Tag Archive for: USGS

GIS Data Reveals Likely Source of NE Houston Flooding Unrelated to Historic Disinvestment

In northeast Houston, where residents and activists frequently chant “historic disinvestment,” I accidentally stumbled onto a much more likely cause of the frequent flooding than systemic racism. It happened while browsing a GIS database with hundreds of layers containing a broad range of information. The instant I saw it, it unlocked a mystery. Tumblers suddenly aligned that unlocked the mystery. But let’s start this story with accusations that made no sense to me.

Accusations of Systemic Racism Not Supported by Spending Data

Three years ago, I joined the Harris County Community Flood Resilience Task Force. Ever since, I have heard a constant drumbeat of “historic disinvestment” by many members who believe they are victims of systemic racism by Harris County Flood Control District (HCFCD).

They claim that they aren’t getting their fair share of flood-mitigation funds when, in fact, financial analysis reveals the opposite. They get the lion’s share.

LMI vs. Non-LMI flood-mitigation funding
LMI vs. Non-LMI flood-mitigation funding through Q3 2021.

Eight watersheds with a majority of low-to-moderate income residents have received almost two thirds of the funding going back to 2000. That’s out of a total of 23 watersheds. The money has flowed to damage – as it should.

Many people, however, don’t believe that. The loudest complaints have come from the Northeast Action Collective. They waged a battle to remove flood-control executives from office who were working tirelessly on their behalf.

Regardless, falsehoods repeated often enough eventually rose to the level of “accepted truth.” Even experts can be fooled. Jim Blackburn, the renowned professor of engineering at Rice, repeated the “historic disinvestment” claim without presenting any proof in a Houston Chronicle story last week.

He claimed residents of Halls and Greens Bayou watersheds weren’t getting their “fair share” of flood mitigation money. In fact, Greens Bayou ranks #2 in terms of money received. Only Brays Bayou has received more.

Spending by Watershed from 2000 through 2023Q1. Source: Harris County Flood Control District via FOIA request.

And tiny Halls Bayou ranks #2 in spending per capita. Together, the two bayous have received more than $390 million to date.

And they could soon receive another $466 million out of the $750 million that the GLO and HUD recently granted Harris County for flood mitigation. If HUD approves the recommended projects totaling $466 million, Halls and Greens will have received $856 million – far more than any other watershed. (Technically Halls is a sub-watershed of Greens, but HCFCD tracks spending as if it were separate.) This is hardly historic disinvestment.

More Likely Cause of Flooding Overlooked by Critics Crying Racism

Today, while learning a new (to me) geographic information system, I randomly clicked on a “wetland” layer. Boom! Guess where the largest concentration of wetlands in Harris County is. The northeast!

Note Lake Houston in the upper right, once home to untold acres of wetlands before the dam was built in the 1950s.

As a reminder of what these wetlands once looked like, see the photos of Emily Murphy who kayaks along the shores of Lake Houston.

Emily Murphy wetland photo by Lake Houston
Photo Courtesy of Emily Murphy

Regulations discourage building in wetlands for good reasons. Water collects there. The soil is less permeable. They are low, poorly drained, and unstable.

In addition, USGS points out the many positive benefits of wetlands. “Wetlands provide habitat for thousands of species of aquatic and terrestrial plants and animals. Wetlands are valuable for flood protection, water quality improvement, shoreline erosion control, natural products, recreation, and aesthetics.”

But because they’re cheap land and available, some less-than-scrupulous developers often try to build in them. I’m told by engineers I trust that that has always been the case and always will be.

Back in the 1950s, farms and ranches occupied most of the northeast Houston area. Here’s what it looked like then.

Note the San Jacinto River in the upper right in this 1953 pre-Lake Houston aerial image from Google Earth.

And here’s what the same area looks like today.

Note the presence of Lake Houston in the upper right in this 2022 image.

There are still big undeveloped areas in the image above. But many developments have also filled in large parts of the northeast that were once wetlands in the 1950s image.

Dangers of Building Over Wetlands

According to USGS, “Wetlands are transitional areas, sandwiched between permanently flooded deepwater environments and well-drained uplands, where the water table is usually at or near the surface or the land… The single feature that most wetlands share is soil or substrate that is at least periodically saturated with or covered by water.”

Wetlands are almost always terrible places to build houses.

Four years ago, I posted about the disadvantages of building over wetlands. Pictures of the Woodridge Village property, then under development by Perry Homes, dramatized how unstable the soils were. Dangers of building over wetlands include shifting slabs, cracked driveways, mold, erosion, clogged storm drains, flooding and more.

Unsuspecting buyers of former wetlands can literally get sucked in by low prices. Seventy years later, the original builders and buyers are long gone. And pre-digital soil samples and drainage analyses (if they were ever done) have long since disappeared into the fog of history or a dusty warehouse.

Wetland-mitigation banks near a development should raise red flags to buyers today. There’s one on the northeast corner of Beltway 8 along, you guessed it, Greens Bayou. There are also two in Colony Ridge: the Houston-Conroe and Tarkington Bayou Mitigation Banks.

