Floodplain Coalition Locally Elected Officials Intro to Floodplains and Floodplain Management

December 17, 2018 Agenda  8AM-10AM - Session 1: Why it on the Colorado River……..Wes Birdwell  10AM-10:15 - Break  10:15-12N - Session 2: Where can I go for help?...... Wes Birdwell  12N-12:30 - Lunch (will be brought in)  12:30-3PM - Session 3: Intro to Floodplain Mgt ………Michael Segner, TWDB  3PM-3:15 - Break  3:15-5PM - Session 4: NFIP 101…..Michael Segner, TWDB “The picture’s pretty bleak, gentlemen … the world’s climates are changing, the mammals are taking over, and we all have a brain about the size of a walnut.” Session 1 Why it floods on the Colorado

 It’s a big watershed  It gets very heavy rainfall occasionally  Hill country terrain is very steep  Lower three counties are very flat  Only one control reservoir  Lower river can produce large floods

Why it floods on the Colorado River

Drainage Area Sq. mi. 6,500 Lake LBJ 5,000 1,800 TOTAL 13,300 Lower River 3,600 The gets very big floods

Location of Maximum Discharge in USA Converging Weather Patterns Central Texas Flood History

1935 20”

2007 19”

October 2018 12” August 2017 60”

Colorado May 2015 25”

River Basin July 2002 45” August 2017 Hurricane Harvey Lower River

October 2018 1935 Flood Austin TX Buchanan July 1938 Flood Total Rainfall July 16-25, 1938 Location of Lower Colorado River Basin and Values of Flash Flood Magnitude Index

(adapted from Beard 1975) Location of Lower Colorado River Basin and Values of Flash Flood Magnitude Index (Adapted from Beard 1975) Colorado River Flow - Time Flood Waters Above Austin Colorado River Flow-Time Flood Waters Below Austin The Flood Protection “System” Structural and Non-Structural

DEED • STRUCTURAL My property • • Levees • Channelization Floods are not the norm

Normal River Elevation Common Floods

Minor Flood Flood Warning Level

Normal River Elevation Occasional Flood

Moderate Flood Low Lying Structures

Normal River Elevation Rare floods

Major Flood Many buildings, homes, roads flooded Normal River Elevation River Flood Side View

Normal River Elevation River Flood Side View

Floodplain

Normal River Elevation

Flood Downstream = Flood Upstream Water Supply Dam

Dam

Water Supply

Flood Downstream < Flood Upstream Water Supply Dam

Flood Upstream

Dam

Flood Downstream Water Supply

Flood Downstream < Flood Upstream Multi-Purpose Dam

Dam

Water Supply Multi-Purpose Dam

Dam Flood Upstream

Control Point Controlled Flood Pool Floodgates Water Supply Flood Downstream

Flood Downstream < Flood Upstream Multi-Purpose Dam

Dam Flood Upstream

Uncontrolled Spillway Uncontrolled Flood Storage Control Controlled Flood Pool Point Floodgates Water Supply Flood Downstream

Flood Downstream < Flood Upstream Flood Mitigation Dam No Flood

Base Flow Upstream Dam

Flood Storage Base Flow Downstream

NO FLOOD Base Flow Upstream = Base Flow Downstream Flood Mitigation Dam In Flood

Flood Upstream Dam

Flood Storage Flood Downstream

IN FLOOD Flood Downstream < Flood Upstream Flood Inflow Volume Storage Flood Total Useable Minor Flood < Flood Time Release Flood Inflow Moderate Flood Total FloodVolume Useable storage volume Flood Time FloodPeak FloodgateRelease Mitigation Flood Flood Inflow Major Flood Time Total FloodVolume storagevolume UseableFlood FloodPeak Release Floodgate Mitigation Mitigation Flood The Highland Lakes System

Lake Buchanan Lake Inks Starcke Dam Lake LBJ

Lake Travis Lake Marble Falls

Lake Austin

Tom Miller Dam

Wirtz Dam Highland Lakes and Dams Highland Lakes Dams Designed Flood Operations Tools Buchanan 37 floodgates 0 floodpool Inks 0 floodgates 0 floodpool Wirtz 10 floodgates 0 floodpool Starcke 10 floodgates 0 floodpool Travis 24 floodgates 2 MAF floodpool Austin 9 floodgates 0 floodpool

