In the School of Hard Knocks, there’s an introductory course called, “Money Has a Short Memory.” Most students fail this free course and, as a consequence, are still paying “tuition” years later. The irony was never more visible than last week. As I reviewed a Houston Public Media Story about how the City of Houston was not attempting to curb development in the 100-year flood plain – despite everything we learned from Harvey – I had a presentation about the 1994 flood waiting for review on my desktop.
1994 Flood Should Have Taught Us Lessons We Still Haven’t Learned
Kingwood received 29″ of rain that week. Rainfall averaged 19.5 inches over the entire 2,880-square mile San Jacinto River watershed. The event lasted four days. It started on Saturday, October 15, 1994 when Pacific Hurricane Rosa met a gulf coast warm front over Texas. It affected 38 Texas Counties, an area as large as Maine.
1.9 million acre-feet of runoff passed through Lake Houston: almost 12 times the volume of the entire lake! The lake crested 8.3 feet above the 3,160-foot spillway.
Homes under construction on Atascocita Point. HCFCD Photo from presentation by Yung and Barrett on 1994 flood.
Stunning Photos of 1994 Flood
The presentation contains photos of flooding:
On Atascocita point, where new construction was just beginning at the time.
In Forest Cove townhomes that would flood at least four more times before buyouts
In Banana Bend below Lake Houston, which is also just now being bought out
Around Toys ‘R Us on 59 – before an entire strip center of big box stores surrounded it
That collapsed the 59 bridge
That downed power lines over Lake Houston
That went up to the roofline of what was then Reeves Furniture on the southbound 59 feeder just north of the West Fork
That ruptured pipelines across the San Jacinto and started a toxic blaze
That buried downstream areas in sand and gravel.
Sound familiar? It should. Virtually all those things happened during Harvey, with the exception of the pipeline fire. However, toxic waste pits were involved during Harvey.
What are the Chances?
At the time, experts opined about how rainfall exceeded the expected 100-year levels. But the new Atlas-14 data released by NOAA, now advises that a four-day flood averaging 19.5 inches would have an average recurrence interval of 50 years.
The latest NOAA Atlas-14 Rainfall Data for the Lake Houston area
After Harvey, people dazed by the devastation, solemnly concluded that the storm must have been a 500-year, a 1,000-year, or even a greater storm. They had absolute faith in the numbers that developers, engineers, bankers, insurers, and government agencies certified. They assumed storm intensity had to be greater than expected. It never occurred to them that perhaps the numbers could be off…in the other direction.
Complicating things, most people are oblivious to the nuances of probabilities. The naming convention (100-year storm) misleads them into thinking that if we had a 100-year storm last year, “we must be good for another 99 years.” Wrong. Theoretically, if you tossed a coin and it came up heads 99 times in a row, you have a 50:50 chance of getting heads on the hundredth toss, too.
How many people read…or understand…the fine print in tables like the one above? Did you read the footnotes? If not, please go back and read them now. It’s important for your own safety and the safety of your investment.
They’re trying to say, “We can’t predict extremes with accuracy.”
Conclusions of 1994 Flood Presentation
Yung and Barrett conclude with several warnings. They include.
Extreme rainfall events will continue to occur.
The adoption of criteria that exceed FEMA minimum requirements should be considered by communities to guard against severe events.
So until the City learns this lesson, what’s someone without a PhD in math supposed to do when buying a home? Forego the river or lake view and buy on the highest ground you can find. Buyer beware! There are huge markups on floodplain property. And money has a short memory.
Posted by Bob Rehak on 6/9/2019, based on a presentation by Andy Yung and Duange Barrett
649 Days since Hurricane Harvey
https://i0.wp.com/reduceflooding.com/wp-content/uploads/2019/06/AtascocitaPoint-in-1994.jpg?fit=1500%2C1037&ssl=110371500adminadmin2019-06-09 19:17:192019-06-09 19:17:30“Money Has a Short Memory” or How Lessons from 1994 Flood Might Have Averted Much Harvey Damage
Rains this week were neither as fast, nor as heavy as the May rains that caused extensive flooding on all four sides of Woodridge Village in May. Also, since the May rains, the developer had excavated much more of a crucial detention pond near the areas hardest hit by the May floods. As a result, I heard of no reported flooding in Elm Grove, North Kingwood Forest or Porter this week.
