Earlier this month, the City of Houston announced that FEMA would pay to dredge another million cubic yards of sediment from the West Fork Mouth Bar. What does that mean in practical terms? What are the objectives of the program? How wide and deep will they go? Neither the objectives, nor a dredging plan, have yet been released.
The official plan will hopefully rely on new survey work and hydraulic modeling. A survey boat has been seen on the lake for several weeks now.
Since January of this year, the City of Houston has been trying to reduce the above water portion of the mouth bar with mechanical dredging, a much slower process than hydraulicdredging. Note how shallow the water is in the foreground.
How to Play Armchair Engineer
In the meantime, since fall football is in doubt due to COVID, here’s a simple way to keep your armchair quarterbacking skills finely honed. What would you do if you were the project engineer or manager? Play what if and experiment with different scenarios.
Download and open Google Earth Pro. It’s free.
Zoom in on the West Fork Mouth Bar.
Select the measuring tool.
Click on the polygon tab.
Select square yards for the unit measurement for the areas you will define.
Now start second guessing the project engineers. Play “what if” by defining an area that you would like to see dredged.
Readjust the points that define the area by dragging them in, out, up or down.
Watch the total square yards recalculate as you move the points.
Examples of Different Scenarios
Here are some examples to show you what I’m talking about.
4.3 Million Square Yard Area, Roughly 8 inches Deep
Largest area. This scenario takes in everything between where the Corps stopped dredging in its Emergency West Fork Program and the FM1960 Bridge.
The scenario above takes in the mouth of Ben’s Branch, plus all the other drainage ditches that empty Fosters Mill, Kings Point, and Atascocita north of the FM1960 Bridge.
The scenario above covers 4.3 million square yards. But with a budget to dredge only 1 million cubic yards, you would divide 1/4.3 = 0.23 yards of depth. That’s less than a third of a yard. It works out to about 8 inches.
3 Million Square Yard Area, 1 Foot Deep
In the next scenario, I pulled the boundaries in so that the area equaled 3 million square yards.
This scenario is a little more intuitive. You’re dredging 1 million cubic yards across an area of 3 million square yards. Within this bounding box, you could reduce the level of sediment roughly a foot.
2 Million Square Yard Area, 18 inches Deep
If you reduced the area to be dredged to 2 million square yards, you could reduce the level of sediment by half a yard or 18 inches.
1 Million Square Yards, 3 Feet Deep
Path followed by the relict channel before Lake Houston was built.
If you reduced the area further, to 1 million square yards, you could dredge to 3 feet. With the five feet of depth already there, you could have an eight foot channel connecting the river and the lake. Make it narrower and you could even go deeper. And perhaps, just perhaps, keep sediment from accumulating so rapidly upstream of the FM1960 bridge.
Difficult Choices Ahead
As you can see, engineers have some difficult choices ahead. They must chose between unblocking channels and streams, or dredging a channel roughly the size of the upstream west fork all the way to the 1960 bridge.
Last year, the Corps reduced the 600-acre area between the mouth bar and Atascocita Point to an average depth of 5.5 feet. So we have a good head start. But there are other considerations:
The West Fork was roughly 22 feet deep where the Corps stopped dredging just west of the mouth bar. Because of scouring, it’s at least that deep where the west fork passes under FM1960.
As a result, water coming down the west fork hits an underwater mesa that still blocks off three quarters of the conveyance.
Prominent area geologists, such as Tim Garfield and RD Kissling, theorize that that wall traps sediment and is rapidly diminishing the value of previous dredging programs. They believe that the most important objective for this phase of dredging should be to “reconnect the West Fork with the Lake.”
But Advancing Delta Now Blocks Major Streams, Channels
Meanwhile, consider this, too. In 2014, Bens Branch and the drainage ditch that empties large parts of Fosters Mill and Kings Point had a clear path to the river. Today, both are blocked by the mouth bar and an advancing delta within the lake. Compare the two images below.
Google Earth view from 2014 shows steams could still easily connect with relict channel.
