The Texas Water Development Board (TWDB) and the federal Interagency Flood Risk Management (InFRM) team (composed of USGS, FEMA, the Army Corps, and National Weather Service) has enhanced their Flood Decision-Support Toolbox. The Toolbox is an interactive online application that provides maps and data that simulates the extent of flooding and shows historical flood extents. It can be used for analyzing potential scenarios, flood risk assessments, damage analysis, and more.
How It Works
Here’s how the Flood Decision-Support Toolbox works:
2. Observe current conditions OR select historical peak floods.
Historical peak floods at US59 and the West Fork. Note the increase in recent years, likely due to upstream development and/or climate.
3. Explore the flood map library by selecting a flood level (river stage)
4. In the “Buildings” Layer, select ALL or INUNDATED BUILDINGS ONLY
5. Note the damage estimates in the bottom right hand corner of the screen.
In the case of a simulated Harvey flood, near the gage at US59, 739 buildings would be inundated at an estimated total cost of $84,914,000.
But at 52.5 feet (the beginning of the “major” flood stage), 83 buildings would flood. Estimated total damage: $1,494,000.
The magic of this toolbox is that you can see exactly which buildings will flood at any given level.
What is your appetite for risk?
Potential Uses
The Flood Decision Support Toolbox also provides real-time data from USGS streamgages connected with flood inundation models to interactively display a range of flood conditions at streamgage locations. The result is a dynamic tool for flood risk assessment that enables planners, emergency responders, and the public to visually understand a flood’s extent and depth over the land surface.
TWDB worked closely with USGS to incorporate building footprints on Texas maps. The Toolbox can now display potential damage to structures within the range of the USGS gages. This will give users the ability to estimate the economic impacts of different flood events on their communities and property. The TWDB has also provided building footprints outside of the current gage ranges in preparation for future mapping updates.
That can help guide:
Rescue efforts
Evacuations and evacuation routes
Mitigation decisions
Property purchases and investment decisions
Risk estimates
New construction and development
Permitting decisions
The site displays flood scenarios that range from minor to major flood events. New updates let users save and share inundation maps with different data layers through a unique URL.
Collaborative Effort
“This collaborative effort,” said Jeff Walker, Executive Administrator of the TWDB. “provides Texas-specific data that will help communities understand their local flood risks and make cost-effective mitigation decisions.”
The InFRM team was formed in 2014 and launched the Flood Decision Support Toolbox in 2019.
The TWDB is the state agency charged with collecting and disseminating water-related data, assisting with regional water and flood planning, and preparing the state water and flood plans.
Posted by Bob Rehak based on information provided by TWDB
1235 Days since Hurricane Harvey
https://i0.wp.com/reduceflooding.com/wp-content/uploads/2021/01/Simulated-Harvey.jpg?fit=1200%2C568&ssl=15681200adminadmin2021-01-15 06:33:322021-01-15 06:38:11Flood Decision-Support Toolbox Enhanced by State, Federal Team
Welcome to Flood Notes. So much has been happening lately on the flood front, it’s hard to keep up with it all. So this post will be a digest of things that affect flooding on the local, state and national fronts.
Humble ISD North Transportation Center Construction Update
We have had ideal construction weather in the last month and contractors at HISD’s north transportation center on Ford Road in Porter had made a lot of progress. They have completed the detention pond. More than half the remaining site is covered with concrete parking lots. And it looks as if the foundation for a building has also been poured. Humble ISD anticipates shorter routes for half the district will save taxpayers $2 million per year. The District hopes to open the Center in 2021.
Humble ISD North Transportation Center 11.7 acre site. Photo taken 11/07/2020.
Colony Ridge
This massive development in Liberty County has turned into the world’s largest trailer park. The developer of Colony Ridge keeps expanding at a record clip. Perhaps he’s anticipating a sales boom when the Grand Parkway creates better access. At the moment, he appears to be cutting and burning another 3000 acres. Nearby Plum Grove residents have complained about the smoke.
Colony Ridge expansion. Photo taken 11/1/2020.Colony Ridge expansion. Photo taken 11/1/2020.Colony Ridge expansion. Photo taken 11/1/2020 after a long period without rain. Notice the wet areas covered up with fill. Wetlands once criss-crossed this area.
