SURFACE WATER AREA VARIATIONS MONITORING AND FLOOD HAZARDS USING LANDSAT IMAGE DATA IN DONGTING LAKE FROM 1988 TO 2016

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Abstract

Dongting Lake is the second largest freshwater lake in China, with rapid seasonal surface water area fluctuations in the middle reach of the Yangtze River and downstream from the Three Gorges Reservoir (TGR). The marked variation of the lake’s surface water area is considered to have been affected by the TGR over the past decades. In this study, Landsat TM/ETM+/OLI time-series imagery data were em ployed to estimate the wet season total surface water area variation in South Dongting Lake and East Dongting Lake from 1988 to 2016. The surface water area was extracted from Landsat data using Modified Normalized Difference Water Index (MNDWI). The results indicated that the surface water area variation was accordant with the variation of precipitation and runoff of Xiangtan, Taojiang, Taoyuan, Shimen, Shadaoguan, Mituosi, Ouchikou and Chenglingji five hydrological stations. Most of the large surface water areas were observed during the pre-TGR period, whereas the small surface water areas were observed during the post-TGR period. Surface water area data, precipitation and runoff from the four hydrological stations (except Shimen station) all indicated downward trends, with reduction rates of 5.866 km²·year⁻¹, 0.802 mm·year⁻¹, 3.950 10⁸m³·year⁻¹, 2.834 10⁸m³·year⁻¹, 0.377 10⁸m³·year⁻¹, 1.282 10⁸m³·year⁻¹, 2.715 10⁸m³·year⁻¹, 0.318 10⁸m³·year⁻¹ and 16.114 10⁸m³·year⁻¹, respectively. The results of correlation analyses indicated precipitation and water from the Yangtze river may affect the fluctuation in the surface water area to a large extent. The results of flood inundation probability analysis indicated that approximately 502.9 km 2 of the study area was in the high flood hazard zone. In addition, the results of this study can provide scientific information to understand the effect of the TGR on downstream lakes and achieve better water resources and flood hazard management in this region.