Today, however, an advancing delta within the lake blocks them.
These are some of the real world trade offs that engineers and project managers must deal with every day.
So to return to the football analogy, do you send your receivers wide or deep? Do you have them hug the sidelines or cut for the goal post?
Understand that this isn’t a game, however. It’s a struggle to return a community to prosperity.
What would you do? And why?
Posted by Bob Rehak on 8/31/2020
1098 Days since Hurricane Harvey
https://i0.wp.com/reduceflooding.com/wp-content/uploads/2020/08/20200831-DJI_0613.jpg?fit=1200%2C900&ssl=19001200adminadmin2020-08-31 20:38:392020-08-31 20:52:02How Much Will Dredging Another Million Cubic Yards Reduce the West Fork Mouth Bar Area?
Developed after Tropical Storm Allison in 2001, the Harris County Flood Control District Flood Education Mapping Tool’s purpose was to help Harris County residents learn the location of their properties in relation to mapped 1-percent (100-year), 0.2-percent (500-year) and coastal floodplains. The Flood Education Mapping Tool includes regularly-updated floodplain information from the Flood Insurance Rate Maps (FIRMs) for Harris County, interactive legend options, a simple map display and easy map navigation.
Easy to Use
The tool itself is easy to use and navigate. Click on Floodplains; it will show you the extent of various floodplains. Click on Backgrounds; choose the one you want. And click on Channels; it will highlight all channels in Harris County and show you their numeric IDs. The last is very useful in helping the District locate a problem you’re reporting.
Unique Ponding Feature
But the Flood Education Mapping Tool contains another feature I have found nowhere else: the Ponding button. Click on it; low areas susceptible to ponding during heavy rains will highlight in shades of reddish brown.
HCFCD’s Mapping Tool contains “ponding” feature that that shows low areas that collect water during heavy rains.Shown above, the Deerbrook Mall area in Humble.
Ponding is the collection of stormwater on streets or on undeveloped land that typically forms when rainfall exceeds the design capacity of a street’s drainage system or the land’s ability to drain. The shade of red indicates the depth of the water. Dark red indicates deep ponding and light red indicates shallow ponding – very helpful when evaluating a home purchase.
Basic Flood Education All on One Page of FAQs
The Flood Education Mapping Tool also contains a treasure trove of useful FAQs. The Flood Control District has broken them down into four main categories:
If you want a basic flood education on a page, this is the page for you. It will help you converse knowledgeably with a flood-insurance or real-estate agent.
This page of FAQs is extremely well written, concise, and easy to understand. Most answers also contain links to other helpful, related sites. So you can drill down into most topics as deeply as you wish.
I’ve listed Harris County Flood Control District’s Flood Education Mapping Tool on the Links page of this web site under Floodplain Maps and Elevation, so you can find it easily in the future.
Posted by Bob Rehak on 8/30/2020
1097 Days since Hurricane Harvey
https://i0.wp.com/reduceflooding.com/wp-content/uploads/2020/08/Ponding.jpg?fit=1200%2C617&ssl=16171200adminadmin2020-08-30 12:57:122020-08-30 13:01:58HCFCD Flood Education Mapping Tool Contains Features Found Nowhere Else, Plus Basic Flood Education on One Page
Because of low interest rates, new developments seem to pop up weekly around the Lake Houston Area. The question often arises, “How will the development of new flood maps affect the development of new subdivisions?” Most people by now have heard that City building code revisions now require elevation at least two feet above the .02-percent-annual-chance flood (formerly known as 500-year flood). But does that mean two feet above the old floodplain or the new? Due to a little-known provision in the City’s floodplain regulations, it means the new floodplain even though the new floodplain maps are not official yet.
Here’s what you need to know if you’re concerned that someone may be building future buyouts next to your neighborhood. First the timetable for new flood maps.
Remaining timetable for new Harris County Flood Maps
Even though FEMA won’t release the new flood maps officially for approximately another five years, developers should still be building to the higher standards associated with newly acquired data (in other words, the data on which the new maps are being built). See below.