Chlorine Creek
Plum Grove residents who live next to Colony Ridge also report the strong smell of sewage and chlorine coming from a new sewage treatment facility along Maple Branch a quarter to a half mile away. TCEQ fined the company that provides these services not long ago for the illegal discharge of 48,000 gallons of raw sewage into the same creek from a lift station.
Sewage treatment plant creating strong odors for Plum Grove residents as well as those in Colony Ridge itself.Wastewater from this plant is apparently discharged into Maple Branch just inside the tree line at the top of the frame.The discharged water has a heavy chlorine smell to it. All life in the creek seems to have died according to residents. That includes, fish, tadpoles, minnows, etc.
Michael Shrader, a Plum Grove resident who lives adjacent to Maple Branch, has affectionately renamed it Chlorine Creek.
HUD Approves New GLO Plans for Disaster Funding
On 11/4, Texas Land Commissioner George P. Bush announced that the US Department of Housing and Urban Development (HUD) approved two state action plans detailing the distribution and eligible uses of more than $285 million. The Community Development Block Grant Disaster Recovery (CDBG-DR) funds will assist in long-term recovery efforts following severe flooding in 2018 and 2019 in South and Southeast Texas. To view the action plans, please visit recovery.texas.gov/action-plans. To expedite the recovery process, the GLO will directly administer and oversee the funds.
TWDB Accepting FEMA Flood Mitigation Assistance Grant Requests
This one affects government officials in Cities, Counties, Special Districts, etc.. FEMA’s Flood Mitigation Assistance (FMA) grant program provides federal funding to help communities pay for cost-effective ways to reduce or eliminate the long-term risk of flood damage to flood prone structures that are insured under the National Flood Insurance Program. FMA program funds can be used for planning and projects. The deadline to apply to the Texas Water Development Board is December 1, 2020. For more information, please visit www.twdb.texas.gov/flood/grant/fma.asp.
FEMA Program Helps Enforce Building Codes, Floodplain Management
FEMA announced the release of a policy to provide communities with resources to enforce building codes and floodplain management following a major disaster declaration. The “Building Code and Floodplain Management Administration and Enforcement” policy can provide funding for the first 180 days following a major declaration for:
Costs associated with extra hires or contracted support
Reviewing and processing building permits and occupancy and compliance certificates
Conducting building inspections and initial substantial damage field surveys
Reviewing disaster-related development in the floodplain
Providing educational services to the public on floodplain requirements.
The policy is a result of the Disaster Recovery Reform Act of 2018, Section 1206. This policy applies to all major disaster declarations declared on or after August 1, 2017.
CBS aired a chilling story tonight about the floods brought by Hurricane Eta. The storm dumped up to 7 inches of rain on the Carolinas. It washed out roads and bridges. In fact, a reporter was standing on one bridge when pieces of it started to fall into the raging floodwater. Very dramatic footage if you missed it.
Eta nearly tied Gordon for the longest hurricane on record. Jeff Lindner, Harris County Meteorologist, says that had the storm lasted until tomorrow, it would have taken the longevity record.
Posted by Bob Rehak on 11/12/2020
1171 Days since 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.
https://i0.wp.com/reduceflooding.com/wp-content/uploads/2020/11/20201101-DJI_0009.jpg?fit=1200%2C900&ssl=19001200adminadmin2020-11-12 20:28:362020-11-12 20:29:28Flood Notes: Highlights of Current Happenings
At the current rate that crews are removing sand from the West Fork San Jacinto Mouth Bar, the remainder of the above-water portion of this once-behemoth sand bar could be gone by Christmas. See the two pictures below. The first taken after Harvey and the second taken today.
These two shots show the West Fork mouth bar two weeks after Harvey and today…more than three years later.
Much Yet to Dredge
Of course, even when the above water portion of the Mouth Bar is removed, that will still leave a huge portion below the surface. However, all progress is welcome.
Like an iceberg, most of a sand bar exists below the waterline.Photo taken 10/26/2020.I can’t say with certainty that this is submerged sand, or water stirred up by dredging. It seems too uniform to be the latter. Compare the picture below looking toward the WLHP bridge from a slightly different position and note how irregular the stirred-up sediment looks.Also note that the picture above was taken upstream from the current dredging.
