Two top geologists, now retired from one of the world’s leading oil companies, have developed a reliable and repeatable way to estimate the volume of sediment deposited in the West Fork mouth bar by Hurricane Harvey. They calculate that Harvey deposited at least 268,000 cubic yards of sediment in that area alone.
Stream mouth bar where the West Fork of the San Jacinto meets Lake Houston creates a sediment dam. It backs water up throughout the entire Hunble/Kingwood area during floods. Water must flow uphill approximately 40 feet to get over this hump.
No Pre-Harvey Measurements Hampered Dredging Program Approval
According to the Army Corps of Engineers and Stephen Costello, the City of Houston’s Chief Resiliency Officer, the lack of a reliable way to estimate the volume due to Harvey was a major stumbling block in funding the dredging effort. The City, FEMA and the Corps have reportedly been arguing about this for at least nine months. The issue has to do with the Stafford Act, FEMA’s enabling legislation. The Stafford Act prohibits FEMA from spending disaster relief funds on cleanup not related to the disaster in question.
Because the City of Houston had no reliable sedimentation survey taken immediately before Harvey, calculating the volume due to Harvey became problematic.
How a Mouth Bar Forms
A mouth bar forms at the mouth of a river where it meets still water (in our case, Lake Houston). As moving water encounters the still water, coarser sediment like sand is deposited. It begins building up and up until sand bars emerge above the surface.
The Insight that Led to a Reliable Way to Estimate Volume
Mainly sand comprises the mouth bar; sand moves only during major floods. The sand above water can only be deposited when floodwater is much higher than the top of the bar. That insight became the key to unlocking the mystery of how much sand Harvey deposited.
RD Kissling and Tim Garfield reasoned that if they could calculate the percentage of above-water growth during Harvey from satellite images, they could then apply that same percentage to the total volume of sand deposited below water between 2011 and 2018.
Calculation for visible “above water” growth of the mouth bar during Harvey.
But to determine the total volume added between 2011 and 2018, they first had to:
Digitize the difference map
Create polygons around the different colors
Calculate the area of the polygons
Multiply area times thickness for each
Add up the results.
Digitized difference map shows boundaries between areas of different thickness.Multiplying the area of the polygons times the thickness from the difference map yielded volumes for each area.
Tetra Tech Delays May Push Project Past Deadline
According to Costello, the City hired a company called Tetra Tech in early January to calculate the Harvey volume. He said they would do that by harvesting and analyzing core samples. The City expected the results of their study by the end of January. But when I talked to Costello in mid-February, he said Tetra Tech still had not finished harvesting core samples and that he wasn’t expecting results of their analysis until the end of February or early March.
Pro Bono Effort Might Save Taxpayers $18 Million
Kissling and Garfield developed their methodology and donated their time to help save money and to get the mouth bar removed before the start of the next hurricane season. If the current dredging program can be extended before the end of April, taxpayers could save the cost of recommissioning all the equipment. That could total $18 million.
The two geologists reasoned that their methodology would give all parties a basis for allowing the dredging to continue. Then, if Tetra Tech came back later with a different figure, the contract could be adjusted up or down.
I am presenting it here to start a dialog that leads to additional dredging without incurring the cost of remobilizing the massive amount of equipment now on the river.
Estimate is Only a Fraction of What Needs to Be Removed
Kissling and Garfield emphasize that this is just a start. Even if all 268,000 cubic yards were removed, the river would still be up to 20 feet shallower than at the time of impoundment. They hope this leads to a broader discussion of additional dredging which could be financed through other sources, such as the county flood bond and Proposition A. Finally, they point out the need for maintenance dredging after major floods to keep the sediment buildup at sub-critical levels.
Said Garfield, “We are confident this estimate of Harvey-specific sedimentation on the mouth bar is reasonable and should be used to support FEMA funded continuation of dredging. However, removing that volume alone still won’t solve the problem, because the mouth bar is much bigger than that and it remains the largest restriction of flow conveyance to the lake.”
Garfield continued:
“At a minimum, to restore flow and reduce flood risk, a 300-400’ wide channel 20’-25’ deep needs to be dredged to connect the river from the upstream dredging now nearing completion, through the mouth bar, to the FM1960 bridge. That is at least 5 or 6 times as much sediment as our estimate of what FEMA can fund, but without that the recent dredging alone has not solved the flood risk problem in our area.”
