At its May Board meeting, the San Jacinto River Authority (SJRA) chose not to reconsider its April decision to lower the level of Lake Conroe temporarily at the peak of hurricane season. The board also chose not to put reconsideration of the resolution on its agenda for next month. This now puts the decision about whether to lower Lake Conroe temporarily into the hands of the City of Houston and the Texas Council on Environmental Quality (TCEQ).
However, the president of the Lake Conroe Association (LCA), Mike Bleier, urged the board to reconsider its decision and was given unlimited time to present his case. Bleier spoke for more than half an hour. Bleier’s main concerns were the potential impacts on recreation, home values and businesses around Lake Conroe. Several other members of the association spoke in support of reconsideration.
Kingwood Residents Speak in Favor of Lowering
More than a dozen Kingwood residents also attended the meeting. Four spoke in favor of letting the motion stand.
Guy Sconzo, former superintendent of the Humble Independent School District, thanked the board for its decision to lower the lake. Then he talked about the impact of flooding on Lake Houston area infrastructure. His talk addressed massive losses by the school district, Kingwood College, and more.
TxDoT hopes to repair damage to the I-69 bridge by September, more than a year after Harvey. In the meantime, residents endure massive traffic jams.
Robert Westover talked about a flooded retirement community where several elderly residents died due to injuries incurred during high-water rescues and related stress.
Amy Slaughter complemented the board for its decision to lower the lake and explained how it would help insure that people had time to rebuild while other flood mitigation measures were completed.
Dennis Albrecht, who owns homes on both Lake Houston and Lake Conroe also spoke. Albrecht compared the relative impacts of flooding and lower lake levels on home values. Albrecht pointed out that the value of his Lake Conroe home has increased steadily despite lower lake levels at times. He also pointed out the devastating impact of the flood on the value of his Lake Houston home. “There’s no comparison,” said Albrecht.
Many other Kingwood residents attended the meeting to support the SJRA Board’s decision.
When is a lowering not really a lowering?
Bleier said that his members would accept a one foot lowering, but not two. Several Kingwood residents pointed out that evaporation already typically reduces the level of the lake by more than a foot and a half during September. The LCA’s decision to accept a one-foot lowering was, therefore, actually no concession at all; they would likely give up nothing.
Assuming average loss due to evaporation, the actual lowering would amount to only 4.8 inches.
Dianne Lansden, co-chair of the Lake Houston Area Grass Roots flood prevention initiative, and I gave Bleier a tour of the devastation in Humble and Kingwood yesterday. After a two-hour tour, while professing to be sensitive to the needs of downstream residents, Bleier proceeded to tell us the concerns of upstream residents. Among them: his members might not be able to take their boats to lakefront restaurants. (Editorial comment: Spooky shades of Marie-Antoinette!)
Not All Lake Conroe Residents Support LCA
To be sure, not all Lake Conroe residents agree with Bleier. Hundreds of homes on Lake Conroe also flooded during Harvey and reportedly most of the owners also favor a temporary seasonal lowering of the lake level, according to SJRA Board Chairman Lloyd Tisdale.
Lake Lowering Could Still be Nixed
Despite the SJRA board’s decision this morning, Lake Conroe still may not be lowered. To take effect, both the City of Houston and the TCEQ must also agree to lower the lake. The City owns two thirds of the water in the lake. The TCEQ must decide whether any lowering will count as an emergency release or be deducted from the City’s draw rights. If not considered an emergency release, the City may not support the decision to lower the lake.
Uncertainty Surrounding Weather Outlook
Some forecasters are beginning to worry about a possible drought. As of May 22, Drought.gov pointed out that abnormal dryness is currently affecting approximately 13,612,000 people in Texas, which is about 54% of the state’s population.
If we got ten inches of rain from a storm, such as the one entering the Gulf this weekend, that could constitute a 50-year rain at a time when the river is clogged with sand. That could produce a higher-than-normal flood for that amount of rainfall, and re-flood parts of Kingwood and Humble before dredging could even begin.
Personal Recommendation
Personally, I favor lowering the level of the lake. The actual amount of manual lowering, assuming this is an average year, would be only 4.8 inches. Even in the depths of the 2011 drought, the loss of 4.8 inches would have not have been disastrous.
There’s little chance, despite the hyperbolic rhetoric from LCA that 4.8 inches will destroy the Lake Conroe area. And it could help protect the Lake Houston area from another disaster.
In fact, in eight of the last 18 years, Lake Conroe has lost more than two feet of water due to evaporation and the lake is still one of the state’s most desirable destinations for tourists.
LCA Vows to Escalate the Fight
LCA has vowed to press its fight with the City and TCEQ and claims to have enough political support lined up to kill the proposal to lower Lake Conroe temporarily.
So get involved. Urge the TCEQ, Mayor and City Council to TEMPORARILY lower Lake Conroe until other mitigation measures, such as dredging, take effect.
Posted on 5/25/18 by Bob Rehak
269 Days since Hurricane Harvey
00adminadmin2018-05-25 00:52:562020-01-17 10:08:28Results of May SJRA Board Meeting and Decision to Temporarily Lower the Level of Lake Conroe
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?
Results of May SJRA Board Meeting and Decision to Temporarily Lower the Level of Lake Conroe
At its May Board meeting, the San Jacinto River Authority (SJRA) chose not to reconsider its April decision to lower the level of Lake Conroe temporarily at the peak of hurricane season. The board also chose not to put reconsideration of the resolution on its agenda for next month. This now puts the decision about whether to lower Lake Conroe temporarily into the hands of the City of Houston and the Texas Council on Environmental Quality (TCEQ).
