A hydrograph traces how streamflow responds to a rainfall event over time. The rising limb reflects rapid runoff reaching the channel; the peak discharge occurs when all sub-catchments contribute simultaneously; the recession limb shows the slower return to baseflow as groundwater drains. The Nash-Sutcliffe efficiency (E = 1 − Σ(Q_obs−Q_sim)²/Σ(Q_obs−Q̄)²) measures hydrological model skill. Flood frequency analysis uses log-Pearson Type III distribution to estimate return periods. Floodplain inundation is governed by Manning's equation: Q = (1/n)·A·R^(2/3)·S^(1/2), where n is roughness and R is hydraulic radius.