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The Importance of Designing for 100-Year Storms

In a difficult economy, many clients question spending additional, already-tight project funding to design their stormwater management projects to accommodate a 100-year storm and/or flood, which has a low probability of occurring. However, this decision should be weighed heavily. Saving project capital now could put your community at a significant risk later.

They Happen More Often than You Think
It is commonly believed that 100-year storms and floods occur once every 100 years, but according to the U.S. Geological Survey (USGS), 100-year storms and floods actually have a one-percent statistical chance of occurring or being exceeded during any given year. In addition, a 100-year flood is not necessarily preceded by a 100-year storm. The USGS states that 100-year floods are actually dependent on several factors: “extent of rainfall in the watershed, soil saturation before the storm, and the relation between the size of a watershed and the duration of a storm.” Each of these factors independently or combined make it possible for 100-year storms and/or floods to happen within back-to-back days of each other.

Know Your Community’s Risk
According to the Federal Emergency Management Agency (FEMA), a home in a high-risk area has a 26-percent chance of experiencing damage from a 100-year storm or flood over the course of a 30-year mortgage. However, in 2009, approximately 25 percent of the flood claims paid by FEMA’s National Flood Insurance Program were for policies held in moderate- to low-risk areas. In 2010, many Texas communities have already experienced record-setting rainfall and are now facing hurricane season with winter storms potentially following. It is important now perhaps more than ever to know your community’s risk, plan for 100-year storm and flood events, and design your stormwater projects accordingly.

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TagsFlooding, Stormwater Design,