In conclusion…

Today’s residents in such areas pay for previous owners’ lack of knowledge – not because of historic disinvestment.

I’m not saying early owners didn’t exercise due diligence. We just didn’t know then what we know now.

Posted by Bob Rehak on 9/22/23

2215 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.

USGS Says One Third of Harris County Now Impervious Cover

Did you know that one-third of the area in Harris County now has impervious cover? That Montgomery County had a 57.12% net increase of impervious surface area between 2001 and 2019? Or that 10% of land cover in the Lower 48 states changed during that same period? I discovered these and a multitude of other fascinating facts in a recently updated United States Geological Survey (USGS) website dedicated to monitoring changes in land cover, for example, from forested to developed.

When you live in an area for a long time, it’s easy to forget what happened two decades ago. And when you move to a new area, you just accept what is and don’t worry about what was.

But USGS gives you a quick and easy way to see and quantify changes in land use down to the county level. It’s useful in telling you where flood threats could develop over time and how fast they are developing.

About the USGS National Land Cover Database

USGS recently released updated land cover maps for the lower 48 United States. They show how the country’s landscapes have changed over an 18 year period in two- to three-year increments. It’s called the United States National Land Cover Database (NLCD). And it’s the fastest way to see how your county is changing.

Updates include 2001, 2004, 2006, 2008, 2011, 2013, 2016, and 2019.

Developed using Landsat imagery, NLCD classifies land cover into 16 groups with 30-meter resolution. The data includes both land-cover and urban imperviousness changes.

USGS claims 91 percent accuracy for the NLCD data. For more detail about how NLCD was developed see: Changes to the National Land Cover Database. More than nine billion pixels make up the land-cover dataset.

The USGS National Land Cover Database’s suite of GIS mapping products even includes a layer that defines the intensity of impervious surfaces across the United States. This information is used in runoff modeling, urban heat estimation, and a variety of other applications.

Mapping Land Cover Change in U.S. Over Time

Users can visualize land cover changes in the United States by accessing the the Enhanced Visualization and Analysis (EVA) tool. The online mapping tool was developed by USGS in partnership with the National Oceanic and Atmospheric Administration.

The tool allows users to select any county in the Lower-48 United States and generate a custom report on land cover change, developed areas, cropland change, and other factors.

Only one caution: the USGS site does not work with Apple’s Safari Browser. Mac users can use Firefox without problems, however. I have not tested other Mac browsers.

I ran two quick searches on Harris and Montgomery Counties by going to the EVA tool mentioned above. The findings astonished me.

Harris County Changes At a Glance

Between 2001 and 2019, in Harris County:

  • Almost one fifth of the land cover changed type (18.23%).
  • Developed portions of the county increased from 54.42% to 65.85% of the total acreage, a 20.99% percent net increase of developed area.
  • Forested parts of the county went from 10.64% to 6.29%, a percent net decrease of 40.92%.
  • The percent covered in wetlands went down from 8.28% to 7.02%, another percent net decrease of 15.24%.
  • The percentage of impervious surface increased from about a quarter to a third (26.28% to 33.39%), a percent net increase of 27.05%.
Screen showing development changes in Harris County with corresponding percentages of impervious cover. Green dots represent changes in land use. Clicking on icons in left column brings up different types of information.

MoCo Changes at a Glance

During the same period, in Montgomery County:

  • Even more land cover changed type (18.99%).
  • Developed portions of the county increased from 21.1% of the land area to 28.27%, a 33.97% net increase.
  • Impervious cover increased from 5.78% off the land area to 9.08%, a 57.12% increase.
  • Forested land decreased from 42.98% of the county to 38.96%, a 9.16% net decrease.
  • Wetlands decreased from 12.17% of the county to 11.35%, a 6.74% net decrease.
  • Agricultural land decreased from 12.28% to 10.31% of the county, a 16.04% net decrease.
Red areas represent areas in Montgomery County that changed land-cover type between 2001 and 2019.
Another screen showing areas in Montgomery County developed between 2001 and 2019.

Key Lesson

This database and GIS mapping system dramatize how quickly the region is growing and land use is changing.

Flood mitigation is or should be a two-pronged effort. We must fix problems that already exist downstream while hopefully preventing future problems from developing upstream. It’s not a just question of one county spending money to help prevent problems in another. It’s about surrounding counties protecting themselves. The outward expansion is relentless. People at the edge today will be downstream from someone else tomorrow.

There’s little anyone can do to change the FACT of development. But we can change the NATURE of development. If all new developments retained their own rain, no one would ever be doomed to the flood-mitigation treadmill of keeping up with ever-increasing amounts of upstream runoff.

Montgomery County already has a serious flooding problem of its own. Thousands of people flooded there during Harvey and Imelda.

Posted by Bob Rehak on 8/5/2021 based on USGS information

1437 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.

Flood Decision-Support Toolbox Enhanced by State, Federal Team

The Texas Water Development Board (TWDB) and the federal Interagency Flood Risk Management (InFRM) team (composed of USGS, FEMA, the Army Corps, and National Weather Service) has enhanced their Flood Decision-Support Toolbox. The Toolbox is an interactive online application that provides maps and data that simulates the extent of flooding and shows historical flood extents. It can be used for analyzing potential scenarios, flood risk assessments, damage analysis, and more.

