In this “post-Harvey” period there are many suggestions about how best to spend the $10 or $20 billion we hope to get from the federal government, the state of Texas, local property taxes, potentially new sales tax collections, and (of course) cash proceeds from new local government bond sales.

For example, some folks are suggesting we should spend $6 billion to buy out homes in the western fringe of the Addicks and Barker flood pools and along Buffalo Bayou from Highway 6 to downtown, and channelize or modify the bayou corridor so it can convey 15,000 cubic feet per second. Others are pushing for the so called coastal spine to protect the region from storm surge.  Still others are suggesting that we build a third flood control reservoir in the Cypress Creek area.

I’m concerned that we are letting our emotions and a few cognitive biases harm our decision-making. Our emotions are telling us that flooding is terrible. People’s homes were destroyed. Their lives were horribly disrupted.  Photo albums destroyed.  Mold grew in bedrooms and living rooms. People died. This high level of emotion impacts decision making.  This high level of emotion increases our willingness to pay for projects that will (supposedly) cost-effectively reduce flood risks and damages. This is known as the “affect heuristic” cognitive bias, which basically means emotions can take over decision-making.

In addition, the “availability heuristic” cognitive bias, makes us all feel that flooding has a much higher likelihood of occurring in the near future if a flooding event has happened recently, regardless of the mathematical probability of the future occurrence.  A vivid example of this relates to how we perceive the risk of dying from a shark attack compared to the risk of dying from a falling airplane part.  Most people mistakenly believe that a shark death is more likely than a death from an airplane part because stories about shark attacks are widely reported and deaths from airplane parts are not.  What we hear about or experience recently is weighted more heavily in decision-making.

To avoid falling into the trap of these and other cognitive distortions we should decide how best to use post-Harvey funds using a risk-based decision making framework.  Here’s how I think it should work.

We need to think about potential projects in two distinct ways.  First, we need to think about the risk of a particular flooding event being addressed (over an appropriate period of time) and, second, we need to think about the consequence of that particular event occurring at any point in time. To help illustrate this approach we will consider two hypothetical projects, each with their own risk level, consequence, and cost.

But first we need to talk a bit more about risk and probability.  I created a graph that displays an array of various risk levels that we will use to help make the best decision.

The graph was constructed using basic probability calculations and it shows the probability of various rainfall events being exceeded during various time periods.  The vertical axis shows the probability from 0% chance to 100% chance.  The horizontal axis shows various time periods ranging from 1 to 10 to 10,000 years. It is plotted using a log scale, which allows us to see a very long period of time in a reasonable graph width. The various colored lines illustrate the probability of a particular 24-hour rain event being exceeded during any time period (duration) of interest.  The smaller events are much more common. The larger events are less common.  By examining the red line (13.2 inches in 24-hours) you can see that the likelihood of that storm falling on your home during your 30-year mortgage is about 26%.

The important thing to notice about this chart is that the longer we are willing to wait, the more likely any storm event becomes.  Let’s take a look at the very rare 18.9 inch rain storm in light blue. Over a 1 year time period we feel safe, because that much rain only has a 0.2% of happening during that time period. But the likelihood of that much rain falling on your home during your 30 year mortgage is about 6%. The chance of that storm hitting your home during 250 years is about 50%. So the crazy thing is that ALL of Houston has a non-zero probability of getting hit with a Harvey type storm or larger. It’s just a matter of time and the longer we wait the more certain the storm becomes. All of the curves eventually hit 100%.

These curves describe the risk of a certain rainfall depth hitting a certain location. Another similar set of curves could be created to illustrate the risk standing or flowing water achieving a certain elevation as a result of runoff from a rain event. This could be from bayou flooding, inundation of a low area, coastal surge, or reservoir pools filling up.

Ok, back to our two hypothetical projects. Here are the estimated or calculated facts about each of the projects. In real life all of this information would be estimated or calculated using engineering principles, computer models, construction cost estimating techniques, appraised property values, land values, and other sources and methods.

Project One – Conveyance Improvements: 

• Description: Acquire land and enlarge bayou channel to increase the channel’s conveyance capacity.
• Design Basis: Improve conveyance of stormwater runoff. Change stormwater carrying capacity to handle runoff from a 9.6 inch storm (4% annual chance) to 13.2 inch storm (1% annual chance).
• Cost: $450 million
• Benefit: Reduces flooding risk for 1,350 structures worth $675 million from a 9.6 inch storm (4% annual chance) to 13.2 inch storm (1% annual chance).

Project Two – Buyouts: 

• Description: Acquire land, demolish structures, regrade land to provide detention, and re-landscape to make park area.
• Design Basis: Remove home from high risk area which floods from 6.2 inches of rain (20% annual chance of flooding).
• Cost: $720 million
• Benefit: Reduces flooding risk for 1,350 structures worth $675 million from 4% per year (rain depth of 9.6 inches) to 0% forever.

Let’s look at each project from a benefit / cost perspective, while factoring in the cumulative risks.

Before Project One the risk of loss over 100 years can be determined from the graph by finding the intersection of the 9.6 inches curve with the 100 year line. This risk is 98%. The value of the loss (the consequence) is $675 million in present dollars. Multiplying the risk times the consequence provides the risk weighted loss for a 100 year period, which, in this case is $661.5 million.

After Project One the risk of loss over 100 years can be determined from the graph by finding the intersection of the 13.2 inches curve with the 100 year line. This risk is 63.5%. The value of the loss (the consequence) is still $675 million in present dollars. Multiplying the risk times the consequence provides the risk weighted loss for a 100 year period, which, in this case is $428.6 million.

