flood risk Archives - Reduce Flooding

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:

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

Factors that Affect Flood Risk and How to Assess Them

When looking at buying property, your flood risk depends on at least ten factors. Unfortunately, people rarely consider most of them. Even if they do, they may not now how to assess them.

So, here’s a list of key factors that can increase or decrease your flood risk. I’ve also included examples and ways to explore their impact on your property or the property you’re considering buying:

Geography and Topography: The natural landscape of an area plays a significant role in its flood susceptibility. Flat, low-lying areas, river valleys, coastal regions, and areas near lakes or other bodies of water are more prone to flooding because water naturally collects in these locations. To investigate a particular area, check out resources such as the USGS National Map and FEMA’s National Flood Hazard Layer Viewer.
Proximity to Water Bodies: Areas near rivers, lakes, oceans, and other water bodies are at a higher risk of flooding. Riverine flooding, coastal flooding, and flash flooding can all occur in these regions. See any map or web sites such as RiskFactor.com.
Rainfall and Precipitation Patterns: Areas that receive heavy or prolonged rainfall are more likely to experience flooding. Rainfall can lead to flash floods, riverine flooding, and urban flooding when drainage systems are overwhelmed. In Texas, generally the farther east and closer to the coast you go, the more rainfall increases. To see the likelihood of precipitation in any given area, check out NOAA’s Atlas-14 site then investigate local infrastructure standards to see if they meet Atlas-14 standards or something less (prior). Also understand that NOAA is revising Atlas-14 already to incorporate impacts of climate change (see Atlas-15).
Climate and Weather Events: Areas prone to hurricanes, tropical storms, or other severe weather events are at risk of storm surges, heavy rainfall, and coastal flooding. Here are several sites that can help you find reliable climate data.
Soil Type and Saturation: The type of soil in an area can impact its flood susceptibility. Soils with poor drainage or soils that are already saturated from previous rain events are more likely to contribute to flooding. Here’s a USDA national soil survey and how to determine whether flood mitigation projects in any given area properly account for the soil types in that area.
Human Development: Urbanization and land development can increase flood risk. Paved surfaces and buildings can reduce natural drainage and increase runoff, overwhelming drainage systems. Harris County has proposed minimum drainage standards for areas draining into Harris County, but not all surrounding areas have adopted these standards yet.
Deforestation and Land Use Changes: Changes in land use, such as deforestation or the construction of roads and buildings, can alter natural water flow patterns and increase flood risk. Think you’re protected? Unfortunately for homeowners, many wetlands are now being destroyed. The EPA and Army Corps amended the definition of protected “waters of the United States” in light of the decision in Sackett v. EPA in May. It narrowed the scope of the Clean Water Act and the EPA’s power to regulate waterways and wetlands.
Infrastructure and Drainage Systems: The condition and capacity of drainage systems, including stormwater sewers and levees, can affect an area’s flood vulnerability. Inadequate or poorly maintained infrastructure can lead to flooding. After Harvey, Harris County Flood Control embarked on an ambitious expansion of flood-mitigation infrastructure, but recently spending has fallen. More in some areas than others. So stay alert to what’s happening in your area.
Historical Flooding: Areas with a history of flooding are often at continued risk, as past floods can indicate a region’s susceptibility to future events. In Harris County, MAAPnext provides an excellent series of historical flood maps to help you understand your flood risk.
Land-Use Planning and Floodplain Management: Effective land-use planning, zoning regulations, and floodplain management can help mitigate flood risk by restricting construction in flood-prone areas and implementing flood control measures. There’s no zoning in Houston and little in surrounding areas. We do have floodplain management regulations. When purchasing property, always look upstream to see if those regulations are effectively enforced.

Few things affect a property’s value more dramatically than flooding.

Yet flood risk can change over time – for better or worse. So buyer beware. Or buyer be wet.

Posted by Bob Rehak on 9/3/2023 with some help from ChatGPT

2196 Days since Hurricane Harvey

The thoughts expressed in this post represent opinions on matters of public concern and safety. They are protected by the First Amendment of the US Constitution and the Anti-SLAPP Statute of the Great State of Texas.

Editorial: Need More Disclosure, Education About Flood Risk

Who teaches young home buyers about flood risk? No one in my experience.

More than forty years ago, I bought a new house next to a creek in a Dallas suburb. The trees and the view attracted me. Before I put money down, I asked about flooding and was assured that the home was two feet ABOVE the hundred-year flood plain. The homebuilder even showed me a survey and a drainage study, and pointed to the engineers’ stamps. I pulled out my checkbook and made the most tragic, costly decision of my young life.

