The upper Texas Coast is famous for intense, frequent rainfall. Sometimes, like during Harvey, rainfall can last for days. So how do you know when you’re experiencing something truly out of the ordinary? Consult the table below. This table relates three factors: rainfall total, rainfall duration, and rainfall classification. From this chart, you can see that all it will take for us to have our fourth five-hundred year storm in four years is about an inch an hour for 18 hours, or about two inches per hour for six hours.
Rainfall Rates, Intensities and Frequencies for The Woodlands Area on the West Fork, near Humble and Kingwood, Texas
What are the odds of getting hit with three 500-year storms in three years (which we did in 2015, 2016 and 2017)? One might think they are 1 in 125 million which was computed by multiplying 1/500 * 1/500 * 1/500.
The odds of getting four 500-year storms in four years would then SEEM astronomical. Using a similar formula, you would arrive at 1 in 62.5 billion!
But that is not necessarily correct because with that calculation you are inferring that the rainfall events are connected. But they actually are not connected. Just because we had a 500-year rainfall event last year, does not mean we may not see another 500- year rainfall event this year.
EVERY year we have a 0.2% chance or 1 in 500 chances of seeing a 500-year flood for a specific location.
This assumes that the odds are no greater in one year than any other year, and that each event is independent of the others.
How do mathematicians compute the probabilities of these rare events? Obviously, it isn’t through observation. The earth is only about 4.5 billion years old. Humans have only walked the earth for about 200,000 years. And reliable rainfall records in this part of the world only go back a little more than a 100 years.
Probabilities for rare events, such as hundred- and five-hundred year storms are based on a branch of statistics called EVA, extreme value analysis. EVA tries to calculate the probabilities of unobserved events by looking at the distribution of observed events.
But all this technical brilliance is based on one particularly flawed assumption that never gets communicated to the public. The assumption is that for the period under examination, nothing changes. Mathematicians even have a word for it: stationarity. It means underlying factors can neither increase, nor decrease.
Duh! Nothing changes in 500 years? In Houston?
Obviously, those folks never rode around for a day in a Ford F350 with a Houston developer.
In 1900, Houston had a population of 44,000 and was the 85th largest city in the U.S.
Today, the Houston region has a population of more than 6.9 million. That’s growth of 157X in a little more than a century. And that’s a lot more concrete than even Bubba and Jim Bob together could spit on in a lifetime.
Diane Cooper, a Kingwood resident with more than 20 years of forecasting experience for the National Weather Service points out a couple other problems with these projections. First, the data is very, very, very thin and rarely updated.
Second, the probabilities are computed for a specific point, not a city, county, region or country. Storms know no geographic boundaries.
In fact, she says, it’s a little bit misleading to say that Houston got hit by three 500-year storms in three years. That’s because any given storm may not have equal intensity over all parts of the city. A storm may have had 500-year intensity on the north side. but only 100-year intensity on the south. Following the same line of logic, but in a different direction, if you expanded the boundaries out to the entire U.S., we might have multiple 500-year storms in one year (each in different places).
Cooper also points out that 500-year storms do not necessarily produce 500-year floods. They are two different beasts.
If the ground is dry, say from a drought, a large percentage of a heavy rain might be absorbed, yielding less than a 500-year flood. Conversely, if the ground is saturated and we get a 100-year rain, get out the oars and inner tubes.
Even though charts like the one above have more uncertainty than a dart player who just downed a fifth of Jack Daniels, they do put big storms in perspective.
By the way, the term “500-year flood” originated in the 1960s when the National Flood Insurance Program was being developed. At the time, people intended it to mean “a storm with a .002% chance of happening in any given year.” However, over the years, the meaning became distorted. Because it had a 1 in 500 chance of occurring each year, insurers started calling it a 500-year storm. People mistook that to mean “the interval between intense storms.”
More on that in a future post and how to calculate the chances of getting hit by a monster storm during the life of your 30-year mortgage. Hint: call your insurance agent now!