Project One reduces the risk weighted loss by the difference between $661.5 million and $428.6 million. This reduction is the project benefit, which equals $232.9 million. The benefit to cost ratio is calculated by dividing the risk weighted benefit of $232.9 million by the project cost of $450 million. For this project the benefit to cost ratio is 0.52, which would not justify doing the project. Most project sponsors would only move forward if the benefit / cost ratio was greater than 1.0.

Now let’s look at Project Two.

Before Project Two the risk of loss over 100 years can be determined by multiplying the 20 year risk weighted loss by five. The 20 year risk can be obtained from the graph by finding the intersection of the 6.2 inches curve with the 20 year line. This risk is 99%. The value of the loss (the consequence) is $675 million in present dollars. Multiplying the risk times the consequence provides the risk weighted loss for a 20 year period, which, in this case is $668.3 million. Multiplying this by five, provides the 100 year risk weighted loss of $3.34 billion. (This assumes that the homes are repeatedly rebuilt and flooded.)

After Project Two the risk of loss over 20 years is zero because the structures are gone. The value of the loss (the consequence) is also zero because the structures are gone. This means the 100 year risk weighted loss is also zero.

Project Two reduces the risk weighted loss by the difference between $3.34 billion and $0.00. This reduction is the project benefit, which equals $3.34 billion. The benefit to cost ratio is calculated by dividing the risk weighted benefit of $3.34 billion by the cost of $720 million. This division yields a benefit to cost ratio of 4.6, which is an excellent ratio which indicates the project should proceed.

These two examples are admittedly simplistic, but we really need to use the methods illustrated to make smart decisions.  Let’s use the change in the risk weighted loss (pre to post project) to derive the project benefit value. Let’s compare that to the project cost.  Let’s calculate the project benefit to cost ratio over an appropriate time frame. Let’s do the projects with benefit to cost ratios of more than 1.0.

In June 1940 the United States Army Corps of Engineers released its Flood Protection Plan for Houston (Buffalo Bayou). I was able to find the original “Definite Project Report” and the associated drawings at the Rice University library.  This post provides some highlights from the documents.

I’ve posted the plan overview before, but its worth reposting here for context.  The green items are levees which form flood damage reduction reservoirs; the blue items are canals or channels; and the yellow text provides identification labels.

The Design Storm

The Corps reviewed a number of different “storms of record” and decided to use a design storm created by combining two of the worst-case scenarios they had seen up to that point.  They derived the design storm by taking the total depths of rain observed from June 27 to July 1, 1899 at Hearne, Texas and combining it with the rainfall intensities (inches per hour) observed in September 9-10, 1921 at Taylor, Texas.  They then placed this hypothetical worst-case storm directly over the planned reservoirs and facilities.

The Hearne storm produced 31.4 inches of rain in 3 days and the average depth of rain over 1,000 square miles was 25.8 inches.  The Taylor storm produced intensities ranging from 4.4 to 0.44 inch per hour.

The combination of these two events is depicted in the graphic below, which shows the hypothetical cumulative rainfall in inches vs. time for the design storm.

The design storm has the total rainfall amount (the horizontal end of the curve in the upper right) of the Hearne event coupled with the crazy steep slope, indicating high rainfall intensity (from 36 to 42 hours) of the Taylor event.  Yikes.

The Design Storm Runoff

To size reservoirs and channels the Corps needed to convert the rainfall depth to actual runoff rates and volumes. This is critical to determining how much of the rain falling from the sky actually runs off and either flows harmlessly around homes and businesses or inundates them.

The Corps conservatively assumed that 90% of the rainfall from the design storm described above would runoff.  To estimate the runoff flowing to each element of the overall plan, the design storm was then moved to be directly above each element.  Runoff timing, total volume, and flow rates (depicted in curves called hydrographs) were estimated using Franklin P. Snyder’s Synthetic Unit Graphs, published in the Transactions of the American Geophysical Union (1938).

Runoff hydrographs for each of the key definite plan elements are presented below.  Note that “second-feet” is equivalent to the flowrate expressed in “cubic feet per second.”  There are about 7.48 gallons in each cubic foot, so you can multiply by 7.48 to get gallons per second and then by 60 to get gallons per minute.  Also, an “acre-foot” is a volume measurement. It is 1 acre of area covered by 1 foot of water or about 325,829 gallons.

Definite Plan Elements

The Corps devised the definite plan to accommodate the design storm and the predicted runoff described above.  The definite plan included the following elements:

• White Oak Reservoir
• Brickhouse Gully Bypass Channel
• North Canal
• Cypress Creek Levee
• Addicks Reservoir
• Barker Reservoir
• Rectification of Buffalo Bayou Above South Canal
• South Canal
• Improvement of Buffalo Bayou Through City

A few details of each of these plan elements are provided below.

White Oak Reservoir

• Peak Design Inflow:                30,800 cubic feet per second
• Total Design Inflow:                103,900 acre-feet
• Levee Length:                         4.7 miles
• Levee Max. Height:                 35 feet
• Levee Max. Elevation:            90 feet above mean sea level
• Storage:                                  24,400 acre-feet
• Max. Pool Elevation:               85 feet above mean sea level

Brickhouse Gully Bypass Channel

• Channel Length:                     1.9 miles
• Lining:                                     Grass / Rip Rap in Selected Locations
• Top Width:                               From 70 to 100 feet
• Bottom Width:                         6 feet
• Side Slopes:                            2 to 1
• Depth:                                      From 10 to 25 feet
• Conveyance:                           1,500 cubic feet per second

North Canal

• Channel Length:                     20 miles
• Lining:                                     Concrete Paving
• Top Width:                               From 140 to 200 feet
• Bottom Width:                         25 feet
• Side Slopes:                            2 to 1
• Depth:                                     From 28 to 38 feet
• Conveyance:                           22,000 cubic feet per second

