FEMA has agreed to dredge another million cubic yards from the the area near the San Jacinto West Fork Mouth Bar. A report produced for the City of Houston by Tetra Tech helped convince FEMA. The report relied on sonar, LIDAR, and core sample data to estimate the total volume of sand deposited by Hurricane Harvey in that area: approximately 1.4 million cubic yards.
Those close to the project have discussed several strategies to date.
The Corps’ initial strategy: Dredge upstream from the mouth bar. They said 1D modeling showed that would accelerate water flowing into mouth bar and give it the velocity needed to push sand from the mouth bar farther out into the lake.
Another strategy: dredge downstream from the mouth bar and let the river push the mouth bar into the dredged area.
A third strategy: reconnect the river and the lake with a narrow channel that accelerated the flow of water and carried suspended sediment out into the broader lake south of the 1960 bridge.
2019 Tetra Tech Report
Stephen Costello, the City’s flood czar, says that new survey and modeling work has yet to be completed. That will ultimately determine where new dredging happens. However, he also added that consulting Tetra Tech’s exhibits would help provide clues as to where dredging might be most effective, based on knowledge accumulated to date.
The first chart in Appendix A showed the coring locations and transects (survey lines) of the lake’s bottom profile.The second chart shows what they foundin various coring locations.The feet indicate the thickness of the top layer.
Composition of the core samples provides clues as to what was laid down when. Sand (the yellow dots) is generally laid down during floods which have the energy to transport the heavy particles. However, clay and silt (the green and blue dots) are smaller. So they tend to drop out of suspension when water is calmer.
Finding sand above silt in a core sample indicates that a storm like Harvey likely laid down the sand.
The third chart is the most crucial. It’s a difference map that shows areas of deposition and scour pre- and post-Harvey. This shows two things: where most sediment fell out of suspension and where the main flow of the river tried to churn a path through the mounting muck.
From the difference map above, you can see that the river tried to scour its way through the sediment along a path from LH-16 to LH-21 to LH-23. You can see another area of scour to the far right from LH-15 to LH-25 to LH-26.
Where River Flowed Before Lake Was Impounded
Interestingly, the area of scour to the left follows the river’s relic channel.
San Jacinto River map before Lake Houston was impounded
Note how the West Fork hugged what is now Atascocita Point – the thumb of high land that sticks up in the Tetra Tech illustrations.
Harnessing Natural Energy of the River
From the third and fourth illustrations above, one might conclude that excavating a channel near Atascocita Point represents the best way to harness the natural energy of the river. That’s the shortest channel where scour is deepest.
Given the million cubic yard limit, that path also represents a chance to dig the deepest, widest channel possible within the budget. When technicians compiled the difference map above, most of that path was already at or below its 2011 level.
500,000 square-yard path outlined in yellow would let dredgers excavate six feet. Average bottom depth is already 5.5 feet in that area.
Following that path also lets you funnel future sediment through the FM1960 causeway and disperse it out into the wider, deeper lake.
Before the additional dredging can begin, several things must happen.
Completion of a new survey
Model different scenarios
Identify best strategy
Locate suitable placement area
Compile scope of work
Bid job
Mobilize
Based on past experience, that could take months to a year or more. It took 13 months after Harvey for the Corps to put equipment in the water for its Emergency West Fork Dredging Project. However, we don’t have as many unknowns this time.
Posted by Bob Rehak on 9/5/2020
1103 Days since Hurricane Harvey
https://i0.wp.com/reduceflooding.com/wp-content/uploads/2020/09/Tetra-Tech-Study_Page_26.jpg?fit=2550%2C1650&ssl=116502550adminadmin2020-09-05 15:39:592020-09-05 15:53:16Tetra Tech Study Provides Clues To Possible Mouth Bar Dredging Strategies
Harris County Flood Control District (HCFCD) and its contractors met today with representatives of Kings Forest, the Bear Branch Trail Association and Kingwood Service Association to discuss the next phase of the Ben’s Branch clean out. On the south, the project lies entirely within the Creekwood Nature Area between Kingwood High School and the old H-E-B shopping center. Rocky Woods Drive forms the northern extent of the project. This will extend northward the work already completed south of Kingwood Drive.
Project extent outlined in red. Kingwood High School is at bottom center; Town Center on right; Kings Forest on left and Bear Branch at top of frame.
Maintenance Objective: Restore Conveyance
The objective: to restore conveyance of Ben’s Branch and reduce potential for flooding in Kings Forest, Bear Branch, the Kingwood High School, and Kingwood Town Center.
The ground these men are standing on is all deposited sediment that needs removal to restore conveyance. The original channel bank is the higher slope behind them. The other side has a similar problem.
Sediment has restricted the flow of the channel gradually during the last three decades. It now contributes to flooding.
