[1] A data set of 2890 field measurements was used to test the ability of several conventional flow resistance equations to predict mean flow velocity in gravel bed rivers when used with no calibration. The tests were performed using both flow depth and discharge as input since discharge may be a more reliable measure of flow conditions in shallow flows. Generally better predictions are obtained when using flow discharge as input

In the Erlenbach stream, a pre‐alpine steep channel in Switzerland, sediment transport has been monitored for more than 25 years. Near the confluence with the main valley river, stream flow is monitored and sediment is collected in a retention basin with a capacity of about 2000 m3. The basin is surveyed at regular intervals and after large flood events. In addition, sediment transport has been continuously monitored with piezoelectric bedload impact and geophone sensors since 1986. In 2008–2009, the measuring system in the Erlenbach stream was enhanced by installing an automatic system to obtain bedload samples. Movable metal baskets are mounted on a rail at the downstream wall of the large check dam above the retention basin, and they can be moved automatically into the flow to take bedload transport samples. The wire mesh of the baskets has a spacing of 10 mm to sample all sediment particles coarser than this size (which is about the limiting grain size detected by the geophones). The upgraded measuring system permits to obtain bedload samples over short sampling periods and to measure the grain size distribution of the transported material and its variation over time and with discharge. The analysis of calibration relationships for the geophone measuring system confirms findings from very similar measurements which were performed until 1999 with piezoelectric bedload impact sensors; there is a linear relationship between impulse counts and bedload mass passing over the sensors. Findings from flume experiments are used to discuss the most important factors which affect the calibration of the geophone signal. The bedload transport rates as measured by the moving baskets are among the highest measured in natural streams, with values of the order of several kilograms per meter per second. Copyright © 2012 John Wiley & Sons, Ltd.

Abstract. Data are compiled on bed load transport and discharge in gravel bed rivers and torrents with bed slopes up to 0.17. The transport characteristics of 19 streams are compared with simple bed load transport equations and with measurements from flume experiments. In simple form the bed load transport is a function of an "effective" discharge times a bed slope factor. The efficiency of the streams in transporting bed load is defined as the deviation from the transport function. It varies over several orders of magnitude, particularly for smaller and steeper streams, whereas flume experiments and larger streams are in better agreement with the simple bed load transport relation. The large variation and the strong decrease in efficiency in smaller streams appears to be associated with substantial form losses for relative flow depths (defined by h/d9o ) smaller than ---4-6.

Sediment transport in the Erlenbach, a small stream with step-pool morphology in the canton of Schwyz, Switzerland, has been monitored for more than 20 years. During this time three exceptional events (events with high sediment yield and long return times that have a large effect on channel morphology) have impacted the stream and partly or completely rearranged the existing step-pool morphology. In the aftermath of the events, sediment transport rates at a given discharge and total sediment yield remained elevated for about a year or longer. For the last event, dated on the 20 June 2007, observations of boulder mobility and step destruction were used to interpret channel stability. Boulders with median diameters of up to 135 cm and estimated weights of more than 2·5 tons have moved during the 2007 event. Using hydraulic observations and shear stress calculations boulders up to 65 cm in diameter were predicted to have been fully mobile in peak conditions, even if form resistance and increased critical stresses needed for the initiation of motion in steep streams were taken into account. For two of the events, estimated peak shear stresses at the bed exceeded 1000 Pa, calculated both from observations of the flow hydraulics and from boulder mobility. This suggests that highly energetic flows occur relatively frequently in small, steep streams and that large boulders can be transported by fluvial processes in such streams. The observations have potential significance for hazard risk mitigation, stream engineering and restoration.

Indirect bedload transport measurements have been made with the Swiss plate geophone system in five gravel‐bed mountain streams. These geophone sensors record the motion of bedload particles transported over a steel plate mounted flush with the channel bed. To calibrate the geophone system, direct bedload transport measurements were undertaken simultaneously. At the Erlenbach in Switzerland, a moving‐basket sampler was used. At the Fischbach and Ruetz streams in Austria, a Helley–Smith type bedload sampler provided the calibration measurements. A Bunte‐type bedload trap was used at the Rofenache stream in Austria. At the Nahal Eshtemoa in Israel, Reid‐type slot bedload samplers were used. To characterize the response of the geophone signal to bedload particles impacting on the plate, geophone summary values were calculated from the raw signal and stored at one second intervals. The number of impulses, i.e. the number of peaks above a pre‐defined threshold value of the geophone output signal, correlated well with field measured gravel transport loads and was found to be a robust parameter. The relations of impulses to gravel transport loads were generally near‐linear, but the steepness of the calibration relations differed from site to site. By comparing the calibration measurements from the different field sites and utilizing insights gained during preliminary flume experiments, it has been possible to identify the main factors that are responsible for site specific differences in the calibration coefficient. The analysis of these calibration measurements indicates that the geophone signal also contains some information about the grain size distribution of bedload. Copyright © 2013 John Wiley & Sons, Ltd.

