Rainfall event volume does not size a gutter or overflow.
Does knowing captured water volume establish hydraulic capacity?
Use the matching calculator
Use this decision sequence
- Use catchment plan area and an entered event rainfall depth.
- Apply only the captured share and diversion volume supplied for the scenario.
- Compare remaining event volume with entered tank space.
- Keep peak flow, drainage sizing, water quality and real performance outside this volume budget.
Keep the quantities distinct
| Quantity or assumption | How to use it |
|---|---|
| Event volume | Total water over an event. |
| Peak flow | A rate requiring additional information and a different assessment. |
| Storage space | Usable supplied capacity minus current contents. |
Worked comparison
An illustrative 100 m² catchment receiving an entered 10 mm event has 1 m³ gross rain volume. With a supplied 80% captured share and 0.1 m³ diversion, the scenario reaches 0.7 m³. If only 0.5 m³ tank space is available, 0.5 m³ is retained and 0.2 m³ exceeds that space. None of these totals states a safe pipe or gutter size.
Check before using the estimate
This is user-supplied scenario arithmetic, not weather prediction or drainage design.
All dimensions, product properties, prices and specifications in this example are illustrative arithmetic inputs. Use the values from your measured plan, selected product data sheet and supplier quote. This guide does not choose construction specifications or certify safety.
Calculation and scope checked 2026-10-04. Methods and scope.