Tag Archive for: mythbuster

Mythbusters: Common Misperceptions about Flooding in Harris County

Since Hurricane Harvey, I’ve continually run into several widely held misperceptions about flooding in Harris County. As we head into another hurricane season, let’s set the record straight about the most common myths. Some of the facts below have been adapted from information provided by the Harris County Flood Control District.

MYTH: The Harris County Flood Control District is responsible for addressing all types of flooding.

FACT: The Harris County Flood Control District is responsible for bayous and many of their tributaries. However, the City of Houston, other municipalities, and Precincts – in unincorporated Harris County – handle storm sewers and roadside ditches.

street flooding

The Texas Department of Transportation handles drainage of highways and their feeder roads.

The moral of this story: make sure you call the right people when you see a problem developing.

MYTH: I’ve lived in my house for more than 30 years and I’ve never flooded. Therefore, I don’t need flood insurance.

FACT: Most Harris County residents live in homes vulnerable to flooding because:

  • Our topography is flat.
  • Many of us have impermeable clay soils that increase runoff.
  • Our subtropical climate can produce large amounts of rain in short periods of time.

Storm rainfall patterns may have spared your area since you have lived there. But that could change like the weather.

Remember. People thought Tropical Storm Allison was the worst. It caused all the flood maps to be revised. Then along came Harvey. Now, HCFCD and FEMA are revising the flood maps again.

During Harvey, more than 68 percent of the homes that flooded in Harris County were outside the 100-year flood plain. So, consult your insurance agent. Most homeowner insurance policies do not cover flooding. You need a separate policy for that.

MYTH: A 1-percent (100-year) flood occurs only once every 100 years.

FACT: A 1-percent (100-year) flood can occur multiple times throughout a century. A 100-year flood has a 1-percent chance of occurring in any given location in any given year. Doesn’t sound like a lot? Think of it this way: A home in a 1-percent (100-year) floodplain has at least a 26-percent chance of flooding during a 30-year period of time – the duration of many home mortgages. And remember, Harris County experienced four hundred-year events in four years (Tax Day, Memorial Day, Harvey, and Imelda).

MYTH: I only need to worry about flooding during hurricane season.

FACT: Flooding can happen any time of the year. Of the four storms mentioned above, two occurred outside of hurricane season.

Short, high intensity rainfalls can cause street flooding that invades vehicles and homes built close to street level or near developments with insufficient mitigation.

Hundreds of homes flooded in Elm Grove on May 7, 2019. The causes: 5.64″ of rain in about 12 hours. And a 270-acre tract upstream that had recently been clearcut with only 9% of the promised detention ponds constructed.

high water rescue truck
High water rescue truck on flooded Elm Grove Street, May 2019
MYTH: If I didn’t flood during Allison or Harvey, chances are I won’t ever flood.

FACT: The greatest rainfall brought by Tropical Storm Allison hit the northeast part of Houston and Harris County, dropping more than 28 inches of rain in 12 hours and 35 inches of rain in five days. However, some areas received fewer than 5 inches of rain. Had the damaging rains of Allison targeted other areas, they would have experienced similar, devastating flooding.

Harvey also hit and missed certain areas. But the differences were even more dramatic. While Friendswood received 56″ of rain, Willis in Montgomery County received only 5″ between August 25 through September 1, 2017. See USGS, Table 1, Page 3.

MYTH: I don’t need flood insurance because I don’t live in a mapped floodplain.

FACT: We are all at risk for flooding regardless of our proximity to a mapped floodplain. Flood Insurance Rate Maps (FIRMs or floodplain maps) published by the Federal Emergency Management Agency are good indicators of flooding risks from bayous and creeks overflowing their banks. However, they do not show flooding risks from storm sewers and roadside ditches exceeding their capacity, risks from unstudied bayous and creeks, or risks from storms greater than a 0.2 percent (500-year) flood — such as Tropical Storm Allison in 2001 or Hurricane Harvey in 2017.

MYTH: New land development causes flooding.

FACT: New development can accelerate the time of concentration of floodwaters, contributing to faster, higher flood peaks. That’s why cities and counties regulate development. But some see lax regulation and enforcement as a tool to attract new development. And even those with strict regulations may find that they aren’t strict enough to handle storms of increasing intensity.

HCFCD graph showing effect of development in Brays Bayou watershed. Insufficiently mitigated development over 85 years accelerated runoff, building flood peaks faster and higher.

Flooding can be inherited from areas developed before our understanding of flooding improved. So it would be safer to say that “Insufficiently mitigated development causes flooding.”

Regulations dating to the early 1980s in many areas require stormwater runoff after development to be no greater than runoff before development. Developers must detain any excess stormwater on site. However:

  • Development prior to the 1980s was not as regulated.
  • Our understanding of what constitutes a 100-year rainfall continues to evolve. So pre/post estimates may be off.
  • Loopholes exist in many jurisdictions that allow developers to avoid building detention ponds.

Today, we have a hodge-podge of regulations throughout the region. Learn regulations in your area and monitor new developments to ensure compliance.

MYTH: A storm surge from a tropical storm or hurricane will inhibit our bayou system’s ability to drain.

FACT: Most of our bayous and creeks are upland and drain by gravity. Because of their natural slope toward Galveston Bay, a storm surge caused by a tropical storm or a hurricane will not impede this process. Of the roughly 2,500 miles of bayous and creeks in Harris County, only a small portion near Galveston Bay will be influenced by storm surge for a short period of time.

