New floodplain maps: Improving flood control plans, insurance planning

Thomas W. Mountz, P.E., CFM
Associate, Public Works Division
Carter & Burgess
Austin, Texas

On June 5, 2001, Tropical Storm Allison made landfall on Galveston Island, Texas. No one expected that, five days later, it would go on record as one of the most devastating rain events in the history of the United States. Neither historical data nor weather forecasts could adequately predict that this extraordinary storm, before leaving Texas, would dump as much as 80 percent of the area's average annual rainfall over Houston and Harris County neighborhoods, simultaneously affecting more than two million people.

When the rains finally eased, the total effect was devastating. With 22 fatalities, 95,000 damaged automobiles and trucks, 73,000 damaged residences, 30,000 stranded residents in shelters, and more than $5 billion in property damage, a presidential disaster declaration was announced.

Tropical Storm Allison Recovery Project
In an effort to aid Harris County residents during the recovery process, the Federal Emergency Management Agency (FEMA) and the Harris County Flood Control District initiated the Tropical Storm Allison Recovery Project (TSARP). The purpose of TSARP was to develop technical products designed to assist the local community in recovering from the devastating flooding and provide the community with a greater understanding of flooding and flood risks. The project will ultimately result in new FEMA Digital Flood Insurance Rate Maps (DFIRMs) for all of Harris County.

The new floodplain maps more clearly define the 1% (100-year) and 0.2% (500-year) floodplains. FEMA defines the flood hazard area as any area that is susceptible to being inundated by water from any source. Property included in the 1% (100-year) floodplain has a 1% chance of being flooded in any given year. These floodplain maps are an indispensable part of long-range flood control, insurance rate setting, and mitigation operations in the Harris County area. Some of the information used in current maps for flood control planning dates back as far as the 1960s.

Flood Insurance Rate Maps
The new Flood Insurance Rate Maps (FIRM) are relevant to all 35 National Flood Insurance Program (NFIP) communities in Harris County. "This will help developers determine the true risk associated with building in a certain area," said Dwayne Culp, former senior engineer with Houston's Department of Public Works and Engineering. The maps will also serve citizens as they make important home-buying and other property-related decisions.

As the new floodplain maps are finalized, there is concern among some property owners as to the effect on property values. Some properties currently not shown in the floodplain will be in the newly-defined FEMA floodplain. Researchers in this area have mixed results, leaning toward the conclusion that floodplain classification may have a minor negative effect, or none at all, on property values.

Property values set by appraisal districts have proven to be an unreliable barometer to use in determining the rise or fall in the value of such properties. Appraisal districts are reluctant to lower property values because of the obvious shortfall it would create in the local treasury. Research also reveals that there are so many variables to consider when purchasing a home that house values, as indicated by the purchase price, cannot be traced to a single factor, such as inclusion in a floodplain. In Harris County, the public "psyche" has adapted to the fact that they live in one of the most flood-prone areas in the nation, and there appears to be a civic confidence that the flood prevention programs that TSARP is conducting are heading in the right direction.

The development of the maps is an ongoing venture, one of continually updating and improving the data critical for flood prevention and control. Using the latest cartographic technology and adopting new regulations and flood control systems, regional officials are working to reduce the impact of any future storms so that the community doesn't experience the level of devastation that Allison created during those five fateful days of June 2001.

Thomas W. Mountz can be reached at (512) 314-3100 or

Carter & Burgess was established in 1939 as a two-man partnership providing civil engineering and landscape architecture services, and has since grown into a full-service, multidiscipline consulting firm with more than 2,700 employees in major metropolitan areas across the nation. For more information please go to

Carter & Burgess prepares Texas Medical Center to be fully operational under flood conditions

No segment of the Houston area was more devastated by Tropical Storm Allison than the Texas Medical Center (TMC), which incurred about 40 percent of the $5 billion in damages suffered by the Houston area as a whole.

From a holistic viewpoint, the damage was immeasurable considering the future lives not saved. Floodwaters cascading through the facility's tunnels and basement laboratories wiped out years of ongoing research; some 30,000 experimental animals drowned; inundated computer files were destroyed; and thousands of irreplaceable preserved tumors were destroyed.

But literally within hours of the flood's treachery, restoration efforts were underway. The Houston office of Carter & Burgess provided an immediate team of engineers, planners, and designers to mitigate the flood-damaged facilities. They also began plans to provide remedial systems and an infrastructure designed to assure that the TMC would remain operational in the event of future floods.

After emergency measures were taken to bring TMC back to an adequate operational status, the Carter & Burgess team was tasked with doing conditional surveys on a number of TMC structures.

TMC, which includes the M.D. Anderson Cancer Center, selected Carter & Burgess to help in planning and designing a FEMA flood solution.

