Inventory of Long-Term Braiding Activity at a Regional Scale as a Tool for Detecting Alterations to a Rivers' Hydromorphological State: A Case Study for Romania's South-Eastern Subcarpathians

摘要

The inventory of long-term braiding activity is a useful tool for detecting alterations in a rivers' hydro-morphological state and for a river's management in the context of the Water Framework Directive on integrated river basin management for Europe. Our study focuses on braided sectors of rivers in South-Eastern Subcarpathians (Romania). The inventory evaluates types of alterations based on the spatial analysis of fluvial morphology indicators (i.e., length of the river sector forming a braided pattern; width of the braided active channel), and vegetation cover (i.e., length of banks covered by forest and shrubs; area of in-stream patches of shrubs) accumulated over the last century. Furthermore, we performed a regional scale hierarchical cluster analysis to estimate the degree of alteration when compared to an historical baseline. In South-Eastern Subcarpathians, the studied rivers experienced a decrease of braiding activity revealed by the shortening and narrowing of their braided sectors, expansion of riparian forests, and the diminishment of vegetated islands' areas. We separated three types of river clusters, corresponding to low (cluster 1), moderate (cluster 2), and high (cluster 3) degree of alteration. Moreover, the clusters demonstrate the evolutionary path of the braided pattern alterations until the functioning of another channel pattern. The inventory is relevant for differing types and levels of alterations. Additionally, this tool may serve as a first step toward the restoration of altered sectors by identifying rivers in cluster 1 as potential candidates of present-day reference sites for altered rivers with similar natural conditions as in cluster 3.