How will rivers respond to environmental alterations

Scientists investigate the response of the rivers across the globe when it comes to the changing environmental conditions. 

Researchers from the California Institute of Technology (Caltech) and the University of California, Santa Barbara, assessed the impact of today's changing environmental conditions with respect to the dynamic behavior of rivers.

The study was recently published in the Proceedings of the National Academy of Sciences of the United States of America.

To understand the effect of climate change and sea water level rise, the team studies the major factors that affect the course of the river or the point where avulsion may occur in the rivers' deltas.

River avulsion refers to the quick formation of a new water channel from which the waterflow is funneled, dropping out of its previous course. Throughout history, they have caused severe implications to human civilization. According to archaeologists, the Harappan civilization in India was highly impacted by the changing course of the Indus River.

Rivers carry massive quantities of ground material that are deposited in their deltas, a procedure that highly affects the earth's landscape. This is a major process that occurs when the river enters a sea, an ocean, a reservoir or even another river where it can no longer carry the aforementioned material. Avulsions are a critical parameter in this process since when they occur, material is deposited in another place and the terrain characteristics rapidly change. The purpose of the study was to evaluate how changing environments and human activities affect this process.

The assessment was challenging since there is no valid pattern or data when it comes to the correlation between avulsion and climate changes. In fact, some researchers suggest that avulsions will increase due to sea level rise while others believe the opposite. “There simply was no unifying theory to explain how river avulsion frequency is dependent on sea level,” Vamsi Ganti, a co-author of the study and an Assistant Professor in Geomorphology and Land Surface Processes at the University of California, Santa Barbara, stated.

By coupling analytical models of river dynamics with geological data and records, the authors created prediction models which were then compared with field data. Their findings suggest that there are three manners that rivers deltas could respond regarding the environmental alterations: 

1. Rivers that will not be affected. Those rivers have large amounts of sediments while the sea-level rise occurs at a slow pace.

2. Rivers where avulsions will increase. In those rivers, there is less sediment and the sea level elevation happens quicker.

3. Rivers where the sea completely permeates the deltas resulting in a phenomenon in which the whole system is transferred inland. 

According to the authors, the third scenario is extreme, however, it is a realistic condition that was not previously identified and will be thoroughly studied in the future.