Floodplain Regs Authorize City Engineer to Use Data Behind New Flood Maps
Section 19-4 of the City’s Floodplain regulations address Use of other flood hazard data to supplement the effective Flood Insurance Rate Map (FIRM). It states, “New elevation and flooding studies are undertaken by or under the auspices of FEMA and local political subdivisions, such as the Harris County Flood Control District. Upon determination that the data generated by such a study appears to be reliable and based upon sound engineering and surveying practices and further that the study’s data indicate that the effective FIRMs are FIRM is materially inaccurate, the city engineer may cause the study data to be administered for purposes of this chapter as though it were a part of the effective FIRM. Any such determination shall be issued in writing and a copy shall be placed on file in the office of the city secretary. The city engineer is authorized to utilize updated information from FIS and floodplain models in administering this chapter.”
Basically, that means even though the new maps have not yet been adopted, the City Engineer can require developers’ plans to reflect the new underlying data as though it were part of the current map. In this case, the new underlying data is already in hand.
MaapNext Website Describes New Data Improvements
Current floodplain maps will change greatly according to Harris County Flood Control. The district has already started releasing information on a new website called MaapNext (Modeling, Assessment and Awareness Project).
Components of the MaapNext program. A $3.5 million FEMA grant made MaapNext possible.
According to the MaapNext site, we now have updated data based on:
County-wide impervious data developed from 2018 aerial imagery
Completed flood risk reduction projects
NOAA’s recently-released Atlas 14
Updated terrain data
We also have new and better ways to model that data since the last survey after TS Allison:
2-Dimensional Hydraulic Modeling
New hydrology method that better accounts for a watershed’s conveyance capacity
Rain-on-Grid analysis that identifies previously unmapped urban flood risk.
And, we are beginning to develop better maps:
Modeling results in GIS (Geographic Information Systems)
New flood-risk data sets describe results in a variety of useful ways
Reportedly, the City is already requiring developers to act on the new “best available data” instead of waiting five years for the next maps.
Chapter 19 of the City Ordinances deals with dozens of other requirements for building in floodplains. But more on those in future posts.
Posted by Bob Rehak on 8/29/2020
1096 Days (Three Years) 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/2020/08/image001-1.png?fit=1182%2C847&ssl=18471182adminadmin2020-08-29 17:17:162020-08-29 17:21:55New Flood-Map Timetable and How It Affects New Development
How Much Will Dredging Another Million Cubic Yards Reduce the West Fork Mouth Bar Area?
Earlier this month, the City of Houston announced that FEMA would pay to dredge another million cubic yards of sediment from the West Fork Mouth Bar. What does that mean in practical terms? What are the objectives of the program? How wide and deep will they go? Neither the objectives, nor a dredging plan, have yet been released.
The official plan will hopefully rely on new survey work and hydraulic modeling. A survey boat has been seen on the lake for several weeks now.
How to Play Armchair Engineer
In the meantime, since fall football is in doubt due to COVID, here’s a simple way to keep your armchair quarterbacking skills finely honed. What would you do if you were the project engineer or manager? Play what if and experiment with different scenarios.
Examples of Different Scenarios
Here are some examples to show you what I’m talking about.
4.3 Million Square Yard Area, Roughly 8 inches Deep
The scenario above takes in the mouth of Ben’s Branch, plus all the other drainage ditches that empty Fosters Mill, Kings Point, and Atascocita north of the FM1960 Bridge.
The scenario above covers 4.3 million square yards. But with a budget to dredge only 1 million cubic yards, you would divide 1/4.3 = 0.23 yards of depth. That’s less than a third of a yard. It works out to about 8 inches.
3 Million Square Yard Area, 1 Foot Deep
This scenario is a little more intuitive. You’re dredging 1 million cubic yards across an area of 3 million square yards. Within this bounding box, you could reduce the level of sediment roughly a foot.
