Discharge and suspended sediment dynamics during two jökulhlaups in the Skaftá river, Iceland

Abstract

This paper investigates the dynamics and significance of discharge and suspended sediment transport (SST) during two jökulhlaups (glacier outburst floods) in the Skaftá River, south Iceland. Jökulhlaups occur frequently in many glacial environments and are highly significant in the geomorphological evolution of river basins and coastal environments. However, direct high-resolution monitoring of jökulhlaups has rarely been accomplished and hardly ever at more than one station in a downstream sequence. Here we present detailed data on jökulhlaup discharge and water quality from an intensive monitoring and sampling programme at two sites in summer 1997 when two jökulhlaups occurred. Evidence is discussed that supports the origin of both jökulhlaups being subglacial reservoirs, produced over several months by subglacial geothermal activity. At the downstream site, Ása-Eldvatn, the larger jökulhlaup (1)

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“…Fig. 2), following rainfall, snowmelt or glacier ablation events (Lawler and Brown, 1992;Old et al, 2005). However, clockwise hysteresis is often observed ( Fig.…”

“…Suspended sediment is an integral part of the functioning of fluvial systems, and indeed may be found in high concentrations even in near-pristine rivers (e.g. Lawler and Brown,1992;Old et al, 2005;Grove et al, 2015), but it can be a problematic water pollutant because of associated contaminants (e.g. Meybeck et al, 2007;Weber et al, 2008;Wetzel et al, 2013); turbidity increases which reduce light reception (Fig.…”

“…The suspended sediment concentration (SSC) limit of 25 mg l -1 set by the EC Freshwater Fish Directive, therefore, has "limitationsand" should be replaced by a dynamic limit reflecting the complexity of the sediment problem and the need to consider rivers and glacioi-fluvial systems with naturally high suspended sediment concentrations and loads (e.g. Old et al, 2005;Bilotta et al, 2012;Grove et al, 2015;Lawler, 2015).…”

“…Turbidity and SSC values vary strongly over time -often over many orders of magnitude (e.g. Walling, 1992;Old et al, 2005). Particulate concentrations, even at a single site, vary non-linearly with river flow levels, upstream sediment-source release and catchment processes ), and antecedent conditions.…”

“…In addition, difficulties are compounded because sediment flux events ("pulsing") may also occur independently of river flow events, especially in mountain and glacial meltwater basins (e.g. Lawler, 2005a;Old et al, 2005), linked to subglacial channel switching or ice-collapse events.…”