DRIFTING TIMBER FORMATION ON MUDFLOW RIVERS ON SAKHALIN ISLAND

The paper considers the regional features of the phenomena of timber drifting on mudflow rivers on Sakhalin Island. The regularities of mudflow formation in Sakhalin rivers and their mudflow regime are established and the factors causing timber drifting in the debris flow watercourses of Sakhalin Island are studied. Due to the history of Sakhalin terrain and macrorelief formation, the main mountain structures are composed of marine sediments. This promotes mudflows on rivers, the active development of exogenous processes on river slopes, and the flow of solid phase and woody vegetation into the channel and talvegs. As a result, the density of streams increases, their eroding and abrasive ability rises, which affects significantly channel deformations and involves timber drifting. High-density flows have an elevated transporting capacity, since they increase the pulling force of the flow affecting the midsection of the drifting timber root system, and also raise the timber buoyancy due to an increase in the pushing Archimedean force. Also, regional features include a large amount of liquid precipitation, the annual amounts of which in the valleys and on the coast are 800–1200 mm, and in mountainous areas can reach 1500–2000 mm. The main species of drifting timber drifting include broad-leaved trees (willow and alder), which, unlike coniferous wood, are more prone to form logjams and are most hazardous for culverts.