Water supply method based on elevation difference:\r When the reduced level (RL) of the water source is higher than the RL of the consumer's location, how is water generally supplied to the distribution system?

Introduction / Context:
In water supply engineering, choosing the conveyance method depends heavily on topography. If the water source sits at a higher elevation than the service area, gravity can be used to deliver flow without mechanical pumping. This question checks understanding of when gravity systems are appropriate and why they are preferred when feasible.

Given Data / Assumptions:

• The reduced level (RL) of the source is higher than the RL of the consumer's location.
• Continuous supply is desired with reliability and energy efficiency.
• Head losses from friction and minor losses are manageable within the available static head.

Concept / Approach:
A gravity system relies on potential energy due to elevation difference. Available head (H_avail) equals elevation head minus head losses in pipes and appurtenances. If H_avail remains positive at required flows and pressures, no pumps are needed. Gravity systems minimize operating costs and maintenance tied to electromechanical equipment.

Step-by-Step Solution:
Identify that source RL > demand RL provides potential energy for flow.Estimate head losses: H_losses = friction loss + minor losses; ensure H_source - H_losses - H_min_pressure > 0.Conclude supply by gravity is feasible and preferred.Recognize pumping is unnecessary when elevation head suffices to meet service pressures.

Verification / Alternative check:
Hydraulic grade line (HGL) plotting from source to consumer shows a downward slope that stays above required service pressure line. If the HGL remains above minimum pressure nodes, gravity-only is confirmed.

Why Other Options Are Wrong:

• By a pumping system: pumps are needless if gravity head is adequate.
• Combination of pumping and gravity: used when some zones are higher or distant; not required under the stated condition.
• “All of these” and “None of these” do not reflect the specific topographic advantage given.

Common Pitfalls:

• Ignoring friction losses that might reduce available head in long mains.
• Forgetting that local high points can create air pockets or pressure deficits even in overall downhill alignments.

Final Answer:
By a gravitational (gravity) system