12/5/2024 – Tsunamis are huge waves caused by earthquakes. Storm surge is a huge wave caused by hurricane winds. Both have unimaginable destructive power.
Destruction on Bolivar Peninsula from Hurricane Ikestorm surge in 2008.
West Coast Tsunami Warning This Morning
This morning, a magnitude 7.3 earthquake struck Northern California. That caused the National Weather Service to issue tsunami warnings from Oregon down to San Francisco and beyond.
About three hours later, the warning was cancelled without explanation. Since then, significant aftershocks ranging from 3.0 to 5.3 magnitude have occurred. We will learn more in coming days.
Different Types of Earthquakes Trigger Different Tsunami Threat Levels
Massive earthquakes don’t always trigger massive tsunamis. The magnitude 7.9 quake that destroyed much of San Francisco in 1906 reportedly produced a wave height of only three inches. Small localized, underwater landslides created 1-2 foot waves, but their destruction was confined to small areas.
Geology determines, in large part, the height of a tsunami. Imagine two different types of geologic faults.
In a thrust fault, one tectonic plate is forced under another, pushing it up and causing a vertical displacement of the seafloor. This type of fault commonly generates a tsunami.
However, a strike-slip fault causes a lateral displacement. Land along a fault moves in opposite directions without causing elevation changes. Strike-slip faults typically do not generate tsunamis because they generally do not displace large volumes of water. (Contrast the animations in the two links above.)
Other factors may also affect tsunami formation. They include:
Depth: Shallow earthquakes (occurring at depths less than 70 km) are more likely to cause tsunamis than deep earthquakes, as the energy has a more direct impact on the seafloor.
Seafloor Topography: The configuration of the ocean floor, including ridges and trenches, can amplify or reduce tsunami formation.
Underwater Landslides or Underwater Volcanic Activity triggered by the earthquake can also contribute to tsunami generation.
In summary, while massive offshore earthquakes increase the risk of tsunamis, they do not guarantee one will occur.
In this case, officials issued the tsunami warning out of an abundance of caution when seismographs first detected the earthquake. Later, they cancelled the warning when it became clear no massive waves threatened. They made the right call initially. Here’s why.
Record Waves, Record Destruction
Some massive earthquakes, like the magnitude 9.0, 2011 Tōhoku earthquake in Japan, did produce devastating tsunamis. One wave reached more than six miles inland. A 48-foot high tsunami wiped out a nuclear power plant at Fukushima. And the death toll ultimately reached almost 20,000 people.
So you can imagine why California officials immediately issued warnings today for residents to evacuate to higher ground.
During the great Galveston hurricane of 1900, a giant wave of water caused by storm surge, not a tsunami, inundated the island with 8- to 12-feet of water. It killed an estimated 6,000 to 12,000 people.
One cubic foot of seawater weighs 64 pounds. Imagine getting stuck by tens of thousands of cubic feet. That’s why storm surge is the leading cause of death associated with tropical events, according to the National Weather Service.
Don’t take either storm surge or tsunamis lightly.
I notice the same spike in traffic every time floods threaten. People want to know whether they live higher than the expected crest of the flood, storm surge or, in this case, tsunami.
Published in 2020, the post has received more than 150,000 page views already this year. The biggest peaks were during the May storm, Beryl, Helene and Milton.
Ironically, when I wrote that post about elevation, tsunamis were the furthest thing from my mind.
Even more ironic, shortly before the warning, someone emailed me asking whether I thought a development near the San Jacinto West Fork was safe from flooding. I replied to her that if she had a concern about flood risk, she should buy on the highest ground she could afford, as far from the water as she could get.
Posted by Bob Rehak on 12/5/2024
2655 Days since Hurricane Harvey
https://i0.wp.com/reduceflooding.com/wp-content/uploads/2024/12/Earthquake-sites-e1733446450615.png?fit=1100%2C654&ssl=16541100adminadmin2024-12-05 18:58:092024-12-05 18:58:10Tsunamis, Storm Surge Demonstrate Power of Moving Water
12/2/24 – System capacity maps for each of Harris County’s 23 watersheds show widespread problems and raise questions about whether the county’s most severe needs are confined to historically underserved areas.
