Calculator inputs
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Example data table
A typical set of inputs and the corresponding outputs (illustrative).
| Case | Q0 (m³/s) | L (m) | D (mm) | Yup/Ydn (m) | Q1/Q0 | Fmin (m²) | Tank Ø (m) | T (s) |
|---|---|---|---|---|---|---|---|---|
| Baseline (defaults) | 1.20 | 3000 | 1000 | 8 / 6 | 0.00 | 15.57 | 4.45 | 489 |
| Partial change | 1.20 | 3000 | 1000 | 8 / 6 | 0.50 | 3.89 | 2.23 | 245 |
Use your project constraints for allowable surges and freeboard.
Formula used
Preliminary sizing using rigid column theory for a simple surge tank.
This calculator applies the undamped (frictionless) rigid column model for a simple surge tank connected to a conduit of length L and area f. For an instantaneous discharge change, the maximum surge amplitude is approximated by:
Y = ΔV · √( (L · f) / (g · F) )
Where ΔV = |V0 − V1|, V0 = Q0 / f, V1 = (Q1/Q0) · V0, g = 9.81 m/s², and F is the surge tank cross-sectional area.
The tool sizes the minimum area to satisfy the tighter allowable amplitude (upsurge vs downsurge):
Fmin = (L · f) / ( g · (Ycrit / ΔV)² )
The undamped oscillation period is estimated as:
T = 2π · √( (L · F) / (g · f) )
Note: This is a fast, conservative screening method. Final design typically requires transient simulation, friction damping, and surge tank throttling checks.
How to use this calculator
- Enter the steady flow rate and conduit geometry (L and D).
- Set allowable upsurge and downsurge based on site limits.
- Choose a post-event flow fraction (0 for full closure).
- Click Calculate to view results above the form.
- Download CSV or PDF for your design package if needed.
Good practice checks
- Ensure the minimum water level avoids air entry into the conduit.
- Confirm the maximum water level stays below spill/overflow limits.
- Review structural height, access, and constructability constraints.
- For pumping stations, consider pump trip and check valve dynamics.