Insights into bedload transport processes of a large regulated gravel‐bed river

A comprehensive monitoring programme focusing on bedload transport behaviour was conducted at a large gravel‐bed river. Innovative monitoring strategies were developed during five years of preconstruction observations accompanying a restoration project. A bedload basket sampler was used to perform 55 cross‐sectional measurements, which cover the entire water discharge spectrum from a 200‐year flood event in 2013 to a rare low flow event. The monitoring activities provide essential knowledge regarding bedload transport processes in large rivers. We have identified the initiation of motion under low flow conditions and a decrease in the rate of bedload discharge with increasing water discharge around bankfull conditions. Bedload flux strongly increases again during high flood events when the entire inundation area is flooded. No bedload hysteresis was observed. The effective discharge for bedload transport was determined to be near mean flow conditions, which is therefore at a lower flow discharge than expected. A numerical sediment transport model was able to reproduce the measured sediment transport patterns. The unique dataset enables the characterisation of bedload transport patterns in a large and regulated gravel‐bed river, evaluation of modern river engineering measures on the Danube, and, as a pilot project has recently been under construction, is able to address ongoing river bed incision, unsatisfactory ecological conditions for the adjacent national park and insufficient water depths for inland navigation. Copyright © 2017 John Wiley & Sons, Ltd.     

In situ measurements of fine sediment infiltration (FSI) in gravel-bed rivers with a hydropeaking flow regime

The overpresence of fine sediment and fine sediment infiltration (FSI) in the aquatic environment of rivers are of increasing importance due to their limiting effects on habitat quality and use. The habitats of both macroinvertebrates and fish, especially spawning sites, can be negatively affected. More recently, hydropeaking has been mentioned as a driving factor in fine sediment dynamics and FSI in gravel-bed rivers. The primary aim of the present study was to quantify FSI in the vertical stratigraphy of alpine rivers with hydropeaking flow regimes in order to identify possible differences in FSI between the permanently wetted area (during base and peak flows) and the so-called dewatering areas, which are only inundated during peak flows. Moreover, we assessed whether the discharge ratio between base and peak flow is able to explain the magnitude of FSI. To address these aims, freeze-core samples were taken in eight different alpine river catchments. The results showed significant differences in the vertical stratification of FSI between the permanently wetted area during base flow and the dewatering sites. Surface clogging occurred only in the dewatering areas, with decreasing percentages of fine sediments associated with increasing core depths. In contrast, permanently wetted areas contained little or no fine sediment concentrations on the surface of the river bed. Furthermore, no statistical relationship was observed between the magnitude of hydropeaking and the sampled FSI rate. A repeated survey of FSI in the gravel matrix revealed the importance of de-clogging caused by flooding and the importance of FSI in the aquatic environment, especially in the initial stages of riparian vegetation establishment. © 2018 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.     

Development of a Neural Network Algorithm for Retrieving Concentrations of Chlorophyll, Suspended Matter and Yellow Substance from Radiance Data of the Ocean Color and Temperature Scanner

An algorithm is presented to retrieve the concentrations of chlorophyll a, suspended pariclulate matter and yellow substance from normalized water-leaving radiances of the Ocean Color and Temperature Sensor (OCTS) of the Advanced Earth Observing Satellite (ADEOS). It is based on a neural network (NN) algorithm, which is used for the rapid inversion of a radiative transfer procedure with the goal of retrieving not only the concentrations of chlorophyll a but also the two other components that determine the water-leaving radiance spectrum. The NN algorithm was tested using the NASA's SeaBAM (SeaWiFS Bio-Optical Mini-Workshop) test data set and applied to ADEOS/OCTS data of the Northwest Pacific in the region off Sanriku, Japan. The root-mean-square error between chlorophyll a concentrations derived from the SeaBAM reflectance data and the chlorophyll a measurements is 0.62. The retrieved chlorophyll a concentrations of the OCTS data were compared with the corresponding distribution obtained by the standard OCTS algorithm. The concentrations and distribution patterns from both algorithms match for open ocean areas. Since there are no standard OCTS products available for yellow substance and suspended matter and no in situ measurements available for validation, the result of the retrieval by the NN for these two variables could only be assessed by a general knowledge of their concentrations and distribution patterns. This revised version was published online in July 2006 with corrections to the Cover Date.     

