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In this study, a new remote sensing tool was used in conjunction with sampling of river bank sediments to map channel migration patterns and estimate the net contribution of bank erosion to the sediment and phosphorus (P) budget of the Nishnabotna River in southwestern Iowa. Between the years 2009 and 2018, we found that at least 1.81 ± 0.57 × 107 Mg of sediment and 8.26 ± 2.5 × 103 Mg of P entered the Nishnabotna River due to channel migration. This equates to 0.87 Mg of sediment per meter of channel per year and 0.40 kg of P per meter of channel per year. Barring additional deposition elsewhere in the river corridor, these values represent as much as 77% of annual suspended sediment and 46% of the annual P export from the watershed. Our results also indicate that the contribution of net sediment and P volume loss by stream order increases sharply from third to sixth order, even though the total channel length is much smaller in the higher orders. These results suggest that bank erosion is an important source of sediment and P within the watershed and that future attempts to decrease riparian exports of sediment and P should focus on high‐order reaches. [ABSTRACT FROM AUTHOR]

Slow, stable shear of granular materials in landslides, beneath glaciers, and along fault surfaces is common, despite little or no intrinsic strengthening of such materials with increasing deformation rate. Compacted, water-saturated sediments, subjected to constant stresses in a ring-shear device, sheared slowly without unstable acceleration in repeated episodes that included pore dilation during shear, attendant pore-water-pressure decline, and consequent strengthening, followed by gradual pore-pressure recovery and weakening. Time-averaged shear velocities (2-800 mm/d) depended inversely on the magnitude of pore dilation with shear and were significantly lower for fine-grained sediment than for coarse-grained sediment, owing to different rates of pore-pressure diffusion in the two materials. When sediment had dilated to its critical-state (steady) porosity and therefore could not dilate further, shear accelerated catastrophically. These data indicate that pore-pressure decreases and consequent strengthening caused by shear-induced dilation may not only suppress rapid shear of landslide debris, subglacial till, and fault gouge, but may also result in slow episodic shear at rates that depend on both material porosity and hydraulic diffusivity. Keywords: shear, porosity, pore-water pressure, landslides, till, gouge.

The article discusses the study which develops a simple instrument circuit to allow measurement of short subglacial waterpressure pulses. It states that the circuit continuously powers a pressure transducer and captures the peak output of the transducer every measurement intervals to determine the maximum pressure attained during the interval. It notes that the circuit provides an option to a data logger in the performance of speedy repeated measurements. It adds that the data-logger microprocessor allows additional instruments to be monitored simultaneously while reducing memory usage and lowering power consumption.