Within a year, other developers just upstream from me built the Collin Creek Mall and Plano became the fastest growing city in America. With each passing month, rains made the creek swell higher. Then one day after a modest rain, I saw a pickup truck floating down the creek and the water creeped into my house.

Alarmed, I called the City Engineer. He convened a task force that included Garland, Richardson and Plano City Engineers. They asked the Army Corps of Engineers to re-survey the creek. The Corps found that…

…instead of being two feet above the 100-year floodplain, we were now 10 feet below it.

Had I known such dramatic change could happen so quickly, I never would have bought the home. I decided to sell, disclosed the flood risk, and lost a pile of money.

Costly Lessons Learned

That experience taught me several lessons.

Flood forecasting is a very inexact science. Changing conditions – such as upstream development, climate and political priorities – make it so. They are beyond the ability of engineers to predict.
Developers use the surveys and analyses that engineers produce to obtain building permits.
Their documents do not reflect the potential for future change.
Homebuilders, nevertheless, use the engineering documents to reassure future buyers that they are safe.

All along the way, people throughout the value chain make expensive binary decisions based on documents that don’t reflect future flood-risk. Permit or don’t? Invest or don’t? Build or don’t? Lend or don’t?

Flood Risk is Non-Binary, Flood Education Non-Existent

Professionals understand the flood risks involved. Members of the public rarely do. And that’s a powerful argument for flood-risk education and fuller disclosure.

But buy a house with a view of a river! You’ve achieved the American Dream, paid a premium, and the only information people volunteer along the way is a reminder to buy flood insurance.

It’s as if the chance of flooding equals the chance of getting hit by lightning.

According to the CDC, the odds of being struck by lightning in a given year are only around 1 in 500,000.

But the odds of flooding in a “500-year rain” are 1 in 500 – a thousand times greater. But most home buyers don’t worry about that. So builders keep building in flood plains. And buyers keep buying.

Everyone along the way – land owners, developers, public officials, engineers, and home builders – is financially incentivized to “make the sale.” Growth is good – especially to the people who enable it.

Example: Need for Flood-Risk Education

Below is a photo that shows part of a new development in Porter between Sorters-McClellan Road and the San Jacinto West Fork. At the start of 2019, it was all woods and wetlands bracketed by streams and a drainage ditch. Wetlands and the proximity to floodways increase flood risk.

*New woodless Northpark Woods development in the floodplain of the San Jacinto West Fork.*

However, FEMA’s current flood map (see below) was developed in 2014. That was before Harvey. It shows about half of the development (outlined in red) to be in the 100- or 500-year floodplains. But those floodplains will soon expand based on data collected after Harvey. The new flood plains will likely cover most of the site. But is anyone disclosing the current or potential flood risk?

*Northpark Woods highlighted in red. Floodplains delineated based on 2014 map which is now being revised and will be released soon.* *Cross-hatch = floodway. Aqua = 100-year floodplain. Brown = 500-year floodplain.* From FEMA’s National Flood Hazard Viewer.

Selling the Dream vs. Disclosing Risk

Young, first-time home buyers will mortgage themselves to the hilt to get a nice home with a water view. But there’s less risk disclosure on this developer’s website than on the back of a candy bar.

New homes here range from $225,000 to more than $300,000 with estimated mortgages starting at about $1,000 per month. The developer claims, “Our homes are where memories are made, families are raised and stories unfold. Our mission is to create thriving, enduring neighborhoods by building new homes with lasting livability.”

The developer’s website also boasts of “close proximity to the West Fork San Jacinto River where locals enjoy swimming, fishing, boating and skiing…” And they brag about nearby championship golf courses, owner financing, online buying, and $95 down. But they never mention flood-risk or even flood insurance once the website that I could find.

A home in the 100-year floodplain has, on average a 1-in-4 chance of flooding during the life of a 30-year mortgage. And keep in mind that those floodplains are shifting targets. Even a home in the 500-year floodplain has a 6% chance of flooding in 30 years.

All up and down the West Fork, East Fork, Bens Branch, Spring Creek, Peach Creek, White Oak Creek, Luce Bayou, Tarkington Bayou, and other area watersheds, similar developments are sprouting up in risky places.

People put their life savings in these homes and there’s less disclosure than on a candy bar.

Realistically, that’s not going to change. So “Buyer Beware”! People must educate themselves about flood risk. Start by referring friends and relatives in the market for a home to these posts. They explain where to find reliable, objective information about flooding and flood risk.