The Carter & Burgess team is elevating systems to higher grounds, including mechanical, electrical, fire protection and building automation systems, along with other critical operations that were previously located in the flood-prone basement levels. The objective is to prevent the loss of critical hospital operations regardless of serious natural flooding. The firm plans to raise all electrical services above flood levels, assuring that light and power remain uninterrupted throughout any flood storm and its aftermath.

In addition, Carter & Burgess engineers and planners are making certain that the water pumps are added to combat internal flood conditions. The plumbing is also being renovated so that it won't back up into the building. One of the major issues during Allison was that a significant amount of damage was caused—not by the floodwaters per se—but by the water from storm drains and sewer drains that were surcharged and backed up into the building.

The entire project is designed to meet a 500-year flood elevation, thereby providing as much security and safety as possible for the M.D. Anderson complex in the event of another Houston area flood.

As flood analysts have warned, it isn't a question of "if" regarding another flood of Allison-like proportions, but realistically, a question of "when."

Potential insurance implications

Depending upon the category of the property, the following scenarios may apply:

  1. No changes in insurance rates are likely since property remains outside of the floodplain.

  2. As long as current flood insurance is maintained, there will be no change in rates (a "grandfathering" concept). Structures are treated as if they are not in a floodplain for determining insurance rates. The lower rate may be transferred to any future owners.

  3. Prior to the new FEMA maps being finalized, it is an opportune time to achieve lower insurance rates as in category 2. However, if this purchase option is not taken prior to the new maps being finalized, insurance rates will be based on designated "pre-firm" rates, which generally will be higher than those in category 2.

  4. Rates are not likely to increase. If the base flood elevation is lowered for the property area, the owner could submit an elevation certificate, based on the new data, to get a rate decrease.

  5. Rates will be based on the difference in the finished floor elevation of the structure and the base flood elevation of the new maps. This category only applies to structures that do not require federally backed loans.

  6. Rates prior to the implementation of the new maps are based on the higher AE zone rate. However, since the property will be outside of the new floodplain map, the rates will be based on the X zone price, which is usually lower than the AE rate. Applicants should contact their insurer after the new maps are issued for potential reductions in insurance rates.

Disclaimer: Harris County Flood Control District and the City of Houston recommend that all property owners purchase flood insurance.

Five points that developers are advised to check during the feasibility study stage

  1. This website functions as the basic information channel regarding floodplain map updates and relevant regulations, along with serving as the website for the Tropical Storm Allison Recovery Project. It is good policy to review the website weekly since it is continually updated with vital flood-related regulation information, map changes and advisories.

  2. Review data: Review all pertinent data relative to updated maps and regulations.

  3. Compare data: Compare the data from the different sets of maps, those of TSARP and the existing maps of FEMA.

  4. Optimize fill-plans: An up-to-the-minute awareness of TSARP flood elevations will help planners decide the best time for construction fill. The construction question posed is: Should a developer try to get the fill completed before the new maps come out or after they are finalized? For example, a property may be currently in the floodplain, but after new maps are finalized, the property may not be in the floodplain. Compared to other geographical areas where fill is plentiful and easily accessible, fill operations in Harris County are a particular problem due to the lack of "fill accessibility." Based on knowing if a particular area will be within a floodplain, the timing of fill operations can have a significant economic impact, negative or positive.

  5. Obtain permits early: Consider obtaining a permit within 30 days of TSARP issuing a new set of maps, which show when the planned construction will become part of the revised floodplain. Within 30 days of the TSARP maps being released, a developer may take advantage of favorable mitigation requirements for development in the area that is brought into the floodplain. Within 10 days of the TSARP maps being released, a developer can construct homes without raising the finished floor elevations to new regulation levels. (This may impact insurance rates and susceptibility to flooding and should be considered very carefully before implementation.)

Four things a property owner or building owner should check on to be certain of minimizing insurance costs and remaining in compliance with TSARP regulations

  1. Review the existing FIRM.

  2. Review the proposed TSARP maps ( If the property is not in the floodplain per current maps, now is an excellent time to purchase flood insurance. According to the NFIP standards, the rate for a structure will be based upon the structure's flood zone that the structure is in at the time the insurance is first purchased. The lower rate is transferable to successive property owners.

  3. Review elevations shown on the relevant TSARP map and compare this data with the appropriate new topographical map. If a lower base flood elevation is revealed in the new map, then it may be advisable to submit a new elevation certificate or request a letter of map amendment, both of which can have a positive economic result by reducing insurance costs.

  4. If the property is in the floodplain per the current maps and will not be in the floodplain in the new maps, review the current insurance rates to ensure that the property is not rated as being in a floodplain.