At the start of October, the above-water (sub-aerial) extent of the mouth bar was down to the width of one excavator. Two excavators are now working toward the middle from each end. See below.
Looking WNW toward the West Lake Houston Parkway Bridge and Kings Harbor.Taken 10/26/2020.
From the wet mark on this excavator’s arm, it looks as though they are excavating up to 10 feet below the waterline. The 10-foot estimate closely agrees with the profile chart below.Taken 10/26/2020.
Like an Iceberg, Most of a Sand Bar Exists Below Water
That’s significant progress given what we started with. But much sand remains below the surface.
Tim Garfield and RD Kissling, two leading geologists now retired from one of the world’s largest oil companies, mapped the depth of the river using sonar and depth poles. They found an underwater plateau exists in this region of the river. See chart below.
The blue line represents the water surface. The gold line indicates the deepest part of the channel as you move downstream from the WLHP bridge to the FM1960 bridge. Numbers on the left scale indicate water depth. Numbers on the bottom scale indicate distance in feet downstream from the WLHP bridge.
Plans for Next Phase Still Not Revealed
FEMA has approved dredging another million cubic yards. And Dan Huberty’s amendment to SB500 in the last legislature dedicated $30 million for dredging the West Fork Mouth Bar. The City is drawing up plans, but they have not been announced yet. The last time I talked to Stephen Costello about this, he said the City was leaning toward dredging a channel somewhere south of the mouth bar. But many details remained to be worked out, such as:
Method of dredging (hydraulic vs. mechanical)
Exact location
Channel width
Finding qualified contractors
Bidding
Determining a suitable placement area, etc.
More news when its available.
Posted by Bob Rehak on 10/26/2020
1154 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.
https://i0.wp.com/reduceflooding.com/wp-content/uploads/2020/10/BeforeNow.jpg?fit=1200%2C1200&ssl=112001200adminadmin2020-10-26 17:09:182020-10-26 17:09:22Above-Water Portion of Mouth Bar Could Be Gone by Christmas
On Friday, October 16, 2020, stakeholders in the Lake Houston Spillway Improvement Project met at the dam to review gate alternatives and progress on the project. The main item of interest: a review of options still under consideration to increase the outflow during major storms, such as Harvey.
Phase One includes preliminary engineering and environmental permitting. It should take 18 months and is on schedule at this point. A key deliverable for phase one is verification of the benefit/cost ratio. But, of course, to determine that, you need to know the cost.
Alternatives Still Under Consideration
FEMA allotted 18 months for Phase 1. We’re six months into that. Work to date has focused on determining the optimal alternative. Five remain:
Expanding the existing spillway by adding new tainter gates
Adding a new gated spillway within the east embankment
Creating a new uncontrolled spillway within the east embankment
Building crest gates within the east embankment
Developing crest gates within the existing spillway
Tainter gates lift up from a radial arm. The tainter gates on Lake Conroe have 15X more release capacity than the lift gates on Lake Houston.
Above: the current conditions at the Lake Houston Dam.Looking slightly upstream. East is on the right.
The east embankment is a solid earthen area 2800 feet long east of the spillway and existing gates. Water cannot get over it in a storm. By adding various structures in this area, engineers could widen the current spillway capacity, allowing release of more stormwater.
One main benefit: additional gates would reduce uncertainty associated with pre-releases. Operators could wait longer until they were certain an approaching storm would not veer away at the last minute. That would avoid wasting water.
Reverse angle.Note the difference in height between the east embankment (left) and the spillway (right).Looking downstream toward Galveston Bay.Looking west toward Beltway 8. This shows the major segments of the dam.
Benefit/Cost Ratio Must Be > 1.0
The lake-level reduction benefits of these gate alternatives during major floods range up to roughly 8x. The costs also vary by roughly 4x. Those are order-of-magnitude, back-of-the-envelope estimates and far from final. Much hard work remains to develop tighter costs and tighter estimates of flood-level reductions. The latter will determine flood-prevention savings in a storm. And the benefits divided by the costs will determine the benefit/cost ratio.