Posted by Bob Rehak on February 24, 2019 with help from R.D. Kissling and Tim Garfield
544 Days after Hurricane Harvey
https://i0.wp.com/reduceflooding.com/wp-content/uploads/2019/01/Harvey-SanJac_437-cropped-e1775595968700.jpg?fit=1100%2C456&ssl=14561100adminadmin2019-02-23 22:18:462019-02-24 18:58:59Local Geologists Develop Way to Estimate Volume of Sediment in Mouth Bar Due to Harvey
Houston City Council Member Dave Martin issued an alert on Feb. 22, 2019, stating that the Coastal Water Authority will soon lower the level of Lake Houston for dam repairs. The City is warning all property and boat owners to take appropriate action.
Lake Houston has an extensive overflow spillway system.
First Step in 18 Month Process
The Coastal Water Authority plans to lower Lake Houston by 12 inches starting Monday, February 25, for scheduled maintenance on the dam. This is the first step in an 18-month project to improve the dam’s stability.
The Lake Houston Dam during Hurricane Harvey Flooding. According to Harris County Flood Control’s final report on Harvey, An estimated discharge of 425,000 cfs or 5.0 times the average flow of Niagara Falls occurred at the peak flow over the Lake Houston spillway. This amount of flow would fill NRG Stadium in 3.5 minutes.
Scope of Dam Repairs
Property owners should secure property along the shoreline before the lowering begins. The planned maintenance includes rehabilitation of two weir structures on the downstream portion of the dam.
This preliminary work includes performing inspections and measurements which is the purpose for lowering the level of the lake on Monday. Once preliminary work is completed, the lake will be allowed to refill naturally. The lower lake level is expected to last approximately one week.
Posted by Bob Rehak on 2/23/2019
543 Days since Hurricane Harvey
https://i0.wp.com/reduceflooding.com/wp-content/uploads/2019/02/LakeHoustonDamDuringHarvey.jpg?fit=1500%2C968&ssl=19681500adminadmin2019-02-23 15:35:372019-02-23 15:35:43City to Lower Lake Houston for Dam Repairs
As we approach the 18 month anniversary of Harvey next week, I am struck by how little we have actually accomplished in terms of flood mitigation. And as the election season heats up, I am also forced to wonder whether changes at City Hall could accelerate the effort.
Looking Back at the Effort to Date
After Harvey, it took several months to analyze the causes of flooding, identify possible solutions, and build political consensus around them. We did that. As a community, we identified four major improvements that we needed: additional flood gates for Lake Houston, additional dredging (through the mouth bar), additional upstream detention, and ditch repairs.
We actually got Phase 1 of the dredging started. And then…nothing. We’ve had six months of virtually nothing. That leads me to wonder whether people were simply telling us what we wanted to hear. Worse, some of the hard won gains seem to be drifting away. For instance…
Change in Direction at County Level
Instead of attacking projects on a worst-first basis, the new county judge has asked the flood control district to reorder priorities for project implementation. Next week, the judge and commissioners will review a protocol that favors neighborhoods with low to moderate income and gives no weight whatsoever to massive infrastructure damage, such as Kingwood sustained. The loss of:
An interstate highway bridge for ten months.
A high school and three other school district facilities totaling $100,000,000
Two-thirds of the buildings at Kingwood College costing $60 million and taking 18 months to repair.
100% of the businesses in two major commercial centers (Kings Harbor and Town Center)
Most of a third commercial district (US 59) destroyed up to FM1960
Damage to 3,300 businesses that employed a large percentage of the local population – 44% of all the business in the Lake Houston Area Chamber of Commerce
Memorial Hermann’s new hospital facility that was days away from opening
Disruption of northbound rail traffic out of the City of Houston for months
Nursing homes and senior assisted living devastated
…all that suddenly counts for nothing now…unless the prevailing political winds change.
Flooding is a public safety issue. We wouldn’t allow the county to say, “affluent neighborhoods don’t deserve police protection for the next 10-15 years.” When it comes to safety, neither rich, nor poor, should be disadvantaged. But that’s our next battle. I digress.
What have we gotten? Approval of a $2+ million study of the entire river basin that will take at least a year to complete. Astoundingly, approving the grant took almost a year in itself.
At what point do you say, “The system is no longer working for me. It’s time for officials to deliver. We need to hold them accountable”? When do you say, “It’s time to bet on someone new to get results”?
It’s Time to Deliver or Else
We may not be there yet. But inevitably, election season raises these questions. One thing is certain. If incumbents don’t show results between now and November, I’m voting for change. I’m not going to cut people slack for four more years. The risk is too high.
Kingwood Has the Power to Change the Outcome
In that regard, someone reminded me today about how close the last mayoral campaign actually was. And how Kingwood could have easily changed the outcome.
