ORIGINAL PAPER Complex reservoir sedimentation revealed by an unusual combination of sediment records, Kangaroo Creek Reservoir, South Australia John Tibby Æ Peter Gell Æ Gary Hancock Æ Malcolm Clark Received: 5 May 2009 / Accepted: 14 May 2009 / Published online: 23 June 2009 Ó Springer Science+Business Media B.V. 2009 Abstract Despite their direct links to human use, reservoirs are not widely utilised, relative to natural lakes, for deriving sediment histories. One explana- tion is the complex sedimentation patterns observed in water storages. Here a highly unusual combination of sedimentary records is used to determine the sedi- mentation history of Kangaroo Creek Reservoir, South Australia. We compare contiguous high reso- lution (0.5 cm sampling interval) diatom records from an almost 1.3 m core extracted from the bottom of the reservoir and from a 0.4 m monolith of sediment perched 15 m above the reservoir bottom on a disused bridge that was submerged following initial reservoir filling in 1970. The diatom histories are supplemented by evidence provided by other indicators, most notably radionuclide concentrations and ratios. Inter- estingly, despite the fact that the reservoir has been [ 20 m deep for more than 70% of its recorded history, distinct sections of the reservoir bottom core, but not the bridge monolith, are dominated by non- planktonic diatoms. We attribute the occurrences of these phases to inflows that occur following heavy catchment rains at times when the reservoir is drawn down. These characteristic sections have, in turn, been used to refine the site’s chronology. Despite having a length of almost 1.3 m, a variety of data suggests that the core has not recovered pre-reservoir sediment, but rather spans the period from 1981 (11 years after first filling) to 2001, when the core was extracted. It is clear, therefore, that sediments in the bottom of the reservoir are accumulating rapidly ( [ 7 cm year -1 ), although more than 40% of this deposition occurs in less than 5% of the time. It appears that in the period 1996–2001, quiescent sedimentation rates, both in the perched bridge locality and on the reservoir bottom, slowed in response to reduced stream flow. Our findings indicate that, with caution, complex patterns of sedimentation in water storages can be disentan- gled. However, it was difficult to precisely correlate diatom sequences from the two records even in periods of quiescent sedimentation, suggesting that reservoir bottom diatom sequences should be inter- preted with considerable caution. Furthermore, while storm-derived inflows such as those identified may Electronic supplementary material The online version of this article (doi:10.1007/s10933-009-9349-0) contains supplementary material, which is available to authorized users. J. Tibby (&)  P. Gell Geographical and Environmental Studies, University of Adelaide, Adelaide, SA 5005, Australia e-mail: john.tibby@adelaide.edu.au P. Gell School of Science & Engineering, University of Ballarat, Ballarat, VIC 3353, Australia G. Hancock Rivers and Coasts, CSIRO Land and Water, Canberra, ACT 2601, Australia M. Clark School of Mathematical Sciences, Monash University, Clayton, VIC 3800, Australia 123 J Paleolimnol (2010) 43:535–549 DOI 10.1007/s10933-009-9349-0