Before Harvey hit, we knew tremendous rains were coming. But we could do little to prepare Lake Houston for the onslaught. The small gates you see in the photo below release a combined 10,000 cubic feet per second (CFS). That’s nothing compared to the 150,000 from the gates at the Lake Conroe Dam.
Lake Houston’s gates release a maximum of 10,000 CFS.The gates at Lake Conroe can release water at up too 150,000 CFS...15X faster.
We Were Sunk
When Lake Conroe had to open its gates during Harvey, we were sunk. Literally. Had we had bigger, more modern gates on Lake Houston, we might have been able to lower the lake fast enough to avoid flooding thousands of homes.
11-Foot High Wall of Water Cascaded Over Spillway
Of course, Lake Houston also has a spillway. In fact, the spillway represents the primary way to shed water from the lake. The top of that spillway is at 42.38 feet.
Interestingly, the WAY more gates would prevent flooding was not through pre-release; Harvey would have refilled the lake in a matter of hours and the storm lasted days. Rather, additional gates would have widened the spillway area so more water could move over the dam every second. Think of it in these terms: twice the width, half the height. (That’s an over-simplified example of how the principle works; ten more gates would not actually double the width.)
Is Pre-Release Practical?
The Frees & Nichols study only considered one case – Harvey. For lesser floods, the gates could help make pre-release a viable strategy for the Lake Houston Area. At least in my opinion.
Here’s how.
More gate capacity could help offset the volume of water released from Lake Conroe, to reduce the risk of Conroe flooding Houston again.
More gate capacity could release more water in less time, thus reducing uncertainty when pre-releasing before a storm. That would allow officials to delay releasing water until they were sure they needed to. And that could save precious water in the event that a storm veers off in another direction at the last minute. We may know that a storm will cross the area. But it’s much harder to tell where the heaviest rainfall will occur. For instance, during Imelda, parts of the East Fork received more than 20 inches of rain while Lake Conroe received only two.
In the last year, the City prevented homes from flooding several times by pre-lowering the lake. But the small gate capacity meant that we had to start releasing water DAYS beforehand to make an appreciable difference in the lake level. That has to be nerve wracking for Public Works.
Where the Gate Project Stands
Earlier this year, the City of Houston secured a FEMA grant to design and construct more gates for the Lake Houston Dam. The two-phase grant covers design and construction. Each phase must be completed within 18 months, though extensions are possible. Currently, we are four months into the 18-month design phase. That means we should see more gates by mid-2022.
In the meantime, the photos below give you a feeling for the immensity of the project.
The height of the trees on the San Jacinto River below the dam gives you a feeling for the height of the dam.Looking SE.Repairs are underway to the structures below the Lake Houston dam.Note the trees caught on top of it.Looking west over the Lake Houston Damwhich dates back to 1953.
Posted by Bob Rehak on 11/14/2019
807 Days since Hurricane Harvey
https://i0.wp.com/reduceflooding.com/wp-content/uploads/2019/11/RJR_3872.jpg?fit=1500%2C1000&ssl=110001500adminadmin2019-11-13 18:38:402020-01-17 10:13:11Aerial Photos of Lake Houston Dam Dramatize Need for More Gates
Provisions Adequate for Ultimate Development Can Be Severely Deficient for Intermediate Stages
The section on Offsite Overland Flow starts out by saying, “Sheet flow from undeveloped areas into an existing or a proposed subdivision can create a localized flood hazard by overloading street inlets and/or flooding individual lots.” This is exactly what happened to Elm Grove Village and North Kingwood Forest in May and September of this year. City of Houston storm drains already taxed to the max became overloaded when water broke out of Woodridge Village and started flowing down the streets of Elm Grove and North Kingwood Forest.
Streets of Elm Grove during May 7th Flood show danger of not planning for runoff during intermediate stages of development.
The text in the Drainage Manual then continues. “Any drainage plan for a proposed subdlvision submitted for review and approval by the Montgomery County Drainage Administrator must address the drainage of all adjacent lands. Both under undeveloped and fully developed conditions. A plan which may be adequate under conditions of ultimate development can be severely deficient during intermediate conditions of development due to sheet flow from adjacent undeveloped land. Provisions must be made to divert 100-year sheet flows to a channel system or to the secondary street and storm sewer system.” [Emphasis added.]
Discuss the drainage of adjacent lands, such as Elm Grove.
Discuss intermediate conditions of development; they focus only on fully developed Phase 1 and Phase 2 Conditions.
Mention the phrase “sheet flow” once.
Make provisions to divert 100-year sheet flows.