How Much Rain We Got
The screen capture below from the Harris County Flood Warning System shows the total rainfall for Lake Houston Area gages on June 5th and 6th. They range from about 1.5″ to 4″, with the higher totals on the southern side of the area. About 90% of these totals fell on Wednesday, June 5, during the morning hours.
Rainfall totals June 5-6 associated with first tropical disturbance of season. The rain fell on dry ground. No flooding was reported in the Lake Houston area, though Fort Bend and coastal counties received up to 14″.Source HarrisCoutyFWS.org.
During the 7 hours from 5 a.m. to noon, we received about 3.5 inches of rain at the nearest official gage.Source HarrisCoutyFWS.org.
Residents Anxious About a Repeat of May 7 Flood
Woodridge Village is the 268-acre clearcut area currently under development between Kingwood and Porter along the Harris/Montgomery County line. Two hundred homes in Kingwood and dozens in Porter that border the new subdivision flooded during more intense rains on May 7th.
However, repeat flooding was avoided. That was because of a combination of factors. Compared to May 7, we had lower rainfall totals, lower rainfall intensity, and most of Woodridge detention pond S2 (the second southern pond) had been excavated.
How Woodridge Village Handled the Rain This Week and Why
This sequence of pictures shows what the part of Woodridge immediately near Elm Grove and North Kingwood Forest looked like after the May 7 storm up through the peak of last Wednesday’s storm (6/5/19).
Engineers planned a huge detention pond for the entire southeast section of Woodridge. It should hold approximately 50 acre-feet of stormwater.
Approved plans for S2 Detention Pond (the second pond in the southern section).Approximate S2 outline superimposed over keyframe from drone footage taken on May 9, 2019, two days after the May flood. This shows percentage of S2 actually excavated at time of flood: very little. Note also, the absence of silt fences. Virtually the entire 268 acres drains toward the culvert in the lower right.Drone footage courtesy of Jim Zura, Zura Productions. Zura is an FAA-licensed drone pilot.By May 30, much more of S2 had been excavated. Outline of pond was becoming visible.Photo Courtesy of Jeff Miller. In the background, notice the black silt fence has finally been installed. It should have been installed before they started clearing land.
On the evening of June 4, Jeff Miller took the shot below from on top of the concrete box culvert where all of Woodridge Village drains into Taylor Gully.
Notice the depth of excavation in the deepest part. It had not rained for three weeks and the water was missing on May 30. Note also, the rocks in wire cages designed to hold back silt in a flood. The height of the bikes gives you a feeling for how tall the rocks are. Photo courtesy of Jeff Miller on 6/4/2019.
The next day, on 6/5/2019, we got the bulk of the rain from the storm. Jeff Miller went out again in the afternoon and took this shot showing how full the pond was.
6/5/2019 photo of S2 by Jeff Miller showing the amount of rainwater detained from the day’s storms.The low area in the center of the image leading to the pond is an overflow channel for the ditch behind the camera position that narrows down into a three-foot pipe.
Just after the rain stopped on the 6/5/19, Nancy Vera took this shot, near the peak of the flow.
At the peak of the flow, water covered the circled rocks (see swimming shot) now lining the channel to prevent silt moving downstream.Photo courtesy of Nancy Vera.It appears that a 4″ rain spread out over a day – when the ground was not saturated – did not tax the capacity of the culvert either.This should be some comfort to residents.Image courtesy of Nancy Vera.Even the 3′ culvert that runs along the western edge of North Kingwood Forest had room to spare. Photo courtesy of Nancy Vera.Even Taylor Gully had plenty of room to spare. Photo courtesy of Nancy Vera.
Sleep a Little Easier
So what can we deduce from all of these observations.
The expansion of the S2 detention pond since the May 7th flood has created a greater margin of safety.
