Dangers of street flooding

Dangers of Street Flooding

The dangers of street flooding can be costly. We’ve all read about people who drown while driving through flooded underpasses. But other dangers exist, too. Costly ones.

On Tuesday 1/24/23, the Lake Houston Area received a 5-year rain. Streets flooded throughout the area because storm sewers are generally designed to carry 1- to 2-year rains.

So, water backed up into streets. When cars and trucks tried to plow through the ponding water, they set up waves that slapped against people’s homes. This video dramatically shows what those waves can do.

And when the ponding water rises over the level of your tailpipe, it will choke your engine and stall your car. It can also flood the interior and ruin your electronics.

It’s impossible to tell the depth of water accurately in these situations.

Progressive Insurance lists common problems with flood-damaged cars. Flooded vehicles can easily turn into total losses. “Flooded cars are often declared a total loss because repairing water damage is complicated and costly,” they say. “A total loss means the insurance company has determined that the damage cannot be repaired safely, or the cost to repair the vehicle is more than the value of the car.”

So, your best bet is to stay home and watch Wheel-of-Fortune reruns until the water recedes.

The roads cleared about an hour after the homeowner took these photos. The dangers of street flooding disappeared down the storm drains.

Diagnosing Street Flooding Problems

If your street flooded and the streets around you didn’t, you may want to call authorities and have them see if your storm sewers are blocked.

You might also be interested in seeing if the storm drain inlets are located at the lowest points on your block. Here’s how to check the elevations.

Finally, examine the storm drain inlets and make sure you have sufficient drainage. There are many different sizes and types.

Posted by Bob Rehak on 1/26/23

1976 Days after Hurricane Harvey

Royal Pines

5-Year Rain Brings White Oak Creek Close to 100-Year Mark in Royal Pines

Between 1:00 and 3:00 PM on 1/24/23, approximately 3.6 inches of rain fell over Royal Pines in southeast Montgomery County. According to Atlas-14 rainfall tables, that qualifies as a 5-year rainfall event. But floodwaters from White Oak creek approached the edge of the 100-year floodplain. And missing silt fences let sediment escape into the wetlands that border the property.

5-Year Rain

A friend who lives a mile from Royal Pines recorded about 4″ on his rain gage for the full day. A check of nearby rain gages on the Harris County Flood Warning System, showed that the official gage at FM1485 and the San Jacinto East Fork recorded approximately 3.6 inches between 1 and 3 PM today.

Harris County Flood Warning System hyetograph shows approximately 3.6 inches fell in two hours on 1/24/23.

Cross-referencing that rate with NOAA’s Atlas-14 rainfall probability estimates for this area, we can see that 3.6 inches in 2 hours equals a 5-year rain.

atlas 14 rainfall probabilities
NOAA Atlas 14 rainfall probabilities for Lake Houston Area.

100-Year Flood Line

Now let’s look at how close that 5-year rain came to the 100-year flood line. In the construction diagram below, the developer shows the edge of the 100-year flood plain. It’s the dotted line between Zone AE and Zone X. I’ve circled the relevant portion in red.

If you were to project that line toward the lower right, it would roughly parallel the heavy black line that forms the eastern boundary of Country Colony, which you can see in the middle right of the photo below.

Floodwaters from Creek Overflow Royal Pines

The water comes almost to the edge of the floodplain shown in the construction diagram above.

Looking SE across Royal Pines. County Colony in upper right.

That big area filled with water, is a part of White Oak Creek cutting across Royal Pines. Think it’s just standing water? Think again.

The closer shot below shows water streaming through the soon-to-be subdivision and filling the Country Colony drainage ditch to overflowing.

Notice the water streaming through the cleared area and carrying away sediment downstream.

Notice also how the floodwaters approach what appears to be some sort of water treatment facility in the upper right.

These shots also document the absence of silt fence on the eastern side of Royal Pines.

All that silt will migrate down White Oak Creek and Caney Creek into the East Fork San Jacinto which the City of Houston just dredged at great public expense. The public also must foot the bill for increased water-purification costs.

From Harris County Flood Education Mapping Tool.

More Missing Silt Fence in NW Corner of Royal Pines

The SE corner of Royal Pines wasn’t the only part of the development missing silt fence. The developer removed it from the NW corner – where a neighbor has now flooded three times in two months.

Looking N toward White Oak Creek. Contractors removed the silt fence last week. Rain then swept sediment into the woods.

Those woods contain sensitive wetlands.

Notice how water coming from the north (left) is clear. But water coming from Royal Pines (right) is filled with sediment.
The muck filled the wetlands for more than a mile downstream.

How Can a 5-Year Rain Reach Almost as Far as a 100-Year Floodplain?

We need an answer to that question before this development starts pouring concrete. There are several possible explanations.

  • Clearcutting accelerated runoff.
  • Bulldozers compacted soil, limiting the rate of infiltration.
  • The developer hasn’t built any stormwater-detention-basin capacity to offset the increased runoff.
  • Planners used old (lower) Montgomery County rainfall data to determine the extent of the floodplain in their plats and plans.
  • Engineers didn’t count on the cumulative impact of insufficiently mitigated upstream development, some of which used beat-the-peak, hydrologic-timing surveys to avoid building detention basins.
  • The developer altered the landscape.
  • More rain fell upstream than at the gage shown above.
  • Some or all of the above.

