Imagine you purchased a new car five years ago.  Remember that wonderful new car smell?  Since then, each year you put 20,000 miles on the vehicle and you’ve watched the odometer move closer and closer, and finally pass the 100,000 mile mark.  Time for a new car right?

Maybe not.  Car and Driver reports that “standard cars in this day and age are expected to keep running up to 200,000 miles, while cars with electric engines are expected to last for up to 300,000 miles.”  Consumer Reports tells us that car longevity “comes down to keeping your car well maintained.”

If your car was well maintained while you drove those first 100,000 miles, you probably could delay the purchase of a new one.  But, if you put off changing the oil and doing the other recommended maintenance work, you might suffer a breakdown late at night, so a new car might be wise.

The same need for maintenance is true for the flood control infrastructure in our area.  The bayous, channels, and ponds designed, built, and maintained by the Harris County Flood Control District help reduce flood risk, but they don’t last forever.  While flood control facilities don’t need oil changes, they do need regular maintenance.  Debris and sediment must be removed.  Trees and landscapes need to be pruned and mowed.  Broken pipes and concrete panels need to be fixed.

If we don’t maintain our flood control facilities, the risk of flooding increases for all of us.

Property owners in Harris County currently pay 3.1 cents per $100 of assessed value to the Flood Control District.  This means the owner of a $100,000 property pays $31 each year to help reduce flood risk.  Each year the property tax generates about $128 million each year.

That sounds like a lot, but current revenue is insufficient to adequately maintain our flood control facilities.  Flood control features, like channels and ponds, have an anticipated lifespan of from 50 to 100 years.  An assessment of the anticipated life span of our flood control facilities showed that current revenue will only allow us to replace our flood control infrastructure once every 270 years — or almost 3 to 6 times longer than they are expected to last!

The new car example helps illustrate this.  Imagine driving a car with 3 to 6 times more miles than its anticipated end of life odometer reading.  Since cars have an anticipated lifespan of 200,000 miles, the old car you are driving in this thought experiment would have 600,000 or 1.2 million miles on the odometer!  Perhaps it is time to get a new car!

On election day, November 5, 2024, voters in Harris County will be presented with a proposed tax rate increase for the Flood Control District.  The proposal will increase the tax rate by 58% from 3.1 cents to 4.8 cents per $100 of assessed value.  This will generate sufficient revenue to allow us to replace our flood control infrastructure once every 67 years.  This proposal was placed on the ballot by all five elected leaders of Harris County.

In the same way most car owners invest in maintenance and save for a replacement vehicle to avoid late night breakdowns on the side of the road; I encourage Harris County voters to vote FOR the proposed tax rate increase to make sure our flood control infrastructure will be well maintained.

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I picked up a fresh first printing of this book from the Island Press booth at the American Planning Association’s National Planning Conference held in April 2024, in Minneapolis. Killed by a Traffic Engineer: Shattering the Delusion that Science Underlies Our Transportation System, the full title, sports a striking black and red cover design showing an damaged STOP sign. While 387 pages long, with twelve parts, and 88 chapters, the book was a fairly quick read.

Don’t let the shocking title discourage you from reading this book. Wes Marshall, PhD, PE, a professor of civil engineering at the University of Colorado (CU), Denver wrote it. He directs the CU Denver Human-Centered Transportation Program and the Transportation Research Center at CU Denver. He obtained his BS Civil Engineering from the University of Virginia and his MS and PhD from the University of Connecticut.

In the first part of his book Marshall reminds the reader of the high number of roadway deaths and injuries in the United States. Marshall reminds us that, “more people have died on US roads than in all US wars and conflicts combined, including the American Revolution.” On a per capita basis, the United States suffers one of the highest fatality rates of all countries tracked by the Organization for Economic Co-Operation and Development (OECD).

Marshall’s writes with a conversational, somewhat emotional tone that may turn some readers off. While his tone (and the book’s title) makes it clear that he is very passionate about the topic, it may hinder the book’s ability to reduce injuries and deaths on our roadways and to change how traffic engineers think about their jobs.

Marshall dives into the history of traffic engineering standards since the dawn of the automobile. He notes a 1900 publication by William Eno (while there were only 8,000 registered cars in the United States) that proposed that drivers stay to the right and wave their arms to indicate their intention to turn or stop. Throughout the book, Marshall quotes articles and papers published in the 122 years during which the number of registered cars increased from 8,000 in 1900 to 283 million in 2022.

Marshall explains the history of the standards and design procedures used by traffic and transportation engineers today. He demonstrates that Level of Service, Clear Zones, Lane Widths, Slip Lanes, Left Turn Lanes, Median Size, Intersection Controls, Design Speed, Sight Distances, and other standards all emerge from a desire to increase motor vehicle volumes and speeds in our transportation system, rather than enhance safety outcomes. He also provides examples of journal articles that claim, without evidence, that these standards improve safety.

I had many “Wow, I did not know that,” “Wow, that’s surprising,” and general “AH-HA!” moments when reading this book. I had an AH-HA! moment when I read Marshall’s discussion of safety factors in structural and traffic engineering. Structural engineers follow standards and design procedures to deliver cost efficient buildings that don’t fall down. They use enough steel or concrete to achieve a safety factor and to accomodate building code required loads. Traffic engineers follow design procedures and seek to meet – or exceed – recommended minimum standards for lane widths, design speeds, clear zones, and other parameters. They think, a 13 foot wide lane must be better than a 12 foot wide lane, because the standard specifies a minimum. Bigger is better right? This leads to roads that encourage high speeds and more injuries and deaths.

He describes how law enforcement, local governments, state governments, federal agencies, and academia track fatalities, injuries, crashes, and other transportation system events and how the current approach fails to provide useful feedback to engineers and policy makers who wish to change standards and design methods to achieve better safety outcomes. Standards can’t be updated if we don’t have the data to demonstrate the improvement.

He provides suggestions for improving safety outcomes throughout the book, but I would have preferred for them to be concisely summarized in one place. Overall I recommend planners, engineers, and policy makers read this book. It is available from Island Press: https://islandpress.org/books/killed-traffic-engineer#desc

In Part 1 of this two-part post, I outlined how I would create a heat map of the county showing areas of high inundation risk, low prior investments, and high vulnerability.

This month, in Part 2 of this two-part post, I will describe how we might build the composite heat map and how it could be used to identify areas for future flood resilience investments.

Building the Composite Heat Map

Last month I described three input variables that I would use to create a composite heat map of flood risk reduction needs. The three layers included:

— The Flood Risk (annual chance of inundation);

— The Flood Mitigation Benefit Index (FMBI); and,

— The Social Vulnerability Index (SVI).

These are useful data, but they are not integrated or combined yet. Each variable can be used to create a separate heat map. How can we combine these three maps into one composite map?

Overhead Transparency Projectors

I attended high school in the 1980s. At that time many teachers used an overhead transparency projector to present information to the class. They would place transparent sheets of plastic on a light box, light would shine up through the sheet, hit a mirror, shine through a lens, and get projected onto a screen for the class to see. The sheets would sometimes have pre-printed information or the teacher might actually write with a marker on the sheet as they presented the information. Here’s a photograph of one of these old devices.

