Stability index for the planview morphology of alluvial rivers and a case study of the Lower Yellow River

Abstract Morphological changes in river channels are influenced by flow and sediment conditions and channel boundaries, and making adjustments to the river morphology within a controllable range is vital for river engineering. Accordingly, scientific methods for efficient assessment and monitoring of river morphological changes have attracted attention from hydrologists and engineers. In this study, inspired by the Taylor series, we propose a novel quantitative metric called relative stability index of river regime (RSIRR), which solely takes geometric properties into consideration to evaluate the steady state of river channels. Corresponding coefficients of the RSIRR were determined by cluster analysis. Furthermore, we present a spatial interpolation algorithm to batch compute RSIRR values for an entire river reach over multiple years, as the extendibility of RSIRR is suitable for multiple scales from a single cross-section to a longer river reach scales. To validate the reliability of RSIRR, we applied this index to the braided reach of the Lower Yellow River (LYR) in China from Tiexie to Gaocun, thereby obtaining final thresholds to distinguish stable and unstable reaches. The spatiotemporal analysis indicates that the study area could be spatially divided into three reaches, while the obtained values of RSIRR at reach-scale expressed a decreasing trend from 1985 to 2009. Additionally, the potential of RSIRR for obtaining an early warning of unstable reaches in the study area is discussed. We conclude that RSIRR plays an important supporting role in ensuring the safety of life and property of the local people residing along a river reach.