Montgomery County has finally updated its drainage criteria manual…eight years after Hurricane Harvey caused widespread flooding that exposed shortcomings in its previous manual which dated to the 1980s.
Unanimously Approved
MoCo Commissioners approved the new manual unanimously this morning. The draft of the new manual was first proposed in early 2024. That followed a minor update in 2019 from the county’s old 1988 drainage criteria manual in effect at the time of Harvey.
The new manual does not adopt all of the minimum drainage recommendations proposed by Harris County for areas draining into Harris, though it is a vast improvement over the previous iteration.
Minimum Drainage Requirements Proposed by Harris County
1. Using Atlas 14 rainfall rates for sizing storm water conveyance and detention systems. 2. Requiring a minimum detention rate of 0.55 acre-feet per acre of detention for any new development on tracts one acre or larger. A single-family residential structure and accessory building proposed on an existing lot is exempt from providing detention. 3. Prohibiting the use of hydrograph timing as a substitute for detention on any project, unless it directly outfalls into Galveston Bay. 4. Requiring “no net fill” in the current mapped 500-year floodplain, except in areas identified as coastal zones only. 5. Requiring the minimum Finished Flood Elevation of new habitable structures be established at or waterproofed to the 500-year flood elevation as shown on the effective Flood Insurance Study.
Major Changes in New MoCo Drainage Criteria Manual
MoCo’s new drainage criteria manual includes some, but not all, of those recommendations.
Comparison of Recommendations
Measure
Harris
Montgomery
Use of Atlas 14 Rainfall Standards
Yes
Yes
Minimum Detention Rate
.55 acre feet/acre
.55 acre feet/acre for areas greater than 20 acres (see page 57)
Prohibit Hydrographic Timing
Yes
Yes, but with limitations (see page 68)
No Net Fill in 500-Yr Floodplain
Prohibited
Still allowed
Finished Floor Elevation
At 500-yr flood elevation
Requires drainage be maintained one foot below lowest finished floor elevation for 100-year event (See page 54)
It’s not perfect. But it’s a vast improvement. Assuming the county enforces them.
Montgomery County resident Chad Price addressed Commissioners Court before the vote. He applauded most of the updates in the manual. However, he also urged commissioners to adopt ALL of Harris County’s minimum requirements.
Price emphasized the uncertainty surrounding rainfall rates, the increasing frequency of storms that exceed predicted maximums, and flood maps that have yet to be updated to reflect Atlas-14.
He made two excellent points:
We must not design drainage systems based on outdated data.
Better flood regulations are not about stopping growth—they’re about making sure growth is sustainable and safe.
In that regard, Price urged commissioners to update building codes, require smarter drainage planning, preserve natural floodplains, and use science-based floodplain mapping. He said, “These steps will reduce long-term costs to taxpayers, protect property values, and most importantly, safeguard our communities.”
Next Up
Montgomery County’s Floodplain Manager currently shows floodplain regulations adopted in 2014. That’s before the Tax Day, Memorial Day, Harvey, Imelda and May Day 2024 floods. Given the thousands of homes in MoCo that flood repeatedly, there may be some opportunities for improvement in those floodplain regs.
Posted by Bob Rehak on 8/26/25
2919 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/2025/08/20250826-MoCo-DCM-Cover.jpg?fit=1100%2C710&ssl=17101100adminadmin2025-08-26 16:41:062025-08-26 17:26:10MoCo Adopts New Drainage Criteria Manual 8 Years After Harvey
8/25/25 – For the first time since authorities broke ground for the Northpark expansion project in April 2023, it’s possible to clearly see the outlines of the finished project on the ground. The first all-weather evacuation route from Kingwood is shaping up nicely.
For the most part, contractors have straightened out the zigs and zags. They have finished large sections of the westbound lanes. Drainage for the eastbound lanes is progressing nicely. And soon they will start pouring concrete for large sections of the remaining eastbound lanes.
Pictures Taken on 8/25/25
The drone pictures below show the progress…starting from Russell Palmer Road and heading east.
Notice how virtually all of the old Eastbound concrete has been removed as far as the eye can see.Looking W from near Warren’s Southern Gardens
Contractors are installing drainage under the westbound lanes. However, the drainage work is moving from west to east.
Looking West from near the Kolache Factory and the entrance to Kings Mill.Today, they were working near the Kolache Factory.Father west, sidewalks have already been installed on the north side of the street.
The photo above shows approximately where the bridge over the railroad tracks and Loop 494 will start. Notice how two lanes veer right to make room for the bridge.
Connecting the drainage from the east and west sides of the railroad tracks will require the twin five foot steel pipes stockpiled in the foreground.
However, work on boring under the tracks has stalled for now. But the Lake Houston Redevelopment Authority believes that the utility conflicts which have delayed that operation will soon be resolved. Then boring under the tracks can resume.
