The location is just one data point in a pollution hotspot map Ebrahimian is building to better understand how stormwater is polluting groundwater across South Florida. That matters because as climate change warms the planet in bustling South Florida, more stormwater and all the stuff running off streets, parking lots, yards and more is mingling with the region\u2019s shallow groundwater.<\/p>\n
That\u2019s troubling for the Everglades and Biscayne Bay because that water can contain nutrients like nitrogen and phosphorus that trigger algae blooms and fuel the growth of macro algae that smothers sea grass.<\/p>\n
Yet across South Florida, Ebrahimian says, little is known about one of the primary ways stormwater is drained: French drains or infiltration trenches.<\/p>\n
\u200a\u201dSurprisingly, we don’t really know their performance. We have never monitored their performance in detail,\u201d he said. \u201cWe have just added them to our projects and they’re working. So we are okay.\u201d<\/p>\n
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Ali Ebrahimian, an engineer at Florida International University who studies urban hydrology, stands in a campus wetland planted with cypress trees. <\/p>\n
Florida, along with the rest of the country, relies heavily on underground infiltration trenches or French drains \u2014shallow perforated pipes that move stormwater while also allowing it to filter out. Miami-Dade County alone has more than 300 linear miles \u2014 about the distance between Miami and St. Augustine. In places where groundwater is deeper, dirty water can be filtered as it percolates through soil or rock to the water table below. But in South Florida, Ebrahimian said the groundwater is often the same depth as French drains, so the water has no chance to be filtered.<\/p>\n
Backbone of the drainage system<\/p>\n
The Miami River Canal is one of the backbones for South Florida\u2019s drainage system. It starts miles away at Lake Okeechobee, then cuts a nearly arrow-straight path across three counties. After about 60 miles, it arrives here in Miami-Dade, where it dumps into Biscayne Bay.<\/p>\n
\u201c\u200aIt passes through different urban areas, including, for example, here in Medley, which is mostly an industrial area,\u201d Ebrahimian said. \u201cIt goes through a lot of different urban land uses are around this, and all of them are discharging their stormwater runoff.\u201d<\/p>\n
So no surprise, the canal is chronically polluted<\/a>. It has repeatedly failed to meet limits for fecal coliform, the bacteria found in human and animal waste. It contains nutrients, heavy metals and microplastics. Fish are loaded with mercury. The canal is also not unique. Canals across South Florida carry stormwater loaded with chemicals.<\/p>\n That\u2019s where Ebrahimian’s pollution hot spot map will come in handy, to identify where water in storm sewers and canals is most polluted.<\/p>\n Then, using the FIU campus as a lab, Ebrahimian and his students are investigating better solutions. For the past three years, they\u2019ve been collecting and tracking pollution, including nutrients and micro plastics, near a campus infiltration trench.<\/p>\n \u200a\u201dWe wanted to see how these systems are working. Are these helping us here? And then how do we get water quality improvement or are we hurting our groundwater quality?\u201d Ebrahimian said. \u200a\u201dWe wanted to see if there’s an effect, and if so, what is the radius of that effect?\u201d<\/p>\n In the Everglades, Florida has spent about $2.5 billion to clean stormwater<\/a> flowing off sugarcane fields that rely heavily on sprawling treatment marshes to scrub water. The marshes cover about 57,000 acres and cost between $35 million and $40 million annually to operate.<\/p>\n But in urban areas, where quarters are tight and the pollution seems to come from everywhere, solutions are more complicated.<\/p>\n \u201cT\u200ahe Clean Water Act is 54 years old now. And we spent a lot of time like, dealing with that problem, I’d say mostly successfully,\u201d said Matthew Cohen, an ecohydrologist and director of \u200athe University of Florida’s Water Institute.<\/p>\n Pollution that degrades water and habitats has been widely identified and limits set to protect bodies of water, he said. But in many cases, those ambitious limits never get met. South Florida canals and rivers, from Broward County to the Keys, are full of nutrient pollution. A 2025 study also found that water is consistently reaching reefs<\/a> where it can damage coral. And this week, the Surfrider Foundation also reported that two beaches in Miami-Dade County ranked among the top 10 it monitors nationwide. <\/p>\n
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