Tucked into the tree line on either side of Bens Branch, you can see the maintenance roads that formed the top of the original banks.
During Harvey, many homes on both sides of the stream flooded. Many also flooded again during Imelda.
Walking along the creek today, the first thing one notices is a craggy channel with sides that seem to have slumped into the stream. Flood control surveys, however, show that is not the case. The channel filled with sediment. Then the stream eroded down again through the accumulated sediment.
Continual cycles of deposition and erosion have clogged, deformed and narrowed the creek.
Approximately 15,000 Cubic Yards of Sediment To Be Removed
Getting the channel back to its original state will require removal of approximately 15,000 cubic yards of sediment. However, engineers have not yet determined the exact number.
The scope of work will include replacement of damaged drain pipes that carry water to the ditch.
The job is still in its planning stages. Actual dirt work should begin sometime in October.
Funded with Help from USDA NRCS
A grant from the USDA Natural Resources Conservation Service (NRCS) will help HCFCD fund the project. Contractors will haul the excavated dirt to nearby TCEQ-approved landfill sites outside of the .02% annual chance (500-year) flood plain.
Looking north. The project will NOT extend into the natural portion of Ben’s Branch at the top of the frame, near Rocky Woods Drive.It will affect only the man-made portion of the channel.
Downstream, the project will stop at Kingwood Drive. Note below how the channel under the Kingwood Drive bridge is virtually twice as large as the channel in the foreground.
Looking south over Ben’s Branch toward Kingwood Drive and the portion of Ben’s Branch restored earlier this year. Note how constricted the channel in the foreground is.
When complete, this project should make the channel north of Kingwood Drive as wide as it is south of Kingwood Drive. It’s all about getting the channel back to its designed carrying capacity.
An exact timetable for the project is not yet available, but it will take several months.
Posted by Bob Rehak on 9/4/2020
1102 Days after Hurricane Harvey
https://i0.wp.com/reduceflooding.com/wp-content/uploads/2020/09/BB-Start-Stop.jpg?fit=1914%2C1404&ssl=114041914adminadmin2020-09-04 18:31:132020-09-04 18:43:03HCFCD to Begin Next Phase of Ben’s Branch Clean Out in October
The graphic above outlines the major steps in the buyout process. The linked video provides more detail.
The Forest Cove Townhomes illustrate some of the problems encountered along that timeline.
Exceptional Sense of Community Makes People Want to Stay
According to Jennifer Parks who lived on Timberline, her townhome flooded eight times in five years. Despite that, she, like most who lived there, loved the secluded neighborhood. It was close to nature, beautiful and quiet. Neighbors looked out for each other. They bonded over backyard barbecues. They enjoyed an exceptional sense of “community.” Then came Harvey. It made the homes uninhabitable. People immediately scattered to find new housing.
Dealing with Chaos and Confusion
When the initial shock wore off, they began exploring options. Could the homes be repaired? Would CenterPoint restore power? Could the sand-filled storm drains and streets be cleared? Which way was the herd moving? One family could fix its home; but if the other neighbors in a building didn’t, their investment would be ruined. This is important because in Harris County, buyouts are voluntary. One holdout in a building with a dozen units could undermine others.
Will buyouts create a checkerboard pattern that creates maintenance issues or will there be full public ownership of an area?
Can HCFCD secure grants to fund all interested sellers?
Of the 154,170 homes flooded in the county during Harvey, only 4,000 property owners volunteered for buyouts and of those, only 1,100 were eligible (0.71% of all flooded homes).
Buyouts reduce flood damages in areas where structural projects (i.e. channel modifications or stormwater detention basins) are not cost-effective and/or beneficial.
After identifying and qualifying candidates comes the difficult process of securing grant funding. That usually takes about 8-18 months. It’s a multi-tiered process. Austin collects and screens grant applications for Washington. Assuming Washington approves, money then flows back through Austin.
Finally, with money in hand, HCFCD must appraise property to confirm its value (which can be pre-flood). HCFCD must then reach an agreement to buy the property and determine relocation benefits. Of the initial 1,100, 349 are in the closing phase now and 560 have already closed.
A little fixer-upper
HCFCD says that roughly a half dozen homes remain to be bought out. Those remain “problem” cases. In one, an out-of-state investor bought property at auction AFTER Harvey. But terms of HCFCD’s Harzard Mitigation Grant specify that the grant cannot be used in cases like that. Otherwise people would buy up flooded properties and resell them to FEMA at pre-flood valuations.
In other cases, sometimes people have walked away from flooded properties leaving lenders holding the bag. That puts property in legal limbo. No one has authority to sell without going through a foreclosure process.
Such problem properties can delay demolition.
