Towards prediction of suspended sediment yield from peak discharge in small erodible mountainous catchments (0.45–22 km2) of France, Mexico and Spain

[EN] The erosion and transport of fine-grained sediment in small mountainous catchments involve complex processes occurring at different scales. The suspended sediment yields (SSYs) delivered downstream are difficult to accurately measure and estimate because they result from the coupling of all these processes. Using high frequency discharge and suspended sediment data collected in eight small mountainous catchments (0.45-22km 2) from four distinct regions, we studied the relationships between event-based SSY and a set of other variables. In almost all the catchments, the event peak discharge (Q max) proved to be the best descriptor of SSY, and the relations were approximated by single power laws of the form SSY=αQmaxβ. The β exponents ranged between 0.9 and 1.9 across the catchments, while variability in α was much higher, with coefficients ranging between 25 and 5039. The broad distribution of α was explained by a combination of site-specific physical factors, such as the percentage of degraded areas and hillslope gradient. Further analysis of the factors responsible for data dispersion in each catchment was carried out. Seasonality had a significant influence on variability; but overall, most of the scattering in the SSY-Q max regressions was explained by the short-lasting memory effects occurring between successive events (i.e. in-channel temporary storage and remobilization of sediment; antecedent moisture conditions). The predictability of SSY-Q max models was also assessed. Simulations of SSY per event and of annual SSY were conducted by using the computed regressions and the measured Q max. Estimates of SSY per event were very uncertain. In contrast, annual SSY estimates based on the site-specific models were reasonably accurate in all the catchments, with interquartile ranges remaining in the ±50% error interval. The prediction quality of SSY-Q max relations was partly attributed to the statistical compensation that likely occurred between extreme values over a year; but it also suggests that the complex processes occurring at the event scale were smoothed at the annual scale. This SSY-Q max rating appears as a parsimonious predicting tool for roughly estimating SSY in small mountainous catchments. However, in its current form the technique needs further improvement as α and β values need to be better constrained. © 2012 Elsevier B.V.This research was funded by the following projects: STREAMS (French National Research Agency – BLAN06-1_139157), DESIRE (European Union FP6 – Contract No. 037046), PROBASE and INDICA (Spanish Government Grants No. CGL2006-11619/HID and CGL2011-27753-C02-01, respectively), and RESEL (Spanish Ministry of Environment). The authors wish to thank the CIEco and CIGA (Universidad Nacional Autónoma de México) for a fruitful collaboration. We are grateful to C. Prat for locally coordinating the DESIRE Project and to C. Obled for sharing constructive discussions. D. Tropeano and B. Fahey are also acknowledged for kindly providing documents. E. Nadal-Romero was the recipient of a research contract from the Spanish Ministry of Science and Innovation (Juan de la Cierva Program). Lastly, we would like to thank the two anonymous reviewers for their helpful comments on an earlier draft of this articlePeer Reviewe