Geographia Technica, Vol 21, Issue 2, 2026, pp. 87-104
MONITORING RESERVOIR WATER LEVEL AND SURFACE AREA DYNAMICS USING SATELLITE ALTIMETRY AND OPTICAL IMAGERY: TSALKA RESERVOIR, GEORGIA
Nika TKESHELASHVILI 
, Tamar PAPACHASHVILI , Giorgi BREGVADZE
ABSTRACT: Monitoring of inland water body dynamics is essential for understanding hydrological variability and supporting sustainable management of freshwater resources, especially in regions with limited hydrometric observations. This study evaluates the potential of integrated use of Sentinel-3 radar altimeter data and PlanetScope optical imagery for monitoring surface water area and level parameters of the Tsalka (Khrami) Reservoir in Georgia over the period 2017–2024. Water level time series were derived from Sentinel-3 SRAL data, while reservoir surface area was extracted from PlanetScope imagery. Validation against in situ measurements demonstrates high accuracy of radar altimeter (Bias = 0.097 m, RMSE = 0.192 m, r = 0.997, NSE = 0.993). The results reveal pronounced seasonal and interannual variability of Tsalka Reservoir, with water levels ranging from 1498.86 m to 1508.42 m and surface area from 5.69 km² to 24.54 km². The study confirms that the combined use of altimetry and high-resolution optical data provides a reliable and cost-effective framework for hydrometric monitoring of medium size inland water bodies.
Keywords: Hydrometric monitoring; Radar altimetry; Optical remote sensing; Tsalka Reservoir.
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