I posted about this study back in June of 2019, when the United States Army Corps of Engineers (USACE) was asking for up front public input on the study before they got too far along. I helped the Houston Branch of the American Society of Civil Engineers (ASCE) provide some input.
Back then, many regional stakeholders chimed in, most supportive of additional federal investment to update the original federally authorized project that built the Addicks and Barker Dams. Many stakeholders encouraged USACE to be creative and to evaluate nature-based systems to reduce flood risks.
At the urging of the Harris County Flood Control District (the most likely local sponsor of any federally funded project to update the Buffalo Bayou federal project) last month the USACE released an interim version of the report for public input. An executive summary of the report is available here. For more detail, the whole report is here.
The main stakeholder reaction? Disappointment.
There are two main reasons for the public’s disappointment.
First, the report includes very traditional detention and conveyance alternatives along with buy-out options. Nothing in the report could be described as creative. There is not much in the way of nature-based solutions. The use of tunnel conveyance facilities were ruled out due to cost.
Second, most of the presented alternatives have very low benefit cost ratios (BCRs). This is very important to note because in order to attract federal support (congressional authorization) and funding (congressional appropriation), projects must have BCRs of much more than 1.0. This is embedded in laws and policies governing the White House Office of Management and Budget (OMB). Limited federal dollars most compete with scores of other projects across the country, each with calculated BCRs. Only the projects with the highest BCRs have a chance at federal funding.
So why did USACE publish a report with these two problems?
Here is my theory.
After Hurricane / Tropical Storm Harvey dropped its unprecedented rain amounts on the Buffalo Bayou system, many upstream and downstream homes and businesses were flooded. This triggered a public outcry and litigation over the federal government’s use of private property to store and convey water. It also triggered support for the resilience study and created expectations that the study would find a “silver-bullet” that would “protect” everyone from a Harvey type event in the future.
Well, the situation is not favorable to identifying projects with high benefit cost ratios (BCRs). The vast majority of homes and businesses in the Buffalo Bayou system have a very, very low likelihood of flooding during any particular time period, even with Atlas 14 rainfall used to map floodplains. This low existing risk is a direct result of the large federal investment to build the existing Addicks and Barker system.
Yes, there are homes in the inundation pools of Addicks and Barker. Yes, there are homes in the floodplain of Buffalo Bayou downstream. Yes, the Cypress Creek overflow does make drainage and land use challenging upstream. But even counting them in, it is still very challenging to identify any infrastructure investment in the Buffalo Bayou watershed that would generate a high enough monetary value of avoided damage — the benefit part (the numerator) in the BCR — to justify the required costs.
To explain this further, let’s dive into how the monetary value of avoided damage is estimated. The monetary value of avoided damage is determined by the difference between the value of avoided damages from a particular flood after a new project is built, call it post-project conditions (ADPost) minus the value of avoided damages from a particular flood before a new project is built, call it pre project conditions (ADPre) with the result multiplied by the likelihood of that particular extreme flood occurring during the study time period. If the avoided damage arising from a particular flood with a new project is not much different from the “no new project” alternative, the difference won’t be very large. This is the numerator in the BCR. If the project costs are high (Cost), the BCR denominator will be high, thus reducing the BCR. Shown as an equation, it looks like this:
Where: BCR is the benefit cost ratio; ADPost is the monetary value of avoided damages after any proposed new project; ADPre is the monetary value of avoided damages today, without any new investment in the existing Addicks and Barker system; P is the probability of the modeled extreme storm occurring during the study time period; and Cost is the cost to design, build, operate, and maintain the project during the study time period.
So let’s pretend we can devise a project that generates $8 billion in avoided damages (ADPost) from a particular extreme, but rare, storm event. Because of the prior investment in the Addicks and Barker system, the ADPre is also a pretty high number, easily $6 billion. This means the difference is about $2 billion in this hypothetical.
To account for the probability of the rare extreme event occurring during the study time period, we need to multiply the damage estimate by the likelihood of that extreme storm actually occurring during the study time period. Let’s assume that over a 100 year period the rare and extreme event has a 10% chance of occurring. That means we would have to multiply the difference in damage estimates, $2 billion, by 0.10 to compute the benefit portion of the BCR fraction. Ten percent of $2 billion is $200 million.
So to obtain a BCR of 1 or more, if the benefit portion of the fraction (the numerator) is $200 million, we need the total cost to design, permit, build, and operate the project for 100 years (the denominator) to be $200 million or less. If you’ve read the report’s executive summary, or know anything about how much infrastructure costs, you know that is pretty much impossible. (The dam safety projects – spillway fixes – should obviously be done as soon as possible. Those smaller projects cost less and yield high benefits.)
Folks who flooded and who live in the Buffalo Bayou watershed, who really want an additional federal project investment to further reduce flood risks in their area may be upset with this post. But they should know that the 1940 “Definite Plan” was a very large federal investment that reduced their flood risks when it was built. The prior federal risk reduction investment makes it harder to justify additional risk reduction investments.
Unrelated to the watershed-specific study discussed in this post, additional local, state, and federal investments should go to areas of Harris County with many more homes, structures, and businesses exposed to higher inundation risks than those in the Buffalo Bayou watershed. Think Greens Bayou, Halls Bayou, and others.
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