Editor’s note: Houston environmental lawyer Jim Blackburn is a keynote speaker at a Chronicle-sponsored symposium, “Greater Houston After Harvey,” scheduled for Wednesday night.
There are a few basics of living with flooding that we all should know. How many of you know the name of the watershed where your home is located? Your business? Your children’s school?
The watershed – the area within which the rainfall runoff flows to one watercourse such as a bayou, a stream, a river – is the basic building block of flood-related information. This and other items are discussed in a document titled “Surviving Houston Flooding” being published Wednesday by Rice’s Baker Institute.
Harris County has 22 watersheds according to the Harris County Flood Control District. You should know yours well and understand its flooding characteristics.
The most common term that we hear with regard to flooding is flood plain – the area flooded by a particular rain event. Because of the federal flood insurance program, we use the term 100-year flood, which means the area flooded by a rain having a 1 percent chance of occurring in any year. There is also a 500-year flood plain that is mapped and that is the area flooded by the 0.2 percent chance rain event. The 100-year flood plain, as currently mapped, covers about 25 percent of Harris County and the 500-year flood plain covers about 34 percent of the county.
Unfortunately, the rainfall statistical studies upon which our mapped flood plains are based are obsolete. Our area is experiencing these very intense rainfall events more frequently than these past studies predict, making our current flood plain maps obsolete. They are not reliable indicators of the 1 percent risk event. While new studies on rainfall are being completed, Harris County has proposed to utilize the 500-year flood plain for planning and regulatory purposes, an excellent proposal that may not go far enough.
In some flood events, as much as 50 percent of Harris County flooding damage is outside of mapped 100-year flood plains. Some of this is due to our 100-year floodplain being too small, but some is also due to the fact that the road system in the city of Houston is our secondary drainage system, holding up to a 25-year (4 percent) storm. When the streets fill up, the water flows into yards and down any slope in the neighborhood, often flooding houses by overtopping the curb. This type of flooding is typically not mapped as a flood plain.
Other items that need to be considered include unsafe roads during rain events, dangerous intersections, unique issues with Addicks and Barker Reservoirs and other aspects of daily life. If you are moving into a hurricane evacuation zone along the coast, you need excellent information about the zone and expected hurricane depths.
At this time, there is no centralized web site in the community to help us become flood-smart citizens. Such information becomes crucial when buying or renting a home as well as understanding safe routes to and from schools, day-care, assisted-care living facilities and medical facilities, among others. In short, key information for a safe life in Houston is sometimes hard to find.
The failure to provide high quality information is a major deficiency that is intended to be addressed by the guide “Surviving Houston Flooding.” I invite you to read it after it goes online Wednesday at: http://bit.ly/2BJsQwK, and send comments on how to improve it.
This survival guide is a beginning rather than an end. This guide will be disseminated, updated and put on-line by a new group that has been formed called the Bayou City Initiative. The initiative has adopted a goal of developing a flood-smart community and, eventually, flood-smart political, business and civic leaders.
Our flooding issues are urgent. And our needs are substantial. Our lives and our long-term economic livelihoods depend on getting this right. Please join the Bayou City Initiative and help us make Houston the city that learned to live with water.