Cypress Creek Levee

• Levee Length:                         14.9 miles
• Levee Max. Height:                 12 feet
• Levee Max. Elevation:             180 feet above mean sea level
• Top Width:                               10 feet
• Max. Bottom Width:                 82 feet
• Side Slopes:                            3 to 1

Addicks & Barker Reservoir System (Combined)

• Max. Combined Outflow:15,000 cubic feet per second (based on navigation in the Houston Ship Channel)
• Release Conduits: Four 8 feet diameter (Addicks); Two gated “spare” conduits of equal size (Addicks); Five 8 feet diameter (Barker); Two gated “spare” conduits of equal size (Barker)

 Addicks Reservoir

• Drainage Area:                         134 square miles
• Peak Design Inflow:                  50,500 cubic feet per second
• Levee Length:                          10.4 miles
• Levee Max. Height:                  43 feet
• Levee Max. Elevation:             115 feet above mean sea level
• Max. Pool Elevation:                108.3 feet above mean sea level
• Design Storage:                       134,000 acre-feet

Barker Reservoir

• Drainage Area:                        152.8 square miles
• Peak Design Inflow:                 40,300 cubic feet per second
• Levee Length:                          13.8 miles
• Levee Max. Height:                  37 feet
• Levee Max. Elevation:             109 feet above mean sea level
• Max. Pool Elevation:                101.7 feet above mean sea level
• Design Storage:                       135,800 acre-feet

Rectification of South Mayde and Buffalo Bayou Above South Canal

• Channel Length:                     7.2  miles
• Lining:                                     Grass / Rip Rap in Selected Locations
• Top Width:                              From 140 to 200 feet
• Bottom Width:                       15 feet
• Side Slopes:                            3 to 1
• Depth:                                     From 5 to 22 feet
• Conveyance:                           15,000 cubic feet per second

South Canal

• Channel Length:                      39.2 miles
• Lining:                                     Concrete Paving
• Top Width:                               From 120 to 270 feet
• Bottom Width:                          From 30 to 163 feet
• Side Slopes:                            2 to 1
• Depth:                                      From 16 to 42 feet
• Max. Conveyance:                  15,000 cubic feet per second (above Brays Bayou)
• Max. Conveyance:                  28,800 cubic feet per second (below Middle Bayou)

Total Cost

The total cost of all plan elements, plus utility work and other associated details was $13,243,700 (in 1940 dollars).

If you are interested in reading more from the 1940 Definite Plan, I’ve made a scan of it available here.

My crazy idea about land development projects being “hydrologically invisible” is featured on the Texas Living Waters Project blog. Shout out to Keiji Asakura and Abigail Phillips of Asakura Robinson for doing the rendering of my wacky idea.

Check out the post here: http://texaslivingwaters.org/natural-drainage-low-impact-development-houston/

[Reposting a worthwhile white paper prepared by Wendell Cox and Tory Gattis, with the Center for Opportunity Urbanism, that provides some valuable context to support informed decision-making during our post-Harvey policy discussions.

My one quibble with this paper relates to their lack of precision in describing how current detention requirements work. They state that our detention regulations “require no net increase in runoff from new developments.” It would be more precise to say that Harris County detention regulations generally restrict the flow rate of runoff leaving the site to the pre-development flow rate, but they don’t generally restrict the total amount (volume) of runoff leaving the site. The City of Houston’s detention regulations are not based on runoff volume or rates, but rather on the site’s imperviousness.]

In the aftermath of Hurricane Harvey, and the disastrous flooding, Houston has come under extreme scrutiny. Some in the global, national as well as local media assaulted the area’s flood control system and its development model, criticisms that were echoed by some in the local area.

Much of the current debate starts from a firm misunderstanding of the region’s realities. This could lead to policies that ultimately undermine the keys that have propelled the region’s success. Below is a primer to inform future discussions of Houston’s future trajectory.

Did Harvey reflect Houston’s failure or a remarkable resiliency?

Harvey was a remarkable event for which there is little precedent. The Harris County Flood Control District estimates the four-day rainfall from Hurricane Harvey to be a once in 500 to 40,000 year flooding event. Whether such events are more likely in the future, the region’s systems worked remarkably well, although they should be bolstered considerably in the future.

Read more…

I was poking around the Atlas 14 website and found a quarterly report from July 2017. Atlas 14 is the national effort to update rainfall statistics based on the very best rain gage data with good geographic coverage and the longest history (time period) available.  The work for most of the country has been completed, except for Texas and some states in the Pacific Northwest. Two key items from the report are discussed in this short post.

First, the results for Texas will be published in May 2018. As I posted earlier, this will likely revise upwards our estimate of the 1% annual chance, 24-hour event, from around 12 or 13 inches to perhaps 14 to 16 inches (depending upon what area of Harris County you are interested in).  This will require bayou modeling updates and updates to the regulatory floodplains – they will get wider and deeper.

Second, the progress report includes a section entitled: “Analysis of Impacts of Non-Stationary Climate on Precipitation Frequency Estimates.” This can be roughly translated to mean: “How might climate change alter rainfall statistics in the future?”

The Atlas 14 effort is a backward-looking effort. The study team is applying standard statistical tools to the available rainfall records to predict the likelihood of rain events of various depths in the future. This assumes that history is good predictor of the future.

The “non-stationary climate” analysis is starting to look at how a changing climate might alter things. The quarterly progress report indicates that the Federal Highway Administration tasked the study team to conduct a pilot project to look at how a changing climate might alter the future. The report indicates that “preliminary findings were inconclusive and the pilot project ended with more questions than answers.”

