Keep your eye on the sky for more severe-weather threats this week. Harris County Flood Control Meteorologist Jeff Linder warns that the coming week could bring us 5-7 inches of rain, and higher totals in places. He says the upper level trough setting up over the southwestern US will send us one storm after another. Linder compared the current pattern to those in the springs of 2015 and 2016. We saw multiple floods across Texas in both of those years.
Rainfall total forecast for May 5 through 12.
Monday Night/Tuesday: Saturating Soils
A strong disturbance will move into southeast Texas on Monday night and Tuesday with widespread showers and thunderstorms. Heavy rainfall of 1-2 inches with higher isolated totals will be possible along with a slight severe weather threat. Lindner thinks “most of the area will be able to handle this round of rainfall as long as there is no sustained cell training that develops and the overall forward progression of the system remains fast enough to prevent rainfall totals from piling up.” What this system will likely accomplish is further saturation of the soil over the area. Lindner calls it a “primer” event for more sustained heavy rainfall toward the end of the week.
Thursday-Saturday: Flood, Severe Weather Threats
Another strong storm system will approach toward the end of the week along with a slow moving and stalling surface frontal boundary. An extremely moist air mass along with the overall slow eastward progression of the storm system moving out of Mexico are significant heavy-rainfall signals during this period. Lindner expects several inches as several rounds of slow-moving thunderstorms impact the region. Flooding and severe weather will be possible during this period.
Rainfall Totals and Flood Risk
Rainfall totals over the next 5 days should average 4-5 inches over much of southeast Texas and there will almost certainly be higher isolated totals. The widespread nature of the incoming weather this week on top of increasingly saturated grounds, and already swollen rivers, creek, and bayous increases the flooding threat. Main concern will be the Brazos, Trinity, and San Jacinto River basins and toward the end of the week the Harris County bayous and creeks if the current forecast holds.
Exact timing of the rainfall and storms as well as amounts and locations of the higher totals will be in flux over the next 5 days.
The Tax and Memorial Day Floods in 2015 and 2016 did as much damage as many hurricanes. So it would be good to prepare an evacuation kit, just in case. Here are some tips.
https://i0.wp.com/reduceflooding.com/wp-content/uploads/2019/05/image001-1.gif?fit=750%2C562&ssl=1562750adminadmin2019-05-05 15:53:362019-05-05 16:15:56Severe Weather, Heavy Rainfall Threats Return for Much of This Week
Storms during the last two days were traumatic for virtually everyone in the Kingwood area. Tragically, one person lost her life when her car hit a downed tree.
Others lost vehicles, trees, and sleep.
Torrential rains for a brief period – at the rate of 4-5 inches in an hour – flooded streets and vehicles.
They also brought water near or into homes.
Parents picking children up from school waited in rising waters as their students sheltered in place.
A small tornado may have briefly touched down near Town Center.
Kingwood Drive was shut down for hours during the Friday afternoon rush hour.
People traumatized by Harvey were re-traumatized.
People without power waited and wondered for hours about what was going on around them.
Lake Conroe: One Less Worry This Time
Despite all that, we did NOT have to worry about one thing: Lake Conroe opening its flood gates again during this storm. The seasonal lowering policy established last year worked.
The SJRA board voted to lower the lake’s level one foot to 200 mean feet above sea level (MSL) from April 1 to May 31.
That action may have saved the Lake Houston area from additional flooding in the last round of storms.
Releasing Water Continuously At Low Rate Created Extra Capacity
Lake Conroe had released water continuously since April 1 at a slow, controlled rate of 350 to 550 cubic feet per second. However, because of spring rains, Lake Conroe had only dropped about a half foot from 201 to 200.66 feet MSL. Had the releases not happened, the lake would have been an estimated 1-1.5 feet higher, according to Mark Micheletti, an SJRA board member from Kingwood. That means the lake level would have been approaching 202 feet, the level at which the SJRA automatically begins releasing water, when the storm hit. That would have forced the SJRA to release water at a higher rate that could have overloaded the downstream watershed.
Buffer Against Downstream Flooding Worked
In other words, the policy worked. The seasonal lowering provided a buffer against downstream flooding. NOAA shows a double crest on the San Jacinto West Fork at US59 during the last two days that coincided with two waves of storms. At peak flow, the river came within about two feet of going out of its banks.
An additional foot of water released from Lake Conroe would have added two feet to Lake Houston and created flooding.
About a mile downstream at River Grove Park, the water was up, but still within its banks.
Despite torrential rains last night and early this morning, the West Fork remained in its banks. The river was up, but no homes flooded from the river.
