9/12/24 – You would think that as more water flows into a ditch, the area under bridges would get larger. But Chris Bloch, a retired Kingwood engineer with an eye for details that affect flooding, made some startling discoveries recently about the areas under four bridges over the Kingwood Diversion Ditch.
Flow areas under two bridges get smaller as you go downstream and flow volume increases.
They constrict flow 30-40% compared to the Kingwood Drive Bridge.
This helps explain flooding problems adjacent to the ditch, he says. Another engineer I interviewed for this article expressed shock. He said, “That can’t be. It’s bewildering.”
The Kingwood Diversion Ditch branches off Bens Branch just north of Northpark Drive by Flowers of Kingwood. Bridges span the ditch in four places: Northpark Drive, Kingwood Drive, Walnut Lane and Deer Springs.
The ditch runs north to south and helps drain the western third of Kingwood. It crosses under Kingwood Drive by the Fire Station. It then continues south to Deer Ridge Park, before turning and outfalling into the San Jacinto West Fork at River Grove Park. See the map below.
Kingwood Diversion Ditch got its name because it diverts water that would otherwise go down Bens Branch. It gives that stormwater an alternate route to the West Fork at bottom of frame.
Not only does the Diversion Ditch carry a percentage of the water from Bens Bench, it also drains streets in several subdivisions along its way to the river.
More and more stormwater empties into it as you move south. But look at the square footage of the areas under the bridges.
Bridge
Opening in SqFt
Northpark
720.8
Kingwood Drive
1,136.5
Walnut Lane
809.7
Deer Springs
689.0
From Kingwood Drive south, the bridge “flow areas” get smaller by approximately 30% and then 40% compared to Kingwood Drive.
Flow area is the size of the opening under the bridge available to convey floodwater without it coming up over the bridge deck.
Pictures of Bridges from Upstream to Down
Here’s what the bridges look like starting upstream, in the same order as the table above. I took all these photos on 9/11/24.
To calculate the square footages, Bloch took physical measurements of depth every two feet from one side of each bridge to the other.
Kingwood Diversion Ditch Bridge at Northpark Drive, looking south.Kingwood Diversion Ditch Bridge at Kingwood Drive, looking NorthKingwood Diversion Ditch Bridge at Walnut Lane looking N, approximately 30% less than Kingwood DriveKingwood Diversion Ditch Bridge at Deer Springs, approximately 40% less than Kingwood Drive.
No wonder many homes and businesses have flooded from the Diversion Ditch!
Flow Area vs. Flow Rates
Of course, flow areas don’t tell the total story, just a large portion of it. Engineers also consider flow rates. But calculating flow rates is more difficult than calculating flow areas.
When water backs up behind a bridge, it can increase pressure which forces more water under, over and around the bridge…faster. Think of spray from a garden hose when you pinch the nozzle with your thumb.
Two problems though:
Water is still backing up to some degree.
The higher pressure causes jetting under the bridge that increases erosion.
For a spectacular example of the damage that jetting can do, look at the Tree Lane Bridge over Bens Branch, slightly east of the Diversion Ditch.
Damage to Tree Lane Bridge over Bens Branch caused by jetting.Photo taken before current repair job started.After repairs started. Note severe erosion downstream from bridge threatening power line corridor. Also note how floodwater downcut underneath 10 inch water line that was once buried.
Engineers perform miracles for us everyday. But sometimes, even their best efforts are no match for Mother Nature when she straps on her Stetson and six shooters. That’s why careful planning, generous safety margins, and coordination between upstream and downstream interests are so crucial.
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/2024/09/KW-Div-Ditch-Bridges-copy.jpg?fit=1100%2C746&ssl=17461100adminadmin2024-09-12 20:47:002024-09-12 21:07:21Bewildering Size of Areas under Diversion-Ditch Bridges
9/11/2024 4 PM CDT – Hurricane Francine is making landfall in southeastern Louisiana.
Although most of my readers live in the Houston area, many have friends and relatives living in Louisiana. This post goes out to them.