Posted by Bob Rehak on 1/16/2022

1601 Days since Hurricane Harvey

The thoughts expressed in this post represent opinions on matters of public concern and safety. They are protected by the First Amendment of the US Constitution and the Anti-SLAPP Statute of the Great State of Texas.

Homes That Didn’t Flood Because of Quick Action: Example of How to Reduce Flood Risk

Coordinated, fast action by the City, Harris County Flood Control, and concerned citizens reduced flood risk for many homes earlier this month. Together, they eliminated many blockages in drains and ditches that likely prevented many homes from flooding during the storms from May 3 through May 10. Perhaps we can learn from the experience and organize neighborhood groups that spot and report developing situations before they get out of hand and cause floods. Here’s what happened.

Triple Whammy: Three Major Storms

On Friday, May 3, late in the afternoon, heavy rains combined with high winds and possible tornadoes downed trees throughout Kingwood. Tree debris littered the ground everywhere. The City worked throughout the weekend to clear streets and drains. But large amounts of debris remained in yards and along greenbelts.

Then on Tuesday, more intense rains hit and flushed much of that debris into drains and ditches.

The City again sprang into action; Public Works sent crews out to inspect the storm drains for blockages. Camera and clean up crews have been here ever since.
Harris County Flood Control also sent crews out to clear ditches. Due to erosion and high winds, many trees had fallen into the ditches and were creating blockages.

Sadly, many homes did flood on Tuesday. The vast majority of those were near a massive construction site that altered drainage.

But had it not been for fast, coordinated action by the City, County and Citizens, many more homes elsewhere might have flooded on Friday, May 10, when Round Three of heavy rains hit the Lake Houston Area.

Example of How Things Can Go Right

Jennifer Coulter, a Kings Forest resident, reported a small creek totally blocked behind her home. The Coulters flooded badly in Harvey and have been hyper vigilant ever since. Jennifer detected a blockage in the ditch behind her home AFTER Tuesday’s storm on May 7. Here’s what it looked like. Harris County Flood Control sent a team out to clear the blockage BEFORE the Friday storm.

*This bridge over a small ditch/creek in Kings Forest had become totally blocked in the previous storms.*

*Another view of the same ditch showing extent of blockage.*

*Wide shot illustrates how water would have been forced out of the ditch during a storm because of the blockage.* *Once blocked, additional debris can quickly pile up, making things even worse.*

When notified, HCFCD immediately dispatched a crew. They managed to clear the blockage before the next storm hit. It took about an hour. Here’s what the same ditch looked like when they left.

A Minor but Important Success

I emailed Coulter after the Friday storm to see how she did. Her response: “Dry here. Looked like the backyard drained well, too. Huge sigh of relief from this address!”

This wasn’t the only success story before Friday’s rains. I’m aware of at least five similar blockages removed before the storm. No homes flooded near those areas that I am aware of…at least as a result of reported blockages.

That’s not to say that no homes flooded anywhere. I am sure some did and that is tragic. But this example underscores the need for better identification of issues and coordination in communicating them.

Importance of the Right Five

Management consultants often talk about the “Right Five” as a key element of success. Success happens when the Right People, get the Right Information, at the Right Time, at the Right Place, in the Right Format.

In this case, residents knew:

The Right People to contact (Flood Control, not the City, and the right people AT Flood Control)
The Right Information to give them (description of problem so they could send crews with the right equipment, photos of what they would encounter, everything they needed to take immediate action).
The Right Place to send them (GPS coordinates, nearest street intersections, and nearest access points for greenbelts).
The Right Format (easy to read and understand; clear; concise; digital for easy transmission to crews in field).
The Right Time (before the storm)

While we are at it, we should also give ourselves a pat on the back. Residents helped clear drains and ditches before the storm, too. That’s not only our right; it’s our duty. The City needs our help. Their crews can’t be everywhere at once; Houston covers a lot of territory.

Organizing to Reduce Flood Risk

How can we learn from our failures and replicate our successes? Last week, the Kings Forest Board of Directors voted to establish a permanent Flood Committee with two objectives:

Raise awareness among residents of issues that contribute to flooding
Identify and communicate problems we can’t resolve on our own to the Right People at the City and County.

In essence, the idea is to create a group like Neighborhood Watch or Crime Stoppers, but focused on flooding: Clog Stoppers! People who can spot problems and report them before they cause flooding.

