Hydrology is applied to which of the following planning and design tasks in water resources engineering?

Introduction:
Hydrology provides the quantitative basis for designing and operating water resources systems. From flood control to water supply, hydrologic analyses inform risk, reliability, and economic decisions.

Given Data / Assumptions:

• Tasks include flood prediction, reservoir sizing, yield estimation, and backwater/level impacts of dams.

Concept / Approach:
Design floods are obtained from frequency analysis or event modeling; dependable yields and storage come from flow duration and mass curve methods; expected river level changes are forecast using inflow hydrographs combined with routing and stage–discharge relations.

Step-by-Step Solution:
Relate each listed task to a standard hydrologic method (flood frequency, reservoir planning curves, yield analysis, hydraulic backwater modeling with hydrologic inputs).All tasks rely on hydrologic inputs and analysis.Therefore, the comprehensive option is correct.

Verification / Alternative check:
Codes of practice and planning manuals explicitly require hydrologic studies for these decisions before hydraulic/structural detailing.

Why Other Options Are Wrong:

• Any single task alone is incomplete—hydrology underpins all the listed tasks.

Common Pitfalls:

• Confusing hydrology (catchment response) with pure hydraulics (reach flow profiles) and ignoring their linkage in design.

Final Answer:
All the above.