By Toby Weber Civil and Environmental Engineering Professor Hanadi Rifai uses everything from population databases to storm patterns to determine what ends up in bodies of water, how it gets there… and how much needs to be removed. (Photo: Environmental engineering graduate students Yaa Kwakye-Amoah, Nathan Howell and Anu Desai collect water samples with Professor Hanadi Rifai at a retaining pond in the Houston area.)

Testing the Waters

Most great cities owe their prominence, at least in part, to a body of water. Some have rivers running through them that make them a stop for trade and, with enough bridges, a good place to cross. Others, like Houston, have a port on a major body of water that brings cargo and commerce to their shores.

One of the challenges for such cities—Houston included—is ensuring the health of these water bodies by limiting the amount of pollutants to which they are exposed.

Professor Hanadi Rifai contributes to these efforts in Houston and beyond by creating sophisticated models of watersheds that help determine how much pollution a body of water is taking in and where that pollution is coming from. The pollution levels Rifai finds are then compared to what is deemed acceptable under the Clean Water Act and the Environmental Protection Agency’s Total Maximum Daily Load (TMDL) Program.

“A body of water can assimilate some pollution, but as a rule, you should not give it more than it can take,” said Rifai. “That’s what the TMDL Program is all about. It’s essentially the pollution calorie count that a body of water can take. The goal of the program is to make the body of water fishable and swimmable.”

Cells of water samples from local sources are subjected to an IDEXX Colilert test. Viewed under a black light, the fluorescent cells indicate the presence of E. coli, while the yellow or dark cells positively identify coliform in the sample.

Building these models, Rifai said, is a hugely complex task. Typically, she and her research team start by combining multiple databases that quantify a watershed’s land use and land coverage, industrial and agricultural activity and potential pollutants that may arise from those activities, population distribution and density, soil types and topography.

Each of these, she said, are fed into a computer to form a single watershed model. Data collected out in the field, such as information gathered through water and sediment tests, soil tests (since what is on the ground usually gets washed into a watershed), and air quality tests (since what is in the air can precipitate into bodies of water and onto the ground), is also used to validate and refine the team’s computer models.

The challenges of gathering information, quantifying it and making it part of a large model differ from area to area, Rifai said. Modeling a watershed in an urban area such as Houston requires tracking more industrial pollutants and understanding how having large areas covered by concrete impacts a watershed. Models of rural areas must account for agricultural pollutants such as pesticides, as well as the impact of any livestock that live in the watershed.

These models and the real-world tests supporting them are then used to determine how much pollution a body of water is exposed to in light of the total amount of pollution that is considered acceptable. This sets the stage for the EPA and other interested parties to solve any pollution problems a body of water might have.

“When we come up with these system-wide models, they’re used for decision making,” Rifai said. “The EPA will sit down with officials and stake holders in these water bodies and figure out who is responsible for reducing pollutants.”

Determining exactly what actions should be taken to reduce pollutants is a separate field of science from Rifai’s watershed modeling, and the strategies and plans change depending on the problems. If sediment is an issue, for example, retaining ponds that allow sediment to settle before it reaches a major body of water can be constructed. If a body of water has too much industrial waste, the businesses responsible for that waste can be mandated to reduce their pollution levels.

Preparing for the Storm

Another area of application for this research lies in the newly formed SSPEED Center, of which Rifai is co-director. The center—whose acronym stands for Severe Storm Prediction, Education, Evacuation from Disasters—is made up of researchers from multiple universities in Texas and Louisiana, including UH, Rice University, Texas A&M University, Texas Southern University, Louisiana State University and others.

Each of these universities, said Rifai, houses expertise in an area directly related to severe storms, disaster preparedness and evacuations. UH researchers, for instance, posses expertise in water quality and sensing; at Rice, in flooding; at TSU, in transportation and traffic flow.

By combining all this talent under the SSPEED umbrella, individual researchers can work together to conduct research projects that take comprehensive approaches to severe storms and flooding (such as connecting localized flooding and rainfall models with the National Hurricane Center’s hurricane projections), evacuations and other issues.

“From the SSPEED perspective, my interest is in looking at our watershed. I’m working on water quality, others are working on flooding. We should be in contact because those things are obviously connected,” she said.

In addition to providing a forum for collaboration, Rifai said SSPEED is designed to offer students at the member institutions an interdisciplinary understanding of what a severe storm or disaster entails from the standpoint of preparation and recovery. The information students will be exposed to may include everything from flooding models, storm tracking and path projections, to fields that deal more heavily with the social sciences, such as what motivates individuals to evacuate.

“As an engineering student, you might be motivated to learn about atmospheric science or other phenomena that you wouldn’t encounter in a traditional engineering curriculum,” Rifai said. “I see the influence of the center growing over time as we reach out to other disciplines and cross-pollinate with different programs.”