Egg-shaped sewers (new section): If D denotes the diameter of the upper circular portion, what is the overall vertical depth of the “new egg-shaped” sewer section expressed as a multiple of D?

Introduction / Context:
Egg-shaped sewer sections are used where wide flow variation is expected, because the shape gives better velocity at low flows and adequate capacity at peak flows. The “new egg-shaped” profile has standardized proportions, and designers often need the overall depth in terms of the upper circular diameter D.

Given Data / Assumptions:

• Section is the standardized “new egg-shaped” sewer.
• D denotes the diameter of the upper circular portion (the crown).
• We seek the overall vertical depth as a multiple of D.

Concept / Approach:

Standard proportion charts (commonly used in sewer design handbooks) provide fixed geometric ratios for old and new egg-shaped sections. The new egg-shaped section is slightly “deeper” than the old type to enhance low-flow hydraulics. The overall depth is tabulated relative to the crown diameter D and does not vary with hydraulic conditions; it is purely geometric.

Step-by-Step Solution:

Verification / Alternative check:

Comparing with the old egg-shaped section (shallower), the new egg-shaped overall depth is larger, in line with the 1.625 D standard ratio used in many civil engineering references and competitive examination keys.

Why Other Options Are Wrong:

1.250 D, 1.350 D, and 1.425 D are too small for the new egg-shaped profile; 1.500 D corresponds to other egg-shaped conventions or rules of thumb, not the standardized new egg-shaped geometry.

Common Pitfalls:

Confusing “old” versus “new” egg-shaped proportions; mixing up the crown diameter with equivalent circular diameter for capacity; or assuming ratios vary with hydraulic slope (they do not—these are geometric).

Final Answer:

1.625 D