Transparencies for Planning

We can create a transparent sheet for each of the layers we’d like to consider when creating the composite heat map. Today we can do this with Geographic Information System (GIS) mapping software, but I thought it would be helpful to illustrate the idea using clear sheet transparencies.

I created a hypothetical area of the county with nine U.S. Census Blocks. I also created three hypothetical transparencies for consideration; one for flood risk, one for FMBI, and one for SVI. In each map, the red color indicates a greater need for future resilience investments and the green color indicates a lower need for future resilience investments. The numbered rectangular shapes are hypothetical U.S. Census Blocks.

The flood risk map shows that Blocks 1, 2, 3, 7, and 8 have very high risks, while 5 has a very low risk.

Here’s the Flood Mitigation Benefit Index (FMBI) map:

The FMBI map shows a wide range of index values within the very high flood risk areas on the left side of the image.

Here’s the SVI map:

The SVI map shows very highly vulnerable people in Block 8 with high to moderate vulnerability in Blocks 2 and 7.

Equal Weight Example

If we place all three transparencies on the overhead transparency projector at the same time and without any adjustment, we see an equal weight composite. This means that all three variables – flood risk, FMBI, and SVI are considered equally. Take a look:

The equal weight composite heat map shows that additional resilience investments are needed in U.S. Census Blocks 7 and 8 (and perhaps 2 if we have sufficient funding). The legend colors don’t exactly match up anymore because of the way the layered colors blend.

Variable Weight Example

Let’s say we decide the current flood risk is the most important factor we should consider, followed by SVI, and then followed by FMBI. Let’s also say we think that flood risk should be six times more important than the FMBI and three times more important than the SVI. This logic would yield the following weight factors and transparency levels. Note that the transparency level goes down with a high weight to allow that layer to influence the composite more strongly. Also, note that the assignment of the weights is a policy choice – not an engineering choice.

	Weight Factor	Transparency Level
Flood Risk	60	40
Flood Mitigation Benefit Index	10	90
Social Vulnerability Index	20	80

Here are the new transparencies with the weight factors and transparency levels applied:

Here is the new composite heat map we see after we place all three of the weighted transparencies on the overhead projector:

The weighted composite heat map shows that future resilience investments are needed in U.S. Census Blocks 1, 2, 3, 7, and 8 (and perhaps 6 and 9 if we have sufficient funding). The legend colors don’t exactly match up anymore because of the way the layered colors blend.

Discussion of Results

Compare the weighted result to the equal weight result.

The equal-weighted composite heat map showed that future resilience investments are needed in U.S. Census Blocks 7 and 8 (and perhaps 2 if we have sufficient funding). The weighted composite heat map showed that future resilience investments are needed in U.S. Census Blocks 1, 2, 3, 7, and 8 (and perhaps 6 and 9 if we have sufficient funding). What accounts for this difference?

In the first example, all three input variables were considered equally. In the second example, flood risk was considered to be six times more important than FMBI and three times more important than SVI.

Implications for Planning

This article shows how policy decisions regarding the relative importance of various factors will lead to different decisions and different outcomes. It shows why elected officials and the public should stay engaged in planning efforts to let planners know what factors and weights they should be considering.

I believe that Harris County elected officials and Harris County Flood Control District (HCFCD) managers have not intentionally set out to make inequitable flood risk reduction investments. I believe that some inequitable investments were a side-effect of relying on the Civil Works program of the U.S. Army Corps of Engineers (USACE) for the vast majority of funding. Why would this reliance lead to some inequitable investments?

By federal law and policy, the USACE can only study a project if the study directive is included in federal legislation passed by both the House and the Senate and signed by the President. The USACE then must evaluate project alternatives using a planning guidance document published in 1983, known by the short title: “Principles and Guidelines” (P&G).

Under the P&G document, planners must calculate the benefits and costs of all project alternatives and, in a broader sense, all projects that are competing for federal funding. Engineers like numbers so we calculate the ratio of benefits over costs and call it the Benefit-Cost Ratio or BCR. Projects (or project alternatives) that deliver higher BCRs are much more attractive to the federal government than those that deliver lower BCRs.

I’m told that in recent years the Executive Branch of the federal government typically only supports projects with a BCR of more than 3.0.

Section IV of the Principles and Guidelines – relating to urban flood damage – requires planners to calculate the benefit portion of the BCR from the value of the avoided “physical damages to … buildings or parts of buildings; loss of contents … loss of roads, sewers, bridges, power lines, etc.”

To illustrate this, consider two projects that each cost $100 million dollars. One project removes 1,000 homes each worth $350,000 from the 100-year floodplain (the 1% annual chance floodplain). The other project removes 1,000 homes each worth $85,000 from the 100-year floodplain. Let’s also assume that both projects benefit 2,300 people (2.3 people per household).

For simplicity let’s compare both projects for just one 100-year flood event and assume that the 100-year flood would completely destroy all of the homes. (I realize this is not true in the real world, but just go with it for the example.)

The first project would avoid $350 million in property damage (1,000 homes times $350,000 for each home). This would yield a BCR of 3.5 ($350 million / $100 million) and benefit 2,300 people.

The second project would avoid $85 million in property damage (1,000 homes times $85,000 for each home). This would yield a BCR of 0.85 ($85 million / $100 million) and benefit 2,300 people.

Which project do you think would secure federal support? In this example, the project that removed the higher-value homes from the floodplain would be supported and would attract federal funding, while the other project would not attract any federal funding. When federal funding is secured, it often pays for 90% of the project cost. So in this case, the federal government – using income taxes from citizens all around the nation – would pay $90 million for the project while HCFCD would pay $10 million using local property tax revenue.

To illustrate just how important property values are to the process, the P&G document provides a flowchart to illustrate the process.

The federal reliance on BCRs determined using the value of avoided property damages outlined above, means that when we rely on federal funding to do projects, we must identify projects that have a high BCR so that the projects can get a favorable recommendation from the USACE to federal lawmakers. This encourages flood mitigation planners and engineers to think up projects that protect higher-value properties, regardless of the number of people helped.

Federal law and policy also direct the USACE to only design and build projects with both a local sponsor – in our case HCFCD – and authorization and appropriated funding by Congress and the President.

A quick review of the Texas law that created the Harris County Flood Control District (HCFCD) in 1937 shows why HCFCD was created in the first place. Section 2.g. of House Bill No. 1131 of the 44th Texas Legislature states:

To cooperate with and contract with the United States of America or with any of its agencies now existing, or which may be created hereafter, for grants, loans, or advancements to carry out any of the powers or to further any of the purposes set forth in this Act and to receive and use said moneys for such purposes; or to contribute to the United States of America or any of its agencies in connection with any project undertaken by it affecting or relating to flood control in Harris County;

HoUSE BILL NO. 1131, 44TH TEXAS LEGISLATURE

So it is clear that we have relied on federal funding to reduce flood risks in Harris County. Maximizing the use of federal dollars is important. Why not take advantage of available federal funding? Many people, myself included, appreciate how HCFCD staff has been able to maximize the federal investments in our region. But I think it’s fair to acknowledge that this reliance on federal funding did inadvertently lead to some inequitable investments.

