Local scour estimation at check dams in torrential streams in south east spain

• Published in: Geografiska annaler. Series A, Physical geography Vol. 91; no. 3; pp. 159 - 177
• Main Authors: Conesa-garcía, C., García-lorenzo, R.
• Format: Journal Article
• Language: English
• Published: Oxford, UK Taylor & Francis 01-09-2009; Blackwell Publishing Ltd; Swedish Society for Anthropology and Geography; Svenska sällskapet för antropologi och geografi
• Subjects: Bgi / Prodig; check dams; Checks; Coefficients; Cultural anthropology; Dams; ephemeral channels; Floods; Flow coefficients; Fluvial forms and processes; Freshwater; Geomorphology; Hydraulics; local scouring; Physical geography; Sediments; south east Spain; Streams; temporal evolution; Watersheds; Murcia; Spain; Spain, Andalucia, Betic Cordilleras, Segura Basin; Dam; Torrent; Flood; Watershed; Arid area; Semi-arid area; Stream; Erosion
• ISSN: 0435-3676; 1468-0459
• DOI: 10.1111/j.1468-0459.2009.00361.x

For several decades, the check dam building has been one of the most commonly used structural measures in the Forestry Hydrological Restoration Programs and Plans in the torrential basins of south east Spain. Two examples are the catchments studied here, drained by the Cárcavo and Torrecilla torrential streams belonging to the Segura Basin. Obtaining a more stable bed and a less powerful flow requires transitory hydro-morphological stages such as check dam filling upstream or local erosion downstream. The main aims of this paper are to estimate local scouring induced by check dams downstream, and to find evolution stages of scouring depth, the response time of the local erosion point and the local maximum depth to reach a stable bed situation. To do this, the results obtained by different methods were compared with measured scour depths for various hydraulic radii. From this comparison, performed in non-uniform sediment size beds and in clear-water conditions, the Fahlbusch's formula gives a better fit, while the Jaeger's and Bormann and Julien's methods tend to underestimate the results. These may be used to calculate local instantaneous scouring in flows less than bankfull, but give a worse estimate for maximum equilibrium scouring. Under active bed conditions, the temporal response of the cross-sections experiencing local scour processes below these structures reflects the variations in hydraulic regime during flooding. In general, a rapid evolution phase is followed by a slow stage, which in the most torrential sectors has still not reached the equilibrium threshold.