Mansfield Dam Flood Control Plan

CORP OF ENGINEERS, MANSFIELD DAM AND RESERVOIR NORMAL FLOOD CONTROL REGULATION SCHEDULE

Reservoir Level Flood Control Release Control Points

3,000 cfs 30,000 cfs (20.5’)33’ @ Austin Forecast: 681-683 45,000 cfs (25.1’)27.2’ @ Bastrop 50,000 cfs (25.5’)35.5’ @ Columbus

30,000 cfs (20.5’)33’ @ Austin Forecast: 683-685 27.2’ 5,000 cfs 45,000 cfs (25.1’) @ Bastrop 50,000 cfs (25.5’)35.5’ @ Columbus

30,000 cfs (20.5’)33’ @ Austin Forecast: 685-691 5,000 cfs 45,000 cfs (25.1’@27.2’ Bastrop (a) during Jan, Feb, 50,000 cfs (25.5’)35.5’ @ Columbus Mar, Apr, Jul, Aug, Nov, Dec 30,000 cfs (20.5’)33’ @ Austin (b) during May, 30,000 cfs 45,000 cfs (25.1’)27.2’ @ Bastrop June, Sept, Oct 50,000 cfs (25.5’)35.5’ @ Columbus

30,000 cfs (20.5’)33’ @ Austin Forecast: 691-710 30,000 cfs 45,000 cfs (25.1’)27.2’ @ Bastrop 50,000 cfs (25.5’)35.5’ @ Columbus

----- 50,000 cfs 50,000 cfs (24.8’) @ Austin Forecast: 710-714 50,000 cfs (26.7’)----- @ Bastrop 50,000 cfs (25.5’)---- @ Columbus

Forecast: 714-722 90,000 cfs* No Controls The Bureau of Reclamation will specify the releases for Forecast: above 722 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 The “System” Structural and Non-Structural

• NONSTRUCTURAL DEED • Hydromet NOAA Weather CurrentRadio Gages Coverage • Forecast Models in Central Texas • NOAA Radios • Local Permitting • Floodplains • Flood Easements

Current Hydromet System

LCRA Hydromet Streamflow Gauges (www.hydromet.lcra.org) LCRA Hydromet Rainfall Gauges Weather Radar Imagery Flood Warning Pre-1980’s

LCRA Upper Col R: LCRA Rainfall All Dams except Mansfield Observers Floodgate Operations are Report via based on lake elevation at telephone Buchanan the dam Inks Wirtz Llano R Mansfield Starcke LCRA USACE WCM: Western Tribs: Mansfield LCRA to fill LCRA Rainfall the flood pool, Observers Austin then evacuate Report via over time telephone Lower Col R: Observers Flood Warning 1980’s All Dams except Mansfield Floodgate Operations based NWS on lake elevation at the dam Upper Col R with increased reliance on NWS Forecast real time lake elevation and Rainfall Observers gaged streamflow

Buchanan Mansfield - LCRA LCRA Inks developed Western Tributaries forecast based on Llano R Wirtz Rainfall Observers Starcke Buchanan operations, lake 1. UT Austin Mansfield 2. Manual Fall-back elevation, and some gaged Austin streamflow USACE approve Real Time Streamflow Lower Col R: Gage NWS Forecast Flood Warning 1990’s All Dams except Mansfield Floodgate Operations Upper Col R: Forecast based on real time NWS Forecast Gaged lake elevation and Manual Fall-back Streamflow with some attempt to use real time gaged rainfall Buchanan Mansfield Inks LCRA develop Western Tribs: Llano R Wirtz forecast based LCRA Forecast Starcke on Buchanan 1. UT Austin Mansfield operations and 2. Manual gaged 3. LCRA (CFS) Austin streamflow USACE approve

Streamflow Gage w/rainfall Lower Col R: Rainfall Gage NWS Forecast Flood Warning 2000’s

Upper Col R: NWS Forecast Manual Fall-back All Dams except Mansfield LCRA Floodgate Operations based on real time gaged lake elevation and streamflow, with increased reliance on real time gaged rainfall

Buchanan Mansfield – Floodgate operations based on LCRA Inks developed forecast from gaged streamflow and rainfall, Llano R Wirtz Starcke USACE approve Western Tribs: Mansfield LCRA Forecast 1. CFS/cal-radar Austin 2. Manual Fall-back