Today, one important policy question for Harris County is this: “To what extent, if any, will we rely on federal funding to further reduce flood risks?”

Since this question depends upon federal policy and regulations, in another post, I will provide an update on pending changes to federal policies and regulations that may allow “counting” other benefits — not just the value of avoided property damages — in the benefits part of the BCR. Other benefits might include favorable social, environmental, and economic outcomes – some that can be converted to a monetary value and some that are qualitative.

This is Part II of my two-part article providing responses to concerns raised by my colleague on the Community Flood Resilience Task Force (CFRTF), Mr. Bob Rehak about the FMBI. If you missed Part I, you can read it here.

Why are we Using the Index When it Produces Inconsistent Results that are Not Intuitive? Mr. Rehak provides an example that holds the current population and current risk the same, but changes the total prior investment amounts, as illustrated in the table below:

Mr. Rehak looks at these results and writes: “So, spending more money to get the same results increases benefits? Shouldn’t it be the opposite? That’s both depressing and confusing. You spend 10X the money; flood risk remains the same; and the “benefit” increases!!!??? You would think spending less money to achieve identical results would be more beneficial. It certainly is for taxpayers.”

Everyone should be depressed and confused by this result if the FMBI was illustrating the results for the same location. Mr. Rehak appears to make that inference when he writes: “spending more money to get the same results increases benefits.”

But Area A and Area B are two different locations. The FMBI is just telling us what the current conditions are at two different locations in the county. One location had 10 times the prior investment than the other – but both locations still have the same current risk.

Worse, in this case, BOTH locations have risks that are ten times the current standard of care for new developments – which require structures to have less than a 1% annual chance of inundation. Clearly, both locations need more flood risk investment. The FMBIs of 2 and 20 both are extremely low, meaning they need help, regardless of the prior investments. A high FMBI indicates that no additional help is needed in that location. A low FMBI indicates that additional help is needed in that location.

The table included in the middle of my February 17, 2022, post entitled “How Should We Decide Where to Invest in Flood Risk Reduction?” presents additional examples showing how the FMBI changes from location to location with only one changed variable. It also provides narrative explanations of each sequence. Notice how the index values are greater than 3,000 (sometimes greater than 20,000 or 100,000) in locations where the current annual chance of inundation is less than 1%? Again, a high FMBI means we don’t need to make more investments in that location. A low FMBI means that location needs more help.

Isn’t the FMBI Trying to Prove Inequitable Investments in Flood Risk Reduction? To some extent, partially, yes, it is. This was always an important aspect of the FMBI, when it was originally proposed as the “Flood Benefits Index (FBI)” by Dr. Erthea Nance and Iris Gonzalez in May 2021. I have continued to advocate for its use as one of four input variables we should use to create our county-wide “heat map.” This is explained in more detail in my other article. Mr. Rehak is concerned about the taxpayer. I am also. I don’t think the taxpayers of Harris County should pay for flood risk reduction projects in areas that already have a high FMBI. Said another way, it is a waste of taxpayer money to invest in additional flood risk reduction projects in areas currently with less than a 1% annual chance of inundation.

Isn’t the FMBI Measuring per capita Investment Associated with a Certain Level of Flood Risk and Mistakenly Calling that a “Benefit?” Mr. Rehak writes: “The more people you help with any given sum, the more the benefit goes down. Voila! That makes it look as though the highly populated watersheds (that have received the overwhelming majority of prior investments) have received little benefit. And that may be the point of this formula. It will send even more money to those same areas.”

This interpretation again seems to stem, I think, from Mr. Rehak’s belief that the index will be used to compare the same location at different times – before and after various investments. This is not the proposed use of the index. The proposal is to use the index to describe the current conditions at all locations in the county at the same time.

I’m not sure I understand Mr. Rehak’s concern about the index being a per capita value. The more people in an area who benefit from prior investments the better. Wouldn’t we want to invest in areas that help the most people?

The blue-shaded area of the table in my earlier post illustrates how population differences between locations will change the index value among those locations. For convenience I’ve repeated the table below:

Mr. Rehak accurately notes that the index goes up in locations with fewer people and down in locations with more people; this will incentivize planners to direct future investments in those higher population areas. He writes: “The more people you help with any given sum, the more the benefit goes down.” This is true, but Mr. Rehak’s statement doesn’t connect it to the past and it omits how the index will be normalized by area size. Index values will be calculated for similarly sized areas. This will allow an apples-to-apples comparison of per capita investments. The index is intended to incentivize future investments in areas with more people in cases where risk and prior investments are equal because we want to help as many people as possible.

One of my colleagues on the Harris County Community Flood Resilience Task Force (CFRTF) – Mr. Bob Rehak, as well as Commissioner Tom Ramsey, P.E., and others have asked me about the proposed Flood Mitigation Benefits Index (FMBI). After hearing some of the questions, and reading two recent blog posts by Mr. Rehak at Reduce Flooding Now, one on July 2, 2022 – Questionable Validity of Flood-Mitigation Equity Formula and on July 6, 2022 – Formula for Allocating Future Flood-Mitigation Funding Deceives, I figured I should provide a more detailed explanation of the index and directly address some of Mr. Rehak’s concerns.

In addition to getting to know Mr. Rehak while attending CFRTF meetings, Mr. Rehak and I have sat down, in person, a few times since both being appointed to the Task Force in order to discuss difficult issues, in particular the FMBI. I appreciate his candor and our ability to respectfully debate things – one might say – politely argue. This post (and Part II) are extensions of those discussions so others can benefit from the exchange.

I first described the FMBI in an article I published on February 17, 2022, entitled “How Should We Decide Where to Invest in Flood Risk Reduction?” The FMBI is explained about halfway down the post. To recap, the index is equal to:

The index is intended to be calculated for all locations in the county at one particular time to help define the baseline conditions. The index will be used to help plan where additional flood risk reduction investments should be made. An area with a high FMBI has already received higher per capita investments, has a low risk, and therefore doesn’t need additional help. An area with a low FMBI has received little per capita prior investments, has a high risk, and therefore does need additional help.

Responses to Specific Concerns

Which Type of Project Costs Are Included? Does including construction costs, but excluding design, right-of-way acquisition, and operational costs skew the data? Since this is an index that will be calculated for all areas of our county, costs included or excluded will not adversely impact the results. Using the index to compare conditions in various areas within our 1,700 square mile county will still be valid if the index is calculated in all areas of the county the same way. This is an example of “normalizing” the data. It allows for an apples-to-apples comparison among and between locations. It will help us pick where to invest in the future. Since land acquisition, design, and other non-construction costs are often a similar percentage of the construction costs, their exclusion from all index calculations will keep things consistent and unskewed.