Looking N along Loop 494. Note how one of the bore pits is blocking completion of the northbound expansion lanes.Looking S along 494 from over Northpark. Between Loop 494 and 59, crews are still connecting drainage under the roadway.Right now, they’re finishing the connection in front of Whataburger.Almost at US59, crews are making room for the surface lanes that will flank the bridge.
Looking in the opposite direction…
Those surface lanes will also connect to the surface lanes east of Loop 494 (right of the pavement.The new development on the SE corner of Northpark and Loop 494 will be called the Enclave.
The developer plans to build a 100 homes in the Enclave.
https://i0.wp.com/reduceflooding.com/wp-content/uploads/2025/08/20250825-DJI_20250825145032_0202_D.jpg?fit=1100%2C619&ssl=16191100adminadmin2025-08-25 18:25:472025-08-25 18:25:48Northpark Shaping Up
8/24/25 – The abandoned Hanson Aggregate sand-mine on the San Jacinto West Fork had a massive breach of its northern dike this evening – unrelated to weather. According to the Montgomery County Appraisal District, Heidelberg Materials Southwest AGG LLC now owns the property where the breach occurred.
Location of breach circled in red.
Breach Discovered Shortly after 6 PM on 8/24/25
A thousand acre-feet of water or possibly more rushed out of the 140-acre pond, obliterating everything in its path, and depositing enough sand and silt in the San Jacinto West Fork to back water up in the river.
I received a call from a neighbor who alerted me to the breach at 6:38 PM. And by the time I arrived shortly after 7 PM, the water level in the pond had dropped an estimated 8-10 feet he said.
Water was still rushing out of the pond fast enough to cause large chunks of the shore to break away, endangering onlookers who had to back away.
The water eroded a channel approximately 800 feet long, 50 to 200 feet wide and perhaps 15-20 feet deep – all in a matter of minutes.
The cause of the breach is unknown. However, aerial photos showed a small excavator and piles of drain pipe near the breach.
Photos, Video Taken Between 7 and 8 PM on 8/24/25
Below are photos and video of the devastation.
Water rushing out through breach in pit wall. West Fork San Jacinto is just out of frame at the top. Looking W.Compare height of breach to height of excavator for scale.Also note amount of decline between water surface and brush along shoreline.Looking upriver at sand and silt expelled from mine.Note large, mature pine trees undermined by rushing water.The raging water mowed down dozens of mature trees as it carved its way to the river.Looking east from over the river at breach and turbulence it created in water.Higher angle looking west shows volume of material swept away.Sediment deposited in West Fork. Looking SEand downriver.Closer shot of water exiting channel.Corrugated pipe next to excavator tracks that were gobbled up by raging water.Close up of excavator at edge of breach.
Here is a 26-second drone video taken while flying from the pond to the river.
There Must Be A Better Way!
Ironically, this mine had one of the largest setbacks on the West Fork. (See satellite image above.) The setback varied from approximately 400 feet to more than 1,000. However, there was a small drainage channel running along the northern edge of the mine that had a narrower setback And that’s where the breach occurred.
This disaster underscores the need to find a permanent, safe solution for abandoned sand mines along area rivers and streams.
I previously proposed aggregating them over time into a West Fork Greenway which could become a state park. I tentatively named the concept the Montgomery County Lake District.
Instead of letting such mines remain a dangerous blight, turn them into a recreational amenity that could add value to area homeowners and developers.
Posted by Bob Rehak on 8/24/25
2917 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/2025/08/20250824-DJI_20250824193037_0189_D.jpg?fit=1100%2C619&ssl=16191100adminadmin2025-08-24 23:13:172025-08-25 09:14:45Massive Sand-Mine Breach Empties Hundreds of Acre-Feet into West Fork
MoCo Adopts New Drainage Criteria Manual 8 Years After Harvey
Montgomery County has finally updated its drainage criteria manual…eight years after Hurricane Harvey caused widespread flooding that exposed shortcomings in its previous manual which dated to the 1980s.
Unanimously Approved
MoCo Commissioners approved the new manual unanimously this morning. The draft of the new manual was first proposed in early 2024. That followed a minor update in 2019 from the county’s old 1988 drainage criteria manual in effect at the time of Harvey.
The new manual does not adopt all of the minimum drainage recommendations proposed by Harris County for areas draining into Harris, though it is a vast improvement over the previous iteration.
Minimum Drainage Requirements Proposed by Harris County
The minimum drainage requirements proposed by Harris County included five key measures:
1. Using Atlas 14 rainfall rates for sizing storm water conveyance and detention systems.
2. Requiring a minimum detention rate of 0.55 acre-feet per acre of detention for any new development on tracts one acre or larger. A single-family residential structure and accessory building proposed on an existing lot is exempt from providing detention.
3. Prohibiting the use of hydrograph timing as a substitute for detention on any project, unless it directly outfalls into Galveston Bay.
