Updating of the water surface area of the Ivankovskoye reservoir based on the earth remote sensing data

The Ivankovskoye Reservoir is a shallow reservoir of the valley-basin type. Low banks and overgrowing of shallow waters cause difficulties in determining its coastline and water surface area. In the Order of Rosvodresursy dated 31.05.2019 no. 125, the area of the reservoir is indicated as 316 km2, while the earlier publications gave the value of 327 km2. However, even a preliminary analysis of remote sensing data proves that the actual area of the Ivankovskoye Reservoir differs significantly from those mentioned in publications. The work is devoted to clarifying the water surface area of the reservoir using satellite data. The available cartographic materials and remote sensing data, starting from the filling of the reservoir to the present were assessed. According to retrospective data, it was established that the area of the reservoir on the maps compiled in the first years after filling was significantly larger than on later maps, which show a significant decrease of the part of the Shoshinsky reach. The total area of the reservoir is equal to or less than the reference values. The first available satellite images of the Ivankovskoye Reservoir water area date back to the early 1970s, which allows estimating the area of the reservoir from that period to the present. The Sentinel-2 satellite images were used for interpretation and analysis. Based on remote sensing data, the values of the actual area of the Ivankovskoye Reservoir water surface were identified at different water levels during the period of no ice formation. According to the obtained data, the actual area of the reservoir at levels close to the normal backwater is in most cases within 220-240 km2, which is 22-31% less than in the interpolation table of the surface area of the Ivankovskoye Reservoir at different water levels given in the “Rules for the Use of Water Resources of the Ivankovskoye Reservoir on the Volga River” (Order of Rosvodresursy dated 31.05.2019 no. 125). The use of an overestimated water surface area of the reservoir in research and design projects distorts the assessment of the reservoir’s impact on the environment and other ecological and hydrological characteristics. The paper provides an example of calculating methane emissions from the Ivankovskoye Reservoir, which turned out to be 20-25% lower based on the adjusted area. It is recommended to clarify the morphometric characteristics of the Ivankovskoye Reservoir in the coming years.