flood pool of Barker reservoir

Homebuyers Beware: Flood Risk is Shifting Target

Homebuyers beware. Flood risk is a shifting target.

This morning, I began reading more than 100 pages of legal briefs in the appeal of the upstream Addicks and Barker awards. I could not help but think how hundreds of millions of dollars in losses and untold heartbreak could have been averted with more due diligence on the part of all involved – buyers, developers and the Army Corps.

Background of Case

For those new to the area, Addicks and Barker are two reservoirs on Houston’s west side. The Army Corps built them back in the 1930s to protect downtown Houston and the ship channel. However, the Corps did not buy all the land inside the reservoirs that was subject to flooding. Later, developers started building on that land. And people bought the homes despite the risks.

During Harvey, hundreds of homes built inside the reservoirs flooded. Residents sued the Corps and won. But the Corps is now appealing the case.

In 2022, a judge ruled in favor of the residents and awarded them more than half a billion in damages. The damages included repair costs, replacement of belongings, and compensation for value lost in their property. But facing hundreds of millions of dollars in payouts, the government isn’t giving up easily. It appealed.

The case has taken more than six years to get to this point and it is far from over. No telling what the legal fees have cost both sides. Or whether plaintiffs will ever see a penny.

This should serve as a lesson to everyone buying a home and to their real estate agents, mortgage lenders, and surveyors.

Tools to Help You Avoid Becoming a Flood Victim

Although tools to identify flood risk may not have been commonly available and readily understandable when the plaintiffs bought homes inside the reservoirs, such tools do exist now.

Two of the easiest to use are the USGS National Map and FEMA’s National Flood Hazard Layer Viewer.

They both show the extent of potential flooding in this area, but each has different strengths. And they show slightly different results. That should raise some cautions if you think of risk as a black-or-white issue.

Use USGS National Map for Elevations, Slopes, Contours

USGS excels at mapping elevations, slopes and contours. This post explains how to use the National Map. Backgrounds include:

  • Satellite imagery
  • Street maps
  • Structures
  • Topographic maps
  • Relief maps
  • Streams
  • Hydro and more.

You can layer these maps and vary their transparency. But the real magic of the USGS National Map is in the measurement tool for elevation profiling. Below is an example.

After activating the elevation profile tool, I drew a line from a residential neighborhood inside the Barker Reservoir, across the dam, to an area outside the reservoir. I chose an area in the southwest corner of the reservoir that flooded during Harvey. It showed this.

Note elevation changes on right where line crosses the dam (gray bar). Homes above the gray are inside reservoir.

The red X shows the height of the dam (108 feet) in the elevation profile. The brown area in the elevation-profile box shows the elevation of the dam, homes, streets and drainage channels.

Homes are generally 6-8 feet BELOW the height of the dam. That should be a giant red flag for anyone considering buying a house inside the reservoir.

Next, zooming out, I turned on the hydro layer. The red circle below, indicated the approximate area and location of the map above.

Note how the flood pool of the reservoir extends beyond the entire neighborhood shown above.

FEMA National Flood Hazard Layer Viewer for Floodplain Information

FEMA actually uses the elevation information from the USGS national map. But FEMA superimposes floodplains to show flood risk in several zones.

Note difference in two maps above in their bottom left corners. FEMA shows some homes inside the reservoir that are outside of mapped flood zones. Aqua = 100-year and tan = 500-year floodplains.

The difference noted above raises an important point. FEMA’s maps are estimates of the probability of unknown future events based on the frequency of extremely rare past events. Those estimates may not have been in effect when the neighborhood in question was built around the time of Tropical Storm Allison in 2001. Maps based on Allison weren’t adopted until around 2007 and are still in effect today.

Harris County Flood Control and FEMA update flood maps periodically when new monster storms come along and surpass past rainfall probability estimates. For instance, FEMA is working on new flood maps based on Harvey, but has not yet released them.

So, if you’re thinking of betting your life savings on a home in a risky area, the best things to do are these:

  1. Ask yourself, “Can I afford to lose everything?” Many families in the reservoirs did.
  2. Consult an independent engineer without any financial incentive in the purchase, i.e., making the deal go though.
  3. Evaluate a variety of homes, not just one. And look closely at the safety margins.
  4. If a home is two feet above the 100-year floodplain, look for one that’s higher. Things change regularly, usually in one direction.
  5. Make “flood avoidance” more important than kitchen appliances in your purchase decision.

A Cautionary Tale Based on Personal Experience

Back in the early 1980s, I owned a house in Dallas near a creek that an engineer and the city certified were 2-feet above the 100-year floodplain. The home flooded within two years, due to rapid, insufficiently mitigated growth upstream.

Several years later, when I bought a house in Kingwood, I looked at ten homes and bought the one on the highest ground. More than 30 years later, all nine of the others flooded during Harvey even though they were all reportedly above the 100-year flood plain.

For a thorough description of why flood risk is a moving target, read this post – Why Do We Flood?

After two years of drought, it’s easy to become complacent about flood risk. Don’t. Ask anyone who has flooded. They will tell you. Your life can change overnight. So homebuyers beware.

Posted by Bob Rehak on 10/21/2023

2244 Days since Hurricane Harvey