Contents Section 10: Tornadoes Why Tornadoes Are a Threat...10-1 Hazard Profile...10-4 History of Tornadoes and Windstorms...10-5 People and Property at Risk...10-15 Potential Damages and Losses...10-17 Why Tornadoes Are a Threat Tornadoes are unquestionably the most violent storms on the planet. A tornado is a violently rotating column of air extending between, and in contact with, a cloud and the surface of the earth. The most violent tornadoes are capable of tremendous destruction with wind speeds of 250 miles per hour or more. In extreme cases, winds may approach 300 miles per hour. Damage paths can be in excess of one mile wide and 50 miles long. The most powerful tornadoes are spawned by super-cell thunderstorms. These storms are affected by horizontal wind shears (winds moving in different directions at different altitudes) that begin to rotate the storm. This horizontal rotation can be tilted vertically by violent updrafts, and the rotation radius can shrink, forming a vertical column of very quickly swirling air. This rotating air can eventually reach the ground, forming a tornado. Creating a Disaster-Resistant Lower Colorado River Basin Page 10-1
Table 10-1. Fujita Tornado Scale F-Scale Number Intensity Wind Speed (mph) F0 Gale tornado 40-72 F1 Moderate tornado 73-112 F2 Significant tornado 113-157 F3 Severe tornado 158-206 F4 Devastating tornado 207-260 F5 Incredible tornado 261-318 Type of Damage Done Some damage to chimneys; breaks branches off trees; pushes over shallow-rooted trees; damages sign boards. The lower limit is the beginning of hurricane wind speed; peels surface off roofs; mobile homes pushed off foundations or overturned; moving autos pushed off roads; attached garages may be destroyed. Considerable damage. Roofs torn off frame houses; mobile homes demolished; boxcars pushed over; large trees snapped or uprooted; light object missiles generated. Roof and some walls torn off well constructed houses; trains overturned; most trees in forest uprooted. Well-constructed homes leveled; structures with weak foundations blown off some distance; cars thrown and large missiles generated. Strong frame houses lifted off foundations and carried considerable distances to disintegrate; automobile sized missiles flying through the air in excess of 100 meters; trees debarked; steel reinforced concrete badly damaged. The Lower Colorado River Basin is known for frequent severe weather and thunderstorms. Thunderstorms form when warm, moist air collides with cooler, drier air. Since these masses tend to come together during the transition from summer to winter, most thunderstorms occur during the spring and fall months. Severe thunderstorms can produce tornadoes, high winds, and hail any of which can cause extensive property damage and loss of life. Tornadoes occasionally accompany tropical storms and hurricanes that move over land. Tornadoes are the most common to the right and ahead of the path of the storm center as it comes ashore. Tornadoes vary in terms of duration, wind speed and the toll that they take, as shown in Table 10-2. Page 10-2 Creating a Disaster-Resistant Lower Colorado River Basin
