Flooding within the Halls Bayou watershed illustrates what happens when development, density, lack of detention and insufficient distance from streams put people and their property in harm’s way. Instead of protecting a strip of green space near the bayou years ago, developers built right up to the edge. As density increased and developers built further upstream without sufficient detention, people who crowded the Bayou then started to flood repeatedly.
As the images below show, once developed, the cost and time of mitigation increases exponentially.
Halls Bayou Not Unique
This same scenario happened repeatedly in other Houston watersheds: Greens Bayou; Brays Bayou, White Oak Bayou, and Cypress Creek, for instance. But let’s save those for future posts. For now, let’s go back in time.
For the most part, people have fixed their homes since the last big flood. These folks may be poor, but the vast majority take great pride in what they have.
The map below shows the route of Halls Bayou through surrounding mid-north neighborhoods. Homes are packed so close to the bayou that it’s hard to see it in places, so I outlined the route in red.
Now, let’s superimpose floodplains over the same area.
North to south along US 59 (on right), the floodplain extends almost 3 miles. And it will extend even farther when new maps based on Atlas 14 are officially released based on Harvey data. The image below shows what the area around US 59 and Halls looked like in 2002 shortly after Tropical Storm Allison.
Next, see how that area looks today where Halls Bayou crosses under US 59. Two large detention ponds exist where the subdivisions used to be.
Each detention basin took about three years to build.
Time, Costs of Buyouts
Before HCFCD could construct the detention ponds, it had to buy out homes in adjacent subdivisions and demolish them. Buyouts near the detention areas above began in 2002 when HCFCD received a large grant from the federal government after Allison. Google Earth images show that the buyouts took at least another three years.
Then Flood Control had to get permits from the City of Houston to demolish the streets. That took additional years.
So from 2002 until the completion of construction took 13 to 16 years (2015 and 2018). But the construction itself took only 3 years.
$1 of Prevention Worth a $1000 of Flood Mitigation
This area started to develop in the 1940s. The earliest image in Google Earth (1944) shows that it was at the edge of the City then. With more wetlands and farm land to absorb rainfall, the flooding problems were probably not as bad. A few scattered subdivisions pressed against the edges of the bayou. But the lots were large. And had green space been set aside then, the story today might be different.
Compare again the shot above with the one below for a dramatic example of infill development. The shot above is NOTHING like today’s below.
Just looking at these two maps, you can see how the dramatic increase in density limits flood mitigation possibilities and raises costs.
To make matters worse, despite flooding, people often fight buyouts. Most people in neighborhoods like this depend on support networks of friends and family. They fear leaving those networks. Many date back generations.
Should Have Known Better
Developers and home buyers knew or should have known this area was flood prone. But still, they built or bought here at great risk to themselves, and ultimately at great cost to the community.
That raises the question: Why were people allowed to build so close to the bayou in the first place? Why wasn’t sufficient green space left along the bayou to widen it or build detention ponds?
There are no simple answers to that question. Residents may not have felt at risk until upstream development sent more water downstream faster. They may not have been knowledgeable enough about flooding to ask the right questions.
Some just wanted to live close to work. Some wanted to be near family and friends. Some needed the support. And some just pushed their luck because they liked the view or location and the lots were cheap. Regardless, everyone is paying the price for decisions often made decades ago.
Posted by Bob Rehak on April 28, 2021
1338 Days since Hurricane Harvey
https://i0.wp.com/reduceflooding.com/wp-content/uploads/2021/04/Halls-Flood-Plains.jpg?fit=1200%2C793&ssl=17931200adminadmin2021-04-28 15:50:252021-07-29 16:01:38Halls Bayou Illustrates Cost, Difficulty of Flood Mitigation in Overdeveloped Areas
FEMA defines base flood elevation as “The elevation of surface water resulting from a flood that has a 1% chance of equaling or exceeding that level in any given year.” In other words, it’s how deep the water would be in a 100-year flood at any given spot.
Let’s take a look at each.
Texas Watershed Viewer
The Texas Watershed Viewer lets users identify local watersheds, sub-watersheds, river basins, and river sub-basins throughout the State of Texas.
