Hydrograph separation for evaluating streamflow recession characteristics in Taiwan

Understanding streamflow recession characteristics is critical for water resource management. Two important streamflow recession characteristics are the recession index, defined as the hydrographic slope of a streamflow on the recession curve, and the critical time, defined as the time required for streamflow to achieve stable discharge from peak flow. These parameters control the variation of the base flow hydrograph. This study analyzes the recession indices and critical times of 57 gauging stations in Taiwan. Based on the recession index spatial distribution diagram of Taiwan, the recession indices of the alluvial fan of Chuosui River, Chianan Plain, Pingtung Plain, Lanyang Plain, Hualien Plain, and Taitung Plain gradually decrease from the coastal areas towards inland. The magnitude of this reduction is highest for Pingtung Plain. The analysis results show that the recession indices are all within a specific numerical range, which gradually decreases (converges) with increasing basin area. The elevation of the gauging stations affects the distribution of critical times, where a lower elevation decreases the distribution and convergence was achieved following a gradual incline in elevation.