Dredging Location as of 10/12/2021. East Fork at Mouth of Luce Bayou on right.From here, pontoons ferry the spoils back to the West Fork opposite Kingwood’s River Grove Park.East Fork Dredging as of 12/3/2021. Photo taken from Huffman side of river looking SW toward Royal Shores and the FM 1960 Bridge in the distance.
Since then, the dredgers have managed to remove about 300 feet of the tip of one sandbar blocking the mouth of Luce Bayou and Red Gully (on the left in the shot above).
Looking upstream. Lots of dredging left to do. Between Harvey and Imelda, the sandbars in this area grew approximately 4000 feet.
Note the sediment plume in the middle of the boat’s wake above. That indicates the shallowness of the river.
According to boater Josh Alberson, the depth through this reach of the river was reduced from 17 feet to about three feet between Harvey and Imelda.
Dredging: A Conveyance Issue
The dredging is far more than a recreational issue. The decreased conveyance of the river creates a sediment dam than backs water up and contributes to the flooding of homes. In fact, I passed by dozens of flooded and abandoned homes while looking for a place to launch my drone.
Mechanical Vs. Hydraulic Dredging
One can only wonder whether the City of Houston is using the right tools for the job. Even Stephen Costello, Houston’s Chief Recovery Officer, called mechanical dredging “unsustainable in the long run” when he addressed a crowd at the Kingwood Community Center on July 9.
But it may come down to a case of slow-go or no-go.
I asked a friend in the dredging business to estimate the costs of mechanical vs. hydraulic dredging. He qualified the discussion by saying that:
To even consider hydraulic dredging you need a pit to pump the material into.
He also suggested that to reduce long-term overhead costs, you want to be able to use the equipment year round and create a perpetual dredging program.
He said the ideal would be to go once around the lake and arrive back at the beginning when it was time to start all over again.
That said, he estimated that hydraulic dredging was 10X faster and one third to one fourth the cost of mechanical dredging.
With hydraulic dredging, the upfront equipment and setup costs are far higher. Mechanical dredging is far slower and more expensive.
I won’t pretend that I have the answer to the question of which is better in this case: mechanical or hydraulic.
Vendor for Long-Range Dredging Plan Due to Be Selected This Month
The submission deadline for vendors bidding on a long range dredging plan for Lake Houston was 9/23. The Request for Qualifications stated that the City hoped to put contract approval on the City Council Agenda for December and start the contract in January. The selected vendor will have two years to complete the dredging plan.
It could easily take that long to finish the East Fork Mouth Bar at the current rate.
Posted by Bob Rehak on 12/3/2021
1557 Days since Hurricane Harvey and 775 since Imelda
https://i0.wp.com/reduceflooding.com/wp-content/uploads/2021/12/20211203-DJI_0925.jpg?fit=1200%2C799&ssl=17991200adminadmin2021-12-03 18:28:162021-12-04 07:27:39Slow-Go: East Fork Dredging Still at Mouth of Luce Bayou
Stormwater detention basins work by storing excess stormwater temporarily until channels can safely carry it away. Water enters the basin quickly during heavy downpours. But the basin releases it slowly at a steady rate that channels are designed to carry. This helps reduce the risk of flooding.
Harris County is so flat that dams are not often options. Therefore, virtually all of our stormwater storage has to be excavated.
Harris County Flood Control District
Willow Water Hole Example
The Harris County Flood Control District (HCFCD) detention basins typically cover several hundred acres and service regions. Willow Water Hole just outside the southwest corner of Loop 610 on a tributary of Brays Bayou is an excellent example.
The 279-acre Willow Waterhole has six compartments. Willow is part of the Brays Bayou Federal Flood Damage Reduction Project (Project Brays), a multi-year, $550 million project that substantially reduces flooding risk in the Brays Bayou watershed. The project is a cooperative effort between the Harris County Flood Control District and the U.S. Army Corps of Engineers.
Willow Waterhole Detention Basin Complex in SW Houston has six compartments.
Why the Need?
As areas develop, buildings and concrete cover up soil, so stormwater can’t sink into the ground. Water runs off concrete faster than it does from native grasslands. When that water all hits channels, streams and bayous simultaneously from different directions, it exceeds the carrying capacity of the channel. And homes flood.
Many, but not all, new developments use stormwater detention basins to offset that negative effect.
When full, detention basins often resemble lakes. When dry, detention basins look like large excavated open space areas. The Willow Water Hole is normally dry. Yesterday, however, it contained water from recent rains and the low (seasonal rate of evaporation).