Which Agency Investments are Included? Will excluding investments from Harris County Commissioner Precincts, cities, municipal utility districts, and other entities skew the data. I actually agree with this, the investment dollars will be slightly low, but only by a little bit. I anticipate that the total amount of flood risk reduction investment dollars made by these entities will be very, very, very small compared to those made by the Harris County Flood Control District (HCFCD) and the Civil Works program of the U.S. Army Corps of Engineers (USACE). Because of this difference in the size of these investments, I anticipate that the impact on the index calculation will be negligible. HCFCD has agreed to provide their investments from 2000 to 2020. Dr. Denae King and I have submitted a Freedom of Information Act (FOIA) request to the U.S. Army Corps of Engineers, the Federal Emergency Management Agency (FEMA), and the Natural Resource Conservation Service (NRCS) to identify all flood risk reduction investments going back to 1937 – the year the HCFCD was created to serve as the “local partner” to help secure federal investments through the USACE. These requests exclude repair and recovery dollars since those expenditures don’t permanently reduce flood risks.

What Risk is Included in the Index? Does the risk used in the calculation reflect the risk before or after mitigation efforts? The risk value used is the current risk. It is the risk remaining after accounting for all risk reduction investments “counted” in the numerator. The index reflects one point in time and should be recalculated every five years or ten years, much like the Social Vulnerability Index published by the Centers for Disease Control. The population and risk values will be based on the same snapshot in time. The investment value will be based on the sum of all investments made prior to that moment in time (adjusted for inflation).

Why Include Investments Back to 1937? Why consider investments made in areas of the county that were undeveloped back then? Won’t this radically skew the comparisons? Including all investments back to 1937 is vitally important because the vast majority of the flood risk reduction investments made in the county were made by the federal government through the Civil Works program of the USACE. HCFCD was CREATED in 1937 to be the local sponsor for USACE projects. Addicks, Barker, Buffalo Bayou, Brays, White Oak, Sims, Clear Creek, and many other projects, many of them initiated prior to 2000, all significantly reduced flood risks for structures that exist today. Even if the project was initially constructed in an undeveloped area, it still benefits structures that were built later and that exist today. That’s why the investment amount is a cumulative value (inflation-adjusted) and the risk value is today’s value. This approach won’t radically skew comparisons because all three of the values will be determined for all parts of the county in the same way.

Why only Consider Mitigation Investments? Doesn’t flood risk depend on many factors – not just mitigation investments? Yes, current flood risk depends on many factors, including development rules, building codes, finished floor elevations, development locations, and improvements to our understanding of rainfall statistics. The risk value in the index is not intended to measure the risk reduction obtained from prior investments. The risk value in the index is intended to present the current risk. The current risk reflects all factors, including prior mitigation investments, development, rainfall, and everything else. The risk value is not a measure of the change in risk, it is a statement of the current risk, no matter the cause or the contributing factors.

Why Use US Census Tracts? Don’t they change over time? US Census Tracts do periodically change, however, that will not diminish the value of the index. US Census Tracts are areas that can more closely match the scale of typical flood risk reduction projects; watersheds are too large to be informative; and smaller areas would be too complex for our planning work.

The originally proposed FMBI used the population density in the denominator. This, admittedly, would cause issues when comparing index values between large US Census Tracts and small US Census Tracts. To address this issue, the CFRTF and the Infrastructure Resilience Team (IRT) have agreed to proceed with the calculation using just population. This will make the index a per capita value. Prorating investment amounts and risk to each Census Tract can be reasonably accomplished using area ratios or other methods. This will be useful as the CFRTF and IRT work together to prepare the 2050 Flood Resilience Plan.

How Can We Use Information From 1937 When the County is So Different Now? How can this approach work without considering the construction of Lake Houston in 1954, the interstate system, Beltway 8, and the conversion of farmland and prairies into entire communities? The risk value captures all of this. The risk value used in the index reflects the current risk of any part of the county. It will be based on state-of-the-art modeling being conducted as part of the MAAPNext project. The current risk is the current risk, regardless of past changes in the watershed.

Why are we Using the FMBI Formula to Reduce Flood Damage when it Doesn’t Measure Flood Damage? The FMBI is not a tool to directly reduce flood damage and it’s not designed to measure flood damage. The FMBI is a tool to better understand past investment patterns and current risk. The FMBI is proposed to be one of four datasets used to create a baseline conditions heat map. The other three under consideration include current inundation risk, social vulnerability index, and community resources. The baseline conditions heat map will then be used to figure out WHERE flood risk reduction and flood damage reduction projects should be located.

How Can the FMBI Compare Benefits without Using Before and After Comparisons? The index is not intended to compare the flood mitigation benefits of the same location at different times. The index is intended to show how different locations across the county at the same time vary when compared to each other. This will help us identify WHERE we have neighborhoods that desperately need help and WHERE we have neighborhoods that don’t.

Part II of this discussion is posted here.

I recently posted a short summary of the 1,800+ page tunnel study prepared by the engineering firm Black & Veatch under contract with Harris County Flood Control District. In today’s post, I will highlight some of the key questions I have about the study.

Before we get to the questions, I wanted to go on record as supporting the use of tunnels to reduce flood risks in Harris County. I support studying them and I support using them to reduce flood risks for areas of the county with the highest current flood risk and the highest social vulnerability.

I also support the use of the January 2021 U.S. Army Corps of Engineers (USACE) Policy Directive known as “Comprehensive Documentation of Benefits in Decision Document.” This policy “emphasizes and expands upon policies and guidance to ensure the USACE decision framework considers, in a comprehensive manner, the total benefits of project alternatives, including equal consideration of economic, environmental and social categories.” I support the use of this approach to help make the case for flood risk reduction projects in areas of the county with the highest current flood risk and the highest social vulnerability.

Now, on to the questions.

Changes to Watershed Screening

Section 3.0 of the report presents the results of a screening process of all 23 watersheds in the county. Black & Veatch screened each watershed to determine if watershed characteristics were favorable for a tunnel system. They considered the number of flooded structures, the social vulnerability of the residents, the location and distance of suitable tunnel discharge points (outfalls), ground elevations needed to allow gravity flow, and the relative cost of tunnels versus traditional flood risk reduction approaches. The table below presents the screening results in summary format.

During their June 16, 2022 presentation, the Harris County Flood Control District (HCFCD) presented a slide that showed the watershed screening results in a map format (below).

While the report indicates that Addicks and Barker Reservoirs were unfavorable for a tunnel system, the map indicated that they both would receive benefits from the installation of a tunnel in those watersheds. Why were these two watersheds presented this way? How can those watersheds receive any benefits from tunnels if those watersheds each have unfavorable characteristics for a tunnel system?

Selection of Evaluation Criteria

As outlined in my prior post, each of the eight tunnel alternatives was evaluated using ten criteria, each with its own weight. The ten criteria were: flood risk, environmental impact, social vulnerability index, operations and maintenance, constructability, community impacts, integration with traditional flood control systems, permitting, land acquisition, and geotechnical. How were the ten criteria selected? Why these ten? Why do some of them include duplicate scoring elements?

Evaluation Criteria Scoring

I have questions about how six of the evaluation criteria were defined and scored.

