Groundwater salinity in densely-populated deltas

Published: 23 November 2020

Joeri van Engelen assessed the status and drivers of the present-day salinity distribution in groundwater in deltas. These areas are vital to the population and economies of many countries all over the world: they are often densely-populated hubs with intensive agriculture due to fertile soils and have excellent transportation possibilities via ports.

Though traditionally depending mainly on surface water to meet freshwater demands, their ever-growing population and intensifying agriculture increasingly rely on groundwater extractions. These extractions will lead to more salt entering the groundwater system, reducing the deltas’ precious fresh groundwater reserves. Despite the increasing importance of these reserves, little is known about the actual size of these fresh groundwater reserves and the factors that control them. Joeri van Engelen’s PhD thesis contributes to a better understanding of the fresh-saline groundwater distribution in these vulnerable areas.

Van Engelen applied computer models of groundwater flow and salt transport, using the national supercomputer in Amsterdam. It was found that the present-day fresh-saline groundwater distribution in deltas was formed over thousands of years, and thus very computationally demanding simulations were required.

 

Calculated fresh-salt groundwater distributions for 15 major deltas across the world. The colours show the salinity of groundwater. Red = salt water, yellow = brackish water, blue = fresh water.

Fresh groundwater reserves under stress in 7 major deltas

Furthermore, he investigated the sustainability of the fresh groundwater reserves in 15 major deltas across the world. With the current amount of groundwater being pumped, the Ganges-Brahmaputra-Meghna (Bangladesh), Nile (Egypt), Pearl River and Yangtze delta (both in China) risk exhaustion of their precious reserves this coming century. With expected increased pumping rates, the Saloum (Senegal), Mekong and the Red River delta (both in Vietnam) can be added to this list. These seven deltas together currently host hundreds of millions of inhabitants, whose lives might be seriously affected by this groundwater exhaustion.

During his research, Van Engelen was supervised by Gualbert Oude Essink (Deltares / Utrecht University) and Marc Bierkens (Utrecht University / Deltares). Oude Essink says that this is an important step forward in the research and work at Deltares for two reasons. The first is to be able to make predictions about the degree of freshwater availability in the long term using rapid instruments, and secondly to develop adaptation strategies towards a sustainable and resilient delta more carefully.