UH researcher unveils new model to evaluate impact of extreme events and natural hazards

(Press-News.org) When you’re on a sandy beach or the banks of a river, transformed by rolling waves or slightly still waters, it’s likely you’re not thinking about what happens just beneath the surface, where dirt and pollution are swirling and traveling through to new destinations.  

But Hanadi Rifai does. The Moores Professor of Civil and Environmental Engineering and director of the Hurricane Resilience Research Institute, has spent two decades examining Galveston Bay – its tides, currents and how fresh and salty water mix, continually extending the knowledge of predicting water levels, pollution spread and how ecosystems stay balanced. 

Now Rifai has created a sophisticated numerical computer model to help scientists and environmental experts understand how water moves in estuaries—places where fresh and saltwater mix. The model is the focus of an article in the journal Environmental Science and Pollution Research.  

“Models such as this one will be critical for evaluating climate variability and sea level fluctuation impacts on these lifeline systems for coastal communities,” reports Rifai, whose work will also guide better decisions to keep water clean, protect wildlife, and prevent flooding and pollution from spreading. 

Through the years Rifai has focused on emerging pollutants and pathogenic pollution and has conducted multiple sampling campaigns including sampling associated with hurricanes Ike and Harvey. She says the importance of taking samples over time and incorporating rainfall events and stream flows into predictive estuarine models cannot be overly emphasized. 

“An important lesson learned has been that the estuary while thriving and vibrant, is a complex system with many 'moving parts', and is sensitive to external influences that include extreme events (hurricanes, high winds, tidal fluctuations, extreme rainfall, drought, extreme heat, and industrial accidents and incidents),” said Rifai. “Historical uses have left their 'footprint' and continuing uses such as navigation, and recreation and municipal and industrial discharges are also associated with a 'trace'.” 

The analysis 

Rainfall made water move faster, especially in the deep water 

Where rivers met the estuary, water flow and speed were more unpredictable 

Storms reduced salt but increased the amounts of suspended sediment in the water column (the surface to the bottom). 

Rainy days also increased sediment, which supports the idea of sediment mobilization during storms. The latter causes redistribution of pollutants within the estuary. 

“The interactions between the water column and the underlying sediment and how to model those was a key focus in addition to evaluating the influence of extreme rainfall and hurricanes on identifying depositional versus erosional parts of the system,” said Rifai. 

Members of the team include Adithya Govindarajan, Gradient Corp., Boston, Martin Nguyen, a graduate student in the Rifai lab. 

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