Environmental Impact: I would expect alternatives with a higher degree of anticipated impacts prior to mitigation would score lower (worse) and those with a lower amount of anticipated impacts prior to mitigation would score higher (better). Was the information in Appendix G – Environmental Constraints Analysis used to estimate the anticipated impacts for each alternative? Why did this criterion include permitting time? Doesn’t that duplicate another evaluation criterion (see below)? Wouldn’t permitting time be similar for all alternatives? Why include potential fines for non-compliance? Wouldn’t HCFCD follow all laws and environmental regulations while implementing any of the alternatives? How was each alternative scored to address the possibility of encountering hazardous materials during construction? Wouldn’t the likelihood of this be the same for all alternatives? Unweighted scores for this criteria range from 12.5 to 17.25. What factors were used to come up with this range of scores?

Operations and Maintenance: All tunnel options are very similar, except for their length and perhaps the number of inlet shafts. The criterion is scored based on the frequency and complexity of operations and maintenance activities. How would these activities differ for each alternative? Unweighted scores for this criteria range from 7.5 to 15.0. What factors were used to come up with this range of scores?

Constructability: All tunnel options are very similar, except for their length and perhaps the number of inlet shafts. The criterion addresses construction risks such as a flood event during construction or constrained surface site access. How would these risks differ for each alternative? Unweighted scores for this criteria range from 15 to 39. What factors were used to come up with this range of scores?

Community Impacts: This criterion includes consideration of the amount of traffic disruption, noise pollution, the number of displaced businesses and homes, and the amount of public outreach “that will be required.” It appears that this criterion considers impacts during project development, construction, and operation. Doesn’t displaced businesses and homes duplicate the Land Acquisition criterion described below? How was the amount of required public outreach scored? Did the report’s authors consider more required outreach a positive or a negative? Most engineers I know consider more outreach a negative, although many planners and elected officials might consider more outreach a positive.

Permitting: This criterion considers “the level of permitting requirements” for each tunnel alternative. This seems like a duplicate of the Environmental Impacts criterion. It appears to be scored higher if less permitting is required and lower if more permitting is required. How would permitting requirements differ for each alternative? Unweighted scores for this criteria range from 8.75 to 18.75. What factors were used to come up with this range of scores?

Land Acquisition: This criterion appears to use at least one of the same scoring elements as Community Impacts. Why duplicate this?

Promotion of Alternatives

As I noted in my summary post, Black & Veatch promoted the Brays Tunnel as a “recommended tunnel concept” because the number of instances of avoided flooding was reduced by assuming that the federal project to continue widening the bayou channel would be constructed in the future. If the federal widening project is not constructed, the construction of a tunnel would increase the number of avoided instances of flooding from 8,700 to 41,252. Why does the report assume that the federal project won’t proceed?

As I noted in my summary post, Black & Veatch promoted the White Oak Tunnel as a “recommended tunnel concept” for reasons that I don’t fully understand. The report states:

The [White Oak Tunnel] rating for flood risk reduction is 1 out of 10, which reflects a relatively low number of instances of structures removed from flooding. However, the cost per instance of structure flooding is considered moderate when compared to all eight (8) tunnel alternatives. Considering this factor and that the alternative received rankings ranging between 4 and 5 for the four evaluation metrics, the White Oak Bayou Tunnel was selected as a “recommended tunnel concept” for further study and refinement.

Why was the White Oak Tunnel selected as a recommended tunnel concept?

Sediment

Black & Veatch considers sediment accumulations in Appendix Q of the report (pp. 1,1818 to 1,849). Heavy storms more easily cause soil erosion and higher runoff flows can more easily move the sediments into our channels, bayous, and any future tunnel systems. This means that sediment will collect in the tunnels and will need to be removed unless we are prepared to accept reduced tunnel capacity as the sediment reduces the effective diameter. In the appendix, Black & Veatch attempts to answer some of the key questions we all should be asking.

Black & Veatch reviewed prior studies and reports sediment concentrations ranging up to 3,180 milligrams of sediment in each liter of water (mg/L). As expected, lower concentrations are associated with lower channel or bayou flow rates and higher concentrations occur with higher flow rates.

This concentration value may not be very meaningful to some of my readers, so I will provide some context. More frequent and smaller rain events generate urban stormwater runoff with sediment concentrations of about 100 mg/L. Imagine pouring some volume of cloudy water with this concentration of sediment floating in it into a collection container. How much water would you need to pour to collect one pound of wet sediment? Using conversion factors we can figure out that you would need to pour about 120,000 gallons of water to collect about 1 pound of sediment. That’s about 5 or 6 days of a garden hose flowing at 15 gallons per minute.

The higher sediment concentration in flood waters would deliver sediment much more quickly. You would only need to pour 4,000 gallons of water with a sediment concentration of 3,000 mg/L to collect about 1 pound of sediment. Since 3,000 mg/L is 30 times larger than 100 mg/L it only takes 1/30th of the flow to get 1 pound collected.

The water flow in the thought experiment above is one way, just into a container. The tunnels will have water flowing in and out at the same time until the floodwaters near the inlets recede. This means the collection of sediment in the tunnel will depend upon other factors, such as sediment particle size (bigger particles settle more easily) and water velocities (higher velocities keep particles from settling).

Black & Veatch notes, in Section 10.3 of the main report, that “sediment will … accumulate in the tunnel” at a rate of “less than a few inches per year.” Black & Veatch suggests that water could be diverted into the tunnel to resuspend the sediment (by moving water over the bed sediment fast enough to exceed the forces that keep it in a nice pile). This water could then be pumped out along with the suspended sediment to keep the tunnel from silting up and losing conveyance capacity over time.

My questions include the following: Where would this water come from? How much water would be needed? What flow rate and volume of water would be needed for each tunnel? To what location would the water and sediment be discharged without harming surface water quality or damaging dredged navigation channels? How much energy would be required to pump the water into and out of the tunnel? What would happen if a large storm occurred while the sediment removal process was underway? How do other tunnel systems handle sediment?

If you think of any questions you’d like to ask, please leave a comment.

Background

In September 2019, Freese & Nichols completed the Harris County Flood Control District‘s (HCFCD’s) Phase I report on Large Diameter Tunnels for Stormwater Conveyance. Mr. Brian Gettinger, a Texas Professional Engineer, sealed the report on September 23, 2019.

The Phase I report was funded by a $320,000 grant by the U.S. Economic Development Administration and $80,000 in HCFCD funding. The $400,000 study concluded that large-diameter tunnels were a feasible option to reduce flood risks. The Phase I report and all appendices (1,700 pages) were published on the HCFCD website. The Phase I study allowed HCFCD to make a “go” or “no go” decision about conducting additional studies. Additional studies were authorized.

On June 16, 2022, Mr. Scott Elmer, P.E., Assistant Director of Operations at the Harris County Flood Control District (HCFCD) provided a virtual briefing on the results of their Phase II Feasibility Study of Stormwater Conveyance Tunnels. The report was prepared by the engineering firm Black & Veatch under contract to HCFCD. Mr. Chris Mueller, a Texas Professional Engineer, sealed the report on March 30, 2022. The Phase II report and all appendices (1,863 pages) were published on the HCFCD website.

