![Page 1: Onion Creek Flood Mitigation Feasibility Study · Flood Risk Amount of rainfall (24 hour) Houses at risk in project area Houses at risk citywide Category of flood Chance of occurring](https://reader036.vdocument.in/reader036/viewer/2022081612/5f2ae48ec2b6cf0c7a5d3b92/html5/thumbnails/1.jpg)
City of Austin Watershed Protection Department
May 16, 2017
1
Onion Creek Flood Mitigation Feasibility Study
![Page 2: Onion Creek Flood Mitigation Feasibility Study · Flood Risk Amount of rainfall (24 hour) Houses at risk in project area Houses at risk citywide Category of flood Chance of occurring](https://reader036.vdocument.in/reader036/viewer/2022081612/5f2ae48ec2b6cf0c7a5d3b92/html5/thumbnails/2.jpg)
• Project Team • Background & Risk • Alternatives Analysis
– Final Alternatives considered
– Evaluation Criteria • Key Issues & Next Steps • Q & A
2
Meeting Agenda
![Page 3: Onion Creek Flood Mitigation Feasibility Study · Flood Risk Amount of rainfall (24 hour) Houses at risk in project area Houses at risk citywide Category of flood Chance of occurring](https://reader036.vdocument.in/reader036/viewer/2022081612/5f2ae48ec2b6cf0c7a5d3b92/html5/thumbnails/3.jpg)
• Watershed Protection Department – Mike Personett, Assistant Director – Pam Kearfott, P.E., Supervising Engineer – Karl McArthur, P.E., Supervising Engineer – Kacey Paul, P.E., Engineer C
• Halff Associates – Michael Moya, P.E., Vice President – Cindy Engelhardt, P.E., Austin Water Resources Lead – Ashley Lowrie, Water Resources Engineer
3
Project Team
![Page 4: Onion Creek Flood Mitigation Feasibility Study · Flood Risk Amount of rainfall (24 hour) Houses at risk in project area Houses at risk citywide Category of flood Chance of occurring](https://reader036.vdocument.in/reader036/viewer/2022081612/5f2ae48ec2b6cf0c7a5d3b92/html5/thumbnails/4.jpg)
4
Background & Risk
![Page 5: Onion Creek Flood Mitigation Feasibility Study · Flood Risk Amount of rainfall (24 hour) Houses at risk in project area Houses at risk citywide Category of flood Chance of occurring](https://reader036.vdocument.in/reader036/viewer/2022081612/5f2ae48ec2b6cf0c7a5d3b92/html5/thumbnails/5.jpg)
5
Flood Risk
Amount of rainfall
(24 hour)
Houses at risk
in project area
Houses at risk
citywide
Category of flood
Chance of occurring
in any year
3.4 inches 0 50 2-year 50%
7.6 inches 0 900 25-year 4%
10.2 inches 139 2,400 100-year 1%
![Page 6: Onion Creek Flood Mitigation Feasibility Study · Flood Risk Amount of rainfall (24 hour) Houses at risk in project area Houses at risk citywide Category of flood Chance of occurring](https://reader036.vdocument.in/reader036/viewer/2022081612/5f2ae48ec2b6cf0c7a5d3b92/html5/thumbnails/6.jpg)
6
Onion Creek Watershed
![Page 7: Onion Creek Flood Mitigation Feasibility Study · Flood Risk Amount of rainfall (24 hour) Houses at risk in project area Houses at risk citywide Category of flood Chance of occurring](https://reader036.vdocument.in/reader036/viewer/2022081612/5f2ae48ec2b6cf0c7a5d3b92/html5/thumbnails/7.jpg)
7
Risk: Where the rain falls matters
May2015
October2013
October2015
May2016
![Page 8: Onion Creek Flood Mitigation Feasibility Study · Flood Risk Amount of rainfall (24 hour) Houses at risk in project area Houses at risk citywide Category of flood Chance of occurring](https://reader036.vdocument.in/reader036/viewer/2022081612/5f2ae48ec2b6cf0c7a5d3b92/html5/thumbnails/8.jpg)
1921 1929 1941 1981 1991 1998 2001 2013 20150
20,000
40,000
60,000
80,000
100,000
120,000
140,000
Flood Event (Year)
Stre
am
Flo
w (
cu
bic
fee
t p
er s
ec
on
d)
Historical Onion Creek Floods at US 183
Flooding in Study Area
8
Risk: How much rain matters