Harris County Flood Control District (HCFCD) released the maps in response to a Freedom of Information Act (FOIA) request.
What “System Capacity” Means
System capacity reflects the ability of a stream or channel to handle rainfall of different intensities before coming out of its banks. The way system capacity is expressed also reflects the expected frequency of over-bank events.
A channel that can hold a:
100-year rainfall has a 1% system capacity
50-year rainfall has a 2% system capacity
25-year rainfall has a 4% system capacity, etc.
“1% system capacity” indicates that the infrastructure is designed to handle the peak flow or volume associated with a 1% event without causing overflow or flooding.
One Key Part of Comprehensive Flood-Risk Picture
System-capacity maps are one piece of information used in determining a comprehensive view of flood risk. They help you quickly spot areas that need closer examination.
Other key factors used to determine flood risk include: topography around the channel, the elevation of a structure, degree of development in an area, building codes in effect when an area was built, population density, and more.
Impact of Atlas 14
The maps released today rely on pre-Atlas 14 data. Harris County did not provide current maps. Nor do they reflect improvements made to channels recently. But the older maps are still instructive because they formed the starting point for spending billions of flood-mitigation dollars. However…
Because these maps are based on old rainfall standards, today’s true system capacity is actually lower than shown.
Said another way, the situation on the ground is worse than the maps show. That’s because the transition from pre-Atlas 14 to Atlas-14 data in Harris County resulted in significant increases in estimated rainfall depths for various storm events.
Notably, the 1% annual exceedance probability (AEP) 24-hour rainfall depth—commonly referred to as the “100-year” event—experienced substantial changes.
Prior to Atlas 14, Harris County was divided into three hydrologic regions with the following 100-year, 24-hour rainfall depths:
Region 1: 12.4 inches
Region 2: 12.8 inches
Region 3: 13.5 inches
With the implementation of Atlas 14, these values increased to:
Region 1: 16.3 inches
Region 2: 16.9 inches
Region 3: 18.0 inches
This represents increases of approximately 31%, 32%, and 33% for Regions 1, 2, and 3, respectively.
These updated figures reflect a more accurate understanding of rainfall patterns, incorporating additional years of data and improved analytical methods. Consequently, infrastructure design and floodplain management practices in Harris County have been adjusted to align with these revised estimates, enhancing resilience against flooding events.
Value of Maps Based on Old Rainfall Standards
Still, these maps have value. They are a starting point for the $2.5 billion 2018 Flood Bond. They also show that:
All watersheds have problem areas
Channel capacity in some areas is extremely low
Some watersheds that are not “historically underserved” have more severe system-capacity issues than those that are underserved.
System Capacity Maps
Below are low-resolution maps for each of the 23 watersheds in Harris County. For high-resolution maps of all watersheds in one file, click here. Caution: [26-meg download.]
Correlation of Maps with Spending
It’s instructive to correlate HCFCD flood-mitigation spending with these maps. Below is where more than $2 billion has gone since Hurricane Harvey, in large part, to address the problems shown above.
Data supplied by HCFCD. Shows relative spending by watershed since Harvey through Q3 2024.HCFCD spending by watershed through Q3 2024 since Harvey in dollars.
Compare the maps with the spending. And use the contact form of this website to let me know if you feel your area is not getting its fair share of flood-mitigation funding.
Note on Next Update with Atlas 14 Data
I have tried to get accurate flood risk data for years. However, HCFCD says it does not routinely update these maps every time it completes a new construction project. The District says it may update them again as part of the MAAPnext project after FEMA approves new maps based on Atlas-14 data.
Posted by Bob Rehak on December 2, 2024
2652 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/2024/12/20241202-Brays-System-Capacity.jpg?fit=1100%2C850&ssl=18501100adminadmin2024-12-02 18:55:522024-12-03 13:20:44System Capacity Maps for Harris County Channels Reveal Widespread Problems
Atypical Season Took Dip Where Peak Should Have Been
But 2024 was an atypical season. It started with a bang, fell into a lull, and then ended with a record.
Hurricane Beryl was the earliest Atlantic basin Category-5 hurricane on record. It caused significant storm surge flooding across parts of Texas and Louisiana after making landfall near Matagorda, Texas, as a Category-1 storm. People on my street are still cleaning up from Beryl!
