Tag Archive for: Estimated Base Flood Elevation Viewer

New MoCo Development Being Built on Wetlands in 10-Year Flood Zone

At least part of Madera, a new 1,700-acre development in Montgomery County that straddles FM1314 immediately north of SH242, is being built on wetlands and is in a 10-year flood zone.

US Fish & Wildlife Map Shows Wetlands Dot Development

Magera Wetlands
From US Fish & Wildlife Service National Wetlands Inventory. Madera will stretch past the left/right edges of this picture north of SH242 (the east/west highway near bottom.) FM1314 bisects picture from N to S in middle.

FEMA’s Base Flood Elevation Viewer Shows Flood Risk

From FEMA’s Base Flood Elevation Viewer. Extent of 100-year flood zone shown on left. 10-year flood zone shown on right.

Note that this survey shows only about a quarter of Madera (see below). The survey stops abruptly on the western margin. So, it is hard to say with certainty how bad flooding is throughout the rest of the site.

Yellow outline shows approximate outline of FEMA BFE survey shown above within Madera tract (black/white outline).

Option to See Depth of 100-Year Flood Waters

Also note that the purple area shows only the extent of 100- and 10-year floods. However, within the FEMA BFE viewer, you also have the option to select a layer that illustrates the depth of 100-year floodwaters. See below. (FEMA does not offer the option to show the depth of 10-year floods.)

FEMA BFE viewer
FEMA’s estimated Base Flood Elevation Viewer showing extent of 100-year flood on left and depth on right.

Limitations of BFE Viewer

Of course, FEMA shows “estimated conditions” before developers bring in fill and alter drainage. But notice how a pre-existing development near Madera would fare in the same 100-year flood. You can see the close up below just above SH242 near the right edge of the image above.

FEMA shows that most homes in this development are still in the flood zone and would still flood to a depth of 1-2 feet in a hundred-year flood.

The street leading out of the development to SH242 could be under more than FIVE FEET of water in places!

FEMA Base flood Elevation Viewer

FEMA’s “Estimated Base Flood Elevation” is “The estimated elevation of flood water during the 1% annual chance storm event.” Structures below the estimated water surface elevation may experience flooding.” A 1%-annual-chance flood is also known as a 100-year flood. FEMA defines properties with a 1% annual chance of flooding as having “high flood risk” and says they have a 26% chance of flooding during the life of a 30-year mortgage.

Purposes of BFE Viewer

The agency developed its Base Flood Elevation viewer with several purposes in mind. To:

  • 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.
  • Provide information for “Letter of Map Amendment” (LOMA) submittals.

A LOMA lets the developer of a subdivision change the depiction of how flooding affects his/her subdivision. It’s the key to offering up-to-date risk assessments.

Full BFE Reports Available

FEMA also lets you download or print full BFE reports that give more specific estimates of flood depth at exact points, not just within a wide area.

FEMA’s BFE Viewer also gives you the option to print out a detailed flood-risk report by clicking on a point.

At the point shown above, you could expect 4.2 feet of water above the land surface in a 1%-chance flood. For the full report, click here.

Here’s what that point looked like last Saturday (1/22/22) from the air.

Madera will eliminate wetlands but claims it will have no adverse impact.
Madera development today at FM1314 and SH242, the point shown in BFE report above.

Cross-check this area on the maps above for wetlands and swamps! Then you can see why it’s so soupy.

BFE, Fill Not Mentioned in Drainage Analysis or Construction Plans

Text searches of Madera’s construction and drainage plans showed no references to “BFE” or “base flood.”

It seems unlikely that a “cut and fill” operation could excavate enough dirt from Madera’s drainage channel (dotted blue line with red parallel lines) and detention ponds to raise the whole site out the hundred-year flood zone. Five feet is a lot of fill for a 1700 acre site.

To raise a site this large, contractors would likely have to bring in fill from outside the property. But a text search from the word “fill” did not turn up any exact matches either.

So maybe they’re just planning to create the world’s biggest drain and hope to carry water off before it can reach homes.

However, a summary of the Madera master drainage plan notes…

“Coordination with MCED [Montgomery County Engineering Department] and adjacent property owners is recommended … on the potential need for inundation easements.”

Revised Channel Alignment Memo, 2/19/21, Page 11

Still, engineers for the development claim it will have “No adverse impact.”

To review Montgomery County regulations regarding flood zones and drainage, see the documents under the “Construction Regs in Flood Hazard Areas” tab on my reports page. You’ll see plenty of opportunities for improvement.

Posted by Bob Rehak on 1/27/22

1612 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.

Two More Websites That Help You Understand Drainage and Flood Risk

Today, readers sent me links to two more websites that help you understand drainage and flood risk. The first by Texas Parks & Wildlife is called the Texas Watershed Viewer. The second is a FEMA site that estimates base flood elevations based on USGS data.

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.

Clicking on Caney Creek showed the extent of the watershed. Clicking on the arrow within the green bar at the top of the info box changes the outline to match the river sub-basin or 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

Where Caney Creek, Peach Creek and the San Jacinto East Fork all come together in FEMA’s Base Flood Elevation Viewer.
Legend shows estimated water depths in image above.

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.

From FEMA’s Estimated Base Flood Elevation Viewer. Light purple represents 1% flood zone. Dark purple represents .2% flood zone.

Compare that to FEMA’s Flood Hazard Layer Viewer below and you will immediately see the difference.

FEMA’s National Flood Hazard Layer Viewer shows danger stopping abruptly at the county line.

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.

“Buyer Aware”

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.