4/29/24 – The rainfall distribution in last night’s storm was very uneven. It ranged from a tenth of an inch in some places to more than 10 inches in others.
Totals to the north and east of Houston approached 8-10 inches in places. But most of Harris County received less than 2 inches.
Regardless, the heaviest rainfall in the upper reaches of the East Fork San Jacinto watershed will migrate downstream in the next 2-3 days and cause flooding in low-lying areas near New Caney. The West Fork should only be moderately affected.
After three hours of driving around this morning, all ditches and minor streams that I saw appeared to be within their banks.
Very Uneven Rainfall Distribution
The farther north and east you went, rainfall increased. The gage at US59 and the West Fork received only 1.76 inches.
My rain gage by Kingwood High School recorded 3.11 inches. And a friend who lives by the Montgomery County line recorded a little more than 4 inches.
The Trinity River Authority recorded 10.92 inches on Caney Creek at a small town called Fryday north of Lake Livingston. That gage recorded a whopping 6 inches in one hour between 8 and 9 PM last night.
A gage in Mont Belvieu recorded almost 9 inches. Almost 5 inches of that fell in one hour between 2 and 3 AM.
Most of the higher totals occurred in watersheds that will not drain directly into Harris County. At 1PM on Monday, only six gages in and around the county showed danger signals (meaning a stream was in danger of coming out of its banks).
Most Streams in Banks
The good news: Only one stream at this hour is in danger of coming out of its banks upstream from Lake Houston. That’s Peach Creek near 2090. Peach Creek forms the western boundary of Lake Houston Park.
The bad news: SJRA is releasing almost 10,800 cubic feet per second from Lake Conroe at noon due to heavy rains north of the lake.
From SJRA.net at noon 2.29.24Rainfall totals north of Lake Conroe and around Lake Livingston. From Harris County Flood Warning System, noon 4.29.24.
Farther south, however, totals dropped off rapidly. Parts of western and southern Harris received only a tenth of an inch!
From Harris County Flood Warning System as of 1PM 4/29/24
Flood Forecasts
Because of the rainfall distribution, you need to look upstream from where you are to see whether your area is in danger of flooding. You also need to factor in travel time for the floodwaters. Due to the distance of the heaviest rainfall, flood impacts will be delayed.
Lake Houston
Inflows from the East Fork, Peach and Caney Creeks, and Luce Bayou will result in a rise in the lake level Tuesday into Thursday. Elevated water levels and flows will be likely through Lake Houston for much of this week, according to Jeff Lindner, Harris County Meteorologist.
West Fork San Jacinto
Lindner expects no flooding at this time…again due to the very uneven rainfall distribution.
Much of the rainfall overnight fell above (north) of Lake Conroe. That will buffer some of this inflow. Additionally heavy rainfall largely missed Spring and Cypress Creeks and only modest amounts occurred along middle and upper Lake Creek. So, additional inflows below Lake Conroe look to be minimal.
The river is not expected to reach flood stage at US 59. However, you should continue to monitor the situation for any changes.
This morning, the West Fork was up slightly. Large amounts of foam and debris were moving downstream. But even low-lying areas such as River Grove Park and the area under the US59 bridge were well above water.
River Grove Park Boat Dock area, around 10AM on 4.29.24West Fork at US59 looking S toward Houston. At 10AM, the river was still well within its banks.
That could change by tomorrow morning.
Worst Flooding Will Be on East Fork at New Caney
A significant rise in the East Fork will start on Tuesday into Wednesday. The river will rise just below major flood level later this week.
At the forecasted levels, FM 1485 will be impassable on the west approaches and several roads downstream of FM 1485 will become flooded and impassable on the west side of the channel. Additionally low lying areas along the river in River Terrace will experience high water, according to Lindner.
Stay tuned for more updates tomorrow and Wednesday.
Posted by Bob Rehak on 4/29/24based on information provided by Harris County Meteorologist Jeff Lindner
2435 Days since Hurricane Harvey
https://i0.wp.com/reduceflooding.com/wp-content/uploads/2024/04/image001-1.png?fit=597%2C463&ssl=1463597adminadmin2024-04-29 14:35:512024-04-29 17:05:57Storm Report: Flooding Delayed Because of Rainfall Distribution
A breach at the giant Hallett Mine on the San Jacinto West Fork that began in late January or early February is still open and expanding.