Success: No Rivers or Streams Out of Banks
At this hour, neither NOAA, the SJRA, nor Harris County Flood Control, predicts any flooding from yesterday’s storms. In fact, all streams and bayous seem to be receding at this time. That’s one less thing to worry about as we clean up from the latest storm. The SJRA’s seasonal lowering DID help.
Remember, Lake Conroe is almost twice as big as Lake Houston (33 sq. mi. vs 18.5 sq. mi.). So one foot released there translates into almost two feet here. And two feet would likely have forced the San Jacinto out of its banks for the fifth time in a year.
Kudos to the SJRA board, the City of Houston, and the TCEQ for enabling this policy. That, in conjunction with the City’s pre-release policy for Lake Houston, have made a difference.
Posted by Bob Rehak on 5/5/2019
614 Days since Hurricane Harvey
https://i0.wp.com/reduceflooding.com/wp-content/uploads/2019/05/hmmt2_hg-1.png?fit=600%2C465&ssl=1465600adminadmin2019-05-04 22:51:322020-01-17 08:59:15One Less Thing to Worry About in Latest Storm: How Seasonal Lowering of Lake Conroe Helped
During Harvey, most of the damage in Kingwood happened from river flooding. Yesterday, it happened from street flooding. What are the respective causes? Differences? Fixes?
River Grove Park the morning after the street flooding during the previous day and night. The river was still well within its banks and is not predicted to come out.
River Flooding Overview
River flooding happens when heavy rainfall exceeds the conveyance capacity of a river. In other words, the river comes up and out of its banks. This happened to the San Jacinto during Harvey. The river, normally a couple hundred feet wide, became three to four miles wide, inundating miles from the main current.
River flooding can be caused by heavy rain, upstream snow melt, dam/levee breaks, dam releases, and more. Most commonly, it takes hours to days for water to work its way through a river system and affect people downstream.
River Flooding Remedies
Fixes for river flooding include things like:
Building dams upstream to reduce the flow downstream.
Increasing the conveyance of the river through widening, deepening or dredging
Removing blockages such as the mouth bar on the West Fork of the San Jacinto
Increasing the outflow capacity, for instance by adding gates to dam
Building levees
Diverting water to tunnels.
Street Flooding Overview
Street flooding, on the other hand, is often much more local and happens over shorter periods of time. It is often referred to as flash flooding because it comes up quickly and goes down quickly. That’s what the Lake Houston Area experienced yesterday. The San Jacinto, its tributaries and drainage ditches were and still are well within their banks.
Flash flooding occurs when the rainfall RATE temporarily exceeds the drainage capacity of storm drains, sewers, swales, and ditches that lead to rivers.
Yesterday, we received 1/20th the amount of rainfall that we did during Harvey, but many people reported the water coming up higher. That’s because storm sewers could not handle the intense rainfall that happened during approximately a one hour period.
Drains on Valley Manor could not handle the sudden surge.
Streets Designed as Part of Flood Retention System
The streets in Kingwood (and most cities) are actually designed to be part of the flood retention system. When developers excavate streets, they often use the fill to build up homesites. By increasing the elevation difference between street level and your foundation, they reduce the chances that you will flood.
They size the sewers so as not to make drainage ditches overflow. Rainfall rates like we experienced yesterday don’t happen for very long. The storm passes. The water in the street goes down and life returns to normal. You just don’t want to be caught out on the road in your car when it happens. Nor do you want to have your car parked on the street!
Street Flooding Remedies
The Greater Houston Flood Mitigation Consortiums’ report on Harvey contains an extensive discussion of the different types of flooding. Their discussion of street flooding starts on page 14. Page 15 identifies solutions, including:
Communicate the role of streets in the drainage system. Many residents may not be aware that roads are intended to act as a secondary short-term storage system and/or conveyance pathway for water. This can lead to severe property damage and loss of life when residents do not move property out of harm’s way. For example, recent street flooding has caused severe flooding of cars, which are frequently parked in the street. It is also important to note that 12 inches of water can float a sedan and 18-24 inches can float a larger vehicle, creating hazardous road conditions during extreme events. It is critical to develop a strategy to communicate to the public that streets are designed to be a secondary short-term storage system so that people can take action to prevent loss of property and life.
Address debris in streets and waterways. Maintaining clear openings to storm sewer inlets is a great way to help reduce street flooding. Flooding in many neighborhoods can be made worse by debris and floating trashcans that clog inlets. Additional city, county and MUD maintenance, or organized community efforts may be required.