Posted May 23, 2018 by Bob Rehak
267 days since Hurricane Harvey
00adminadmin2018-05-23 21:25:482018-05-23 22:16:07Rainfall Rates, Durations and Frequencies for This Area
Our San Jacinto River is clogged with sand that impedes the flow of water and contributes to flooding. Where did all the sand come from? When? Under what conditions? Are there ways to reduce the volume of sand coming downstream? As the U.S. Army Corps of Engineers prepares to dredge the San Jacinto for the first time, we should ask ourselves these questions.
The river has eight tributaries that affect the Lake Houston Area: Spring Creek, Cypress Creek, Lake Creek and the West Fork on the west; and Peach Creek, Caney Creek, Luce Bayou and the East Fork on the east. All produce sand naturally.
They send sand downstream at different rates at different times, depending on the location of rainfall within the watershed, the volume of flow, the speed of flow, and management of the flood gates at Lake Conroe.
San Jacinto River Watershed Map. Tributaries affecting the Humble/Kingwood area include: Cypress Creek, Spring Creek, Lake Creek, West Fork, Peach Creek, Caney Creek, East Fork, and Luce Bayou.
Other factors include the percentage of sand content in soil and the health of vegetation along stream banks. Vegetation retains and slows runoff, reducing erosion.
The Natural Resources Conservation Service of the USDA produced this soil map of Montgomery County. Blue colors indicate highest percentage of sand; red colors indicate the lowest. Note huge concentrations of sand on Spring Creek and West Fork.
The map above helps us understand why so many sand miners chose to locate along the West Fork – lots of sand. The West Fork is also sparsely populated compared to Spring Creek as you can see in the satellite image below. It shows the sand mines around the Humble/Kingwood area highlighted in red. One is located on Caney Creek (right); the rest are on the West Fork (left).
Satellite image from Google Earth with sand mines around Kingwood outlined in red. Image dated 10/28/2017.
While sand has been coming down the river and streams for thousands of years, rapid sedimentation in the West Fork between Humble and Kingwood didn’t become an issue until the growth of sand mining on the West Fork in the late 1980s.
Notice how most of the areas in red above are filled with natural vegetation in the 1985 image below.
Satellite photo of Kingwood area in 1985 before rapid growth of sand mining. Compare areas in red to previous image.
Today, mines expose approximately 20 square miles of loose sand on the West Fork alone between I-45 and US59.
Aerial photo taken on 9/14/18 of sand mining operation on West Fork.
Dikes around the mines are supposed to keep sand from being discharged into the river. However, Harvey inundated the mines.
Harvey’s floodwaters topped the dikes of sand mines. Image taken 8/30/2017.
During floods like Harvey when the SJRA releases water from Lake Conroe, dikes are overtopped and broken. I suspect that sand then comes down the West Fork in tremendous volumes that dwarf Spring Creek’s contribution.
To test this hypothesis, I looked at USGS flow data for both tributaries. I also reviewed all my aerial photos and Google Earth’s historical images.
Under normal conditions, Spring Creek flows at 80 cubic feet per second (cfs) and the West Fork of the San Jacinto at 150 cfs. These are not sufficient flow rates to suspend sediment the size of sand. (For an excellent discussion of sedimentation, see Fundamentals of Sediment Transport at Fondriest.com.)
However, during Harvey, Sring Creek flowed at 78,200 cfs; and the West Fork at 55,000 cfs. Then the San Jacinto River Authority opened the gates at Lake Conroe. That flipped the ratio dramatically. With the flood gates open, Spring Creek still flowed at 78,200 cfs, but the West Fork increased to 130,000 cfs. Flow rates that high can (and did) move houses off their foundations.
Four hundred and fifty aerial photos in the gallery of this web site show a bright, white trail of sand between sand mines and the sand clogging the East and West Forks around Humble and Kingwood. Flood waters swept that sand from a to b. The giant sand deposits at River Grove Park and elsewhere grew exponentially during recent floods.
