Formation, expansion and restoration of a sedimentation fan: the case of the Arroyo del Partido stream (Spain)

Abstract

The Arroyo del Partido is a small stream flowing into the Doñana National Park marsh. In its lower part, the stream used to flow in a wide, low-gradient area, where the channel was highly dynamic with frequent avulsions. As a result of a channel rectification, the subsequent floods heavily eroded the artificial banks and created over time a depositional fan within the Doñana marsh. The bedload dynamic at the annual scale was estimated from the expansion of the sedimentation fan, assessed from aerial photographs analysis and repetitive topographic surveys. The bedload transport ranged from 3.7×10 6 to 2.1×10 3 m 3 per year, depending on the sequences of occurring floods and on the changing geometrical conditions of the main channel. The progressive erosion of the artificial banks led to self-established cross-sections and slope geometry, which reduced shear stress acting on the bed and favoured sediment deposition on the floodplains, reducing overtime the expansion of the sedimentation fan. This evidence has been used to plan a restoration strategy for the fan and floodplains, aimed to mitigate the effect of the embankment and to improve the overall functionality of the stream. As a result of the restoration, an artificial levee was eliminated and a wide floodplain area was recreated as a free-meandering floodplain.

An update of the sediment fluxes investigation in the Rio Cordon (Italy) after 25 years of monitoring

“…Therefore, only a portion of finer (gravel and cobble) particles is likely to be entrained annually (Wohl, 2000;Lenzi, 2004;Yager et al, 2012). The monitoring activity of bed-load transport in small, steep (<10 km 2 ) mountain catchments poses problems that are very complex due to the impulsive or high-energy nature of this process, where intense sediment transport can even lead to non-Newtonian flows, such as hyper-concentrated flows or debris flood (Di Stefano et al, 2007;Mintegui et al, 2010;Lenzi et al, 2011).…”

Stability of the new alluvial fan of el partido stream, located in the eastern side of el rocío village in the doñana national park (spain), after the actions carried out to restore its hydrological regime

“…Moreover, this new situation also triggered retrogressive erosion processes. In July 2003, the new alluvial fan surface was evaluated in 4.31 km 2 with a volume of 4.48 × 10 6 m 3 [1][2][3][4][5][6].…”