Ensure that developers have sufficient “upstream” information. Land development engineers typically focus on mitigating the runoff generated by their development project, and as such, flows entering onto their site from other sources may not be considered in their design analysis. Examining strategies to share information about upstream conditions with developers during the design analysis phase could help maximize site-based mitigation.
Maximize on-site retention. Green infrastructure may provide a viable alternative for managing stormwater and reducing nuisance flooding through implementing on-site retention or by providing additional in-line storage capacity within the street (examples include Cottage Grove and Bagby Street).
Identify & target high-risk areas. Determining the neighborhoods most vulnerable to flooding from local drainage challenges would be a pivotal step to targeting public education and mitigation strategies.
For More Information
The flooding yesterday happened so quickly that it scared people. For many, it brought back vividly the trauma of Harvey and the pain that followed. One person even died when her car ran into a downed tree that fell across Kingwood Drive.
The most damage happened, not to homes, but to vehicles caught in high water on flooded streets – streets DESIGNED to hold water. There’s a simple answer to that. Unfortunately many people did not get the warnings that could have kept them off the streets.
For more information on different types of flooding, see the first part of this FloodWarn Training Seminar that Katie Landry-Guyton of the National Weather Service presented last year at Kingwood College.
Posted by Bob Rehak on 5/4/19
613 Days since Hurricane Harvey
https://i0.wp.com/reduceflooding.com/wp-content/uploads/2019/05/5.3.19-rain.jpg?fit=1500%2C2000&ssl=120001500adminadmin2019-05-04 12:23:012019-05-04 12:23:24Street Flooding vs. River Flooding
Severe Weather, Heavy Rainfall Threats Return for Much of This Week
Keep your eye on the sky for more severe-weather threats this week. Harris County Flood Control Meteorologist Jeff Linder warns that the coming week could bring us 5-7 inches of rain, and higher totals in places. He says the upper level trough setting up over the southwestern US will send us one storm after another. Linder compared the current pattern to those in the springs of 2015 and 2016. We saw multiple floods across Texas in both of those years.
Monday Night/Tuesday: Saturating Soils
A strong disturbance will move into southeast Texas on Monday night and Tuesday with widespread showers and thunderstorms. Heavy rainfall of 1-2 inches with higher isolated totals will be possible along with a slight severe weather threat. Lindner thinks “most of the area will be able to handle this round of rainfall as long as there is no sustained cell training that develops and the overall forward progression of the system remains fast enough to prevent rainfall totals from piling up.” What this system will likely accomplish is further saturation of the soil over the area. Lindner calls it a “primer” event for more sustained heavy rainfall toward the end of the week.
Thursday-Saturday: Flood, Severe Weather Threats
Another strong storm system will approach toward the end of the week along with a slow moving and stalling surface frontal boundary. An extremely moist air mass along with the overall slow eastward progression of the storm system moving out of Mexico are significant heavy-rainfall signals during this period. Lindner expects several inches as several rounds of slow-moving thunderstorms impact the region. Flooding and severe weather will be possible during this period.
Rainfall Totals and Flood Risk
Rainfall totals over the next 5 days should average 4-5 inches over much of southeast Texas and there will almost certainly be higher isolated totals. The widespread nature of the incoming weather this week on top of increasingly saturated grounds, and already swollen rivers, creek, and bayous increases the flooding threat. Main concern will be the Brazos, Trinity, and San Jacinto River basins and toward the end of the week the Harris County bayous and creeks if the current forecast holds.
Exact timing of the rainfall and storms as well as amounts and locations of the higher totals will be in flux over the next 5 days.
Although some street flooding is possible, I suspect the main threat will be river flooding this time.
Things You Can Do to Prepare
The Tax and Memorial Day Floods in 2015 and 2016 did as much damage as many hurricanes. So it would be good to prepare an evacuation kit, just in case. Here are some tips.
Get a backup battery charger for your cell phone in case of extended power outages. Remember the 13 days Kingwood went without power after Hurricane Ike?
Change out the batteries in your flashlights and weather radio. Remember those? They still work!
Learn how to read cloud formations and what they mean. Here’s a link to a well-illustrated article about threatening cloud formations. You may also want to search for “cloud formations before tornados.”
Move your vehicle to higher ground, preferably inside a garage. Remember, large hail often occurs with severe storms and can destroy a car’s finish.
After a flash flood, stay home or stay at work.