4. Requiring “no net fill” in the current mapped 500-year floodplain, except in areas identified as coastal zones only.
5. Requiring the minimum Finished Flood Elevation of new habitable structures be established at or waterproofed to the 500-year flood elevation as shown on the effective Flood Insurance Study.
Major Changes in New MoCo Drainage Criteria Manual
MoCo’s new drainage criteria manual includes some, but not all, of those recommendations.
It’s not perfect. But it’s a vast improvement. Assuming the county enforces them.
For ease of future reference, you can find Montgomery County’s new, updated Drainage Criteria Manual on the Reports page under the Regulations tab.
Suggestions by MoCo Resident
Montgomery County resident Chad Price addressed Commissioners Court before the vote. He applauded most of the updates in the manual. However, he also urged commissioners to adopt ALL of Harris County’s minimum requirements.
Price emphasized the uncertainty surrounding rainfall rates, the increasing frequency of storms that exceed predicted maximums, and flood maps that have yet to be updated to reflect Atlas-14.
He made two excellent points:
In that regard, Price urged commissioners to update building codes, require smarter drainage planning, preserve natural floodplains, and use science-based floodplain mapping. He said, “These steps will reduce long-term costs to taxpayers, protect property values, and most importantly, safeguard our communities.”
Next Up
Montgomery County’s Floodplain Manager currently shows floodplain regulations adopted in 2014. That’s before the Tax Day, Memorial Day, Harvey, Imelda and May Day 2024 floods. Given the thousands of homes in MoCo that flood repeatedly, there may be some opportunities for improvement in those floodplain regs.
Posted by Bob Rehak on 8/26/25
2919 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.
Northpark Shaping Up
8/25/25 – For the first time since authorities broke ground for the Northpark expansion project in April 2023, it’s possible to clearly see the outlines of the finished project on the ground. The first all-weather evacuation route from Kingwood is shaping up nicely.
For the most part, contractors have straightened out the zigs and zags. They have finished large sections of the westbound lanes. Drainage for the eastbound lanes is progressing nicely. And soon they will start pouring concrete for large sections of the remaining eastbound lanes.
Pictures Taken on 8/25/25
The drone pictures below show the progress…starting from Russell Palmer Road and heading east.
Contractors are installing drainage under the westbound lanes. However, the drainage work is moving from west to east.
The photo above shows approximately where the bridge over the railroad tracks and Loop 494 will start. Notice how two lanes veer right to make room for the bridge.
However, work on boring under the tracks has stalled for now. But the Lake Houston Redevelopment Authority believes that the utility conflicts which have delayed that operation will soon be resolved. Then boring under the tracks can resume.
Looking in the opposite direction…
The developer plans to build a 100 homes in the Enclave.
For more information, consult the Lake Houston Redevelopment Authority website.
Posted by Bob Rehak on 8/25/25
2918 Days since Hurricane Harvey
Massive Sand-Mine Breach Empties Hundreds of Acre-Feet into West Fork
8/24/25 – The abandoned Hanson Aggregate sand-mine on the San Jacinto West Fork had a massive breach of its northern dike this evening – unrelated to weather. According to the Montgomery County Appraisal District, Heidelberg Materials Southwest AGG LLC now owns the property where the breach occurred.
Breach Discovered Shortly after 6 PM on 8/24/25
A thousand acre-feet of water or possibly more rushed out of the 140-acre pond, obliterating everything in its path, and depositing enough sand and silt in the San Jacinto West Fork to back water up in the river.
I received a call from a neighbor who alerted me to the breach at 6:38 PM. And by the time I arrived shortly after 7 PM, the water level in the pond had dropped an estimated 8-10 feet he said.
Water was still rushing out of the pond fast enough to cause large chunks of the shore to break away, endangering onlookers who had to back away.
The water eroded a channel approximately 800 feet long, 50 to 200 feet wide and perhaps 15-20 feet deep – all in a matter of minutes.
The cause of the breach is unknown. However, aerial photos showed a small excavator and piles of drain pipe near the breach.
Photos, Video Taken Between 7 and 8 PM on 8/24/25
Below are photos and video of the devastation.
Here is a 26-second drone video taken while flying from the pond to the river.
There Must Be A Better Way!
Ironically, this mine had one of the largest setbacks on the West Fork. (See satellite image above.) The setback varied from approximately 400 feet to more than 1,000. However, there was a small drainage channel running along the northern edge of the mine that had a narrower setback And that’s where the breach occurred.
This disaster underscores the need to find a permanent, safe solution for abandoned sand mines along area rivers and streams.
I previously proposed aggregating them over time into a West Fork Greenway which could become a state park. I tentatively named the concept the Montgomery County Lake District.
Instead of letting such mines remain a dangerous blight, turn them into a recreational amenity that could add value to area homeowners and developers.
Posted by Bob Rehak on 8/24/25
2917 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.