To find your watershed and river basin, simply type your address into the search bar and press enter. The map will zoom into the address. From here, click anywhere on the map and the name of the sub watershed will appear. If you click the next arrow on the feature label, the name of the watershed will appear. If you click the next arrow again, the name of the river sub basin will appear followed by the larger river basin.
This lets you quickly visualize the extent of a watershed so you can see where water is coming from and going to.
After you click on map to see the feature’s name, you can view the geographic extent of the sub watershed, watershed, river sub basin, and river basin, by clicking the minus sign on the top left corner to zoom out from the address level to the boundaries of the other features. The boundaries of these features will be light blue.
Other Texas Watershed Viewer tools
Zoom: You can zoom in on your neighborhood or zoom out to the entire state of Texas.
Layers: adds the layers window in the top right corner. You can turn the layers on and off by click on the check box.
Basemap gallery: lets you change the basemap of the viewer. The topographic map, for instance, is a useful layer because river, lakes, and streams are labeled.
Measure: lets you measure the distance from your home to a water feature.
Share: lets you show your friends what you see on social media.
Print: lets you print out a copy for your records.
This site helps viewers understand where water comes from and how it converges. As land is cleared and leveled, it also helps you understand where streams used to flow. (Note: This feature only works until background maps are updated, however.)
One reader used this feature to show how a developer had filled in natural drainage on the developer’s property and blocked off drainage from the reader’s subdivision. With three potential tropical systems moving in our direction at this moment, that information could be very useful if his home floods and he needs to call a lawyer.
Using the topographic base layer, you can also predict where and how runoff will flow during a flood. Many homes near the East Fork flooded during Imelda when Caney Creek captured the Triple PG mine and started flowing south through an area where several other creeks converge. Homeowners report being flooded from overland flow before the creek rose. The topographic feature shows the path that the water likely took.
Those who have a passion for understanding the physical world around them could spend days exploring this website.
FEMA Estimated Base Flood Elevation Viewer
Like most flood maps of this sort, you can turn layers on and off and change base maps.
For instance, by clicking buttons, you can have it show the estimated flood extent and depths for a 1%-chance flood and a .02%-chance flood. You can also view stream center lines, cross sections, and view detailed information on flood insurance rate maps.
You can even activate a split screen mode and compare different features side by side, i.e., ten and hundred year flood extents.
The point of this whole site is to understand not just the extent of floods, but their DEPTH as well.
FEMA says information from this site helps:
Inform personal risk decisions related to the purchase of flood insurance and coverage levels.
Inform local and individual building and construction approaches.
Prepare local risk assessments, Hazard Mitigation Plans, Land Use Plans, etc.
Prepare information for Letter of Map Amendment (LOMA) submittals.
Helpful Where Flood Maps Not Yet Available
The BLE (Base Level Engineering) Data in this website provides flood hazard information where flood insurance rate maps may not yet be available. We saw this, for instance, in Woodridge Village (north of Elm Grove) where flood maps stopped at the Harris/Montgomery county line. LJA Engineering claimed there were no floodplain issues on the Montgomery County side of the line. In fact, most of the Woodridge Village was in a flood plain as you can clearly see below; it just had not been mapped yet.
Compare that to FEMA’s Flood Hazard Layer Viewer below and you will immediately see the difference.
FEMA’s estimated base-flood elevation viewer helps reputable land developers identify flood risk, expected flood elevation, and estimated flood depth where Base Level Engineering has been prepared (i.e., as in the Lake Houston Area).
Reportedly, the information in this tool is not yet Atlas-14 compliant. But it’s still better than nothing.
The more tools you have to evaluate the purchase of insurance and property, the safer you will be.
No one tool can do everything. But together, the can make you “buyer aware.”
Posted by Bob Rehak on 8/20/2020
1087 Days since Hurricane Harvey and 335 since Imelda
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.
https://i0.wp.com/reduceflooding.com/wp-content/uploads/2020/08/Screen-Shot-2020-08-19-at-10.30.14-PM.png?fit=1422%2C1080&ssl=110801422adminadmin2020-08-19 23:17:552020-08-19 23:39:41Two More Websites That Help You Understand Drainage and Flood Risk
Clarification: General plans, as described below, are primarily about street layouts. However, many people have been trying to raise awareness at the Planning Commission that street patterns are affected to a significant degree by the volume and and layout of drainage and detention features. And, of course with Atlas 14 that is more true than ever. Danny Signorelli, CEO of the Signorelli Companies, took issue with this post. I offered him an opportunity to print a rebuttal verbatim. He refused the offer.