![Page 9: Onion Creek Flood Mitigation Feasibility Study · Flood Risk Amount of rainfall (24 hour) Houses at risk in project area Houses at risk citywide Category of flood Chance of occurring](https://reader036.vdocument.in/reader036/viewer/2022081612/5f2ae48ec2b6cf0c7a5d3b92/html5/thumbnails/9.jpg)
• Pinehurst Neighborhood (116 houses at risk)
9
Existing Condition 100-year Flood Risk
![Page 10: Onion Creek Flood Mitigation Feasibility Study · Flood Risk Amount of rainfall (24 hour) Houses at risk in project area Houses at risk citywide Category of flood Chance of occurring](https://reader036.vdocument.in/reader036/viewer/2022081612/5f2ae48ec2b6cf0c7a5d3b92/html5/thumbnails/10.jpg)
• Wild Dunes Neighborhood (23 houses at risk)
10
Existing Condition 100-year Flood Risk
![Page 11: Onion Creek Flood Mitigation Feasibility Study · Flood Risk Amount of rainfall (24 hour) Houses at risk in project area Houses at risk citywide Category of flood Chance of occurring](https://reader036.vdocument.in/reader036/viewer/2022081612/5f2ae48ec2b6cf0c7a5d3b92/html5/thumbnails/11.jpg)
• 1997 – Loomis and Moore • 2006 – U.S. Army Corps of Engineers • 2013 – U.S. Army Corps of Engineers, Hays County
11
Previous Studies
![Page 12: Onion Creek Flood Mitigation Feasibility Study · Flood Risk Amount of rainfall (24 hour) Houses at risk in project area Houses at risk citywide Category of flood Chance of occurring](https://reader036.vdocument.in/reader036/viewer/2022081612/5f2ae48ec2b6cf0c7a5d3b92/html5/thumbnails/12.jpg)
12
Alternatives Analysis
![Page 13: Onion Creek Flood Mitigation Feasibility Study · Flood Risk Amount of rainfall (24 hour) Houses at risk in project area Houses at risk citywide Category of flood Chance of occurring](https://reader036.vdocument.in/reader036/viewer/2022081612/5f2ae48ec2b6cf0c7a5d3b92/html5/thumbnails/13.jpg)
• Stand-Alone Options – Regional Detention Ponds – Channel Clearing – Voluntary Buyouts
• Pinehurst Neighborhood • Wild Dunes Neighborhood
• Combined Options – Centex West Detention Pond with Channel Modifications – Pinehurst Flood Protection Wall with Voluntary Buyouts – Pinehurst Flood Protection Wall with Channel Modifications
13
Final Alternatives Considered
![Page 14: Onion Creek Flood Mitigation Feasibility Study · Flood Risk Amount of rainfall (24 hour) Houses at risk in project area Houses at risk citywide Category of flood Chance of occurring](https://reader036.vdocument.in/reader036/viewer/2022081612/5f2ae48ec2b6cf0c7a5d3b92/html5/thumbnails/14.jpg)
14
Evaluation Criteria
• Benefits & Costs • Environmental Impacts • Land & Easement Acquisition Required • Complexity of Permitting • Funding Constraints • Time of Implementation • Neighborhood Input
![Page 15: Onion Creek Flood Mitigation Feasibility Study · Flood Risk Amount of rainfall (24 hour) Houses at risk in project area Houses at risk citywide Category of flood Chance of occurring](https://reader036.vdocument.in/reader036/viewer/2022081612/5f2ae48ec2b6cf0c7a5d3b92/html5/thumbnails/15.jpg)
15
Centex West Regional Detention Pond
![Page 16: Onion Creek Flood Mitigation Feasibility Study · Flood Risk Amount of rainfall (24 hour) Houses at risk in project area Houses at risk citywide Category of flood Chance of occurring](https://reader036.vdocument.in/reader036/viewer/2022081612/5f2ae48ec2b6cf0c7a5d3b92/html5/thumbnails/16.jpg)
16
Centex West Regional Detention Pond
Project Cost $51 million
Time of Completion (if funded)
Over 10 years
Protected from 100-year flood
79 houses
Still at risk in 100-year flood
60 houses
![Page 17: Onion Creek Flood Mitigation Feasibility Study · Flood Risk Amount of rainfall (24 hour) Houses at risk in project area Houses at risk citywide Category of flood Chance of occurring](https://reader036.vdocument.in/reader036/viewer/2022081612/5f2ae48ec2b6cf0c7a5d3b92/html5/thumbnails/17.jpg)
17
Channel Clearing
