More than 150 million Americans live in coastal counties, which can be adjacent to the Pacific or Atlantic oceans, the Gulf of Mexico, or the Great Lakes. As such, they all live at some risk of flooding from storm surges and waves. Around the rest of the nation, uncounted millions more and their homes are vulnerable to river, stream, or lake flooding.

Yet, the total flood risk for the country is not exactly known, because many of the official maps that document the flood risk are imprecise and outdated. What is known is that floods represent the biggest natural hazard to people’s homes and can account for $6 billion of damage in an average year.

And let’s take a moment to pray for an average year. That would not be 2005, of course, when hurricanes Katrina and Rita hit the Gulf Coast. In just a few days, these two storms ran up a $120 billion damage tab, the vast majority of which came from flooding.

Unfortunately, that level and type of damage came as no surprise to the thousands of state and local officials tasked with floodplain management. Many floodplain managers have been pushing for years for the government to upgrade how it guards homes and businesses against floods. In the wake of Katrina, their recommendations—or at least some of them--are starting to turn into reality. Across the nation, and In the coastal counties of Mississippi and Louisiana, flood maps and flood zone construction rules have started to change.

While the updates may be necessary, the work is leaving builders and developers with a patchwork arrangement of old and new procedures, changing flood maps, and an evolving body of codes and standards. Even the authorities have trouble keeping up. “It seems as if every day we get some new rule,” Sandra Johnson, floodplain administrator in Tallahatchie County, Miss., and chairman of the state’s Association of Floodplain Managers, told BUILDER this week. “It’s all I can do to keep track of the changes in my own jurisdiction.”

Like floods themselves, flood rules are a moving target that calls for flexible thinking and innovative approaches. As such, builders who fail to understand the problem can land themselves in trouble, but those who do master its complexities can grasp opportunity and achieve success. Let’s take a closer look.

Learn more about markets featured in this article: New Orleans, LA, Atlantic City, NJ.