Elm Grove and North Kingwood Forest residents should sleep a little better knowing that they are protected from storms as large as we got on Wednesday, June 5.
Based on the latest NOAA Atlas 14 figures (see below), it looks like Wednesday’s rain ranked as a 1- to 2-year event.
It appears that there may be even more capacity to absorb even bigger rains.
However, with all ponds not yet complete, it’s unclear whether these ponds could handle a storm like we had on May 7th or a major hurricane.
NOAA Atlas-14 Rainfall Frequency Chart. Find the line that represents how much rain fell during a given period of time. Then look up to the top of that column to find the average recurrence interval (ARI).3.5 inches of rain in a 7-hour period would be a rain we could expect every year or two.
Posted by Bob Rehak on June 8, 2019with help from Nancy Vera, Jim Zura and Jeff Miller.
648 Days since Hurricane Harvey and One Month since the May 7th Flood
https://i0.wp.com/reduceflooding.com/wp-content/uploads/2019/06/S2.jpg?fit=1500%2C884&ssl=18841500adminadmin2019-06-07 22:25:192019-06-07 23:45:22How Woodridge Village Neighbors Fared in Last Large Rain and Why
Houston Council Member Dave Martin announced that the City of Houston and Montgomery County will host a flood claims workshop from 6:00 p.m. to 7:30 p.m. on Wednesday, June 19, 2019.
Kingwood Community Center
4102 Rustic Woods
Kingwood, Texas 77345
This event is for anyone (resident or business owner) who has: a) suffered flood damages, b) has flood insurance through the National Flood Insurance Program (NFIP) and c) has questions about the policy claims process. FEMA representatives will be available to provide resources and answer questions. It does not matter what event caused the flood damage. Although the time has passed for submitting a Harvey claim, some people may still be struggling with the process. If they are protesting a settlement, they might benefit from this event.
“Money Has a Short Memory” or How Lessons from 1994 Flood Might Have Averted Much Harvey Damage
In the School of Hard Knocks, there’s an introductory course called, “Money Has a Short Memory.” Most students fail this free course and, as a consequence, are still paying “tuition” years later. The irony was never more visible than last week. As I reviewed a Houston Public Media Story about how the City of Houston was not attempting to curb development in the 100-year flood plain – despite everything we learned from Harvey – I had a presentation about the 1994 flood waiting for review on my desktop.
1994 Flood Should Have Taught Us Lessons We Still Haven’t Learned
The presentation, “Rain by the Cubit: The Great Southeast Texas Flood of 1994,” brought back memories. That was the year I started my company. I was supposed to move into my first commercial office space when this flood hit.
Kingwood received 29″ of rain that week. Rainfall averaged 19.5 inches over the entire 2,880-square mile San Jacinto River watershed. The event lasted four days. It started on Saturday, October 15, 1994 when Pacific Hurricane Rosa met a gulf coast warm front over Texas. It affected 38 Texas Counties, an area as large as Maine.
Stunning Photos of 1994 Flood
The presentation contains photos of flooding:
Sound familiar? It should. Virtually all those things happened during Harvey, with the exception of the pipeline fire. However, toxic waste pits were involved during Harvey.
What are the Chances?
After Harvey, people dazed by the devastation, solemnly concluded that the storm must have been a 500-year, a 1,000-year, or even a greater storm. They had absolute faith in the numbers that developers, engineers, bankers, insurers, and government agencies certified. They assumed storm intensity had to be greater than expected. It never occurred to them that perhaps the numbers could be off…in the other direction.
How Average Recurrence Interval is Determined
All these numbers (500-year, etc.) are based on extremely small data sets. Forecasters use a branch of mathematics called Extreme Value Analysis (EVA). With EVA, they try to forecast the probability of unobserved future events based on the frequency of somewhat smaller past events. EVA may produce the best numbers possible, but predicting 500-years into the future based on 100 years of data takes a lot of guess-work.
Limitations of Numbers
Complicating things, most people are oblivious to the nuances of probabilities. The naming convention (100-year storm) misleads them into thinking that if we had a 100-year storm last year, “we must be good for another 99 years.” Wrong. Theoretically, if you tossed a coin and it came up heads 99 times in a row, you have a 50:50 chance of getting heads on the hundredth toss, too.