In FEMA’s eyes, the benefit/cost ratio must exceed 1.0 to justify the project. Said another way, it must produce more benefits than it costs.
FEMA allotted 18 months for phase 1. We’re six months into that phase with a year left. Project partners expect results of the alternatives analysis before the end of the year.
Benefit/Cost Calculation
Given the ballpark costs of some of these gate alternatives, we will need very tight estimates of the benefits.
Potential Benefits include:
Upstream flood risk reduction
Reduced maintenance (debris management) for CWA
Improved Water Quality (post storm)
Potential Impacts include:
Increased scour and erosion potential to wetlands downstream
Increased water surface elevations to structures downstream
Calculating Benefits
Benefit Cost Ratio = (Net Present Value of Benefits)/(Project Costs)
Project Costs = (Capital costs) + (Net Present Value of Operations and Maintenance Costs)
Major Tasks Remaining in Phase 1
Barring surprises, the preliminary engineering report is due in February 2021 and environmental permitting should be complete by the Fall of 2021. Other tasks that must be completed by then include:
Hydrologic modeling of flows into and out of Lake Houston using the latest Atlas 14 data
Hydraulic modeling of Lake Houston, its Dam, and the San Jacinto River downstream of the dam to Galveston Bay
Calibration of models to historic storms
Examination of upstream benefits to residents/businesses removed from flood impacts
Examination of downstream impacts associated with additional flow release scenarios
It’s important to understand that not everyone who flooded in the Lake Houston Area did so because of the lake level. Some on the periphery of the flood flooded because water backed up in streams leading to the lake. If you got two feet of water in your living room, it doesn’t automatically mean a lake level reduction of two feet would eliminate your flooding by itself.
Congressman Dan Crenshaw (left) reviews the project with team members at the Lake Houston Dam and listens to their needs.
Phase 2 Still Not Certain
Assuming all goes well in the planning, accounting, and conceptual validation, FEMA will make a go/no go decision on construction at the end of next year or the beginning of the following year. Construction should take another 18 months.
Credits
Funding for this project comes from FEMA, Texas Division of Emergency Management, City of Houston and Harris County Flood Control. Other stakeholders include the Coastal Water Authority, Harris County, Fort Bend County, Baytown, Deer Park, and other communities adjacent to Lake Houston.
Posted by Bob Rehak on 10/17/2020
1145 Days since Hurricane Harvey and 394 since Imelda
Aerial photos of the West Fork Mouth Bar show that the above-water portion on this once-massive sand bar is now down to the width of one excavator for most of its length. A mouth bar is a sand bar where the mouth of a river or stream meets a standing body of water, such as Lake Houston. As water slows when it reaches the standing water, sediment carried downstream drops out of suspension.
The Before Shot
The first photo below shows the West Fork Mouth Bar immediately after Harvey and before any remediation work took place.
Looking south toward Lake Houston and the FM1960 Bridge from Kingwood.Photo of West Fork Mouth Bar taken on 9/15/2017, about two weeks after Harvey.
At that point in time, the mouth bar extended five feet above water in places. It was 3/4 of a mile wide and a half mile from the northernmost part to the small island in the channel south of the bar. But the part you can’t see, below water, is even bigger.
This massive blockage backed water up throughout the Humble/Kingwood/Atascocita area, and contributed to the flooding of thousands of homes and businesses.
Today
I took the shot below on Sunday night, 10/4/2020. While the camera position and lens perspective are slightly different, they are close enough to show the progress made in removing the blockage, or at least the portion above water.
Photo of West Fork Mouth Bar taken on 10/4/2020.The white dots appear to be ducks.
Close comparison of these two photos shows several smaller islands beyond the mouth bar that the Army Corps removed a year ago. At the completion of the Emergency West Fork Dredging Program (2018/19), FEMA agreed to dredge 500,000 cubic yards (CY) of sediment in a 600-acre area between the mouth bar and Atascocita Point in the upper right of the photos. After dredging the 500,000 CY, the Corps increased the average depth of that area to 5.5 feet. However, within weeks, Imelda filled much of that back in.
This year, the City of Houston started excavating the above-water portion of the mouth bar. The bar is now down to width of the excavators used for mechanical dredging. To fund this effort, the City used money left over from Hurricane Harvey cleanup.
