Algorithm grwat for Automated Hydrograph Separation by B.I. Kudelin’s Method: Problems and Perspectives

An algorithm for automated graph-analytical separation of hydrograph, underlying grwat software package is described in detail and analyzed. This system is designed for separation of runoff hydrograph into base runoff, spring flood, rain and thaw runoff events by the method proposed by B.I. Kudelin. The starts and ends of water regime phases are identified by algorithms for distinguishing breaks on the hydrograph and analyzing their meeting some criteria for passage of water regime phases, based on the physics of runoff formation in river basins. The input data are daily series of water discharges, air temperatures, and rainfall values. Weather data are used as an indicator and means to refer hydrograph peaks to groups of events, i.e., thaws or rain (mixed) floods, and to determine the start of winter low-water season. A series of calibrated parameters are used to specify criteria for phase separation. The program calculates 52 annual runoff characteristics, as well as more than 30 characteristics for each individual flood: time characteristics (the dates of start, end, and maximum; the duration, and the time of rise), discharge characteristics (maximal discharge, flood volume, water discharge before flood start, the excess of maximal discharge over basic flood level), various weather characteristics (the regimes of air temperature and precipitation before the flood and during it), and others. The values of calibrated parameters of grwat were found to be stable for the majority of rivers throughout the calculation period, and their values were similar for rivers with the same type of water regime and size. Algorithm gwart also showed high tolerance to changes in the values of calibration parameters. Recommendations are given for specifying their values. The main causes of errors in determination of water regime phases and the development perspectives of the algorithm are discussed.