In a 4-hour unit hydrograph, what is the most nearly effective rainfall or runoff depth in each hour?

The effective rainfall or runoff depth in a unit hydrograph is determined by the concept of unit hydrograph theory, which portrays the response of a watershed to a unit of effective rainfall that occurs over a specific duration. In this instance, the question asks for the effective rainfall or runoff depth for a 4-hour unit hydrograph.

The key factor here is that the effective rainfall is distributed evenly across the duration of the hydrograph. Given that the effective rainfall in the hydrograph is cumulative over the specified period, an effective depth of 0.25 inches per hour across four hours would yield a total runoff depth of 1.00 inch for the entire duration. This aligns with the definition of a unit hydrograph, where the overall runoff resulting from the effective rainfall is scaled by the rainfall depth over the time period analyzed.

Therefore, the selection of 0.25 inches as the effective rainfall per hour is consistent with achieving the total effective runoff depth expected from a 4-hour duration unit hydrograph.