The Flood Education Mapping Tool was initially developed as a mapping tool for the Tropical Storm Allison Recovery Project (TSARP), which was launched shortly after Tropical Storm Allison struck Harris County in June 2001. Its purpose was to serve as a tool for Harris County residents to learn the location of their properties in relation to mapped 1 percent (100-year), 0.2 percent (500-year) and coastal floodplains. The Flood Education Mapping Tool includes regularly-updated floodplain information from the Federal Emergency Management Agency’s Flood Insurance Rate Map (FIRM or floodplain map) for Harris County, interactive legend options, a simple map display and easy map navigation. While the floodplains shown on the Flood Education Mapping Tool are the floodplains delineated on the FIRM for Harris County, the Flood Education Mapping Tool is not the effective FIRM.



The Tropical Storm Allison Recovery Project (TSARP)

In the aftermath of Tropical Storm Allison in 2001, the Federal Emergency Management Agency (FEMA) and the Harris County Flood Control District launched a multi-year, joint initiative: the Tropical Storm Allison Recovery Project (TSARP). TSARP was an unprecedented effort to produce a new Flood Insurance Rate Map (FIRM or floodplain map) for Harris County and its 22 watersheds.


In September 2001, FEMA and the Flood Control District embarked on the $32 million effort using newly-developed technology from NASA called Light Detection and Ranging (LiDAR). A specially-equipped aircraft flew over Harris County projecting millions of laser signals onto the ground and measuring the reflected signals. This process generated highly-detailed ground elevation data, which, when combined with field surveys of bayous and creeks, led to the development of new hydrologic and hydraulic models that resulted in unprecedented detailed boundaries of the mapped 1 percent (100-year), 0.2 percent (500-year) and coastal floodplains of Harris County.


Harris County’s new FIRM was officially adopted by the city of Houston, unincorporated Harris County and the 33 other municipalities of Harris County on June 18, 2007. The FIRM is used by the National Flood Insurance Program to set flood insurance rates and by local government entities to assist in floodplain management and in the regulation of land development. The Flood Control District also uses the FIRM to help assess the need for capital improvement projects.



Tropical Storm Allison

When Tropical Storm Allison suddenly formed 80 miles off the coast of Galveston, Texas, on Tuesday, June 5, 2001, 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 this extraordinary storm that, before leaving Texas, would dump as much as 80 percent of the area's average annual rainfall over some Houston and Harris County neighborhoods, simultaneously affecting more than 2 million people. When the local rains finally eased, Allison had left Harris County with 22 fatalities, 95,000 damaged automobiles and trucks, 73,000 damaged residences, 30,000 residents in shelters, and more than $5 billion in property damage in its wake.


One thing everyone in our area realized, without qualification, is that it does not take a "perfect storm" to produce a perfect flood maker. Allison’s slow and erratic progress – first moving inland to the north, then meandering back to the Gulf of Mexico – combined for a horrific one-two punch that dealt many localities in the Houston region a critical blow. After flooding about 1,000 residences during its initial pass through the area June 5-7, Allison returned June 8-9 to deliver its knockout shot. At one point during this second pass, 28 inches of rain fell during a 12-hour period just northeast of downtown Houston. Such incredibly intense cloudbursts over heavily populated areas set Allison apart from every storm to hit Texas in the past century.


Originally a mere "disturbance" passing through the Yucatan Peninsula into the Gulf of Mexico, Tropical Storm Allison formed Tuesday, June 5 – 80 miles off the Southeast Texas coastline. That night, it made landfall west of Galveston, with sustained winds of 48 miles per hour. Hovering over Harris County initially for four hours, it dumped as many as 12 inches of rain and flooded some 800 residences as it drifted slowly to the north. During the next day, Allison continued its inland track and eventually reached Lufkin on the morning of Thursday, June 7 where it appeared to weaken and stall. Even then, when the storm seemed to be moving away from Harris County, it still produced enough rainfall locally on June 7 to flood an additional 200 area residences.