Table 10-2. Variations Among Tornadoes Weak Tornadoes Strong Tornadoes Violent Tornadoes 69% of all tornadoes Less than 5% of tornado deaths Lifetime 1-10+ minutes Winds less than 110 mph 29% of all tornadoes Nearly 30% of all tornado deaths May last 20 minutes or longer Winds 110 205 mph 2% of all tornadoes 70% of all tornado deaths Lifetime can exceed one hour Winds greater than 205 mph Creating a Disaster-Resistant Lower Colorado River Basin Page 10-3
Hazard Profile The impact of tornadoes can be substantial. They can cause multiple deaths, completely shut down facilities for thirty days or more, and cause more than fifty percent of affected properties to be destroyed or suffer major damage. Figure 10-1. Tornado and Windstorm Hazard Profile Summary Based on historical events, it is expected that there will be 20-40 tornadoes in the Lower Colorado River Basin every five years. Seasonal patterns are relevant to tornadoes. Thunderstorms form when warm, moist air collides with cooler, drier air. Since these masses tend to come together during the transition from summer to winter, most thunderstorms and resulting tornadoes occur during the spring (April, May and June) and fall (October, November, and December). Warning time for tornadoes is minimal. Page 10-4 Creating a Disaster-Resistant Lower Colorado River Basin
History of Tornadoes and Windstorms Historical evidence, as reflected in Figure 10-2, shows that most of the Lower Colorado River Basin is vulnerable to tornadic activity. There is no defined hazard boundary for tornadoes. Figure 10-2. Historical Tornado Events (NOAA Data 1950-2002) Brown Mills San Saba Lampasas Burnet Mason Llano Williamson Blanco Travis Bastrop Fayette Colorado Historical Tornadoes [Fujita Intensity Scale] FO F1 F2 F3 F4 F5 Wharton Matagorda 0 30 60 miles Table 10-6 identifies reported tornado events in the Lower Colorado River Basin, by County. Creating a Disaster-Resistant Lower Colorado River Basin Page 10-5
Table 10-3. History of Tornado Events in the Lower Colorado River Basin, by County Event Year Date Fujita Injuries Deaths Lower Basin COLORADO COUNTY Tornado 1954 6 Jul F2 0 0 Colorado Tornado 1955 5 Jun F2 0 0 Colorado Tornado 1958 7 Jul 0 0 Colorado Tornado 1962 8 Sep F1 0 0 Colorado Tornado 1964 4 Feb F2 0 1 Colorado Tornado 1966 28 Mar F3 0 0 Colorado Tornado 1967 14 May F0 0 0 Colorado Tornado 1967 19 Sep 0 0 Colorado Tornado 1967 20 Sep 0 0 Colorado Tornado 1967 21 Sep F2 0 0 Colorado Tornado 1970 1 Sep F1 0 0 Colorado Tornado 1971 25 Feb F2 0 0 Colorado Tornado 1973 13 Jun F0 0 0 Colorado Tornado 1988 29 Apr F0 0 0 Colorado Tornado 1991 14 Jan F1 11 1 Colorado Tornado 1991 18 Jan F1 0 0 Colorado Tornado 1994 13 May F0 0 0 Colorado Tornado 1995 12 Jan F0 0 0 Near Eagle Lake Tornado 1995 13 Mar F0 0 0 Bernardo Tornado 1995 13 Mar F0 0 0 Washington Tornado 1997 21 May F0 0 0 Sheridan Tornado 1999 29 Aug F0 0 0 Eagle Lake Tornado 2000 12 Nov F0 0 0 Borden Funnel cloud 2000 12 Nov 0 0 Columbus Funnel cloud 2000 12 Nov 0 0 Sheridan MATAGORDA COUNTY Tornado 1954 15 Apr F1 0 0 Matagorda Tornado 1955 18 May F2 0 0 Matagorda Tornado 1956 1 Nov F0 0 0 Matagorda Tornado 1957 31 Mar F1 0 0 Matagorda Tornado 1959 29 Sep F0 0 0 Matagorda Page 10-6 Creating a Disaster-Resistant Lower Colorado River Basin