This post provides a high-level summary of the key elements of the Phase II report after my initial review.

Identify Flood Damage Centers

The report identified flood damage centers (FDCs) using both the number of historical flooded structures and using the projected (modeled) number of flooded structures by comparing the structure floor elevation against the modeled water surface elevation during a particular design flood. We would like to use tunnels to take flood waters away from FDCs, especially when the existing channels and bayous are not able to do so effectively.

FDCs were identified both along bayous in the existing floodplain areas mapped by the National Flood Insurance Program and outside of floodplains, based on a computer model of how intense rainfall can sometimes fall on neighborhoods and streets and how it collects and ponds. This type of ponding often floods homes and structures in our community.

The engineering team identified 107 FDCs inside the existing floodplains and 34 FDCs outside the mapped floodplains, as shown below:

Here’s a map of the FDC’s identified by the report authors:

There are a few different ways to address the higher risk of flooding in the mapped Flood Damage Centers (FDCs). We could buy-out the properties and convert the area to green space; we could enlarge and deepen the channels and bayous that drain the area; we could excavate new detention basins; we could install new tunnel systems; or we could do a combination of these.

Watershed Screening

The engineering team screened all 23 watersheds in Harris County to determine if the conditions in each watershed were favorable or unfavorable for the use of a tunnel to reduce flood risks. Screening factors included the historical number of structures flooded, the projected number of instances of flooding over 100 years of operation, flood insurance claims, the social vulnerability index within the area, the distance from flood damage centers (FDCs) to any potential tunnel outlet (discharge point), number and concentration of FDCs identified by the engineering team, ground elevation differences (since height about sea level is required to use gravity to convey water), and costs relative to non-tunnel options like channel widening, detention, and buyouts. Watershed screening resulted in ten favorable watersheds, as follows:

The engineering team developed eight preliminary tunnel alternatives that reduced flooding in the identified Flood Damage Centers. Here’s a map showing all eight tunnel alignments:

Weighted Decision Matrix

To see which of the eight alternatives provide the best results, the team then conducted a detailed weighted decision matrix evaluation of the alternatives.

A weighted decision matrix allows various factors to influence a decision to different degrees. Say you’d like to attend a movie but you have three alternatives before you. Here’s a weighted decision matrix you might consider:

Factor	Weight		Theater 1	Theater 2	Theater 3
Restaurant Food Available 0 = no, or 1 = yes	3		0	0	1
Seat Comfort 1 = low, 2 = medium, or 3 = high	2		3	2	2
Distance from Home 1 = far, 2 = medium, or 3 = close	1		2	1	3
Total Weighted Score	NA		8	5	10

The weights in this example indicate that this person thinks that good food is three times more important than distance and 30% more important than comfort. This example shows they would choose to see the movie at Theater No. 3.

The engineering team used a similar approach to evaluate the eight tunnel alternatives. The tunnel evaluation factor weights were as follows:

Notice that flood risk reduction is much more important than any of the other factors. It is six times more important than the degree to which the tunnel helps socially vulnerable people. It is twelve times more important than how easy the tunnel is to construct or the likelihood of encountering adverse soil or fault conditions (geotechnical issues). The assignment of these weights is a policy decision, not an engineering decision.

The results of the evaluation of the eight tunnel alternatives are presented below:

Recommended Tunnels

Section 12 of the Black & Veatch report provides an overview of the four recommended tunnel alternatives. At first glance, one would expect to see the engineers recommend the top four scoring tunnel alternatives: Halls, Greens, Sims, and Cypress; however, the report does not recommend proceeding with these four. Black & Veatch promoted two of the lower-scoring alternatives.

Black & Veatch promoted the Brays Tunnel to a “recommended tunnel concept” because the number of instances of avoided flooding was reduced by assuming that the federal project to continue widening the bayou channel would be constructed in the future. If the federal widening project is not constructed, the construction of a tunnel would increase the number of avoided instances of flooding from 8,700 to 41,252.

Black & Veatch promoted the White Oak Tunnel to a “recommended tunnel concept” for reasons that I don’t fully understand. The report states:

The [White Oak Tunnel] rating for flood risk reduction is 1 out of 10, which reflects a relatively low number of instances of structures removed from flooding. However, the cost per instance of structure flooding is considered moderate when compared to all eight (8) tunnel alternatives. Considering this factor and that the alternative received rankings ranging between 4 and 5 for the four evaluation metrics, the White Oak Bayou Tunnel was selected as a “recommended tunnel concept” for further study and refinement.

After the promotion of Brays and White Oak, the report presents four “recommended tunnel concepts” as follows:

— Brays Bayou
— Greens, Halls, and Hunting Bayou
— Halls and Hunting Bayou
— White Oak Bayou

Here’s a summary of these four tunnel alternatives (highlighted in green) along with the other tunnels evaluated:

The total cost of all eight projects is $21.08 billion. The total cost of the recommended projects is $10.08 billion. The public presentation indicated a total cost of $30 billion. I don’t know why the total reported during the presentation was different. It might be an inflation adjustment or added costs to cover contingencies or both. It certainly would not be unexpected to have estimated costs increase as the design progresses from conceptual designs, to preliminary designs, and on to more refined design stages.

People who saw my earlier post explaining why I don’t support the Buffalo Bayou Community Plan should not be surprised by the low ranking for the Buffalo Bayou Tunnel Alternative.

Next Steps

Harris County Flood Control is planning to conduct a Phase III tunnel study in 2023. That study will include community engagement, additional planning, additional design work, additional cost estimates, estimates of benefits, and an examination of funding sources.

Harris County Flood Control is accepting comments on the report and input on the scope of their pending Phase III report which will be starting in 2023. Comments are being accepted through September 30, 2022, and may be submitted on the project website.

Most readers of this blog know that I’m a somewhat atypical engineer. I often look at problems as sketches on a map or layers in a geographic information system (GIS). Other times I consider the long-term economics of any particular project — think investments in water conservation. Maybe I was a planner in a prior life?

With my planning hat firmly in place, this post will outline one approach the Harris County region might take to decide where to invest in future flood risk reduction projects. This is about projects beyond the current 2018 bond program. This is about what we might try to accomplish with another large bond initiative.

While I am a member of the Harris County Community Flood Resilience Task Force, this post is my personal view and does not represent the views of the Task Force.

BASELINE CONDITIONS

Before we decide where to invest, we need to create a heat map that will clearly illustrate areas that need more flood risk reduction investment. Today’s mapping software can create heat maps from any type of location data. Google Map displays traffic speeds using a green to red color scale based on cell phone velocities. Pedestrian injuries can be mapped using a heat map format, as shown in the example below from the Los Angeles Times.

So what data should we use to create a Harris County area heat map showing areas that need flood risk reduction investment?

If it were up to me, I would use the following three datasets, combined in some weighted fashion, to generate a composite heat map. The following sections describe the three datasets I’d like to use.