Only 4,000 votes City-wide determined the winner of the last election. 28,000 registered Kingwood voters did not vote.
I’m not saying Turner has ignored Kingwood. The cleanup was impressive. But we’ve had several opportunities to jumpstart mitigation projects such as additional gates and dredging that have sputtered since then. And the City is trying to turn over ditch maintenance to the County, whose marching orders suddenly favor low-to-moderate income.
Turner has several months to turn things around. If he can’t, I suspect a much higher percentage of Kingwood voters will turn out in November. And we clearly have the capacity to change the outcome if we choose.
Posted by Bob Rehak on 2/23/2019
543 Days after Hurricane Harvey
https://i0.wp.com/reduceflooding.com/wp-content/uploads/2019/02/I-votecd.jpg?fit=6016%2C4016&ssl=140166016adminadmin2019-02-22 21:57:172019-02-22 21:57:23Sometimes the Difference Between Winning and Losing is Showing Up
Local Geologists Develop Way to Estimate Volume of Sediment in Mouth Bar Due to Harvey
Two top geologists, now retired from one of the world’s leading oil companies, have developed a reliable and repeatable way to estimate the volume of sediment deposited in the West Fork mouth bar by Hurricane Harvey. They calculate that Harvey deposited at least 268,000 cubic yards of sediment in that area alone.
No Pre-Harvey Measurements Hampered Dredging Program Approval
According to the Army Corps of Engineers and Stephen Costello, the City of Houston’s Chief Resiliency Officer, the lack of a reliable way to estimate the volume due to Harvey was a major stumbling block in funding the dredging effort. The City, FEMA and the Corps have reportedly been arguing about this for at least nine months. The issue has to do with the Stafford Act, FEMA’s enabling legislation. The Stafford Act prohibits FEMA from spending disaster relief funds on cleanup not related to the disaster in question.
Because the City of Houston had no reliable sedimentation survey taken immediately before Harvey, calculating the volume due to Harvey became problematic.
How a Mouth Bar Forms
A mouth bar forms at the mouth of a river where it meets still water (in our case, Lake Houston). As moving water encounters the still water, coarser sediment like sand is deposited. It begins building up and up until sand bars emerge above the surface.
The Insight that Led to a Reliable Way to Estimate Volume
Mainly sand comprises the mouth bar; sand moves only during major floods. The sand above water can only be deposited when floodwater is much higher than the top of the bar. That insight became the key to unlocking the mystery of how much sand Harvey deposited.
Everyone could see from satellite images how much the above-water portion of the bar had grown. But there was no way to tell how much the bar grew below water. Then in October of 2018, Costello presented a “difference map” that showed the sediment buildup between 2011 and 2018.
RD Kissling and Tim Garfield reasoned that if they could calculate the percentage of above-water growth during Harvey from satellite images, they could then apply that same percentage to the total volume of sand deposited below water between 2011 and 2018.
But to determine the total volume added between 2011 and 2018, they first had to:
Tetra Tech Delays May Push Project Past Deadline
According to Costello, the City hired a company called Tetra Tech in early January to calculate the Harvey volume. He said they would do that by harvesting and analyzing core samples. The City expected the results of their study by the end of January. But when I talked to Costello in mid-February, he said Tetra Tech still had not finished harvesting core samples and that he wasn’t expecting results of their analysis until the end of February or early March.
Pro Bono Effort Might Save Taxpayers $18 Million
Kissling and Garfield developed their methodology and donated their time to help save money and to get the mouth bar removed before the start of the next hurricane season. If the current dredging program can be extended before the end of April, taxpayers could save the cost of recommissioning all the equipment. That could total $18 million.
The two geologists reasoned that their methodology would give all parties a basis for allowing the dredging to continue. Then, if Tetra Tech came back later with a different figure, the contract could be adjusted up or down.
Kissling and Garfield emphasize that their methods are conservative, reliable and repeatable. For peer review and public comment, this presentation shows how they arrived at their estimates in a step by step fashion.
I am presenting it here to start a dialog that leads to additional dredging without incurring the cost of remobilizing the massive amount of equipment now on the river.
Estimate is Only a Fraction of What Needs to Be Removed
Kissling and Garfield emphasize that this is just a start. Even if all 268,000 cubic yards were removed, the river would still be up to 20 feet shallower than at the time of impoundment. They hope this leads to a broader discussion of additional dredging which could be financed through other sources, such as the county flood bond and Proposition A. Finally, they point out the need for maintenance dredging after major floods to keep the sediment buildup at sub-critical levels.