Event Year Date Fujita Injuries Deaths Tornado 1961 11 Sep F2 0 0 Matagorda Tornado 1962 17 Sep F1 0 0 Matagorda Tornado 1964 18 Jul F0 0 0 Matagorda Tornado 1967 20 Sep F3 4 7 Matagorda Tornado 1969 11 Apr F3 0 13 Matagorda Tornado 1969 15 May F0 0 0 Matagorda Tornado 1970 11 Oct F1 0 0 Matagorda Tornado 1972 20 Mar F1 0 0 Matagorda Tornado 1975 25 Jun F0 0 0 Matagorda Tornado 1975 3 Aug F0 0 0 Matagorda Tornado 1976 26 Sep F1 0 0 Matagorda Tornado 1977 16 Apr F0 0 0 Matagorda Tornado 1977 10 Sep 0 0 Matagorda Tornado 1981 31 May F1 0 0 Matagorda Tornado 1984 31 Dec F1 0 0 Matagorda Tornado 1991 14 Jan F0 0 0 Matagorda Tornado 1991 18 Jan F0 0 0 Matagorda Tornado 1992 17 Apr F1 0 0 Matagorda Tornado 1994 30 May F0 0 0 Dayton Tornado 1995 17 Dec F0 0 0 Collegeport Tornado 1995 17 Dec F0 0 0 Blessing Tornado 1995 17 Dec F0 0 0 Markham Tornado 1998 10 Sep F0 5 0 Sargent Funnel cloud 2000 28 May 0 0 Sargent Funnel cloud 2001 13 May 0 0 Palacios Tornado 2001 25 May F0 0 0 Matagorda Tornado 2002 6 Sep F0 0 0 Van Vleck WHARTON COUNTY Tornado 1953 2 Dec F2 0 0 Wharton Tornado 1955 23 May F2 0 0 Wharton Tornado 1955 30 Aug F1 0 5 Wharton Tornado 1959 21 Aug F0 0 0 Wharton Tornado 1960 24 Jun F1 0 0 Wharton Tornado 1961 22 Nov F3 0 1 Wharton Tornado 1964 15 Jun F2 0 0 Wharton Tornado 1966 14 Apr F2 0 0 Wharton Tornado 1967 19 Sep F0 0 0 Wharton Creating a Disaster-Resistant Lower Colorado River Basin Page 10-7
Event Year Date Fujita Injuries Deaths Tornado 1967 20 Sep F1 1 4 Wharton Tornado 1967 21 Sep 0 0 Wharton Tornado 1968 23 Jun F1 0 0 Wharton Tornado 1970 23 Oct F2 0 0 Wharton Tornado 1972 20 Mar F2 0 0 Wharton Tornado 1973 13 Jun F1 0 0 Wharton Tornado 1976 14 Jul 0 0 Wharton Tornado 1977 8 Nov F1 0 0 Wharton Tornado 1977 13 Dec F1 0 1 Wharton Tornado 1978 22 Apr F1 0 0 Wharton Tornado 1979 20 Jan F1 0 0 Wharton Tornado 1983 31 Jan F1 0 0 Wharton Tornado 1983 18 Aug F0 0 0 Wharton Tornado 1991 14 Jan F1 0 0 Wharton Tornado 1991 4 May F1 0 0 Wharton Tornado 1991 7 Aug F0 0 0 Wharton Tornado 1992 19 Nov F1 0 0 Wharton Tornado 1992 21 Nov F1 0 0 Wharton Tornado 1993 7 Apr F2 0 0 Egypt Tornado 1995 13 Mar F1 0 0 Egypt Tornado 1996 12 Aug F0 0 0 El Campo Tornado 1997 11 Apr F0 0 0 Wharton Tornado 1997 21 Jun F0 0 0 El Campo Funnel cloud 2000 21 Oct 0 0 Mustang Funnel cloud 2001 31 May 0 0 Hillje Funnel cloud 2001 2 Sep 0 0 El Campo Funnel cloud 2001 4 Sep 0 0 El Campo Tornado 2002 30 Mar F0 0 0 Hungerford Tornado 2002 30 Mar F0 0 0 Wharton Tornado 2002 7 Sep F0 0 0 Boling Middle Basin Event Year Date Fujita Injuries Deaths BASTROP COUNTY Tornado 1953 28 Apr F3 0 3 Bastrop Tornado 1954 19 May F 0 0 Bastrop Page 10-8 Creating a Disaster-Resistant Lower Colorado River Basin