This tells me that when discussing the origins of the sand, we need to primarily evaluate the river during floods. More water is moving faster under greater pressure. That’s when erosion and deposition happen quickly. That’s when the river overtops and ruptures dikes. And that’s when twenty additional square miles of exposed sand surface on the West Fork make their major contribution to our sediment and flooding problems.
We can’t control sand coming down rivers naturally. However, with better sand mining practices, we may be able to reduce mankind’s contribution to our flooding problem, not to mention the related cleanup costs borne by taxpayers.
In upcoming posts, I will discuss my research into sand mining best practices.
Posted May 22, 2018 by Bob Rehak
266 Days since Hurricane Harvey
00adminadmin2018-05-22 08:08:322018-05-22 08:14:46Where did all the sand come from?
The United States Geological Service (USGS) has introduced a new, real-time, web-based, all-purpose water app called “Water On the Go” that enhances situational awareness. The new GPS-aware, web app locates flood gages in 360 degrees around your current location within a user-defined radius.
Water On The Go provides real-time information throughout Texas for:
stream flows
lake levels
rainfall
User-Defined Alerts
Water On the Go also allows users to have alerts sent to them whenever the gages exceed user-defined parameters. For instance, if the gage at the West Fork and US59 exceeded X feet in height or Y cubic feet per second, the app would text an alert to your cell phone or email you (your choice).
How Water On the Go Works
The app automatically finds data near your current location (or any chosen location in Texas) for rapid access to water information. When you first enter the app, you are in preference pane that lets you define the type of information you are looking for. From there, you enter a map view like the one below. The app finds your location (or lets you select one. Then it automatically locates gages around you. Icons pop up representing each of the gages.
When you first enter Water on The Go, the app finds gages around you within a user-defined radius.
Special icons indicate rapidly rising streams and lakes or heavy rain that may pose a flood risk. Note the red triangles in the image above.
When you click on a gage in the radius view, detailed information from the gage pops up. You can designate it to display the type of information most important to you.
When you click on any gage, you can dig down to more information about the water at that location, including current water levels, a graph of levels in recent days, and links to more data and information.
Deceptively Deep (No Pun Intended)
The Water on the Go app is deceptively deep. It provides a wealth of historical information in graphic formats that make it easy to understand and convenient to use.
This is definitely a site that you will want to bookmark during hurricane season. In one place you can find information that used to be scattered all over the web.
I have only one suggestion. The mobile experience needs to be enhanced. Smaller screen sizes hamper functionality somewhat. The app works like a dream on desktops and laptops. It works well on tablets. But on cell phones, it can be a bit of a struggle to pinpoint locations with fat fingers. Of course, I had GPS tracking on my phone turned off for privacy reasons. I’m sure it works much better with GPS tracking turned on.
For Flood Warnings, Fishermen and More
I expect that most members of the public would find this app especially valuable in several situations.
When approaching storms dump massive rainfalls upstream, you could see floods coming downstream at you and monitor the closest gages to determine whether and when you should evacuate..
When boating, you can set lake an stream level alerts to warn you when water levels drop below minimums.
When traveling vacationing, as I was during Harvey, you could use the app to navigate around trouble spots and check whether your home is in danger.
When you have friends, relatives or children whom you are concerned about in another location, you can check their safety at a glance.
The app even lets you monitor water temp, oxygen levels and turbidity – factors that fishermen could find valuable.
This application was developed by the U.S. Geological Survey Texas Water Science Center Data and Spatial Studies group and is fueled by USGS Water Services.
My thanks to Diane Cooper for alerting me to this new tool. Diane is a FEMA employee who has more than 20 years of experience forecasting floods and weather for the National Weather Service.
A Testimonial
As I was composing this post on Sunday evening, I received a text alert from Jeff Lindner of Harris County Flood Control. He warned that parts of Spring and Little Cypress Creeks might be coming out of their banks. I checked them with the app about an hour later. Sure enough, the gages for those creeks indicated trouble exactly where he indicated.