Unexpectedly, Allison looped back to the southwest – drawing new moisture off the Gulf and re-intensifying. The storm's previous heavy rains had saturated the ground and caused immediate, excessive runoff when Allison returned to deliver the knockout punch the evening of Friday, June 8 and morning of Saturday, June 9. Friday night, as many as 28 inches of rain fell in parts of Harris County – flooding thousands of residences, stranding thousands of cars on hundreds of roads, and prompting Texas Governor Rick Perry and then U.S. President George W. Bush to declare Harris County a disaster area. On Saturday, June 9, alone, units of the U. S. Coast Guard, the Texas National Guard, and local emergency agencies rescued nearly 7,000 people. In addition to these documented rescues, individual citizens acting on their own rescued thousands of other flood victims. On the evening of Monday, June 11, some 30,000 Houston area residents sought refuge in 51 shelters countywide.


Leaving Texas, Allison produced rainfall amounts ranging from 20 to nearly 30 inches over parts of southeastern Louisiana. The storm also brought heavy rains across the northern Gulf Coast, with amounts of 10-to-12 inches from Gulfport, Mississippi to Tallahassee, Florida. Areas of North Carolina received as many as 21 inches of rain while southeastern Pennsylvania recorded amounts of 8-to-10 inches – capping nearly two weeks of devastation.


There is no precise way to count the loss, hurt and plain frustration Harris County residents experienced as a result of Tropical Storm Allison. There is no accurate way to measure the 22 lives the storm claimed, the priceless possessions and precious mementos it ruined, and the subsequent worry and hardship it randomly cast upon so many families and business owners. Furthermore, there is no scientific method to calculate the sense of community loss from the dozens of neighborhoods Allison destroyed. Yet, to statistically place the damage Allison caused in Harris County into perspective, consider the following facts:


• Total damages directly associated with Tropical Storm Allison are estimated to be more than $5 billion in Harris County alone.


• Of the 73,000 flooded residences, some homes were completely destroyed, while more than 2,800 residences sustained what is termed as substantial damage, or damage that is 50 percent or greater than a structure's pre-flood value, not including land.


• Flooding in downtown Houston was responsible for tens of millions of dollars in damages to buildings, the tunnel system and related infrastructure, and parking garages – not to mention the displacement of many workers from their places of business and lost productivity.


• Four hospitals in the Texas Medical Center (TMC) were closed temporarily because of flooding and damage to electric service equipment. Although this flooding did not cause loss of life at the TMC, it certainly made situations difficult for affected patients and healthcare providers. Also, of the county’s two level-one trauma centers, one was closed while the other was at times unreachable because of the flooding.


• Approximately 95,000 vehicles sustained $450 million in damages in Harris County. The damages resulted from the flooding of vehicles at residences, in underground parking garages and along flooded roads and highways.


• State and local highway facilities sustained approximately $5.5 million in damages. Impassable highways and major roads paralyzed many parts of the city throughout Allison.


• About 200 Houston area schools and three major Houston college campuses sustained significant damages. Rice University and Texas Southern University experienced significant flood damages, while the University of Houston's main campus was especially hard hit. Of the University of Houston's 105 buildings, 90 sustained water damage – with 55 critically affected. The total damages to area schools was estimated at more than $250 million.


• Damages to Harris County’s facilities reached approximately $40.5 million, including the Criminal Justice Center, which faced repairs and flood proofing costs of $19.6 million. Eleven other county buildings were also damaged.


• The city of Houston spent more than $53 million to repair city-owned facilities and estimated its total damage figure to approach $80 million.



Flooding History in Harris County

Every part of the country must deal with the threat of natural disasters. For Harris County, an area that is prone to severe rainfall, is generally topographically flat and has impermeable clay soils, the No. 1 threat is flooding.


This area has flooded long before the Allen brothers founded the city of Houston in 1836. Written excerpts from early settlers have helped document this area’s flooding history: Jacob de Cordova, one of the early encyclopedists of Texas, wrote in 1858, “The principle objection to these lands is that in consequence of their extreme flatness they are often in the wet season covered with water.”


Francis Richard Lubbock, a former Texas governor, wrote in his 1900 book called Six Decades of Texas, “The surface of the entire region is very level and even, with a descent to the coast so gradual as to afford no drainage to the soils, and as a natural consequence, water remains in pools upon the prairies of the region until removed by evaporation.”


As the city of Houston's population grew, more property naturally became damaged by flooding. The flood of 1929 covered all bridges over Buffalo and White Oak bayous west and northwest of the city and put all homes in Alief under 4 feet of water.