The project team promises to work with academia (Penn State and University of Illinois, Urbana-Champaign) and to report on further work in the next quarterly report.

So stay tuned.

I’ve written many times about the depth of the current, statistically-derived, 1% annual chance, 24-hour storm in the Houston area. Its currently defined by the Harris County Flood Control District (HCFCD) as ranging from 12.4 to 13.5 inches in 24 hours, depending on the location. As you move closer to the coast (towards the southeast) the depth of the 1% event increases. This variation is addressed in HCFCD’s Hydrology and Hydraulics Guidance Manual by dividing the county into three rainfall regions as shown below:

The National Oceanic Atmospheric Administration (NOAA) is updating the nation’s storm statistics to include a longer period of rainfall records.  This effort is known as “Atlas 14.” The work is being accomplished on a state by state or region by region basis. The Texas analysis is currently underway, however, the work won’t wrap up for a year or two.

To get an idea of what the updated 1% event might be for Houston I browsed to the NOAA Atlas 14 website. This website has a map that let’s you pick any point in the United States. The website then provides the storm event statistics for that point based on the most recent data available. Since the update for Texas is not yet complete, you’ll get a message below the location picker map pointing you to the three older documents that provide information on Texas. (For the Houston area, folks should rely on the HCFCD Hydrology and Hydraulics Guidance Manual, which is more detailed and up to date.)

I picked a location along the Sabine River on the border of Texas and Louisiana, about 50 miles in from the coast (about equivalent to the distance from the Galveston coast to Memorial Park) to get an idea of what the Houston area Atlas 14 rainfall amounts might be when the NOAA study is finished.

After clicking on the map near the right-hand star above I was presented with the following table:

The Atlas 14 table for Starks, Louisiana shows that the 1% annual chance, 24-hour rainfall (equivalent to the 100 year recurrence interval in the table) is 14.3 inches, with a 90% confidence interval ranging from 10.9 inches to 19.0 inches.  Here’s what that looks like in graphical format.

The rainfall information from this point in Louisiana should be a pretty good predictor of what the rainfall statistics will show for the Houston area.  Based on this, I’d expect the 1% annual chance, 24-hour event for Houston will increase from 12.4 to 13.5 inches to something closer to 14 to 16 inches in a 24-hour period.

If the Atlas 14 analysis was updated to include rain events from 2016 and 2017 these 1% annual chance depths might increase a bit more.

One important outcome of this pending change: HCFCD will need to re-run our bayou models to determine the water surface elevation that results from the new, larger, 1% annual chance event and update all the regulatory floodplain maps to match this new elevation. This will likely enlarge our regulatory floodplains and increase the number of structures in the floodplain.

On September 26, 2017 the Harris County Commissioners Court and the Board of Directors of the Harris County Flood Control District will conduct a special meeting at 9 am to review mid-year progress.  At 10 am they will be conducting their regular bi-monthly meeting.

The mid-year review includes a lot about Hurricane Harvey and possible responses. The report highlights significant damage to Harris County facilities, including the Criminal Justice Center and Jury Assembly facility. There is some discussion of how the county is tracking expenses and labor costs to help ensure reimbursement for those costs from the Federal Emergency Management Agency (FEMA).  The report indicates that recovery will require additional capital dollars to help make infrastructure and facility repairs. The report provides some insight regarding potential impact on county revenues from lower total property value appraisals. The report indicates that about 50,000 single family homes in the county were flooded. This reduced revenue will be absorbed with some departments reducing spending by 5%.

The mid-year report includes a discussion of some possible solutions to flooding events, including new reservoirs, changes or enhancements to waterways, changes in development rules, and buyouts. It calls for a Master Plan to be developed and local, state, and federal funding. No increase in the property tax rate for HCFCD is proposed.

Read the entire Harris County Mid-Year Review Report.

The regular meeting agenda has one noteworthy item; The County Engineer seeks authorization to hold a “workshop to discuss regulatory changes needed to the flood plain management and infrastructure regulations in response to Hurricane Harvey.”

By Brian Bledsoe September 13, 2017, Washington Post

[Re-posted from the Washington Post]

As the tragedies of Harvey and Irma continue to unfold, it’s disconcerting but hardly surprising to hear a chorus of voices from all walks of life — laypeople, politicians and technical experts — perpetuate our ignorance of extreme weather and flood events.

Harvey is extreme by any measure, but we don’t really know how rare Harvey is because we simply don’t have long enough records, nor enough knowledge of how storms will behave in the future to pin down a number. Undeterred, we extrapolate and get what Mark Twain called “wholesale returns of conjecture out of such a trifling investment of fact.”

Our inability to understand and effectively communicate flood hazards is especially well-established. For decades, researchers have asked: Do the public and policymakers understand the 100-year flood concept? Do we understand what flood plain maps are telling us (and not telling us)?

The answer is a resounding no. The 100-year flood, the flood that has a 1 percent chance of being exceeded in any given year, simply does not register in our consciousness. Just the sound of it — a 100-year flood, longer than a lifetime — lulls us into believing such events are rare and immutable acts of God. But to paraphrase the geographer Gilbert White: Floods are acts of God — flood losses are largely acts of people. Harvey is no exception.

Cities in the United States have tried to regulate development in “100-year floodplains” and provide maps of flood hazard zones to the public for several decades. Yet most people are still surprised, if not astonished, to learn that the 100-year flood at a given location has more than a 1 in 4 chance of occurring within the term of a 30-year mortgage. For most of us, this 26 percent chance our home will be flooded before we have a chance to pay it off is troubling if not unacceptable.

