Monitoring the Spring Flood in Lena Delta with Hydrodynamic Modeling Based on SAR Satellite Products

Avi Putri Pertiwi,Claudia Kuenzer,Markus Disse,Felix Reuß,Timo Schaffhauser,Punit Kumar Bhola,Samuel Stettner,Achim Roth

doi:10.3390/rs13224695

Abstract

Due to the remote location and the extreme climate, monitoring stations in Arctic rivers such as Lena in Siberia have been decreasing through time. Every year, after a long harsh winter, the accumulated snow on the Lena watershed melts, leading to the major annual spring flood event causing heavy transport of sediments, organic carbon, and trace metals, both into as well as within the delta. This study aims to analyze the hydrodynamic processes of the spring flood taking place every year in the Lena Delta. Thus, a combination of remote sensing techniques and hydrodynamic modeling methodologies is used to overcome limitations caused by missing ground-truth data. As a test site for this feasibility study, the outlet of the Lena River to its delta was selected. Lena Delta is an extensive wetland spanning from northeast Siberia into the Arctic Ocean. Spaceborne Synthetic Aperture Radar (SAR) data of the TerraSAR-X/TanDEM-X satellite mission served as input for the hydrodynamic modeling software HEC-RAS. The model resulted in inundation areas, flood depths, and flow velocities. The model accuracy assessed by comparing the multi-temporal modeled inundation areas with the satellite-derived inundation areas ranged between 65 and 95%, with kappa coefficients ranging between 0.78 and 0.97, showing moderate to almost perfect levels of agreement between the two inundation boundaries. Modeling results of high flow discharges show a better agreement with the satellite-derived inundation areas compared to that of lower flow discharges. Overall, the remote-sensing-based hydrodynamic modeling succeeded in indicating the increase and decrease in the inundation areas, flood depths, and flow velocities during the annual flood events.

Highlights

The Lena is one of the four largest Arctic watersheds, the others being Mackenzie, Ob, and Yenisei [1]
This study aims to integrate information derived from datasets of the twin radar satellite TerraSAR-X and TanDEM-X into a hydrodynamic model to monitor the spring flood in a subset of the Lena Delta, an extensive wetland spanning from northeast Siberia into the Arctic Ocean
The flood events were modeled in three different stages each year: (1) before the flood—in early May; (2) the flood peak—in late May to early June; and (3) after the flood—in mid to late June

Summary

Introduction

The Lena is one of the four largest Arctic watersheds, the others being Mackenzie, Ob, and Yenisei [1] These Arctic watersheds drain into the Arctic Ocean, influencing the sea ice cover and the ocean conveyor belt [2], which significantly affects the Earth’s radiation budget. Among its impacts is the 7% rise of the recorded average annual freshwater discharge from the six largest Eurasian rivers to the Arctic Ocean in the last century [3]. This direct impact makes Arctic surface water crucial for environment- and climate-related studies.

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Results

Conclusion