Street inlets and spacing: Which statements about road-surface drainage inlets are correct for urban stormwater design?

Introduction / Context:
Stormwater inlets collect runoff from streets and convey it to the underground drainage network. Correct siting and selection of inlet types (curb vs grate) reduce ponding, improve safety, and limit nuisance flooding.

Given Data / Assumptions:

• Urban roadway with kerbs and underground storm sewer.
• Typical design practice for inlet placement and types.
• Moderate rainfall intensities and standard crossfall.

Concept / Approach:
Designers place inlets at local sag points and space them periodically along grades to prevent spread of water beyond acceptable widths. Curb inlets present vertical openings in the kerb face; grate inlets accept flow through horizontal grates in the gutter flowline. Combining both can improve capture efficiency.

Step-by-Step Solution:
Evaluate (a): Low points (sags) accumulate runoff; inlets are essential there.Evaluate (b): Spacing of roughly 30–60 m on grades is typical for many urban streets (adjusted for intensity and crossfall).Evaluate (c): Curb inlets indeed have vertical openings at the kerb line.Evaluate (d): Grate inlets provide horizontal intake via grating—statement is correct.Therefore (e) All of the above is correct.

Verification / Alternative check:
Municipal design guides illustrate similar spacing ranges and distinguish curb vs grate inlet configurations, often recommending combinations at sags.

Why Other Options Are Wrong:
Individual statements (a–d) are each correct; selecting a single one would be incomplete.

Common Pitfalls:

• Ignoring sags, where inlet capacity must be highest.
• Relying only on grates where bicycle or debris concerns suggest using combination (curb + grate) inlets.

Final Answer:
All of the above