Morphological and sedimentary features of sandy‐muddy transitional beaches in estuaries and bays along mesotidal to macrotidal coasts. Issue 7 (9th March 2020)

• Record Type: Journal Article
• Authors: Zhao, Shaohua; Qi, Hongshuai; Cai, Feng; Zhu, Jun; Zhou, Xiang; Lei, Gang
• Is Part Of: Earth surface processes and landforms. Volume 45:Issue 7(2020)
• Page Start: 1660
• Page End: 1676
• Publication Date: 2020-03-09
• Subjects: sandy‐muddy transitional beach -- morphology -- sedimentology -- sand–mud transition -- Taiwan Strait coast; Geomorphology -- Periodicals; 551.4
• DOI: 10.1002/esp.4837
• Languages: English
• ISSNs: 0197-9337

Abstract

Abstract: Sandy‐muddy transitional beaches (SMT‐Beaches), representing the transition from sandy beaches to tidal mudflats, should theoretically develop very different morphological and sedimentological characteristics in river estuaries and in semi‐enclosed bays due to their contrasting dynamic sedimentary environments. Evidence, however, is rare in the scientific literature. To reveal these morphological and sedimentary differences, the sand–mud transition (SMT) boundary distribution, beach profiles, and surface and downcore sediment grain‐size compositions of 27 SMT‐Beaches located along mesotidal to macrotidal coasts of the western Taiwan Strait, southeastern China, were investigated. The results show that typical estuarine SMT‐Beaches are mainly characterized by an ambiguous SMT, a long distance between the SMT and the coastline (31–302 m), lower SMT and inflection point altitudes (average –0.76 m and –0.04 m), and lower upper beach gradients (~0.068) with fine sand. Estuarine SMT‐Beach sediments display clear interbedded mud and sand layers, implying potential SMT migrations over various timescales. By contrast, typical bay SMT‐Beaches are characterized by distinct SMT, a short distance between the SMT and the coastline (11–52 m), higher SMT and inflection point altitudes (~0.24 m and ~0.35 m), and narrower upper beaches with higher gradients (~0.095) and coarse sand. Bay SMT‐Beaches present relatively stable sedimentary sequences and a narrow gravel belt surrounding the inflection point and/or SMT. These morphological and sedimentary differences between the two SMT‐Beach types are initially constrained by sediment supply and transport and are further affected by tide conditions and wave climate. Sediment supply and transport predominately control the sediment structures, while the tidal range strongly influences spatial variations in SMT distances. Wave climate normally drives SMT altitude variations. This study highlights the morphological and sedimentary differences in SMT‐Beaches in estuaries and bays, providing important knowledge for further revealing their morphodynamic processes and potential future nourishment. © 2020 John Wiley & Sons, Ltd. Abstract : This study presents contrasting morphological and sedimentary characteristics of sandy‐muddy transitional beaches (SMT‐Beaches) located in river estuaries and semi‐enclosed bays located along mesotidal to macrotidal coasts of the western Taiwan Strait, East Asia. The morphological and sedimentary differences between estuarine SMT‐Beaches and bay SMT‐Beaches are initially constrained by sediment supply and transportation and are further affected by tide conditions and wave climate. A conceptual model that compiles the morphological and sedimentary differences in SMT‐Beaches in estuaries and bays is then proposed.