The Facts on Flooding

It may be a relief for many new homeowners to learn their homes are not located in a mapped floodplain-especially when lenders don’t require them to have flood insurance. Many may think, “Great! I must not be at risk for flooding.” However, that kind of thinking could be a costly mistake. About 70 percent of the 2,300 homes that flooded in west Harris County last April were not in a mapped floodplain, and 65 percent of the area that flooded during Tropical Storm Allison in 2001 was not in mapped floodplain. While Flood Insurance Rate Maps, also called “floodplain maps,” are good indicators of certain flooding risks, they do not show all flooding risks for our area, which receives about 4 feet of rain every year.

Floodplain maps, which are produced by the Federal Emergency Management Agency to help determine flood insurance rates, show flooding risks from bayous and streams topping their banks during certain theoretical floods, namely the 100-year and 500-year floods, and from coastal flooding. A 100-year flood has a minimum of a 1 percent chance of occurring every year, and a 500-year flood has a .2 percent chance of occurring every year. To put that into perspective, during a 30-year period of time – the duration of many home mortgages – a home in a 100-year floodplain has a minimum of a 26 percent chance of flooding, and a home in the 500-year floodplain has a minimum of a 6 percent chance of flooding. The closer the home is to a bayou or a stream, the greater the chances of flooding.

But there are other types of flooding risks not depicted on floodplain maps. The maps do not show flooding risks from street flooding caused by roadside ditches and storm sewers exceeding their capacity, or from “sheet flow,” which is water traveling over land to reach the bayous. Unfortunately, half or more of the flooding that occurs in Harris County falls into these categories. The maps also do not show flooding risks from extreme flooding events, such as Allison.

While the Harris County Flood Control District works year-round to widen bayous and to excavate stormwater detention basins to reduce flooding risks, homeowners are advised to do their part and protect their property with flood insurance, as flooding is the No. 1 natural threat to this area.

All Harris County residents are eligible for flood insurance, which is relatively inexpensive, especially for homes outside a mapped floodplain. To buy a policy, homeowners can call their insurance agent or company. Because flood insurance is administered by the federal government, rates will not vary. Some insurance carriers allow the premium to be paid through an escrow account.

While flood insurance won’t keep a home from flooding, it can help homeowners recover from costly damages. To get more information on flooding and flood insurance, visit the National Flood Insurance Program on-line at or the Harris County Flood Control District at

Submitted by the Harris County Flood Control District. For more information, visit