RS-based analysis of land cover change in the region surrounding Tianshengqiao No.1 hydropower reservoir before and after its construction

Construction of hydroelectric projects has often been linked to negative environmental effects, such as climate change, decline of amount or diversity of aquatic life, fragmentation of natural habitat, disturbance of natural sedimentation processes, and land cover change. These effects occur because reservoir construction disturbs the natural hydrological process and human activities change land cover. This has lead to numerous studies on land use/cover change (LUCC) caused by hydro power construction. This research investigated the LUCC impact of a specific hydropower station, Tianshengqiao No.1, using satellite data. Result showed that its construction had slightly adverse effects on land cover and landscape structure. Tianshengqiao No.1 hydropower station is located in southwest China on the border of Guizhou Province and Guangxi Zhuang Autonomous Region. With a controlled catchment area of 50 139 km² and installed capacity 1200 MW, it is the first in the series of cascade hydropower stations along the Hongshuihe River, which is the upper reach of the Pearl River with rich hydroelectric potential. This project involved six counties in three provinces and took ten years to construct (1990-2000) with a total investment of 8.4 billion RMB. Remote sensing has been widely used to study land cover change. It is well suited to study rugged terrain surrounding Tianshengqiao No.1. In this study, ENVI software was used to geoprocess and classify Landsat TM images. ArcView and Photoshop were used to make two land use maps, and FRAGSTATS calculation method was applied in landscape ecological structure analysis. This study analyzed land cover before and after the construction of the hydropower station using 1987 and 2002 TM images for a 2520 km² area surrounding Tianshengqiao No.1. FRAGSTATS was used to analyze seven representative quantitative indices of landscape spatial structure and heterogeneity. Result showed that land cover in the region surrounding Tianshengqiao No.1 was moderately influenced by the hydropower construction. The share of land cover in shrubbery, which was the largest before the construction, decreased from 33% to 20%. Grassland became the most widespread land use pattern in 2002 TM image, increasing from 31% to 39% over the study per- iod. The change in land cover from shrub-dominated to grass-dominated implies certain degree of land degradation, which needs to be monitored. The analysis of landscape structure and landscape heterogeneity indicates that in the past 15 years, landscape spatial pattern in this region has tended to become fragmented and diversified, which indicates that the construction of Tianshengqiao No.1 may have had other important effects on landscape pattern.