Abstract
Analyzing the long-term behavior of the coastlines in the vicinity of river mouths and estuaries usually relies on the mean (predicted) values of the sediment discharge from the river. However, this approach does not consider low frequency, severe events, such as El Niño (EN), that can have a large effect on coastlines. While the effects of an EN on flooding and droughts are well studied, little information exists about its effects on coastal zones, and especially on the evolution of coastlines. In early 2017, an EN occurred in the equatorial Pacific Ocean, and the country of Peru was affected with high precipitation levels, and extreme river discharges and flooding. During this event, in the district of Lima, the Rimac River discharged a huge amount of sediment into the Callao Bay, and the shoreline accreted approximately 1 km, demonstrating the significant effects that an EN can have on coastal zones. To explore these effects, this paper studies the influence of an EN on shoreline evolution in the Callao Bay by analyzing Landsat images from 1985–2019 to understand the shoreline evolution and identify changes to the coastline. Results show that when an extraordinary EN occurs (e.g., 1982–1983, 1997–1998, and 2017), the shoreline experiences high accretion compared to when a smaller, or no EN occurs. During these events, a significant delta forms at the south end of the bay, and the redistribution of the accumulated sediment by wave action causes the accretion of the adjacent coastlines for as far as 7 km north of the river mouth. This shows the importance of these events for the wellbeing of coastlines adjacent to river mouths affected by EN.
Highlights
Analyzing the long-term behavior of coastlines in the vicinity of river mouths and estuaries usually relies on the mean values of sediment discharge from the river to the coast [1,2]
Rivers located on the eastern side of the Americas or southwest Africa, where El Niño (EN) events cause less precipitation than in normal years [30], have lower sediment flux when compared to the Rimac River
The major shoreline variations occurred during the extraordinary EN events of 1982–1983, 1997–1998, and 2017
Summary
Analyzing the long-term behavior of coastlines in the vicinity of river mouths and estuaries usually relies on the mean (predicted) values of sediment discharge from the river to the coast [1,2] This approach does not consider low frequency, severe events that can have a large effect on the coastline, even changing its evolution, and affecting the environmental, commercial, and social interests of the region. An EN is a recurrent phenomenon that affects countries around the Pacific Ocean, characterized by an anomalous increase of the sea surface temperature (SST), as well as an increase in the sea level in the central-eastern equatorial Pacific These ocean effects can cause an increase in precipitation on land that overwhelms natural catchment systems, raises river water levels, inundates flood plains, and eventually results in abnormally large discharges of sediment into the coastal zones at the estuary. Using the available satellite imagery from Landsat from the years 1985–2019, this study will focus on the influence of these EN events on the coastline evolution of the Callao Bay in Peru
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