Looking back to the period immediately after Harvey, check out this NASA photo of a sediment plume coming out of Galveston Bay on 8/31/2017. An astronaut took the photo using a Nikon D4 with a wide angle lens from 216 miles above the Earth.
As Harvey moved away from Houston, note the sediment plumes spilling out of bays in this photo of the Texas Coastline.
Talk about a dredging problem! The entire northern Gulf of Mexico looks like a Mint Oreo Shake. The brightest part of the plume coming out of Galveston Bay in this shot of the Texas Coastline measures 20 – 30 miles offshore. But the faintest part of the sediment plume extends approximately another 80 miles. Houston is northwest of the bright, light brown area under the clouds that form an arrowhead in the middle of the photo.
Zooming in and boosting contrast. We can see Lake Houston above Galveston Bay on the right of the clouds in the middle.
The mind boggling thing is that enough pressure existed to push the plumes out that far that fast.
Technical Data
NASA PHOTO ID iss052e078795.NEF
GMT 2017:08:31 19:23:43
MODEL NIKON D4
Shutter 1/500
Aperture 18.0
ISO Speed 400
Focal Length 24.0 mm
Lens ID AF-S Nikkor 17-35mm f/2.8D IF-ED
Compensation -1/3
Mission: ISS052 Roll: E Frame: 78795
Country or Geographic Name: USA-TEXAS
Features: HURRICANE HARVEY, HOUSTON, GALVESTON B., MATAGORDA B., FLOODING, DRAINAGE
Center Point: Latitude: 29.0 Longitude: -95.5 (Negative numbers indicate west for longitude)
Spacecraft Altitude: 216 nautical miles
Sun Elevation Angle: 65 (Angle in degrees between the horizon and the sun, measured at the nadir point)
Posted on 7/14/2018 by Bob Rehak
319 Days Since Hurricane Harvey
Photo: Courtesy of NASA
00adminadmin2018-07-14 04:42:072018-07-14 04:49:26Sediment Plume from Above the Storm
Sand and sediment clog our rivers and lake. “Dredge!” you say.
“Not that simple,” say the experts. “Who will pay for it? How much should we dredge? Where will the sediment go?”
That’s why we need planning for sediment management. We need to dredge the worst parts of the river now; the U.S. Army Corps of Engineers (USACE) has already started that as an emergency project. But we also need to dredge other parts of the river that are not quite critical yet. And we need to figure out how to do all this on a regular basis so that it never gets this bad again.
A giant sand dune has formed at the mouth of the west fork of the San Jacinto. It is not being addressed by the Army Corps dredging project but should be. Thousands of homes upstream from this massive blockage flooded during Harvey.
Sediment Management Challenges That Lie Ahead
I have talked about these issues with experts from Harris County Flood Control and USACE. Both say planning is crucial to a successful maintenance dredging/sediment management program. One provided this document: Galveston-Bay-Programmatic-RSM-Plan-Rev-1, as an example of what we need for the San Jacinto. It’s a long document – 112 pages. But it is worth reading the executive summary, introduction and table of contents at the very least. Parts of it discuss the upper reaches of the San Jacinto. But the main value it provides is that it outlines the challenges ahead.
Who will lead the effort? Who will support it?
How much money is needed per year? How can we budget for it? Who will share in the costs?
Where will the dredged materials go? How can we identify opportunities to reuse and sell them? Who will market them and how? To what extent can sales defray dredging costs?
What are the true life-cycle costs of the sand and sediment that miners send downstream to us?
How can we reduce their contribution to the problem? Is there a way to make them part of the solution?
How can we coordinate upstream and downstream efforts so that the entire river system flows freely?
How can we remove channel blockages more quickly after floods to help prevent additional flooding?
All of these are difficult questions. Starting such an extensive program is like starting a new business.
Budgeting Comes First
A business plan and budgeting are the first issues we need to address. Where will the money for all this come from? Without answering that first, everything else is moot.
