The use of short-lived radionuclides to quantify transitional bed material transport in a regulated river

Nira L. Salant, Carl E. Renshaw, Francis J. Magilligan, James M. Kaste, Keith H. Nislow, Arjun M. Heimsath

Research output: Contribution to journalArticle

27 Scopus citations

Abstract

We investigate the use of the short-lived fallout radionuclide beryllium-7 (7Be; t1/2 = 53.4 days) as a tracer of medium and coarse sand (0.25-2 mm), which transitions between transport in suspension and as bed load, and evaluate the effects of impoundment on seasonal and spatial variations in bed sedimentation. We measure 7Be activities in approximately monthly samples from point bar and streambed sediments in one unregulated and one regulated stream. In the regulated stream our sampling splanned an array of flow and management conditions during the annual transition from flood control in the winter and early spring to run-of-the-river operation from late spring to autumn. Sediment stored behind the dam during the winter quickly became depleted in 7Be activity. This resulted in a pulse of 'dead' sediment released when the dam gates were opened in the spring which could be tracked as it moved downstream. Measured average sediment transport velocities (30-80 metres per day (m d-1)) exceed those typically reported for bulk bed load transport and are remarkably constant across varied flow regimes, possibly due to corresponding changes in bed sand fraction. Results also show that the length scale of the downstream impact of dam management on sediment transport is short (c. 1 km); beyond this distance the sediment trapped by the dam is replaced by new sediment from tributaries and other downstream sources.

Original languageEnglish (US)
Pages (from-to)509-524
Number of pages16
JournalEarth Surface Processes and Landforms
Volume32
Issue number4
DOIs
StatePublished - Apr 15 2007
Externally publishedYes

Keywords

  • Beryllium-7
  • Dams
  • Flow regulation
  • Sand
  • Sediment transport

ASJC Scopus subject areas

  • Geography, Planning and Development
  • Earth-Surface Processes
  • Earth and Planetary Sciences (miscellaneous)

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