Two Pairs of Pictures, Two Weeks Apart
I first reported the breach on April 10. Below are pictures taken then and today.
Hallett Breach, April 10, 2024Hallett Breach, April 24, 2024
In the pictures above, note the difference in the river bank on the left. It appears much more eroded. Also note the freestanding tree in the water on the right in the second photo that is not visible in the first.
Comparison of these wider shots shows more differences.
Hallett Breach, April 10, 2024Hallett Breach, 4/28/2024.
The first shots in each pair were taken when the water was up due to heavy rains upstream. The second shots were taken when the river was at its normal level (57 feet at SH99 as opposed to 66 feet).
In the shot immediately above, note the lack of vegetation on the sidewalls of the pond. That’s one indication that the height of water in this pond was much higher at one time.
Google Earth Image
This image from Google Earth shows water draining out of the pond on February 19.
Hallett Breach in satellite image from Google Earth taken on 2/19/2024shows silty water pouring out of the mine.
Impacts on River
One boater I interviewed for this post last Wednesday when SJRA was releasing 530 cubic feet per second from Lake Conroe said he could normally get all the way to Conroe in his flat bottomed boat at that flow rate. But on that day, he was frequently hitting bottom.
This is consistent with the experience of boaters launching farther downstream in River Grove Park. There, the river depth is now just 1-2 feet in places. And that’s after it was dredged just four years ago.
The Kingwood Service Association is studying ways to keep its boat launch open. But the need for dredging is becoming more expensive and frequent.
I should add in fairness that the river creates a fair amount of erosion on its own and that Hallett isn’t the only mine on the West Fork with breaches in its dikes.
It is, however, the largest mine by far and has a history of dumping its waste into the West Fork. Searching on the keyword “Hallett” in this website reveals 30 posts that include references to the controversial mine.
It has now been approximately three months since the breach.
Posted by Bob Rehak on 4/28/2024
2434 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/2024/04/20240428-DJI_20240428150341_0458_D-2.jpg?fit=1100%2C778&ssl=17781100adminadmin2024-04-28 17:35:382024-05-14 17:23:32Breach at Hallett Mine Expanding
In 2019, Montgomery County posted a minor update to a drainage criteria manual first published in 1989. However, in February 2024, the County published a draft of a comprehensive new update to the county’s drainage standards. The 124-page manual is a thorough rewrite that brings the County’s standards up to date and more in line with surrounding areas.
Some Major Revisions
Because the manual is targeted to engineers, it gets very complex very fast. However, it is obvious that Montgomery County took pains to remedy some of the shortcomings of the past. For instance:
Section 1.4
Addresses approved hydraulic modeling software packages. It’s not that the packages are revolutionary. It’s that it requires the use of industry-standard packages. The previous manual did not; it only recommended certain packages. According to one flood plain manager I talked to, this will greatly facilitate the checking of plans. (See Page 10.)
Section 1.5
Specifies “No Adverse Impact” from drainage. The County says, “…one property owner should not be allowed to adversely affect the rights of other members of the community.” This protects the rights of neighboring property owners and also protects the natural systems that provide flood mitigation benefits to the community. It specifically prohibits flooding of downstream neighbors.
Significantly, No Adverse Impact includes impacts other than water surface elevation. They include peak flow, velocity and flow type. (See Page 11.)
Section 2.2.1
Mandates use of certain roughness coefficients for use in different situations. This affects calculations for the speed of runoff. They are critical for determining how fast and high flood peaks will build. In the old manual, calculating the roughness was somewhat subjective. (See pages 16, 48 and 50.)
Section 3.3
Unifies the discussion of erosion controls (both structural and natural) in great detail.
Section 5.3
Requires more storm drain inlets along roads by reducing spacing to 500 feet from 750.
Section 5.4
Requires land plan and street layout changes to improve stormwater conveyance in 100-year events.
Section 6.2
Stipulates that all projects shall mitigate and attenuate the runoff for 5-, 10- and 100-year storm events.
Section 6.3
Requires detention for all proposed developments, regardless of size. It also specifies how the amount will be calculated, and minimum rates (acre feet per acre) for different sizes and types of developments. In addition to other things, it specifies that post-development runoff rates shall not exceed pre-development rates.