Check out Water on the Go. Better yet, bookmark it and sign up for alerts.
Rainfall Rates, Durations and Frequencies for This Area
The upper Texas Coast is famous for intense, frequent rainfall. Sometimes, like during Harvey, rainfall can last for days. So how do you know when you’re experiencing something truly out of the ordinary? Consult the table below. This table relates three factors: rainfall total, rainfall duration, and rainfall classification. From this chart, you can see that all it will take for us to have our fourth five-hundred year storm in four years is about an inch an hour for 18 hours, or about two inches per hour for six hours.
Rainfall Rates, Intensities and Frequencies for The Woodlands Area on the West Fork, near Humble and Kingwood, Texas
What are the odds of getting hit with three 500-year storms in three years (which we did in 2015, 2016 and 2017)? One might think they are 1 in 125 million which was computed by multiplying 1/500 * 1/500 * 1/500.
The odds of getting four 500-year storms in four years would then SEEM astronomical. Using a similar formula, you would arrive at 1 in 62.5 billion!
But that is not necessarily correct because with that calculation you are inferring that the rainfall events are connected. But they actually are not connected. Just because we had a 500-year rainfall event last year, does not mean we may not see another 500- year rainfall event this year.
This assumes that the odds are no greater in one year than any other year, and that each event is independent of the others.
How do mathematicians compute the probabilities of these rare events? Obviously, it isn’t through observation. The earth is only about 4.5 billion years old. Humans have only walked the earth for about 200,000 years. And reliable rainfall records in this part of the world only go back a little more than a 100 years.
Probabilities for rare events, such as hundred- and five-hundred year storms are based on a branch of statistics called EVA, extreme value analysis. EVA tries to calculate the probabilities of unobserved events by looking at the distribution of observed events.
But all this technical brilliance is based on one particularly flawed assumption that never gets communicated to the public. The assumption is that for the period under examination, nothing changes. Mathematicians even have a word for it: stationarity. It means underlying factors can neither increase, nor decrease.
Duh! Nothing changes in 500 years? In Houston?
Obviously, those folks never rode around for a day in a Ford F350 with a Houston developer.
In 1900, Houston had a population of 44,000 and was the 85th largest city in the U.S.
Today, the Houston region has a population of more than 6.9 million. That’s growth of 157X in a little more than a century. And that’s a lot more concrete than even Bubba and Jim Bob together could spit on in a lifetime.
Diane Cooper, a Kingwood resident with more than 20 years of forecasting experience for the National Weather Service points out a couple other problems with these projections. First, the data is very, very, very thin and rarely updated.
Second, the probabilities are computed for a specific point, not a city, county, region or country. Storms know no geographic boundaries.
In fact, she says, it’s a little bit misleading to say that Houston got hit by three 500-year storms in three years. That’s because any given storm may not have equal intensity over all parts of the city. A storm may have had 500-year intensity on the north side. but only 100-year intensity on the south. Following the same line of logic, but in a different direction, if you expanded the boundaries out to the entire U.S., we might have multiple 500-year storms in one year (each in different places).
Cooper also points out that 500-year storms do not necessarily produce 500-year floods. They are two different beasts.
If the ground is dry, say from a drought, a large percentage of a heavy rain might be absorbed, yielding less than a 500-year flood. Conversely, if the ground is saturated and we get a 100-year rain, get out the oars and inner tubes.
Even though charts like the one above have more uncertainty than a dart player who just downed a fifth of Jack Daniels, they do put big storms in perspective.
By the way, the term “500-year flood” originated in the 1960s when the National Flood Insurance Program was being developed. At the time, people intended it to mean “a storm with a .002% chance of happening in any given year.” However, over the years, the meaning became distorted. Because it had a 1 in 500 chance of occurring each year, insurers started calling it a 500-year storm. People mistook that to mean “the interval between intense storms.”