This low-level shot facing west shows just how narrow the mouth bar now is.
Biggest Part Remains Below Water
But like icebergs, most of the sediment in sand bars lies below the surface. So even when there’s nothing left for me to photograph from the air, most of the blockage will remain. Two local geologists recently measured several cross sections of the river. The river’s profile looks like this.
Compiled by RD Kissling and Tim Garfield using sonic depth finders and measurement poles.
River depth upstream near Kings Harbor and downstream near the 1960 Bridge is more than 22 feet. Between those two points (which lie about three miles apart), the deepest part of the channel is only about 6-7 feet. Not far from the main channel, however, the river gets much shallower. It’s one to three feet in most places.
In other words, at this point in the West Fork, we still have an underwater plateau – extending three miles – that continues to restrict the conveyance of the river.
The continued presence of this plateau will slow water down and trap more sediment, undermining the effectiveness of earlier efforts.
RD Kissling’s knee. Kissling, a kayaker is standing in 1-2 feet of water about three hundred yards south of the mouth bar. The homes in the background are in Atascocita Point across the river. Photo is looking west.
More Dredging Slated
Restoring the conveyance of the river after decades of deferred maintenance will require much more dredging after the above-water mouth bar is gone.
Luckily, FEMA has agreed to dredge another million cubic yards, according to Houston Mayor Pro Tem Dave Martin. State Representative Dan Huberty also secured an additional $30 million in funding in the last legislature to continue the effort.
Stephen Costello, the City’s Flood Czar, is currently working on developing a next-phase plan, but has not yet announced it.
Posted by Bob Rehak on 10/5/2020
1133 Days since Hurricane Harvey
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Harvey households withFEMA group flood insurance policies must buy standard policy by Oct. 24. Lack of coverage may affect eligibility for future disaster assistance.
Flooded Street during Harvey by Julie Yandell.
Three-Year Policies End in October
Approximately 6,690 Hurricane Harvey survivors have been notified that their Group Flood Insurance Policy (GFIP) will expire Oct. 24. These three-year policies end soon, so policyholders must plan now to switch to a standard flood insurance policy to ensure continuous flood insurance coverage.
Insurance a Condition for Future Disaster Assistance
Following the devastating disasters and hurricane season of 2017, FEMA purchased GFIP policies for thousands of disaster survivors whose homes were flooded. Part of the eligibility of receiving future financial assistance after a flood is that a homeowner or renter must obtain and maintain flood insurance to ensure that there is no lapse in coverage. If a property affected by a flood is sold, the new owners are required to have flood insurance for the property as well.
This means Harvey households who received a group policy need to purchase a new, standard flood insurance policy. Alternatively, they may obtain other flood insurance for at least the amount of assistance that they received for repairs and replacement of property. This keeps them eligible for future FEMA assistance.
Those who received a GFIP policy as part of their FEMA disaster assistance after Harvey but don’t buy a standard flood insurance policy will likely not receive federal disaster assistance for home repairs if they experience another flood event.
Flood Insurance Can Be Key to Recovery
Flood insurance policies are crucial to recover quickly following a flood event as homeowners and renters’ policies do not typically cover flood damage.
Additionally, flood insurance will pay claims regardless of whether there is a major disaster declaration. Flood insurance claims can be paid for such events as flash flooding, storm sewer backup, river overflow, storm surge, mudslides or tropical systems.
$69 Billion Paid by FEMA through NFIP
Since its inception in 1968, FEMA’s National Flood Insurance Program has paid more than $69 billion in flood claims to help survivors rebuild their lives following flood events.
How to Learn Your Status and Find an Agent
To find an insurance carrier or agent, visit FloodSmart.gov, or call FEMA NFIP Direct toll-free, (800) 638-6620, option 2.
For more information about the National Flood Insurance Program and or insurance, call the National Flood Insurance General Call Center at 800-427-4661.
If you have questions about your Group Flood Insurance Policy call the National Flood Insurance Direct Call Center at 800-638-6620.
To find out if you have a flood insurance requirement:
Call FEMA toll-free at 800-621-3362 (voice, 711/VRS – Video Relay Service) (TTY: 800-462-7585).
