Ready to calculate
Calculator Inputs
Example Data Table
| Scenario | Aquifer | K (m/day) | b (m) | H0 (m) | Hw (m) | R (m) | rw (m) | Wells | Safety | Typical use |
|---|---|---|---|---|---|---|---|---|---|---|
| Baseline pit | Confined | 10 | 8 | 12 | 6 | 250 | 0.25 | 1 | 1.20 | Small excavation with a single sump or wellpoint line. |
| Higher permeability | Confined | 25 | 8 | 12 | 6 | 250 | 0.25 | 2 | 1.25 | Gravelly strata requiring increased pumping capacity. |
| Unconfined drawdown | Unconfined | 8 | — | 9 | 4 | 200 | 0.30 | 3 | 1.30 | Shallow water table control around open cuts. |
Formula Used
This calculator uses steady, radial flow approximations commonly applied for preliminary dewatering sizing. The flow rate depends on conductivity, drawdown, and the logarithmic term ln(R/r).
- Confined aquifer (Thiem): Q = 2π · K · b · (H0 − Hw) / ln(R/r)
- Unconfined aquifer (Dupuit): Q = π · K · (H0² − Hw²) / ln(R/r)
Advanced options apply simple multipliers for anisotropy and partial penetration, plus a safety factor for design capacity. Use detailed hydrogeologic analysis for final design and compliance.
How to Use This Calculator
- Choose aquifer condition based on stratigraphy and monitoring data.
- Enter conductivity from tests, then set heads H0 and Hw.
- Set radii R and rw using geometry and pumping test guidance.
- Adjust anisotropy, penetration ratio, and number of wells if needed.
- Press Calculate, review total and design inflow, then export.
Export Options
After a successful calculation, use the buttons in the results panel to download CSV and PDF reports. Exports capture your inputs, selected model, and computed inflow values.
Groundwater Inflow Planning Notes
Key inputs that drive inflow
Inflow estimates depend heavily on hydraulic conductivity, drawdown, and geometry. For sandy strata, K often ranges from 1 to 50 m/day, while gravels can exceed 100 m/day. A small increase in drawdown can materially increase the required pumping rate.
Selecting confined or unconfined behavior
Confined conditions assume a saturated thickness b controls flow capacity, so b directly scales discharge. Unconfined conditions use squared heads, so changes near the water table can dominate. When field data is limited, compare both modes to bracket expected inflow.
Interpreting radius terms
The logarithmic term ln(R/r) is a sensitivity hotspot. If R is only ten times r, ln(R/r) is about 2.30, producing higher flow than a larger influence radius. Use pumping tests or monitoring wells to refine R and avoid oversizing.
From computed flow to pump selection
Convert design inflow to practical units before procurement. For example, 20 L/s equals 72 m³/hr and may require multiple pumps for redundancy. Include head losses from discharge piping, elevation lift, and treatment systems when selecting pump curves.
Managing uncertainty during construction
Dewatering performance can degrade due to clogging, drawdown interference, or seasonal recharge. Safety factors help, but monitoring is essential: track piezometric levels daily and compare to targets. If inflow rises, add standby capacity and reassess assumptions for K and effective radius.
FAQs
1) What is hydraulic conductivity in this calculator?
Hydraulic conductivity (K) represents how easily water flows through soil. Higher K means higher inflow for the same drawdown, so confirm K using field tests whenever possible.
2) How do I choose radius of influence R?
Use pumping test interpretation or monitoring well response when available. If estimating, start with conservative values and run scenarios; smaller R values typically increase computed inflow.
3) Why must Hw be lower than H0?
H0 is the initial head and Hw is the target head at the excavation or well. Dewatering requires drawdown, so Hw must be lower to create a driving gradient.
4) When should I use the trench method?
Use it for long, narrow excavations where inflow behaves more like a slot than a single well. The calculator approximates a trench using an equivalent radius based on plan area.
5) Does the well count simply multiply the flow?
This tool scales inflow by the number of wells for preliminary sizing. In practice, well interference can reduce per-well performance, so confirm spacing with field data or detailed modeling.
6) What does partial penetration change?
Partial penetration reduces effective inflow capture compared to a fully penetrating screen. The calculator applies a conservative correction based on the penetration ratio to reflect reduced efficiency.
7) Is this suitable for final dewatering design?
It is intended for planning and comparison of scenarios. Final design should incorporate site investigations, pumping tests, groundwater chemistry, and method statements aligned with local requirements.