Magic Sand and Degradation, at the Shi-Ting River

Degradation, over long periods of time, is a worry to some scientists, as is evident in this new study:

Can magic sand cause massive degradation of a gravel-bed river at the decadal scale? Shi‑ting River, China,” Chenge An, Gary Parker, Marwan A. Hassan, and Xudong Fu, Geomorphology, vol. 327, February 15, 2019, pp. 147-158. (Thanks to Tom Gill for bringing this to our attention.) The authors, at Tsinghua University, Beijing, China; the University of Illinois, USA; and the University of British Columbia, Canada, report:

Massive bed degradation (20 m in 7 years) has been observed in the Shi‑ting River, Sichuan Province, China, since the 2008 Wenchuan Ms. 8.0 earthquake. The reason for the massive bed degradation has not been well understood. A hypothesis has been proposed that relates bed degradation to the augmentation of sand supply after the earthquake. The effect of sand on gravel mobility (magic sand effect) has long been observed in laboratory experiments. In this paper, we study whether the augmentation of sand supply and its magic sand effect can lead to the observed massive degradation at decadal scales….

Our simulation results also indicate that despite the fact that magic sand effects are not explicitly included in most sediment transport relations, they are at least partly built in via the hiding function that is contained in most sediment transport relations for gravel-sand mixtures.