Corridor Dev Cert. Process• What.
• Why
• When
• Who
• Where
• How
• Status
• Process to stabilize flooding risks along the
Trinity River
• Development is allowed, but must not:
— raise flood water levels
— reduce flood storage capacity
— increase erosive water velocities
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2. Floodplain permitting could
dramatically reduce flood risk
• 1 st edition of manual implemented in 1991
• 2nd edition of manual implemented in 1998
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• 49th edition of manual implemented in ? ? ??
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NEW MAPPING - Will be "State of the Art"
• Digital format
• From aerial photography
• Covers 240 square mile area
• 1" = 200'
• 2' topography
Development projects in the Regulatory Zone
must meet the following permit criteria:
• NO rise in the 100 -year flood elevation
• maximum valley storage loss of-
- 0% for the 100 -year discharge and
— 5% for the Standard Project Flood discharge
• no increase in erosive water velocities
based on equal conveyance reductions on both sides of the channel
incorporated into hydraulic modeling.
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• Hydraulic computations must be done using HEC-
RAS model maintained by USACE
• The HE.0 -RAS model incorporates existing and
permitted projects
• Hydrologic discharges are based on future
conditions (2050)
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• US Army Corps of Engineers (USAGE) reviews
hydraulic and hydrologic modeling supporting
CDC application
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• Fee is $1500 or $750 based on effective or
ineffective flow area
• USACE periodically incorporates permitted
projects into their HEC -RAS hydraulic model M
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• Exemptions for specific activities outlined in the
manual (e.g. bank stabilization activities, backfill
for utility lines)
• Variances may be issued, following Preliminary
Technical Review and Regional Review &
Comment, when:
— the project is deemed to be in the public interest
— strict enforcement of the process would cause undue
hardship
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• Flooding risks stabilized
• Common permit criteria
• State -of -the -art floodplain mapping
• Improved hydraulic modeling
• Guarantee of local control of floodplain
permitting decisions
• Organize a group of representatives from
communities along the stream corridor to guide
development of the process
— City /county policy leaders
— Technical staff
• Develop mapping and hydraulic modeling for the
stream corridor
— Necessary for evaluating whether proposed projects
will raise water surface elevations and/or reduce valley
storage
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