Event Year Date Fujita Injuries Deaths Tornado 1957 24 Apr F3 0 1 Bastrop Tornado 1957 26 Apr F 0 0 Bastrop Tornado 1962 5 Sep F0 0 0 Bastrop Tornado 1965 18 May F2 0 0 Bastrop Tornado 1970 23 Oct F0 0 0 Bastrop Tornado 1971 17 Nov F2 0 0 Bastrop Tornado 1974 20 Mar F1 0 0 Bastrop Tornado 1977 2 May F 0 0 Bastrop Tornado 1980 7 Apr F3 0 0 Bastrop Tornado 1980 10 Aug F2 0 0 Bastrop Tornado 1991 14 Jan F2 0 0 Bastrop Tornado 1991 17 Apr F0 0 0 Bastrop Tornado 1991 28 Apr F0 0 0 Bastrop Tornado 1994 13 May F0 0 0 Bastrop Tornado 1998 17 Oct F1 0 0 Elgin Tornado 2000 12 Nov F0 0 0 Rosanky Tornado 2000 12 Nov F0 0 0 Elgin FAYETTE COUNTY Tornado 1954 14 Apr F1 0 0 Fayette Tornado 1954 30 Apr F2 0 0 Fayette Tornado 1959 3 Jun F1 0 0 Fayette Tornado 1960 18 Oct F1 0 2 Fayette Tornado 1965 21 Jan F2 0 0 Fayette Tornado 1967 20 Sep 0 0 Fayette Tornado 1967 21 Sep F1 0 0 Fayette Tornado 1967 22 Sep F 0 0 Fayette Tornado 1970 15 May F1 0 0 Fayette Tornado 1971 25 Feb F2 0 0 Fayette Tornado 1971 22 Nov F1 0 0 Fayette Tornado 1973 6 Jul F0 0 0 Fayette Tornado 1973 11 Oct F2 0 1 Fayette Tornado 1974 1 Jun F0 0 0 Fayette Tornado 1975 29 Apr F1 0 0 Fayette Tornado 1988 17 Sep F0 0 0 Fayette Tornado 1991 17 Apr F0 1 0 Fayette Tornado 1995 13 Mar F0 0 0 La Grange Funnel cloud 1998 11 Jan N/A 0 0 Holman Creating a Disaster-Resistant Lower Colorado River Basin Page 10-9
Event Year Date Fujita Injuries Deaths Funnel cloud 1998 5 Jun N/A 0 0 Flatonia Tornado 1998 5 Jun F1 0 0 Engle Tornado 2000 12 Nov F0 0 0 West Pt Tornado 2002 23 Dec F1 0 0 Ledbetter TRAVIS COUNTY Tornado 1953 23 Oct F1 0 0 Travis Tornado 1954 30 Apr F3 0 0 Travis Tornado 1956 20 Oct F1 0 0 Travis Tornado 1957 31 Mar F2 0 0 Travis Tornado 1957 31 Mar F1 0 0 Travis Tornado 1957 22 Apr F 0 0 Travis Tornado 1957 24 Apr F0 0 0 Travis Tornado 1959 10 May F3 0 0 Travis Tornado 1960 20 Jul F1 0 0 Travis Tornado 1964 16 Apr F0 0 0 Travis Tornado 1965 17 May F1 0 0 Travis Tornado 1965 18 May F0 0 0 Travis Tornado 1967 20 Sep F1 0 1 Travis Tornado 1970 4 Jul F2 1 4 Travis Tornado 1972 3 Aug F0 0 0 Travis Tornado 1973 20 Jan F2 0 0 Travis Tornado 1973 6 Mar F1 0 0 Travis Tornado 1973 10 Mar F1 0 2 Travis Tornado 1974 9 May F1 0 10 Travis Tornado 1975 5 May F0 0 0 Travis Tornado 1975 7 May F2 0 0 Travis Tornado 1975 23 May F0 0 0 Travis Tornado 1975 29 May F1 0 0 Travis Tornado 1976 5 Mar F0 0 0 Travis Tornado 1976 30 Mar F0 0 8 Travis Tornado 1976 12 May F1 0 0 Travis Tornado 1977 14 Apr F2 0 0 Travis Tornado 1977 2 May F 0 0 Travis Tornado 1979 1 May F0 0 0 Travis Tornado 1980 Feb 29 F1 0 0 Travis Tornado 1980 7 Apr F3 0 3 Travis Tornado 1980 10 Aug F2 0 4 Travis Page 10-10 Creating a Disaster-Resistant Lower Colorado River Basin
Event Year Date Fujita Injuries Deaths Tornado 1981 16 May F1 0 0 Travis Tornado 1981 13 Jun F1 0 0 Travis Tornado 1982 22 Jun F0 0 0 Travis Tornado 1983 18 May F1 0 0 Travis Tornado 1996 20 Sep F1 0 0 Lago Vista Tornado 1997 27 May F2 0 0 Four Pts Tornado 1997 27 May F4 5 1 Lakeway Tornado 1998 29 Aug F1 0 0 Lake Travis Funnel cloud 1999 13 Jul N/A 0 0 Lago Vista Tornado 2000 16 Mar F0 0 0 Bergstrom AFB Tornado 2000 16 Mar F0 0 0 Pflugerville Tornado 2001 15 Nov F1 0 0 Bergstrom AFB Tornado 2001 15 Nov F0 0 0 Pflugerville Tornado 2002 23 Dec F1 0 0 Near Manor WILLIAMSON COUNTY Tornado 1954 30 Apr F3 0 6 Williamson