Risks of Downstream Flooding of the Irkutsk Hydropower Plant in Regulating the Lake Baikal Level

This paper presents findings on modeling the flood zone boundaries and assessing the resultant damage in the downstream of the Irkutsk Hydropower Plant (IHPP) due to high water flows through it which are possible in high-water years when the Lake Baikal level goes beyond the established range. A description of the relief model and the data sources used are provided. The hydraulic model of steady flow of the Angara River, which is developed in the form of automatic generation of a large number of cross sections by calculating their characteristics, is presented. Currently, downstream flooding is observed when flow rate of IHPP is 2800 m³/s, while the bulk of possible flooding occurs in the city of Irkutsk. The results were verified using actual satellite image data. The paper presents the estimates of flooded areas and objects (buildings and structures) susceptible to flooding at various flow rates of the IHPP. Based on the estimates for the areas of the objects and the length of utility lines, which fall into the flood zones when the flow of IHPP ranges from 2800 to 6000 m³/s, socioeconomic damage and losses for the downstream pool as a whole were determined. The results showed an increase in the damage starting with a flow rate of IHPP of 4000 m³/s and its much higher increase with a flow rate of 4500 m³/s. The estimates for the damage due to elevated flow rates of IHPP are compared with the estimates of damage in the upstream pool, which can occur when the level of Lake Baikal rises under similar water conditions. The critical level for the upstream pool is 457.20 m (according to the Pacific Elevation System). The critical flow rate for the downstream pool is 4000–4500 m³/s. These levels and flow rates are within the range of comparable damage in the upstream and downstream pools and have a probability of about 2%.