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Floodplain Management Definition Floodplain Management is a decision-making process that aims to achieve the wise use of the nation's floodplains. Environmental Impacts Health and Safety Economics Resiliency Sustainability Considerations

Floodplain Management Reality Insurance Technology & Engineering Regulatory Science & Research

Atlas 14 Update What is NOAA Rainfall Atlas 100 Year Flood: 1% annual chance exceedance Statistical fact: 1-(0.99)^30 = 27% chance of a home in the 100-year floodplain will flood over a 30-year mortgage 1-(0.998)^30 = 6% chance of a home in the 500-year floodplain will flood over a 30-year mortgage Atlas 14 is an ongoing study used to analyze historical rainfall data in order to update statistical hypothetical rainfall events in Texas.

Atlas 14 Update Progress Atlas 14 replaces TP-40 – 1961 Texas is the last state to be updated

Atlas 14 Update What’s changed from 1961 Average record length of gauge now over 50 years Oldest data set from 1836 (Ft. Snelling/Minneapolis St. Paul Airport) Results Shows higher intensity during short storms More regional relationships

Atlas 14 Update

Atlas 14 – Next Steps Adopted by local agencies Change regulations Update FEMA maps – Incorporate new technology Update is scheduled to be completed in October as NOAA Atlas 14 Volume 11 Version 2 Each jurisdiction will be able to analyze the data and determine practical applications for their location through engineering reviews.

COH Chapter 19 Update Changes Effective September 1st for both sets of City of Houston Regulations Chapter 19 Ordinance – Floodplain Regulations 500-year storm basis for new regulations Increases 51,000 acres (13% of overall city) Floodplain mitigation for fill in 500-year Minimum Slab elevations go from 100 year + 1’ to 500 year + 2’

COH Chapter 19 Update

COH Chapter 19 Update

COH Chapter 9 Chapter 9 of Infrastructure Design Manual Detention No reduced detention rate for redevelopment COH is extending their detention review to ETJ projects COH detention rates will default to higher storage volume if more than one jurisdiction (HCFCD, TxDOT) is involved Fill Placement Removing 1-acre Threshold – must demonstrate no impact to sheet flow for all development

Harris County Updates Non-Conforming Subdivision (NCS) NCS developed prior to county extreme sheet flow regulations Conforming Subdivision (CS) CS meets criteria set in August 2009 regarding extreme even sheet flow CS performance in Harvey (less than 1% of permitted structures flooded) New Development CS - Move forward as existing regulations with only new requirement that homes be set at minimum 500-year elevation NCS – cheat sheet

Harris County Updates

COH County Updates

Open House – Regulation Updates