Sediment Transport Mechanisms in a Lagoon with High River Discharge and Sediment Loading

Jovita Mėžinė,Petras Zemlys,Rasa Idzelytė,Georg Umgiesser,Diana Vaičiūtė,Christian Ferrarin

doi:10.3390/w11101970

Abstract

The aim of this study was to investigate the sediment dynamics in the largest lagoon in Europe (Curonian Lagoon, Lithuania) through the analysis of in situ data and the application of a sediment transport model. This approach allowed to identify the propagation pathway of the riverine suspended sediments, to map erosion-accumulation zones in the lagoon and calculate the sediment budget over a 13-year-long simulation. Sampled suspended sediment concentration data are important for understanding the characteristics of the riverine and lagoon sediments, and show that the suspended organic matter plays a crucial role on the sediment dynamics for this coastal system. The numerical experiments carried out to study sediment dynamics gave satisfactory results and the possibility to get a holistic view of the system. The applied sediment transport model with a new formula for settling velocity was used to estimate the patterns of the suspended sediments and the seasonal and spatial sediment distribution in the whole river–lagoon–sea system. The numerical model also allowed understanding the sensitivity of the system to strong wind events and the presence of ice. The results reveal that during extreme storm events, more than 11.4 × 106 kg of sediments are washed out of the system. Scenarios without ice cover indicate that the lagoon would have much higher suspended sediment concentrations in the winter season comparing with the present situation with ice. The results of an analysis of a long-term (13 years) simulation demonstrate that on average, 62% of the riverine sediments are trapped inside the lagoon, with a marked spatially varying distribution of accumulation zones.

Highlights

Sediment transport is an important process for all aquatic environments, especially lagoons where the amount and transport directions of the suspended matter have a direct effect on the water turbidity and can cause changes in primary production or other ecological processes in the system [1]
This study aims to identify the propagation of the suspended sediments from the Nemunas River to the lagoon, to map the erosion-accumulation zones in the lagoon due to the sediment dynamics and calculate the sediment budget changes over a 13-year-long simulation
Long-term simulation results gave usFigure the possibility to analyze general dynamics were in a good agreement with the measured data, with a model performance quality index of 72%

Summary

Introduction

Sediment transport is an important process for all aquatic environments, especially lagoons where the amount and transport directions of the suspended matter have a direct effect on the water turbidity and can cause changes in primary production or other ecological processes in the system [1]. Lagoons are the most productive water bodies in coastal environments, but are vulnerable to human activity, sensitive to climate change [2], and must be monitored and managed for saving the good environmental status. The processes in such complex systems at the land–sea transitional zone are extremely dynamic and require a holistic approach in which the river–lagoon–sea continuum should be considered [3]. Deficiency of sediments reaching the sea may cause coastal erosion, with the consequent loss of land and tidal wetlands, resulting in the necessity of coast protections and saltmarsh or beach nourishment strategies.

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Conclusion