How It Works

Here’s how the Flood Decision-Support Toolbox works:

  1. Go to https://webapps.usgs.gov/infrm/fdst/?region=tx

2. Observe current conditions OR select historical peak floods.

Historical peak floods at US59 and the West Fork. Note the increase in recent years, likely due to upstream development and/or climate.

3. Explore the flood map library by selecting a flood level (river stage)

4. In the “Buildings” Layer, select ALL or INUNDATED BUILDINGS ONLY

5. Note the damage estimates in the bottom right hand corner of the screen.

In the case of a simulated Harvey flood, near the gage at US59, 739 buildings would be inundated at an estimated total cost of $84,914,000.
But at 52.5 feet (the beginning of the “major” flood stage), 83 buildings would flood. Estimated total damage: $1,494,000.

The magic of this toolbox is that you can see exactly which buildings will flood at any given level.

What is your appetite for risk?

Potential Uses

The Flood Decision Support Toolbox also provides real-time data from USGS streamgages connected with flood inundation models to interactively display a range of flood conditions at streamgage locations. The result is a dynamic tool for flood risk assessment that enables planners, emergency responders, and the public to visually understand a flood’s extent and depth over the land surface.

TWDB worked closely with USGS to incorporate building footprints on Texas maps. The Toolbox can now display potential damage to structures within the range of the USGS gages. This will give users the ability to estimate the economic impacts of different flood events on their communities and property. The TWDB has also provided building footprints outside of the current gage ranges in preparation for future mapping updates.

That can help guide:

  • Rescue efforts
  • Evacuations and evacuation routes
  • Mitigation decisions
  • Property purchases and investment decisions
  • Risk estimates
  • New construction and development
  • Permitting decisions

The site displays flood scenarios that range from minor to major flood events. New updates let users save and share inundation maps with different data layers through a unique URL.

Collaborative Effort

“This collaborative effort,” said Jeff Walker, Executive Administrator of the TWDB. “provides Texas-specific data that will help communities understand their local flood risks and make cost-effective mitigation decisions.”

The InFRM team was formed in 2014 and launched the Flood Decision Support Toolbox in 2019.

The TWDB is the state agency charged with collecting and disseminating water-related data, assisting with regional water and flood planning, and preparing the state water and flood plans.

Posted by Bob Rehak based on information provided by TWDB

1235 Days since Hurricane Harvey

Beta Downgraded to Tropical Depression

At 10 a.m. CDT, the National Hurricane Center (NHC) downgraded Tropical Storm Beta to a tropical depression. The NHC also cancelled the tropical storm and storm surge warnings that were in effect. However, flash flood warnings remain in effect for large parts of the seven-county Houston region, especially the southern part. A flash flood watch remains in effect for the entire region.

RadarScope split image. Left half shows track of active storms as of 9:06AM CDT. Right half shows total rainfall accumulation for Beta. Note band of extreme rainfall near Sugar Land and sharp drop-off near Kingwood.

Flash Flood Warnings and Watches

A flash flood warning means that flooding is in progress. A Flash Flood Watch means that conditions may develop that lead to Flash Flooding.

Source: National Weather Service. Updated at 10:29 a.m. 9/22/2020. Reddish area = Flash flood warning. Green = Flash flood watch.

Lake Conroe/Lake Houston Within Banks

Neither Lake Conroe, nor Lake Houston have yet been adversely affected by Beta.

The level of Lake Conroe stands at 199.63 feet. Normal conservation pool equals 201.

According to the Coastal Water Authority, Lake Houston is at:

Lake Level41.41 ft.
Normal Pool42.4 ft.
Source: Coastal Water Authority

USGS shows that even though the lake has received about 1.75 inches of rainfall to date…

…the lake level has been dropping, no doubt due to a preemptive release.

Posted by Bob Rehak at 10:50 on 9/22/2020 based on NHC, NWS, and RadarScope data

1120 Days since Hurricane Harvey and 369 since Imelda

Easy Way to Find the Elevation of a Home and the Slopes Around It

Ever wonder how high your slab is compared to the elevation of your street? Or where water is likely to collect in a neighborhood? The US Geological Survey (USGS) has given us a quick and easy way to lean more about elevation.

While the site says the elevations are not as good as a survey’s, I found the elevation for my house to be within inches. This is not something to take to the bank, but if you’re trying to:

  • Screen several properties for purchase
  • Figure out why some people in a neighborhood flooded and others didn’t
  • Understand where floodwaters might collect

…this is a good place to start.

To Find Elevation

  • Go to this U.S. Geological Survey website called the National Map Viewer.
  • Enter an address or just zoom into the area of interest.
  • Select a base map by clicking on the icon with the four squares that form another square. Different base maps allow different degrees of zooming and show various features such as streets, water features, topography, etc., so experiment.
  • Above the map area, click on the icon that shows an XY.
  • A box will pop up on the right side of the screen. Within it, click “Activate.”
  • Click on the map location or locations that interest you.
  • An info box will pop up that shows the location and elevation at the blue dot(s) where you clicked.
  • To erase the points you selected, click “Deactivate.”
Elevations for Riverwood and East End Park Parking Lot

You can click as many different points as you want. A list of ALL the places you clicked with their elevations will show up in the right hand box.