So who are the stakeholders?
City of Houston – Ensuring the future of Lake Houston is essential to ensuring the future of the City. It’s the City’s main source of water.
Harris County Flood Control – Half of the people that live in the county, live in the City.
San Jacinto River Authority (SJRA) – The State created the Authority back in the 1930s to impound water and protect people from flooding. Those missions were recently reconfirmed by the Governor.
Coastal Water Authority – CWA is the contract operator for Lake Houston Dam and Reservoir. They sell water just like SJRA and can raise money thru water rates to fund flood mitigation. Their enabling legislation mentions drainage and flood responsibilities – same as SJRA.
State of Texas – This region has a quarter of all the people who live in the state. Nuff said.
Expecting all costs to be covered by the Harris County Flood Bond in perpetuity is just wishful and foolish thinking. The bond is for capital projects, not ongoing maintenance. You might be able to justify the first dredging as “channel improvements.” But after that, for the sake of the community, we need to find a way to make this program sustainable. Paying interest for ongoing operations is unwise.
Cost Sharing and 5-Year Intervals Can Make It More Doable than Avoidable
In 2000 Brown & Root, recommended dredging every 5 years – a perfect match for a venture with five partners. If each budgeted one fifth of the cost annually, and you did only one fifth of the job each year, this just might be more doable than avoidable. (Avoidance seems to have been the preferred approach in the past.)
We can’t budget sediment management forever on an emergency basis. That’s like using an emergency room for basic medical care. It’s probably not the best idea, nor the most cost effective. So let’s begin the dialog with stakeholders. As Grandma used to say, “An ounce of prevention…”
Posted on July 13, 2018 by Bob Rehak
318 Days since Hurricane Harvey
00adminadmin2018-07-13 09:33:352018-07-13 11:40:46Need for Sediment Management Planning
Flood during Harvey looking east from the south side of the West Fork of the San Jacinto. Photo courtesy of Harris County Flood Control District.
Hurricane Harvey’s widespread 8-day rainfall, which started on August 25, 2017, exceeded 60 inches in some locations. That’s about 15 inches more than average annual amounts of rainfall for eastern Texas and the Texas coast. The area affected was also much larger than previous events.
New High Water Marks and Record Streamflows
USGS field crews collected 2,123 high-water marks in 22 counties in southeast Texas and three parishes across southwest Louisiana.
Record streamflows were measured at 40 USGS streamgages in Texas that have been in operation at least 15 years. At two streamgage locations, scientists determined that the percent chance for flooding of this magnitude to happen in any given year was 0.2 percent. This probability is also referred to as a 500-year flood. Thirty other USGS streamgages experienced flooding at levels with a 1 percent chance of occurring each year, also known as a 100-year flood.
The USGS conducts research on the physical and statistical characteristics of flooding, estimating the probability of flooding at locations around the United States.
The purpose of the study was to check the probability of future occurrences and map the extent of flooding in Texas.
These records will assist officials in updating building codes, planning evacuation routes, creating floodplain management ordinances, providing environmental assessments and planning other community efforts to become more flood-resilient. FEMA will also use this information to revise their Flood Insurance Rate Maps. These maps help identify areas most likely to experience flooding in any given year.
Gages Closest to Lake Houston
The section on the San Jacinto Watershed starts on page 33. The maps for the San Jacinto watershed appear on pages 35 and 36. Use the maps to see the new high water marks in the area and to find the USGS gages nearest you. For most people in the upper Lake Houston Area, it will be one of these gages:
08068090 – Grand Parkway and West Fork near Porter
08069500 – West Fork and I-69 near Humble/Kingwood
08070500 – Caney Creek near Splendora
08069000 – Cypress Creek near Westfield
08068500 – Spring Creek near Spring
08071000 – Peach Creek near Splendora
08070200 – East Fork near New Caney
08071280 – Luce Bayou above Lake Houston near Huffman
After you locate the gages nearest you, cross reference the numbers of those gages with data at the front of the report. It helps to use the search function in Adobe Acrobat because much of the information is in tables with very small type.
