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Flood Gains: It's About Reducing the Risks
By Michael D. Talbott, P.E.
Director, Harris County Flood Control District
As originally printed in the Houston Chronicle, Outlook section, March 7, 2004.
March 07, 2004
Flooding will once again be the center of attention this week, although (hopefully) not due to an actual flood event.
On Monday, March 8th, the Harris County Flood Control District will release important Flood Hazard Recovery Data for the Brays Bayou, Goose Creek, Jackson Bayou, Luce Bayou, and San Jacinto River watersheds of Harris County. Similar Data for the remaining 17 watersheds of Harris County will be released on a weekly basis as the work is completed.
Flood Hazard Recovery Data represents the most current understanding of the 1% and 0.2% floodplains (100- and 500-year) and floodways of these watersheds using the latest engineering and technology.
This information is being developed through the Tropical Storm Allison Recovery Project (TSARP), a partnership between the District and the Federal Emergency Management Agency.
The Flood Hazard Recovery Data will be used by FEMA to issue new preliminary Digital Flood Insurance Rate Maps (DFIRMs) for all communities in Harris County in late Spring. Issuing the DFIRMs will initiate the administrative process to make the new floodplain information official for flood insurance purposes.
While the Flood Hazard Recovery Data must be considered to be a "preview" of the information that will be contained on the preliminary DFIRMs, and therefore subject to change, the information should be nearly identical. Our confidence is based on the applications of the most advanced engineering methods and technology used throughout the project. One of the most dramatic advances involves a NASA-developed airborne laser technology called LiDAR to establish ground surface elevations with a level of precision never before possible. TSARP has also produced excellent results due to the active involvement of concerned citizens, building officials, and technical organizations to advise us throughout the study process.
Beginning tomorrow, residents of the released watersheds will be able to view our best understanding of where the floodplains lie by visiting www.tsarp.org. On this web site, (as well as the District's - www.hcfcd.org) they will also be able to learn about our area's natural and historic risk of flooding, what is being done about it, and of the importance of carrying flood insurance.
To the District's knowledge, it is unprecedented that Data of this nature is being made available to the community in this accessible a format prior to FEMA issuing preliminary DFIRMs.
Put simply, the District and FEMA want the public to have as much time as possible to become aware of their flooding risks. An informed community is a more damage-resistant community.
Toward that end, it is important that the community keep a series of facts in mind so that the Data can be placed in proper perspective.
A common misconception is that the current county floodplain maps are "wrong." In fact, they are a solid and largely accurate representation of where the highest risks of flooding exist. However, new technologies and engineering methods allow for a more detailed understanding of these risks.
TSARP represents an entirely new study of flooding potential, not an update of old information. As such, it is not appropriate to characterize mapped floodplain changes as an "increase" or "decrease" in flood risk - it is simply a new understanding of our flood risk.
Indeed, a number of technical differences in the new study approach make direct comparisons to the old study inappropriate. For example, the detail of the ground surface defined by LiDAR is unprecedented and represents a significant difference. Another is the use of new (larger) rainfall values than the old study based on additional years of rainfall records.
These and other differences make it impossible to attribute any change in our understanding of flood risk to an individual cause. Also, each watershed is unique and possesses independent flooding conditions; information released from one watershed should not be used to make generalizations about another.
Nevertheless, there will be those who will attribute changes in our floodplains to a single source - new development. Development has played a role in our flooding problems, but not in the way most people realize. Historically, what development has done is place people in the path of a naturally flood prone landscape.
Quantifying our flood risk is a fairly recent development - the 1% (100-year) flood was not adopted as a standard until the National Flood Insurance Program was established in 1968, local floodplain regulations were not established until the early 1970's, and the first detailed studies of flooding for Harris County were not published until 1985. The unfortunate result is that most of the chronic flooding problems in our region are found in areas that were developed before adopting the standard of measuring risk (the 1% flood), and before regulations.
