Flood mitigation is a complex process with hundreds of moving parts, all dependent on each other. When you focus intensely on the pieces, periodically it helps to review how they fit together. Only when you do this can you see progress toward your goals. In that spirit, I created this presentation. It has a Kingwood slant, but really addresses the whole Lake Houston Area. Everything connects.
What Caused Flooding
First, let’s look at what caused the flooding during Harvey and other recent storms…apart from record rainfalls.
The rain fell on a landscape that was ill-prepared the handle it.
Look at flooding like a process engineer. There’s always a bottleneck in the system somewhere between the sky and Galveston Bay. Both local and regional issues contributed to the magnitude of the Harvey and Imelda disasters.
Underestimating Rainfall Meant Underpreparing
When we built communities, such as Kingwood, we underestimated the amount of rainfall we could get. After four so-called 500 year rains in five years, we’re now working with higher rainfall precipitation frequency estimates (called Atlas 14). For this area, the 100-year rain is about 30-40% higher than the previous standard. That means floodplains will soon expand when new flood maps are released. Some people in the 500-year floodplain will find themselves in the 100-year. And people in the 100-year may find themselves in the floodway of rivers and streams. Unless we do something.
Lake Conroe Release Coincided with Downstream Peaks
On top of record rainfalls, during Harvey, the SJRA released water from Lake Conroe at a time that coincided with downstream peaks from other tributaries. The release by itself would have created the ninth largest flood in West Fork history. It comprised about one third of all the water coming down the West Fork.
Population Growth in MoCo
On top of that, Montgomery County has seen tremendous population growth in the last decade. Conroe was the fastest growing city in America in 2017 and is still #6. The county itself is the second fastest growing in the region.
To pave the way for all that development, we’ve seen a huge increase in sand mining upstream in the last 25 years. Before 2011, unregistered, bootleg operators went unregulated. But even those who are registered don’t follow common-sense regulations common in other states, which protect the environment and downstream residents. For instance, they mine so close to the river that dikes frequently fail. As a result, they have contributed to a greater than than natural buildup of sediment in our rivers. After Harvey, the US Army Corps of Engineers found that the West Fork was 90% blocked just downstream from River Grove Park.
Another factor contributing to flooding: Lake Conroe can release water 15 times faster than Lake Houston. That makes it difficult to lower lake levels in advance of a major storm. Storms have a nasty habit of veering away at the last minute. The small gates on Lake Houston mean you have to start lowering the lake far in advance. That raises the risk of wasting precious water. Larger gates would make managing lake levels easier.
Ditches, Streams Filling In
Finally, sediment built up in more places than the San Jacinto. It has also built up in the ditches and streams that lead to the river. This reduces convenance within neighborhoods. There’s less room to store water in streams, so it backs up into storm sewers and streets, and can eventually flood homes.
But what can we do to remedy the damage already done? Leaders in the Lake Houston Area identified a four-part strategy and are working with the SJRA, City of Houston, Montgomery County and Harris County Flood Control to implement it. Elements include:
Increasing upstream detention to reduce the volume of water coming downstream during floods
Dredging the river to remove sediment dams that back water up
Increasing the number of gates on the Lake Houston Spillway to release water faster
Restoring or expanding ditches to handle more water
Let’s look at each of those in a little more detail.
Upstream Detention
The Humble/Kingwood area sits at the tip of a funnel. 535 square miles in a seven-county region drain into Lake Houston.
The San Jacinto River Basin Master Drainage Study identified 16 potential detention projects to hold water back during major storms. However, they would cost roughly $3 billion to reduce damage by less than $1 billion. So that’s a stretch. FEMA evaluates projects based on their benefit/cost ratio.
The SJRA has already applied for a grant for a detention project on Caney Creek which empties into the east fork. But we also need something that can help offset releases from the Lake Conroe Dam on the West Fork. Next step: figure out the funding piece of the puzzle.
The slide below shows why we need additional dredging.
An 18-foot high underwater plateau exists between where the Army Corps stopped dredging on the West Fork and the FM1960 Bridge where scouring during Harvey reduced the channel depth.
The chart above shows the deepest part of the channel between those two areas. If left in place, this plateau will force flood water out of banks during floods. It will also trap sediment, negating the value of previous dredging efforts.
