hydrographseparation

Hydrograph separation is a set of techniques used to decompose a streamflow hydrograph into distinct components, most commonly baseflow and quickflow. Baseflow represents groundwater discharge to the stream and contributes the relatively steadier portion of discharge, while quickflow (or runoff) captures the faster response to precipitation, including surface runoff and interflow. The separation helps in understanding watershed processes, groundwater–surface water interactions, and in supporting water resources management, hydrological modeling, and ecological assessments.

Conceptually, hydrograph separation aims to isolate the portion of flow sustained by storage in the subsurface (baseflow) from the portion derived from immediate rainfall response (quickflow). In practice, methods range from simple graphical approaches to advanced quantitative techniques, and may also consider additional fractions in some studies.

Methods fall into several categories. Graphical separation relies on visual estimation of a baseflow line through the hydrograph. Digital filtering methods, such as recursive baseflow filters, estimate baseflow from the stream record using parameterized equations (common examples include Lyne–Hollick and related filters, with variations like Eckhardt-type filters). Recession–based approaches use periods of declining discharge to infer baseflow and groundwater contribution, often applying a constant or variable recession constant. The choice of method and parameters influences the resulting split and requires calibration and sensitivity analysis.

Applications include estimating baseflow for water-resource planning, assessing groundwater recharge, evaluating nutrient and contaminant transport, and informing flood risk and drought analyses. Limitations include non-uniqueness of the split, data quality dependencies, and sensitivity to method assumptions and parameter choices.