However, later in the year, Mother Nature hit the pause button on tropical formation. Matthew Rosencrans, lead hurricane forecaster at NOAA’s Climate Prediction Center, a division of NOAA’s National Weather Service said, “Several possible factors contributed to the peak season lull in the Atlantic region. The particularly intense winds and rains over Western Africa created an environment that was less hospitable for storm development.”
But, strangely, at the time tropical activity should have been tapering off, we saw record-setting activity.
“Twelve named storms formed after the climatological peak of the season in early September. Seven hurricanes formed in the Atlantic since September 25 — the most on record for this period,” said the NHC.
Record Setters
Hurricane Beryl was the earliest Cat 5 storm on record for the Atlantic Basin.
Cat 4 Helene became the deadliest since Katrina in 2005. It caused more than 150 direct fatalities, mostly in North and South Carolina. Helene was also the strongest hurricane ever to make landfall in Florida’s Big Bend region.
In late September, Hurricane Helene also marked the first time ever that NOAA’s National Hurricane Center (NHC) forecasted a system to become a major hurricane before it became a tropical depression or tropical storm.
Hurricane Milton’s rate of rapid intensification was among the highest ever observed, with a 90-mile-per-hour increase in wind speed during the 24-hour period from early October 6 to early October 7.
Milton’s central pressure dropped to 897 millibars – the lowest pressure for an Atlantic Hurricane since Wilma in 2005.
Storm-By-Storm Summary
The table below shows the dates and maximum winds of each named storm in the Atlantic basin during 2024.
Name
Dates
Max Wind (mph)
TS Alberto
19-20 June
50
MH Beryl
28 June – 9 July
165
TS Chris
30 June – 1 July
45
H Debbie
3-9 August
80
H Ernesto
12-20 August
100
H Francine
9-12 September
100
TS Gordon
11-17 September
45
MH Helene
24-27 September
140
H Isaac
26-30 September
105
TS Joyce
27 September – 1 October
50
MH Kirk
29 September – 7 October
145
H Leslie
2-12 October
105
MH Milton
5-10 October
180
TS Nadine
19-20 October
60
H Oscar
19-22 October
85
TS Patty
2-4 November
65
MH Rafael
4-10 November
120
TS Sara
14-18 November
50
Source: NOAA. TS = Tropical Storm, H = Hurricane, MH = major hurricane.
While the Atlantic hurricane season officially ended on November 30, NOAA satellites continue to keep watch for any developing storms.
NHC reminds us that hurricanes can and do form during any month of the year.
Posted by Bob Rehak on 12/1/2024
2651 Days since Hurricane Harvey
https://i0.wp.com/reduceflooding.com/wp-content/uploads/2024/12/Hurricane-Outlook-List-End-English-Nov-2024-PLACEHOLDER-scaled.jpg?fit=2560%2C1592&ssl=115922560adminadmin2024-12-01 11:14:492024-12-01 11:14:50Looking Back at the 2024 Hurricane Season
Tsunamis, Storm Surge Demonstrate Power of Moving Water
12/5/2024 – Tsunamis are huge waves caused by earthquakes. Storm surge is a huge wave caused by hurricane winds. Both have unimaginable destructive power.
West Coast Tsunami Warning This Morning
This morning, a magnitude 7.3 earthquake struck Northern California. That caused the National Weather Service to issue tsunami warnings from Oregon down to San Francisco and beyond.
About three hours later, the warning was cancelled without explanation. Since then, significant aftershocks ranging from 3.0 to 5.3 magnitude have occurred. We will learn more in coming days.
Different Types of Earthquakes Trigger Different Tsunami Threat Levels
Massive earthquakes don’t always trigger massive tsunamis. The magnitude 7.9 quake that destroyed much of San Francisco in 1906 reportedly produced a wave height of only three inches. Small localized, underwater landslides created 1-2 foot waves, but their destruction was confined to small areas.
Geology determines, in large part, the height of a tsunami. Imagine two different types of geologic faults.
In a thrust fault, one tectonic plate is forced under another, pushing it up and causing a vertical displacement of the seafloor. This type of fault commonly generates a tsunami.