Francine Making Landfall in Louisiana
At 3:30 PM on 9/11/24
Stats
According to the National Hurricane Center, at 4 PM CDT, Francine’s eyewall was nearing the Southern Louisiana coast with hurricane force winds.
Maximum sustained winds were measured at 100 mph.
Minimum central pressure was 28.79.
40 Miles SSW of Morgan City
100 Miles WSW of New Orleans
Expected Rainfall: 4-8 inches with local amounts to 12 inches across Southeastern Louisiana, Mississippi and Alabama.
Storm surge: 3-10 feet
Eyewall diameter: 40 nautical miles
Movement to the NE at 17 MPH
Will become extra-tropical cyclone by Friday
Life threatening surf and rip currents
Tornadoes possible.
Graphics
Remembering Another 9/11
Thoughts and prayers for all our neighbors in Louisiana. Just two months ago, we saw what Beryl’s 80 MPH winds did to the Houston area. These winds are 20 MPH faster.
Thoughts and prayers also for all the victims of the 9/11 terrorist attacks in 2001. I had clients who worked near the top floors of the World Trade Center. I will never forget the sickening feeling as the towers fell, knowing they didn’t make it out alive.
Posted by Bob Rehak on 9/11/24
8401 Days since the Twin Towers
2570 since Hurricane Harvey
65 since Beryl
https://i0.wp.com/reduceflooding.com/wp-content/uploads/2024/09/Francine-Just-Before-Landfall.jpg?fit=1000%2C1000&ssl=110001000adminadmin2024-09-11 16:26:242024-09-11 16:26:24Francine Making Landfall in Louisiana
9/10/24 – Update: At 7 PM, the National Hurricane Center announced that Francine became a hurricane with sustained winds of 75 MPH and higher gusts. By 10:20, hurricane hunter aircraft found sustained winds of 85 MPH with central pressure of 979 mb. Hurricane-force winds extend outward up to 35 miles from the center and tropical-storm-force winds extend outward up to 115 miles. Other details have not changed much since 4PM. See below.
The National Hurricane Center’s (NHC) 4 PM update shows Tropical Storm Francine taking aim for Louisiana. Its impacts will likely diminish in the Houston area. However, tropical storm warnings and watches now extend past Louisiana into Mississippi and Alabama, as the forecast track shifts farther east.
Francine at 3:46 PM CDT, 9/10/24
Francine Winds and Forward Speed
At 4 PM, Francine still packed 65 MPH winds with higher gusts. But NHC expects it to reach hurricane strength tonight. By convention, storms become hurricanes at 74 MPH.
A Hurricane Warning is in effect from Sabine Pass eastward to Grand Isle. NHC forecasts that Francine could reach 80 knots/92 MPH at landfall in central Louisiana. If accurate, that would put it just shy of a Category 2 hurricane.
Hurricane hunter aircraft found that pressure in the central core had dropped to 987 mb. The storm has become better organized with increased banding.
Tropical-storm-force winds extend outward up to 140 miles (220 km) from the center. To put that in perspective, Beaumont is 175 miles from Baton Rouge, which is in central Louisiana.
Two NHC graphics depict the probability of damaging winds reaching the Houston area. The first shows the north Houston area has a 5-10 percent chance of experiencing tropical-storm-force winds.
The second shows we have a zero percent chance of experiencing hurricane force winds.
Track
According to NHC, Francine has made a turn toward the northeast and increased its forward motion to 10+ MPH. It should reach the central Louisiana coast sometime Wednesday afternoon or evening. A continued northeastward motion and a faster forward speed are expected tonight and Wednesday.
Surge
We still can expect storm surge in coast areas all the way from Freeport to the Florida Panhandle.
With that comes the associated risk of rip currents.
Rainfall
Francine is expected to bring storm total rainfall of 4 to 8 inches, with local amounts to 12 inches across eastern Louisiana, Mississippi, far southern Alabama and the western Florida Panhandle through Friday morning. This rainfall could lead to considerable flash and urban flooding in those locations.
However, Jeff Linder, Harris County’s meteorologist less than an inch of rain in the Lake Houston Area.