No Swales to Redirect Sheet Flow
The next paragraph of the Montgomery County Drainage Criteria Manual starts, “Redirection of the sheet flow can usually be achieved through the use of drainage swales located in temporary drainage easements along the periphery of the subdivision.” Perry Homes built no such swales … at least not adequate ones.
No Berms to Block Sheet Flow
Later in that same paragraph, the Manual talks about building berms between the swales and adjoining neighborhoods to prevent the flow from overrunning the swale. Unfortunately, on May 7th, no such berms existed. They did for Imelda, but they proved inadequate to divert the sheet flow and they had gaps in them.
No Additional Storm Sewer Capacity
The next paragraph talks about building “additional inlet and storm sewer capacity … to prevent prolonged street ponding in the (neighboring) subdivision resulting from flow from the undeveloped area.” That didn’t happen either.
No Planning for Rain Before Detention Ponds Fully Built
Perry Homes took none of these precautions. LJA never planned for them (as far as I can see from publicly available documents). Reading LJA’s drainage analysis, one gets the impression that no one ever even conceived of rainfall before they could build all the detention ponds for Woodridge Village. That turned out to be yet another fatal assumption. Despite all the warnings and mitigation advice in Montgomery County’s Drainage Criteria Manual.
Add this to a long and growing list of other things they ignored, underestimated, or mischaracterized.
The list goes on and on. I have barely started. This series could last for weeks. The MoCo Drainage Manual goes on for almost 200 pages. And Woodridge Village is far from the only Perry Homes Development.
Perhaps the biggest question in all of this is for the Montgomery County Judge and Commissioners. How do plans like this get approved?
Posted by Bob Rehak on 11/12/2019 with thanks to Jeff Miller
806 Days since Hurricane Harvey and 55 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.
For those who are interested, I have reprinted verbatim the full text of Section 5.3.5 from the Montgomery County Drainage Criteria Manual below.
Sheet flow from undeveloped areas into an existing or a proposed subdivision can create a locallzed flood hazard by overloading street inlets and/or flooding individual lots. Any drainage plan for a proposed subdlviston submitted for review and approval by the Montgomery County Drainage Administrator must address the drainage of all adjacent lands. Both under undeveloped and fully developed conditions. A plan which may be adequate under conditions of ultimate development can be severely deficient during intermediate conditions of development due to sheet flow from adjacent undeveloped land. Provisions must be made to divert 100-year sheet flows to a channel system or to the secondary street and storm sewer system.
Redirection of the sheet flow can usually be achieved through the use of drainage swales located in temporary drainage easements along the periphery of the subdivision. As the adjacent area develops to the point at which the street system can effectlvely handle the sheet flow condition, the temporary drainage swales and easements may be abandoned.. The drainage swales should be relatively shallow, with the excavation spoiled continuously along the subdivision side of the swale to prevent flow from overrunnmg the swale. The swale should have sufficient grade to avoid standing water, but not enough to create erosion problems. Generally, a minimum. grade of 0.1% should be maintained with the maximum grade strongly dependent on local soil conditions.
Such temporary drainage swales may be directed to inlets in the storm sewer system or, preferably, to the appropriate primary outfall channel. lf an undeveloped area is to be drained to a storm sewer, additional inlet and storm sewer capacity must be provided to prevent prolonged street ponding In the subdivision resulting from flow from the undeveloped area. Provisions for this flow must also be included in the design of the street drainage overflow system. The design of temporary drainage swales directed to Montgomery County drainage channels must include adequate provisions to drop the flow into the channel through an approved structure in order to avoid excessive erosion of the channel banks.
Outfalling the temporary swale into the backslope drainage system for the channel is unacceptable because the backslope drainage interceptor structures are not adequate to convey flow from an off-site swale. A typical approved structure is shown in Figure 6.3, With the exception of the pipe dimension. The pipe must be sized to handle the 100-year flow from the off-site area.
https://i0.wp.com/reduceflooding.com/wp-content/uploads/2019/05/SchoolBus.jpg?fit=1500%2C1689&ssl=116891500adminadmin2019-11-12 20:48:302019-11-12 21:32:47Provisions for Off-Site Overland Sheet Flow in Montgomery County Drainage Criteria Manual Warned Perry Homes of Dangers to Elm Grove
“IV. SEDIMENT CONTROL AND SEDIMENTATION PONDS. The subdivider shall provide effective sediment control measures in the planning and construction of subdivisions. Practical combinations of the following technical principles should be applied:
No more than ten acres of land in road right-of-way shall be exposed at any one time during development, without prior approval of the County Engineer.
When land is exposed during development, the exposure shall be kept to the shortest practical period of time.
Temporary vegetation and/or mulching shall be used to protect critical area exposed during development.