![Page 18: Onion Creek Flood Mitigation Feasibility Study · Flood Risk Amount of rainfall (24 hour) Houses at risk in project area Houses at risk citywide Category of flood Chance of occurring](https://reader036.vdocument.in/reader036/viewer/2022081612/5f2ae48ec2b6cf0c7a5d3b92/html5/thumbnails/18.jpg)
18
Channel Clearing
Project Cost $36 million
Time of Completion (if funded)
2 to 5 years (plus perpetual, intensive
maintenance)
Protected from 100-year flood
52 houses
Still at risk in 100-year flood
87 houses
![Page 19: Onion Creek Flood Mitigation Feasibility Study · Flood Risk Amount of rainfall (24 hour) Houses at risk in project area Houses at risk citywide Category of flood Chance of occurring](https://reader036.vdocument.in/reader036/viewer/2022081612/5f2ae48ec2b6cf0c7a5d3b92/html5/thumbnails/19.jpg)
19
Voluntary Buyouts
![Page 20: Onion Creek Flood Mitigation Feasibility Study · Flood Risk Amount of rainfall (24 hour) Houses at risk in project area Houses at risk citywide Category of flood Chance of occurring](https://reader036.vdocument.in/reader036/viewer/2022081612/5f2ae48ec2b6cf0c7a5d3b92/html5/thumbnails/20.jpg)
20
Voluntary Buyouts
Project Cost $99 million
Time of Completion (if funded)
2 years
Protected from 100-year flood
139 houses
Still at risk in 100-year flood
0 houses
![Page 21: Onion Creek Flood Mitigation Feasibility Study · Flood Risk Amount of rainfall (24 hour) Houses at risk in project area Houses at risk citywide Category of flood Chance of occurring](https://reader036.vdocument.in/reader036/viewer/2022081612/5f2ae48ec2b6cf0c7a5d3b92/html5/thumbnails/21.jpg)
21
Centex West Detention Pond with Channel Modifications
![Page 22: Onion Creek Flood Mitigation Feasibility Study · Flood Risk Amount of rainfall (24 hour) Houses at risk in project area Houses at risk citywide Category of flood Chance of occurring](https://reader036.vdocument.in/reader036/viewer/2022081612/5f2ae48ec2b6cf0c7a5d3b92/html5/thumbnails/22.jpg)
22
Centex West Detention Pond with Channel Modifications
Project Cost $71 million
Time of Completion (if funded)
Over 10 years
Protected from 100-year flood
111 houses
Still at risk in 100-year flood
28 houses
![Page 23: Onion Creek Flood Mitigation Feasibility Study · Flood Risk Amount of rainfall (24 hour) Houses at risk in project area Houses at risk citywide Category of flood Chance of occurring](https://reader036.vdocument.in/reader036/viewer/2022081612/5f2ae48ec2b6cf0c7a5d3b92/html5/thumbnails/23.jpg)
23
Pinehurst Flood Protection Wall with Voluntary Buyouts
![Page 24: Onion Creek Flood Mitigation Feasibility Study · Flood Risk Amount of rainfall (24 hour) Houses at risk in project area Houses at risk citywide Category of flood Chance of occurring](https://reader036.vdocument.in/reader036/viewer/2022081612/5f2ae48ec2b6cf0c7a5d3b92/html5/thumbnails/24.jpg)
24
Pinehurst Flood Protection Wall with Voluntary Buyouts
Project Cost $62 million
Time of Completion (if funded)
5 to 7 years
Protected from 100-year flood
139 houses
Still at risk in 100-year flood
0 houses
![Page 25: Onion Creek Flood Mitigation Feasibility Study · Flood Risk Amount of rainfall (24 hour) Houses at risk in project area Houses at risk citywide Category of flood Chance of occurring](https://reader036.vdocument.in/reader036/viewer/2022081612/5f2ae48ec2b6cf0c7a5d3b92/html5/thumbnails/25.jpg)
25
Pinehurst Flood Protection Wall with Channel Modifications
![Page 26: Onion Creek Flood Mitigation Feasibility Study · Flood Risk Amount of rainfall (24 hour) Houses at risk in project area Houses at risk citywide Category of flood Chance of occurring](https://reader036.vdocument.in/reader036/viewer/2022081612/5f2ae48ec2b6cf0c7a5d3b92/html5/thumbnails/26.jpg)
26
Pinehurst Flood Protection Wall with Channel Modifications
Project Cost $88 million