We barely have a chance for flash flooding. And significant rainfall accumulations will be concentrated east of Texas.
5-Day Accumulated Rainfall Predictions from the National Weather Service
While the Lake Houston Area may be spared the storm’s worst effects, the Mississippi Valley won’t. NHC predicts significant flooding for that area.
To put that in perspective, during the last 30 years, we usually have had 10 named storms by September 4 and 11 by September 14. So despite early dire warnings, this season has been less severe than normal.
The 2017 hurricane season should remind us all that it only takes one storm to change lives forever. Pray for our neighbors to the east. And remain vigilant.
Posted by Bob Rehak on 9/10/24
2569 Days since Hurricane Harvey and 69 since Beryl
https://i0.wp.com/reduceflooding.com/wp-content/uploads/2024/09/211929.png?fit=897%2C738&ssl=1738897adminadmin2024-09-10 16:41:512024-09-10 22:48:12Latest NHC Forecasts Show Francine Aiming for Louisiana
Bewildering Size of Areas under Diversion-Ditch Bridges
9/12/24 – You would think that as more water flows into a ditch, the area under bridges would get larger. But Chris Bloch, a retired Kingwood engineer with an eye for details that affect flooding, made some startling discoveries recently about the areas under four bridges over the Kingwood Diversion Ditch.
They constrict flow 30-40% compared to the Kingwood Drive Bridge.
This helps explain flooding problems adjacent to the ditch, he says. Another engineer I interviewed for this article expressed shock. He said, “That can’t be. It’s bewildering.”
One of Two Most Important Projects in Kingwood
Harris County Flood Control District ranked flood-mitigation along the Diversion Ditch as one of the two most important projects in Kingwood.
The Kingwood Diversion Ditch branches off Bens Branch just north of Northpark Drive by Flowers of Kingwood. Bridges span the ditch in four places: Northpark Drive, Kingwood Drive, Walnut Lane and Deer Springs.
The ditch runs north to south and helps drain the western third of Kingwood. It crosses under Kingwood Drive by the Fire Station. It then continues south to Deer Ridge Park, before turning and outfalling into the San Jacinto West Fork at River Grove Park. See the map below.
Not only does the Diversion Ditch carry a percentage of the water from Bens Bench, it also drains streets in several subdivisions along its way to the river.
More and more stormwater empties into it as you move south. But look at the square footage of the areas under the bridges.
Flow area is the size of the opening under the bridge available to convey floodwater without it coming up over the bridge deck.
Pictures of Bridges from Upstream to Down
Here’s what the bridges look like starting upstream, in the same order as the table above. I took all these photos on 9/11/24.
To calculate the square footages, Bloch took physical measurements of depth every two feet from one side of each bridge to the other.
No wonder many homes and businesses have flooded from the Diversion Ditch!
Flow Area vs. Flow Rates
Of course, flow areas don’t tell the total story, just a large portion of it. Engineers also consider flow rates. But calculating flow rates is more difficult than calculating flow areas.
When water backs up behind a bridge, it can increase pressure which forces more water under, over and around the bridge…faster. Think of spray from a garden hose when you pinch the nozzle with your thumb.
Two problems though:
For a spectacular example of the damage that jetting can do, look at the Tree Lane Bridge over Bens Branch, slightly east of the Diversion Ditch.
Engineers perform miracles for us everyday. But sometimes, even their best efforts are no match for Mother Nature when she straps on her Stetson and six shooters. That’s why careful planning, generous safety margins, and coordination between upstream and downstream interests are so crucial.
With some of the fastest growth in the region just upstream from Kingwood, we must plan for ever-increasing volumes of water coming downstream.
Posted by Bob Rehak and Chris Bloch on 6/12/23
2571 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.
Francine Making Landfall in Louisiana
9/11/2024 4 PM CDT – Hurricane Francine is making landfall in southeastern Louisiana.
Although most of my readers live in the Houston area, many have friends and relatives living in Louisiana. This post goes out to them.