Major examples of things that contribute to flooding:

Yard waste swept into sewers or dumped on greenbelts
Dead or dying trees about to fall into ditches
Not cutting deadfall into small pieces [large ones block culverts; max 2′ pieces recommended]
Irresponsible construction practices
Sand mining in floodways behind inadequate dikes
People altering drainage illegally

I hope the other community, trail, and commercial associations can form similar committees. Working together through KSA or some other grass roots organization, we can reduce flood risk for everyone. We can also help improve government efficiency by getting the right people, the right information, in the right place, at the right time, in the right format.

Posted by Bob Rehak on 5/20/2019

629 Days since Hurricane Harvey

A Quick Way to Assess Flood Risk In Your Neighborhood During Storms

For decades, weather services have forecasted flood warnings, watches and alerts for general areas, such as the Houston region. But what is the risk to your particular neighborhood? Web-based, interactive tools now make it possible to forecast flood risk near you. However, they require some “do-it-yourself” interpretation. Hence, this post.

YESTERDAY morning (TUESDAY 6/19), I woke up and saw standing water in my backyard. The sky was black. I heard thunder. I remembered the forecast from Monday night about storms training across the area. My heart started racing as I fired up my laptop.

Here is what I did. (NOTE: TODAY’S RAINFALL IS DIFFERENT; THE INFORMATION BELOW IS AN EXAMPLE ONLY TO ILLUSTRATE A PROCEDURE.)

I first went to Space City Weather to get a good feeling for the big picture and learn of any National Weather Service warnings or Harris County Flood Control District insights; it’s always a good idea to consult the professionals first. The threat appeared both east and west of Lake Houston; it seemed as though we might have threaded the needle with this storm. However, forecasters felt the storm over Beaumont at the time might move west during the day.
Houston threaded the needle overnight and avoided the major parts of the storm.
So next, I wanted to see how much capacity the San Jacinto river and Lake Houston had. To figure that out, I went to USGS to find the level of Lake Houston. The spillway is at 42.5 feet shown at the top of this graph. The blue line represents the actual water level.
USGS showed that Lake Houston was still well below the spillway at 42.5 feet, even though it had risen 3 or 4 inches overnight.

You can see from the widening gap between those two lines how the city lowered the lake to create extra capacity before the storm. However, you can also see how the blue line started to turn up at the far right.
Next, I wanted to see if a huge upstream rainfall was rushing toward Lake Houston. So I went to the SJRA site to check the level of Lake Conroe. I determined that the threat from the west was minimal. Lake Conroe was also below its normal level.
On Tuesday, Lake Conroe was about .4 feet below its normal level.

The lake level had only risen a few hundredths of an inch since the day before.
Next, I followed another link on the SJRA website to the Lake Operations and Rainfall Dashboard. It is located right below the information in #3 above. Montgomery County gages showed that not much rain had fallen to our north and west. Only one of 14 gages showed more than an inch of rain. Most showed less than a half inch. At this point, I felt that the threat was more in the future than the present.
Only one of 14 SJRA gages showed more than an inch of rain.
To see what was happening with that two inches that fell on Lake Creek, I went to the Harris County Flood Warning System. I could see from the home page that the gage at US59 had received 1.36 inches of rain and the one at West Lake Houston Parkway 1.44 inches. Not a huge threat! But rainfall doesn’t correlate perfectly with flood levels.
From the Harris County Flood Warning System home page, I was able to quickly locate the gages for the US59 and West Lake Houston Parkway bridges over the San Jacinto River.
I still needed to see how much the San Jacinto was below its banks. So I clicked on the gage at West Lake Houston Parkway for more information. That’s the gage nearest me. The link took me to a page that showed a breakdown of rainfall at that location. Right next to it was a tab called Stream Elevation. In the graph, I could see that the river was near 41 one feet. The banks were six feet higher! Better, there was no sharp rise in the river level. I let out a big “Whew!”
Difference between top of banks and water level

All of this took about 5 minutes. I could have waited for a weather report on TV or checked the weather app on my iPhone. However, they would have only told me what was happening in the region, but not at my exact location. Try it for yourself the next time you have a pitter patter panic.

Had the river been coming out of its banks, I could have accessed the new, near-real-time, inundation mapping system on the Harris County Flood Warning System home page. It is updated every 15 minutes. The map allows you to zoom into your neighborhood and see where flood waters are predicted to go based on the Flood Control District’s models and the river’s height.

Diane Cooper, a Kingwood resident who has 20+ years of forecasting experience with the National Weather Service, also suggested this shortcut. It lets you look at upstream and downstream rainfall over the entire region all at once. My thanks to Diane.

Posted 6/20/2018 by Bob Rehak

295 Days Since Hurricane Harvey

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