Figure 3 shows the result from the band set B4( red), B3( green), and B1( aerosol) segmentation and the unsupervised K-means clustering. It could be used further not only for delineations of water body limits, but also for analysis of turbidity and phytoplankton.
Table 2 presents the area of the defined reservoir boundaries, determined by the methods used in the present study.
The Kappa coefficient values for NDWI, Sentinel VM, WRI, and object-oriented analysis are 0.9850, 0.9805, 0.9787, and 0.9856, respectively.
The visual interpretation and these statistical data show high accuracy of the results. A small difference in the area was obtained between the boundaries determined by the NDWI, Sentinel Water Mask, WRI and OBIA indices for 1.11.2022 and 28.07.2024, respectively( Fig. 4).
Fig. 4. Batak Reservoir limits delineated by the object-based analysis of Sentinel 2 Level 1C 2022-11- 01 and Sentinel 2 Level 1C 2024-07-28( 1 and 3) and by data from the Ministry of Agriculture and Food( 2 and 4)
� Field research in September 2024 confirmed the reduced reservoir area due to the extreme drought this year compared to previous years, as well as the use of the dam for drinking and domestic water supply, electricity production, and irrigation, as the " available " and " available useful " volume, respectively 233.375 million m3 and 213.425 million m3 for June 2024, decreased to 221.803 million m3 and 9 201.853 million m3 in July 2024, respectively [ 30-31 ]
According to the spatial data by the Ministry of Agriculture and Food, the Batak Reservoir has a larger extent due to the large-scale used, and includes adjacent parcels.
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