According to residents in other parts of the Commons, Signorelli tried to develop this property before and reportedly wanted to add 4-6 feet of fill to the floodplain. It’s not yet clear what they have in mind for this iteration of the project. However, comparing the general plan to FEMA’s National Flood Hazard Layer Viewer shows that parts of the development are still in the flood plain. (See below.)
No Detention Ponds Shown on Plans
The general plan filed with the planning commission also shows that the developer shows no plans for detention ponds on the property. A best practice to reduce flooding is to “retain your rain.”
Here are satellite and close-up views of where the new subdivision would be relative to the the surrounding area and existing parts of the development.
Parts of the proposed development will be in the floodplain. And those floodplains will soon expand to include even more homes. See the two dotted lines below.
Ironically, just last night, the City of Houston and its partners (Harris County Flood Control, Montgomery County and the SJRA) presented a draft of the findings of the San Jacinto River Master Drainage Plan. In it, they recommended avoiding flood plain development to keep people out of harm’s way. See slide below from their presentation.
The presenter also discussed how the floodplains were expanding due to revisions of flood maps based on new hydraulic and hydrologic modeling not yet been shared with FEMA.
The 100-year flood plain in many areas will like expand well into the 500. And the 500-year flood plain will likely expand into areas previously not shown in ANY floodplain.
San Jacinto River Master Drainage Plan Draft Report 8/13/2020
Thus, the number of homes affected by floods could greatly expand beyond the number shown above.
Drainage in Commons Already a Problem
Plans also show that homes will be built very close to a drainage easement. Yet existing ditches in the Commons are eroding badly due to lack of maintenance. Below is a picture of one taken in January last year. Residents say the trees are still there and the erosion became much worse during floods in May and Imelda.
Less Than One Fourth of Property Now Under Consideration
The tract is 332 acres, but only 75.3 is proposed for development at this time. It is entirely located within the incorporated limits of the City of Houston. The entire tract is adjacent to COH flooding easements for Lake Houston.
How to Voice Concerns, If You Have Them
Here’s how you can voice concerns, if you have them. The City Planning Commission will hold virtual meetings until further notice. So it’s very easy to make public comments. You can sign up to speak by going to the Planning Commission Home Page.
The next Planning Commission meeting is Thursday, August 20, 2020. If you’d like to speak, you must sign up at least 24 hours before the meeting.
Speakers have only TWO MINUTES. Key points to consider:
Floodplain will officially be expanding soon.
Some of these homes are already in it.
Many more soon will be.
That could require fill.
And fill will make flooding worse for other homes near the river on both sides.
No detention ponds or drainage plans are shown.
The Planning Commission should consider these things.
Posted by Bob Rehak on 8/14/2020
1081 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.
https://i0.wp.com/reduceflooding.com/wp-content/uploads/2020/08/GE-screenshot.jpg?fit=949%2C708&ssl=1708949adminadmin2020-08-14 17:45:352020-08-16 20:21:30Developer Seeks City Approval to Expand Commons of Lake Houston into Floodplain – Without Detention Ponds
An article in the New York Times yesterday discussed a new flood-risk website called FloodFactor.com. The article’s headline trumpeted “New Data Reveals Hidden Flood Risk Across America.” The new website was developed by First Street Foundation, which defines itself and its mission as, “a non-profit research and technology group defining America’s Flood Risk.” Past. Present. AND FUTURE. That’s your first clue as to what this new site offers that FEMA doesn’t.
According to the Times, FloodFactor estimates that 14.6 million properties are at risk from what experts call a 100-year flood, far more than the 8.7 million properties shown on federal government flood maps.
Purpose of This Post
This article will examine the advantages and limitations of both of the FEMA and FloodFactor sites. Together they can give property owners a fuller understanding of their flood risk. Individually, each can mislead.
