9/16/19
Texas Floodplain Management
Wes Birdwell, PE
August 29, 2019 1
Lower Colorado River Authority River Operations Manager
Lake Buchanan Buchanan Dam
Lake Inks Starcke Dam
Lake LBJ Mansfield Dam
Lake Travis Lake Marble Inks Dam Falls
Lake Austin Tom Miller Dam
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Wirtz Dam
3 LCRA Hydromet Streamflow Gauges (www.hydromet.lcra.org)
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4 LCRA Hydromet Rainfall Gauges (www.hydromet.lcra.org)
LCRA/USACE Flood Damage Evaluation Project 1998-2004
• Regional flood study of a major Texas river • Colorado River from San Saba to Matagorda • New 100 and 500-year flood information • Estimated flood damages • Developed concept damage reduction alternatives • Evaluated benefit and cost 5
2004 Main Stem Study of 500-Year Floodplain
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Developed New Storms
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Routed the Floods
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Operated the Dams Lady Bird Lake Flood Profiles
Normal Pool Elevation
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Counted Structures in the Colorado River Floodplains
12 ,0 00 50 0- y ear f lo od pl ai n Total Structures 10 0- y ear f lo od pl ai n 9,863 10 ,0 00 100-year: 15,775 + 500-year: 28,229 8,183 8, 00 0 TOTAL = 44,004 6,486
6, 00 0
4,087 4,083 4, 00 0 3,213
2,034 2,059 1,785 2, 00 0 1,407 803
0 (Note: Bar graphs are cumulative) are graphs Bar (Note: Number of Structures
Inks LBJ
Buchanan LakeTravis *Tra vis C o. FayetteCo. Marb le Falls Bastrop Co. Wh arto n C o. Colorado Co. MatagordaCo . *Downstream of Mansfield Dam
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Estimated Potential Flood Damages
$200 $180.6 $150
$100 62.3 $43.3 $50 $16.1 $16.9 $22.2 $16.1 $5.4 $6.2 $7.6 $0 $0.4 Damages in Million $
Inks L. L. LBJ L. Travis Ba s trop Co. Fayette Co. L. Buchanan Colora do Co. Wharton Co. L. Marble Falls Matagorda Co. Travis Co. Below • $377 million in Damages • Over 12,000 Structures Flooded 11
Mansfield Dam Flood Control Plan
CORPS OF ENGINEERS, MANSFIELD DAM AND RESERVOIR NORMAL FLOOD CONTROL REGULATION SCHEDULE Flood Control Reservoir Level Release Control Points 30,000 cfs (20.5’) @ Austin 3,000 cfs FORECAST: 681-683 45,000 cfs (25.1’) @ Bastrop 50,000 cfs (25.5’) @ Columbus
30,000 cfs (20.5’) @ Austin FORECAST: 683-685 5,000 cfs 45,000 cfs (25.1’) @ Bastrop 50,000 cfs (25.5’) @ Columbus
30,000 cfs (20.5’) @ Austin FORECAST: 685-691 5,000 cfs 45,000 cfs (25.1’@ Bastrop (a) during Jan, Feb, 50,000 cfs (25.5’) @ Columbus Mar, Apr, Jul, Aug, Nov, Dec 30,000 cfs (20.5’) @ Austin (b) during May, 30,000 cfs 45,000 cfs (25.1’) @ Bastrop June, Sept, Oct 50,000 cfs (25.5’) @ Columbus
30,000 cfs (20.5’) @ Austin FORECAST: 691-710 45,000 cfs (25.1’) @ Bastrop 50,000 cfs (25.5’) @ Columbus 30,000 cfs
50,000 cfs (24.8’) @ Austin FORECAST: 710-714 50,000 cfs 50,000 cfs (26.7’) @ Bastrop 50,000 cfs (25.5’) @ Columbus
FORECAST: 714-722 No Controls 90,000 cfs*
FORECAST: above 722 The Bureau of Reclamation will specify the releases for safety of the structure. * Releases shall not exceed the associated peak flood reservoir inflow. Note: No curtailment of normal hydroelectric turbine releases shall be required due to flood control operations. EXHIBIT E-2 From Corps of Engineers Water Control Manual December 1979 12
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Lake Travis Structures at Four Flood Levels 2004
4,000 3,788 3,404 3,500 FEMA 3,000 2,698 Curre nt Study 2,500 2,089 2,025 Reference Elevations 2,000 Flood FEMAStudy 500 Year 729 733 1,500 1,308 100 Year 716 722.0 50 Year 710 716.7 1,000 10 Year 691 697.0
