Post-eruption morphological evolution and vegetation dynamics of the Blanco River, southern Chile

In this study, we analysed the morphological evolution of a channel segment in the Blanco River in southern Chile that was affected by the Chaitén Volcano eruption occurred in 2008–2009. Through a series of high-resolution satellite images from 2005 to 2019 that represents the entire pre- and post-eruptive dynamics and land covers, we tracked the geomorphological evolution of a 5.65-km-long river segment using channel form indices and also monitored the vegetation dynamics using object-based image analysis (OBIA). Discharge record for the Blanco River was also reconstructed to support the analysis of channel morphologic process. The study aims at examining whether a) the river channel is still adjusting 10 years after the eruption and if so, at what magnitude and, b) the recovered riparian vegetation plays a significant role in stabilising the river streambanks and terraces. We found that even 10 years after the eruption, the Blanco River channel planform is still adjusting, showing a simpler and stable channel configuration in the upstream reaches of the valley, where a certain degree of equilibrium appears to have been attained. More dynamic morphologies were observed in the reaches downstream that have to accommodate the arrival of large amounts of freshly eroded sediments. Our analysis showed that the occurrence of competent floods capable of reworking the river channel matches with the geomorphic indices and mark the post-eruption adjustments of the channel. Finally, the in-channel and riparian vegetation does not play a significant role in stabilising the active channel, streambanks, and terraces, reinforcing the recolonization of sedimentary active areas occurring elsewhere in the valley.This research was developed within the frame of the project FONDECYT 1170413 funded by the Chilean Government. Authors acknowledge the support of the Economy and Knowledge Department of the Catalan Government through the Fluvial Dynamics Research Group (RIUS) SGR017-459

Flume and field-based calibration of surrogate sensors for monitoring bedload transport

Bedload transport assessment is important for geomorphological, engineering, and ecological studies of gravel-bed rivers. Bedload can be monitored at experimental stations that require expensive maintenance or by using portable traps, which allows measuring instantaneous transport rates but at a single point and at high costs and operational risks. The need for continuously measuring bedload intensity and dynamics has therefore increased the use and enhancement of surrogate methods. This paper reports on a set of flume experiments in which a Japanese acoustic pipe and an impact plate have been tested using four well-sorted and three poorly sorted sediment mixtures. Additional data were collected in a glacierized high-gradient Andean stream (Estero Morales) using a portable Bunte-type bedload sampler. Results show that the data provided by the acoustic pipe (which is amplified on 6 channels having different gains) can be calibrated for the grain size and for the intensity of transported sediments coarser than 9 mm (R2 = 0.93 and 0.88, respectively). Even if the flume-based calibration is very robust, upscaling the calibration to field applications is more challenging, and the bedload intensity could be predicted better than the grain size of transported sediments (R2 = 0.61 and 0.43, respectively). The inexpensive impact plate equipped with accelerometer could be calibrated for bedload intensity quite well in the flume but only poorly in the field (R2 = 0.16) and could not provide information on the size of transported sediments

Large wood load fluctuations in an Andean basin

The importance of monitoring and analysing wood fluxes in mountain environments is widely recognized. However, there is a lack of information related to the long-term fluctuations in wood load and associated to the changes in large wood (LW) characteristics. The main aims of the research were to analyse (i) changes in wood characteristics, (ii) fluctuations in wood load, and (iii) the relationship between wood load and sub-reach settings, proposing an ad hoc roughness index (RI). Repeated field surveys to measure wood load and LW characteristics during a 13-year period were conducted within a 2.2 km-long reach of the Rio Toro (Chile), which flows through the Malleco Forest National Reserve that was affected by wildfires in 2002 and 2015. Two spatial scales (i.e. study reach and sub-reach) were considered. Irrespective of the adopted scale wood load fluctuated considerably, in both number and volume, with significant changes in LW characteristics (i.e. mean diameter and length). Moreover, a clear tendency to the aggregation in wood jams (WJs) was observed within the entire study reach. Based on our results, we conclude that 17 years after the first wildfire wood recruitment has started in the upper parts of the basin. Moreover, Generalized Linear Mixed Models (GLMM) analyses were carried out to investigate the relationship between RI and both number and volume of LW. Both models are characterized by high adjusted R2 of 74.9% and 72.8% for volume and number, respectively. This demonstrated that the RI can characterize the reaches in terms of tendency to deposition and trapping of wood. These results are promising, particularly in improving the knowledge related to potential deposition areas that can control wood load fluctuations, also permitting its management to be improved. \ua9 2020 John Wiley & Sons, Ltd