That’s both good and bad. Good that information is debated. Bad that sometimes pushback from landowners and local governments distorts true flood risk. No one wants to be reclassified INTO a flood zone that would require paying more for flood insurance. And no one wants his or her property to become undevelopable or unsaleable after a map revision.
Another flaw in the FEMA system: many areas remain unmapped. That allows developers to say they are not in a flood zone when, in fact, they are. We saw that loophole exploited by LJA Engineering with Perry Home’s Woodridge Village. They showed the Taylor Gully floodplain magically stopping at Harris county line. The area on the other side of that county line had not been mapped, therefore they claimed, it wasn’t in a floodplain. That enabled the developer to follow more lenient development guidelines.
FEMA maps also do not estimate future flood risk due to factors such as climate change.
Sometimes it even feels as though FEMA’s trying to catch up with the past.
FEMA maps in Montgomery County are currently based on flood data developed during the 1980s. However, the county has been one of the fastest growing in the country. New unmapped upstream development has significantly altered downstream flood risk, as we saw in Elm Grove twice last year.
Finally, FEMA maps, at present, don’t define risk for individual properties (although FEMA hopes to introduce that capability next year). “This leaves millions of households and property owners unaware of their true risk. There has long been an urgent need for accurate, property-level, publicly available flood risk information in the United States,” says FloodFactor.com.
Pros and Cons of FloodFactor.com
FloodFactor.com addresses many of FEMA’s shortcomings. That’s a huge benefit.
During Harvey, HCFCD says that of the 154,170 homes flooded, 70,370 were outside of the 1% (100-yr) and .2% (500-yr) floodplains. 105,340 or 68% were outside the 1% (100-yr) floodplain. 64% of the homes flooded did not have a flood insurance policy in effect.
Perhaps with a better understanding of true flood risk, many more home and business owners would have purchased flood insurance and avoided financial pain.
Claims include insurance and disaster relief claims on National Flood Insurance Program policies
FEMA Individual Assistance flood claims for those who do not have NFIP policies
Disaster assistance provided by the Small Business Administration.
However, during Harvey, of the 154,170 homes across Harris County that flooded, 68% did not have flood insurance. Many of those sought government assistance. But many also did not. Most government assistance is biased against upper income households.
Regardless, FloodFactor.com claims that it:
Shows flood risk to individual properties
Calculates street flooding risk due to heavy rainfall
Incorporates areas unmapped by FEMA
Compensates for adaptations such as levees and berms that protect people from flooding
Projects future changes such as precipitation increases, stronger storms, and sea level rise
Predicts risk 30 years into the future, theoretically at least, enabling users to gage the probability of flooding during a 30-year mortgage
Intends to update its models annually
Shows risk to individual properties on a sliding scale of 1-10, instead of a yes/no, “I’m in/out of the 100-year floodplain” as FEMA does.
Shows users an estimate of risk in increments (500-year, 100-year, 20-year and 5-year floods or 0.2%, 1%, 5% and 20% annual risk).
Explains what parts of a building are affected by floods of varying depths
Presents flood mitigation solutions individuals can implement
Provides area-wide “risk overviews” and predicts how they will change in the future
FloodFactor.com Looks at Texas and Houston
FloodFactor posted a national outlook with state-by-state discussions. The discussion on Texas says, “The First Street Foundation Flood Model calculates the number of properties facing any risk of flooding in Texas as 2,116,800 over the next 30 years. Of these properties, 218,700 were categorized as facing almost certain risk, with a 99% chance of flooding at least once over the next 30 years.”
They continued, “The city of Houston has the greatest number of properties at risk of flooding in the state with 186,500 currently at risk, or 32% of its total number of properties.”
First Street Foundation
Interestingly, when FloodFactor.com modeled Texas flood risk, they used four historical storms that did NOT include Harvey. They did not explain why.
Shortcomings of Both FEMA and FloodFactor
As far as I can tell, neither FEMA, nor FloodFactor, account for upstream development in their flood mapping. However, FloodFactor does allude at one point to factoring in impervious cover. FloodFactor’s annual updates could help address that issue (if everything is really updated annually).
My background does not qualify me to critique FloodFactor’s methodology or documentation. But I have lived in the north Houston area for 35 years. So I do feel qualified to talk about their predictions for the Lake Houston area.
