Considering the Order and Symmetry to Improve the Traditional RVA for Evaluation of Hydrologic Alteration of River Systems

摘要

Hydrologic alteration is one of the key factors influencing the aquatic health of a river basin, particularly that of highly fragmented rivers. In this study, we propose an improved range of variability approach (RVA) by considering the order and symmetry of indicators of hydrologic alteration (IHA) to comprehensively assess the hydrologic alteration of river flows. Three indices, i.e., index for the alteration of periodicity, index for the alteration of trend, and index for the alteration of symmetry, were used to improve the traditional RVA for evaluation of hydrologic alteration of river systems. Two main control stations located in the upper Pearl River Delta, the Sanshui and Makou stations, were selected as case studies. The results show that (1) each evaluation index reflects only partial characteristics of the alteration of each IHA parameter, which vary over the stations, and (2) the traditional RVA underestimates hydrologic alteration, because the trend and periodicity components and symmetry in the temporal order of IHAs were significantly altered, while the results of the traditional RVA varied slightly for some IHAs, e.g., the multiday maximum flow at the Sanshui station and monthly flows for May, July, and September at the Makou station. These indicated that, by considering frequency, trend, periodicity, and symmetry, the improved RVA provides a more accurate quantitative evaluation of ecological flow alteration.