Streamflow Gage w/rainfall Lower Col R: Rainfall Gage NWS Forecast Flood Warning Today

Upper Col R: NWS Real Time Streamflow Gage w/rainfall

Buchanan Inks Highland Lakes: LCRA

Llano R Wirtz Starcke Western Tribs: LCRA Mansfield Austin

Lower Col R: NWS FEMA’s Map Modernization Program 2004

 Nationwide  5-Year Plan  $ 1 Billion Budget Texas’ Map Mod Counties The Process.....  No New Studies  Information Search

 Base Map

 Terrain Data

 Engineering Studies

 Hydrology

 Hydraulics  Mapping  Report  Coordination /Outreach Floodplain Map Production

Flood Mapping Project Phases

Community Coordination Project Topographic Post & Mapping DFIRM Preliminary Scoping Data Preliminary Needs Production DFIRM Acquisition Processing Assessment

30 Days 30-90 Days 1-8 Months 12-18 Months 30 Days 12-24 Months

Time frames given are approximate and will vary from study to study New Floodplain Maps are Digital Layers

Base Map (Roads)  New DFIRM Aerial Photography Terrain (Contours) Streams, lakes, rivers  Old FIRM Engineered Flood Zones Zone A Refinement Zone A Refinement LIDAR Acquisition

 LIght Detection and Ranging (LIDAR)  Airborne Laser System  Fixed Wing  Helicopter  Potential for High Level accuracy (1 foot range)

LIDAR: Affordable, Accurate Topo Main St. Main Bastrop County 2007 LiDAR

Highway 71

Bare Earth Points

Raw Surface Bare Earth Surface Point Density

►LiDAR

 Photogrammetry Lake Travis Mapping Example – Gilleland Creek Detailed Engineering Study

 Field Survey  New Topo/Orthophoto  Detailed Hydrologic and Hydraulic Modeling  Floodway Computations  Flood Profiles  Calibrated to Historical Events  Most Expensive Type of Study Field Surveys Engineering Study – Hydrology

HOW MUCH? Engineering Study - Hydraulics

HOW HIGH? Base + Terrain + Engineering Study

Digital Flood Insurance Rate = Map (DFIRM) Zone AE (Detailed Study) Redelineation Sample of Zone AE (Detailed Study) Stream

 Sample Detail Study Stream  Cross- Sections, BFEs, & Floodways Unstudied Streams

Flood Damages $$$$ Expensive Insurance $$$$ Flood Elevation???

Floodplain

Normal Elevation

River or stream -- cross-section Studied Streams

Existing Structures Flood Insurance (known risk) Base Flood Elevation Known

Known flooding depth Normal Elevation

River or stream -- cross-section Studied Stream With Improvement

Existing and New Structures No Flood Insurance Required

Base Flood Elevation

Excavated Areas

River or stream - cross-section Studied Streams Help Reduce Future Flood Risk

New Structures

Base Flood Elevation

Required Freeboard Normal Elevation

River or stream - cross-section Effects of Urbanization Structures in the 100-yr. Floodplain Are Increasing Around the Highland Lakes

6000 5254 5000 4000 2626 3000 2238 2000 1277

Structures 712 1000 361 663 608 2 115 273 124 0

Inks LBJ Travis Austin 1989 Buchanan Marble Falls 1998 Source: Phase 1 Contour Mapping Project, LCRA 1999 and Recon Study for Central Colorado River Watershed, USACE, 1989 Overall >180 % Increase in 10-yrs. 12000 10496 10000 8000 6000 3749

4000 Structures 2000 0 1989 1998

Source: Phase 1 Contour Mapping Project, LCRA 1999 and Recon Study for Central Colorado River Watershed, USACE, 1989 9% County-wide 15% 31% Percentage of Growth from 47% 51% 79% 1990-2000

41% 41% 51% 48% 9% 11%

3% 3%

Source: 2000 US Census Data 12% County-wide 15% 43% Percentage of Growth from 58% 87% 204% 1990-2010

78% 78% 95% 138% 23% 17%

3% 3%

Source: 2000 US Census Data 12% County-wide 15% 50% Percentage of Growth from 75% 104% 293% 1990-2018