“Ground-Truthing” Accuracy Claims
I evaluated some areas that I know flooded during recent large storms to get a feeling for how well FloodFactor performed.
After all, if FloodFactor can’t predict the past, why should I believe it can predict the future any better?
I looked at four areas in Kingwood and SE Montgomery County. I was extremely familiar with homes and businesses that flooded or didn’t flood in each during major storms.
FloodFactor seemed to nail it. FEMA did not. FEMA shows no flooding north of the county line. FloodFactor even showed areas flooding on Perry Homes’ undeveloped property, plus around it.
However, the background map appears to be about 10 years old, judging by the extent of development in Woodridge Forest (lower left). Much of that area has since been built up by developers.
So has Woodridge Village (center forested area). It has been cleared for about two years now. Five large detention ponds have been constructed. And the dirt excavated from those has built up the remainder of the property. So in that sense, FloodFactor is outdated from the git-go.
It’s unclear whether Floodfactor’s predictions, say for the Taylor Gully area through Elm Grove (bottom center), take those new upstream detention ponds into account.
River Club/River Ridge:
Between FM 1314 and the West Fork just south of Northpark Drive, lie two small subdivisions called River Club and River Ridge. FEMA nailed it. FloodFactor missed. Badly.
Mixed results. FEMA nailed areas that flooded during Harvey, but missed some street flooding during Imelda. FloodFactor makes me scratch my head. For instance, FloodFactor showed most of North and South Woodland Hills flooding, presumably from street flooding, after climate change will make rainfalls even more intense. However, they don’t specify exactly where most of the risk comes from. These are among the two highest subdivisions in Kingwood.
Two Better than One
Given the fact that neither FEMA, nor FloodFactor, is perfect, it’s best to use them in conjunction with each other. With a knowledge of the limitations of each, one can gain a better understanding of flood risk. There’s just no substitute for talking to people in the neighborhood.
One more example in that regard.
Northpark Commercial Area Near Woodland Hills Drive
FEMA correctly shows historical flood risk. Note the location of red dot for reference below.
The red dot above shows the location of a building that was raised 3 feet before construction, but not listed with FEMA because it was far outside the 500-year floodplain.
One big benefit of the FEMA maps is that property owners who elevate their homes can have them reclassified out of the floodplain. It’s not clear how that might work with FloodFactor.
However, with input from both websites, if I were buying a property, I would know enough to start asking questions:
What’s happening around this area to increase flood risk? (Upstream development in the Ben’s Branch Watershed? Environmental change?)
Should I check the elevation of my property against FloodFactor’s estimate? (Yes!)
Could floodproofing or elevation strategies help my property? (Yes!)
Should I look again at getting flood insurance? (Yes!)
This is like getting a second repair estimate for your car. You are always safer with at least two estimates.
Another benefit of the FEMA site is that it spans county boundaries, i.e., if you live on the Harris/Montgomery County Line.
Harris County operates a site called “Flood Education Mapping Tool.” The Harris County site superimposes drainage ditches, streams, creeks, bayous and rivers and even gives you their names and numbers. Very helpful if you want to report a problem some day, or track up or downstream to see where drainage issues may be originating.
According to Diane Cooper, a hydrologist with more than 20 years of experience in forecasting floods, both of the County sites have better imagery and more layers than the FEMA site.
Layers comprise one of the key features of both county sites. Experiment with them. I’m especially fond of the background layers.
They let you see the flood zones superimposed over simple maps, satellite images, historical satellite images, and more. The Montgomery County site even lets you click on streets and information about them pops up. I learned, for instance, that one subdivision in MoCo has a street named Paper Wasp Lane. You really don’t want to mess with the people on that street! It’s not far from Killerbee Lane. Let’s get up a football game between those two streets! I’d pay to see that.
Posted by Bob Rehak on October 10, 2019, with help from Diane Cooper
771 Days since Hurricane Harvey and 20 since Imelda
https://i0.wp.com/reduceflooding.com/wp-content/uploads/2019/10/MoCo-Map.jpg?fit=1500%2C1117&ssl=111171500adminadmin2019-10-08 20:35:402019-10-08 20:41:56Three Ways to Find Out If You Are In a Floodplain