http://hdl.handle.net/2160/5926 2013-05-22T21:59:12Z http://hdl.handle.net/2160/7645 An appraisal of the contemporary sediment yield in the Ebro Basin Batalla, Ramon J.; Vericat, Damià Purpose The main aim of this work is to provide a comprehensive estimation of the sediment yield of the Ebro Basin (NE Iberian Peninsula) in the twentieth century. Materials and methods For this purpose, we have used the reservoir sedimentation records available for a series of large dams distributed in the catchment. Records started in 1916 and ended in 2001. In addition to the sediment yield estimates, bathymetrical records permit an evaluation of spatial variations in the sediment load of the basin and the assessment of the sediment yield of the lower reaches of the river downstream of major dams. Results and discussion Total sedimentation in the reservoirs of the basin is estimated to be in the order of 670 x 10(6) t. Sediment yield is five times higher in the northern catchments (Pyrenean Range, 370 t km(-2) year(-1)) than in the southern ones (Iberian Massif, 78 t km(-2) year(-1)), reflecting the particular hydromorphic conditions of these areas. Specific sediment yield (SSY) decreases with catchment area but in the southern zone is more scale-dependent. The highest SSY occurs at 350 mm year(-1) showing a decline as runoff increases. SSY of the northern zone plots high in comparison to curves found in the literature, and this is interpreted as the consequence of historical human impact on sediment delivery. The sediment load of the Ebro Basin before the widespread construction of dams and the beginning of land abandonment is estimated to be 21 x 10(6) t year(-1). Conclusions The data illustrate the distinct hydrological and geomorphic behaviour of the two hydro-climatic areas analysed in this study. The SSY data show, for instance, the lower capability of the semi-arid catchments to transfer sediment loads. SSY does not show a linear relation with runoff, a fact that corroborates general patterns previously reported in the literature. Finally, the contemporary sediment load represents around the 1% of what was potentially transported during the beginning of the twentieth century, illustrating the sedimentary deficit of the lower section of the Ebro Basin. Batalla, R. J., Verticant, D. (2011). An appraisal of the contemporary sediment yield in the Ebro Basin. Journal of Soils and Sediments, 11 (6), 1070-1081. 2011-10-31T00:00:00Z http://hdl.handle.net/2160/7643 In-channel sediment storage in a highly erodible catchment: the River Isábena (Ebro Basin, Southern Pyrenees) López-tarazón, José Andrés; Batalla, Ramon J.; Vericat, Damià In-channel fine-sediment storage, especially in areas draining highly erodible materials, constitutes an important part of the sediment budget of a drainage basin. This phenomenon occurs when sediment production in the basin is greater than the river's transport capacity, resulting in large accumulations of fines along the river channel. In-channel sediment storage has been studied in a similar to 3-km channel length reach of the River Isabena during an average hydrological year (2007-2008). The River Isabena drains an area of 445 km(2). It is located at the Southern Pyrenees and the channel network flows through an area of extremely erodible materials producing an enormous amount of suspended sediment. Total in-channel sediment storage for the study period has been estimated at approximately 679 t, which equates to 0.32% of the annual suspended sediment load calculated at the basin's outlet. Sediment storage values obtained in the study reach have been extrapolated to the whole main channel length (45 km), resulting in a total storage of 9,810 t, representing the 4.7% of the annual total load. In-channel storage shows both temporal and spatial trends. In relation to the former, sediment is continuously accumulated during low-flows while the latter shows that sediment accumulation increases in the downstream direction. Results suggest that the fine-grained sediment stored in the channel may represent an important component of the suspended sediment budget of rivers draining highly erodible materials such as the River Isabena. 2011-09-01T00:00:00Z http://hdl.handle.net/2160/7153 Accuracy assessment of aerial photographs acquired using light-than-air blimps: low cost tools for mapping river corridors Brasington, James; Wheaton, Joe; Vericat, Damià; Cowie, Michaela Monitoring river systems with repeat aerial photography is a powerful tool although the temporal resolution of surveys is rarely performed at anything better than annual time-scales. In recent years, a variety of low-cost aerial platforms for acquiring aerial photography have emerged. While these economical options may facilitate more frequent repeat surveys, the accuracy of imagery needs further consideration. The accuracy of imagery obtained from a Lighter-Than-Air Blimp is investigated through two simple experiments. The first looks at the geospatial error of aerial photographs derived using five geometric transformation models, and the sensitivity of the photo registration quality to various ground control point (GCP) configurations and densities. At high GCP densities, higher order polynomial transformation models provide the highest quality registrations. However, at more modest GCP densities (i.e. 19-28 GCPs Ha(-1)), simple aerotriangulation and 2nd order polynomial transformation models perform modestly, resulting in registration errors at standards equal to or better than obtained with conventional aerial photography (e.g. 0.5-1 m). The quality of image registration is highly dependent oil the configuration of GCPs. In a second experiment, the practical utility of producing a mosaic of blimp acquired imagery is explored over a kilometre long braided reach. Even at relatively low GCPs densities (e.g. 9 GCPs Ha(-1)), a mosaiced aerial of the entire reach can be produced of adequate quality to support bar-scale mapping of patch-scale features. The survey required less than a single day of field work and laboratory processing, and presents a cost-effective alternative to traditionally commissioned flights. Copyright (C) 2008 John Wiley & Sons, Ltd. Vericat, D., Brasington, J., Wheaton, J., Cowie, M. (2009). Accuracy assessment of aerial photographs acquired using light-than-air blimps: low cost tools for mapping river corridors. River Research and Applications, 25(8), 985-1000. 2011-07-18T00:00:00Z http://hdl.handle.net/2160/7134 Bed-material mobility in a large river below dams Vericat, Damià; Batalla, Ramon J.; Garcia, C. The mobility of river-bed surface particles is examined in the lower Ebro River downstream from dams that were closed several decades ago. Mobility is analysed by comparing photographs of painted bed areas taken before and after the 2003-2004 flood season, and also by comparing lines of painted particles after the floods. The peak of the maximum flood had a recurrence interval of 2 years. Medium and coarse gravels were widely exported from all the study reach, reflecting a disequilibrium between the competence of the flow to entrain and transport them and the rate of supply from upstream. By contrast, very coarse gravels and larger particles remained immobile, since floods were not competent enough to mobilise them. The partial entrainment of surface particles caused a coarsening of the river-bed surface, even in areas where sediments are loose and the river-bed is highly active during small floods. Verticat, D., Batalla, R. J., Garcia, C. (2008). Bed-material mobility in a large river below dams. Geodinamica Acta, 21 (1-2), 3-10. 2008-01-01T00:00:00Z