Response to Concerns About Flood Mitigation Benefits Index (Part I)

The letter below expresses disagreement with two recent posts about a proposed Flood Mitigation Benefits Index. It is from Michael Bloom, P.E. While I don’t agree with all of his claims, I am reprinting his letter verbatim because I encourage healthy debate. Compare the posts and draw your own conclusions. – Bob Rehak, Host,

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, 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:

Variation on formula presented to Commissioners Court on 6/28/22. It omits the word “Density” after population. See discussion below.

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.

Harris County outlined in red, census tracts in blue. Map supplied by Michael Bloom.

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.

By Michael Bloom, P.E.

Posted by Bob Rehak on 7/9/22

1775 Days since Hurricane Harvey

Part II will be posted tomorrow. If you have thoughts you would like to share on this subject, please send them via the contact form on this website.