Hydrograph essentials: select the correct statements about stream hydrographs and peak flow identification.

Introduction / Context:
Hydrographs are foundational tools in hydrology used to describe how streamflow varies with time at a gauging station. They inform flood estimation, reservoir operation, and watershed management.

Given Data / Assumptions:

• A fixed river cross-section where discharge is measured.
• Time series of discharge covering a storm event and baseflow recession.
• Storm variability in intensity, duration, and spatial pattern.

Concept / Approach:
A hydrograph plots discharge (vertical axis) against time (horizontal axis). It typically has a rising limb, a crest (peak), and a recession limb. The peak flow is the maximum discharge attained during the event and is influenced by rainfall and catchment characteristics.

Step-by-Step Solution:
Confirm definition: discharge vs time ⇒ hydrograph.Axes convention: time on X-axis, flow on Y-axis ⇒ standard practice.Peak flow definition: maximum event discharge ⇒ correct.Variability: differing storms and antecedent conditions produce different peak flows ⇒ correct.

Verification / Alternative check:
Comparison with hyetographs (rainfall intensity vs time) and mass curves (cumulative volume vs time) reinforces correct hydrograph interpretation.

Why Other Options Are Wrong:
Since all four statements are correct, any single choice would be incomplete. The comprehensive answer is “All the above.”

Common Pitfalls:
Confusing hydrographs with hyetographs; misidentifying the inflection points and timing of the peak relative to rainfall centroid.

Final Answer:
All the above.