Time of Completion (if funded)
7 to 10 years
Protected from 100-year flood
139 houses
Still at risk in 100-year flood
0 houses
![Page 27: Onion Creek Flood Mitigation Feasibility Study · Flood Risk Amount of rainfall (24 hour) Houses at risk in project area Houses at risk citywide Category of flood Chance of occurring](https://reader036.vdocument.in/reader036/viewer/2022081612/5f2ae48ec2b6cf0c7a5d3b92/html5/thumbnails/27.jpg)
27
Evaluation Criteria
• Benefits & Costs • Environmental Impacts • Land & Easement Acquisition Required • Complexity of Permitting • Funding Constraints • Time of Implementation • Neighborhood Input
![Page 28: Onion Creek Flood Mitigation Feasibility Study · Flood Risk Amount of rainfall (24 hour) Houses at risk in project area Houses at risk citywide Category of flood Chance of occurring](https://reader036.vdocument.in/reader036/viewer/2022081612/5f2ae48ec2b6cf0c7a5d3b92/html5/thumbnails/28.jpg)
28
Criteria: Summary Criteria Best Worst
Benefits and Costs • Wall with Buyouts • Wall with Chl. Mods. • Voluntary Buyouts
• Centex West Pond • Pond with Chl. Mods. • Channel Clearing
Environmental Impacts • Voluntary Buyouts • Centex West Pond • Pond with Chl. Mods. • Wall with Buyouts
• Wall with Chl. Mods. • Channel Clearing
Time of Implementation • Voluntary Buyouts • Wall with Buyouts • Wall with Chl. Mods. • Channel Clearing
• Centex West Pond • Pond with Chl. Mods.
Land Acquisition Required
• Voluntary Buyouts • Wall with Buyouts • Wall with Chl. Mods.
• Centex West Pond • Pond with Chl. Mods. • Channel Clearing
Complexity of Permitting • Voluntary Buyouts • Wall with Buyouts • Wall with Chl. Mods. • Channel Clearing
• Centex West Pond • Pond with Chl. Mods.
Neighborhood Input • Centex West Pond • Pond with Chl. Mods. • Channel Clearing
• Wall with Chl. Mods. • Voluntary Buyouts • Wall with Buyouts
Funding Constraints • Voluntary Buyouts
• Pond with Chl. Mods. • Wall with Buyouts • Wall with Chl. Mods. • Channel Clearing
• Centex West Pond
![Page 29: Onion Creek Flood Mitigation Feasibility Study · Flood Risk Amount of rainfall (24 hour) Houses at risk in project area Houses at risk citywide Category of flood Chance of occurring](https://reader036.vdocument.in/reader036/viewer/2022081612/5f2ae48ec2b6cf0c7a5d3b92/html5/thumbnails/29.jpg)
29
Key Issues & Next Steps
![Page 30: Onion Creek Flood Mitigation Feasibility Study · Flood Risk Amount of rainfall (24 hour) Houses at risk in project area Houses at risk citywide Category of flood Chance of occurring](https://reader036.vdocument.in/reader036/viewer/2022081612/5f2ae48ec2b6cf0c7a5d3b92/html5/thumbnails/30.jpg)
30
Key Issues
Level of Protection (Benefit vs. Cost)
Funding Limitations • Ineligible for federal and state funding
• City sources:
- Drainage Utility Fund (City Council approval)
- Bonds (City Council and/or voter approval)
Time of Implementation
![Page 31: Onion Creek Flood Mitigation Feasibility Study · Flood Risk Amount of rainfall (24 hour) Houses at risk in project area Houses at risk citywide Category of flood Chance of occurring](https://reader036.vdocument.in/reader036/viewer/2022081612/5f2ae48ec2b6cf0c7a5d3b92/html5/thumbnails/31.jpg)
31
Next Steps
Present to Environmental Commission
subcommittee June 7th
Finalize feasibility
study
Present to City Council
![Page 32: Onion Creek Flood Mitigation Feasibility Study · Flood Risk Amount of rainfall (24 hour) Houses at risk in project area Houses at risk citywide Category of flood Chance of occurring](https://reader036.vdocument.in/reader036/viewer/2022081612/5f2ae48ec2b6cf0c7a5d3b92/html5/thumbnails/32.jpg)
Questions?
32
City of Austin Watershed Protection Department
Karl McArthur (512) 974-9126
Website: http://www.austintexas.gov/onioncreekstudy
Pam Kearfott (512) 974-3361