However, a strike-slip fault causes a lateral displacement. Land along a fault moves in opposite directions without causing elevation changes. Strike-slip faults typically do not generate tsunamis because they generally do not displace large volumes of water. (Contrast the animations in the two links above.)
Other factors may also affect tsunami formation. They include:
In this case, officials issued the tsunami warning out of an abundance of caution when seismographs first detected the earthquake. Later, they cancelled the warning when it became clear no massive waves threatened. They made the right call initially. Here’s why.
Record Waves, Record Destruction
Some massive earthquakes, like the magnitude 9.0, 2011 Tōhoku earthquake in Japan, did produce devastating tsunamis. One wave reached more than six miles inland. A 48-foot high tsunami wiped out a nuclear power plant at Fukushima. And the death toll ultimately reached almost 20,000 people.
So you can imagine why California officials immediately issued warnings today for residents to evacuate to higher ground.
During the great Galveston hurricane of 1900, a giant wave of water caused by storm surge, not a tsunami, inundated the island with 8- to 12-feet of water. It killed an estimated 6,000 to 12,000 people.
One cubic foot of seawater weighs 64 pounds. Imagine getting stuck by tens of thousands of cubic feet. That’s why storm surge is the leading cause of death associated with tropical events, according to the National Weather Service.
Don’t take either storm surge or tsunamis lightly.
Elevation: Key to Survival
The National Weather Service’s Tsunami Warning Center offers an excellent FAQ page concerning tsunami warnings.
Interestingly, shortly after NWS issued the tsunami warning for the San Francisco area this afternoon, I had a huge spike in traffic on ReduceFlooding.com. Everyone was going to a post with the headline “Easy way to find the elevation of your home and the slopes around it.“
I notice the same spike in traffic every time floods threaten. People want to know whether they live higher than the expected crest of the flood, storm surge or, in this case, tsunami.
Published in 2020, the post has received more than 150,000 page views already this year. The biggest peaks were during the May storm, Beryl, Helene and Milton.
Ironically, when I wrote that post about elevation, tsunamis were the furthest thing from my mind.
Even more ironic, shortly before the warning, someone emailed me asking whether I thought a development near the San Jacinto West Fork was safe from flooding. I replied to her that if she had a concern about flood risk, she should buy on the highest ground she could afford, as far from the water as she could get.
Posted by Bob Rehak on 12/5/2024
2655 Days since Hurricane Harvey
System Capacity Maps for Harris County Channels Reveal Widespread Problems
12/2/24 – System capacity maps for each of Harris County’s 23 watersheds show widespread problems and raise questions about whether the county’s most severe needs are confined to historically underserved areas.
Harris County Flood Control District (HCFCD) released the maps in response to a Freedom of Information Act (FOIA) request.
What “System Capacity” Means
System capacity reflects the ability of a stream or channel to handle rainfall of different intensities before coming out of its banks. The way system capacity is expressed also reflects the expected frequency of over-bank events.
A channel that can hold a:
“1% system capacity” indicates that the infrastructure is designed to handle the peak flow or volume associated with a 1% event without causing overflow or flooding.
One Key Part of Comprehensive Flood-Risk Picture
System-capacity maps are one piece of information used in determining a comprehensive view of flood risk. They help you quickly spot areas that need closer examination.
Other key factors used to determine flood risk include: topography around the channel, the elevation of a structure, degree of development in an area, building codes in effect when an area was built, population density, and more.
Impact of Atlas 14
The maps released today rely on pre-Atlas 14 data. Harris County did not provide current maps. Nor do they reflect improvements made to channels recently. But the older maps are still instructive because they formed the starting point for spending billions of flood-mitigation dollars. However…
Said another way, the situation on the ground is worse than the maps show. That’s because the transition from pre-Atlas 14 to Atlas-14 data in Harris County resulted in significant increases in estimated rainfall depths for various storm events.
Notably, the 1% annual exceedance probability (AEP) 24-hour rainfall depth—commonly referred to as the “100-year” event—experienced substantial changes.
Prior to Atlas 14, Harris County was divided into three hydrologic regions with the following 100-year, 24-hour rainfall depths:
With the implementation of Atlas 14, these values increased to:
This represents increases of approximately 31%, 32%, and 33% for Regions 1, 2, and 3, respectively.