The flood of 1935 covered two-thirds of Harris County with one day of rain. Buffalo Bayou overwhelmed an emergency sandbag levee and shut down Houston’s central water plant. White Oak Bayou overflowed its banks and left residents in the Heights stranded in their homes. This flood lasted four days, killed seven people and partially disabled the Houston Ship Channel for eight months.



Creation of the Harris County Flood Control District

These two floods prompted the Texas legislature to create the Harris County Flood Control District in 1937 to be a local partner for the U.S. Army Corps of Engineers so that local federal tax dollars could return and be used for local flood damage reduction projects.


The Flood Control District oversees 22 watersheds and approximately 1,500 bayous and creeks in Harris County. Simply speaking, the way our drainage system works is: stormwater travels through storm sewers and roadside ditches and flows into small tributaries and large tributaries, ultimately emptying into our bayous, which carry the water to the Houston Ship Channel and then to Galveston Bay.


The mission of the Flood Control District is to build flood damage reduction projects that work, with appropriate regard for community and natural values. Essentially, that means we build projects that reduce people’s flooding risks, and these projects include:


• Widening and deepening bayous and their tributaries,


• Excavating large, regional stormwater detention basins that hold millions of gallons of stormwater when water levels in the bayous threaten to overflow,


• Implementing voluntary home buyout programs to relocate families whose homes are located hopelessly deep in the floodplain and that repeatedly flood,


• Acquiring floodplain property adjacent to bayous and creeks for stormwater storage and for floodplain preservation, and


• Maintaining more than 2,500 miles (basically the distance from Los Angeles to New York City) of bayous and creeks in the county to keep erosion in check, maintain the unobstructed flow of stormwater and mow our right of way.




Major Projects

The Harris County Flood Control District’s largest projects are currently taking place on Brays, Sims and White Oak bayous and include the countywide Voluntary Home Buyout Program:


The roughly $500 million “Project Brays” is the largest undertaking ever by the Flood Control District in partnership of the U.S. Army Corps of Engineers. It consists of widening 21 miles of Brays Bayou, excavating four massive stormwater detention basins and replacing or modifying 32 bridges. When completed in 2017, Project Brays is expected to remove the mapped 1 percent (100-year) floodplain from an estimated 30,000 homes and businesses.


The $379 million Sims Bayou Federal Flood Damage Reduction Project consists of widening and deepening 19 miles of Sims Bayou and replacing or modifying 21 bridges. Led by the U.S. Army Corps of Engineers in partnership with the Flood Control District, this project is supplemented by three stormwater detention basins constructed using local funds. The project is expected to be complete in 2012. It is expected to remove the mapped 1 percent (100-year) floodplain from 35,000 homes and 2,000 businesses.


Furthermore, the Flood Control District has spent an approximately $75 million reducing flooding risks along White Oak Bayou by widening and deepening the bayou from Cole Creek (near Tidwell Road) to Beltway 8 and excavating 10 stormwater detention basins totaling roughly 1 billion gallons of stormwater storage. The District also has constructed the Jersey Village Channel, which allows roughly 30 percent of the water in White Oak Bayou to flow around the flood-prone city of Jersey Village during times of heavy rain. There are plans to continue widening and deepening White Oak Bayou from Beltway 8 upstream to F.M. 1960. Efforts are currently being made to qualify many of these projects built with local dollars as federal projects in order to leverage local funding.


Through its Voluntary Home Buyout Program, the Flood Control District has purchased approximately 3,000 homes, which were located hopelessly deep in the floodplain and repeatedly flooded. After helping homeowners move to higher ground, the District demolishes the flood-prone homes located along major bayous and creeks throughout Harris County. The land remains vacant and functions as a natural floodplain.


The Flood Control District also has ongoing capital projects taking place in the following watersheds: Brays Bayou, Sims Bayou, White Oak Bayou, Buffalo Bayou, Greens Bayou, Cypress Creek, Spring Creek, Armand Bayou, Halls Bayou, Hunting Bayou, Goose Creek, San Jacinto River, Mason Creek, Vince Bayou, Spring Gully, Cedar Bayou and the Addicks Reservoir.


Furthermore, the Flood Control District maintains more than 2,500 miles (basically the distance from Los Angeles to New York) of bayous and creeks in the county, keeping erosion in check, maintaining the unobstructed flow of stormwater and mowing right of way.