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Atlas 14 PrecipitationFrequency Estimates & LID Practices - Status
Jan 24, 2020
ACEC San Antonio Annual Seminar
San Antonio, TX
Nefi Garza, PEAssistant Director
Flash Flood Alley
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Source: http://www.floodsafety.com/media/maps/texas/index.htm
South Texas Rainfall Records
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• Thrall (1921): 36”/18 hrs• Ingram (1932): 36”/24 hrs• D’Hanis (1935): 22”/3 hrs• Pandale (1954): 32”/24 hrs• New Braunfels (1972): 10”/1 hr• TS Amelia (1978): 48”/52hrs• TS Claudette (1979): 43”/24 hrs• Zorn (1998): 32”/18 hrs• TS Charley (1998): 18”/4 hrs• Kerr County (2002): 42”/5 days• Harvey, Houston area (2017): 52”/4 days
Source: NWSFO Austin/San Antonio
Note: San Antonio annual rainfall average is 30”/ per year
Flash Flood Alley
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July 2002: US - 281 facing south at Quarry
Flash Flood Alley
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July 2002: IH-10 facing North at Rim/Fiesta Texas
• Provide background for Atlas 14.
• What is Atlas 14?
• How does it apply to Texas and Bexar County?
• How does it relate to upcoming DFIRM updates?
• Discuss stakeholder engagement plan and timeline for implementation.
• Share coordination results to date.
Today
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• National Oceanographic &
Atmospheric Administration (NOAA)
• National Weather Service
(NWS)
• Hydrometeorological Design
Studies Center (HDSC)
• Precipitation Frequency Estimates
• Precipitation Frequency Data Server
(PFDS)
What is Atlas 14?
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• Conducted by Hydrometeorological Design Studies Center (HDSC)
• Funded from State & Municipal sources (not in San Antonio area)
• Federally mandated?
• Not exactly
• NOAA/NWS providing Atlas 14 as “Best Available Data”
• Becomes regulatory as entities adopt data (e.g., FEMA)
Atlas 14, Volume 11: Texas
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• Current standards for Bexar County
• 100-year Storm → 10” Rainfall Depth
• Weather Bureau’s Tech. Paper No. 40 (TP-40)
• Published in 1961
• Modified in 2000’s
• Atlas 14, Volume 11
• 3,900 gauges used for analysis
• Adds decades of data (1960s through fall 2017)
• Web Publication: September 28, 2018
• Full Document Publication: December 2018
Atlas 14, Volume 11: Texas
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Atlas 14, Volume 11: Texas
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Atlas 14, Volume 11: Texas
• City Management• Mayor & City Council• City Manager’s Office
• Public• Neighborhoods
• Bexar Regional Watershed Management Partners (BRWM)
• Bexar County, TCI, SARA• SAWS, CPS• Suburban Cities
• Development Community
Stakeholder Engagement
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AGENCIES
• Bexar County
• Development Services (DSD)
• San Antonio River Authority (SARA)
• Transportation & Capital Improvements (TCI)
• Texas Department of Transportation (TxDOT)
DEVELOPERS & INDUSTRY GROUPS
• KB Homes
• Meritage Homes
• Professional Engineers in Private Practice (PEPP)
• Real Estate Council (RECSA)
CONSULTANTS
• Big Red Dog Engineers
• Civil Engineering Consultants
• HDR Engineers
• KFW Engineering
• Maestas & Associates
• Pape-Dawson Engineers
• RESPEC
• San Antonio Design Group (SADG)
Development Stakeholder Group
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Atlas 14 , Vol. 11 Timeline
Public Comment Period+/- Dec through mid Jan
TAC, CHE Comm, PC, & CouncilFeb through March
Watershed Technical Committee- Focus Groups
• Rainfall Depth Determination
• FEMA Mapping
• Land Development Impacts
• Capital Project Impacts
• Outreach/Communication- Community Rating System (CRS)
BRWM Coordination
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Increase in depth and intensity
• Currently 10” for all of Bexar County
• Atlas 14 depths range from ±10.8” to ±12.5”
Provide multiple rainfall depth areas
• 5 major watersheds
• Medina, Leon, San Antonio, Salado, Cibolo
• 2 - 3 depth areas per watershed
• Zonal averages range from 10.97” - 12.39”
Rainfall Depth Determination
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Incorporate Atlas 14 Rainfall Data with DFIRM 2.0
• Floodplains will be updated by watershed
• Hydrology adopted first, then maps will be updated
What happens between Atlas 14 adoption and DFIRM 2.0?
• Use effective data (2010 DFIRM) for C/LOMR
• Provide additional studies/profiles with Atlas 14 rainfall intensities
• Design infrastructure based on worst case scenario
FEMA Mapping
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• Land Development Impact Analysis
• Policy and procedure implications
• How do we handle phased projects?
• What qualifies as an adverse impact?
• FEMA Mapping
• Effective vs. Atlas 14
• Remapping homes into the floodplain
• Insurance impacts
• Recommended comments prior to Atlas 14 adoption
Land Development Concerns
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Low Impact Development
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The term low impact development (LID) refers to systems and practices that use or mimic natural processes that result in the infiltration, evapotranspiration or use of storm water in order to protect water quality and associated aquatic habitat. There are many practices that have been used to adhere to these principles such as:
Bio-retention facilities Rain gardens Vegetated rooftops Rain barrels Permeable pavements
What is LID?
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- Environmental Protection Agency (EPA)
Examples
Tower of the Americas23
Examples in San Antonio
Ray Ellison24
Maintenance
Ray Ellison25
Current Policy
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RIO Overlay Districts
LID Design Requirements• Water Quality Volume (WQV)
– New Development- 1.5” Rainfall – Redevelopment- 1.18” Rainfall – Minimum 60% WQV treatment
• Performance Based Code
– Design for volume– Presumed treatment
• Total Suspended Solids (TSS)- 80% removal• Bacteria- 60% removal
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www.unce.unr.edu
Voluntary LID Incentives• Landscape & Tree Credits & Offsets
– Stream Buffer/Restoration → Parkland Acreage/Tree Canopy
– Linear Park → Parkland Acreage– LID BMP → Tree Canopy/Streetscape/
Parkland/Landscape
• Fee Based Incentives– Reduction in fee-in-lieu-of detention (FILO)- 5%-30%
• Permeable pavement = No FILO
– Reduction in monthly storm water utility fee- 30%28
Mandatory LID Areas• River Improvement Overlay (RIO) Districts
– RIO Districts 1- 6, excluding Downtown
• Park Reach• Museum Reach• Mission Reach• Adjacent to the San Antonio River
– RIO District 7 • Adjacent to the San Pedro Creek
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Future Direction• San Antonio –
Water Quality VisionDocument
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