Examples of What You Will Find
Here’s an example of what you can find. For the gage nearest many of the sand mines on the West Fork (08068090), peak streamflow was estimated at 131,000 cubic feet per second. That was the highest of the 33 peaks previously observed at that location (from Table 3 on Page 9).
Now here’s the big news: From the same table, we can see that the Annual Exceedance Probability (AEP) is 2.4. That’s the likelihood of occurrence of a flood of given size or larger occurring in any one year, expressed as a percentage.
AEP is often expressed as the reciprocal of ARI (Average Recurrence Interval). For instance, A 10-year flood has a 10 percent probability of occurring in any given year, a 50-year event a 2% probabaility, a 100-year event a 1% probability, and a 500-year event a .2% probability.
In this case, a 2.4% AEP would have a likely recurrence interval of 42 years, given the new realities of upstream development, any changes in climate, and pocket calculators with more computing power. This means that the West Fork Gage ((08068090) at the Grand Parkway DID NOT even experience a 100-year flood! Yes, we can expect to see worse in the future.
That’s a far cry from the 1,000-year flood that some talked about earlier and raises real public policy questions about locating sand mines in floodways.
Despite the fact that Harvey was the largest rainfall event in recorded U.S. history, USGS now predicts that it would take even bigger floods to reach the reconfigured 100-year, 200-year and 500-year recurrence intervals: 196,000, 263,000 and 374,000 cfs respectively for West Fork Gage at Grand Parkway (Gage #08068090 from Table 5, Page 14). So the new 500-year flood would have almost triple the volume of Harvey.
Humble Gage Data Missing From Report
Unfortunately, the Humble Gage at I-69 does not show up in the tables even though it is on the map and the cover of the report. This is likely in part due to the fact that the gage stopped reporting during the event due to the excessive streamflow
They may also have not reported the exceedance probability due to the shorter recent record.
For all the other gages, the Annual Exceedance Probabilities translate to new recurrence intervals ranging from 35 to 250 years. The gages at the low end of that range tend to be in the fastest developing neighborhoods.
Implications of New Findings
The report will stimulate public policy debate about development near rivers and the most effective methods of flood mitigation.
After reading this, I believe more than ever that we need more detention, dredging and gates (DDG). We need all three to help us handle the volumes of floodwater that USGS expects at more frequent intervals. Prayer, while advisable, is a less certain option in my mind than including DDG in the flood bond and passing it.
BTW, there was some confusion Tuesday night at the flood bond meeting. A small number of flood control employees incorrectly told residents that dredging would not be possible under the bond. It will be according to Matt Zeve, whom I contacted today.
Posted July 12, 2018 by Bob Rehak
317 Days since Hurricane Harvey
00adminadmin2018-07-11 19:46:322018-07-11 23:53:18USGS Report on Peak Streamflows During Harvey Significantly Revises Flood Probabilities
Sediment Plume from Above the Storm
Looking back to the period immediately after Harvey, check out this NASA photo of a sediment plume coming out of Galveston Bay on 8/31/2017. An astronaut took the photo using a Nikon D4 with a wide angle lens from 216 miles above the Earth.
As Harvey moved away from Houston, note the sediment plumes spilling out of bays in this photo of the Texas Coastline.
Zooming in and boosting contrast. We can see Lake Houston above Galveston Bay on the right of the clouds in the middle.
