Storm 2

Integrated Stormwater Pump Station Design Calculator (Metric MKS)

This tool integrates the stormwater pump station design steps using the Metric MKS system. Outputs from earlier steps can automatically populate inputs for later steps. Calculations use standard engineering formulas (e.g., Rational Method for inflow, simplified hydrograph routing). Results are approximate—consult a professional engineer for real designs.

Step 1: Calculate Design Inflow Hydrograph

Explanation: Use the Rational Method for peak flow: Q = C × i × A / 360 (Q in m³/s, C is runoff coefficient, i is rainfall intensity in mm/hr, A is area in hectares). For a full hydrograph, assume a triangular shape with base = 2 × Tc (time of concentration).

Runoff Coefficient (C, 0-1): Rainfall Intensity (i, mm/hr): Catchment Area (A, hectares): Time of Concentration (Tc, min):

Peak Inflow (Q, m³/s):

Hydrograph base duration: 2 × Tc minutes.

Step 2: Estimate Pump Rate, Number, and Storage Volume

Explanation: Pump rate should match or exceed peak inflow. Number of pumps for redundancy. Storage volume estimated: V ≈ (Peak Inflow - Pump Rate) × Storm Duration × 3600 / 2 (in m³, triangular hydrograph).

Peak Inflow (m³/s, from Step 1): Desired Total Pump Rate (m³/s): Number of Pumps: Storm Duration (hours):

Single Pump Capacity (m³/s):

Estimated Storage Volume (m³):

Step 3: Set Maximum Permissible Water Level in Wet Well

Explanation: Max level = Ground Elevation - Freeboard, to prevent flooding. Freeboard typically 0.3-1 m.

Ground Elevation (m): Safety Freeboard (m):

Max Water Level (m):

Step 4: Determine Pump Pit Dimensions

Explanation: For rectangular wet well, base area = Required Storage / Effective Height. Assume square shape. Effective height is from sump bottom to max level.

Required Storage (m³, from Step 2): Wet Well Height (m, effective):

Wet Well Base Area (m²):

Suggested Side Length (m, square):

Step 5: Derive Stage-Storage Relationship

Explanation: For prismatic wet well: Storage Volume = Base Area × Stage (in m³). Linear relationship.

Wet Well Base Area (m², from Step 4): Stage (water depth, m):

Storage at Given Stage (m³):

Use to verify or plot the relationship.

Step 6: Determine Pump Cycling Time, Calculate Usable Storage

Explanation: Cycle time = 60 / Max Starts per Hour. Usable storage = Pump Rate × Min Cycle Time × 60 (in m³, between start/stop levels).

Total Pump Rate (m³/s, from Step 2): Min Cycle Time (min, typically 5-15): Max Starts per Hour (typically 4-10):

Cycle Time (min):

Usable Storage (m³):

Ensure total storage > usable storage.

Step 7: Choose Trial Pump Size

Explanation: Select based on single pump capacity from Step 2. Refine in later steps.

Trial Single Pump Capacity (m³/s, from Step 2):

Proceed to Step 8 with this value.

Step 8: Calculate Total Head

Explanation: Total Dynamic Head (TDH) = Static Lift + Friction Losses + Minor Losses (in meters). Use Darcy-Weisbach or Hazen-Williams for friction (simplified input).

Static Lift (m): Friction Losses (m): Minor Losses (m):

Total Dynamic Head (m):

Step 9: Locate Pump Operating Point

Explanation: Intersection of pump curve (H = a - b×Q²) and system curve (H = Static + k×Q²). Solve for Q = sqrt( (a - Static) / (b + k) ), H in meters, Q in m³/s.

Pump Curve Coefficient a (m, shutoff head): Pump Curve Coefficient b (m/(m³/s)²): System Loss Coefficient k (m/(m³/s)²): Static Head (m, from Step 8):

Operating Flow (Q, m³/s):

Operating Head (H, m):

Step 10: Calculate Power Requirements

Explanation: Power (kW) = (Q × H × ρ × g) / (1000 × Efficiency), where ρ=1000 kg/m³ for water, g=9.81 m/s², Q in m³/s, H in m.

Flow Q (m³/s, from Step 9): Head H (m, from Step 9): Pump Efficiency (decimal, 0-1):

Required Power (kW):

Select motor with safety factor (e.g., 1.15 × kW).

Step 11: Perform Routing Calculation

Explanation: Simplified level pool routing: ΔStorage = (Average Inflow - Outflow) × Δt (in m³). Use for simulation; repeat for full hydrograph.

Average Inflow (m³/s, e.g., from Step 1): Outflow (m³/s, pump rate): Time Step Δt (seconds):

Change in Storage (m³):

For full routing, use software like SWMM; this is a single-step example.