Natural Hazards | FLOODS

Austin is "Flash-Flood Alley"

Flooding is the most serious hazard for the Austin area and is a threat across the entire city year-round. A common myth is that flooding only occurs in creek or river floodplains. Many do not realize that flooding can occur anywhere in Austin.

75% of Greater Austin Area flood fatalities are automobile related!

Never drive around a barricade. Two feet of water will carry away most automobiles and SUVs. As little as six inches of moving water can be dangerous.

The combination of these factors cause the large, violent storms here in “Flash Flood Alley”:

• Big sources of moisture from both the Gulf of Mexico and the Pacific Ocean;
• The jet stream that crosses the state from the Rocky Mountains;
• Closeness to the unstable West Texas “dry line” separating the dry desert air from the moist Gulf air;
• An uplift created along the Balcones Escarpment that runs across Central Texas;
• Storms northwest of us on the Edwards Plateau send flood waters downstream into Austin area creeks and rivers.
• Limestone and thin soils do not absorb much rain water.
• Violent weather creates cell storms that release heavy rains in any size area from a small neighborhood to a whole region. When a cell storm pours, it causes instant “flash flooding”, making it almost impossible to predict in advance where flooding will occur.

Creeks
Urban and rural creeks run through all areas of Austin creating the beautiful greenbelt and parks system. Unfortunately, this means we live in and near their floodplains. A floodplain is the land area these bodies of water will spill over into when it rains heavily. We can’t control a floodplain-- nature wins eventually.

Colorado River
The Colorado River bisects the city, and a series of dams provides us with the Highland Lakes and Town Lake for recreation, drinking water and power. As with creeks, many people have built in the floodplain of the river. The dams along the river do not prevent flooding, but can help reduce the intensity of the flow of floodwaters. The Colorado River crosses the entire state of Texas, so flooding in any area of the river’s watershed may affect Austin as well as many communities upstream and downstream of us. The Lower Colorado River Authority (LCRA) regulates the dams in the Austin area.

Urban Flooding
Developed areas cannot absorb as much rainfall as a natural area. Water runoff in urban areas is faster and there is much more of it, creating very dangerous conditions for people, especially drivers. Also, drainage systems can be overwhelmed, causing flooding in areas outside of floodplains.

Hurricanes & Tropical Storms
Even deep in the heart of Texas, we are vulnerable to the effects of a dying hurricane or tropical storm traveling inland.

Before a Flood
To prepare for a flood, you should:

• Avoid building in a floodplain unless you elevate and reinforce your home.
• Elevate the furnace, water heater, and electric panel if susceptible to flooding.
• Install "check valves" in sewer traps to prevent flood water from backing up into the drains of your home.
• Construct barriers (levees, beams, floodwalls) to stop floodwater from entering the building.
• Seal walls in basements with waterproofing compounds to avoid seepage.

During a Flood
If a flood is likely in your area, you should:

• Listen to the radio or television for information.
• Be aware that flash flooding can occur. If there is any possibility of a flash flood, move immediately to higher ground. Do not wait for instructions to move.
• Be aware of streams, drainage channels, canyons, and other areas known to flood suddenly. Flash floods can occur in these areas with or without such typical warnings as rain clouds or heavy rain.

If you must prepare to evacuate, you should do the following:

• Secure your home. If you have time, bring in outdoor furniture.
• Move essential items to an upper floor.
• Turn off utilities at the main switches or valves if instructed to do so. Disconnect electrical appliances.
• Do not touch electrical equipment if you are wet or standing in water.

If you have to leave your home, remember these evacuation tips:

• Do not walk through moving water. Six inches of moving water can make you fall.
• If you have to walk in water, walk where the water is not moving.
• Use a stick to check the firmness of the ground in front of you.
• Do not drive into flooded areas. If floodwaters rise around your car, abandon the car and move to higher ground if you can do so safely. You and the vehicle can be quickly swept away.

Driving Flood Facts
The following are important points to remember when driving in flood conditions:

• Six inches of water will reach the bottom of most passenger cars causing loss of control and possible stalling.
• A foot of water will float many vehicles.
• Two feet of rushing water can carry away most vehicles including sport utility vehicles (SUV’s) and pick-ups.

After a Flood
The following are guidelines for the period following a flood:

• Listen for news reports to learn whether the community’s water supply is safe to drink.
• Avoid floodwaters; water may be contaminated by oil, gasoline, or raw sewage. Water may also be electrically charged from underground or downed power lines.
• Avoid moving water.
• Be aware of areas where floodwaters have receded. Roads may have weakened and could collapse under the weight of a car.
• Stay away from downed power lines, and report them to the power company.
• Return home only when authorities indicate it is safe.
• Stay out of any building if it is surrounded by floodwaters.
• Use extreme caution when entering buildings; there may be hidden damage, particularly in foundations.
• Service damaged septic tanks, cesspools, pits, and leaching systems as soon as possible. Damaged sewage systems are serious health hazards.
• Clean and disinfect everything that got wet. Mud left from floodwater can contain sewage and chemicals.