This 26 percent is the risk if one lives at the upper edge of the 100-year flood “fringe,” the regulated outer zone of a flood plain. Structures at lower elevations are at even greater risk. To reduce the likelihood of flooding to a more tolerable 1 in 10 chance over a 30-year mortgage, structures need to be above the height of the 285-year flood. That is, if floods behave in the future as they did in the past records used to estimate these probabilities.

Will flooding behave in the future as it has in the past? Most of us intuitively grasp that intense rainfall interacts with increases in impervious surfaces such as roads, sidewalks, parking lots and rooftops to amplify the volume and speed of storm runoff. We are less inclined to think about where the water goes from there — how flood mitigation measures like ponds and detention basins can become less effective over time or fail if not properly maintained, or how the ability of streams and rivers to carry runoff changes due to sediment movement and other natural processes. It’s not just the rain that can change. It’s the rain, the urban footprint and the drainage systems all changing together.

Engineers and hydrologists are trained to look to the past to understand the future. They analyze records of past events (where the information exists) to assign probabilities to future events. This approach will always be necessary and useful; however, it generally presumes that the future will continue to behave within the same range of variability observed in the past.

In the context of warmer seas, mounting urbanization and intensifying rainfall, solely relying on the past becomes questionable at best. Asserting that rain and floods will continue to behave as they have in the past is akin to building a taller water tower that increases the pressure on a town’s pipes but believing that the flows from showers and faucets will remain the same.

Flood hazards are moving targets that often reflect a mix of circumstances. A 50-year rainstorm may produce a greater than 100-year flood if it falls on soaked or burned ground, melts a snowpack or coincides with a coastal storm surge or dam failure. Yet even the most up-to-date insurance maps portray the edges of flood hazard zones as a bright line in the sand — you’re either in or out. This clarity is an illusion. Basic engineering analysis reveals that there is substantial uncertainty as to where the lines should be drawn. But flood plain maps still depict it as a precise line, regardless of whether the potential error is 10 feet or 1,000 feet.

What can we do? Let’s start talking about flood risks over time frames we truly care about — for example, over the term of a mortgage, a lifetime or other planning horizon of tangible concern.

When one realizes their home has a 1-in-4 chance of experiencing a 100-year flood in 30 years, or a 15 percent chance of a 500-year flood over an 80-year lifetime, then perceptions shift and denial becomes more conspicuous. We need to invest in better flood hazard maps and update them to transparently show the uncertainty in flood levels due to model inaccuracies and potential changes in weather, urbanization and drainage. Simply knowing whether the margin of error in mapped flood extents is a big or little number would help.

Ultimately, improved communication of natural hazards must translate to vision and action if we are to avoid repeating the mistakes of the past. To some extent, our language and misconceptions around floods have enabled a status quo in which policy decisions are driven by election cycles and business cycles rather than by analysis of the potential costs of underinvesting in flood resilience over the long run.

The future is unknowable, but investments in hybrid systems of traditional “gray” and natural “green” infrastructure that work together along with nonstructural measures such as insurance reform, zoning, buyout and relocation can improve outcomes across a wide range of future scenarios. Building such redundancy and resilience into flood mitigation projects should boost their benefit to cost ratios, not decrease them as is the case when we focus on a single, oversimplified version of the future.

Regardless of which solution one favors, they all hinge on better communication. Crises open windows of opportunity for doing things better — windows that all too often close before we get unstuck from the status quo. Let’s hope Harvey and Irma will inspire many communities to rethink how they talk about floods, and to begin preparing in earnest for when their window opens.

The author, Brian Bledsoe, is a professor of civil and environmental engineering at the University of Georgia. His research focuses on the interface of hydrology, ecology and urban water sustainability.

In addition to the huge list of recovery and reconstruction activities, we need to think about our next planning and engineering activities to be better prepared and informed for our next large rain event. There is no engineering solution that will prevent large rain events – so we WILL have another one.  Here’s a list of ten list of planning and engineering activities we should undertake:

