Hydraulic self-cleansing criterion: What is a commonly adopted self-cleansing velocity for water flowing in pipelines to avoid deposition?

Introduction / Context:
Self-cleansing velocity is the minimum velocity that keeps particles from settling in a conduit. For clean water pipelines, maintaining adequate velocity prevents sediment accumulation, biofilm growth, and service degradation.

Given Data / Assumptions:

• Clean water or relatively low-solids flow in closed pipelines.
• Typical municipal practice values.
• Objective: avoid deposition under normal operation.

Concept / Approach:
Empirical practice suggests about 1.0 m/s as a practical target for water pipelines to discourage deposition and maintain freshness. Higher velocities increase headloss and energy consumption, whereas lower velocities may allow settling and growth.

Step-by-Step Solution:
1) Identify the operational trade-off between energy use and cleanliness.2) Note that 1.0 m/s is a widely cited benchmark for potable water mains.3) Choose 1.00 m/s as the self-cleansing velocity.

Verification / Alternative check:
Network design guides often recommend 0.6–1.0 m/s minimums, with 1.0 m/s a convenient round target for routine flushing and distribution performance.

Why Other Options Are Wrong:
0.25 or 0.50 m/s: Typically too low; risk of deposition increases.2.00 or 1.75 m/s: Possible for scouring/line flushing but not economical as a continuous design minimum.

Common Pitfalls:

• Confusing self-cleansing velocity of water pipelines with that of sanitary sewers (which consider grit and organics).
• Designing to excessive velocities that waste energy.

Final Answer:
1.00 m/s