Protest by Lake Conroe Association
The Lake Conroe Association protested last month’s board resolution to temporarily lower the level of Lake Conroe by up to two feet in September. The resolution was intended to help protect Lake Houston area residents from flooding until other mitigation measures, such as dredging, can be implemented. The Governor specifically directed the SJRA to make such protection part of its mission.
However, the president of the Lake Conroe Association (LCA), Mike Bleier, urged the board to reconsider its decision and was given unlimited time to present his case. Bleier spoke for more than half an hour. Bleier’s main concerns were the potential impacts on recreation, home values and businesses around Lake Conroe. Several other members of the association spoke in support of reconsideration.
Kingwood Residents Speak in Favor of Lowering
More than a dozen Kingwood residents also attended the meeting. Four spoke in favor of letting the motion stand.
Guy Sconzo, former superintendent of the Humble Independent School District, thanked the board for its decision to lower the lake. Then he talked about the impact of flooding on Lake Houston area infrastructure. His talk addressed massive losses by the school district, Kingwood College, and more.
TxDoT hopes to repair damage to the I-69 bridge by September, more than a year after Harvey. In the meantime, residents endure massive traffic jams.
Robert Westover talked about a flooded retirement community where several elderly residents died due to injuries incurred during high-water rescues and related stress.
Amy Slaughter complemented the board for its decision to lower the lake and explained how it would help insure that people had time to rebuild while other flood mitigation measures were completed.
Dennis Albrecht, who owns homes on both Lake Houston and Lake Conroe also spoke. Albrecht compared the relative impacts of flooding and lower lake levels on home values. Albrecht pointed out that the value of his Lake Conroe home has increased steadily despite lower lake levels at times. He also pointed out the devastating impact of the flood on the value of his Lake Houston home. “There’s no comparison,” said Albrecht.
Many other Kingwood residents attended the meeting to support the SJRA Board’s decision.
When is a lowering not really a lowering?
Bleier said that his members would accept a one foot lowering, but not two. Several Kingwood residents pointed out that evaporation already typically reduces the level of the lake by more than a foot and a half during September. The LCA’s decision to accept a one-foot lowering was, therefore, actually no concession at all; they would likely give up nothing.
Dianne Lansden, co-chair of the Lake Houston Area Grass Roots flood prevention initiative, and I gave Bleier a tour of the devastation in Humble and Kingwood yesterday. After a two-hour tour, while professing to be sensitive to the needs of downstream residents, Bleier proceeded to tell us the concerns of upstream residents. Among them: his members might not be able to take their boats to lakefront restaurants. (Editorial comment: Spooky shades of Marie-Antoinette!)
Not All Lake Conroe Residents Support LCA
To be sure, not all Lake Conroe residents agree with Bleier. Hundreds of homes on Lake Conroe also flooded during Harvey and reportedly most of the owners also favor a temporary seasonal lowering of the lake level, according to SJRA Board Chairman Lloyd Tisdale.
Lake Lowering Could Still be Nixed
Despite the SJRA board’s decision this morning, Lake Conroe still may not be lowered. To take effect, both the City of Houston and the TCEQ must also agree to lower the lake. The City owns two thirds of the water in the lake. The TCEQ must decide whether any lowering will count as an emergency release or be deducted from the City’s draw rights. If not considered an emergency release, the City may not support the decision to lower the lake.
Uncertainty Surrounding Weather Outlook
Some forecasters are beginning to worry about a possible drought. As of May 22, Drought.gov pointed out that abnormal dryness is currently affecting approximately 13,612,000 people in Texas, which is about 54% of the state’s population.
However, NOAA issued an outlook saying that 2018 will be a slightly above average hurricane season.
And, Thursday night, the National Hurricane Center predicted a 90% chance of tropical development in the Gulf this weekend. That system could dump up to ten inches of rain on neighboring Louisiana and other gulf states.
How a 10-Inch Rain Could Affect Kingwood
If we got ten inches of rain from a storm, such as the one entering the Gulf this weekend, that could constitute a 50-year rain at a time when the river is clogged with sand. That could produce a higher-than-normal flood for that amount of rainfall, and re-flood parts of Kingwood and Humble before dredging could even begin.
Personal Recommendation
Personally, I favor lowering the level of the lake. The actual amount of manual lowering, assuming this is an average year, would be only 4.8 inches. Even in the depths of the 2011 drought, the loss of 4.8 inches would have not have been disastrous.
There’s little chance, despite the hyperbolic rhetoric from LCA that 4.8 inches will destroy the Lake Conroe area. And it could help protect the Lake Houston area from another disaster.
In fact, in eight of the last 18 years, Lake Conroe has lost more than two feet of water due to evaporation and the lake is still one of the state’s most desirable destinations for tourists.
LCA Vows to Escalate the Fight
LCA has vowed to press its fight with the City and TCEQ and claims to have enough political support lined up to kill the proposal to lower Lake Conroe temporarily.
So get involved. Urge the TCEQ, Mayor and City Council to TEMPORARILY lower Lake Conroe until other mitigation measures, such as dredging, take effect.
Posted on 5/25/18 by Bob Rehak
269 Days since Hurricane Harvey
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