Francine Making Landfall in Louisiana
Stats
According to the National Hurricane Center, at 4 PM CDT, Francine’s eyewall was nearing the Southern Louisiana coast with hurricane force winds.
Graphics
Remembering Another 9/11
Thoughts and prayers for all our neighbors in Louisiana. Just two months ago, we saw what Beryl’s 80 MPH winds did to the Houston area. These winds are 20 MPH faster.
Thoughts and prayers also for all the victims of the 9/11 terrorist attacks in 2001. I had clients who worked near the top floors of the World Trade Center. I will never forget the sickening feeling as the towers fell, knowing they didn’t make it out alive.
Posted by Bob Rehak on 9/11/24
8401 Days since the Twin Towers
2570 since Hurricane Harvey
65 since Beryl
Latest NHC Forecasts Show Francine Aiming for Louisiana
9/10/24 – Update: At 7 PM, the National Hurricane Center announced that Francine became a hurricane with sustained winds of 75 MPH and higher gusts. By 10:20, hurricane hunter aircraft found sustained winds of 85 MPH with central pressure of 979 mb. Hurricane-force winds extend outward up to 35 miles from the center and tropical-storm-force winds extend outward up to 115 miles. Other details have not changed much since 4PM. See below.
The National Hurricane Center’s (NHC) 4 PM update shows Tropical Storm Francine taking aim for Louisiana. Its impacts will likely diminish in the Houston area. However, tropical storm warnings and watches now extend past Louisiana into Mississippi and Alabama, as the forecast track shifts farther east.
Francine Winds and Forward Speed
At 4 PM, Francine still packed 65 MPH winds with higher gusts. But NHC expects it to reach hurricane strength tonight. By convention, storms become hurricanes at 74 MPH.
A Hurricane Warning is in effect from Sabine Pass eastward to Grand Isle. NHC forecasts that Francine could reach 80 knots/92 MPH at landfall in central Louisiana. If accurate, that would put it just shy of a Category 2 hurricane.
Hurricane hunter aircraft found that pressure in the central core had dropped to 987 mb. The storm has become better organized with increased banding.
Tropical-storm-force winds extend outward up to 140 miles (220 km) from the center. To put that in perspective, Beaumont is 175 miles from Baton Rouge, which is in central Louisiana.
Two NHC graphics depict the probability of damaging winds reaching the Houston area. The first shows the north Houston area has a 5-10 percent chance of experiencing tropical-storm-force winds.
The second shows we have a zero percent chance of experiencing hurricane force winds.
Track
According to NHC, Francine has made a turn toward the northeast and increased its forward motion to 10+ MPH. It should reach the central Louisiana coast sometime Wednesday afternoon or evening. A continued northeastward motion and a faster forward speed are expected tonight and Wednesday.
Surge
We still can expect storm surge in coast areas all the way from Freeport to the Florida Panhandle.
With that comes the associated risk of rip currents.
Rainfall
Francine is expected to bring storm total rainfall of 4 to 8 inches, with local amounts to 12 inches across eastern Louisiana, Mississippi, far southern Alabama and the western Florida Panhandle through Friday morning. This rainfall could lead
to considerable flash and urban flooding in those locations.
However, Jeff Linder, Harris County’s meteorologist less than an inch of rain in the Lake Houston Area.
We barely have a chance for flash flooding. And significant rainfall accumulations will be concentrated east of Texas.
While the Lake Houston Area may be spared the storm’s worst effects, the Mississippi Valley won’t. NHC predicts significant flooding for that area.
Today Is Statistical Peak of Hurricane Season
Today is the statistical peak of hurricane season and Francine makes our sixth named storm in the Atlantic Basin.
To put that in perspective, during the last 30 years, we usually have had 10 named storms by September 4 and 11 by September 14. So despite early dire warnings, this season has been less severe than normal.
The 2017 hurricane season should remind us all that it only takes one storm to change lives forever. Pray for our neighbors to the east. And remain vigilant.
Posted by Bob Rehak on 9/10/24
2569 Days since Hurricane Harvey and 69 since Beryl