2 Million Square Yard Area, 18 inches Deep
1 Million Square Yards, 3 Feet Deep
If you reduced the area further, to 1 million square yards, you could dredge to 3 feet. With the five feet of depth already there, you could have an eight foot channel connecting the river and the lake. Make it narrower and you could even go deeper. And perhaps, just perhaps, keep sediment from accumulating so rapidly upstream of the FM1960 bridge.
Difficult Choices Ahead
As you can see, engineers have some difficult choices ahead. They must chose between unblocking channels and streams, or dredging a channel roughly the size of the upstream west fork all the way to the 1960 bridge.
Last year, the Corps reduced the 600-acre area between the mouth bar and Atascocita Point to an average depth of 5.5 feet. So we have a good head start. But there are other considerations:
The West Fork was roughly 22 feet deep where the Corps stopped dredging just west of the mouth bar. Because of scouring, it’s at least that deep where the west fork passes under FM1960.
Prominent area geologists, such as Tim Garfield and RD Kissling, theorize that that wall traps sediment and is rapidly diminishing the value of previous dredging programs. They believe that the most important objective for this phase of dredging should be to “reconnect the West Fork with the Lake.”
But Advancing Delta Now Blocks Major Streams, Channels
Meanwhile, consider this, too. In 2014, Bens Branch and the drainage ditch that empties large parts of Fosters Mill and Kings Point had a clear path to the river. Today, both are blocked by the mouth bar and an advancing delta within the lake. Compare the two images below.
These are some of the real world trade offs that engineers and project managers must deal with every day.
So to return to the football analogy, do you send your receivers wide or deep? Do you have them hug the sidelines or cut for the goal post?
Understand that this isn’t a game, however. It’s a struggle to return a community to prosperity.
What would you do? And why?
Posted by Bob Rehak on 8/31/2020
1098 Days since Hurricane Harvey
HCFCD Flood Education Mapping Tool Contains Features Found Nowhere Else, Plus Basic Flood Education on One Page
Developed after Tropical Storm Allison in 2001, the Harris County Flood Control District Flood Education Mapping Tool’s purpose was to help Harris County residents learn the location of their properties in relation to mapped 1-percent (100-year), 0.2-percent (500-year) and coastal floodplains. The Flood Education Mapping Tool includes regularly-updated floodplain information from the Flood Insurance Rate Maps (FIRMs) for Harris County, interactive legend options, a simple map display and easy map navigation.
Easy to Use
The tool itself is easy to use and navigate. Click on Floodplains; it will show you the extent of various floodplains. Click on Backgrounds; choose the one you want. And click on Channels; it will highlight all channels in Harris County and show you their numeric IDs. The last is very useful in helping the District locate a problem you’re reporting.
Unique Ponding Feature
Ponding is the collection of stormwater on streets or on undeveloped land that typically forms when rainfall exceeds the design capacity of a street’s drainage system or the land’s ability to drain. The shade of red indicates the depth of the water. Dark red indicates deep ponding and light red indicates shallow ponding – very helpful when evaluating a home purchase.
Basic Flood Education All on One Page of FAQs
The Flood Education Mapping Tool also contains a treasure trove of useful FAQs. The Flood Control District has broken them down into four main categories:
Flood Insurance Rate Maps
• What is a Flood Insurance Rate Map and how do I use it?
Floodplains and Floodways:
• What is a floodplain? / What is a floodway?
• What is a 1 percent (100-year) flood/floodplain? / What are my chances of flooding in a 1 percent (100-year) floodplain?
• What is a 0.2 percent (500-year) flood/floodplain? / What are my chances of flooding in a 0.2 percent (500-year) floodplain?
• What is a coastal floodplain?
• What is a Special Flood Hazard Area?
• What is meant by Base Flood Elevation?
• Who determines the boundaries of a floodplain? / What data is used to create a Flood Insurance Rate Map?
Floodplain Status/Floodplain Determination:
• Is my home located in a mapped floodplain? / Which mapped floodplain is my home in? / How do I get an official floodplain determination?
• What is an Elevation Certificate? / What is a Letter of Map Amendment? / What is a Letter of Map Revision?