Said Garfield, “We are confident this estimate of Harvey-specific sedimentation on the mouth bar is reasonable and should be used to support FEMA funded continuation of dredging. However, removing that volume alone still won’t solve the problem, because the mouth bar is much bigger than that and it remains the largest restriction of flow conveyance to the lake.”
Garfield continued:
Posted by Bob Rehak on February 24, 2019 with help from R.D. Kissling and Tim Garfield
544 Days after Hurricane Harvey
City to Lower Lake Houston for Dam Repairs
Houston City Council Member Dave Martin issued an alert on Feb. 22, 2019, stating that the Coastal Water Authority will soon lower the level of Lake Houston for dam repairs. The City is warning all property and boat owners to take appropriate action.
First Step in 18 Month Process
The Coastal Water Authority plans to lower Lake Houston by 12 inches starting Monday, February 25, for scheduled maintenance on the dam. This is the first step in an 18-month project to improve the dam’s stability.
Scope of Dam Repairs
Property owners should secure property along the shoreline before the lowering begins. The planned maintenance includes rehabilitation of two weir structures on the downstream portion of the dam.
This preliminary work includes performing inspections and measurements which is the purpose for lowering the level of the lake on Monday. Once preliminary work is completed, the lake will be allowed to refill naturally. The lower lake level is expected to last approximately one week.
Posted by Bob Rehak on 2/23/2019
543 Days since Hurricane Harvey
Sometimes the Difference Between Winning and Losing is Showing Up
As we approach the 18 month anniversary of Harvey next week, I am struck by how little we have actually accomplished in terms of flood mitigation. And as the election season heats up, I am also forced to wonder whether changes at City Hall could accelerate the effort.
Looking Back at the Effort to Date
After Harvey, it took several months to analyze the causes of flooding, identify possible solutions, and build political consensus around them. We did that. As a community, we identified four major improvements that we needed: additional flood gates for Lake Houston, additional dredging (through the mouth bar), additional upstream detention, and ditch repairs.
We met with the Mayor who agreed and promised to deliver. We met met with the County Judge and the Flood Control District. They worked the community’s requests into the flood bond last August. Kingwood voters turned out in record numbers to support it. And we had five of the top eight precincts in the county in terms of turnout percentage.
…And Then Nothing
We actually got Phase 1 of the dredging started. And then…nothing. We’ve had six months of virtually nothing. That leads me to wonder whether people were simply telling us what we wanted to hear. Worse, some of the hard won gains seem to be drifting away. For instance…
Change in Direction at County Level
Instead of attacking projects on a worst-first basis, the new county judge has asked the flood control district to reorder priorities for project implementation. Next week, the judge and commissioners will review a protocol that favors neighborhoods with low to moderate income and gives no weight whatsoever to massive infrastructure damage, such as Kingwood sustained. The loss of:
…all that suddenly counts for nothing now…unless the prevailing political winds change.
Flooding is a public safety issue. We wouldn’t allow the county to say, “affluent neighborhoods don’t deserve police protection for the next 10-15 years.” When it comes to safety, neither rich, nor poor, should be disadvantaged. But that’s our next battle. I digress.
Meanwhile, Back at City Hall
Back to the City. Six months ago, after the “Everybody-but-Trump” meeting in Austin, we were told that we were close to a dredging solution to remove the mouth bar.
What have we gotten? Approval of a $2+ million study of the entire river basin that will take at least a year to complete. Astoundingly, approving the grant took almost a year in itself.
At what point do you say, “The system is no longer working for me. It’s time for officials to deliver. We need to hold them accountable”? When do you say, “It’s time to bet on someone new to get results”?
It’s Time to Deliver or Else
We may not be there yet. But inevitably, election season raises these questions. One thing is certain. If incumbents don’t show results between now and November, I’m voting for change. I’m not going to cut people slack for four more years. The risk is too high.
Kingwood Has the Power to Change the Outcome
In that regard, someone reminded me today about how close the last mayoral campaign actually was. And how Kingwood could have easily changed the outcome.
Turner beat King by about 4000 votes city wide in the runoff election of 2015. But 28,747 registered voters in Kingwood didn’t bother to vote – about three fourths of all those registered. That’s significant because King carried Kingwood by more than a 6 to 1 margin. Clearly, Kingwood could have swung the election to King had more people voted.
I’m not saying Turner has ignored Kingwood. The cleanup was impressive. But we’ve had several opportunities to jumpstart mitigation projects such as additional gates and dredging that have sputtered since then. And the City is trying to turn over ditch maintenance to the County, whose marching orders suddenly favor low-to-moderate income.
Posted by Bob Rehak on 2/23/2019
543 Days after Hurricane Harvey