1. Update Rain Event Statistics:  Harris County Flood Control District (HCFCD) is currently a funding partner with the National Oceanic Atmospheric Administration’s (NOAA’s) “Atlas 14” effort, which is recalculating all rain event statistics for the entire country. The work for the Texas area is currently underway and we should try to accelerate that effort if at all possible. We also should make sure that the rain events of 2016 and 2017 are included in analysis. This will update the depth of the 1% annual chance, 24-hour event – our design basis for all new infrastructure.
2. Estimate Future Conditions: If we graph the frequency of daily rainfall depth measurements over time we see a gradual increase in the frequency of 1″ days, 2″ days, and 3″ days going into the future. We should use this data to estimate how much the 1% annual chance, 24-hour event is increasing each year going into the future. This would allow us to estimate the depth of rain associated with the 1% annual chance, 24-hour event in any future year. This would help inform how we design new infrastructure, which is currently sized to handle about 12.5″ in 24-hours.
3. Prepare Cost Estimates:  We should estimate the costs associated with infrastructure and development designs that can handle the 0.2% and the 1% annual chance, 24-hour event; 25, 50, and 75 years into the future. This would allow policy makers and tax payers (you and me) to see the cost differences alongside the policy options. These costs should be “life-cycle” costs – that is they should include the initial capital costs plus the future replacement or repair costs (prorated by the probability of loss).
4. Discuss Policy Options and Costs: We need to have some robust discussions about our willingness to pay for reducing flood risks. Today, just days after the storm, people seem very willing to pay a lot for nearly zero risk. But as the memory of the storm fades that willingness to pay diminishes. If we present and discuss the cost of achieving a few different levels of risk (say the 0.2% annual chance or the 1% annual chance), then tax payers, elected officials, and interest groups can hopefully reach an informed consensus.
5. Invest to Reduce Existing Risks: No planning and engineering effort would be complete without looking at existing risks. We have thousands of homes inside the EXISTING 1% annual chance, 24-hour event floodplains, we have channels and drainage systems that can’t handle the EXISTING 1% annual chance, 24-hour event, much less the estimated future event size. HCFCD has reported a $27 billion cost to upgrade all channels and bayous to handle the 1% annual chance, 24-hour event.  The City of Houston and Harris County (and other local governments) would also have costs to upgrade their local drainage systems. In 1999 the City of Houston received an estimate of $2.7 billion for drainage improvement needs. These investments might include buying out structures, elevating structures, channel improvements, drainage system improvements, detention facility construction, roadway flood gauges, underpass warning lights and gates, and many other facilities.  We need to make these investments (see Item 7).
6. Pick a Risk Level and Update Design Rules: Based on the results of Items 1-5, local governments should pick a common risk level and update their drainage and floodplain management rules. The rule updates could include a variety of measures. We could elevate structures, establish riparian buffers. We could impose larger minimum detention requirements and add minimum volume control requirements (retention) to address not just peak runoff rates, but also increases runoff volumes. We could impose minimum “free-board” requirements (the height difference between the anticipated flood water level [at the selected risk level] and the structure you are trying to protect). We could incentivize or require the use of natural drainage systems (see Item 8 below).
7. Increase Spending on Public Drainage Infrastructure, Especially in Older Areas: The current property tax rate allocated to Harris County Flood Control District is $0.02827 for each $100 of appraised value. So if you live in a home appraised at $100,000 your current annual tax payment to Harris County Flood Control District is $28.27 per year.  If you live in the City of Houston you would also be subject to the 11.8 cents property tax capture to Rebuild Houston and perhaps another $4.00 per month in the city’s drainage fee (depending upon the size of your property and how much of it was impervious). I think most people would support increasing their contribution to our drainage infrastructure, but see Items 4 and 5 above. Any revenue collection approach could be structured to minimize the burden to lower income citizens and the amount collected should be proportional to the amount of stormwater runoff from each property. Retrofitting under served areas should be our focus. See Item 6 above.
8. Use Green Stormwater Infrastructure or Natural Drainage Systems: Traditional drainage uses concrete pipes to move stormwater away from properties quickly. We then store the water in large holes in the ground (called detention basins) and release the water slowly. The release rate is restricted so the flowrate after development is less than pre-development flowrate. This doesn’t control the total volume of runoff, which is a key issue in flooding of flat areas like Houston. We should design stormwater systems to slow the water down and encourage more evaporation, infiltration, and consumption by plants. This green stormwater approach is not a silver bullet, but it would help with flooding issues and it sometimes costs less than traditional systems. Every cubic foot of stormwater we can manage or control where it falls is one less we need to convey or worry about flooding something. I’ve written about this before, here and here.
9. Enhance Risk Communication and Citizen Engagement: We have the information and technology to provide citizens with better information about their risk of flooding. The risk of flooding should be communicated during real estate transactions or when someone rents an apartment.  We can provide very accurate and timely notifications and warnings to each citizen, home owner, and business. Rainfall estimates, actual rainfall amounts, bayou levels, reservoir release rates, gate status, and other information can be served up to each citizen’s cell phone. We need to set up a system to do this. This might be done using an “op-out” format, so everyone’s signed up automatically. Public safety could be the justification for the op-out approach.
10. Implement a Volume Trading Program: Local governments should join together to create, for each drainage area or watershed in the region, a stormwater volume capture target and unit cost for each cubic foot of stormwater. All new projects would then need to comply with the new design rules. The stormwater volume cost would create an incentive to build more detention or capture volume into the project, because any excess could be sold to another party in the same drainage area. This scheme would incentivize building more detention and volume capture facilities which would reduce flooding risks.  I wrote more about this in my post about policy options for the new City of Houston “Flood Czar.”
    

There is no silver bullet to SOLVE Houston’s flooding issues, but these planning and engineering actions would help us all deal with the next large rain event.

by Leo Linbeck III 09/02/2017

[This is a re-post copied directly from New Geography ]

Narratives are not necessarily built on facts; they’re built on stories, pictures, graphics, and videos. Ideally, we want our narratives to be aligned with the facts; but that doesn’t always happen.

Here is a synthesis of some of the predictable narratives being spun in the immediate aftermath of Hurricane Harvey from such places as The Washington Post, Slate, The Guardian, Newsweek and NPR:

Hurricane Harvey was a catastrophe of epic proportions. Floodwater is everywhere; people can only move around the city using boats and helicopters. Local officials failed to order evacuations, so Houstonians have been forced from their homes as flood waters rose, and the death toll is horrific and rising.

But Houston had it coming. It is a miserably hot swamp where no one really wants to live. It embraced a “wild west” approach to growth, paved over wetlands, and refused to implement zoning, which would have lessened the impact of Harvey by requiring developers to mitigate the impacts of new projects. Moreover, it is the global center of the energy business, which is the biggest driver of climate change – one impact of which is the increased frequency and severity of hurricanes like Harvey.

Look at these pictures of flooded streets; families in boats, or shopping carts, or floating on inflatable mattresses; bridges that are totally submerged, and littered with abandoned cars. Check out these graphics showing how Houston has paved over much of the land, destroying wetlands and creating impermeable barriers and exacerbating the impact of major rainstorms. Read these interviews with experts who bemoan Houston’s lack of centralized planning, and who implore the city leaders in Houston to use their power to address the many failures that became evident during Hurricane Harvey.

