Determination of flooding zones of the floodplain islands on the territory of the Kuibyshevsky water reservoir using remote sensing data

Water reservoirs islands, particularly islands of the Kuibyshev reservoir (the largest in Eurasia), are little-studied formations with both natural and anthropogenic origin. The reservoir water regime, which can have not only seasonal, but also weekly and daily dynamics, determines high dynamism of islands boundaries, as well as areas of surface and subsurface flooding. Determination of islands flooding zones is necessary both for monitoring of island systems and for efficient and sustainable land use management. The current study was performed to determine the flooding zones of islands of the Kazan District of Variable Backwater, which is located on the territory from the Zelenodolsk-Nizhnie Vyazovye bridge (55°49'27.1"N; 48°31'05.6"E) to the Kazan area (55°42'51.2"N 49°01'52.9"E). The water level on that part of the reservoir is characterized by significant annual fluctuations from 48.6 m to 53.5 m with a Normal Water Level of 53 m. On the area under investigation 262 object were distinguished with the total area of 1856.25 hectares (Fig. 1). To determine the boundaries of island systems at different water levels two multispectral Landsat 8 scenes were picked up: (1) scene from 1st October 2018 (water level in the reservoir - 51.55 m); (2) scene from 28th May 2013 (water level in the reservoir - 53.28). Landsat scenes were converted from Digital Numbers to Top of Atmosphere Reflectance values with subsequent atmospheric correction using DOS1 method. Finally, multispectral imagery was classified as ground or water land cover using Radom Forest technique. To train the classification model 300 points were randomly created on the territory of islands and 89 extra points were distributed on the full scene area. Overall accuracies of land use classification were 93.76% and 90.64% for the scene of 28th May 2013 and the scene of 1st Oct 2018, respectively. The results of land use classification of islands showed that according to the water level, significant areas become flooded (Fig. 3). At minimal water level of 51.55 m islands area were estimated as 2718.97 hectares. When the water level reaches normal water level (53 m), the surface area of islands reduces by 31.7% and estimates as 1857.25 hectares. At maximal water levels of 53.28 m, the island area reduces by another 14% and reaches 1596.76 hectares. Thus, the flood zone for all the floodplain islands of the Kazan region of variable backwater was estimated at 1122.21 hectares. The results showed, that depending on the water level, about 41.2% of the total islands area is subjected to periodic flooding. These areas are characterized by hydromorphic conditions with a corresponding effect on island ecosystems.

Keywords

Authors

References