Plan lock operations faster with clear inputs, unit conversions, and checks built-in. See time, net discharge, and cycle estimates instantly, then export cleanly today.
These examples are illustrative. Always verify discharge conditions on site.
| Case | Volume method | Volume to empty (m³) | Outflow model | Raw outflow (m³/s) | Loss factor | Inflow (m³/s) | Net discharge (m³/s) | Emptying time (min) |
|---|---|---|---|---|---|---|---|---|
| A | Known volume | 12,000 | Direct | 2.80 | 0.90 | 0.00 | 2.52 | 79.37 |
| B | Area × level drop | 9,000 | Orifice estimate | 3.10 | 0.85 | 0.05 | 2.585 | 58.03 |
| C | Known volume | 5,500 | Direct | 1.60 | 0.92 | 0.02 | 1.452 | 63.10 |
The calculator estimates emptying time from an effective net discharge:
If you select “Area × level drop”, the drained volume is:
If you select “Orifice equation”, the outflow estimate is:
Lock emptying time affects vessel scheduling, gate operations, and temporary works planning. A realistic drain time also supports safe sequencing for inspections, dewatering pumps, and access control around chambers and culverts. This calculator focuses on transparent inputs so teams can review assumptions quickly.
Start with the volume to be drained. If drawings provide chamber volume, enter it directly. If not, measure plan area and the level drop (for example, 3,000 m² area and a 3 m drop gives 9,000 m³). Next, confirm discharge conditions: outlet count, diameter, and an estimated average head during emptying. Typical discharge coefficients range from 0.6 to 0.8.
Field flow tests often give raw discharge, but valves, bends, and friction reduce performance. Apply a loss factor (η) to convert raw outflow to effective outflow (Qeff = η·Qout). If seepage or backflow exists, enter an inflow rate and compute net discharge (Qnet = Qeff − Qin). Net discharge must remain positive for emptying.
Suppose a lock needs to drain 12,000 m³. With 2.80 m³/s raw outflow and η = 0.90, effective outflow is 2.52 m³/s. With negligible inflow, the predicted emptying time is about 79.4 minutes. If inflow increases to 0.10 m³/s, net discharge becomes 2.42 m³/s and time rises to about 82.6 minutes. Small inflows can noticeably change schedules.
Use conservative heads and loss factors when conditions are uncertain. Confirm outlet dimensions, screen blockage risk, and allowable drawdown rates. If using the orifice estimate, treat it as a screening value and validate against commissioning data. Export CSV/PDF outputs to document assumptions for approvals and shift handovers.
It is a multiplier (0–1) that reduces raw discharge to reflect friction, valve losses, partial opening, and non‑ideal flow. Use lower values when field conditions are uncertain.
Use known volume when drawings or surveys provide it. Use area × level drop when volume is not available and the chamber cross‑section is approximately uniform over the drained range.
A common approximation is half of the starting head if the head decreases roughly linearly. If the head varies differently, use a conservative lower average and verify with measurements.
Leakage, backflow, or connected water pathways can add water while draining. Including inflow produces a net discharge and prevents overly optimistic emptying times.
The chamber will not empty under those conditions. Increase effective outflow, reduce inflow, or revise assumptions (loss factor, head, or outlet settings) before planning operations.
They are best for planning and preliminary checks. Final design should use project hydraulic models, verified coefficients, and operational constraints such as allowable drawdown rates.
Exports help document inputs, assumptions, and calculated times for reviews. They are useful for permits, method statements, shift handover notes, and comparing scenarios consistently.
Use verified inputs; results support safe construction planning always.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.