More on that in a future post and how to calculate the chances of getting hit by a monster storm during the life of your 30-year mortgage. Hint: call your insurance agent now!
Posted May 23, 2018 by Bob Rehak
267 days since Hurricane Harvey
Where did all the sand come from?
Our San Jacinto River is clogged with sand that impedes the flow of water and contributes to flooding. Where did all the sand come from? When? Under what conditions? Are there ways to reduce the volume of sand coming downstream? As the U.S. Army Corps of Engineers prepares to dredge the San Jacinto for the first time, we should ask ourselves these questions.
The river has eight tributaries that affect the Lake Houston Area: Spring Creek, Cypress Creek, Lake Creek and the West Fork on the west; and Peach Creek, Caney Creek, Luce Bayou and the East Fork on the east. All produce sand naturally.
They send sand downstream at different rates at different times, depending on the location of rainfall within the watershed, the volume of flow, the speed of flow, and management of the flood gates at Lake Conroe.
San Jacinto River Watershed Map. Tributaries affecting the Humble/Kingwood area include: Cypress Creek, Spring Creek, Lake Creek, West Fork, Peach Creek, Caney Creek, East Fork, and Luce Bayou.
Other factors include the percentage of sand content in soil and the health of vegetation along stream banks. Vegetation retains and slows runoff, reducing erosion.
The Natural Resources Conservation Service of the USDA produced this soil map of Montgomery County. Blue colors indicate highest percentage of sand; red colors indicate the lowest. Note huge concentrations of sand on Spring Creek and West Fork.
The map above helps us understand why so many sand miners chose to locate along the West Fork – lots of sand. The West Fork is also sparsely populated compared to Spring Creek as you can see in the satellite image below. It shows the sand mines around the Humble/Kingwood area highlighted in red. One is located on Caney Creek (right); the rest are on the West Fork (left).
Satellite image from Google Earth with sand mines around Kingwood outlined in red. Image dated 10/28/2017.
While sand has been coming down the river and streams for thousands of years, rapid sedimentation in the West Fork between Humble and Kingwood didn’t become an issue until the growth of sand mining on the West Fork in the late 1980s.
Notice how most of the areas in red above are filled with natural vegetation in the 1985 image below.
Satellite photo of Kingwood area in 1985 before rapid growth of sand mining. Compare areas in red to previous image.
Today, mines expose approximately 20 square miles of loose sand on the West Fork alone between I-45 and US59.
Aerial photo taken on 9/14/18 of sand mining operation on West Fork.
Dikes around the mines are supposed to keep sand from being discharged into the river. However, Harvey inundated the mines.
Harvey’s floodwaters topped the dikes of sand mines. Image taken 8/30/2017.
An analysis of satellite images before, during and after Harvey shows massive loss of sand from stockpiles within many of these mines.
During floods like Harvey when the SJRA releases water from Lake Conroe, dikes are overtopped and broken. I suspect that sand then comes down the West Fork in tremendous volumes that dwarf Spring Creek’s contribution.
To test this hypothesis, I looked at USGS flow data for both tributaries. I also reviewed all my aerial photos and Google Earth’s historical images.
Under normal conditions, Spring Creek flows at 80 cubic feet per second (cfs) and the West Fork of the San Jacinto at 150 cfs. These are not sufficient flow rates to suspend sediment the size of sand. (For an excellent discussion of sedimentation, see Fundamentals of Sediment Transport at Fondriest.com.)
However, during Harvey, Sring Creek flowed at 78,200 cfs; and the West Fork at 55,000 cfs. Then the San Jacinto River Authority opened the gates at Lake Conroe. That flipped the ratio dramatically. With the flood gates open, Spring Creek still flowed at 78,200 cfs, but the West Fork increased to 130,000 cfs. Flow rates that high can (and did) move houses off their foundations.