In the example shown above, you can see that Riverwood Middle School at the intersection of High Valley and Kingwood Drive is at 65.03 feet. You can also see that the entry for East End Park is at 53.68 feet – more than 11 feet lower just a couple blocks away.

How High Is A Home Above Street Level?

This question is crucial if you want to avoid street flooding during high intensity rainfalls that overwhelm the capacity of storm drains and force water to back up in the streets.

  • Switch to the base map called Streets (if you were in something else)
  • Zoom in on the area of interest or enter an address.
  • Again select the XY tool.
  • Click on the home that interests you to see the elevation of the slab.
  • Click on the street in front of it.
Note 3 foot elevation difference between slab and house in Streets Basemap.

Three feet is a pretty good difference. But another home in the same neighborhood has a 4.5 foot difference!

This home sits 4.5 feet above the street.

Click around in different neighborhoods, especially those that flooded. On a block that flooded badly in Elm Grove, one home escaped. It was also 4.5 feet above street level. Others around it ranged from 1 to 3 feet above street level.

When buying a home, elevation above street level can be a valuable consideration.

Streets are usually considered part of the flood retention system. Developers size storm drains to hold a 1- or 2-year rain. Everything beyond that up to a 100-year rain backs up into the street until it can be safely released into drainage ditches. If you aren’t high enough…

Slope Within Neighborhoods

USGS offers another useful tool called elevation profiling. To the left of the XY tool, click the tool called Profile.

  • A box will pop up on the right of the screen. To activate this tool, click on the ruler icon in the box.
  • Define a path with two or more points.
  • In the example below, I followed the curves of a street by clicking multiple times.
  • When you get to the end of the area of interest, DOUBLE click.
  • Double clicking changes the tab in the right hand box and starts compiling an elevation profile result.
  • Give the site a few seconds to compile and display the profile.

When this profile popped up, I saw that this street had six feet of slope from the west end of the block to a low point in the middle and then rose back up three feet to the school on the right.

Example of Elevation Profile Tool. Note the U-shaped profile in blue and brown on the right.

It’s common practice to slope streets; developers must to ensure that water drains to storm sewers. But when the rain comes down so fast that the storm drains can’t handle it, guess where the rain will collect. I’m not sure I would want to buy the house at the bottom of the bowl. (At least not without a discount to compensate for the risk.)

Powerful Tools at Your Fingertips

USGS has given us a fascinating tool kit. I have just begun to explore the power of this site.

Several people in Kingwood’s Woodstream Village approached me about some flooding on their street. Using the tools on this site, I quickly developed a theory that accounted for all the eyewitness stories.

Have fun exploring this fascinating tool.

Posted by Bob Rehak on 8/1/2020 with thanks to Laura Norton

1068 Days since Hurricane Harvey and 316 since Imelda

How High Water Marks Help Fill Gaps in Flood Knowledge

Note: the post below was condensed and adapted from a longer USGS article. The U.S. Geological Survey (USGS) records continuous stream stage (height of a river) and streamflow (how much water is flowing) with thousands of gages throughout the nation. But how can they determine flood height where no gages exist?

Simple, USGS correlates high water marks after floods with peak gage heights during floods.

“If, for example, records show that stream stage reached 17 feet during a storm, a high-water mark will show the hydrologist what a stage of 17 feet means in terms of how high the water was on the riverbanks and surrounding land.”

USGS Water School Website

Finding high water marks on or near buildings is easy. You look for the mud line or the edge of debris fields. The same principle applies in nature. Sometimes it’s easy.

Think of high water marks like a bathtub ring around a flooded area. Shown here: East End Park after Imelda.

But they’re not always that obvious.

Can You Spot High Water Marks In Pictures Below?

Below are two pictures used by USGS for demonstration purposes. They took the pictures a few days after a record storm. High-water marks show in both pictures, although a hydrologist would only regard one of the marks as being reliable.

Photos showing high water marks on vegetation after a storm.
Spot the high water marks.

The pictures below are close-ups of the high-water indicators in the top pictures. Did you spot them?

Pictures showing high water marks on vegetation.

The left picture shows a poison ivy vine with the bottom leaves covered in dried mud. Where the mud stops shows how high the floodwaters reached.

The right-side picture shows a limb that hangs over the same creek. During a flood, rapidly-moving water carries leaves and pine needles, etc.! They stick on limbs that are partially submerged. When the stream recedes the signs remain. The top of the leaves and pine straw indicate how high the creek was during the storm.

The mud on the vine is a much better high-water mark than the tree limb, though. During high water, the fast-moving water will cause partially submerged limbs to move up and down. Therefore, hydrologists would not use the limb to estimate high water.

How High Water Marks Are Used

Planning Development

Documenting high water marks helps plan development near floodplains. If you know that water reaches a certain mark on the bank every few years, you certainly don’t want people building homes and businesses there.

