In surface hydrology, who originally enunciated the Unit Hydrograph theory that relates excess rainfall of unit depth to direct runoff hydrograph at a watershed outlet?

Introduction / Context:
The Unit Hydrograph is a cornerstone concept in engineering hydrology. It provides a linear-response tool that converts a specific depth of effective rainfall over a catchment into a direct runoff hydrograph at the outlet, enabling design flood estimations and storm hydrograph synthesis.

Given Data / Assumptions:

• The question asks for the original proponent of the Unit Hydrograph theory.
• Assumes familiarity with basic hydrology terms like excess rainfall, direct runoff, and watershed response.
• Historical attributions are important for exam recall.

Concept / Approach:
The Unit Hydrograph assumes linearity and time invariance of the catchment response for small storms. The original method describes a 1 cm (or 1 inch) effective rainfall pulse of specified duration and the resulting runoff hydrograph.

Step-by-Step Solution:
Identify key hydrology pioneers associated with runoff theory and hydrograph analysis.Robert E. Horton is known for infiltration and overland flow concepts, not for enunciating the Unit Hydrograph.Le-Roy K. Sherman published the Unit Hydrograph concept in the early 1930s, formalizing the linear unit response approach.Therefore, the correct attribution is to Le-Roy K. Sherman.

Verification / Alternative check:
Standard hydrology textbooks and historical reviews consistently credit Sherman with the first formal articulation of the Unit Hydrograph method.

Why Other Options Are Wrong:

• W. W. Horner: not associated with origination of the Unit Hydrograph.
• Robert E. Horton: renowned for infiltration and hydrologic cycle insights but not for the Unit Hydrograph origination.
• Merrill Bernard: not credited with this specific theory.

Common Pitfalls:

• Confusing Horton infiltration theory with Sherman Unit Hydrograph development.
• Assuming any early hydrology pioneer originated all common methods.

Final Answer:
Le-Roy K. Sherman