Annual Chance of Inundation

First I would suggest using the annual chance of inundation. Almost all ground surface in Harris County has an annual chance of inundation ranging from 0.1% (higher ground elevations away from bayous) to perhaps as high as 100% (low areas next to bayous, newer suburban streets that are designed to carry water away from houses).

I believe that no ground surface in Harris County has a 0% annual chance of flooding, except perhaps the very top of a few constructed hills. The top of the Memorial Park Land Bridge (when it’s completed) might come close.

Maps used to govern the National Flood Insurance Program (NFIP) provide a very coarse understanding of inundation likelihood – only along bayous and channels above a certain size. Those maps typically only show three “zones.” They show areas with an annual chance of flooding of less than 0.2%, areas with between 0.2% and 1%, and areas with more than 1%. About 37% of the county’s land area has greater than a 0.2% annual chance of inundation. The image below is from Harris County Flood Control District’s Flood Education Mapping Tool and shows the current NFIP flood zones associated with Carpenter’s Bayou. Notice how we have no information about the areas far from the bayou? We can’t tell if those areas have a 0.19% annual chance of inundation (just barely less than 0.2%) or if they have a 0.019% annual chance of inundation (10 times less risky). We also can’t identify areas with zero flood risk, because there aren’t any of those areas in our county, no matter who promises to “make you safe” or to “protect you from flooding.”

The Harris County Flood Control District is currently working on a detailed remapping of the flood risks in our county. The effort is known as the Modeling, Assessment and Awareness Project (MAAPnext). The output from MAAPnext will be an updated map of flood risk for every portion of the county’s ground surface. This will include all areas, not just areas adjacent to bayous and channels and lakes. I’m not sure how fine-grained the inundation risk levels presented will be, but I suspect we may be able to see color-coded maps showing areas with 0.2%, 1.0%, 2%, and 10% annual chance of inundation. My sources tell me this will be shown using square grids 9 feet on a side.

So based on MAAPNext results we will be able to create a heat map of flood risk across the county. I would suggest red for areas with greater than a 10% annual chance of inundation, orange for areas between 10 and 2%, yellow for areas between 2 and 1%, light green for areas between 1 and 0.2%, and dark green for areas with less than 0.2% annual chance of inundation. Using mapping software we can “overlay” this information with the other data layers to create a composite heat map.

MAAPNext information will also be critical in calculating a new proposed comparative index that I will describe next.

Flood Mitigation Benefit Index

The second dataset I would suggest using was originally proposed by Dr. Earthea Nance, when she was with Texas Southern University and Iris Gonzales of the Coalition for Environment, Equity and Resilience (CEER). It was originally called the flood benefits index, but the name was changed to Flood Mitigation Benefit Index by the Harris County Community Flood Resilience Task Force for clarity and to avoid any association with the Federal Bureau of Investigation – which is really not that involved in flood risk reduction efforts.

This is a new index value that will be calculated for all U.S. Census Tracts in the county to allow “apples to apples” comparisons between areas of the county with similar populations. The Flood Mitigation Benefit Index — or FMBI — because who doesn’t love acronyms — is calculated as follows:

The total prior investment in flood mitigation should be expressed in inflation-adjusted dollars and should be the sum of all investments in the area of interest intended to reduce flood risks. This should be the sum of all city, county, state, and federal investments in the area of interest. This is the most difficult data to obtain because the sum needs to include investments going back to 1937 when HCFCD was created to serve as the local sponsor for projects with large amounts of federal funding, which arrived starting in the 1940s and continues to this day.

The population should be the current population living in the area of interest, based upon US Census Bureau information.

The annual chance of inundation should be the current percentage value converted to a number from 0 to 100. This means that the FMBI would be calculated using 0.2 in the denominator if the area of interest had a 0.2% annual chance of inundation. An area with a 4% annual chance of inundation would use the value 4 in the calculation.

Everything else being equal, areas with higher FMBI’s have received higher prior investments in flood risk reduction and currently have a lower likelihood of inundation compared to areas with lower FMBIs. Here’s a table of hypothetical situations to illustrate how the changes to the input variables (prior investment, population, and inundation likelihood) impact the calculated FMBI result.

To evaluate these examples, consider how you would feel if you were one of the 6,000 people living in one of the example U.S. Census Tracts. In which tract would you want to live? Which tract should get the next flood risk reduction project?

The green shaded examples illustrate what happens when we increase prior investment, hold population constant, and decrease inundation likelihood. The FMBI goes up dramatically with increasing prior investment and decreasing inundation risk.

The blue shaded examples illustrate what happens when we only increase population in the area of interest. This shows that the FMBI is a per capita value.

The yellow shaded examples illustrate what happens when we only increase the prior investment in the area of interest. This shows how more prior investment drives the FMBI higher.

The grey shaded examples illustrate what happens when we lower inundation likelihood. Lower risk areas have higher FMBIs.

The current “goal-post” for floodplain management and development — the standard of care for engineers — requires us to do no harm to any properties and structures both upstream and downstream of our new project — this means no increase in inundation depths. The standard of care also requires us to design new stormwater management facilities around structures so they have less than a 1% annual chance of inundation. Can you tell which tracts in the list above meet the current standard of care?

A review of the annual chance column should help us determine the answer. Reading down that column we can see certain tracts have annual chances of less than 1%. They are Tracts 4, 5, 11, 12, 13, 14, 15, 18, 19, and 20. These tracts are currently meeting the standard of care and have “good” flood protection. Their FMBI scores range from 3,333 to 166,667.

All of the other tracts, with higher likelihoods of inundation, need help. They have between two to ten times the risk of flooding than the standard of care. Notice how low the FMBI values are for those tracts? It would not be good to live in those areas, right? The areas with inundation chances of more than 1% don’t look so good. Their FMBI scores range from 8 to 9,000, with most below 2,500.

Like MAAPNext results, we will be able to use FMBI values to create a heat map for the county. If we examine the entire range of calculated FMBI values, we can divide them up into five buckets. The lowest 20%, the next highest 20%, and onwards to the top 20%. I would suggest red for the lowest quintile, orange for the next, yellow for the next, light green for the next, and dark green for the top 20%. Here’s a hypothetical “mock-up” of how the FMBI heat map might appear. Both the cost and risk input data are still being collected, so this hypothetical map is purely for illustration purposes.

Social Vulnerability Index

The third, and last, dataset I would suggest we use is the Social Vulnerability Index (SVI) published by the Agency for Toxic Substances and Disease Registry of the Centers for Disease Control. SVI values for US Census Tracts are calculated from 15 different input variables including poverty rates, employment rates, income levels, educational achievement, age, disabilities, family structure, racial composition, spoken languages, type of dwelling units, crowding, access to vehicle, and group living conditions (for example nursing homes).

SVI values are normalized to range from 0 to 1. A value of 0 means the area is very resilient to disasters, with no poverty, high employment rates, high income levels, high educational attainment, few disabilities, etc. A value of 1 means the area is very vulnerable to disasters, with high poverty rates, low employement rates, low income levels, little education, more disabilities, etc.