I took these photos within an hour of the end of the rain. So there wasn’t much time for water to work its way downstream very far.

Two floodplain experts I consulted pointed to the cumulative impact of upstream development as a possible culprit. Engineers are likely working with flood data acquired in the 1980s before Montgomery County became one of the fastest growing counties in the region. The data is simply too complex to adjust after each new development. So, it never gets revised and errors compound over time.

I’m sure the Montgomery County Engineers Office and TCEQ will want to get to the bottom of this before the developer starts building homes. If homebuyers flood on rains that are far less than 100-year rains, tremendous liabilities could result.

When Perry Homes attempted to build Woodridge Village – only one-half mile from Royal Pines – its engineers pretended no floodplains existed. That cost Perry Homes millions of dollars and its reputation.

If Royal Pines or Montgomery County would like to rebut the issues I’ve raised, I will be happy to publish their point of view. The public deserves to know what’s going on.

Posted by Bob Rehak on 1/25/23

1975 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.

Rainfall associated with Severe weather threat

Severe Weather Threat Tuesday with High Winds, Rain Up to 3″ and Possible Tornados

The National Weather Service and Harris County warn of a severe weather threat for Tuesday.

Harris County Meteorologist Jeff Lindner warns that severe thunderstorms, some of which could turn into tornados are likely with heavy rainfall, and gusty winds across SE Texas Tuesday.

The National Weather Service Storm Prediction Center also warns of the potential for supercell development and hail.

Up to 3 inches of rain are likely with isolated higher amounts (up to 6″ according to Lindner) where thunderstorm training exists.

Rainfall for Tuesday from the NWS Weather Prediction Center.
Posted at 2:38PM Central Time, Monday 1/23/23.
Hail probabilities for Tuesday range from 5-15% across region.

Overview

A deepening upper level trough over the SW US will move eastward and into SW/W TX tonight/Tuesday and then exit the state early Wednesday morning to the east. This system will bring dynamic weather to much of Texas starting late Monday tonight.

The National Weather Service Storm Prediction Center warns that “supercells will be likely along the developing line of storms.”

The dry air now over SE TX will undergo significant changes in the next 24 hours. A low level jet will quickly transport extreme moisture northward from the SW/W Gulf of Mexico. Moisture levels in the atmosphere will quintuple overnight, driven by the 50-60 mph winds just above the surface. NWS indicates strong winds are the primary threat.

A wind advisory will likely be required for much of the area with isolated to scattered power outages possible.

Jeff Lindner, Harris County Meteorologist

Lift should rapidly increase Tuesday morning with scattered to numerous showers and thunderstorms developing from SW to NE across the region.

Look for scattered showers to begin developing around sunrise, then increase in coverage through the day. The highest potential for thunderstorms in the Houston metro area should be mid-afternoon. But they should move out of the state by early evening.

Heavy Rainfall Expected

Models hint at some sort of low-level convergence boundary becoming established along the US 59 corridor around mid-morning Tuesday. That should trigger heavy rainfall well ahead of the approaching front and boost rainfall in the Fort Bend, Harris, and Liberty County areas. Lindner worries that this could lead to a period of training storms and quick rainfall accumulations.

He predicts widespread rainfall of 1-3 inches with isolated totals of 4-6 inches possible.

Street flooding will be a concern in areas that catch heavier rainfall. Hourly rates may approach 1-3 inches.

Given the time of year, wet grounds, and dead vegetation from recent freezes, maximum run-off is likely. Lindner expects rises on area streams, but also says that the current forecasted rainfall amounts should not lead to creek, bayou, or river flooding.

Severe

The National Weather Service Storm Prediction Center suggests that an impressive 80-100kt mid-level jet carving across SE TX Tuesday afternoon could bring enough instability south of I-10 for severe thunderstorms to develop. SPC has upgraded the risk in that area into a (2 out of 5) slight risk.

Wind gusts of 60-70mph will be possible. Near the coast, a tornado or two will be possible. The highest threat of severe weather is currently offshore, but the severe threat could be upgraded south of I-10.

Winds

Starting late tonight, the strong low level jet overhead will bring sustained winds of 25-35mph and gusts of 40-45mph at the surface much of Tuesday. Gusts may be higher near the coast and inland bays. A wind advisory will likely be required for much of the area and these winds may down trees and tree limbs, result in isolated to scattered power outages, and move unsecured outdoor objects.

Marine

Dangerous marine conditions will quickly develop late tonight into Tuesday as southerly winds rapidly increase into the 35-45kt range for all waters.

A gale watch is in effect for all waters and will be upgraded to a warning this afternoon. Seas will quickly build 6-8 ft in bays and 10-12ft offshore on Tuesday.

The strong winds may result in elevated tides in the northern portion of Galveston Bay Tuesday along with wave run-up on the Gulf facing beaches.

The line of strong to severe thunderstorms arriving Tuesday afternoon/evening will bring W/NW winds at 30-40 kts. Wind gusts of 50-55kts will be possible. Small craft should be in port by this evening and remain in port until winds and seas subside on Wednesday.   

One Year Anniversary of Kingwood Tornado

Although January tornados are rare, we should not forget what happened last January when several twisters slashed through Kingwood downing trees and power lines. Exercise caution.

Posted by Bob Rehak on 1/23/2023 at 2PM based on information from the NWS and Jeff Lindner

1973 Days since Hurricane Harvey