Determining Extent and Severity of Flooding

Gages can determine the height of a flood. But high water marks can also show the width and extent relative to topography.

After most major flood events, USGS partners with FEMA and other state and federal agencies to flag and survey high water marks in areas that flooded. USGS did so here after Harvey to determine the extent and severity of the flooding.

Prediction of Future Floods

Forecasters can use the data associated with high-water marks to predict the severity of future floods, delineate flood zones, and update current maps that may account for changes in upstream conditions.

Flood Frequency Calculations

High-water mark data is also part of the flood-frequency (or recurrence interval) calculations that FEMA uses to identify areas that are likely to experience a 1 percent chance of happening in any given year. These floods, known as 100-year floods, serve as the foundation for flood management planning.

Inundation Mapping

Another significant use: Flood-Inundation Mapping. A flood-inundation map shows the extent and depth of flooding that occurred in various communities as a result of a major storm or flood event. Inundation maps help determine things like:

  • Changes needed in building codes
  • Evacuation routes
  • Heights of bridges and roads.

Once inundation maps are complete, USGS documents them and makes them publicly available online.

Recreating Data from Damaged Gages

If a flood knocks out a gage, as it did with the one at US59 bridge and the Kingwood Country Club on the San Jacinto West Fork, high-water marks can provide maximum height of a flood after the fact. If the cross section of the river is known (or surveyed), hydrologists can even back-calculate the flow rate.

Posted by Bob Rehak on 7/16/2020 with thanks to USGS and Diane Cooper

1052 Days after Hurricane Harvey and 301 since Imelda

Why You Never Want to Buy a Home Built Over Wetlands

The pictures below show why you should never, ever buy a home built over wetlands.

Standing water after one month with only an inch of rain. Perry Homes’ Woodridge Village in Montgomery County, Texas.

Standing Water One Inch of Rain A Month Before

I took these shots while circling Perry Homes’ Woodridge Village construction site in Montgomery County, Texas, on 12/3/2019. At that point, the nearest USGS rain gage (at US59 and the San Jacinto West Fork) indicated we had only had one inch of rain in the previous month. The most recent rain at the time was a quarter inch three weeks prior!

That’s far below the normal 4.3 inches of rainfall for November in Houston. So it was less than one quarter of the normal rainfall. Still, the land held standing water in numerous places, despite having been cleared and graded for months.

Soupy soil on the northeast portion of Perry Homes Woodridge Village.

Standing water should have soaked in long before I took these shots. But when you build a development on wetlands, that’s not always true.

This article by the National Wildlife Federation details the problems of building homes over wetlands: shifting slabs, damp basements, cracked driveways, mold, erosion, clogged storm drains, downstream flooding and more.

These pictures vividly illustrate how unstable wetlands soil can be.

Looking west over the northern portion of Perry Homes’ Woodridge Village
Southwestern portion of Perry Homes’ Woodridge Village fronting Woodland Hills Drive.

They remind me of the famous saying the Bible.

Matthew 7:24-27: Build Your House on the Rock

24 “Everyone then who hears these words of mine and does them will be like a wise man who built his house on the rock. 25 And the rain fell, and the floods came, and the winds blew and beat on that house, but it did not fall, because it had been founded on the rock. 26 And everyone who hears these words of mine and does not do them will be like a foolish man who built his house on the sand.27 And the rain fell, and the floods came, and the winds blew and beat against that house, and it fell, and great was the fall of it.”

Area classified as wetlands in the USGS National Wetlands Inventory within Perry Homes’ Woodridge Village.
Perry Homes’ contractors mired in more muck on the northern portion of Woodridge Village where wetlands once stood.

Five Previous Developers Passed on This Property

When Perry Homes bought this property, five other developers had previously bought and sold it without developing anything. Perhaps they realized the dangers once they investigated it more thoroughly. Regardless, one of Perry Homes’ subsidiaries bought the land and the company wound up in a literal quagmire.

That sinking feeling you get when you try to build over wetlands

Environmental Survey Not on File with Montgomery County

Perry Homes claims to have done an environmental survey. But if they did, they did not file it with Montgomery County. A FOIA request with the county turned up no such document. A survey, performed by a private consultant, cleared the way for developing this property.

Normally, the Army Corps would investigate wetlands and determine whether they fell under their jurisdiction. If so, developing them would have required permitting and possible mitigation.

That process would have taken much longer and Perry Homes was trying to beat the clock. They were trying to start development before new, stricter Atlas-14 regulations took effect that would have required 40% more detention.

The Corps is currently investigating this case but has not yet issued a decision as to whether Perry Homes’ consultant erred.

Regardless of what the Army Corps decides, these pictures should be a sobering reminder of the dangers of building over wetlands.

Beware of Dry-Season Sales

Wetlands do not necessarily remain wet year around. Unscrupulous developers often sell homes in the dry season without revealing the presence of former wetlands. But water naturally drains to these low-lying areas. Buying a home in one could turn into a perpetual headache.

If you are concerned about investing your life savings in such an area, both the U.S. Geological Survey and U.S. Fish and Wildlife Service keep national databases of wetlands.

