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 《地球表面变化过程与地形》2007,32(4):509-524

We investigate the use of the short‐lived fallout radionuclide beryllium‐7 (⁷Be; t_1/2 = 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 spanned 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. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

Damming Knowledge Flows: POWER as a Constraint on Knowledge Pluralism in River Flow Decision-making in the Saskatchewan River Delta     

Evan J. Andrews  Maureen G. Reed  Timothy D. Jardine  Toddi A. Steelman 《社会与自然资源》2018,31(8):892-907

Rivers and dams are increasingly contested venues where knowledge pluralism is critical for effective governance. To navigate change, decision-makers can adopt culturally-sensitive interventions to address the needs of diverse stakeholders and rights holders. Calls for Indigenous flows have become important as dam operators seek to renew their legal and social licenses to operate. Knowledge pluralism is needed to enhance decision-making about flows that better address complexity and change to Indigenous livelihoods and cultural practices. However, leveraging diverse knowledge types to inform these interventions is not simply a matter of changing management practice. Power relations can constrain knowledge pluralism. We contribute an empirical example that links power in a decision-making process about a dam in Saskatchewan, Canada, to the losses experienced by downstream Indigenous communities. This paper operationalizes power to illustrate its methodological utility and documents the interconnected losses, experienced by resources users, resultant from the marginalization of Indigenous knowledge.  相似文献