More Gates for Lake Houston
FEMA has conditionally approved up to approximately $50 million to increase the outflow capacity of Lake Houston. During Havey, the flow of water over the spillway was estimated at 11-13 feet. That’s reportedly higher than the flow over Niagra Falls.
In Kingwood, they identified nine projects and recommended two for immediate implementation that should improve drainage on a third tributary, Ben’s Branch.
Recommendations include expanding:
Kingwood Diversion Ditch to take water out of the Ben’s Branch watershed and also improve drainage from surrounding subdivisions from Woodland Hills down to the West Fork.
Taylor Gully – if a deal cannot be reached to purchase Woodridge Village and build a regional detention basin on it.
In addition, Flood Control and the City are looking at minor improvements to other ditches that back water up in places, for instance, at culverts under Kingwood Drive.
Goal: Restore 100-Year Level of Service
Engineers solving all these problems have a goal: to restore your home to what they call a 100-year level of service. That means if your home was built above the 100-year floodplain, it should not flood in a 100-year rain – based on new Atlas 14 standards. In places, sedimentation and upstream development have reduced the level of service to 2 years over time.
We need to restore the capacity of ditches, streams, the river and lake to handle 100-year rains. So we can get water from the sky to the Bay without it going through your living room.
While progress may feel painfully slow, many improvements have already been made.
For instance, in addition to dredging, Flood Control has divided Ben’s Branch up into five projects. Three are already complete:
You can help by remaining engaged. Without public pressure, it’s easy for elected officials to ignore these problems and defer expensive solutions. Keep flood mitigation a high priority. Floods can strike at any time. We had four tropical systems barely miss us this year.
Posted by Bob Rehak on 10/27/2020
1155 Days since Hurricane Harvey and 404 since Imelda
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.
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
Since June, I’ve posted about problems in the Colony Ridge development in Liberty County. Among them: the washout of FM1010 where it crosses over Rocky Branch. Authorities have closed the busy road which provides access to Colony Ridge for three years, forcing tens of thousands of residents to seek alternate access routes, such as FM1485 and FM2090.
However, it’s difficult to see all the damage. So today I took a drone and captured some previously unseen details.
Colony Ridge drainage ditch leading to Rocky Branch contributed to washing out FM1010 at far end of ditch.
Lack of Functional Detention Capacity Likely Contributed to Washout
The damage is likely the result of inadequate, poorly engineered, or poorly maintained detention. Another contributing factor: a steep drop in elevation as water leaves the massive ditch (see above) in Colony Ridge and descends through a wooded area toward FM1010. That drop accelerated more water than should have been traveling down Rocky Branch, an East Fork San Jacinto tributary. As a result, floodwaters swept trees and other debris downstream.
One Thing Leads to Another
The debris:
Clogged culverts under the road…
Then, when the roadbed became a dam…
…Water churned through the roadbed next to the culverts…
…And deposited more “beaver dams” downstream…
…that, in turn, contributed to the flooding of surrounding homes.
Years of Neglect Still Ignored
Amazingly, no one in Liberty County corrected these problems after Harvey. As a result, many homes flooded again in 2019, during heavy downpours on May 7th and September 19th. The problems still have not been fixed. See the pictures below. I took them this afternoon.
Just yesterday, I had lunch with a couple who were considering moving to Liberty County because they were seeking a quieter lifestyle. I told them about this story. They are reconsidering.
FM1010 Washout at Rocky Branch has not been repaired for more than three years. Note flood debris clogged in culvert. Also note straps around logs!
“Beaver dam” just downstream from culverts is building up and up, contributing to additional flooding.
Not All Business is Good Business
Colony Ridge has grown into the world’s largest trailer park in less than a decade. It brought more than its fair share of problems:
Legendary traffic backups – even on Sunday afternoons.
A hard lesson for some people to learn is that not all business is good business. Lax enforcement of regulations allowed Colony Ridge to grow out of control. Now county commissioners have a nightmare on their hands, cannot fix their problems, and cannot enforce their own regulations.
Posted by Bob Rehak on 10/25/2020
1153 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/2020/10/20201025-DJI_0919.jpg?fit=1200%2C900&ssl=19001200adminadmin2020-10-25 21:08:132020-10-25 23:49:28New Drone Shots Reveal Need for Better Flood Control in Liberty County
October 2020 Regional Flood Mitigation Update
Flood mitigation is a complex process with hundreds of moving parts, all dependent on each other. When you focus intensely on the pieces, periodically it helps to review how they fit together. Only when you do this can you see progress toward your goals. In that spirit, I created this presentation. It has a Kingwood slant, but really addresses the whole Lake Houston Area. Everything connects.
