This article by Doug Coenen and Ray Drexler originally appeared in the Fall 2022 issue of Stormwater Magazine.
Overview
Across the United States, many areas are experiencing more extreme weather. This includes higher highs and lower lows in regard to temperature and precipitation— as well as a greater frequency of severe weather events such as rainstorms, hurricanes, tornadoes, and floods.
The result has been an increase in weather-related damage to commercial and residential properties—however, a property can mitigate these damages with a solid flood protection system.
Historically, flooding is one of the costliest natural disasters in the U.S. on an annual basis. The National Oceanic and Atmospheric Administration (NOAA) periodically updates estimates of local rainfall intensity, which can impact how communities calculate their local 100- or 500-year storm event(s). These storm events are used to model and map the new 100- and 500-year floodplains that the Federal Emergency Management Agency (FEMA) approves.
Flood Insurance Rate Maps (FIRMs) attempt to address area-wide flood risks retroactively and may not reflect the increased rainfall intensities and localized street flooding that now occur more frequently.
For example, Houston, Texas, experienced three consecutive years of 100-year storm events starting in 2015. These were the Memorial Day flood in 2015, the Tax Day flood in 2016, and flooding associated with Hurricane Harvey in 2017. The impacts of these three different storms were significant: the first two produced localized flooding while the third was regional in nature and set a new national rainfall record.
The impact of severe weather can be significant in one region of a city and not affect another part. This is due to how localized some storms may be. Localized flooding typically has less to do with the rising of floodplain floodwaters and, instead, is due to inlets not being able to handle the demand of incoming stormwater. In some cases, grading can accomplish stormwater improvements to ensure that water is able to continue to move downstream—rather than becoming trapped because it can no longer flow downstream with gravity.
Learn more about flood protection in Walter P Moore’s paper An Introduction to Flood Protection: What Owners Need to Know to Protect Their Properties.
