Causes of Flooding

What causes flooding? The answer is complex because every flood is different. Some are the result of extreme weather events which push water atop the ground, or produce more rainfall than the system has the capacity to absorb. Some are the result of water bubbling up from underneath us and through the porous rock atop which we live. But for any given flood, the why will depend upon recent rainfall, how saturated the ground is already, the force of the winds and their effect on tides, the level of the sea, and the effectiveness of our water management systems in light of all these factors.

There are three general sources of floods: overflowing bodies of water, coastal tidal surges and rainfall. The most common type of flood is when a river rises and water flows over its banks into the land which surrounds it. The City’s water bodies consist mainly of navigable waterways and sensitive drainage basins, including the Atlantic Ocean, Intracoastal Waterway, Middle River, C-13 East, C-12, and the New River. In the event of a hurricane, tropical depression, rainstorm, high tide, storm surge, or other natural disaster, these waterways can overflow and cause flooding.

Yet even normal wet season, rains can produce flooding. Our sub-tropical climate increases the probability of flooding here in Fort Lauderdale relative to other coastal areas. South Florida typically gets 52 inches of rain annually, mostly during June through October when 70 percent of the year’s rain falls and most hurricanes occur.

Living in an urbanized center has an impact too. Compared to our neighbors to the west, some of whom have more open space, we experience greater flood risk. Miles of roadway, driveway and parking lot have altered the natural course of water. Before South Florida was developed, water management happened naturally via the Everglades, mangrove and other habitats, and river flow to the sea. Development, made possible by the building of canals, beginning in the late 1800s and going through the mid-twentieth century, unknowingly damaged the natural system’s ability to control water in our region effectively. In the recent past, local and Federal government has been working together to mitigate this.

With sea level rising, all of these causal factors are aggravated because the land cannot absorb as much water as it did in years past. Ocean water does not just flow atop the land, more frequently is pushes up from underneath. It pushes against fresh water already in the ground, causing the fresh water to rise. The result is that our underground stormwater system, which in years past was sufficient, is challenged anew. When it rains, the stormwater does not have as many places to flow safely as it did before.

Yet this new challenge has produced innovation. Through a combination of structural and non-structural approaches, as well as continued collaboration between federal, state, and local stakeholders, our Public Works Department is ensuring that we will be prepared.