Section 7.2
Discusses acceptable floodplain mitigation measures. For instance, “Natural channel clearing to reduce friction losses within the floodplain shall not be allowed as an acceptable floodplain mitigation measure.”
Maintenance
The name and contact information for the entity responsible for maintenance of detention facility, channels, and storm sewers must be listed on construction drawings under the proposed guidelines. “Maintenance shall be the responsibility of the private property owner and not the County,” says the draft manual in various sections.
Still Doesn’t Completely Embrace Harris County Recommendations
From a public protection standpoint, the changes in the new drainage criteria manual may not be revolutionary, but they are a vast improvement according to several hydrologists and a flood forecaster I consulted.
Does it incorporate the minimum drainage standards that Harris County urged surrounding counties to adopt after Hurricane Harvey? Some, but not all of them.
The table below summarizes Harris County’s recommendations and the recommendations reflected in Montgomery County’s draft drainage criteria manual.
Montgomery County already uses Atlas 14 rainfall rates as the basis for all its drainage calculations. That will continue if the new draft drainage criteria are adopted. That’s great.
Even better though is this news. With a few minor exceptions, Montgomery County will require a minimum detention rate of .55 acre-feet per acre. It’s not quite up to Harris County rates, but it’s WAAAAAY better than nothing.
Previously, many developments used hydrographic timing surveys to avoid building any stormwater detention at all. But if adopted, the new drainage criteria will prohibit the use of such surveys. They will require detention for all new developments.
Timing surveys encouraged developers to get their water to bayous as fast as they could, which built flood peaks faster and higher for people downstream.
Fill, Finished-Floor Elevations
Sadly, Montgomery County’s draft drainage criteria would allow fill to be brought into the 500-year flood plain. In extreme events, this could constrict the width of the floodplain and cause a rise in flood levels.
The proposed finished-floor-elevation requirements in MoCo are also less stringent than Harris County. That, however, is the sort of thing more likely to affect Montgomery County residents than those downstream.
I remember owning a new home in the Dallas area back in the early 1980s that was supposed to be 1-foot above the 100-year flood plain. Within three years, it flooded. A new survey by the Army Corps of Engineers found that because of insufficiently mitigated upstream development during those three years, we were actually ten feet below the 100-year floodplain instead of a foot above it.
Montgomery County is also revising its subdivision regulations. They may have more to say on this topic.
Complete Manuals and Summary of Drainage Revisions
To see the old and proposed new drainage criteria manuals, see these links:
Storm Report: Flooding Delayed Because of Rainfall Distribution
4/29/24 – The rainfall distribution in last night’s storm was very uneven. It ranged from a tenth of an inch in some places to more than 10 inches in others.
Totals to the north and east of Houston approached 8-10 inches in places. But most of Harris County received less than 2 inches.
Regardless, the heaviest rainfall in the upper reaches of the East Fork San Jacinto watershed will migrate downstream in the next 2-3 days and cause flooding in low-lying areas near New Caney. The West Fork should only be moderately affected.
After three hours of driving around this morning, all ditches and minor streams that I saw appeared to be within their banks.
Very Uneven Rainfall Distribution
The farther north and east you went, rainfall increased. The gage at US59 and the West Fork received only 1.76 inches.
My rain gage by Kingwood High School recorded 3.11 inches. And a friend who lives by the Montgomery County line recorded a little more than 4 inches.
The Trinity River Authority recorded 10.92 inches on Caney Creek at a small town called Fryday north of Lake Livingston. That gage recorded a whopping 6 inches in one hour between 8 and 9 PM last night.
A gage in Mont Belvieu recorded almost 9 inches. Almost 5 inches of that fell in one hour between 2 and 3 AM.
Most of the higher totals occurred in watersheds that will not drain directly into Harris County. At 1PM on Monday, only six gages in and around the county showed danger signals (meaning a stream was in danger of coming out of its banks).
Most Streams in Banks
The good news: Only one stream at this hour is in danger of coming out of its banks upstream from Lake Houston. That’s Peach Creek near 2090. Peach Creek forms the western boundary of Lake Houston Park.
The bad news: SJRA is releasing almost 10,800 cubic feet per second from Lake Conroe at noon due to heavy rains north of the lake.
Farther south, however, totals dropped off rapidly. Parts of western and southern Harris received only a tenth of an inch!