Public-Policy Concern
In multi-family housing (such as the Forest Cove Townhomes), EVERY family in a building must have completed a buyout before the building can be demolished.
The thoughts expressed in this post represent opinions on matters of public concern and safety. They are protected by the First Amendment of the US Constitution and the Anti-SLAPP Statute of the Great State of Texas.
https://i0.wp.com/reduceflooding.com/wp-content/uploads/2020/09/20200902-RJR_0194.jpg?fit=1200%2C800&ssl=18001200adminadmin2020-09-03 16:54:492020-09-03 17:00:05Why Buyouts Take So Long
Tetra Tech Study Provides Clues To Possible Mouth Bar Dredging Strategies
FEMA has agreed to dredge another million cubic yards from the the area near the San Jacinto West Fork Mouth Bar. A report produced for the City of Houston by Tetra Tech helped convince FEMA. The report relied on sonar, LIDAR, and core sample data to estimate the total volume of sand deposited by Hurricane Harvey in that area: approximately 1.4 million cubic yards.
Need for Ruthless Efficiency
While another million cubic yards may sound like a lot, the area is huge. Dredging the whole 4.3 million square yard area would add only about 8 inches of water depth and leave an underwater mesa between the West Fork and the Lake. According to local geologists Tim Garfield and RD Kissling, who have studied the problem extensively, that would create a sediment trap that accelerates accumulation of sand from future storms.
So, what to do?
Three Strategies Discussed to Date
Those close to the project have discussed several strategies to date.
2019 Tetra Tech Report
Stephen Costello, the City’s flood czar, says that new survey and modeling work has yet to be completed. That will ultimately determine where new dredging happens. However, he also added that consulting Tetra Tech’s exhibits would help provide clues as to where dredging might be most effective, based on knowledge accumulated to date.
Composition of the core samples provides clues as to what was laid down when. Sand (the yellow dots) is generally laid down during floods which have the energy to transport the heavy particles. However, clay and silt (the green and blue dots) are smaller. So they tend to drop out of suspension when water is calmer.
From the difference map above, you can see that the river tried to scour its way through the sediment along a path from LH-16 to LH-21 to LH-23. You can see another area of scour to the far right from LH-15 to LH-25 to LH-26.
Where River Flowed Before Lake Was Impounded
Interestingly, the area of scour to the left follows the river’s relic channel.
Note how the West Fork hugged what is now Atascocita Point – the thumb of high land that sticks up in the Tetra Tech illustrations.
Harnessing Natural Energy of the River
From the third and fourth illustrations above, one might conclude that excavating a channel near Atascocita Point represents the best way to harness the natural energy of the river. That’s the shortest channel where scour is deepest.
Given the million cubic yard limit, that path also represents a chance to dig the deepest, widest channel possible within the budget. When technicians compiled the difference map above, most of that path was already at or below its 2011 level.
Following that path also lets you funnel future sediment through the FM1960 causeway and disperse it out into the wider, deeper lake.
Next Steps and Timing
At this point, we don’t know what Imelda did to this area. Imelda struck shortly after the Army Corps completed its post-dredging survey in this area last year.
Before the additional dredging can begin, several things must happen.
Based on past experience, that could take months to a year or more. It took 13 months after Harvey for the Corps to put equipment in the water for its Emergency West Fork Dredging Project. However, we don’t have as many unknowns this time.
Posted by Bob Rehak on 9/5/2020
1103 Days since Hurricane Harvey
HCFCD to Begin Next Phase of Ben’s Branch Clean Out in October
Harris County Flood Control District (HCFCD) and its contractors met today with representatives of Kings Forest, the Bear Branch Trail Association and Kingwood Service Association to discuss the next phase of the Ben’s Branch clean out. On the south, the project lies entirely within the Creekwood Nature Area between Kingwood High School and the old H-E-B shopping center. Rocky Woods Drive forms the northern extent of the project. This will extend northward the work already completed south of Kingwood Drive.
Maintenance Objective: Restore Conveyance
The objective: to restore conveyance of Ben’s Branch and reduce potential for flooding in Kings Forest, Bear Branch, the Kingwood High School, and Kingwood Town Center.
Sediment has restricted the flow of the channel gradually during the last three decades. It now contributes to flooding.
During Harvey, many homes on both sides of the stream flooded. Many also flooded again during Imelda.
Walking along the creek today, the first thing one notices is a craggy channel with sides that seem to have slumped into the stream. Flood control surveys, however, show that is not the case. The channel filled with sediment. Then the stream eroded down again through the accumulated sediment.
Approximately 15,000 Cubic Yards of Sediment To Be Removed
Getting the channel back to its original state will require removal of approximately 15,000 cubic yards of sediment. However, engineers have not yet determined the exact number.
The scope of work will include replacement of damaged drain pipes that carry water to the ditch.
