Bed stability variations after check dam construction in torrential channels (South‐East Spain)

Abstract

The effects of check dams on the bed stability of torrential channels have been analysed in several tributary basins of the Segura and Guadalentín rivers (South-East Spain). In order to illustrate the large variability in channel bed-forms and bed sediment sizes along the stream, 52 reaches of 150 m in length were surveyed. This variability is due to the behaviour of check dams, which depends on bedrock control, bed slope, channel roughness, lateral sediment input and a highly variable sediment transport capacity. Though the purpose of check dams is to diminish the boundary shear stress, reducing the longitudinal slope, and to stabilize the channel bed, downstream they reduce the volume of channel-stored material, favouring local scour processes, and upstream they can destabilize the sidewalls. The results enable us to evaluate the impact of every check dam on the bed morphology, distinguishing the structures installed in limy marl areas (e.g. catchment of the Cárcavo rambla, Cieza) and in schist and slate terrains (e.g. catchment of the Torrecilla rambla, close to Lorca). In the first type, bedrock and moderately thick granular beds predominate downstream from the check dams, so that the length of bedrock reaches and increase of roughness due to scour processes are the best indicators to verify its geomorphological effectiveness. On the other hand, the metamorphic areas drained by ramblas and gullies produce great quantities of gravel that are retained by check dams, creating more uniform and permeable beds, where the balance between sedimentation and scouring, and the ratio τ τ τ τ τ c84 /τ τ τ τ τ 0 (RBS), appear to be the parameters most frequently adopted to estimate the bed stability. Analysis of slope adjustments and the application of other indices to estimate the bed substrate stability (LRBS, SRI) and the structural influence of the dams (SIBS) corroborate the differences in bed stability found in the corrected reaches in each catchment.Major disruption of the natural regimes of large rivers, principally by damming and channelizing, has received extensive attention in the last decades (Petts, 1979;Graf, 1988;Brandt, 2000). However, relatively scant attention has been directed toward the responses of smaller streams to flood-control measures (Martínez Castroviejo et al., 1990;Martín Rosales, 1997). The problem of small-stream alteration is especially important in regions that are more densely populated, such as Japan, China, India and many parts of Europe. In an effort to develop low-cost means of stabilizing degrading small streams, several different types of low-head drop structure, some of them quite novel, have been developed.Determining their degree of efficiency requires an evaluation of which types of hydraulic, hydrological and geomorphological effect are caused upstream and downstream from these structures. In general, and especially in arid and semiarid environments, the spacing of check dams in a drainage network involves a sudden interruption in the conditions of transport, producing a rapid ...

Final Analysis of the Accuracy and Precision of Methods to Calculate the Sediment Retained by Check Dams

“…In general, the conclusions reached regarding check dams have been based on the amount of sediment retained and their effects both downstream and upstream of these structures. Some authors have shown that check dams produce negative effects downstream due to bed scouring (Boix-Fayos et al, 2007;Conesa-García et al, 2007;Conesa-García & García-Lorenzo, 2009) or that erosion problems could sometimes exist downstream under heavy rainfall conditions (Hooke & Mant, 2002). Some changes in diversity of riparian vegetation have been detected by Bombino et al (2013).…”

Physical and numerical modelling of a bedload deposition area for an Alpine torrent

“…The focus of the study was the optimization of the outlet area of the first retention structure. Other work on mitigation measures for torrent catchments concentrates on design criteria for the geometry of open silt-check dams (Armanini and Larcher, 2001), morphologic changes due to construction of check dams (Busnelli et al, 2001;Conesa-García et al, 2007) and impact on vegetation due to check dam construction (Bombino et al, 2009). Our study investigated the spatial deposition of bedload on a wider area without significant change of the inflow hydrograph.…”

Hydraulic Geometry, GIS and Remote Sensing, Techniques against Rainfall-Runoff Models for Estimating Flood Magnitude in Ephemeral Fluvial Systems

“…In extreme floods, where the flood-prone area is completely covered, the bed of these reaches is very unstable, registering Relative Bed Stability (RBS) values and Log Relative Bed Stability (LRBS) values which are often below 0.25 and −0.60 respectively [32]. This bed instability means that these reaches also have greater potential bed transport (6.5· 10 −3 −0.013 m 2 /s) [34].…”