Pool-fills: a window to palaeoflood history and response in bedrock-confined rivers

Jansen, J.D. and Brierley, G.J. (2004) Pool-fills: a window to palaeoflood history and response in bedrock-confined rivers. Sedimentology, 51(5), pp. 901-925. (doi: 10.1111/j.1365-3091.2004.00643.x)

Abstract

Channel-scale sedimentary units associated with bedrock-controlled riffle-pool morphology are examined in detail along Sandy Creek gorge, an ephemeral stream in arid south-eastern central Australia. Pool-fills comprise cut-and-fill assemblages of poorly sorted sediments ranging in texture from muds to boulders. Five unit types are defined based on particle size, sedimentary structures, geometry and bounding surface character: (1) coarse-grained bar platform; (2) fine-grained bar supraplatform; (3) fine-grained pool-fill; (4) fine-grained bench; and (5) modern pool-fill. The last coarse-grained unit currently lining the pools suggests an altered sedimentation style over the post-settlement period (post-ad 1860s). Situated at bedrock valley constrictions, pool-fills are compared with other sedimentary units associated with recirculating currents: eddy bars and slackwater deposits. But only the fine-grained bench units reflect eddy recirculation; the pool-fills are principally forced-bars associated with bedrock-controlled or 'forced' riffle-pool morphology. A late Holocene palaeoflood history is proposed based on radiocarbon ages from the pool-fills: multiple phases of cut-and-fill activity were preceded by a superflood 3400–1900 years ago that eroded the pool-fills to bedrock. The resilience of the pool-fills was illustrated by the passage of a 1-in-100-year flood in 1992, which caused only minor erosion. The presence of pool-fills may provide a window to past phases of river activity that cannot be extracted from either historical records/observations or palaeoflood slackwater sediment analyses. The formation and sedimentary preservation potential of these landforms reflect a combination of hydraulic and structural influences, but the occurrence of high-magnitude floods exerts the dominant control.

• Item Type: Articles
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Jansen, Dr John
• Authors: Jansen, J.D., and Brierley, G.J.
• College/School: College of Science and Engineering > School of Geographical and Earth Sciences
• Journal Name: Sedimentology
• ISSN: 0037-0746
• ISSN (Online): 1365-3091
• Published Online: 29 July 2004
• Copyright Holders: Copyright © 2004 Blackwell
• First Published: First published in Sedimentology 51(3):901-925
• Publisher Policy: Reproduced in accordance with the copyright policy of the publisher