Flood Forecasts
Because of the rainfall distribution, you need to look upstream from where you are to see whether your area is in danger of flooding. You also need to factor in travel time for the floodwaters. Due to the distance of the heaviest rainfall, flood impacts will be delayed.
Lake Houston
Inflows from the East Fork, Peach and Caney Creeks, and Luce Bayou will result in a rise in the lake level Tuesday into Thursday. Elevated water levels and flows will be likely through Lake Houston for much of this week, according to Jeff Lindner, Harris County Meteorologist.
West Fork San Jacinto
Lindner expects no flooding at this time…again due to the very uneven rainfall distribution.
Much of the rainfall overnight fell above (north) of Lake Conroe. That will buffer some of this inflow. Additionally heavy rainfall largely missed Spring and Cypress Creeks and only modest amounts occurred along middle and upper Lake Creek. So, additional inflows below Lake Conroe look to be minimal.
The river is not expected to reach flood stage at US 59. However, you should continue to monitor the situation for any changes.
This morning, the West Fork was up slightly. Large amounts of foam and debris were moving downstream. But even low-lying areas such as River Grove Park and the area under the US59 bridge were well above water.
That could change by tomorrow morning.
Worst Flooding Will Be on East Fork at New Caney
A significant rise in the East Fork will start on Tuesday into Wednesday. The river will rise just below major flood level later this week.
At the forecasted levels, FM 1485 will be impassable on the west approaches and several roads downstream of FM 1485 will become flooded and impassable on the west side of the channel. Additionally low lying areas along the river in River Terrace will experience high water, according to Lindner.
Stay tuned for more updates tomorrow and Wednesday.
Posted by Bob Rehak on 4/29/24 based on information provided by Harris County Meteorologist Jeff Lindner
2435 Days since Hurricane Harvey
Breach at Hallett Mine Expanding
Correction: This sand pit in this post was sold by Hallett to Riverwalk Porter LLC on January 23, 2024.
A breach at the giant Hallett Mine on the San Jacinto West Fork that began in late January or early February is still open and expanding.
Two Pairs of Pictures, Two Weeks Apart
I first reported the breach on April 10. Below are pictures taken then and today.
In the pictures above, note the difference in the river bank on the left. It appears much more eroded. Also note the freestanding tree in the water on the right in the second photo that is not visible in the first.
Comparison of these wider shots shows more differences.
The first shots in each pair were taken when the water was up due to heavy rains upstream. The second shots were taken when the river was at its normal level (57 feet at SH99 as opposed to 66 feet).
In the shot immediately above, note the lack of vegetation on the sidewalls of the pond. That’s one indication that the height of water in this pond was much higher at one time.
Google Earth Image
This image from Google Earth shows water draining out of the pond on February 19.
Impacts on River
One boater I interviewed for this post last Wednesday when SJRA was releasing 530 cubic feet per second from Lake Conroe said he could normally get all the way to Conroe in his flat bottomed boat at that flow rate. But on that day, he was frequently hitting bottom.
This is consistent with the experience of boaters launching farther downstream in River Grove Park. There, the river depth is now just 1-2 feet in places. And that’s after it was dredged just four years ago.
The Kingwood Service Association is studying ways to keep its boat launch open. But the need for dredging is becoming more expensive and frequent.
I should add in fairness that the river creates a fair amount of erosion on its own and that Hallett isn’t the only mine on the West Fork with breaches in its dikes.
It is, however, the largest mine by far and has a history of dumping its waste into the West Fork. Searching on the keyword “Hallett” in this website reveals 30 posts that include references to the controversial mine.
It has now been approximately three months since the breach.
Posted by Bob Rehak on 4/28/2024
2434 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.
Recommended Changes in New MoCo Drainage Criteria Manual
In 2019, Montgomery County posted a minor update to a drainage criteria manual first published in 1989. However, in February 2024, the County published a draft of a comprehensive new update to the county’s drainage standards. The 124-page manual is a thorough rewrite that brings the County’s standards up to date and more in line with surrounding areas.
Some Major Revisions
Because the manual is targeted to engineers, it gets very complex very fast. However, it is obvious that Montgomery County took pains to remedy some of the shortcomings of the past. For instance:
Section 1.4
Addresses approved hydraulic modeling software packages. It’s not that the packages are revolutionary. It’s that it requires the use of industry-standard packages. The previous manual did not; it only recommended certain packages. According to one flood plain manager I talked to, this will greatly facilitate the checking of plans. (See Page 10.)