Part of the study effort to understand Tropical Storm Allison confirmed that floodplains today are smaller than they were 100 years ago - evidence that the massive flood damage reduction projects have been very effective. Flood risks continue to be reduced every day as flood damage reduction projects are provided, and building regulations are enforced to help ensure that new problems are not created.
On Monday (and for weeks thereafter) there will undoubtedly be those who will check to see if their residence falls within the estimated mapped floodplain, and if it does not will improperly surmise that they posses no flood risk.
It is imperative to keep in mind that every portion of Harris County possesses some risk of flooding due to the flat terrain, clay soils, and high levels of annual rainfall. Intense local rainfall can cause flooding well away from any channel as water tries to flow overland, and severe storms can produce more rainfall than what is depicted by the mapped floodplains (both scenarios were very evident with Tropical Storm Allison).
Moreover, as advanced as our engineering technologies have become, mapped floodplains still represent simulations (albeit highly informed) of a theoretical rainfall event - about 13 inches of rain in 24 hours for the 1% (100-year) event. Although there are extensive checks against actual storm and flooding events to be sure the computer models can reproduce observed information, the mapping is not directly based on any flooding event that has ever occurred - it is still theoretical.
The Data should also be viewed as a snapshot in time of flood risk. Ongoing and future flood damage reduction projects will help shrink floodplains in many areas, while preventing their enlargement in others.
For example, Brays Bayou watershed is in the first group of Data to be released, and is one of the areas where historical flooding is well documented. Brays Bayou also has underway the largest flood damage reduction project in the history of Harris County, a $450 million effort being conducted in partnership with the U.S. Army Corps of Engineers.
The District will start using the Flood Hazard Recovery Data on "Project Brays" now and we will apply similar knowledge to all of our other current and planned projects as it becomes available.
The countywide potential of Flood Hazard Recovery Data and TSARP will not be fully realized, however, if the District alone uses the information, or if people wait for the new DFIRMs to be approved before applying the knowledge.
The Harris County Flood Control District is not a floodplain administrator, nor is it a regulatory agency. It is a special purpose district charged by the Texas legislature (in part) with responsibility for "the control, storing, preservation and distribution" of Harris County's rivers, streams, tributaries, and flood waters.
Local regulatory oversight of floodplain maps rests with each of Harris County's 35 communities. Typically, communities have waited for floodplain maps to be formally approved by FEMA before adopting them into their building ordinances. However, in light of the fact that Flood Hazard Recovery Data represents the latest information, it is advisable (at a minimum) that each community ensure that developers applying for permits are asked to confirm that the new information was made available.
Government cannot address flooding alone, however. You will recall the damage suffered by the Texas Medical Center during Tropical Storm Allison. Since that time, various institutions in the Medical Center have undertaken a significant effort to flood-proof buildings and tunnels to protect themselves and ensure they do not suffer similar damage in the future. They deserve tremendous credit for setting an example of enlightened flood control leadership that other institutions and land developers are following.
Individuals too have a responsibility. They have a responsibility to pay attention to the Flood Hazard Recovery Data as it is released and make informed decisions about protecting themselves against a possible flood, including a responsibility to carry flood insurance whether or not they are required to do so.
While flooding will be the center of attention over the next few months because of the new floodplain maps, I can assure you we will focus on actual flooding again in the future. The storm will be called by a name other than Allison (that name has been retired) or it may not have a name at all.
This is not to say that we cannot reduce the risk of flooding. We can do that, we have done that, and we are doing that - in a more innovative and effective manner than at any time in the Harris County Flood Control District's 67-year history.
As devastating as Tropical Storm Allison was for Harris County, it did have some positive aspects - especially a renewed public awareness of flooding and flood damage reduction as one of the most important issues affecting our community.
We are also witnessing an unprecedented energy and long-term commitment by the majority of our county's communities to tackle local flooding issues.
I am confident that countywide we can harness this energy to understand our flooding problems and continue to construct new stormwater systems that will improve our quality of life - by reducing the devastation of flooding and creating wonderful open space for use between floods.
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