DEPARTMENT: Transportation & Capital Improvements
DEPARTMENT HEAD: Razi Hosseini, P.E., R.P.L.S.
COUNCIL DISTRICTS IMPACTED: Citywide
SUBJECT: UDC Amendments- Drainage Manual & Atlas 14
SUMMARY:
TCI recommends amending Chapter 35, Unified Development Code, of the City Code of San Antonio, Texas, Appendix H- Storm Water Design Criteria Manual including Sections 35H-1.2 Acronyms and Abbreviations; 35H-5.5 Rainfall Data; 35H-5.5.1 Rainfall Intensity-Duration; 35H-5.5.2 Rainfall Depth-Duration Frequency; and associated Table of Contents and Lists of Figures and Tables changes.
BACKGROUND INFORMATION:
Atlas 14 is a study of rainfall frequency and intensity. The most recent study (Atlas 14, Volume 11), which includes Texas, was published by the National Oceanic and Atmospheric Administration (NOAA) in September 2018. The UDC requires the use of best available data for drainage and floodplain design, so TCI proposes to implement the Atlas 14 rainfall data through a UDC Amendment. The proposed amendment includes increasing design rainfall depths by 10-30%.
Implementation of Atlas 14 has implications for City of San Antonio flood risk reduction policies and programs, capital project development and delivery, and implications for the community as a whole. Issues of concern include:
* Floodplain Maps- Redefinition of the extent and possible widening of the 100-year floodplain, which affects the City's overall floodplain management program and regulatory policies. Redefining floodplains will likely result in more structures within the effective FEMA floodplains, which means more residents and business will likely be required to purchase flood insurance.
* Drainage Project Design- An increase in design rainfall depths will likely impact design of drainage systems for subdivisions and for flood risk reduction.
* Increased Perception of Risk- An increase in the perceived risk to our community in areas with flooding and drainage issues occur.
* Funding Needs- Potential...
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