Sediment Budgets and Sediment Delivery Ratios in River Systems
- LAST MODIFIED: 27 July 2016
- DOI: 10.1093/obo/9780199363445-0058
- LAST MODIFIED: 27 July 2016
- DOI: 10.1093/obo/9780199363445-0058
The term sediment flux refers to sediment movement through landscapes. Analogous to “flux” in physics, i.e., the rate of flow of a property per unit area, sediment flux is the amount of sediment that flows through a cross-section of river per unit time. The magnitude of sediment flux is moderated by catchment processes such as sediment production (erosion), sediment accumulation (deposition) and intervening processes of sediment storage and reworking (transfer). Patterns and rates of sediment flux vary over a wide range of spatial and temporal scales, from grain to grain and landform scale analyses over near instantaneous timeframes through reach and catchment-scale analyses that are typically performed over decadal to millennial timescales to continental-scale appraisals over millions of years. Sediment movement is a key physical driver of natural environments. It exerts a critical influence upon the morphology, process regime, and evolutionary traits of landscapes. For example, as sediment budgets quantify sediment transport pathways, they can be used to analyze the critical factors that affect landscape development. Sediment flux exerts a critical influence upon the physical template (habitat distribution) of river systems. As such, it is a key consideration in river management and restoration. Analysis of source-to-sink relationships at the catchment scale (and associated sediment budgets) highlights controls upon sediment delivery and the influence of landscape connectivity. Emphasis here is placed upon valley floor processes, giving only partial attention to hillslope forms and processes or consideration of lakes, deltas, and nearshore marine environments. Textbooks and journals that present overviews of sediment flux in river systems are considered first. A brief overview of global scale sediment flux summarizes the movement of sediment from terrestrial areas to the ocean and the imprint of human activities. Most of this contribution focuses on catchment-scale sediment budgets, emphasizing variability in sediment sources (hillslope inputs and reworking on valley floors), the thorny question of scale relations, controls upon the sediment delivery ratio, and the influence of landscape connectivity. In many instances, disturbance events disrupt the sediment regime of a river, creating distinct pulses (or waves) that are transferred downstream by dispersion or migration processes. This is followed by an analysis of approaches to measurement of sediment flux, differentiated in relation to conventional field techniques, use of sediment fingerprinting, and the emergence of a range of remotely sensed technologies. The final sections of this article outline implications of human-induced alterations to sediment flux for river management. Appraisal of sediment disasters (impacts of dams, fine-grained sediment accumulation, and mining activities) is followed by an assessment of implications for river restoration.
The study of sediment flux encompasses a wide range of issues from differing disciplinary perspectives. Here focus is placed upon geomorphic perspectives, rather than hydraulically based understandings of sediment erosion, transport, and deposition processes, or ecological and geochemical applications. In a companion article, consideration is given to sediment regime and river morphodynamics. Schumm 2003 (originally published in 1977) differentiates among sediment source, transfer, and accumulation zones in catchments (also referred to as watersheds or drainage basins). This work provides a framework to assess sediment movement in terms of source-to-sink relationships at the catchment scale. Process relationships between these three compartments of landscapes determine the sediment budget of a catchment, wherein sediment storage exerts a primary control upon the sediment delivery ratio (the proportion of eroded sediment within a system that reaches the basin outlet within a given time period). Landscape connectivity relationships and associated notions of sediment residence times in sinks and stores are key determinants of the sediment delivery ratio. Reid and Dunne 1996 provides a helpful overview of key considerations in constructing a sediment budget. Burt and Allison 2010 presents a synthesis of process relationships that influence sediment cascades. These approaches build upon coherent geomorphic understanding of catchment-scale interactions, elegantly summarized in Knighton 1998. The importance of field and laboratory experiments as tools to support predictions of sediment flux is demonstrated in Schumm, et al. 1987. Sediment sources, controls upon soil erosion, and management prospects are summarized in Toy, et al. 2002. Applied aspects of sediment budgets are considered in Calow and Petts 1992 and Brierley and Fryirs 2005.
Brierley, G. J., and K. A. Fryirs. 2005. Geomorphology and river management: Applications of the river styles framework. Oxford: Blackwell.
This textbook outlines how cross-scalar geomorphic relationships can inform river management applications through appraisal of process-form linkages and evolutionary traits, emphasized through analyses of sediment dynamics (routing and storage). These principles are related to network connectivity, assessing river response to disturbance at the catchment scale.
Burt, T., and R. Allison. 2010. Sediment cascades: An integrated approach. Chichester, UK: John Wiley.
This text provides an authoritative and comprehensive overview of sediment regime, from source areas to estuaries and the continental slope. Examples demonstrate how the sediment budget framework captures the dynamics of sediment flux and storage through various landscapes. Conceptual problems such as magnitude and frequency and equilibrium timescales are evaluated.
Calow, P., and G. E. Petts. 1992. The rivers handbook: Hydrological and ecological principles. Vol. 1. Oxford: Blackwell.
This text provides a comprehensive overview of links among hydrological processes, river forms, and ecological functions of river systems. The chapter by Church summarizes links among gradient, bed material size, sediment storage on the valley floor, and discharge along longitudinal profiles. See also Volume 2, The Rivers Handbook: Hydrological and Ecological Principles, edited by P. Calow and G. E. Petts (Oxford: Blackwell Scientific, 1994).
Knighton, D. 1998. Fluvial forms and processes: A new perspective. 3d ed. London: Routledge.
This readily accessible text presents an overview of controls upon fluvial forms and processes. Empirical and theoretical approaches are combined to provide a summary of differing approaches to assessment of river adjustment.
Reid, L. M., and T. Dunne. 1996. Rapid evaluation of sediment budgets. Reiskirchen, Germany: Catena Verlag.
This book provides a comprehensive overview of strategies and tools to assess sediment production and transport in watersheds. Guidance in constructing a sediment budget builds upon information on the amount and grain size characteristics of sediment contributed by each type of source, the volumes and grain sizes of sediment in storage, and the transport rate of sediment through channels. Several examples of rapidly constructed sediment budgets are documented.
Schumm, S. A. 2003. The fluvial system. Caldwell, NJ: Blackburn.
Originally published in 1977. This critical overview of the influence of catchment structure on the sediment delivery system differentiates between process relationships in sediment source, transfer, and deposition zones. The text provides a bridge between the stratigraphic record and the behavior of the fluvial system, relating controls such as changes to river base level and tectonic uplift to morphological and behavioral attributes of rivers.
Schumm, S. A., M. P. Mosley, and W. E. Weaver. 1987. Experimental fluvial geomorphology. New York: Wiley.
Laboratory and modeling applications are used alongside field investigations of process relationships in river systems to assess issues such as drainage basin evolution, river morphology, and sedimentology. Insights into controls upon the behavior of incised rivers (gullies) are especially noteworthy.
Toy, T. J., G. R. Foster, and K. G. Renard. 2002. Soil erosion: Processes, prediction, measurement, and control. New York: John Wiley.
This overview of the physical causes, processes, and effects of soil erosion uses real-world examples to highlight implications for future conservation and remediation. This includes practical guidance into erosion-prediction technologies, erosion measurements, and the use of erosion models as erosion-control tools.
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