USGS National Wetlands Inventory showing Perry Homes Woodridge Village

Be a wise man or woman. Consult these databases before you buy a home to determine whether your property was once wetlands.

Posted by Bob Rehak on 12/15/2019

838 Days since Hurricane Harvey and 87 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.

Truth is the First Casualty In Water Wars, Too

Aeschylus, the ancient Greek playwright coined the phrase, “The first casualty in war is truth.” The same is true of water wars. In an attempt to justify unlimited groundwater pumping from the Jasper aquifer, a headline in a Montgomery County online newspaper trumpeted, “University Of Houston Study Shows No Linkage Between Deep Groundwater Production And Subsidence In Montgomery County.” But wait! Is that what the study really said? The article did not provide a link to the actual study. So how could you tell if the review was accurate? It’s not. Below are just a few of the reasons why.

Contradictions Between Study and Newspaper’s Summary

The UH study didn’t study Montgomery County. It looked only at Harris-Galveston Subsidence District Regulatory Areas 1 and 2. They cover only SOUTHERN Harris and Galveston counties! Researchers found no subsidence associated with the Jasper there. That’s because virtually no one pumps the Jasper there (See Jasper well location map below).  The article’s anonymous author forgot to mention that though.

“Don’t Extrapolate Results,” But They Did

The UH study also carefully cautions readers not to extrapolate the results from the study area to other areas. But the newspaper did it and forgot to mention the caution also.

Newspaper Falsely Claims Study Suggests “No Subsidence”

The newspaper author claimed that the study “suggests that Montgomery County utilities, municipalities, homeowner’s associations, and other large-scale groundwater users could draw water production from the Jasper aquifer without causing any subsidence at the surface of Montgomery County.” The UH study makes no such suggestion. 

Claimed “No Need for Regulation,” Contrary to UH Findings

The newspaper author goes on to claim that the study “also suggests that, as long as groundwater production comes from the Jasper or lower formations (such as the Upper Catahoula Formation), there is little need, if any, for any groundwater regulation whatsoever.” Again, the UH study makes no such suggestion. 

Quite the contrary, the UH study says that regulation was effective in slowing the subsidence found in other aquifers along the gulf coast that were being depleted, such as the Evangeline and Chicot. 

Newspaper Claim of 100% Annual Recharge Not Substantiated by Study

The newspaper author also says that, “Since the quantity of groundwater in Montgomery County is essentially unlimited, and since Montgomery County aquifers enjoy almost 100% recharge annually after production drawdowns have occurred, there would seem to be no reason whatsoever to regulate groundwater production from the Jasper aquifer and the Catahoula aquifer.” The study makes no mention of recharge rates in either of those aquifers.

Newspaper Implies “No Need for Regulation” but Study Says It Helped

Finally, the anonymous newspaper author concludes by saying, “The University of Houston study suggests that it’s time for the Lone Star Groundwater Conservation District to bring the entire over-regulation of groundwater to a crashing halt.” The study made no such recommendation.

Inferring that the UH scientists even implied that would require turning the the study’s findings on their head. Quite the contrary. The study explicitly states that regulations implemented in 1975 with the formation of the Harris-Galveston Subsidence District slowed out-of-control subsidence.

Newspaper Article Not Signed

Jumpin’ Jasper! What’s going on here? Who wrote this unsigned article? Was it someone who stands to profit financially from pumping the Jasper dry? 

Why Water Not Pumped From Southern Part of Jasper

For the record, the Jasper dips toward the coast along a roughly north-to-south axis. The Jasper aquifer contains fresh water in Montgomery County and northern Harris County. But south of that, it becomes brackish. The water is too salty to use. That’s a big reason why virtually no one pumps it in the southern part of the region.

This map shows the freshwater limits of the Jasper aquifer in 2010. For the most part, the freshwater portion of the Jasper aquifer does not extend to the area of interest studied by the UH scholars.

The down-dip part of the Jasper toward the coast also goes very deep. At the southern limit of freshwater, depth ranges to thousands of feet in places (see bottom of colored area below). Why would you drill that deep if you could get fresher water from aquifers like the Chicot and Evangeline much closer to the surface?

From Page 30 of Hydrogeology and Simulation of Ground-Water Flow and Land-Surface Subsidence in the Northern Part of the Gulf Coast Aquifer System, Texas, Scientific Investigations Report 2004–5102, USGS

Subsidence Already Noted in Northern Part of Jasper

Those are the reasons why the UH scholars do not associate subsidence with the Jasper in southern Harris and Montgomery Counties. That does NOT mean subsidence won’t happen in other areas where utilities DO pump the Jasper. It already has.

Map showing contours of the average subsidence rate (mm/year) during the time span from 2006 to 2012. From “Is There Deep-Seated Subsidence in the Houston-Galveston Area?”, Page 2.

However, USGS well-water height readings north of Highway 99 show severe drawdown near the population centers in southern Montgomery and northern Harris Counties. And surprise, surprise! That also happens to be the area where most subsidence has occurred in Montgomery County.