Multilingual operators are available (press 2 for Spanish).
The Texas Recovery Office GFIP Help Desk phone number is 877-503-6053.
If It Rains Where You Live, It Can Flood
Harvey impacted 41,500 square miles of Texas. If it rains, it can flood, which means all Texans should purchase or renew flood insurance policies. The 2020 hurricane season began June 1 and ends on November 30, but a policy protects you from financial losses from other flood events all year. Just 1 inch of water can cause $25,000 of damage to a home.
For additional information about Hurricane Harvey and Texas recovery, visit the:
Posted by Bob Rehak on 9/28/2020 with thanks for the reminder to Congressman Dan Crenshaw
1126 Days after Hurricane Harvey
https://i0.wp.com/reduceflooding.com/wp-content/uploads/2019/02/IMG_0048-1-e1646428414628.jpg?fit=900%2C1200&ssl=11200900adminadmin2020-09-28 15:36:572020-09-28 15:38:39FEMA Group Flood Insurance from Harvey Expiring October 24
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
Earlier this month, the City of Houston announced that FEMA would pay to dredge another million cubic yards of sediment from the West Fork Mouth Bar. What does that mean in practical terms? What are the objectives of the program? How wide and deep will they go? Neither the objectives, nor a dredging plan, have yet been released.
The official plan will hopefully rely on new survey work and hydraulic modeling. A survey boat has been seen on the lake for several weeks now.
Since January of this year, the City of Houston has been trying to reduce the above water portion of the mouth bar with mechanical dredging, a much slower process than hydraulicdredging. Note how shallow the water is in the foreground.
How to Play Armchair Engineer
In the meantime, since fall football is in doubt due to COVID, here’s a simple way to keep your armchair quarterbacking skills finely honed. What would you do if you were the project engineer or manager? Play what if and experiment with different scenarios.
Download and open Google Earth Pro. It’s free.
Zoom in on the West Fork Mouth Bar.
Select the measuring tool.
Click on the polygon tab.
Select square yards for the unit measurement for the areas you will define.
Now start second guessing the project engineers. Play “what if” by defining an area that you would like to see dredged.
Readjust the points that define the area by dragging them in, out, up or down.
Watch the total square yards recalculate as you move the points.
Examples of Different Scenarios
Here are some examples to show you what I’m talking about.
4.3 Million Square Yard Area, Roughly 8 inches Deep
Largest area. This scenario takes in everything between where the Corps stopped dredging in its Emergency West Fork Program and the FM1960 Bridge.
The scenario above takes in the mouth of Ben’s Branch, plus all the other drainage ditches that empty Fosters Mill, Kings Point, and Atascocita north of the FM1960 Bridge.
The scenario above covers 4.3 million square yards. But with a budget to dredge only 1 million cubic yards, you would divide 1/4.3 = 0.23 yards of depth. That’s less than a third of a yard. It works out to about 8 inches.
3 Million Square Yard Area, 1 Foot Deep
In the next scenario, I pulled the boundaries in so that the area equaled 3 million square yards.
This scenario is a little more intuitive. You’re dredging 1 million cubic yards across an area of 3 million square yards. Within this bounding box, you could reduce the level of sediment roughly a foot.
2 Million Square Yard Area, 18 inches Deep
If you reduced the area to be dredged to 2 million square yards, you could reduce the level of sediment by half a yard or 18 inches.
1 Million Square Yards, 3 Feet Deep
Path followed by the relict channel before Lake Houston was built.
If you reduced the area further, to 1 million square yards, you could dredge to 3 feet. With the five feet of depth already there, you could have an eight foot channel connecting the river and the lake. Make it narrower and you could even go deeper. And perhaps, just perhaps, keep sediment from accumulating so rapidly upstream of the FM1960 bridge.
Difficult Choices Ahead
As you can see, engineers have some difficult choices ahead. They must chose between unblocking channels and streams, or dredging a channel roughly the size of the upstream west fork all the way to the 1960 bridge.
Last year, the Corps reduced the 600-acre area between the mouth bar and Atascocita Point to an average depth of 5.5 feet. So we have a good head start. But there are other considerations:
The West Fork was roughly 22 feet deep where the Corps stopped dredging just west of the mouth bar. Because of scouring, it’s at least that deep where the west fork passes under FM1960.