[1] Steep mountain streams typically feature macro-roughness elements like boulders, step-pool sequences, and a varying channel width. Flow resistance because of such roughness elements appears to be an important control on bedload transport rates. Many commonly used bedload transport equations overestimate the transport in steep streams by orders of magnitude. Few approaches take into account the typical macro-roughness elements, and systematic tests of these models with field observations are lacking. In the present study several approaches were considered that allow calculating the contribution of macro-roughness elements to flow resistance. These approaches were combined with bedload transport equations and the predictions were compared to field measurements of discharge, transported bedload volumes, and channel characteristics in 13 Swiss mountain streams. The streams have channel slopes ranging from 2% to 19%, and catchment areas of 0.5 to 170 km 2 . For six streams there were time series of sediment yields, mostly measured annually, and for the other seven streams sediment volume estimates were available for large flood events in 2000 and 2005. All tested equation combinations achieved an improvement in bedload prediction compared to a reference equation that was uncorrected for macro-roughness. The prediction accuracy mainly depended on the size and density of the macro-roughness and on flow conditions. The best performance overall was achieved by an empirical approach accounting for macro-roughness, on the basis of an independent data set of flow resistance measurements.

Debris flow is a common process in the Swiss Alps and in other mountainous parts of the world. The understanding of debris-flow behaviour is essential to assess the hazards they present. An important approach towards improving the knowledge of debris-flow processes is the gathering of real-time data by debris-flow observation stations. Observation stations were established in three Swiss debris flow prone watersheds and equipped with video cameras, ultrasonic devices, a radar device, geophones, and rain gauges. In 2000, four significant debris flows were observed. The data provided useful information on the mechanics of debris flows and on the efficiency of the measuring devices. The observed debris flows are characterized by volumes between 5 000 and 35 000 m3, front velocities ranging from 2 to 5 m/s, and peak discharges between 20 and 125 m3/s. The analysis of the monitoring data revealed that ultrasonic and radar devices are very helpful tools, whereas the quality of the geophone signal strongly depends on the substrate on which the instrument is installed (i.e., bedrock versus unconsolidated material). Video images are useful to verify the data obtained by the other devices. A dynamic analysis of one debris flow was carried out and the simulated results are in fair agreement with the observed data.Key words: debris flow, Swiss Alps, monitoring, dynamic analysis.

The partitioning of the total sediment load of a river into suspended load and bedload is an important problem in fluvial geomorphology, sedimentation engineering and sedimentology. Bedload transport rates are notoriously hard to measure and, at many sites, only suspended load data are available. Often the bedload fraction is estimated with 'rule of thumb' methods such as Maddock's Table, which are inadequately field-tested. Here, the partitioning of sediment load for the Pitzbach is discussed, an Austrian mountain stream for which high temporal resolution data on both bedload and suspended load are available. The available data show large scatter on all scales. The fraction of the total load transported in suspension may vary between zero and one at the Pitzbach, while its average decreases with rising discharge (i.e. bedload transport is more important during floods). Existing data on short-term and long-term partitioning is reviewed and an empirical equation to estimate bedload transport rates from measured suspended load transport rates is suggested. The partitioning averaged over a flood can vary strongly from event to event. Similar variations may occur in the year-to-year averages. Using published simultaneous short-term field measurements of bedload and suspended load transport rates, Maddock's Table is reviewed and updated. Long-term average partitioning could be a function of the catchment geology, the fraction of the catchment covered by glaciers and the extent of forest, but the available data are insufficient to draw final conclusions. At a given drainage area, scatter is large, but the data show a minimal fraction of sediment transported in suspended load, which increases with increasing drainage area and with decreasing rock strength for gravel-bed rivers, whereby in large catchments the bedload fraction is insignificant at ca 1%. For sand-bed rivers, the bedload fraction may be substantial (30% to 50%) even for large catchments. However, available data are scarce and of varying quality. Longterm partitioning varies widely among catchments and the available data are currently not sufficient to discriminate control parameters effectively.