What are Typical d/D Design Limits?

• Many design standards limit dry-weather d/D to about 0.5 for small sewers (≤ 15 in) and 0.75 for larger sewers to ensure reserve capacity and ventilation.
• Peak or wet-weather design is often limited to d/D between about 0.7 and 0.83; for example some agencies require d/D ≤ 0.7–0.83 at peak flow to avoid chronic surcharge.