How many people read…or understand…the fine print in tables like the one above? Did you read the footnotes? If not, please go back and read them now. It’s important for your own safety and the safety of your investment.
Conclusions of 1994 Flood Presentation
Yung and Barrett conclude with several warnings. They include.
So until the City learns this lesson, what’s someone without a PhD in math supposed to do when buying a home? Forego the river or lake view and buy on the highest ground you can find. Buyer beware! There are huge markups on floodplain property. And money has a short memory.
Posted by Bob Rehak on 6/9/2019, based on a presentation by Andy Yung and Duange Barrett
649 Days since Hurricane Harvey
How Woodridge Village Neighbors Fared in Last Large Rain and Why
Rains this week were neither as fast, nor as heavy as the May rains that caused extensive flooding on all four sides of Woodridge Village in May. Also, since the May rains, the developer had excavated much more of a crucial detention pond near the areas hardest hit by the May floods. As a result, I heard of no reported flooding in Elm Grove, North Kingwood Forest or Porter this week.
How Much Rain We Got
The screen capture below from the Harris County Flood Warning System shows the total rainfall for Lake Houston Area gages on June 5th and 6th. They range from about 1.5″ to 4″, with the higher totals on the southern side of the area. About 90% of these totals fell on Wednesday, June 5, during the morning hours.
Residents Anxious About a Repeat of May 7 Flood
Woodridge Village is the 268-acre clearcut area currently under development between Kingwood and Porter along the Harris/Montgomery County line. Two hundred homes in Kingwood and dozens in Porter that border the new subdivision flooded during more intense rains on May 7th.
So when the first tropical depression of the year approached earlier this week and merged with a second low coming out of the west, residents were on edge. Especially when the National Weather Service announced a flash flood watch that spread over two days.
However, repeat flooding was avoided. That was because of a combination of factors. Compared to May 7, we had lower rainfall totals, lower rainfall intensity, and most of Woodridge detention pond S2 (the second southern pond) had been excavated.
How Woodridge Village Handled the Rain This Week and Why
This sequence of pictures shows what the part of Woodridge immediately near Elm Grove and North Kingwood Forest looked like after the May 7 storm up through the peak of last Wednesday’s storm (6/5/19).
Engineers planned a huge detention pond for the entire southeast section of Woodridge. It should hold approximately 50 acre-feet of stormwater.
On the evening of June 4, Jeff Miller took the shot below from on top of the concrete box culvert where all of Woodridge Village drains into Taylor Gully.
The next day, on 6/5/2019, we got the bulk of the rain from the storm. Jeff Miller went out again in the afternoon and took this shot showing how full the pond was.
Just after the rain stopped on the 6/5/19, Nancy Vera took this shot, near the peak of the flow.
Sleep a Little Easier
So what can we deduce from all of these observations.
Posted by Bob Rehak on June 8, 2019 with help from Nancy Vera, Jim Zura and Jeff Miller.
648 Days since Hurricane Harvey and One Month since the May 7th Flood
City and MoCo Offer NFIP Flood Claims Workshop with FEMA
Houston Council Member Dave Martin announced that the City of Houston and Montgomery County will host a flood claims workshop from 6:00 p.m. to 7:30 p.m. on Wednesday, June 19, 2019.
This event is for anyone (resident or business owner) who has: a) suffered flood damages, b) has flood insurance through the National Flood Insurance Program (NFIP) and c) has questions about the policy claims process. FEMA representatives will be available to provide resources and answer questions. It does not matter what event caused the flood damage. Although the time has passed for submitting a Harvey claim, some people may still be struggling with the process. If they are protesting a settlement, they might benefit from this event.
For more information please contact the District E Office at DistrictE@houstontx.gov or Diane Cooper, Montgomery County Floodplain Administrator at Diane.Cooper@mctx.org.
Posted by Bob Rehak on 6/7/19
647 Days since Hurricane Harvey and One Month since May 7th