As a result, water coming down the west fork hits an underwater mesa that still blocks off three quarters of the conveyance.
Prominent area geologists, such as Tim Garfield and RD Kissling, theorize that that wall traps sediment and is rapidly diminishing the value of previous dredging programs. They believe that the most important objective for this phase of dredging should be to “reconnect the West Fork with the Lake.”
But Advancing Delta Now Blocks Major Streams, Channels
Meanwhile, consider this, too. In 2014, Bens Branch and the drainage ditch that empties large parts of Fosters Mill and Kings Point had a clear path to the river. Today, both are blocked by the mouth bar and an advancing delta within the lake. Compare the two images below.
Google Earth view from 2014 shows steams could still easily connect with relict channel.
Today, however, an advancing delta within the lake blocks them.
These are some of the real world trade offs that engineers and project managers must deal with every day.
So to return to the football analogy, do you send your receivers wide or deep? Do you have them hug the sidelines or cut for the goal post?
Understand that this isn’t a game, however. It’s a struggle to return a community to prosperity.
What would you do? And why?
Posted by Bob Rehak on 8/31/2020
1098 Days since Hurricane Harvey
https://i0.wp.com/reduceflooding.com/wp-content/uploads/2020/08/20200831-DJI_0613.jpg?fit=1200%2C900&ssl=19001200adminadmin2020-08-31 20:38:392020-08-31 20:52:02How Much Will Dredging Another Million Cubic Yards Reduce the West Fork Mouth Bar Area?
Because of low interest rates, new developments seem to pop up weekly around the Lake Houston Area. The question often arises, “How will the development of new flood maps affect the development of new subdivisions?” Most people by now have heard that City building code revisions now require elevation at least two feet above the .02-percent-annual-chance flood (formerly known as 500-year flood). But does that mean two feet above the old floodplain or the new? Due to a little-known provision in the City’s floodplain regulations, it means the new floodplain even though the new floodplain maps are not official yet.
Here’s what you need to know if you’re concerned that someone may be building future buyouts next to your neighborhood. First the timetable for new flood maps.
Remaining timetable for new Harris County Flood Maps
Even though FEMA won’t release the new flood maps officially for approximately another five years, developers should still be building to the higher standards associated with newly acquired data (in other words, the data on which the new maps are being built). See below.
Floodplain Regs Authorize City Engineer to Use Data Behind New Flood Maps
Section 19-4 of the City’s Floodplain regulations address Use of other flood hazard data to supplement the effective Flood Insurance Rate Map (FIRM). It states, “New elevation and flooding studies are undertaken by or under the auspices of FEMA and local political subdivisions, such as the Harris County Flood Control District. Upon determination that the data generated by such a study appears to be reliable and based upon sound engineering and surveying practices and further that the study’s data indicate that the effective FIRMs are FIRM is materially inaccurate, the city engineer may cause the study data to be administered for purposes of this chapter as though it were a part of the effective FIRM. Any such determination shall be issued in writing and a copy shall be placed on file in the office of the city secretary. The city engineer is authorized to utilize updated information from FIS and floodplain models in administering this chapter.”
Basically, that means even though the new maps have not yet been adopted, the City Engineer can require developers’ plans to reflect the new underlying data as though it were part of the current map. In this case, the new underlying data is already in hand.
MaapNext Website Describes New Data Improvements
Current floodplain maps will change greatly according to Harris County Flood Control. The district has already started releasing information on a new website called MaapNext (Modeling, Assessment and Awareness Project).
Components of the MaapNext program. A $3.5 million FEMA grant made MaapNext possible.
According to the MaapNext site, we now have updated data based on:
County-wide impervious data developed from 2018 aerial imagery
Completed flood risk reduction projects
NOAA’s recently-released Atlas 14
Updated terrain data
We also have new and better ways to model that data since the last survey after TS Allison:
2-Dimensional Hydraulic Modeling
New hydrology method that better accounts for a watershed’s conveyance capacity
Rain-on-Grid analysis that identifies previously unmapped urban flood risk.