Technical Data
NASA PHOTO ID iss052e078795.NEF
GMT 2017:08:31 19:23:43
MODEL NIKON D4
Shutter 1/500
Aperture 18.0
ISO Speed 400
Focal Length 24.0 mm
Lens ID AF-S Nikkor 17-35mm f/2.8D IF-ED
Compensation -1/3
Mission: ISS052 Roll: E Frame: 78795
Country or Geographic Name: USA-TEXAS
Features: HURRICANE HARVEY, HOUSTON, GALVESTON B., MATAGORDA B., FLOODING, DRAINAGE
Center Point: Latitude: 29.0 Longitude: -95.5 (Negative numbers indicate west for longitude)
Spacecraft Altitude: 216 nautical miles
Sun Elevation Angle: 65 (Angle in degrees between the horizon and the sun, measured at the nadir point)
Posted on 7/14/2018 by Bob Rehak
319 Days Since Hurricane Harvey
Photo: Courtesy of NASA
Need for Sediment Management Planning
Sand and sediment clog our rivers and lake. “Dredge!” you say.
“Not that simple,” say the experts. “Who will pay for it? How much should we dredge? Where will the sediment go?”
That’s why we need planning for sediment management. We need to dredge the worst parts of the river now; the U.S. Army Corps of Engineers (USACE) has already started that as an emergency project. But we also need to dredge other parts of the river that are not quite critical yet. And we need to figure out how to do all this on a regular basis so that it never gets this bad again.
A giant sand dune has formed at the mouth of the west fork of the San Jacinto. It is not being addressed by the Army Corps dredging project but should be. Thousands of homes upstream from this massive blockage flooded during Harvey.
Sediment Management Challenges That Lie Ahead
I have talked about these issues with experts from Harris County Flood Control and USACE. Both say planning is crucial to a successful maintenance dredging/sediment management program. One provided this document: Galveston-Bay-Programmatic-RSM-Plan-Rev-1, as an example of what we need for the San Jacinto. It’s a long document – 112 pages. But it is worth reading the executive summary, introduction and table of contents at the very least. Parts of it discuss the upper reaches of the San Jacinto. But the main value it provides is that it outlines the challenges ahead.
All of these are difficult questions. Starting such an extensive program is like starting a new business.
Budgeting Comes First
A business plan and budgeting are the first issues we need to address. Where will the money for all this come from? Without answering that first, everything else is moot.
So who are the stakeholders?
Expecting all costs to be covered by the Harris County Flood Bond in perpetuity is just wishful and foolish thinking. The bond is for capital projects, not ongoing maintenance. You might be able to justify the first dredging as “channel improvements.” But after that, for the sake of the community, we need to find a way to make this program sustainable. Paying interest for ongoing operations is unwise.
Cost Sharing and 5-Year Intervals Can Make It More Doable than Avoidable
In 2000 Brown & Root, recommended dredging every 5 years – a perfect match for a venture with five partners. If each budgeted one fifth of the cost annually, and you did only one fifth of the job each year, this just might be more doable than avoidable. (Avoidance seems to have been the preferred approach in the past.)
We can’t budget sediment management forever on an emergency basis. That’s like using an emergency room for basic medical care. It’s probably not the best idea, nor the most cost effective. So let’s begin the dialog with stakeholders. As Grandma used to say, “An ounce of prevention…”
Posted on July 13, 2018 by Bob Rehak
318 Days since Hurricane Harvey
USGS Report on Peak Streamflows During Harvey Significantly Revises Flood Probabilities
The U.S. Geological Survey (USGS) in cooperation with the Federal Emergency Management Agency (FEMA) released a report this week that shows inundation maps, peak streamflows, detailed flood information, and new flood probabilities from Hurricane Harvey. Hurricane Harvey, it says, was the most significant multi-day rainfall event in U.S. history, both in scope and peak rainfall amounts, since records began in the 1880s.
Flood during Harvey looking east from the south side of the West Fork of the San Jacinto. Photo courtesy of Harris County Flood Control District.
Hurricane Harvey’s widespread 8-day rainfall, which started on August 25, 2017, exceeded 60 inches in some locations. That’s about 15 inches more than average annual amounts of rainfall for eastern Texas and the Texas coast. The area affected was also much larger than previous events.
New High Water Marks and Record Streamflows
USGS field crews collected 2,123 high-water marks in 22 counties in southeast Texas and three parishes across southwest Louisiana.
