El’vira А. Rumyantseva; NELLY N. BOBROVITSKAYA. FORMATION OF VARIABILITY OF FLOW QUALITY IN THE TOP OF THE LUGA RIVER IN INTER-ANNUAL AND SHORT-TERM TIME. PART 1. INTERANNUAL VARIABILITY. Hydrosphere. Hazard processes and phenomena, v. 3, n. 1, p. 39-58, 1 Apr. 2021.