Like MAAPNext results and the FMBI results, we will be able to use SVI values to create a heat map for the county. I would suggest green for areas with the first quartile of SVI values (least vulnerable), light green for the second quartile values, orange for third quartile values, and red for fourth quartile values. Here’s what this looks like for the entire county using 2018 SVI values.

COMING UP NEXT

In Part 2 of this post, I will describe how we might build the composite heat map and how it could be used to identify areas for future flood risk reduction investments.

Part 2 has been posted here.

This will be my third post about this study, officially called the Buffalo Bayou & Tributaries Resiliency Study.

My first post included a copy of the comments I helped prepare for the Houston Branch of the American Society of Civil Engineers in response to the U.S. Army Corps of Engineers’ (USACE’s) request for public input.

My second post was about how difficult it will be to devise a storage and conveyance project that will have a sufficiently favorable benefit cost ratio (BCR) to secure federal support.

This post is about why I don’t support the Buffalo Bayou Community Plan proposed by Houston Stronger. I have two main reasons, but first, I want to provide a short summary of the Community Plan.

The Buffalo Bayou Community Plan includes the following proposed elements:

Tunnel: 23 miles long and about 40 feet in diameter. Estimated to cost $4.2 Billion by Houston Stronger.

Addicks Excavation: Excavate and relocate 166,000 acre-feet of soil to increase storage capacity. The Astrodome is about 965 acre-feet, so the plan would be to remove 172 Astrodomes of soil and find a place to put it that won’t cause flooding elsewhere. Estimated to cost $1.35 Billion by Houston Stronger.

Barker Excavation: Excavate and relocate 191 Astrodomes of soil. Estimated to cost $1.10 Billion by Houston Stronger.

Cypress Creek Storage: Add storage and conveyance in Cypress Creek area. Estimated to cost $700 million by Houston Stronger.

The total cost, as estimated by Houston Stronger is $7.35 Billion. A diagram of the plan is presented below, from Houston Stonger’s website.

My first reason to oppose the plan relates to who pays for it. Put simply, we will never get the federal government to pay for it. As I explained in my prior post, low BCRs for conveyance and storage, the key elements of the Buffalo Bayou Community Plan, were calculated because the existing risk of flooding in the watershed is already very low.  Since spending $7.35 Billion to implement the plan will only slightly reduce an already very low inundation risk – the value of avoided damages is very small compared to the project cost. This means that the United States Congress will be very unlikely to authorize the work and very unlikely to appropriate any federal funding to conduct the work.

If we have to pay for it ourselves I think we should invest in other portions of the county that have a lower prior investment in flood risk reduction projects, a higher risk of flooding, and where people with higher vulnerability live. More on these points in a bit.

Since my post in November 2020, Harris County Commissioner Precinct 3 and Harris County Commissioner Precinct 4 allocated $1.68 million in local funding to assist the USACE to conduct additional studies of the Buffalo Bayou, Addicks, and Barker watersheds. These funds were unanimously approved by Harris County Commissioner Court on May 11, 2021. In addition, the Assistant Secretary of the Army for Civil Works, Michael Conner, approved the USACE Galveston District’s request for additional time and funding to expand the study. According to the website of U.S. Congresswoman Fletcher (TX-7), this approval was obtained in January 2022 and the total cost of the additional work is $3.367 million.

I don’t think the additional funding will be able to uncover any new projects that will result in a more favorable BCR. 

Now you are probably thinking: Michael, you always talk about how projects can deliver better social, environmental, and economic outcomes — maximizing the so-called ‘triple bottom line,’ – won’t the additional study funding allow the USACE to estimate the value of these benefits (those other than avoided damages)? Won’t that allow the USACE to generate a benefit value greater than the proposed $7.35 billion cost?

If the USACE uses current policy and procedures, benefits other than the value of avoided structure and property damage won’t be included. This calculation will not magically find more than $7.35 billion in benefits, especially, when the very low likelihood of the extreme storm event is considered (even if the likelihood is increased somewhat to account for climate change).

Even if the USACE can create updated guidance on how to consider all triple bottom line benefits in accordance with this January 2021 “Comprehensive Documentation of Benefits in Decision Document” memorandum from the former Assistant Secretary of the Army for Civil Works and if the Buffalo Bayou Community Plan is evaluated using the new guidance, I still don’t think the project will generate a benefit value greater than the $7.35 billion project cost.

Harris County is pushing as hard as it can to secure federal support for some type of additional investment by increasing the estimated benefit value. On October 26, 2021, the county hired Lowry Crook of the BBK law firm to help with this effort. According to his biography, Mr. Crook served as counsel in the White House and oversaw the Army Corps of Engineers.

My second reason for opposing the Buffalo Bayou Community Plan is based on fairness and equity. The maps below illustrate the situation.  The first map illustrates all Harris County watersheds. 

The second map illustrates the existing flood risk areas identified by the National Flood Insurance Program, mapped by Harris County Flood Control District, and approved by the U.S. Federal Emergency Management Agency (FEMA), mostly around 2017. Most of the blue zone — which shows areas with greater than 0.2% annual chance of inundation — will be expanding after the completion of the MAAPNext project which is using the updated rainfall statics included in Atlas 14.  Notice how narrow the blue zone is along Buffalo Bayou? While the blue area is very large in Addicks and Barker, there are no structures in most of that area because the federal government owns most of the land and prohibited development. Areas outside of federally owned land did see development, but virtually all of those structures are outside of the 1% annual chance flood zone.

The third map illustrates the 2018 Social Vulnerability Index (SVI) scores in all mapped flood zones. SVI scores are calculated for all U.S. Census tracts nationally by the Centers for Disease Control using U.S. Census data.  SVI scores range from zero to one and indicate how susceptible a population is to the harms and disruption caused by flooding.  An SVI of zero means extremely low vulnerability (dark green in the map below). An SVI of one means extremely high vulnerability (red in the map below).  For example, a homeowner with a car, an annual salary, and four weeks of personal time off is less vulnerable than a renter without a car, an hourly wage, and no time off.

SVI scores in the Buffalo Bayou watershed range from 0.0 to 0.50 – indicating a very low level of vulnerability.  SVI scores inside Halls Bayou, Hunting Bayou, and Greens Bayou, just to name a few, range from 0.50 to 1.00, with many areas greater than 0.75.

These maps illustrate that the Buffalo Bayou Community Plan is the opposite of equity. The plan suggests we spend $7.35 billion in a watershed that is one of the least vulnerable of all Harris County watersheds and one with the smallest number of homes and structures exposed to a greater than 0.2% annual chance of inundation.

As a member of the Harris County Community Flood Resilience Task Force (CFRTF)* I have to ask:

With over $50 billion in identified flood risk reduction needs across the county and a limited amount of public investment dollars to spend, why would we want to invest $7.35 billion in an area with a very low risk of flooding and with a highly resilient population when we have citizens living in Greens, Halls, and Hunting Bayous with much higher flood risks and much higher vulnerability? 

*This post represents my own views and does not in any way represent the views of the CFRTF.