Nearly 16,000 structures sit in the path of a large flood on the lower Colorado River, from Lake Buchanan through Matagorda County. The source of this figure — an interim flood study report by the U.S. Army Corps of Engineers — shows that the number of structures and the risk of flood damages along the lower Colorado River are greater than previously thought. The report provides the first definitive count of higher risk structures along the river and lakes. The Army Corps of Engineers and its partners, LCRA and the Texas Colorado River Floodplain Coalition, will use this information to help evaluate alternatives for reducing the risk or magnitude of flood damages. The coalition is an organization of 45 cities and counties in the lower Colorado River basin formed in 2001 to address flood issues. This fact sheet reports on the results of the flood study so far.

What is the source and purpose of gathering this information?
This piece of information builds on earlier flood-risk findings that relate to the Army Corps of Engineers Lower Colorado River Basin Feasibility Study. The Army Corps of Engineers, LCRA and the floodplain coalition are cooperating on the flood study with two goals in view: (1) improving their knowledge of flooding in the basin and (2) identifying ways to reduce property damage and loss of life during major floods. The three study partners, along with the Federal Emergency Management Agency (FEMA), each may play a vital role in achieving these goals.

The survey of structures is the second substantive report from the study. The first report was released in April 2002, showing that Lake Travis' 100-year flood level is 6 feet higher than the official figure adopted in the 1970s. Based on that dramatic difference, the partners expanded the study to look more closely at flood damage reduction alternatives that could address the projected rise in the 100-year flood elevation.

How many structures lie in the path of large floods on the Colorado River?
There are 15,774 structures at risk along the Colorado River from a 100-year flood, and another 13,346 would be at risk from a 500-year flood. The study team based the results on a mapping survey and appraisal district data covering the area along the river from Lake Buchanan through Matagorda County. For information on 100-year and 500-year floods, see water glossary.

What types of structures does this represent? What is their value?
The structures include homes and outbuildings on the ground — not docks, boathouses or other structures built on the water. In the next phase, the Army Corps of Engineers will evaluate the monetary value of the structures and other potential economic and environmental damages. The next report is scheduled for release in late December.

What makes this information new?
For most of the Colorado River downstream of Austin, this is the first comprehensive survey of structures at risk of flooding. The number of structures, particularly from Bastrop County to Matagorda County, was unknown prior to the study. The survey indicates that a 100-year flood would affect about 8,500 structures downstream of Mansfield Dam.

On Lake Travis, the flood study indicates that a 100-year flood would reach a level 6 feet higher than previously thought — 722 feet above mean sea level (msl) instead of 716 feet above msl. Thus, a 100-year flood would affect about 700 more structures than previously thought — 2,698 structures instead of 2,025.

How will the study partners respond to the new information about damage risks?
The study partners intend to evaluate a number of alternatives for reducing the risk or magnitude of flood damages. The possible responses identified so far include:

• Take no action.
• Raise floodplain levels and make insurance available. This requires action by FEMA in cooperation with individual communities.
• Buy and remove structures from the floodplains to reduce the potential for damages.
• Modify Mansfield Dam operating rules for releasing floodwaters. This requires action by the Army Corps of Engineers.
• Construct one or two new reservoirs upstream of Mansfield Dam
• Combine one or more of the alternatives.

The Army Corps of Engineers will examine the consequences of each alternative, including the economic and environmental costs and benefits. The Army Corps of Engineers will split the study costs with local partners, which may include LCRA and communities in the basin through the Texas Colorado River Floodplain Coalition. The local partners also will help the Corps of Engineers choose the most effective and practical courses of action and share the costs of any projects they choose to pursue.

In addition to basinwide flooding issues, individual communities have issues specific to their regions. The Army Corps of Engineers and LCRA will work with these communities, such as Wharton, Travis County and the City of Austin, on studies to address their particular flood issues. The results of all the studies will provide valuable and relevant information in the search for the most effective and practical ways to manage floods.

How long will it take to choose and carry out a course of action?
It will take at least two to three years to assess the costs and benefits of the alternatives. After deciding on a course of action, the partners will need additional time to obtain congressional approval and federal funding for any projects that the solution may involve, and to make any changes involving the Army Corps of Engineers, FEMA or other federal agencies.

Although the risk to life and property and rapid urbanization make quick action vital, determining the best course of action will take time and careful consideration. Each alternative could present substantial and conflicting consequences for basin residents, depending on where they live, that would need to be addressed.

Does this study affect my flood insurance or building requirements?
No. The study itself does not change the officially designated 100-year floodplain on FEMA's flood insurance rate maps or local floodplain building ordinances. However, flood officials strongly recommend that property owners take the study results into account when making decisions about structural elevation and flood insurance coverage. You should contact your local floodplain administrator to determine whether a particular property is in the 100-year floodplain and to discuss flood protection options. Information on how to contact your local floodplain administrator can be found on the Web site of the Texas Colorado River Floodplain Coalition.

Should one of the flood damage reduction implementation measures include raising the officially designated 100-year floodplain based on the study, there may be flood insurance rate benefits to property owners in the newly designated floodplain who had obtained and maintained flood insurance prior to the change. In addition, there would be a lower risk of flood damage to new structures that had been built above the new, higher flood elevation. For more information about FEMA flood insurance regulations, contact Carl Watts at the FEMA Region VI office, (940) 898-5128, or Diana Herrera with FEMA's National Flood Insurance Program, (281) 829-6880.

Whom should I contact for more information about the study?
Contact Mark Jordan at LCRA about the Lower Colorado River Basin Feasibility Study. In the Austin area, call LCRA at 473-3200. Outside Austin, call toll-free (800) 776-5272.