Organisational controls, typologies and time scales of paraglacial gravel-dominated coastal systems Julian D. Orford a, * , Donald L. Forbes b , Simon C. Jennings c a School of Geography, Queen’s University, Belfast, BT7 1NN, UK b Geological Survey of Canada, Bedford Institute of Oceanography, P.O. Box 1006, Dartmouth, Nova Scotia, Canada, B2Y 4A2 c School of Biological and Applied Sciences, University of North London, London N7 8DB, UK Received 1 December 1999; received in revised form 10 June 2000; accepted 24 January 2002 Abstract The fundamental controls on the initiation and development of gravel-dominated deposits (beaches and barriers) on paraglacial coasts are particle size and shape, sediment supply, storm wave activity (primarily runup), relative sea-level (RSL) change, and terrestrial basement structure (primarily as it affects accommodation space). This paper examines the stochastic basis for barrier organisation as shown by variation in gravel barrier architecture. We recognise punctuated self-organisation of barrier development that is disrupted by short phases of barrier instability. The latter results from positive feedback causing barrier breakdown when sediment supply is exhausted. We examine published typologies for gravel barriers and advocate a consolidated perspective using rate of RSL change and sediment supply. We also consider the temporal variation in controls on barrier development. These are examined in terms of a simple behavioural model (BARCH) for prograding gravel barrier architecture and its sensitivity to such controls. The nature of macroscale (10 2 –10 3 years) gravel barrier development, including inherited characteristics that influence barrier genesis, as well as forcing from changing RSL, sediment supply, headland control and barrier inertia, is examined in the context of long-surviving barriers along the southern England coastline. Crown Copyright D 2002 Published by Elsevier Science B.V. All rights reserved. Keywords: Relative sea level; BARCH; Back-barrier morphology 1. Introduction Gravel-dominated shore face, beach, and barrier systems have attracted a growing scientific effort and literature over the past 20 years. Their importance in a variety of modern settings is now generally recog- nised and there is a wider understanding of the need for specific management strategies on gravel-domi- nated coasts (e.g. Carter and Orford, 1980; Carr, 1983; Kirk, 1992). At the same time, there has been a rapid acceleration of interest in ancient conglomeratic coastal deposits (e.g. Howell and Link, 1979; Bour- geois and Leithold, 1984; Bergman and Walker, 1987; Massari and Parea, 1988; Arnott, 1991; Hart and Plint, 1991). It is clear that gravel and mixed sand–gravel beaches display lithofacies relations and morphody- namic responses distinct from those associated with sand-dominated coasts (e.g. Bluck, 1967, 1999; For- bes and Taylor, 1987; Carter and Orford, 1993; Hart 0169-555X/02/$ - see front matter. Crown Copyright D 2002 Published by Elsevier Science B.V. All rights reserved. PII:S0169-555X(02)00175-7 * Corresponding author. E-mail addresses: j.orford@qub.ac.uk (J.D. Orford), forbes@agc.bio.ns.ca (D.L. Forbes), s.jennings@unl.ac.uk (S.C. Jennings). www.elsevier.com/locate/geomorph Geomorphology 48 (2002) 51 – 85