• The Flood Insurance Rate Map shows that my lot is in a mapped 1 percent (100-year) floodplain, but my house sits on higher ground/is raised on pier and beam construction/is elevated. Do I still need flood insurance? / Can I obtain cheaper flood insurance?
• My home is not in a mapped 1 percent (100-year), 0.2 percent (500-year) or coastal floodplain. Does this mean I am not at risk for flooding?
• The Harris County Flood Control District is constructing a project on a bayou in my neighborhood. Will my home be out of the floodplain when it’s complete?
Flood Insurance
• Does standard homeowners insurance cover losses and damages from flooding?
• Am I required to have flood insurance? / Do I still need flood insurance if I live outside a mapped 1 percent (100-year) floodplain?
• If my home floods, will federal disaster assistance pay for all of my damages?
• Is damage from wind-driven rain or rain that comes through my roof covered by my flood insurance policy?
• How can I obtain flood insurance?
• How much does flood insurance cost? / Why is my flood insurance so expensive?
• Can I get flood insurance if I rent?
This page of FAQs is extremely well written, concise, and easy to understand. Most answers also contain links to other helpful, related sites. So you can drill down into most topics as deeply as you wish.
I’ve listed Harris County Flood Control District’s Flood Education Mapping Tool on the Links page of this web site under Floodplain Maps and Elevation, so you can find it easily in the future.
Posted by Bob Rehak on 8/30/2020
1097 Days since Hurricane Harvey
New Flood-Map Timetable and How It Affects New Development
Because of low interest rates, new developments seem to pop up weekly around the Lake Houston Area. The question often arises, “How will the development of new flood maps affect the development of new subdivisions?” Most people by now have heard that City building code revisions now require elevation at least two feet above the .02-percent-annual-chance flood (formerly known as 500-year flood). But does that mean two feet above the old floodplain or the new? Due to a little-known provision in the City’s floodplain regulations, it means the new floodplain even though the new floodplain maps are not official yet.
Timetable for Updating Flood Maps
Here’s what you need to know if you’re concerned that someone may be building future buyouts next to your neighborhood. First the timetable for new flood maps.
Even though FEMA won’t release the new flood maps officially for approximately another five years, developers should still be building to the higher standards associated with newly acquired data (in other words, the data on which the new maps are being built). See below.
Floodplain Regs Authorize City Engineer to Use Data Behind New Flood Maps
Section 19-4 of the City’s Floodplain regulations address Use of other flood hazard data to supplement the effective Flood Insurance Rate Map (FIRM). It states, “New elevation and flooding studies are undertaken by or under the auspices of FEMA and local political subdivisions, such as the Harris County Flood Control District. Upon determination that the data generated by such a study appears to be reliable and based upon sound engineering and surveying practices and further that the study’s data indicate that the effective FIRMs are FIRM is materially inaccurate, the city engineer may cause the study data to be administered for purposes of this chapter as though it were a part of the effective FIRM. Any such determination shall be issued in writing and a copy shall be placed on file in the office of the city secretary. The city engineer is authorized to utilize updated information from FIS and floodplain models in administering this chapter.”
Basically, that means even though the new maps have not yet been adopted, the City Engineer can require developers’ plans to reflect the new underlying data as though it were part of the current map. In this case, the new underlying data is already in hand.
MaapNext Website Describes New Data Improvements
Current floodplain maps will change greatly according to Harris County Flood Control. The district has already started releasing information on a new website called MaapNext (Modeling, Assessment and Awareness Project).
According to the MaapNext site, we now have updated data based on:
We also have new and better ways to model that data since the last survey after TS Allison:
And, we are beginning to develop better maps:
Reportedly, the City is already requiring developers to act on the new “best available data” instead of waiting five years for the next maps.
Chapter 19 of the City Ordinances deals with dozens of other requirements for building in floodplains. But more on those in future posts.
Posted by Bob Rehak on 8/29/2020
1096 Days (Three Years) 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.