Section 1.5
Specifies “No Adverse Impact” from drainage. The County says, “…one property owner should not be allowed to adversely affect the rights of other members of the community.” This protects the rights of neighboring property owners and also protects the natural systems that provide flood mitigation benefits to the community. It specifically prohibits flooding of downstream neighbors.
Significantly, No Adverse Impact includes impacts other than water surface elevation. They include peak flow, velocity and flow type. (See Page 11.)
Section 2.2.1
Mandates use of certain roughness coefficients for use in different situations. This affects calculations for the speed of runoff. They are critical for determining how fast and high flood peaks will build. In the old manual, calculating the roughness was somewhat subjective. (See pages 16, 48 and 50.)
Section 3.3
Unifies the discussion of erosion controls (both structural and natural) in great detail.
Section 5.3
Requires more storm drain inlets along roads by reducing spacing to 500 feet from 750.
Section 5.4
Requires land plan and street layout changes to improve stormwater conveyance in 100-year events.
Section 6.2
Stipulates that all projects shall mitigate and attenuate the runoff for 5-, 10- and 100-year storm events.
Section 6.3
Requires detention for all proposed developments, regardless of size. It also specifies how the amount will be calculated, and minimum rates (acre feet per acre) for different sizes and types of developments. In addition to other things, it specifies that post-development runoff rates shall not exceed pre-development rates.
Section 7.2
Discusses acceptable floodplain mitigation measures. For instance, “Natural channel clearing to reduce friction losses within the floodplain shall not be allowed as an acceptable floodplain mitigation measure.”
Maintenance
The name and contact information for the entity responsible for maintenance of detention facility, channels, and storm sewers must be listed on construction drawings under the proposed guidelines. “Maintenance shall be the responsibility of the private property owner and not the County,” says the draft manual in various sections.
Still Doesn’t Completely Embrace Harris County Recommendations
From a public protection standpoint, the changes in the new drainage criteria manual may not be revolutionary, but they are a vast improvement according to several hydrologists and a flood forecaster I consulted.
Does it incorporate the minimum drainage standards that Harris County urged surrounding counties to adopt after Hurricane Harvey? Some, but not all of them.
The table below summarizes Harris County’s recommendations and the recommendations reflected in Montgomery County’s draft drainage criteria manual.
Atlas 14, Minimum Detention Rates, Hydrologic Timing
Montgomery County already uses Atlas 14 rainfall rates as the basis for all its drainage calculations. That will continue if the new draft drainage criteria are adopted. That’s great.
Even better though is this news. With a few minor exceptions, Montgomery County will require a minimum detention rate of .55 acre-feet per acre. It’s not quite up to Harris County rates, but it’s WAAAAAY better than nothing.
Previously, many developments used hydrographic timing surveys to avoid building any stormwater detention at all. But if adopted, the new drainage criteria will prohibit the use of such surveys. They will require detention for all new developments.
Timing surveys encouraged developers to get their water to bayous as fast as they could, which built flood peaks faster and higher for people downstream.
Fill, Finished-Floor Elevations
Sadly, Montgomery County’s draft drainage criteria would allow fill to be brought into the 500-year flood plain. In extreme events, this could constrict the width of the floodplain and cause a rise in flood levels.
The proposed finished-floor-elevation requirements in MoCo are also less stringent than Harris County. That, however, is the sort of thing more likely to affect Montgomery County residents than those downstream.
I remember owning a new home in the Dallas area back in the early 1980s that was supposed to be 1-foot above the 100-year flood plain. Within three years, it flooded. A new survey by the Army Corps of Engineers found that because of insufficiently mitigated upstream development during those three years, we were actually ten feet below the 100-year floodplain instead of a foot above it.
Montgomery County is also revising its subdivision regulations. They may have more to say on this topic.
Complete Manuals and Summary of Drainage Revisions
To see the old and proposed new drainage criteria manuals, see these links:
Also see Montgomery County’s Summary of the Revisions.
For easy future reference, you can also find these documents under the Regulations tab in the reports page.
As of this writing, it is not clear when the new manual will go before Commissioners Court for approval.
Posted by Bob Rehak on 4/27/24
2433 Days since Hurricane Harvey
For the more technically inclined, Montgomery County provided this summary of significant revisions.