based on standard engineering formulas and assumptions. Results are approximate and should be verified by a professional engineer.

1. Calculate Design Inflow Hydrograph

Using the Rational Method for peak flow estimation: Q = C * i * A

Runoff Coefficient (C, 0-1): Rainfall Intensity (i, in/hr): Catchment Area (A, acres):

Peak Inflow (Q, cfs):

Note: For full hydrograph, assume triangular shape with base 2*Tc, peak Q. Time of Concentration (Tc, min):

2. Estimate Pump Rate, Number, and Storage Volume

Pump Rate typically matches or exceeds peak inflow. Storage Volume estimated as V = (Peak Inflow - Pump Rate) * Duration / 2 (simplified triangular).

Desired Pump Rate (cfs, use peak from Step 1): Number of Pumps: Storm Duration (hours):

Single Pump Capacity (cfs):

Estimated Storage Volume (cu ft):

3. Set Maximum Permissible Water Level in Wet Well

Typically set based on site elevation to prevent flooding.

Ground Elevation (ft): Safety Freeboard (ft):

Max Water Level (ft):

4. Determine Pump Pit Dimensions

For rectangular wet well: Area = Storage / Height.

Required Storage (cu ft, from Step 2): Wet Well Height (ft):

Wet Well Area (sq ft):

Suggested Length/Width (assuming square, ft):

5. Derive Stage-Storage Relationship

For rectangular: Storage = Area * Stage.

Wet Well Area (sq ft, from Step 4): Stage (water depth, ft):

Storage at Stage (cu ft):

6. Determine Pump Cycling Time, Calculate Usable Storage

Usable Storage = Pump Rate * Min Cycle Time / Max Starts per Hour.

Pump Rate (cfs, from Step 2): Min Cycle Time (min): Max Starts per Hour:

Cycling Time (min):

Usable Storage (cu ft):

7. Choose Trial Pump Size

Select based on capacity. Input trial size.

Trial Pump Capacity (cfs):

Use this for further calculations.

8. Calculate Total Head

Total Dynamic Head (TDH) = Static Head + Friction Losses + Minor Losses.

Static Head (ft): Friction Loss (ft): Minor Losses (ft):

Total Head (ft):

9. Locate Pump Operating Point

Simplified: Assume pump curve H = a - b*Q^2, system curve H = static + k*Q^2.

Pump Curve a (ft): Pump Curve b (ft/cfs^2): System k (ft/cfs^2): Static (ft):

Operating Flow (cfs):

Operating Head (ft):

10. Calculate Power Requirements

Brake Horsepower (BHP) = (Q * H * SG) / (3960 * Efficiency), SG=1 for water.

Flow Q (cfs): Head H (ft): Efficiency (decimal):

Power (HP):

11. Perform Routing Calculation

Simplified level pool routing: ΔS = (I - O) * Δt, new stage from stage-storage.

Average Inflow I (cfs): Outflow O (cfs): Time Step Δt (sec):

Change in Storage (cu ft):

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