100% 110% 124% 230% 25% 41%

7% 3%

Source: 2000 US Census Data LCRA/USACE Flood Damage Evaluation Project 1998-2004

 Texas’ first comprehensive study of the potential for flooding on a major river  Colorado River from San Saba to Matagorda  Seamless 4 foot topography in the 500-Yr FEMA mapped floodplain  Preliminary new 100 and 500-year flood information  Estimated costs of flood damages  Developed damage reduction alternatives along the Colorado River Evaluated costs and benefits Detailed Topo Map of 500 Yr Floodplain Developed topographic maps

Scale 1:2400 s ll a F le rb a M e k a L Model the Floods

82 Routed the floods Counted Structures in the Colorado River Floodplains Total Structures 100-year: 15,775 + 500-year: 28,229

TOTAL = 44,002

(Note: Bar graphs are cumulative) are graphs Bar (Note: NumberStructuresof

*Downstream of Mansfield Dam

84 Damages in Million $ Estimated Potential Flood Step Step 4

L. Buchanan $100 $150 $200 $50 $0 -

Inks L. $0.4 Estimate the Damages

L. MarbleL. Falls LBJ $5.4

$43.3 Damages

Travis Co.L. TravisBelow $16.1

$180.6 Bastrop Co.

$16.9 OverStructures 12,000 Flooded in million Damages $377 Colorado Co.

$6.2 Fayette Co. $22.2 Wharton Co.

Matagorda Co. $7.6

$62.3

$16.1 Lake Travis Structures at Four Flood Levels 2004

4,000 3,788

3,500 3,404 FEMA 3,000 2,698 Current Study 2,500 2,089 2,025 2,000 Reference Elevations Flood FEMA Study 1,500 1,308 500 Year 728.7 732.6 100 Year 716.2 722.0 1,000 50 Year 710.2 716.7 Number of Number Structures 424 500 10 Year 691.2 697.0 136 0 10 Year 50 Year 100 Year 500 Year

Note: Bar graphs are cumulative

86 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  Combine one or more of the above 87 Lake Buchanan FDEP Profiles FDEP Profiles Inks Lake October Flood

Inks Lake peak 895’ October 18, 2018

Inks Lake at Buchanan Dam peak TW October 16, 2018 Lake LBJ FDEP Profiles Lake LBJ October 2018 Flood

El 836 @ Sandy Harbor El 837 @ RM1431 and Inks El 828 @ Gage Datum 970’

Llano Gage Datum...... 970’ October 16...... 40’ MSL……………1010’ FDEP Profiles Lake Marble Falls October Flood

Lake Marble Falls El 753’ October 16, 2018

Lake Marble Falls @ Wirtz Dam El 769’ October 16, 2018 Lake Travis FDEP Profiles Lake Travis October Flood

Lake Travis elevation 704.4’ peak at noon on October 20, 2018

Starcke Dam peak TW El 721 October 16, 2018 FDEP Profiles Lake Austin FDEP Profiles

Lake Austin elevation 492.5’ peak at Tom Miller, 499’ at RR 620 FDEP Profiles Bastrop County Colorado River FDEP Profiles

Bastrop Gage Datum....307.4’ Harvey……...... 25.9’ Oct 2018……....22.3’ MSL Harvey….333.3’ MSL Oct………329.7’

H Oct Upper Colorado County Colorado River FDEP Profiles Columbus and LaGrange Harvey HWM

LaGrange Gage Datum..210.04’ Harvey……..... 54.10’ MSL………….264.14’

Columbus Gage Datum...145.52’ Harvey……...... 48.09’ MSL………….193.61’ Lower Colorado County Colorado River FDEP Profiles Wharton County Colorado River FDEP Profiles Wharton County Harvey HWM

Gage Datum 52.42’ Harvey……...50.50’ MSL………..102.92’ Upper Matagorda County Colorado River FDEP Profiles

Gage Datum….0’ Harvey……...46.1’ MSL…………46.1’ Lower Matagorda County Colorado River FDEP Profiles Flood Damage on the Highland Lakes and Colorado River Average Annual Precipitation Texas

TP-40 24 hour 100 Year Rainfall

above Austin, but may be impacted below Austin TP 40 100-Yr Rainfall Probability in TCRFC district