Airborne bathymetric LiDAR was collected for 220 river kilometres in the Yakima and Trinity River Basins in the USA. Concomitant with the aerial data collection, ground surveys of the river bed were performed in both basins. We assess the quality of the bathymetric LiDAR survey from the perspective of its application toward creating accurate, precise and complete streambed topography for numerical modelling and geomorphological assessment. Measurement error is evaluated with respect to ground surveys for magnitude and spatial variation. Analysis of variance statistics indicate that residuals from two independent ground surveys in similar locations do not come from the same population and that mean errors at different study locations also come from different populations. Systematic error indicates a consistent bias in the data and random error falls within values of expected precision.

Sediment pulses can cause widespread, complex changes to rivers and coastal regions. Quantifying landscape response to sediment-supply changes is a long-standing problem in geomorphology, but the unanticipated nature of most sediment pulses rarely allows for detailed measurement of associated landscape processes and evolution. The intentional removal of two large dams on the Elwha River (Washington, USA) exposed ~30 Mt of impounded sediment to fluvial erosion, presenting a unique opportunity to quantify source-to-sink river and coastal responses to a massive sediment-source perturbation. Here we evaluate geomorphic evolution during and after the sediment pulse, presenting a 5-year sediment budget and morphodynamic analysis of the Elwha River and its delta. Approximately 65% of the sediment was eroded, of which only ~10% was deposited in the fluvial system. This restored fluvial supply of sand, gravel, and wood substantially changed the channel morphology. The remaining ~90% of the released sediment was transported to the coast, causing ~60 ha of delta growth. Although metrics of geomorphic change did not follow simple time-coherent paths, many signals peaked 1–2 years after the start of dam removal, indicating combined impulse and step-change disturbance responses.

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[1] The emphasis of this research was placed on the development of a methodology that allows (1) an adequate representation of the distribution of the near-bank shear stress t s when secondary currents are present and (2) estimation of the critical erosional strength t cr and other sediment erodibility parameters for fluvial erosion. These two factors combine to form the overarching objective of this investigation, which was carried out in Union Flat Creek, a stream with pronounced cross-sectional irregularities located within the loess region of the Palouse basin of Washington State, United States. The study has shown that the presence of the secondary currents increases the magnitude of the depth-averaged sidewall shear stress at least by a factor of 2.0. It was also found that the ratio of the maximum to the depth-averaged sidewall shear stress t s is greater than 5. These findings suggest therefore that use of the t s may be a good approximation of the fluid shear stress magnitude for simple channel geometries but not for natural channels characterized by complex geometries. The measured critical erosional strength (t cr = 4.16 Pa) was comparable with the findings of other laboratory and field studies that also focused on Palouse sediments.