What Caused Flooding
First, let’s look at what caused the flooding during Harvey and other recent storms…apart from record rainfalls.
Look at flooding like a process engineer. There’s always a bottleneck in the system somewhere between the sky and Galveston Bay. Both local and regional issues contributed to the magnitude of the Harvey and Imelda disasters.
Underestimating Rainfall Meant Underpreparing
When we built communities, such as Kingwood, we underestimated the amount of rainfall we could get. After four so-called 500 year rains in five years, we’re now working with higher rainfall precipitation frequency estimates (called Atlas 14). For this area, the 100-year rain is about 30-40% higher than the previous standard. That means floodplains will soon expand when new flood maps are released. Some people in the 500-year floodplain will find themselves in the 100-year. And people in the 100-year may find themselves in the floodway of rivers and streams. Unless we do something.
Lake Conroe Release Coincided with Downstream Peaks
On top of record rainfalls, during Harvey, the SJRA released water from Lake Conroe at a time that coincided with downstream peaks from other tributaries. The release by itself would have created the ninth largest flood in West Fork history. It comprised about one third of all the water coming down the West Fork.
Population Growth in MoCo
On top of that, Montgomery County has seen tremendous population growth in the last decade. Conroe was the fastest growing city in America in 2017 and is still #6. The county itself is the second fastest growing in the region.
Bad Development Practices
Combine the rapid growth in impervious cover with bad development practices and you are laying the groundwork for disaster. The bad development practices include lack of detention, clearcutting huge areas before detention is installed, and calculating detention for the old rainfall standards knowing that higher standards will soon go into effect.
Out-of-Control Sand Mining
To pave the way for all that development, we’ve seen a huge increase in sand mining upstream in the last 25 years. Before 2011, unregistered, bootleg operators went unregulated. But even those who are registered don’t follow common-sense regulations common in other states, which protect the environment and downstream residents. For instance, they mine so close to the river that dikes frequently fail. As a result, they have contributed to a greater than than natural buildup of sediment in our rivers. After Harvey, the US Army Corps of Engineers found that the West Fork was 90% blocked just downstream from River Grove Park.
But the biggest blockage was where the West Fork meets Lake Houston. There, sediment drops out of suspension as the water slows. The sediment built up for decades, forming a mouth bar that backed water up during Harvey and contributed to the flooding of thousands of homes and businesses.
Flood Gate Disparity
Another factor contributing to flooding: Lake Conroe can release water 15 times faster than Lake Houston. That makes it difficult to lower lake levels in advance of a major storm. Storms have a nasty habit of veering away at the last minute. The small gates on Lake Houston mean you have to start lowering the lake far in advance. That raises the risk of wasting precious water. Larger gates would make managing lake levels easier.
Ditches, Streams Filling In
Finally, sediment built up in more places than the San Jacinto. It has also built up in the ditches and streams that lead to the river. This reduces convenance within neighborhoods. There’s less room to store water in streams, so it backs up into storm sewers and streets, and can eventually flood homes.
Four-Part Solution
Montgomery County has now adopted Atlas-14, the new rainfall standard. And residents are pushing commissioners to close loopholes that let developers get away without building detention. Residents are also working with the TCEQ and TACA to adopt better sand mining practices.
But what can we do to remedy the damage already done? Leaders in the Lake Houston Area identified a four-part strategy and are working with the SJRA, City of Houston, Montgomery County and Harris County Flood Control to implement it. Elements include:
Let’s look at each of those in a little more detail.
Upstream Detention
The Humble/Kingwood area sits at the tip of a funnel. 535 square miles in a seven-county region drain into Lake Houston.
The San Jacinto River Basin Master Drainage Study identified 16 potential detention projects to hold water back during major storms. However, they would cost roughly $3 billion to reduce damage by less than $1 billion. So that’s a stretch. FEMA evaluates projects based on their benefit/cost ratio.
The SJRA has already applied for a grant for a detention project on Caney Creek which empties into the east fork. But we also need something that can help offset releases from the Lake Conroe Dam on the West Fork. Next step: figure out the funding piece of the puzzle.
Dredging
We’ve already removed almost three million cubic yards of sediment from the West Fork. The third phase of West Fork dredging should wrap up shortly. But there’s still more work to do.