Sediment basins and traps shall be installed and maintained in properly designated places to remove sediment from runoff waters on land undergoing development.
Provisions shall be made to accommodate the increased runoff caused by changed soil and surface conditions during and after development.
The permanent final vegetation and structures shall be installed as soon as practical in the development.
The development plat shall be fitted to the topography and soils so as to create the least erosion potential.”
Let’s compare these principles with Perry’s practices.
Strike One
Shall provide effective sediment control measures in construction?
Photo taken shortly after May 7th flood on southern section of Woodridge Village.
Strike Two
No more than 10 acres of land shall be exposed at any one time?
How about 268 acres?
Strike Three
Land exposed for shortest practical period of time?
Drone footage of Woodridge Village southern section from May 9. Shot of same area (from different angle) six months later.
Strike Four
Temporary vegetation?
Photo taken 11/4/2019, months after land was clearcutAND after two major floods.
Strike Five
Provisions to accommodate increased runoff?
Block after block of Elm Grove residents dragged their lives to the curb after being inundated by increased runoff from May 7th and Imelda.
Strike 6
Final structures installed as soon as practical? Let’s look at detention ponds…that aren’t there…despite months of ideal construction weather.
The N1 Detention pond should have been installed in the foreground months ago. TheN2 Detention Area (green triangle excavated by MoCo in 2006) was supposed to be expanded, but was not. The N3 detention pond was to stretch from Taylor Gully in the bottom of the frame, almost to the tree line at the top. But nothing has been done.
Strike 7
Plat fitted to soils to create the least erosion possible?
Wetlands abounded on this property. But Perry contractors filled in natural wetlands and streams.
Seven Strikes and You’re Out?
Not if you’re Perry Homes. Because when I first complained to the TCEQ about sediment flowing from the site in May, the TCEQ referred the investigation to Montgomery County. Then Montgomery County referred it to LJA Engineering. Perry Homes, of course, hired LJA to do the engineering on this site. So LJA was investigating itself and its client. Surprise, surprise, everyone called the problem fixed after installing some silt fencing in May. But it wasn’t fixed. Five months later, even more people flooded during Imelda than on May 7.
With the exception of some work on detention pond S2 last summer, Perry has not bothered to:
Expand detention capacity
Plant vegetation
Install sediment basins
Reduce runoff
Compensate for the wetlands and streams they filled in
Perry has done nothing in SEVEN months that reduced flood risk to Elm Grove. The work they did last summer didn’t prevent flooding in September. And they haven’t done anything since.
Posted by Bob Rehak on 11/12/2019, with thanks to Jeff Miller
805 Days since Hurricane Harvey and 54 since Imelda
The thoughts expressed in this post represent my opinions on matters of public policy 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/2019/11/RJR_4399.jpg?fit=1500%2C1000&ssl=110001500adminadmin2019-11-11 22:59:332019-11-11 23:06:13Perry Homes Apparently Violating Montgomery County Development Regulations, Too
Aerial Photos of Lake Houston Dam Dramatize Need for More Gates
Before Harvey hit, we knew tremendous rains were coming. But we could do little to prepare Lake Houston for the onslaught. The small gates you see in the photo below release a combined 10,000 cubic feet per second (CFS). That’s nothing compared to the 150,000 from the gates at the Lake Conroe Dam.
We Were Sunk
When Lake Conroe had to open its gates during Harvey, we were sunk. Literally. Had we had bigger, more modern gates on Lake Houston, we might have been able to lower the lake fast enough to avoid flooding thousands of homes.
11-Foot High Wall of Water Cascaded Over Spillway
Of course, Lake Houston also has a spillway. In fact, the spillway represents the primary way to shed water from the lake. The top of that spillway is at 42.38 feet.
But Harris County Flood Control District’s (HCFCD) final report on Hurricane Harvey stated that a record pool elevation of 53.1 ft was recorded at the Lake Houston Spillway.
HCFCD estimated that’s 5 times the average flow of Niagara Falls and that the flow rate would fill NRG Stadium in 3.5 minutes.
Ten More Gates Could Have Lowered Harvey Flood by 1.9 Feet
HCFCD commissioned a study by Frees & Nichols about what effect additional gates would have in the event of another Harvey. The study found that ten more gates could have lowered the level of the flood by up to 1.9 feet (about 23 inches). That would have saved thousands of homes from flooding in the Lake Houston Area.
Interestingly, the WAY more gates would prevent flooding was not through pre-release; Harvey would have refilled the lake in a matter of hours and the storm lasted days. Rather, additional gates would have widened the spillway area so more water could move over the dam every second. Think of it in these terms: twice the width, half the height. (That’s an over-simplified example of how the principle works; ten more gates would not actually double the width.)
