The effects of cascade dam construction and operation on riparian vegetation

Abstract

ABSTRACT Riparian vegetation acts as a corridor, filter, or barrier for the flow of material, energy, and information between terrestrial and aquatic ecosystems. While, dam construction, especially cascade dam construction, bring huge changes to riparian vegetation. In this study, the changing of riparian vegetation cover in response to the construction and operation of large dams at different scale was analyzed. The variations of the normalized difference vegetation index (NDVI) in longitudinal and transverse directions during pre- and post-dam construction were calculated and analyzed. The results showed that dam height was the main determining factor for the range of riparian vegetation affected in the longitudinal direction, whereas valley contour and distance to dam site affect the transverse direction vegetation together. A linear or logarithmic relation between submerged area in transverse and the distance to dam were founded. After dam construction, the NDVI in the valley becomes uniform, and the vegetation grows more homogeneously. Influence extent of different elevation in different reaches was discussed. The intensive affected area including inundated area and 200 m from the water surface in vertical direction. As the altitude grows, the influence gets weak. Positive effect of a single dam on vegetation in upstream reservoir was found except near channel grade, and a potential oligotrophic threat for the downstream vegetation was posted. For cascade dams, the vegetation in the upstream of Xiaowan dam became better from elevation 200–400 m above original water surface. The NDVI between Xiaowan dam and Manwan dam, which at downstream of Xiaowan but in reservoir of Manwan, degraded after Xiaowan dam constructed. Cascade dams have cumulative effects on vegetation, the influence are positive or negative mainly depend on diversion of the dam.