as well as at several subcatchment outlets. All samples were dried and measured for spectral 50 properties in the laboratory using an ASD spectroradiometer. Colour parameters and physically based 51 features (e.g. organic carbon, iron oxide and clay content) were calculated from the spectra. Principal 52 component analyses (PCA) were applied to all three types of samples to determine natural clustering 53 of samples, and a mixing model was applied to determine source contributions. 54Results and discussion: We found that fine sediment stored in the river bed seems to be mainly 55 influenced by grain size and seasonal variability, while sampling location -and thus the effect of 56 individual tributaries or subcatchments -seem to be of minor importance. Suspended sediment 57 sources were found to vary between, as well as within, flood events; although badlands were always 58 the major source. Forests and grasslands contributed little (<10%) and other sources (not further 59 determinable) contributed up to 40%. The analyses further suggested that sediment sources differ 60 among the subcatchments and that subcatchments comprising relatively large proportions of 61 badlands contributed most to the four flood events analyzed. 62Conclusions: Spectral fingerprints provide a rapid and cost-efficient alternative to conventional 63 fingerprint properties. However, a combination of spectral and conventional fingerprint properties 64 could potentially permit discrimination of a larger number of source types. 81Knowledge of sediment provenance is a key factor in understanding sediment transport and delivery 82 processes and thus a first step in the design of sustainable watershed management strategies 88with little or no vegetation […] in an intensely dissected landscape" (Gallart et al. 2002). Lithology is a 89 major factor for badland development and though they are commonly considered characteristic of 90 dryland regions they also occur in more humid climates with high topographic gradients and intense 91 rainstorms (Gallart et al. 2002). Despite badlands being considered as major sediment sources, 92 significant changes in the colour of the suspended sediments have been observed between, and even 93 within, runoff events, suggesting the influence of varying sources. 94A direct approach to trace the origin of sediment is a method called fingerprinting. It is founded on the 95 principal assumptions that: (1) potential sediment sources can be discriminated based on a set of 96 characteristic properties ("fingerprints"); and (2) the comparison of these source characteristics with 97 those of (suspended) sediment allow for determination of relative source contribution (Collins and 100However, the adaptation of the technique as a management tool is hampered due to several reasons. 101Most importantly, the choice of successful fingerprint properties is highly site-specific and the lack of Poulenard et al. 2009Poulenard et al. , 2011 Martínez-Carreras 2010a, 2010b, 2010c Evrard et al. 2012; Legout et 108 al. 2013; Bros...

No abstract

Abstract:Water scarcity and climatic variability in the Mediterranean region have traditionally required the construction of dams to guarantee water supply for irrigation, industrial and urban uses and hydropower production. Reservoirs affect the hydrology of the river downstream, but the magnitude and persistence of these effects are still poorly unknown. Understanding the magnitude of these effects is the objective of this paper, in which we analyse the flow regimes of twelve rivers located in the NW Mediterranean region. Different temporal scales (daily, monthly and annual) are used for the analysis and also to estimate flow variables associated with flow magnitude, frequency, duration and variability. It is shown that dams alter the hydrological regime of most of the studied rivers, with special influence on monthly flows and flood magnitude and frequency. The most altered rivers (Muga and Siurana, NE Iberian Peninsula) experience a complete overturn in their flow regime with, for instance, flood reduction reaching up to 76% for the 2-year flood event. Other rivers showed lower changes in hydrology (e.g. Orb and Têt). Annual runoff showed a pattern of decrease in all the studied rivers (regulated and non-regulated) indicating that besides dams (i.e. reservoir evaporation), other factors likely affect water yield. A general recovery downstream from dams is also observed at all temporal scales, mainly because of the inflow from tributaries. Although dams have a clear impact on the hydrology of Mediterranean rivers, water withdrawals and diversions for irrigation and other consumptive uses also affected the hydrological patterns.