Four hundred and fifty aerial photos in the gallery of this web site show a bright, white trail of sand between sand mines and the sand clogging the East and West Forks around Humble and Kingwood. Flood waters swept that sand from a to b. The giant sand deposits at River Grove Park and elsewhere grew exponentially during recent floods.
This tells me that when discussing the origins of the sand, we need to primarily evaluate the river during floods. More water is moving faster under greater pressure. That’s when erosion and deposition happen quickly. That’s when the river overtops and ruptures dikes. And that’s when twenty additional square miles of exposed sand surface on the West Fork make their major contribution to our sediment and flooding problems.
We can’t control sand coming down rivers naturally. However, with better sand mining practices, we may be able to reduce mankind’s contribution to our flooding problem, not to mention the related cleanup costs borne by taxpayers.
In upcoming posts, I will discuss my research into sand mining best practices.
Posted May 22, 2018 by Bob Rehak
266 Days since Hurricane Harvey
New Water-On-The-Go App Enhances Situational Awareness
The United States Geological Service (USGS) has introduced a new, real-time, web-based, all-purpose water app called “Water On the Go” that enhances situational awareness. The new GPS-aware, web app locates flood gages in 360 degrees around your current location within a user-defined radius.
Water On The Go provides real-time information throughout Texas for:
User-Defined Alerts
Water On the Go also allows users to have alerts sent to them whenever the gages exceed user-defined parameters. For instance, if the gage at the West Fork and US59 exceeded X feet in height or Y cubic feet per second, the app would text an alert to your cell phone or email you (your choice).
How Water On the Go Works
The app automatically finds data near your current location (or any chosen location in Texas) for rapid access to water information. When you first enter the app, you are in preference pane that lets you define the type of information you are looking for. From there, you enter a map view like the one below. The app finds your location (or lets you select one. Then it automatically locates gages around you. Icons pop up representing each of the gages.
When you first enter Water on The Go, the app finds gages around you within a user-defined radius.
Special icons indicate rapidly rising streams and lakes or heavy rain that may pose a flood risk. Note the red triangles in the image above.
When you click on a gage in the radius view, detailed information from the gage pops up. You can designate it to display the type of information most important to you.
When you click on any gage, you can dig down to more information about the water at that location, including current water levels, a graph of levels in recent days, and links to more data and information.
Deceptively Deep (No Pun Intended)
The Water on the Go app is deceptively deep. It provides a wealth of historical information in graphic formats that make it easy to understand and convenient to use.
This is definitely a site that you will want to bookmark during hurricane season. In one place you can find information that used to be scattered all over the web.
I have only one suggestion. The mobile experience needs to be enhanced. Smaller screen sizes hamper functionality somewhat. The app works like a dream on desktops and laptops. It works well on tablets. But on cell phones, it can be a bit of a struggle to pinpoint locations with fat fingers. Of course, I had GPS tracking on my phone turned off for privacy reasons. I’m sure it works much better with GPS tracking turned on.
For Flood Warnings, Fishermen and More
I expect that most members of the public would find this app especially valuable in several situations.
The app even lets you monitor water temp, oxygen levels and turbidity – factors that fishermen could find valuable.
This application was developed by the U.S. Geological Survey Texas Water Science Center Data and Spatial Studies group and is fueled by USGS Water Services.
My thanks to Diane Cooper for alerting me to this new tool. Diane is a FEMA employee who has more than 20 years of experience forecasting floods and weather for the National Weather Service.
A Testimonial
As I was composing this post on Sunday evening, I received a text alert from Jeff Lindner of Harris County Flood Control. He warned that parts of Spring and Little Cypress Creeks might be coming out of their banks. I checked them with the app about an hour later. Sure enough, the gages for those creeks indicated trouble exactly where he indicated.
Check out Water on the Go. Better yet, bookmark it and sign up for alerts.
https://txpub.usgs.gov/water-onthego/
Posted May 21, 2018 by Bob Rehak
265 Days since Hurricane Harvey