Abstract
Sediment dynamics have an important influence on the morphological evolution of tidal wetlands, which consist of mudflats and salt marshes. To understand the nature of sediment behavior under combined current-wave action at an exposed tidal wetland, we measured the waves, currents, water depths, bed-level changes, and sediment properties at a mudflat-salt marsh transition on the Yangtze Delta, China, during five consecutive tides under onshore winds of ~8m/s, and calculated the bed shear stresses due to currents (τc), waves (τw), combined current-wave action (τcw), and the critical shear stress for erosion of the bottom sediment (τce). The bed shear stresses under combined current-wave action (τcw) were approximately five times higher on the mudflat (up to 1.11N/m2; average 0.27N/m2) than on the salt marsh (up to 0.14N/m2; average, 0.06N/m2). On the mudflat, τcw was larger than the critical erosion shear stress (τce=0.103N/m2) for 70% of the period of submergence, whereas τcw was always lower than τce at the salt marsh site (τce=0.116N/m2). This result indicates that the sediment dynamics on the mudflat were dominated by erosion, whereas at the salt marsh they were governed by deposition, which is in agreement with the observed bed-level change during the study period (-3.3mm/tide on the mudflat and 3.0mm/tide on the salt marsh). A comparison of τcw values calculated using the van Rijn (1993) and Soulsby (1995) models for bed shear stresses under combined current-wave action indicates that both models are applicable to the present case and effectively predict the bottom shear stress under combined current-wave action. Overall, we conclude that τcw in combination with τce is useful in assessing the hydrodynamic mechanisms that underlie the morphological evolution of exposed tidal wetlands.
| Original language | English |
|---|---|
| Pages (from-to) | 380-389 |
| Number of pages | 10 |
| Journal | Geomorphology |
| Volume | 138 |
| Issue number | 1 |
| DOIs | |
| Publication status | Published - Feb 2012 |
Bibliographical note
Funding Information:This study was funded by the Natural Science Foundation of China ( 41071014 ) and the Ministry of Science and Technology of China ( 2010CB951202, 2008DFB90240 ) and the Committee of Science and Technology of Shanghai. We acknowledge the THESEUS project for supporting SKLEC and NIOO for research on the use of salt marshes as a coastal defense. We thank S. te Slaa, Y. Wang, C. S. Wu, C. Li, and J. Zhao for their assistance in the field, A. J. Wang for providing useful materials, and P. Li for providing wind datasets from weather and tide gauging stations. Special thanks are extended to B. C. Van Prooijen and D. S. vanMaren for their comments and suggestions, which helped to improve the manuscript. Two anonymous reviewers are thanked for their helpful comments and suggestions. We also thank Prof. Andrew Plater, Editor-in-Chief, for granting us the opportunity to submit a revised manuscript.
Funding
This study was funded by the Natural Science Foundation of China ( 41071014 ) and the Ministry of Science and Technology of China ( 2010CB951202, 2008DFB90240 ) and the Committee of Science and Technology of Shanghai. We acknowledge the THESEUS project for supporting SKLEC and NIOO for research on the use of salt marshes as a coastal defense. We thank S. te Slaa, Y. Wang, C. S. Wu, C. Li, and J. Zhao for their assistance in the field, A. J. Wang for providing useful materials, and P. Li for providing wind datasets from weather and tide gauging stations. Special thanks are extended to B. C. Van Prooijen and D. S. vanMaren for their comments and suggestions, which helped to improve the manuscript. Two anonymous reviewers are thanked for their helpful comments and suggestions. We also thank Prof. Andrew Plater, Editor-in-Chief, for granting us the opportunity to submit a revised manuscript.
Keywords
- Combined current-wave action
- Mudflat
- Salt marsh
- Sediment dynamics
- Shear stress
- Tidal wetland