Extreme sediment fluxes in a dryland flash flood

Abstract

A flash flood on 28th September, 2012, rose to a peak discharge of 2357 m3 s−1 from zero within one hour in the ephemeral Nogalte channel in SE Spain. Channel morphology and sediment sizes were measured at existing monitored sites before and after the flood and peak flow hydraulics calculated from surveyed floodmarks and cross-sections. Maximum peak sediment fluxes were calculated as ~600 kg s−1 m−1, exceeding maximum published, measured dryland channel values by 10 times and common perennial stream fluxes by 100 times. These high fluxes fit the established simple bedload flux - shear stress relations for dryland channels very well, but now extended over a much wider data range. The high sediment fluxes are corroborated by deposits at >1 m height in a channel-side tank, with 90 mm diameter sediment carried in suspension, by transport of large blocks and by massive net aggradation as extensive, structureless channel bars. Very high sediment supply and rapid hydrograph rise and recession produced the conditions for these exceptional sediment dynamics. The results demonstrate the extreme sediment loads that may occur in dryland flash floods and have major implications for catchment and channel management.

Grain‐energy release governs mobility of debris flow due to solid–liquid mass release

“…This is significant and particularly timely, noting the acceleration in glacier melt and increasing trend in extreme precipitation amount, intensity, and frequency (Donat et al ., 2013), which are likely to trigger more debris flows. The study also has broad implications for unravelling a spectrum of earth surface processes, including heavily sediment‐laden floods due to storms and glacier lake outbursts (Laronne and Reid, 1993; Xiao et al ., 2010; Grinsted et al ., 2017; Cook et al ., 2018; Hook, 2019), and subaqueous debris flows and turbidity currents in rivers, reservoirs, estuaries, and the ocean (Weirich, 1988; Wright and Friedrichs, 2006; Talling et al ., 2007; Armanini, 2013; Cao et al ., 2015b; Paull et al ., 2018; Stevenson et al ., 2018; Li et al ., 2019).…”

Relevance of Intermittent Rivers and Streams in Agricultural Landscape and Their Impact on Provided Ecosystem Services—A Mediterranean Case Study

“…Dry channels also play an important role as sinks for floodwater and recharges for alluvial aquifers [36] that, together with the water retention and runoff reduced by vegetation, can increase flood control in the area downstream and improve basin and channel management [67].…”

Sensitivity Analysis of Flash Flood Hazard on Sediment Load Characteristics

“…Steep slopes in mountainous regions promote soil erosion and result in high sediment concentration in flash floods. Impacts of a high amount of sediment on flooding hazard have been wellobserved in the field (Hooke 2019). For instance, sediment deposition was observed to reach as high as over 7.5 m in a flash flood on July 28, 2001 in Sichuan (Liu et al, 2020).…”

“…With important roles of flood modeling in fields of water conservation projects, urban planning, and flash flood early warning systems (Testa et al, 2007;Siviglia and Crosato. 2016), models' efficiency and accuracy are still far from satisfaction for some cases such as flash flood in mountainous areas because of neglecting sediment effects (Guan et al, 2013;Hooke 2019;Contreras and Escauriaza. 2020).…”