These narratives, alas, are a combination of ignorance, and arrogance that tells the reader more about the narrative spinners’ flawed view of Houston than about the city itself.

Let’s start with some facts and perspective:

• Harvey is the wettest storm ever to hit the continental US. Over 50 inches of rainfall and 1 trillion gallons of water fell during the event. No one builds a church for Easter, or a gated community for the zombie apocalypse. It’s pretty naive to expect people to expect the unexpected.
• So far, there have been fewer than 50 storm-related deaths. Each of these deaths is tragic, but even if that number creeps higher, it is a stunning low fatality rate for such a major event in such a large city. The Houston region has more than 6.6 million people, and every year more than 40,000 of them die – so Hurricane Harvey increased the annual death tally by about 0.1%. Sad, but not catastrophic.
• An estimated 30,000 people have been forced from their homes. This is approximately 0.5% of the population of the Houston region. In other words, 99.5% of people in the Houston region have been able to stay in their homes. Unfortunate, but not catastrophic.
• The Trump Administration has estimated that 100,000 homes were damaged or destroyed. While it is unclear how that estimate was obtained – if 30,000 people were forced from their home, then probably 70-90% of those homes did not sustain enough damage to force an evacuation – the Houston region has more than 1.6 million housing units, so about 6% of homes sustained damage of some kind. Lamentable, but not catastrophic.
• Economic impact estimates are all over the map at this point; initial estimates were in the $30-40 billion range, but have been rising since then. Let’s say they end up being comparable to Superstorm Sandy, which caused about $70 billions of damage in today’s dollars. The Houston region GDP is about half a trillion dollars a year, so Harvey’s economic cost would be about 14% of our total economic output. Expensive, but not catastrophic.

A dispassionate weighing of these facts would tell you that while stressful events always help identify areas for improvement, by and large our infrastructure and leadership performed admirably well under extraordinary circumstances.

It other words, the facts would tell you that Harvey was not a catastrophe for Houston; it was our finest hour.

But the narrative spinners have an agenda: they want to assert that this event was an utter failure for Houston, and shame our city and county leadership into embracing centralized planning, and ultimately zoning. They believe in a top-down, expert-driven technocracy that rewards current real estate owners by actions that restrict new supply, raise property value (and therefore taxes), stifle opportunity and undermine human agency. As a life-long Houstonian, I would like to politely ask the narrative spinners to please pound sand.

Peter Drucker once said that culture eats strategy for breakfast, and Houston’s culture is one of opportunity. People come to this city to build a better life for themselves, to start and raise a family, and to do so with the support and encouragement of neighbors. This culture of opportunity means that Houstonians welcome newcomers, in a way that older or more status-conscious cities do not. Houston may not be a nice place to visit during the summer, but it is a great place to create a life all year round.

This culture really shines through during events like Hurricane Harvey. Despite what the narrative spinners would have you believe, we are not rugged individualists; we are rugged communitarians. We know that when times are tough, you must rely first on family, then friends, then neighbors, and then – and only if you’re one of the few, unfortunate folks who cannot rely on any of those three – on the government. And if we have family, friends, or neighbors who can help, reaching out for government support is actually taking resources away from those who need them more.

In short, the best governance to rely upon is self- governance.

When the storm hit, I saw these networks in action. People first took care of family – in my case, my five siblings and I were in regular communication, checking in on how each of us was weathering the storm. Good news: everyone came through pretty much unscathed.

Once it was clear that my family was OK, my wife and I began to focus on neighbors and friends. Yesterday, I spent several hours with neighbors clearing away trees that had fallen across streets in our neighborhood, making them unpassable. It was hard work – lots of chain sawing and branch hauling – and we were helped by a crew that was distributing power poles in our area. But folks just driving in the area would also stop and help, doing what they could, or just providing fellowship and encouragement.

One lady in the neighborhood brought us some chicken meatballs for lunch – no one asked her to do that, she just wanted to help however she could. (The meatballs were delicious – thanks Costco!)

Also, in our network of friends, there were a couple of families who were forced from their home. We worked together to find them places to stay, and today a group of about 40 men, women, and children went to their house today to box up and move out their valuables, throw away everything else, and tear out the damaged drywall. People brought tools, gloves, and a can-do attitude, and a job that might have taken weeks was finished in about 6 hours. Our friends now have their valuables with them in a rented home (found by another friend in our network), ready for the next step in returning to normalcy.

These stories are real, and not about heroes doing the unusual. They are commonplace and just the way things get done in Houston. If you have friends in Houston, just ask they will tell you similar stories.

Of course, leadership is important, and our regional leadership did great. Mayor Sylvester Turner and Judge Ed Emmett were both calm, deliberate, and stayed on task throughout the crisis. Governor Abbott and President Trump did their parts, but make no mistake about it – this was a local challenge that required top-notch response from local officials. And they did their jobs well.

Houston was able to absorb the wettest storm on record with remarkably little loss of life and property also because of good engineering, informed by the experience of previous storms. A good engineer designs systems that won’t fail when hit with an expected event; a great engineer designs systems that fail gracefully and non-catastrophically when hit with an unexpected event. Hats off to our great engineers.

However, a focus on Houston’s public officials or public infrastructure will lead you away from the more important truth: our response was driven by thousands of Houstonians who voluntarily stepped up to the challenge, and didn’t wait for some central authority to tell us what to do. The truth is that Houston’s culture was its biggest asset, a culture of mutual support that is extraordinary in a city of this size and diversity.

And this culture is not an accident; it the consequence of a system that was designed to be driven from the bottom-up, by regular folks, responding to needs on the ground rather than some kind of theoretical plan put together by experts with no stake in our future, or interest in our family, friends, or neighbors.