Unsustainable Pumping Rates

While the advocates of unlimited groundwater pumping want you to believe that the aquifer recharge rates in Montgomery County equal the drawdown rate, they don’t. The Jasper aquifer is being drawn down in populated places at more than 10 FEET per year (see graph below). But USGS estimates that the recharge rate for the Jasper is as little as ONE-TENTH of an INCH per year. That means some utilities have been using up Jasper water 1200 times faster than nature replaces it.

This well drilled in the Jasper aquifer near the Woodlands showed an average decline of approximately 10 feet per year (about 180 feet in 18 years).
USGS map showing 2000-2018 Water-Level Decreases/Increases (left) vs. Well Locations (right) for the Jasper Aquifer. This USGS viewer lets you see different aquifers over different time periods and check water level changes for any well near you. Most of Montgomery County’s major declines happened near major population centers.

Truth or Consequences

Ground level declines produce fault movement and subsidence. They translate to infrastructure damage and flooding. 

As water levels decline, water wells begin to have problems producing. They lose “yield,” which means they can’t produce as much water in a given time period. This requires the wells to run longer to meet demand. It costs more to lift water. Longer run times increase maintenance costs.  Pumps have to be lowered. The motors have to be upsized, which requires electrical rewiring. 

Some well pumps can’t be lowered any farther, which may mean abandoning and replacing the well. Some water level decline is expected. But those who argue that Montgomery County has an unlimited supply of water are just ludicrous. The harder you pump, the more decline you get, and with that comes all the consequences of declines. 

Why People Want to Believe the Unbelievable

Montgomery County residents have found the change from well to surface water financially difficult. People WANT to believe that unlimited groundwater pumping is safe. I just hope they don’t wind up putting all their water lillies in one pond, so to speak. 

The only thing worse than expensive water is no water. Or no water plus infrastructure damaged by subsidence.

Selective Perception Amplified by Selective Deception

Selective perception is a well known cognitive bias. It describes the process by which people perceive what they want to in media messages while ignoring opposing viewpoints. However, in this case, it seems that selective deception is amplifying the bias.

Don’t take my word. Read the newspaper article and then read the actual study on which the article is based. I provide links so you can make up your own mind; the newspaper article did not.

Other Useful References

Below are some other useful publications from the U.S. Geological Survey which is part of the Department of the Interior.

USGS Subsidence home page. Contains dozens of useful publications on Texas Gulf Coast Groundwater and Land Subsidence, plus raw data in numerous formats.

Hydrogeology and Simulation of Ground-Water Flow and Land-Surface Subsidence in the Northern Part of the Gulf Coast Aquifer System, Texas By Mark C. Kasmarek and James L. Robinson, 2004

Groundwater Withdrawals 1976, 1990, and 2000–10 and Land-Surface-Elevation Changes 2000–10 in Harris, Galveston, Fort Bend, Montgomery, and Brazoria Counties, Texas, Scientific Investigations Report 2013–5034, By Mark C. Kasmarek and Michaela R. Johnson

Land Surface Subsidence in Harris County between 1915 and 2001.

Water-Level Altitudes 2016 and Water-Level Changes in the Chicot, Evangeline, and Jasper Aquifers and Compaction 1973–2015 in the Chicot and Evangeline Aquifers, Houston-Galveston Region, Texas, Scientific Investigations Report 2013–5034, U.S. Department of the Interior U.S. Geological Survey

Evaluation of Ground-Water Flow and Land-Surface Subsidence Caused by Hypothetical
Withdrawals in the Northern Part of the Gulf Coast Aquifer System, Texas
, Scientific Investigations Report 2005–5024, U.S. Department of the Interior U.S. Geological Survey by Mark C. Kasmarek, Brian D. Reece, and Natalie A. Houston

Also, don’t forget to check out the subsidence tab under the Reports page of this web site.

Posted by Bob Rehak on 7/27/2019

697 Days after Hurricane Harvey

“Is There Deep-Seated Subsidence in the Houston-Galveston Area?” by Jiangbo Yu, Guoquan Wang, Timothy J. Kearns, and Linqiang Yang, Department of Earth and Atmospheric Sciences, National Center for Airborne LiDAR Mapping, 312 Science & Research Building 1, Room 312, University of Houston, Houston, TX 77204-5007, USA. Copyright © 2014 Jiangbo Yu et al. This is an open access article distributed under the Creative Commons Attribution License. Hindawi Publishing Corporation, International Journal of Geophysics, Volume 2014, Article ID 942834, 11 pages.

Note: All thoughts in this post represent my opinions on matters of public interest and safety. They are protected by the First Amendment of the U.S. Constitution and the Anti-SLAPP statute of the great State of Texas.

USGS Report on Peak Streamflows During Harvey Significantly Revises Flood Probabilities

The U.S. Geological Survey (USGS) in cooperation with the Federal Emergency Management Agency (FEMA) released a report this week that shows inundation maps, peak streamflows, detailed flood information, and new flood probabilities from Hurricane Harvey. Hurricane Harvey, it says, was the most significant multi-day rainfall event in U.S. history, both in scope and peak rainfall amounts, since records began in the 1880s.