Variance of collapse capacity of SDOF systems under earthquake excitations

The variance of collapse capacity is an important constituent of probabilistic methodologies used to evaluate the probability of collapse of structures subjected to earthquake ground motions. This study evaluates the effect of ground motion randomness (i.e. record‐to‐record (RTR) variability) and uncertainty in the deterioration parameters of single‐degree‐of‐freedom (SDOF) systems on the variance of collapse capacity. Collapse capacity is evaluated in terms of a relative intensity defined as the ratio of ground motion intensity to a structure strength parameter. The effect of RTR variability on the variance of collapse capacity is directly obtained by performing dynamic analyses of deteriorating hysteretic models for a set of representative ground motions. The first‐order second‐moment (FOSM) method is used to quantify the effect of deterioration parameter uncertainty. In addition to RTR variability, the results indicate that uncertainty in the displacement at the peak (cap) strength and the post‐capping stiffness significantly contribute to the variance of collapse capacity. If large dispersion of these parameters exists, the effect of uncertainty in deterioration parameters on the variance of collapse capacity may be comparable to that caused by RTR variability. Copyright © 2011 John Wiley & Sons, Ltd.     

Temporal evolution of weathered cataclastic material in gravitational faults of the La Clapiere deep-seated landslide by mechanical approach

After a few years of research, the observation and the analysis of the deep-seated landslides suggest that these are mainly controlled by tectonic structures, which play a dominant role in the deformation of massif slopes. The La Clapière deep-seated landslide (Argentera Mercantour massif) is embedded in a deep-seated gravitational slope deformation affecting the entire slope, and characterized by specific landforms (trenches, scarps??). Onsite, the tangential displacement direction of the trenches and the scarps are controlled by the tectonic structures. The reactivation of the inherited fault in gravitational faults create a gouge material exposed to an additional mechanical and chemical weathering as well as an increased of leaching. The displacement of these reactivated faults gets increasingly important around the area of the La Clapière landslide and this since 3.6?ka BP. In this study, mechanical analysis and grain size distributions were performed and these data were analysed according to their proximity the La Clapiere landslide and times of initiation of the landslide by ¹⁰Be dating. Triaxial test results show that the effective cohesion decreases and the effective angle of internal friction increases from the unweathered area to the weathered area. The whole distribution of the grain size indicates that the further the shear zone is open or developed, the further the residual material loses its finest particles. This paper suggests that the mechanical evolution along the reactivated fault is influenced by the leaching processes. For the first time, we can extract from these data temporal behaviour of the two main mechanical parameters (cohesion and angle of internal friction) from the beginning of the La Clapiere landslide initiation (3.6 ka BP) to now.     

The impact of discharge change on physical instream habitats and its response to river morphology

The impact of climate-induced discharge change on fish habitats, based on 1951–2008 time series, was investigated within the crystalline catchment of the Grosse Mühl River in Northern Austria. A significant trend change of air temperature, based on Mann–Whitney statistical testing, was recorded for spring 1989 (P?=?98.9 %) and summer 1990 (P?=?99.9 %). This led to a pronounced increase in summer low flow periods. Hydrodynamic-numerical (one-dimensional/two-dimensional) modelling was applied to simulate the changing habitat characteristics due to decreasing discharge in relation to various morphological patterns (riffle-pool/plane-bed reaches). Using bathymetric data, which were sampled on cross sectional measurements, we clearly determined that plane-bed reaches (featureless bed forms) are sensitive to climate-related, reduced discharge, whereas riffle-pool reaches continued to exhibit suitable physical fish habitats even under extreme low-flow conditions. The impact of the decreased summer discharge on instream habitats was strong for subadult and adult grayling which have been used as target fish species. In situ measurements in microhabitats (velocity/depth) revealed habitat suitabilities. These values were taken as biotic input for habitat evaluation on the micro scale. The findings clearly show that river morphology is a decisive parameter in terms of habitat preservation and restoration in the context of the future impacts of climate change (decreased discharge).