Tornado 1955 5 Jun F1 0 0 Williamson Tornado 1956 4 Sep F2 0 0 Williamson Tornado 1957 24 Apr F3 0 0 Williamson Tornado 1958 2 May F1 0 0 Williamson Tornado 1961 29 Jun F1 0 0 Williamson Tornado 1963 10 Mar F1 0 0 Williamson Tornado 1964 26 Apr F2 0 0 Williamson Tornado 1966 18 May F2 0 0 Williamson Tornado 1967 4 Sep F0 0 0 Williamson Tornado 1968 8 Apr F0 0 0 Williamson Tornado 1972 27 Apr F0 0 0 Williamson Tornado 1972 24 May F1 0 0 Williamson Tornado 1972 21 Oct F1 0 0 Williamson Tornado 1974 30 Oct F2 0 0 Williamson Tornado 1975 7 May F1 0 0 Williamson Tornado 1977 14 Apr F2 0 0 Williamson Tornado 1978 28 Jul F2 0 0 Williamson Tornado 1980 Feb 29 F1 0 0 Williamson Tornado 1980 7 Apr F3 1 2 Williamson Tornado 1980 10 Aug F0 0 0 Williamson Tornado 1981 10 Feb F2 0 0 Williamson Creating a Disaster-Resistant Lower Colorado River Basin Page 10-11
Event Year Date Fujita Injuries Deaths Tornado 1981 16 May F1 0 4 Williamson Tornado 1982 20 Apr F1 0 0 Williamson Tornado 1983 18 May F1 0 0 Williamson Tornado 1983 4 Jun F1 0 0 Williamson Tornado 1983 19 Sep F0 0 0 Williamson Tornado 1985 10 Dec F2 0 3 Williamson Tornado 1989 17 May F3 1 28 Williamson Tornado 1991 28 Apr F0 0 0 Williamson Tornado 1992 1 Jun F0 0 0 Williamson Tornado 1994 13 May F0 0 0 Georgetown Funnel cloud 1996 19 Sep N/A 0 0 Georgetown Tornado 1997 27 May F5 12 27 Jarrell Tornado 1997 27 May F3 15 0 Cedar Park Tornado 1998 4 Jul F1 0 0 Round Rock Funnel cloud 1999 13 Jul N/A 0 0 Granger Tornado 2000 16 Mar F2 0 0 Leander Tornado 2000 16 Mar F0 0 0 Georgetown Tornado 2001 15 Nov F0 0 0 Taylor Upper Basin BLANCO COUNTY Tornado 1969 6 May F3 0 2 Blanco Tornado 1972 23 Aug F0 0 0 Blanco Tornado 1973 1 Jun F0 0 0 Blanco Tornado 1976 23 May F1 0 0 Blanco Tornado 1976 31 May F1 0 0 Blanco Tornado 1980 10 Aug F2 0 0 Blanco Tornado 1982 20 Apr F1 0 0 Blanco Tornado 1995 19 Apr F0 0 0 E Stonewall Funnel cloud 2001 1 Jun 0 0 Round Mtn Tornado 2001 15 Nov F0 0 0 Blanco BROWN COUNTY Tornado 1955 4 Jun F2 0 0 Brown Tornado 1958 21 Jun F1 0 0 Brown Tornado 1960 13 Oct F2 0 1 Brown Tornado 1964 24 Apr F1 0 0 Brown Tornado 1969 12 Jun F0 0 0 Brown Page 10-12 Creating a Disaster-Resistant Lower Colorado River Basin
Event Year Date Fujita Injuries Deaths Tornado 1970 26 Apr F1 0 1 Brown Tornado 1976 19 Apr F5 0 11 Brown Tornado 1979 20 Apr F1 0 0 Brown Tornado 1979 1 May F1 0 0 Brown Tornado 1979 30 Oct F1 0 0 Brown Tornado 1984 6 Jun F0 0 0 Brown Tornado 1986 17 Aug F1 0 0 Brown Tornado 1987 11 Aug F0 0 0 Brown Tornado 1988 2 Jun F1 0 0 Brown Tornado 1988 3 Jul F1 0 0 Brown Tornado 1989 10 Jun F1 0 0 Brown Tornado 1994 25 May F0 0 0 Early Tornado 1994 29 May F1 0 0 Lake Brownwood Tornado 1995 7 May F0 0 0 Grosvenor Tornado 1995 7 May F1 0 0 May Tornado 1996 29 May F0 0 0 Bangs Tornado 1997 9 May F1 0 0 Brownwood Tornado 1997 19 May F1 0 0 Owens BURNET COUNTY Tornado 1961 15 Jun F1 0 0 Burnet Tornado 1962 16 Aug F1 0 0 Burnet Tornado 1967 20 Sep F1 0 1 Burnet Tornado 1967 21 Sep 0 0 Burnet Tornado 1967 24 Sep 0 0 Burnet Tornado 1969 6 May F3 0 0 Burnet Tornado 1973 10 Mar F3 0 40 Burnet Tornado 1976 26 May F1 0 0 Burnet Tornado 1981 16 May F1 0 0 Burnet Tornado 1992 21 Sep F1 0 0 Burnet Tornado 1993 19 Oct F0 0 0 Spicewood Tornado 1994 13 May F3 0 1 Marble Falls Tornado 1995 28 Jun F1 0 0 Burnet Tornado 1996 20 Sep F0 0 0 Smithwick Tornado 1999 12 Mar F0 0 0 Marble Falls Tornado 2000 5 Nov F0 0 0 Burnet Creating a Disaster-Resistant Lower Colorado River Basin Page 10-13