Record streamflows were measured at 40 USGS streamgages in Texas that have been in operation at least 15 years. At two streamgage locations, scientists determined that the percent chance for flooding of this magnitude to happen in any given year was 0.2 percent. This probability is also referred to as a 500-year flood. Thirty other USGS streamgages experienced flooding at levels with a 1 percent chance of occurring each year, also known as a 100-year flood.
Check out the “event viewer” noted in the report, especially if you are interested in high water marks in your neighborhood.
How Data Will Be Used
The USGS conducts research on the physical and statistical characteristics of flooding, estimating the probability of flooding at locations around the United States.
These records will assist officials in updating building codes, planning evacuation routes, creating floodplain management ordinances, providing environmental assessments and planning other community efforts to become more flood-resilient. FEMA will also use this information to revise their Flood Insurance Rate Maps. These maps help identify areas most likely to experience flooding in any given year.
Gages Closest to Lake Houston
The section on the San Jacinto Watershed starts on page 33. The maps for the San Jacinto watershed appear on pages 35 and 36. Use the maps to see the new high water marks in the area and to find the USGS gages nearest you. For most people in the upper Lake Houston Area, it will be one of these gages:
After you locate the gages nearest you, cross reference the numbers of those gages with data at the front of the report. It helps to use the search function in Adobe Acrobat because much of the information is in tables with very small type.
Examples of What You Will Find
Here’s an example of what you can find. For the gage nearest many of the sand mines on the West Fork (08068090), peak streamflow was estimated at 131,000 cubic feet per second. That was the highest of the 33 peaks previously observed at that location (from Table 3 on Page 9).
Now here’s the big news: From the same table, we can see that the Annual Exceedance Probability (AEP) is 2.4. That’s the likelihood of occurrence of a flood of given size or larger occurring in any one year, expressed as a percentage.
AEP is often expressed as the reciprocal of ARI (Average Recurrence Interval). For instance, A 10-year flood has a 10 percent probability of occurring in any given year, a 50-year event a 2% probabaility, a 100-year event a 1% probability, and a 500-year event a .2% probability.
In this case, a 2.4% AEP would have a likely recurrence interval of 42 years, given the new realities of upstream development, any changes in climate, and pocket calculators with more computing power. This means that the West Fork Gage ((08068090) at the Grand Parkway DID NOT even experience a 100-year flood! Yes, we can expect to see worse in the future.
Despite the fact that Harvey was the largest rainfall event in recorded U.S. history, USGS now predicts that it would take even bigger floods to reach the reconfigured 100-year, 200-year and 500-year recurrence intervals: 196,000, 263,000 and 374,000 cfs respectively for West Fork Gage at Grand Parkway (Gage #08068090 from Table 5, Page 14). So the new 500-year flood would have almost triple the volume of Harvey.
Humble Gage Data Missing From Report
Unfortunately, the Humble Gage at I-69 does not show up in the tables even though it is on the map and the cover of the report. This is likely in part due to the fact that the gage stopped reporting during the event due to the excessive streamflow
They may also have not reported the exceedance probability due to the shorter recent record.
For all the other gages, the Annual Exceedance Probabilities translate to new recurrence intervals ranging from 35 to 250 years. The gages at the low end of that range tend to be in the fastest developing neighborhoods.
Implications of New Findings
The report will stimulate public policy debate about development near rivers and the most effective methods of flood mitigation.
After reading this, I believe more than ever that we need more detention, dredging and gates (DDG). We need all three to help us handle the volumes of floodwater that USGS expects at more frequent intervals. Prayer, while advisable, is a less certain option in my mind than including DDG in the flood bond and passing it.
BTW, there was some confusion Tuesday night at the flood bond meeting. A small number of flood control employees incorrectly told residents that dredging would not be possible under the bond. It will be according to Matt Zeve, whom I contacted today.
Posted July 12, 2018 by Bob Rehak
317 Days since Hurricane Harvey