Evaluating the effect of river discharge and meteorological parameters on the expansion of dry land in delta areas; (case study: Wax Lake Delta, US)

Document Type : Research Paper

Authors

Department of environmental engineering-coastal, Faculty of Environment, University of Tehran, Tehran, IRAN

Abstract

The fluctuations in the extent of the dry area have profound implications for the delta's ecology, sediment transport, and overall geomorphological development. This study aims to elucidate the effects of various factors, including storms and cold fronts, as well as river discharge, on the dry area of the Wax Lake Delta (WLD), US. Utilizing the Delft3D hydrodynamic model, a series of simulations covering from August to September 2021 was performed to quantify these influences. The model was calibrated and validated using measured water level data, ensuring the reliability of the simulations. Results indicate that the average dry area of the WLD for September 2021 is approximately 25.1 km², which largely depends on meteorological forces and river discharge. Specifically, extreme storms have the potential to submerge the delta, resulting in prolonged periods of inundation. Moreover, the passage of a cold front can lead to a submersion of up to 48% of the delta's area during the pre-frontal phase, followed by an 80% increase in the dry area in the subsequent post-frontal phase, illustrating the transient but significant impact of such events. The study also determines that river discharge has an inverse relationship with the dry area of the delta; an increase in discharge corresponds to a decrease in the dry area, and conversely, a decrease in discharge leads to an expansion of the dry area. The insights gained from this research underscore the importance of integrating meteorological and hydrological data in the management and conservation strategies of deltaic environments.

Keywords

Main Subjects

Evaluating the Effect of River Discharge and Meteorological Parameters on the Expansion of Dry Land in Delta Areas; (Case Study: Wax Lake Delta, US)

EXTENDED ABSTRACT

 

Introduction

Louisiana's coastal zone, encompassing 40% of the U.S. coastal and estuarine wetlands, faces significant environmental challenges, including a high rate of coastal erosion and wetland loss. The Wax Lake Delta (WLD) in this region is notable for its active expansion and plays a key role in the area's ecology, sediment transport, and geomorphology. Since fluctuations in water levels and the subsequent changes in the dry area have profound implications for these aspects, this study aims to examine the spatial variations in the WLD's inundation area and understand the impacts of riverine discharge, storms, and cold fronts on these dynamics. This research is crucial for enhancing ecosystem health monitoring and improving coastal management practices, addressing a gap in previous studies.

Material and Methods

The hydrodynamic simulation in this study was conducted using the Delft3D-FLOW model, employing a grid model with a horizontally curvilinear orthogonal grid of 12 vertical layers and a 456 by 259 horizontal grid. The model's capability to simulate hydrodynamics was evaluated by comparing predicted water levels with actual field data from four stations in August 2021, serving as the calibration phase. This process was followed by validating the model, where simulated data for September 2021 was compared against actual measurements to ensure accuracy and reliability of the model's performance. Furthermore, a series of detailed simulations were carried out to meticulously evaluate the impact of varying hydrological conditions on the dry area within the WLD. These simulations were conducted under three distinct river discharge scenarios - low (1250 m³/s), moderate (2500 m³/s), and high (5000 m³/s) - to find how different levels of water flow affect the dry regions of the delta.

Results and Discussion

The results for September 2021 revealed significant dynamics in the WLD dry area due to meteorological forces, including the Nicholas storm and various cold fronts. It revealed significant changes in the dry area, with a total average of 25.1 km². During the storm, the dry area surged to approximately 48 km² and then decreased to around 5 km² as wind directions shifted. The passing of cold fronts also plays significant role variations of the dry area. A northwesterly cold front further reduced the dry area to 12 km² during pre-frontal phase, later increasing it to about 45 km² in the post-frontal one. Furthermore, the study highlighted uneven distribution across floodplains in the WLD. Sherman and Fred Island are significant contributors, accounting for about 24.1% and 21.1% of the dry area, respectively. In contrast, floodplains such as Chester's, Mike, and Pintail contribute less to the overall dry area, ranging between 5% and 6.3%.

In terms of River discharge, this study indicated a clear relationship between river discharge rates and the dry area in the WLD. High discharge conditions consistently result in a reduced dry area compared to moderate and low discharge conditions. This pattern highlights a direct link between the volume of water discharged and the flooding of floodplain areas. Additionally, the combined effects of high river flow and meteorological forces significantly increase the delta's vulnerability to flooding, emphasizing the importance of considering these factors in flood risk management and ecological conservation strategies.

Conclusion

The conclusion of the study on the Wax Lake Delta (WLD) emphasizes significant variability in the delta's dry area, mainly influenced by the discharge from the Wax Lake Outlet and varying between 11 and 25 km². It highlights the substantial impact of severe storms, which can either inundate the delta or significantly expand the dry area, depending on factors like the storm's intensity and wind direction. Cold fronts also have notable effects, with the potential to submerge large portions of the delta, followed by substantial dry area expansion. This study underscores the diverse responses of individual floodplains to meteorological events, revealing the intricate interplay between hydrological and meteorological factors in shaping the delta's landscape. The findings also suggest that high river discharge conditions can mitigate the effects of storms and cold fronts on the delta's dry area, whereas low discharge conditions enhance these impacts, reflecting the complex dynamics governing the WLD's environment.

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Iranian Journal of Soil and Water Research
Volume 55, Issue 5
August 2024
Pages 799-814

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