Event Year Date Fujita Injuries Deaths LAMPASAS COUNTY Tornado 1956 1 May F1 0 0 Lampasas Tornado 1957 25 May F1 0 0 Lampasas Tornado 1968 18 Jan F1 0 0 Lampasas Tornado 1973 24 May F2 0 0 Lampasas Tornado 1976 5 May F1 0 0 Lampasas Tornado 1981 15 May F1 0 0 Lampasas Tornado 1993 18 Oct F0 0 0 Lampasas Tornado 1993 18 Oct F0 0 0 Lometa Tornado 1994 26 May F0 0 0 Kempner Tornado 2000 22 Feb F0 0 0 Lampasas LLANO COUNTY Tornado 1962 16 Aug F1 0 0 Llano Tornado 1976 23 May F1 0 0 Llano Tornado 1976 25 May 0 0 Llano Tornado 1978 26 Jul F1 0 0 Llano Tornado 1981 15 May F0 0 0 Llano Tornado 1981 13 Oct F1 0 0 Llano Funnel cloud 1997 25 Apr 0 0 Llano Tornado 2000 10 Mar F1 0 0 Llano Tornado 2000 10 Mar F0 0 0 Kingsland MASON COUNTY Tornado 1965 6 Jun F2 0 0 Mason Tornado 1967 20 Sep 0 0 Mason Tornado 1974 28 Sep F0 0 0 Mason Tornado 1976 23 May F1 0 0 Mason Tornado 1979 2 Mar F3 0 1 Mason Tornado 1999 11 May F4 1 6 Loyal Valley Tornado 2002 13 Apr F0 0 0 Katemcy MILLS COUNTY Tornado 1967 26 Mar F1 0 0 Mills Tornado 1974 31 Oct F1 0 0 Mills Tornado 1975 13 May F0 0 0 Mills Tornado 1978 30 Apr F1 0 0 Mills Tornado 1982 12 May F2 0 0 Mills Page 10-14 Creating a Disaster-Resistant Lower Colorado River Basin
Event Year Date Fujita Injuries Deaths Tornado 1991 13 Apr F0 0 0 Mills Tornado 1998 5 Jan F1 0 0 Goldthwaite Tornado 1999 26 Apr F0 0 0 Goldthwaite SAN SABA COUNTY Tornado 1956 20 Jul F1 0 0 San Saba Tornado 1973 20 Jan F1 0 0 San Saba Tornado 1978 30 Apr F1 0 0 San Saba Tornado 1981 15 May F2 0 0 San Saba Tornado 1982 15 Jun F0 0 0 San Saba Tornado 1987 19 May F0 0 0 San Saba Tornado 1992 28 Jun F1 0 0 San Saba Tornado 1993 19 Apr F0 0 0 Hall Valley Tornado 1998 5 Jan F0 0 0 San Saba Tornado 1999 12 Mar F2 0 0 Richland Springs Tornado 1999 11 May F0 0 0 Elm Grove Tornado 1999 11 May F0 0 0 San Saba Source: National Climatic Data Center, National Oceanic and Atmospheric Administration. People and Property at Risk Because it cannot be predicted where a tornado will touch down, all buildings and facilities are considered to be exposed to the tornado hazard and could potentially be impacted. All the population, buildings, critical facilities, infrastructure and lifelines, and hazardous materials facilities are considered exposed to the hazard and could potentially be impacted. Table 10-4. Exposure to Tornadoes, by County, in the Lower Colorado River Basin Population Critical Residential Buildings Commercial Buildings Facilities Jurisdiction (2000) Number Value ($) Number Value ($) Number Bastrop 57,733 25,225 5,217,746,000 279 703,610,000 54 Blanco 8,418 4,323 952,587,000 32 145,325,000 24 Brown 37,674 15,396 3,458,440,000 118 543,457,000 46 Burnet 34,147 16,142 3,468,080,000 119 501,632,000 43 Creating a Disaster-Resistant Lower Colorado River Basin Page 10-15