The job is still in its planning stages. Actual dirt work should begin sometime in October.
Funded with Help from USDA NRCS
A grant from the USDA Natural Resources Conservation Service (NRCS) will help HCFCD fund the project. Contractors will haul the excavated dirt to nearby TCEQ-approved landfill sites outside of the .02% annual chance (500-year) flood plain.
Downstream, the project will stop at Kingwood Drive. Note below how the channel under the Kingwood Drive bridge is virtually twice as large as the channel in the foreground.
When complete, this project should make the channel north of Kingwood Drive as wide as it is south of Kingwood Drive. It’s all about getting the channel back to its designed carrying capacity.
An exact timetable for the project is not yet available, but it will take several months.
Posted by Bob Rehak on 9/4/2020
1102 Days after Hurricane Harvey
Why Buyouts Take So Long
In the private sector, it can take just days to buy a home. In the public sector, it can take years. Here’s why buyouts take so long.
Major Steps in Process
The graphic above outlines the major steps in the buyout process. The linked video provides more detail.
The Forest Cove Townhomes illustrate some of the problems encountered along that timeline.
Exceptional Sense of Community Makes People Want to Stay
According to Jennifer Parks who lived on Timberline, her townhome flooded eight times in five years. Despite that, she, like most who lived there, loved the secluded neighborhood. It was close to nature, beautiful and quiet. Neighbors looked out for each other. They bonded over backyard barbecues. They enjoyed an exceptional sense of “community.” Then came Harvey. It made the homes uninhabitable. People immediately scattered to find new housing.
Dealing with Chaos and Confusion
When the initial shock wore off, they began exploring options. Could the homes be repaired? Would CenterPoint restore power? Could the sand-filled storm drains and streets be cleared? Which way was the herd moving? One family could fix its home; but if the other neighbors in a building didn’t, their investment would be ruined. This is important because in Harris County, buyouts are voluntary. One holdout in a building with a dozen units could undermine others.
Meanwhile, HCFCD assessed damage county wide to identify eligible properties. Harvey damaged so many, that it took nine months for the flood control district to even issue its final report on the storm.
Assessment Necessary; Not All Properties Eligible
Identifying eligible properties requires looking at them from several different perspectives. For instance:
Of the 154,170 homes flooded in the county during Harvey, only 4,000 property owners volunteered for buyouts and of those, only 1,100 were eligible (0.71% of all flooded homes).
Qualifying for Buyout
To learn more about the HCFCD buyout process, see this document: Voluntary Buyout Guidance.
Buyout candidates were simply built in the wrong place, prior to the knowledge we have today.
HCFCD’s Home Buyout Program does not provide immediate flood recovery assistance – its primary function is to help prevent future flood damages.
To see where HCFCD is interested in buyouts, check this map of Buyout Areas, last updated in July.
Funding and Closing
After identifying and qualifying candidates comes the difficult process of securing grant funding. That usually takes about 8-18 months. It’s a multi-tiered process. Austin collects and screens grant applications for Washington. Assuming Washington approves, money then flows back through Austin.
Finally, with money in hand, HCFCD must appraise property to confirm its value (which can be pre-flood). HCFCD must then reach an agreement to buy the property and determine relocation benefits. Of the initial 1,100, 349 are in the closing phase now and 560 have already closed.
HCFCD says that roughly a half dozen homes remain to be bought out. Those remain “problem” cases. In one, an out-of-state investor bought property at auction AFTER Harvey. But terms of HCFCD’s Harzard Mitigation Grant specify that the grant cannot be used in cases like that. Otherwise people would buy up flooded properties and resell them to FEMA at pre-flood valuations.
In other cases, sometimes people have walked away from flooded properties leaving lenders holding the bag. That puts property in legal limbo. No one has authority to sell without going through a foreclosure process.
Such problem properties can delay demolition.
Public-Policy Concern
In multi-family housing (such as the Forest Cove Townhomes), EVERY family in a building must have completed a buyout before the building can be demolished.
The last point raises a public-policy concern. We are now starting YEAR FOUR AFTER HARVEY! Units in six Forest Cove Townhome Buildings still need to be purchased. Those buildings look like the one above and drag down property values in an entire community.
It’s one thing to repair properties built BEFORE flood problems became apparent; another to permit new construction AFTER. And developers keep throwing up new units faster than flooded ones can be bought out.
For More Information
For general information about HCFCD’s buyout program, see this video.
For the portal to the buyout section of HCFCD’s website, click here.
Posted by Bob Rehak on 9/3/2020
1101 Days after Hurricane Harvey
The thoughts expressed in this post represent opinions on matters of public concern and safety. They are protected by the First Amendment of the US Constitution and the Anti-SLAPP Statute of the Great State of Texas.