These updated figures reflect a more accurate understanding of rainfall patterns, incorporating additional years of data and improved analytical methods. Consequently, infrastructure design and floodplain management practices in Harris County have been adjusted to align with these revised estimates, enhancing resilience against flooding events.
Value of Maps Based on Old Rainfall Standards
Still, these maps have value. They are a starting point for the $2.5 billion 2018 Flood Bond. They also show that:
System Capacity Maps
Below are low-resolution maps for each of the 23 watersheds in Harris County. For high-resolution maps of all watersheds in one file, click here. Caution: [26-meg download.]
Correlation of Maps with Spending
It’s instructive to correlate HCFCD flood-mitigation spending with these maps. Below is where more than $2 billion has gone since Hurricane Harvey, in large part, to address the problems shown above.
Compare the maps with the spending. And use the contact form of this website to let me know if you feel your area is not getting its fair share of flood-mitigation funding.
Note on Next Update with Atlas 14 Data
I have tried to get accurate flood risk data for years. However, HCFCD says it does not routinely update these maps every time it completes a new construction project. The District says it may update them again as part of the MAAPnext project after FEMA approves new maps based on Atlas-14 data.
Posted by Bob Rehak on December 2, 2024
2652 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.
Looking Back at the 2024 Hurricane Season
12/1/24 – The 2024 Atlantic Hurricane Season ended yesterday. The season predicted to be “extreme” turned out to be “above average,” according to the National Hurricane Center (NHC).
The Atlantic basin, which includes the Caribbean and Gulf of Mexico, saw 18 named storms in 2024.
Of the 18, 11 became hurricanes and five became major hurricanes.
Comparison of 2024 to 30-Year Average
Each of these numbers is greater than the average for the 30-year period from 1991-2020. See table below.
Landfalls in U.S.
According to NHC, five hurricanes made landfall in the continental U.S. Significantly, two of those storms made landfall as major hurricanes.
Comparison to Predictions
The Atlantic seasonal activity fell within the predicted ranges for named storms and hurricanes issued by NOAA’s Climate Prediction Center in the 2024 August Hurricane Season Outlook.
Atypical Season Took Dip Where Peak Should Have Been
But 2024 was an atypical season. It started with a bang, fell into a lull, and then ended with a record.
Hurricane Beryl was the earliest Atlantic basin Category-5 hurricane on record. It caused significant storm surge flooding across parts of Texas and Louisiana after making landfall near Matagorda, Texas, as a Category-1 storm. People on my street are still cleaning up from Beryl!
However, later in the year, Mother Nature hit the pause button on tropical formation. Matthew Rosencrans, lead hurricane forecaster at NOAA’s Climate Prediction Center, a division of NOAA’s National Weather Service said, “Several possible factors contributed to the peak season lull in the Atlantic region. The particularly intense winds and rains over Western Africa created an environment that was less hospitable for storm development.”
“Twelve named storms formed after the climatological peak of the season in early September. Seven hurricanes formed in the Atlantic since September 25 — the most on record for this period,” said the NHC.
Record Setters
Hurricane Beryl was the earliest Cat 5 storm on record for the Atlantic Basin.
Cat 4 Helene became the deadliest since Katrina in 2005. It caused more than 150 direct fatalities, mostly in North and South Carolina. Helene was also the strongest hurricane ever to make landfall in Florida’s Big Bend region.
In late September, Hurricane Helene also marked the first time ever that NOAA’s National Hurricane Center (NHC) forecasted a system to become a major hurricane before it became a tropical depression or tropical storm.
Hurricane Milton’s rate of rapid intensification was among the highest ever observed, with a 90-mile-per-hour increase in wind speed during the 24-hour period from early October 6 to early October 7.
Milton’s central pressure dropped to 897 millibars – the lowest pressure for an Atlantic Hurricane since Wilma in 2005.
Storm-By-Storm Summary
The table below shows the dates and maximum winds of each named storm in the Atlantic basin during 2024.
While the Atlantic hurricane season officially ended on November 30, NOAA satellites continue to keep watch for any developing storms.
NHC reminds us that hurricanes can and do form during any month of the year.
Posted by Bob Rehak on 12/1/2024
2651 Days since Hurricane Harvey