Number of Structures of Number 424 500 136 0 10Year 50Year 100 Year 500 Year
Note: Bar graphs are cumulative
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Investigated Alternatives for Reducing Flood Damages
• Do nothing • Non-structural • Raise floodplain elevations and make insurance available • Buy and remove structures to reduce potential for damages • Modify Mansfield Dam operating rules for releasing floodwaters • Structural • Construct new reservoir(s) upstream of Mansfield Dam • Build levees • Build local detention • Increase stream channel 14 • Combine one or more of the above
www.tcrfc.org
Connie Schroeder Board Treasurer Mayor, City of Bastrop
Interim Ex Dir
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Results 20 years later……
• Community buy-in of the new data • New floodplain maps with new information • Tributary studies in Llano, Burnet, Travis, Bastrop, Hays, Wharton and Matagorda counties, Tres Palacios and San Bernard River • TWDB CTP studies for San Bernard and Colorado Cummins • New 100% USACE federally funded levees for City of Wharton • Millions % in local and federal buyouts along Onion Creek • $7M channelization in City of El Campo FEMA HMGP • $1M detention in City of Smithville FEMA HMGP • Certified Matagorda ring levee and avoided certifying river levees
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USACE Lower Colorado River Projects Onion Creek Buyouts
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USACE Lower Colorado River Projects City of Wharton Levee System
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1960 USACE Ponds 4% ACE
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Current Effective FEMA Floodplain Map
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1% Flood Depth
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TWDB State Flood Assessment
• Charts a path to flood resilience: • Mapping • Planning • Mitigation
• Consider 4 types of flood • Coastal • Riverine • Structural • Urban
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What is our Desired Quality of Mapping?
• Tier 0 – Unmapped Miles • Tier 1 – Not Digital • Tier 2 – Digital but not based on LiDAR and/or not model backed • Tier 3 – Digital, LiDAR and model backed • Tier 4 – Considers future conditions
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Wes’ Watershed Flood Plans: Potential Mapping Goals
• Urban and Rural Areas: • Tier 3 – Digital, LiDAR and model backed • Urbanizing Areas: • Tier 4 – Considers future conditions • Tier 5 – 2-Dim?
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Estimate of Current status:
• Coastal: Tier 3 90% • Riverine: Tier 0, 1, 2, 3, 4 10% • Structural: Tier 0, 1, 2, 3 25% • Urban: Tier 0, 1, 2, 3, 4 1% • Tier 0 – Unmapped Miles • Tier 1 – Not Digital • Tier 2 – Digital but not based on LiDAR and/or not model backed • Tier 3 – Digital, LiDAR and model backed • Tier 4 – Considers future conditions
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Brown Coleman Lower Colorado River Mills Concho Counties* which potentially McCulloch San Saba Lampasas could be included in the Lower Colorado Flood Planning Group Schleicher Menard Burnet
Mason Llano Williamson Sutton Kimble
Gillespie Lee
Travis Blanco Kerr Hays Bastrop
Edwards Fayette Colorado
* Coleman, Brown, Mills, Lampasas, San Saba, McCulloch, Wharton Concho, Schleicher, Menard, Mason, Llano, Burnet, Williamson, Travis, Blanco, Gillespie, Kimble, Sutton, Edwards, Kerr, Hays, Bastrop, Fayette, Lee, Colorado, Matagorda Wharton, and Matagorda counties 27
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Questions?
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