Christopher A. Curran

Comparison of fluvial suspended‐sediment concentrations and particle‐size distributions measured with in‐stream laser diffraction and in physical samples

Laser-diffraction technology, recently adapted for in-stream measurement of fluvial suspended-sediment concentrations (SSCs) and particle-size distributions (PSDs), was tested with a streamlined (SL), isokinetic version of the Laser In Situ Scattering and Transmissometry (LISST) for measuring volumetric SSCs and PSDs ranging from 1.8 to 415 μm in 32 log-spaced size classes. Measured SSCs and PSDs from the LISST-SL were compared to a suite of 22 data sets (262 samples in all) of concurrent suspended-sediment and streamflow measurements using a physical sampler and acoustic Doppler current profiler collected during 2010–2012 at 16 U.S. Geological Survey streamflow-gaging stations in Illinois and Washington (basin areas: 38–69,264 km2). An unrealistically low computed effective density (mass SSC/volumetric SSC) of 1.24 g/mL (95% confidence interval: 1.05–1.45 g/mL) provided the best-fit value (R2 = 0.95; RMSE = 143 mg/L) for converting volumetric SSC to mass SSC for over two orders of magnitude of SSC (12–2,170 mg/L; covering a substantial range of SSC that can be measured by the LISST-SL) despite being substantially lower than the sediment particle density of 2.67 g/mL (range: 2.56–2.87 g/mL, 23 samples). The PSDs measured by the LISST-SL were in good agreement with those derived from physical samples over the LISST-SLs measureable size range. Technical and operational limitations of the LISST-SL are provided to facilitate the collection of more accurate data in the future. Additionally, the spatial and temporal variability of SSC and PSD measured by the LISST-SL is briefly described to motivate its potential for advancing our understanding of suspended-sediment transport by rivers.

Analysis of low flows and selected methods for estimating low-flow characteristics at partial-record and ungaged stream sites in western Washington

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Morphodynamic evolution following sediment release from the world’s largest dam removal

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.

Transport and deposition of asbestos-rich sediment in the Sumas River, Whatcom County, Washington

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