Is Pre-Release Practical?
The Frees & Nichols study only considered one case – Harvey. For lesser floods, the gates could help make pre-release a viable strategy for the Lake Houston Area. At least in my opinion.
Here’s how.
In the last year, the City prevented homes from flooding several times by pre-lowering the lake. But the small gate capacity meant that we had to start releasing water DAYS beforehand to make an appreciable difference in the lake level. That has to be nerve wracking for Public Works.
Where the Gate Project Stands
Earlier this year, the City of Houston secured a FEMA grant to design and construct more gates for the Lake Houston Dam. The two-phase grant covers design and construction. Each phase must be completed within 18 months, though extensions are possible. Currently, we are four months into the 18-month design phase. That means we should see more gates by mid-2022.
In the meantime, the photos below give you a feeling for the immensity of the project.
Posted by Bob Rehak on 11/14/2019
807 Days since Hurricane Harvey
Provisions for Off-Site Overland Sheet Flow in Montgomery County Drainage Criteria Manual Warned Perry Homes of Dangers to Elm Grove
Section 5.3.5 of the Montgomery County Drainage Criteria Manual (Pages 83-84) specifically address flooding of established subdivisions by land under development. For example when Elm Grove was flooded from clearcut land in Woodridge Village. Had Perry Homes, its subsidiaries and contractors followed the requirements in the Manual, Elm Grove might not have flooded.
Provisions Adequate for Ultimate Development Can Be Severely Deficient for Intermediate Stages
The section on Offsite Overland Flow starts out by saying, “Sheet flow from undeveloped areas into an existing or a proposed subdivision can create a localized flood hazard by overloading street inlets and/or flooding individual lots.” This is exactly what happened to Elm Grove Village and North Kingwood Forest in May and September of this year. City of Houston storm drains already taxed to the max became overloaded when water broke out of Woodridge Village and started flowing down the streets of Elm Grove and North Kingwood Forest.
The text in the Drainage Manual then continues. “Any drainage plan for a proposed subdlvision submitted for review and approval by the Montgomery County Drainage Administrator must address the drainage of all adjacent lands. Both under undeveloped and fully developed conditions. A plan which may be adequate under conditions of ultimate development can be severely deficient during intermediate conditions of development due to sheet flow from adjacent undeveloped land. Provisions must be made to divert 100-year sheet flows to a channel system or to the secondary street and storm sewer system.” [Emphasis added.]
The LJA Drainage Analysis claimed Woodridge would create “No adverse impacts to neighboring developments or Taylor Gully.” However, the LJA analysis did not:
No Swales to Redirect Sheet Flow
The next paragraph of the Montgomery County Drainage Criteria Manual starts, “Redirection of the sheet flow can usually be achieved through the use of drainage swales located in temporary drainage easements along the periphery of the subdivision.” Perry Homes built no such swales … at least not adequate ones.
No Berms to Block Sheet Flow
Later in that same paragraph, the Manual talks about building berms between the swales and adjoining neighborhoods to prevent the flow from overrunning the swale. Unfortunately, on May 7th, no such berms existed. They did for Imelda, but they proved inadequate to divert the sheet flow and they had gaps in them.
No Additional Storm Sewer Capacity
The next paragraph talks about building “additional inlet and storm sewer capacity … to prevent prolonged street ponding in the (neighboring) subdivision resulting from flow from the undeveloped area.” That didn’t happen either.
No Planning for Rain Before Detention Ponds Fully Built
Perry Homes took none of these precautions. LJA never planned for them (as far as I can see from publicly available documents). Reading LJA’s drainage analysis, one gets the impression that no one ever even conceived of rainfall before they could build all the detention ponds for Woodridge Village. That turned out to be yet another fatal assumption. Despite all the warnings and mitigation advice in Montgomery County’s Drainage Criteria Manual.
Add this to a long and growing list of other things they ignored, underestimated, or mischaracterized.
Stay Tuned for More
The list goes on and on. I have barely started. This series could last for weeks. The MoCo Drainage Manual goes on for almost 200 pages. And Woodridge Village is far from the only Perry Homes Development.
Perhaps the biggest question in all of this is for the Montgomery County Judge and Commissioners. How do plans like this get approved?
Posted by Bob Rehak on 11/12/2019 with thanks to Jeff Miller
806 Days since Hurricane Harvey and 55 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.
For those who are interested, I have reprinted verbatim the full text of Section 5.3.5 from the Montgomery County Drainage Criteria Manual below.
