We explore the challenges of avalanche and debris flow hazard assessment for urban areas exposed in the Sakhalin region. Avalanches are a threat to more than 60 settlements in the region and debris flows to more than 30. Data are provided for avalanche and debris flow events that occurred in the Sakhalin region between 1928 and 2015. In this paper, the method for the design of hazard maps for snow avalanches and debris flows is described, providing the starting point for any planning constraints in general settlement planning schemes. These maps further allow conducting an assessment of avalanche and debris flow risk within a short time period for a larger territory and at minimum cost.

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The determination of maximum water discharges of floods and rain floods at small mountain streams is relevant for engineering and construction purposes. However, currently, the accounting of the surface runoff of small watercourses is often neglected when construction works are being carrying out. This fact leads to various problems with the exploitation of constructed objects. The purpose of this work is to assess the impact of the construction of the biathlon complex in the recreational area of Yuzhno-Sakhalinsk on the maximum surface runoff from the territory that it occupies. Maps of natural and anthropogenically transformed catchments of the territory were created with the usage of the data, collected during the field work in the summer of 2018. Hydrographical characteristics of both kinds of catchments were determined in accordance with generally accepted recommendations. On the basis of the obtained data, there was carried out the comparative analysis of the current state of the study area and its characteristics before the creation of sports facilities in years 2016–2017. The calculations of the maximum runoff in periods of flood and rain floods according to analytical formulas recommended in the literature were made. The results of the calculations clearly show that water discharges from this area during the period of flood and rain floods increased after the construction of the complex in comparison with discharges observed before construction. Studies have confirmed that the construction of biathlon tracks on the mountainside led to the increase in surface runoff from this area, which is the reason for the overflow of the urban storm sewer of Yuzhno-Sakhalinsk during the period of flood and rain floods, stormwater outlets on the day surface and the activation of erosion processes, suffusion on the considered territory.