Calculate runoff, void storage, and trench dimensions accurately. Test scenarios using clear inputs and outputs. Support smarter drainage planning with transparent, practical field calculations.
| Scenario | Catchment Area (m²) | Rainfall (mm) | Runoff Coefficient | Length (m) | Width (m) | Depth (m) | Void Ratio |
|---|---|---|---|---|---|---|---|
| Small Lot | 250 | 30 | 0.75 | 8 | 1.2 | 1.0 | 0.35 |
| Parking Edge | 500 | 40 | 0.85 | 12 | 1.5 | 1.2 | 0.40 |
| Industrial Strip | 900 | 50 | 0.90 | 18 | 2.0 | 1.4 | 0.42 |
1. Runoff Volume
Runoff Volume = Catchment Area × (Rainfall / 1000) × Runoff Coefficient
2. Bottom Area
Bottom Area = Trench Length × Trench Width
3. Sidewall Area
Sidewall Area = 2 × (Length + Width) × Media Depth × Sidewall Factor
4. Effective Infiltration Area
Effective Infiltration Area = Bottom Area + Sidewall Area
5. Usable Storage Volume
Usable Storage = Length × Width × Media Depth × Void Ratio
6. Infiltration Capacity During Drawdown
Infiltration Capacity = Effective Area × (Soil Infiltration Rate / 1000) × Drawdown Hours
7. Required Storage
Required Storage = max(0, Runoff Volume − Infiltration Capacity)
8. Factored Required Storage
Factored Required Storage = Required Storage × Safety Factor
Enter the contributing catchment area and choose a realistic runoff coefficient.
Add the design rainfall depth for the storm event you want to test.
Fill in trench geometry, including length, width, media depth, and freeboard.
Enter the aggregate void ratio and the verified soil infiltration rate.
Use the drawdown time and safety factor to reflect project requirements.
Submit the form to review runoff volume, trench storage, infiltration capacity, and design adequacy.
Use the graph and export buttons to save the result for reporting.
This calculator helps estimate infiltration trench performance for construction drainage planning. It combines runoff generation, trench storage, and soil infiltration capacity in one workflow. That makes it useful during concept design, feasibility checks, and quick comparison studies.
The tool starts with drainage demand from the contributing catchment. It then compares that demand with available void storage inside the trench and the amount of water that can infiltrate during the selected drawdown period. The result shows whether the proposed trench geometry appears adequate under the chosen assumptions.
Field conditions rarely match perfect laboratory values. Clogging risk, soil variability, sediment loading, and installation tolerances can reduce real performance. The safety factor increases the required storage volume so the design review remains conservative and more practical for site decisions.
If usable storage exceeds the factored required storage, the section is marked adequate. If the storage margin is negative, the trench may need greater length, width, depth, or improved infiltration conditions. The recommended plan area and equivalent length provide quick guidance for resizing.
Final trench sizing should still reflect local standards, groundwater separation, utility clearances, inspection access, pretreatment needs, and overflow routing. Use verified infiltration testing and project criteria before issuing final drawings or specifications.
It estimates runoff volume, trench storage, infiltration capacity, and a basic adequacy check. It also suggests the plan area needed when the current trench does not provide enough usable storage.
Void ratio represents the portion of aggregate volume that can actually store water. A lower void ratio means less usable storage, so trench dimensions may need to increase for the same runoff target.
It is the fraction of rainfall expected to become runoff. Hard surfaces usually have higher values, while landscaped areas often produce lower runoff. Use project-appropriate values from accepted design references.
Drawdown time limits how long stored water is allowed to infiltrate. A longer drawdown period increases potential infiltration volume, while a shorter period makes the design more demanding.
It lets you partially include sidewall infiltration in the effective infiltration area. Designers may reduce this factor when sidewall contribution is uncertain or when clogging risk is expected.
No. It is a screening and planning tool. Final design should also consider local codes, groundwater elevation, soil testing, pretreatment, structural requirements, access, and overflow routing.
Increase trench dimensions, improve infiltration assumptions only when justified, reduce the contributing area, or add upstream controls. The recommended plan area helps guide a revised layout quickly.
Yes. The page includes a CSV export for tabular data and a PDF export for a quick report copy. These options help with documentation and design review records.
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.