Of course, there is always room for improvement. By studying what happened, we will find ways to improve the system for the next storm – and there will always be a next storm. We learned a lot from Ike, Rita, and earlier storms. When I was a child, a couple of inches of rain would flood my neighborhood; today, that same neighborhood absorbed 25 inches of rain and made it through. We have come a long way.

Harvey was a difficult challenge, but not a catastrophe. However, it would be catastrophic for city leaders to accept the narrative spinners’ version of what happened in Houston. It is demonstrably wrong on all counts:

• Houston is a miserably hot swamp where no one really wants to live.

It’s hot during the summer, but it is pleasant the rest of the year. As this map shows, Houston actually gets more “pleasant days” than Miami, Raleigh-Durham, Chicago, Portland, or Phoenix. Forget your preconceptions for a moment, and answer a simple question: how could a place get to a population of 6.6 million if no one wanted to live there?

• It embraced a “wild west” approach to growth.

Houston’s approach is not the “wild west.” We have land use that is managed from the bottom up, through a system of deed restrictions that often include local homeowners’ associations to police those restrictions. What we don’t have is a top-down, expert-driven, bureaucratic system of centralized planning. As a result, it’s easier to develop real estate than most cities, which keeps real estate prices – especially housing prices – low relative to the rest of the country. It is actually a more sophisticated and economically efficient system than the antiquated politically-driven zoning system that generally favors entrenched interests over new entrants.

• Paved over wetlands

Over an 18 year period, Houston lost about 25,000 acres of wetlands. But this amounts to about 4 billion gallons of storm water detention capacity. As stated above, Harvey dumped about 1 trillion gallons; so the lost capacity represents about of 0.4% of Harvey’s deluge. But it’s also important to understand that the streets – a huge portion of the paved area – are used as detention, places to hold storm water temporarily when there is nowhere for it to drain. Houston’s strategy for many years has been to use streets as detention and runoff channels, the idea being that it is better to flood a street than a house. And the city’s performance under Harvey confirms the wisdom of that strategy.

• Refused to implement zoning, which would have lessened the impact of Harvey by requiring developers to mitigate the impacts of new projects.

This is the most ridiculous of all the claims made by the narrative spinners. Mayor Turner put it best: “Zoning wouldn’t have changed anything. We would have been a city with zoning that flooded.” Proof positive of this fact: one of the harder hit areas was Sugar Land, just south of Houston. Sugar Land has zoning. Alas, Harvey was unaware of that fact and dropped 30+ inches on them anyway (and they handled it well, just like the City of Houston, evidence that zoning was not correlated with impact).

• Moreover, it is the global center of the energy business, which is the biggest driver of climate change – one impact of which is the increased frequency and severity of hurricanes like Harvey.

Yes, Houston is the center of the energy business. But Houston’s energy industry is as much about natural gas as crude oil, and the increasing use of gas in power generation has led to a much-improved carbon dioxide picture in the US. If you believe that CO2 is causing climate change, you should be thanking the energy entrepreneurs in Houston for bringing cheap, clean natural gas to the nation. Moreover, the hypothesis that greenhouse gas emissions impact Atlantic hurricane activity is controversial; an official NOAA publication stated that “neither our model…nor our analyses…support the notion that greenhouse gas-induced warming leads to large increases in either tropical storm or overall hurricane numbers in the Atlantic.”

A final point about who pays for all this.

The narrative spinners have made a big deal about how federal funds will be needed to rebuild Houston, and therefore Houston must do what they say.

My take on this is: we are going to rebuild with or without you, so you are not the boss of us.

Most of the money from previous Texas hurricanes has come from private insurance. And, in some ways, this process of rebuilding restores a balance in the economy. For the past couple of decades, almost all homeowners have paid for insurance but few people make a claim. Most of that money sits on the balance sheet of big insurance companies to pay out future claims, and those companies often invest those dollars on Wall Street and real estate. That’s all fine – good, healthy commerce.

Now the time has come for the flow to go the other way. Big insurance companies will be paying out money to settle insurance claims, and most of that will go to working class Americans who will rebuild damaged property. Demand for labor will rise, as will wages, as the money starts to flow. The tilting of the economy away from physical labor toward the financial sector will reverse – maybe only temporarily, but it will still reverse.

Of course, if the federal government decides to give away money, I suppose people will sign up for it. But this madness eventually needs to end. The federal government is broke, and insisting that folks in Kansas or Vermont pay for a hurricane in Houston is silly on the face of it. This is not an invading army we’re talking about here. It’s a really bad storm. The Constitution doesn’t contain the words “storm,” “weather,” or “insurance.” Why are we continuing to twist its meaning to make Congress and the President look like heroes? If they want to help, let them help with their own time, talent, and treasure. Like the rest of us.

But we also don’t want to be suckers. If Washington DC decides not to help Houston, they should end it for everyone in the future. Which they should, in my opinion.

Bottom line: I believe we should celebrate the ability of the nation’s fourth largest city to absorb the wettest storm on record and bounce back with gusto. It is a testament to the culture of my hometown and the leadership that supports and nurtures that culture.

Now, if you will excuse me, I have to get back to work. That wet drywall won’t remove itself.

Leo Linbeck III is a husband, father of 5, CEO of Aquinas Companies, Executive Chairman of Linbeck Group, a Houston-based institutional construction firm, Founder and Chairman of Fannin Innovation Studio, a biomedical startup studio, and Lecturer at Stanford Graduate School of Business. He was also the Founding Chairman, and is currently the Vice Chairman, of the Center for Opportunity Urbanism, a Houston-based think tank.