And, we are beginning to develop better maps:
Modeling results in GIS (Geographic Information Systems)
New flood-risk data sets describe results in a variety of useful ways
Reportedly, the City is already requiring developers to act on the new “best available data” instead of waiting five years for the next maps.
Chapter 19 of the City Ordinances deals with dozens of other requirements for building in floodplains. But more on those in future posts.
Posted by Bob Rehak on 8/29/2020
1096 Days (Three Years) since 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.
https://i0.wp.com/reduceflooding.com/wp-content/uploads/2020/08/image001-1.png?fit=1182%2C847&ssl=18471182adminadmin2020-08-29 17:17:162020-08-29 17:21:55New Flood-Map Timetable and How It Affects New Development
Houston Mayor Pro Tem Dave Martin announced today that FEMA will fund the dredging of an additional million cubic yards of sediment from the area around the San Jacinto West Fork Mouth Bar. The giant sand bar partially blocked the mouth of the West Fork during Harvey and backed water up. It contributed to the flooding of thousands of homes and businesses in Kingwood, Humble and Atascocita.
Only a skeleton of the above-water portion of the mouth bar remains. But water remains shallow on both sides of it. Note all the trees and little islands poking up between the bar and camera position. Photo taken 8/20/2020.
Ending a Three-Year Debate
The City and FEMA debated for almost three years about how much sediment Harvey deposited in the area between Kings Point and Atascocita Point. The disaster declaration following Harvey only allowed FEMA to fund dredging of sediment deposited by that storm, not to pay for any deposits there previously.
Back before Great Lakes removed its hydraulic dredge, the City commissioned TetraTech to determine the quantity. In April 2019, the City submitted TetraTech’s ninety-four-page report. Based on core sampling, TetraTech estimated that Harvey deposited approximately 1,012,000 cubic yards of sand/sediment.
Subsequently, Martin, Senator Brandon Creighton and Representative Dan Huberty gained support from Governor Greg Abbott to provide a $50 Million grant for additional debris removal. Approximately $7 Million went to dredging the mouth bar land mass, a project which is still underway.
Huberty’s amendment to Senate Bill (SB) 500 set aside another $30 Million for Harris County for dredging at the confluence of the San Jacinto River and Lake Houston. The City is currently a sub-recipient of approximately $10 Million of those funds. Dredging will continue until the City exhausts the funds. According to Martin, the money should cover approximately 242,000 more cubic yards.
Then the FEMA money for the additional million cubic yards will kick in.
Said State Representative Dan Huberty, “After two years of showing FEMA the data, I am thrilled that we are allowed to continue this project due to the hard work of Mayor Pro Tem Martin and Mayor Turner. The funds we secured from the State during the last budget cycle to continue where FEMA left off are nearly depleted. This new funding source will let us complete this necessary and critical project. It is great news for our community. It also recognizes how important the Lake Houston Watershed is to our region.”
Other Lake Houston Dredging Projects
Approximately $10 Million of local funds are earmarked for the dredging activity within Lake Houston south of FM 1960. The City plans to coordinate with Harris County Flood Control District to utilize a portion of the $10 Million to remove the mouth bar obstruction at Roger’s Gully.
Rogers Gully Mouth Bar
However, it won’t happen anytime soon. Based on the bond priorities pushed through Harris County by Precinct One Commissioner Rodney Ellis, County funds will not be available until July 2021 at the earliest. And maybe not until March 2022.
Credits
Mayor Pro Tem Martin, Congressman Dan Crenshaw, State Representative Dan Huberty, State Senator Brandon Creighton, Texas Division Emergency Management Chief Nim Kidd, Mayor Sylvester Turner, and Chief Recovery Officer Stephen Costello have all worked together to make these projects happen.
Another view of the slowly disappearing San Jacinto West Fork mouth bar.
Posted by Bob Rehak on 8/21/2020
1088 Days after Hurricane Harvey
https://i0.wp.com/reduceflooding.com/wp-content/uploads/2020/08/20200820-DJI_0501.jpg?fit=1200%2C900&ssl=19001200adminadmin2020-08-20 17:31:122020-08-20 17:51:55FEMA to Fund Additional Million Cubic Yards of Dredging from West Fork Mouth Bar Area