Two of the compartments bracket South Willow Drive. See location above. Note the weir (discussed below) leading to the channel.
Some systems have water in them permanently, so they resemble small lakes. These provide flood storage between the normal surface of the lake and the top of the bank. See the difference in the photograph below.
Willow Water Hole southwestern pond. Note extra capacity between the top of the water and the top of the banks.
Detention? Retention? Which is It?
A detention basin normally has a dry bottom. It holds excess stormwater temporarily.
A retention basin always has a wet bottom. It stores water indefinitely. Retention basis normally have no outlet. Evaporation and infiltration usually keep the lake levels manageable.
The Harris County Flood Control District always builds and uses detention basins. Developers more likely will use retention ponds and market the resulting “lakes” as residential amenities.
HCFCD owns approximately 70 large regional detention basin sites throughout Harris County. They supplement hundreds of smaller developer-built basins. Countywide, these basins hold billions of gallons of stormwater during heavy rainstorms.
Two northeastern retention ponds within Willow Water Hole complexon either side of South Post Oak Road.
How Water Gets In
Sometimes HCFCD designs stormwater detention basins with a weir (visible in the first and second drone photos above). The weir, or low dam, lets stormwater rising in the channel spill into the detention basin when it reaches a certain height. Other detention basins have no weirs. They are simply open to a channel. In this case, stormwater fills the basin as it rises in the channel.
But there’s also a third alternative for stormwater detention basins, i.e., those not near a channel. Storm sewers and/or sheet flow fill these detention basins. “Big pipes in – little pipes out” is the rule in this instance. The basin gets the water away from streets and homes quickly. Then lets it drain off slowly.
How Water Gets Out
HCFCD typically designs detention basins to drain by gravity, as opposed to using pumps. This lets basins function when power goes out, a frequent occurrence during floods.
In ponds that drain by gravity, depth of the drain (outfall) is dictated by the depth of the receiving channel. The rate at which stormwater drains depends on the stormwater level in the receiving channel. Typically, stormwater drains out of the detention basin after channel levels recede.
Complex engineering calculations determine the volume of stormwater that a detention basin must hold to protect surrounding homes and businesses. That volume, usually measured in acre-feet, determines the width, length and depth of a basin. The amount of time stormwater stays in a basin depends on levels in the receiving channel and how full the basin got. In Harris County, detention time is usually measured in hours, not days.
How the Process Works
Normal Flow
When there is normal flow in a bayou or channel, the detention basin is generally empty.
Initial Storm Effects
Basins begin to fill as bayous or channels rise, or as surrounding developments drain into them through storm sewers.
Capturing the Flow of a Heavy Storm
As water continues to fill the detention basin, it spreads out into the excavated area. Often culverts connect multiple “compartments” within a larger basin, as above.
Detaining the Flow
By holding water in the detention basin, it does not flood homes and businesses downstream.
Draining Detained Water
As the level of the channel recedes, the channel water level drops and lets the basin drain, but only as fast as the channel can handle it.
Back to Normal Flow
With the water level in the channel normal, the basin is once again empty and ready for the next rainstorm.
End Result
Often, HCFCD partners with local groups, such as the Houston Parks Board, to build trails around these ponds that provide a retreat from busy city life. Areas such as Willow Water Hole also provide habitat for birds. People out for a stroll or a jog may think they are in a beautiful park and not even realize the role it plays in reducing flood risk.
The City of Houston has scheduled a repaving project for West Lake Houston Parkway from Dec. 6-27, 2021. This is a bit off-topic for a flood blog, but it affects thousands of readers. This follows several previous repaving and bridge repair projects on West Lake Houston Parkway. The following is based on a press release by Mayor Pro Tem Dave Martin’s office.
Mayor Pro Tem Dave Martin would like to make Kingwood area residents aware Houston Public Works will start a panel replacement project on West Lake Houston Parkway beginning Monday, December 6, weather permitting.
The scope of work includes replacing damaged concrete panels along the north and southbound lanes of W Lake Houston Parkway from Kingwood Drive to Magnolia Cove Drive.
The cost of the project is $38,200 and is funded through Mayor Pro Tem Martin’s Council District Service Funds.
Crews will mobilize on-site beginning Monday, December 6 and should finish the project by Monday, December 27, weather permitting.
