Storm Center

Tropical Storm Allison Recovery Project

In the aftermath of Tropical Storm Allison, the Federal Emergency Management Agency (FEMA) and the Harris County Flood Control District began a multi-year initiative called the Tropical Storm Allison Recovery Project (TSARP) that comprehensively assessed the flood risks associated with the major flooding sources within Harris County.

> Tropical Storm Allison "Off the Charts" Report (English) PDF
> Tropical Storm Allison "Off the Charts" Report (Spanish) PDF


FEMA and the Flood Control District have worked closely together in the past to identify major flooding sources and associated flood risks within Harris County, but never on such a scale.

For TSARP, both agencies used innovative scientific techniques to determine the current flood risks posed by bayous and creeks throughout the county's approximate 1,700 square mile area, including 22 major watersheds and 35 communities. The information developed as a result of TSARP has been provided to the public, government officials and numerous other Harris County stakeholders, so that they can make informed, scientifically-based flood management decisions about the places in which they work and reside.

Better Tools for Drainage and Flood Damage Reduction Planning

Each of Harris County's 35 communities is responsible for planning and regulating land development projects within its municipal boundaries. TSARP has provided access to more accurate flood risk information, and it allows community planners and engineers to make decisions based on up-to-date technology and conditions. This is critically important as the population of Harris County continues to grow and land development projects are considered, planned and constructed. In addition, the District has been able to use the TSARP products as new tools for planning and design of new flood damage reduction projects within Harris County.

Comprehensive Remapping of Harris County's Floodplains

FEMA's Flood Insurance Rate Map, commonly referred to as a FIRM or a floodplain map, shows which areas of the county are at a higher risk of flooding than others.

Periods of heavy rain regularly occur in Harris County, an area historically prone to flooding. As a result, it is very important that citizens possess the best possible knowledge of their flooding risks for their homes and businesses. The Flood Control District and FEMA believe that the citizens of Harris County want to and should know what these risks are so that they can plan accordingly.

During the late 1970s and early 1980s, the first comprehensive effort was undertaken to map the floodplains for major flooding sources in Harris County. Since that time, updates for particular areas have occurred to reflect changes in conditions resulting from things such as land development and the completion of flood damage reduction projects. These map updates were made with reference to the original data from the first comprehensive effort.

As a result of TSARP, not only were Harris County's floodplains entirely remapped, but brand new and more accurate data and computer models were created using important advances in science and technology.

The Science Behind TSARP

TSARP was a massive undertaking involving extensive use of a sophisticated laser technology called Light Detection and Ranging, commonly referred to as LiDAR, to map the ground's topography.

Developed by NASA, this laser technology has already been successfully employed by FEMA on other important projects, including recovery efforts at Ground Zero after the 9-11 attacks.

The use of LiDAR for the Tropical Storm Allison Recovery Project involved directing millions of laser beams toward the ground from low-flying aircraft, and measuring the time it took for that light to bounce off the earth and back to the recording equipment on the plane. The measurable differences in the laser's bounce time represent different heights, or the relief, of the land.

The information generated by this laser technology, along with many other parameters, was used in computer models to estimate flood elevations. Flood elevations were then mapped on base topographic maps, also produced from the laser technology. This information became the basis of the new FEMA Flood Insurance Rate Map for Harris County.

The Impact of the FEMA Flood Insurance Rate Map

FEMA's National Flood Insurance Program (NFIP) – of which every community in Harris County is a member – underwrites flood insurance for the entire nation. FEMA uses Flood Insurance Rate maps (FIRMs or floodplain maps) to help determine flood risk zones and associated rates for flood insurance policies.

For many, the new FEMA Flood Insurance Rate Map for Harris County had little or no impact on their flood zone designation and associated policy rate, and for some, their status actually improved. However, there were instances in which the maps showed new boundaries that required a homeowner to purchase flood insurance for the first time.

FEMA and the NFIP were mindful that such changes would be unwelcome. For that reason, the NFIP created a "Grandfather Rule" that allowed alternative rating rules for certain structures. Contact an insurance agent for more information.