Section 5.3.5 Off-Site Overland Flow from the Montgomery County Drainage Criteria Manual (See Pages 83 and 84)
Sheet flow from undeveloped areas into an existing or a proposed subdivision can create a locallzed flood hazard by overloading street inlets and/or flooding individual lots. Any drainage plan for a proposed subdlviston submitted for review and approval by the Montgomery County Drainage Administrator must address the drainage of all adjacent lands. Both under undeveloped and fully developed conditions. A plan which may be adequate under conditions of ultimate development can be severely deficient during intermediate conditions of development due to sheet flow from adjacent undeveloped land. Provisions must be made to divert 100-year sheet flows to a channel system or to the secondary street and storm sewer system.
Redirection of the sheet flow can usually be achieved through the use of drainage swales located in temporary drainage easements along the periphery of the subdivision. As the adjacent area develops to the point at which the street system can effectlvely handle the sheet flow condition, the temporary drainage swales and easements may be abandoned.. The drainage swales should be relatively shallow, with the excavation spoiled continuously along the subdivision side of the swale to prevent flow from overrunnmg the swale. The swale should have sufficient grade to avoid standing water, but not enough to create erosion problems. Generally, a minimum. grade of 0.1% should be maintained with the maximum grade strongly dependent on local soil conditions.
Such temporary drainage swales may be directed to inlets in the storm sewer system or, preferably, to the appropriate primary outfall channel. lf an undeveloped area is to be drained to a storm sewer, additional inlet and storm sewer capacity must be provided to prevent prolonged street ponding In the subdivision resulting from flow from the undeveloped area. Provisions for this flow must also be included in the design of the street drainage overflow system. The design of temporary drainage swales directed to Montgomery County drainage channels must include adequate provisions to drop the flow into the channel through an approved structure in order to avoid excessive erosion of the channel banks.
Outfalling the temporary swale into the backslope drainage system for the channel is unacceptable because the backslope drainage interceptor structures are not adequate to convey flow from an off-site swale. A typical approved structure is shown in Figure 6.3, With the exception of the pipe dimension. The pipe must be sized to handle the 100-year flow from the off-site area.
Perry Homes Apparently Violating Montgomery County Development Regulations, Too
On September 26th, the City of Houston fired off a Cease-and-Desist Letter to Perry Homes regarding its Woodridge Village development just north of Elm Grove. The letter warned Perry and its subsidiaries to stop sending sediment into Houston storm drains. Now it appears the Perry gang is violating Montgomery County regulations, too. Let me call your attention to page 28 of the Montgomery County Subdivision Rules and Regulations. The sediment section reads (and I quote verbatim):
“IV. SEDIMENT CONTROL AND SEDIMENTATION PONDS. The subdivider shall provide effective sediment control measures in the planning and construction of subdivisions. Practical combinations of the following technical principles should be applied:
Let’s compare these principles with Perry’s practices.
Strike One
Shall provide effective sediment control measures in construction?
Strike Two
No more than 10 acres of land shall be exposed at any one time?
Strike Three
Land exposed for shortest practical period of time?
Strike Four
Temporary vegetation?
Strike Five
Provisions to accommodate increased runoff?
Strike 6
Final structures installed as soon as practical? Let’s look at detention ponds…that aren’t there…despite months of ideal construction weather.
Strike 7
Plat fitted to soils to create the least erosion possible?
Seven Strikes and You’re Out?
Not if you’re Perry Homes. Because when I first complained to the TCEQ about sediment flowing from the site in May, the TCEQ referred the investigation to Montgomery County. Then Montgomery County referred it to LJA Engineering. Perry Homes, of course, hired LJA to do the engineering on this site. So LJA was investigating itself and its client. Surprise, surprise, everyone called the problem fixed after installing some silt fencing in May. But it wasn’t fixed. Five months later, even more people flooded during Imelda than on May 7.
With the exception of some work on detention pond S2 last summer, Perry has not bothered to:
Yet Kathy Perry Britton, Perry Homes CEO, talks about the value of character, integrity and decisive action. The value of practicing good corporate responsibility. And Perry Homes’ commitment to excellence and distinguished reputation.
News flash, Ms. Britton. Going 0-7 doesn’t show a commitment to excellence. And suing flood victims certainly won’t establish a distinguished reputation. Although it may put you in the Hall of Shame with Montgomery County Commissioners who refuse to enforce their own regulations.
Posted by Bob Rehak on 11/12/2019, with thanks to Jeff Miller
805 Days since Hurricane Harvey and 54 since Imelda
The thoughts expressed in this post represent my opinions on matters of public policy and safety. They are protected by the First Amendment of the US Constitution and the Anti-SLAPP Statute of the Great State of Texas.