Construction activities are expected to take place Monday through Friday from 8:00 a.m. to 5:00 p.m., and on Saturdays from 7:00 a.m. to 12:00 p.m.
Please stay alert for flagmen and orange traffic cones that will help traffic flow through the construction zone. The project may require a one-lane closure at times, but two-way traffic will be maintained at all times.
Businesses and residents will have access to driveways and sidewalks at all times, but may experience an increase in noise levels.
Slow-Go: East Fork Dredging Still at Mouth of Luce Bayou
In July, the City announced it was wrapping up West Fork dredging and starting on East Fork dredging. It took three months for the dredgers to dredge their way through the Royal Shores channel before they could even start on the East Fork. Since then, it’s been a slow-go as round trip travel times to the placement area get longer.
Since then, the dredgers have managed to remove about 300 feet of the tip of one sandbar blocking the mouth of Luce Bayou and Red Gully (on the left in the shot above).
Note the sediment plume in the middle of the boat’s wake above. That indicates the shallowness of the river.
According to boater Josh Alberson, the depth through this reach of the river was reduced from 17 feet to about three feet between Harvey and Imelda.
Dredging: A Conveyance Issue
The dredging is far more than a recreational issue. The decreased conveyance of the river creates a sediment dam than backs water up and contributes to the flooding of homes. In fact, I passed by dozens of flooded and abandoned homes while looking for a place to launch my drone.
Mechanical Vs. Hydraulic Dredging
One can only wonder whether the City of Houston is using the right tools for the job. Even Stephen Costello, Houston’s Chief Recovery Officer, called mechanical dredging “unsustainable in the long run” when he addressed a crowd at the Kingwood Community Center on July 9.
But it may come down to a case of slow-go or no-go.
I asked a friend in the dredging business to estimate the costs of mechanical vs. hydraulic dredging. He qualified the discussion by saying that:
He said the ideal would be to go once around the lake and arrive back at the beginning when it was time to start all over again.
With hydraulic dredging, the upfront equipment and setup costs are far higher. Mechanical dredging is far slower and more expensive.
This website has an excellent discussion about seven factors that drive dredging costs.
I won’t pretend that I have the answer to the question of which is better in this case: mechanical or hydraulic.
Vendor for Long-Range Dredging Plan Due to Be Selected This Month
The submission deadline for vendors bidding on a long range dredging plan for Lake Houston was 9/23. The Request for Qualifications stated that the City hoped to put contract approval on the City Council Agenda for December and start the contract in January. The selected vendor will have two years to complete the dredging plan.
It could easily take that long to finish the East Fork Mouth Bar at the current rate.
Posted by Bob Rehak on 12/3/2021
1557 Days since Hurricane Harvey and 775 since Imelda
How Stormwater Detention Basins Work
Stormwater detention basins work by storing excess stormwater temporarily until channels can safely carry it away. Water enters the basin quickly during heavy downpours. But the basin releases it slowly at a steady rate that channels are designed to carry. This helps reduce the risk of flooding.
Willow Water Hole Example
The Harris County Flood Control District (HCFCD) detention basins typically cover several hundred acres and service regions. Willow Water Hole just outside the southwest corner of Loop 610 on a tributary of Brays Bayou is an excellent example.
The 279-acre Willow Waterhole has six compartments. Willow is part of the Brays Bayou Federal Flood Damage Reduction Project (Project Brays), a multi-year, $550 million project that substantially reduces flooding risk in the Brays Bayou watershed. The project is a cooperative effort between the Harris County Flood Control District and the U.S. Army Corps of Engineers.
Why the Need?
As areas develop, buildings and concrete cover up soil, so stormwater can’t sink into the ground. Water runs off concrete faster than it does from native grasslands. When that water all hits channels, streams and bayous simultaneously from different directions, it exceeds the carrying capacity of the channel. And homes flood.
Many, but not all, new developments use stormwater detention basins to offset that negative effect.
When full, detention basins often resemble lakes. When dry, detention basins look like large excavated open space areas. The Willow Water Hole is normally dry. Yesterday, however, it contained water from recent rains and the low (seasonal rate of evaporation).
Some systems have water in them permanently, so they resemble small lakes. These provide flood storage between the normal surface of the lake and the top of the bank. See the difference in the photograph below.
Detention? Retention? Which is It?
A detention basin normally has a dry bottom. It holds excess stormwater temporarily.
A retention basin always has a wet bottom. It stores water indefinitely. Retention basis normally have no outlet. Evaporation and infiltration usually keep the lake levels manageable.