Posted by Bob Rehak on May 5, 2019
614 Days since Hurricane Harvey
One Less Thing to Worry About in Latest Storm: How Seasonal Lowering of Lake Conroe Helped
Storms during the last two days were traumatic for virtually everyone in the Kingwood area. Tragically, one person lost her life when her car hit a downed tree.
Lake Conroe: One Less Worry This Time
Despite all that, we did NOT have to worry about one thing: Lake Conroe opening its flood gates again during this storm. The seasonal lowering policy established last year worked.
That action may have saved the Lake Houston area from additional flooding in the last round of storms.
Releasing Water Continuously At Low Rate Created Extra Capacity
Lake Conroe had released water continuously since April 1 at a slow, controlled rate of 350 to 550 cubic feet per second. However, because of spring rains, Lake Conroe had only dropped about a half foot from 201 to 200.66 feet MSL. Had the releases not happened, the lake would have been an estimated 1-1.5 feet higher, according to Mark Micheletti, an SJRA board member from Kingwood. That means the lake level would have been approaching 202 feet, the level at which the SJRA automatically begins releasing water, when the storm hit. That would have forced the SJRA to release water at a higher rate that could have overloaded the downstream watershed.
Buffer Against Downstream Flooding Worked
In other words, the policy worked. The seasonal lowering provided a buffer against downstream flooding. NOAA shows a double crest on the San Jacinto West Fork at US59 during the last two days that coincided with two waves of storms. At peak flow, the river came within about two feet of going out of its banks.
About a mile downstream at River Grove Park, the water was up, but still within its banks.
Success: No Rivers or Streams Out of Banks
At this hour, neither NOAA, the SJRA, nor Harris County Flood Control, predicts any flooding from yesterday’s storms. In fact, all streams and bayous seem to be receding at this time. That’s one less thing to worry about as we clean up from the latest storm. The SJRA’s seasonal lowering DID help.
Kudos to the SJRA board, the City of Houston, and the TCEQ for enabling this policy. That, in conjunction with the City’s pre-release policy for Lake Houston, have made a difference.
Posted by Bob Rehak on 5/5/2019
614 Days since Hurricane Harvey
Street Flooding vs. River Flooding
During Harvey, most of the damage in Kingwood happened from river flooding. Yesterday, it happened from street flooding. What are the respective causes? Differences? Fixes?
River Flooding Overview
River flooding happens when heavy rainfall exceeds the conveyance capacity of a river. In other words, the river comes up and out of its banks. This happened to the San Jacinto during Harvey. The river, normally a couple hundred feet wide, became three to four miles wide, inundating miles from the main current.
River flooding can be caused by heavy rain, upstream snow melt, dam/levee breaks, dam releases, and more. Most commonly, it takes hours to days for water to work its way through a river system and affect people downstream.
River Flooding Remedies
Fixes for river flooding include things like:
Street Flooding Overview
Street flooding, on the other hand, is often much more local and happens over shorter periods of time. It is often referred to as flash flooding because it comes up quickly and goes down quickly. That’s what the Lake Houston Area experienced yesterday. The San Jacinto, its tributaries and drainage ditches were and still are well within their banks.
Flash flooding occurs when the rainfall RATE temporarily exceeds the drainage capacity of storm drains, sewers, swales, and ditches that lead to rivers.
Streets Designed as Part of Flood Retention System
The streets in Kingwood (and most cities) are actually designed to be part of the flood retention system. When developers excavate streets, they often use the fill to build up homesites. By increasing the elevation difference between street level and your foundation, they reduce the chances that you will flood.
They size the sewers so as not to make drainage ditches overflow. Rainfall rates like we experienced yesterday don’t happen for very long. The storm passes. The water in the street goes down and life returns to normal. You just don’t want to be caught out on the road in your car when it happens. Nor do you want to have your car parked on the street!
Street Flooding Remedies
The Greater Houston Flood Mitigation Consortiums’ report on Harvey contains an extensive discussion of the different types of flooding. Their discussion of street flooding starts on page 14. Page 15 identifies solutions, including:
For More Information
The flooding yesterday happened so quickly that it scared people. For many, it brought back vividly the trauma of Harvey and the pain that followed. One person even died when her car ran into a downed tree that fell across Kingwood Drive.
The most damage happened, not to homes, but to vehicles caught in high water on flooded streets – streets DESIGNED to hold water. There’s a simple answer to that. Unfortunately many people did not get the warnings that could have kept them off the streets.
For more information on different types of flooding, see the first part of this FloodWarn Training Seminar that Katie Landry-Guyton of the National Weather Service presented last year at Kingwood College.
Posted by Bob Rehak on 5/4/19
613 Days since Hurricane Harvey