Colorado 20,390 8,668 1,913,971,000 80 324,172,000 42 Fayette 21,804 10,551 2,374,106,000 96 371,805,000 44 Lampasas 17,762 7,263 1,625,322,000 58 272,173,000 19 Llano 17,044 12,235 2,798,204,000 55 227,209,000 29 Mason 3,738 2,040 457,552,000 15 58,275,000 8 Matagorda 37,957 15,786 3,661,791,000 80 409,273,000 73 Mills 5,151 2,190 499,705,000 12 63,211,000 16 San Saba 6,186 2,318 572,886,000 12 81,222,000 13 Travis 812,280 462,371 151,547,615,000 3,874 16,786,680,000 336 Wharton 41,188 14,626 3,480,988,000 121 538,973,000 52 Williamson 249,967 155,280 44,379,555,000 723 3,477,991,000 176 TOTAL 1,371,439 754,414 226,408,548,000 5,674 24,505,008,000 975 Infrastructure and Lifelines Hazardous Materials Facilities Oil Pipe Gas Pipe Highway Railroad Number of Number of Jurisdiction (km) (km) (km) (km) Sites Materials Bastrop 197 83 237 168 4 18 Blanco 77 39 104 - - - Brown - 37 191 114 4 19 Burnet - 104 177 76 2 4 Colorado 107 304 212 141 4 4 Fayette 112 232 337 164 3 19 Lampasas - - 136 99 2 2 Llano 1-196 35 - - Mason 99 49 141 - - - Matagorda 209 1,011 161 132 2 23 Mills - - 123 60 - - San Saba - 156 110 58 - - Travis 202 61 446 122 25 95 Wharton 162 1,022 219 70 3 6 Williamson 81 175 323 217 4 5 TOTAL 1,247 3,271 3,113 1,456 53 195 Page 10-16 Creating a Disaster-Resistant Lower Colorado River Basin
Potential Damages and Losses A review of the data on historical tornado events indicates a relative constant frequency of tornado events, with 20 to 40 tornadoes occurring every five years in the Lower Colorado River Basin. Figure 10-3. Frequency of Tornadoes (NOAA Data 1950-2002) Frequency 60 50 40 30 20 10 0 51-55 56-60 61-65 66-70 71-75 76-80 81-85 86-90 91-95 96-02 Year Williamson Wharton Travis San Saba Mills Matagorda Mason Llano Lampasas Fayette Colorado Burnet Brown Blanco Bastrop On average, the Lower Colorado River Basin experiences an annualized loss of over $14.5 million from tornadoes. Table 10-5 shows potential annualized expected property losses and annualized percent loss ratios for each county in the Lower Colorado River Basin. Colorado County, followed by Mason County, experiences the highest relative risk as measured against replacement value. Creating a Disaster-Resistant Lower Colorado River Basin Page 10-17
Table 10-5. Potential Annualized Losses and Percent Loss Ratio for Tornadoes, by County, in the Lower Colorado River Basin Annualized Expected Property Losses ($) Annualized Percent Loss Ratio Jurisdiction Bastrop 26,448 0.0004% Blanco 1,146,394 0.0945% Brown 154,348 0.0034% Burnet 169,559 0.0041% Colorado 1,029,095 0.0419% Fayette 88,745 0.0030% Lampasas Negligible 0.0001% Llano 17,400 0.0006% Mason 167,889 0.0305% Matagorda 113,816 0.0026% Mills 7,500 0.0012% San Saba 11,400 0.0016% Travis 8,022,735 0.0046% Wharton 43,030 0.0010% Williamson 3,617,078 0.0074% TOTAL 14,616,891 LCRA facilities (described starting on page 3-34) are also at risk from this hazard. However, no estimate is currently available of potential damages and losses to those facilities. Page 10-18 Creating a Disaster-Resistant Lower Colorado River Basin