The Harris County Flood Control District always builds and uses detention basins. Developers more likely will use retention ponds and market the resulting “lakes” as residential amenities.
HCFCD owns approximately 70 large regional detention basin sites throughout Harris County. They supplement hundreds of smaller developer-built basins. Countywide, these basins hold billions of gallons of stormwater during heavy rainstorms.
How Water Gets In
Sometimes HCFCD designs stormwater detention basins with a weir (visible in the first and second drone photos above). The weir, or low dam, lets stormwater rising in the channel spill into the detention basin when it reaches a certain height. Other detention basins have no weirs. They are simply open to a channel. In this case, stormwater fills the basin as it rises in the channel.
But there’s also a third alternative for stormwater detention basins, i.e., those not near a channel. Storm sewers and/or sheet flow fill these detention basins. “Big pipes in – little pipes out” is the rule in this instance. The basin gets the water away from streets and homes quickly. Then lets it drain off slowly.
How Water Gets Out
HCFCD typically designs detention basins to drain by gravity, as opposed to using pumps. This lets basins function when power goes out, a frequent occurrence during floods.
In ponds that drain by gravity, depth of the drain (outfall) is dictated by the depth of the receiving channel. The rate at which stormwater drains depends on the stormwater level in the receiving channel. Typically, stormwater drains out of the detention basin after channel levels recede.
Complex engineering calculations determine the volume of stormwater that a detention basin must hold to protect surrounding homes and businesses. That volume, usually measured in acre-feet, determines the width, length and depth of a basin. The amount of time stormwater stays in a basin depends on levels in the receiving channel and how full the basin got. In Harris County, detention time is usually measured in hours, not days.
How the Process Works
Normal Flow
When there is normal flow in a bayou or channel, the detention basin is generally empty.
Initial Storm Effects
Basins begin to fill as bayous or channels rise, or as surrounding developments drain into them through storm sewers.
Capturing the Flow of a Heavy Storm
As water continues to fill the detention basin, it spreads out into the excavated area. Often culverts connect multiple “compartments” within a larger basin, as above.
Detaining the Flow
By holding water in the detention basin, it does not flood homes and businesses downstream.
Draining Detained Water
As the level of the channel recedes, the channel water level drops and lets the basin drain, but only as fast as the channel can handle it.
Back to Normal Flow
With the water level in the channel normal, the basin is once again empty and ready for the next rainstorm.
End Result
Often, HCFCD partners with local groups, such as the Houston Parks Board, to build trails around these ponds that provide a retreat from busy city life. Areas such as Willow Water Hole also provide habitat for birds. People out for a stroll or a jog may think they are in a beautiful park and not even realize the role it plays in reducing flood risk.
Posted by Bob Rehak on 12/2/2021 based on information provided by HCFCD
1556 Days since Hurricane Harvey
West Lake Houston Parkway Repaving Project Scheduled
The City of Houston has scheduled a repaving project for West Lake Houston Parkway from Dec. 6-27, 2021. This is a bit off-topic for a flood blog, but it affects thousands of readers. This follows several previous repaving and bridge repair projects on West Lake Houston Parkway. The following is based on a press release by Mayor Pro Tem Dave Martin’s office.
Mayor Pro Tem Dave Martin would like to make Kingwood area residents aware Houston Public Works will start a panel replacement project on West Lake Houston Parkway beginning Monday, December 6, weather permitting.
The scope of work includes replacing damaged concrete panels along the north and southbound lanes of W Lake Houston Parkway from Kingwood Drive to Magnolia Cove Drive.
The cost of the project is $38,200 and is funded through Mayor Pro Tem Martin’s Council District Service Funds.
Crews will mobilize on-site beginning Monday, December 6 and should finish the project by Monday, December 27, weather permitting.
Construction activities are expected to take place Monday through Friday from 8:00 a.m. to 5:00 p.m., and on Saturdays from 7:00 a.m. to 12:00 p.m.
Please stay alert for flagmen and orange traffic cones that will help traffic flow through the construction zone. The project may require a one-lane closure at times, but two-way traffic will be maintained at all times.
Businesses and residents will have access to driveways and sidewalks at all times, but may experience an increase in noise levels.
For more information, please contact Mayor Pro Tem Dave Martin’s office at (832) 393-3008 or districte@houstontx.gov.
Posted by Bob Rehak on 12/1/2021
1555 Days since Hurricane Harvey