Luckily:
The slide below shows why we need additional dredging.
An 18-foot high underwater plateau exists between where the Army Corps stopped dredging on the West Fork and the FM1960 Bridge where scouring during Harvey reduced the channel depth.
The chart above shows the deepest part of the channel between those two areas. If left in place, this plateau will force flood water out of banks during floods. It will also trap sediment, negating the value of previous dredging efforts.
More Gates for Lake Houston
FEMA has conditionally approved up to approximately $50 million to increase the outflow capacity of Lake Houston. During Havey, the flow of water over the spillway was estimated at 11-13 feet. That’s reportedly higher than the flow over Niagra Falls.
The FEMA grant initially covers preliminary engineering and environmental surveys. If the benefit/cost ratio is positive, they will release the remainder of the funds for construction.
So far, engineers have identified five possible solutions. Each produces a different flood reduction benefit, but also comes with different costs and environmental issues.
The next step: to analyze the benefit/cost ratio of each and submit the results to FEMA.
We are six months into the first phase, scheduled to take a total of 18 months. Construction, if approved, will take another 18 months.
Ditch Restoration/Expansion
Harris County Flood Control District has studied area ditches for the last year or more. Results of their analyses are now complete.
In Kingwood, they identified nine projects and recommended two for immediate implementation that should improve drainage on a third tributary, Ben’s Branch.
Recommendations include expanding:
In addition, Flood Control and the City are looking at minor improvements to other ditches that back water up in places, for instance, at culverts under Kingwood Drive.
Goal: Restore 100-Year Level of Service
Engineers solving all these problems have a goal: to restore your home to what they call a 100-year level of service. That means if your home was built above the 100-year floodplain, it should not flood in a 100-year rain – based on new Atlas 14 standards. In places, sedimentation and upstream development have reduced the level of service to 2 years over time.
We need to restore the capacity of ditches, streams, the river and lake to handle 100-year rains. So we can get water from the sky to the Bay without it going through your living room.
While progress may feel painfully slow, many improvements have already been made.
For instance, in addition to dredging, Flood Control has divided Ben’s Branch up into five projects. Three are already complete:
A fourth project, to restore Ben’s Branch from Kingwood Drive north to Rocky Woods should start soon. And a fifth, to restore conveyance between the YMCA and the River, will follow.
How You Can Help
You can help by remaining engaged. Without public pressure, it’s easy for elected officials to ignore these problems and defer expensive solutions. Keep flood mitigation a high priority. Floods can strike at any time. We had four tropical systems barely miss us this year.
Posted by Bob Rehak on 10/27/2020
1155 Days since Hurricane Harvey and 404 since Imelda
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.
Above-Water Portion of Mouth Bar Could Be Gone by Christmas
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.
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.
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.
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.
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:
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.
New Drone Shots Reveal Need for Better Flood Control in Liberty County
Since June, I’ve posted about problems in the Colony Ridge development in Liberty County. Among them: the washout of FM1010 where it crosses over Rocky Branch. Authorities have closed the busy road which provides access to Colony Ridge for three years, forcing tens of thousands of residents to seek alternate access routes, such as FM1485 and FM2090.
However, it’s difficult to see all the damage. So today I took a drone and captured some previously unseen details.
Lack of Functional Detention Capacity Likely Contributed to Washout
The damage is likely the result of inadequate, poorly engineered, or poorly maintained detention. Another contributing factor: a steep drop in elevation as water leaves the massive ditch (see above) in Colony Ridge and descends through a wooded area toward FM1010. That drop accelerated more water than should have been traveling down Rocky Branch, an East Fork San Jacinto tributary. As a result, floodwaters swept trees and other debris downstream.
One Thing Leads to Another
The debris:
Years of Neglect Still Ignored
Amazingly, no one in Liberty County corrected these problems after Harvey. As a result, many homes flooded again in 2019, during heavy downpours on May 7th and September 19th. The problems still have not been fixed. See the pictures below. I took them this afternoon.
Just yesterday, I had lunch with a couple who were considering moving to Liberty County because they were seeking a quieter lifestyle. I told them about this story. They are reconsidering.
Not All Business is Good Business
Colony Ridge has grown into the world’s largest trailer park in less than a decade. It brought more than its fair share of problems:
Posted by Bob Rehak on 10/25/2020
1153 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.