Posted by Bob Rehak on 6/20/22 with thanks to the Harris County Flood Control District

1756 Days after Hurricane Harvey


Equity Myth Buster: “Rich Neighborhoods Get All the Flood-Mitigation Funding”

A myth being promulgated in Harris County Commissioners Court and certain low-to-moderate income (LMI) watersheds these days goes something like this:

  • The FEMA Benefit/Cost Ratio (used to rank grant applications for flood-mitigation projects) favors high-dollar homes.
  • That disadvantages less affluent, inner-city neighborhoods compared to more affluent suburbs.
  • Therefore, less affluent neighborhoods get no help and the more affluent neighborhoods get it all.

This post busts that myth. But it won’t stop activists from demanding more “equity.”

If you look at all flood-mitigation spending in Harris County since 2000, on average, less affluent watersheds already receive 4.7X more partner funding per watershed than their more affluent counterparts.

Analysis of data obtained via FOIA request

Myth Ignores Other Factors, Frequently Leaps to Wrong Conclusions

Like much of political discourse these days, the myth focuses on a narrow sliver of truth, ignores other factors, and frequently leaps to the wrong conclusions.

An analysis of Harris County Flood Control District data going back to the start of this century shows how far off the myth can be.

There are dozens of different ways to slice and dice the data. I’ve looked at most of them and validated “dollars invested” with aerial photography.

Today, I focus on partner grants because they represent such a huge percentage of the flood-bond budget and because there is so much misinformation floating around about them.

And I will look at partner funding from the standpoint of outcomes, not just processes (as in the myth).

Methodology for Analysis

For this analysis I obtained Harris County Flood Control District spending data between 1/1/2000 and 9/31/2021 via a Freedom of Information Act (FOIA) request. I requested the data by watershed, decade, pre-/Post Harvey, source of funding (local vs. partner), and type of activity (i.e., engineering, right-of-way acquisition, construction and more). I cross-referenced this with other data such as flood-damaged structures, population, population density, and percentage of low-to-moderate income (LMI) residents.

When considering grants, the percentage of LMI residents in a watershed takes on special significance. Department of Housing and Urban Development (HUD) grants often require high percentages of LMI residents in the area under consideration.

In the charts below, you will see references to watersheds with LMI populations above and below 50%. Above 50% means more than half the residents in the watershed have an income LESS THAN the average for the region. Below 50% means more than half the residents earn more than the regional average.

Harris County has 23 watersheds. Eight have LMI percentages above 50% (less affluent). Fifteen have LMI percentages below 50% (more affluent).

When reviewing the charts below, pay particular attention to the italicized words: Total, Partner, and On Average. They represent three different ways to look at the same question: Do housing values disadvantage an area when applying for grants?

For this analysis, I focused only on the long term, since decisions on more than a billion dollars in flood-bond grants are still outstanding.

FOIA Analysis Contradicts the Popular Myth

One of the first things you notice when you look at watersheds above and below 50% LMI, is that the eight least affluent watersheds have gotten more than 60% of all dollars actually spent on flood mitigation since 2000.

Less affluent watersheds, despite being half as numerous, received 60% of all dollars since 2000.

Because the allegation was that partnership grants favored affluent areas, I then analyzed whether partner dollars went mostly to affluent or less-affluent watersheds. The answer is less affluent…overwhelmingly.

More than 70% of all partner dollars in the last 22 years went to the eight less-affluent watersheds.

The last observation by itself is telling. But because of the widely different number of watersheds in each group, I also wanted to calculate the average partner dollars per watershed in each group. This blows the “rich neighborhoods get all the grants” argument to pieces. Less affluent watersheds got, on average, 4.7X more.

Dividing the total partner dollars by the number of watersheds in each group shows that less affluent watersheds average 4.7X more than affluent ones.

This busts the myth. But digging even deeper into the data reveals two things: wide variation between sources of funding and within LMI groupings.

USACE Funding Skews Partner Totals

The U.S. Army Corps of Engineers (USACE) accounts for much of the partner funding. USACE has provided significant funding for projects in the Sims, Brays, White Oak, Hunting, and Greens Bayou watersheds. The Clear Creek watershed will also soon see work on a new USACE project. USACE has completed its planning process and proved positive benefits to national economic development. That made projects worthy of Federal investment. 

Halls Bayou: Digging Deeper

The Halls Bayou watershed also went through the USACE planning process, but the results did not show enough flood-damage-reduction benefits to outweigh the costs of the proposed projects. Thus, the Halls Bayou watershed currently has no USACE-funded projects.

Despite that, Halls has received more partner funding than 16 other watersheds since 2000. Only two watersheds in the affluent group of 15 received more partner funding. See the table below.

Total and partner spending by watershed since 2000 arranged in order of highest to lowest LMI percentages.

USACE also evaluated the more affluent Buffalo Bayou; results showed that costs outweighed the flood-damage-reduction benefits there.

Despite Halls having the highest percentage of LMI residents in Harris County, Halls has received more total funding and 2.5X more partner funding than Buffalo Bayou in the more affluent group.

FEMA Considers More than Home Values, Not All Grants Come From FEMA

While it’s true that FEMA considers housing values as a factor in benefit/cost ratios, benefit/cost ratios (BCRs) also consider factors such as:

  • The number of structures damaged
  • Threats to infrastructure
  • Proximity to employment centers
  • Need for economic revitalization
  • Percentage of low-to-moderate income residents in an area
  • Number of structures that can be removed from the floodplain by a project.

And not all grants come from FEMA. For instance:

So don’t settle for soundbites. They often mislead.

Posted by Bob Rehak on 12/30/2021

1584 Days since Hurricane Harvey