Flood during Harvey looking east from the south side of the West Fork of the San Jacinto. Photo courtesy of Harris County Flood Control District.

Hurricane Harvey’s widespread 8-day rainfall, which started on August 25, 2017, exceeded 60 inches in some locations. That’s about 15 inches more than average annual amounts of rainfall for eastern Texas and the Texas coast. The area affected was also much larger than previous events.

New High Water Marks and Record Streamflows

USGS field crews collected 2,123 high-water marks in 22 counties in southeast Texas and three parishes across southwest Louisiana.

Record streamflows were measured at 40 USGS streamgages in Texas that have been in operation at least 15 years. At two streamgage locations, scientists determined that the percent chance for flooding of this magnitude to happen in any given year was 0.2 percent. This probability is also referred to as a 500-year flood. Thirty other USGS streamgages experienced flooding at levels with a 1 percent chance of occurring each year, also known as a 100-year flood.

Check out the “event viewer” noted in the report, especially if you are interested in high water marks in your neighborhood.

How Data Will Be Used

The USGS conducts research on the physical and statistical characteristics of flooding, estimating the probability of flooding at locations around the United States.

The purpose of the study was to check the probability of future occurrences and map the extent of flooding in Texas.

These records will assist officials in updating building codes, planning evacuation routes, creating floodplain management ordinances, providing environmental assessments and planning other community efforts to become more flood-resilient. FEMA will also use this information to revise their Flood Insurance Rate Maps. These maps help identify areas most likely to experience flooding in any given year.

Gages Closest to Lake Houston

The section on the San Jacinto Watershed starts on page 33. The maps for the San Jacinto watershed appear on pages 35 and 36. Use the maps to see the new high water marks in the area and to find the USGS gages nearest you. For most people in the upper Lake Houston Area, it will be one of these gages:

  • 08068090 – Grand Parkway and West Fork near Porter
  • 08069500 – West Fork and I-69 near Humble/Kingwood
  • 08070500 – Caney Creek near Splendora
  • 08069000 – Cypress Creek near Westfield
  • 08068500 – Spring Creek near Spring
  • 08071000 – Peach Creek near Splendora
  • 08070200 – East Fork near New Caney
  • 08071280 – Luce Bayou above Lake Houston near Huffman

After you locate the gages nearest you, cross reference the numbers of those gages with data at the front of the report. It helps to use the search function in Adobe Acrobat because much of the information is in tables with very small type.

Examples of What You Will Find

Here’s an example of what you can find. For the gage nearest many of the sand mines on the West Fork (08068090), peak streamflow was estimated at 131,000 cubic feet per second. That was the highest of the 33 peaks previously observed at that location (from Table 3 on Page 9).

Now here’s the big news: From the same table, we can see that the Annual Exceedance Probability (AEP) is 2.4.  That’s the likelihood of occurrence of a flood of given size or larger occurring in any one year, expressed as a percentage.

AEP is often expressed as the reciprocal of ARI (Average Recurrence Interval). For instance, A 10-year flood has a 10 percent probability of occurring in any given year, a 50-year event a 2% probabaility, a 100-year event a 1% probability, and a 500-year event a .2% probability.

In this case, a 2.4% AEP would have a likely recurrence interval of 42 years, given the new realities of upstream development, any changes in climate, and pocket calculators with more computing power. This means that the West Fork Gage ((08068090) at the Grand Parkway DID NOT even experience a 100-year flood! Yes, we can expect to see worse in the future.

That’s a far cry from the 1,000-year flood that some talked about earlier and raises real public policy questions about locating sand mines in floodways.

Despite the fact that Harvey was the largest rainfall event in recorded U.S. history, USGS now predicts that it would take even bigger floods to reach the reconfigured 100-year, 200-year and 500-year recurrence intervals: 196,000, 263,000 and 374,000 cfs respectively for West Fork Gage at Grand Parkway (Gage #08068090 from Table 5, Page 14). So the new 500-year flood would have almost triple the volume of Harvey.

Humble Gage Data Missing From Report

Unfortunately, the Humble Gage at I-69 does not show up in the tables even though it is on the map and the cover of the report. This is likely in part due to the fact that the gage stopped reporting during the event due to the excessive streamflow

They may also have not reported the exceedance probability due to the shorter recent record.

For all the other gages, the Annual Exceedance Probabilities translate to new recurrence intervals ranging from 35 to 250 years. The gages at the low end of that range tend to be in the fastest developing neighborhoods.

Implications of New Findings

The report will stimulate public policy debate about development near rivers and the most effective methods of flood mitigation.

After reading this, I believe more than ever that we need more detention, dredging and gates (DDG). We need all three to help us handle the volumes of floodwater that USGS expects at more frequent intervals. Prayer, while advisable, is a less certain option in my mind than including DDG in the flood bond and passing it.

BTW, there was some confusion Tuesday night at the flood bond meeting. A small number of flood control employees incorrectly told residents that dredging would not be possible under the bond. It will be according to Matt Zeve, whom I contacted today.

Posted July 12, 2018 by Bob Rehak

317 Days since Hurricane Harvey