Sensitivity assessment of the deltaic coast of Medjerda based on fine-grained sediment dynamics, Gulf of Tunis, Western Mediterranean Oula Amrouni 1 & A. Sánchez 2 & N. Khélifi 3,4 & T. Benmoussa 5 & D. Chiarella 6 & G. Mahé 7 & S. Abdeljaouad 5 & P. McLaren 8 Received: 25 April 2018 /Revised: 15 May 2018 /Accepted: 25 February 2019 # Springer Nature B.V. 2019 Abstract As coastal areas become increasingly vulnerable to climate change, the study of nearshore sediment textures along the littoral cell of the Medjerda delta in the Gulf of Tunis, southern Mediterranean coast can provide valuable information (i) on the origin (continental or marine) of the sediment, (ii) its transport direction, and (iii) constitutes an important tool in the assessment of coastal sensitivity. A total of 120 sediments samples underwent grain size analysis and statistic parameters have been calculated. These allowed the identification of five different Sedimentary Types (ST). Accordingly, using grain size indexes (i.e. Mz, SKI and Ku), Sediment Trend Analysis (STA) modeling tools were applied to define the seasonal sediment transport pathways throughout the nearshore of the Medjerda sedimentary cell. Results show that grain size distribution (GSD) and STA model pathways are determined by cross-shore geomorphology, location of the sediment-cell, seasonal incident wave and local terres- trial supply. The appearance in an atypical seabed location of the finer (Mo = 0.1 mm) and the coarser STs (Mo = 0.8 mm) can be indicative of human influence since the coarser particles are usually retained by dam structures. Moreover, the bimodality and the increased distribution of mud are also related to the seasonal incident wave winnowing of the historic deltaic plain submerged by the relative rise in sea level. The evolution of the sediment pattern towards a greater proportion of very fine grains indicates a deficit of sediment supply, particularly of the coarser grains, and demonstrates the coastal vulnerability of the Gulf of Tunis due to anthropic effects. Keywords Grain size distribution . Sedimentary type . Sediment transport analysis . Sensitivity . Medjerda coast . Gulf of Tunis Introduction Rivers carry the products of both natural geological processes and anthropogenic pollutants to the sea (Presley et al. 1980) contributing for ~90% of the total seaward transport of dis- solved and suspended solids (Garrels and Mackenzie 1971). The sandy coast of the Gulf of Tunis bordering the River plain of Medjerda is mainly the result of a terrestrial sediment trans- port driven by Medjerda River during the last ~1700 y (Paskoff and Trousset 1992; Paskoff 1994; Delile et al. 2015). The deltaic plain of this River also contains a mixture of riverine mud and sand supplied by long-shore transport from the surrounding coast (Kalai 1985; Paskoff 1994). In this context, the Tunisian coast has been a subject of scientific interest since the mid-nineteenth century (e.g. Paskoff 1981; Paskoff and Sanlaville 1983; Kouki 1984; Oueslati 1993; Maghrebi 1995; El Arrim 1996; Amrouni 2002, 2008; Gargouri 2009; Bardi 2010; Saidi 2013; Louati 2014; Hzami 2015). Building on these previous studies, characterization of the textural parameters of the sediment and their evolution * Oula Amrouni oula.amrouni@instm.rnrt.tn; oulaamrouni@gmail.com 1 Laboratory of Marine Environment, National Institute of Marine Sciences and Technologies, University of Carthage, 2025 Carthage Salammbô, Tunisia 2 Centro Interdisciplinario de Ciencias Marinas, Instituto Politécnico Nacional, La Paz, BCS, Mexico 3 GEOMAR Helmholtz Center for Ocean Research Kiel, 24148 Kiel, Germany 4 Middle East and North African Program, Springer, a part of Springer Nature, 69121 Heidelberg, Germany 5 Laboratory of Energetic, Mineral Resources and Environment, Department of Geology, Faculty of Sciences, University of Tunis-El Manar, 2092 Tunis, Tunisia 6 Department of Earth Sciences, Royal Holloway, University of London, Egham TW20 0EX, UK 7 IRD – HydroSciences Montpellier, UMR5569, Université de Montpellier 2, Case courrier MSE, Place Eugène Bataillon, 34095 Montpellier cedex 5, France 8 SedTrend Analysis Limited, Brentwood Bay, BC V8M1C5, Canada Journal of Coastal Conservation https://doi.org/10.1007/s11852-019-00687-x