Clay County Cooperating Technical Partners CTP Project Minnesota Association of Floodplain Managers

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Clay County Cooperating Technical Partners (CTP)
ProjectMinnesota Association of Floodplain
Managers September 13, 2005
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Presenters Tim Magnusson - Director, Planning
and Environmental Programs, Clay County,
Minnesota C. Gregg Thielman, P.E., CFM
Project Manager, Houston Engineering, Inc.
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Buffalo River Study Reach
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Project Background

• Clay County entered agreement to become a CTP
  with FEMA Region V in July 2001
• Work Products
• Topographic maps for
• Floodplain Mapping
• Updated Hydrology
• Hydraulic Analysis for
• Flood Profiles and
• Floodway
• Floodplain Mapping

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Project Background

• Phase I - Acquisition of LIDAR
• 104 Square miles of mapping
• Phase II - Hydrologic and Hydraulic Analysis and
  Floodplain Mapping
• 98.5 River Miles of the Buffalo, South Branch of
  the Buffalo River, and the Glyndon Tributary.
• 2 Miles of County Ditch 50 through the City of
  Dilworth also being studied

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Phase I - Acquisition of LIDAR

• Clay Count Contracted with Horizons, Inc. for
  LIDAR acquisition
• Buffalo River
• - 94 sq. miles acquired
• in December 2002
• South Branch of the
• Buffalo River
• - 10 sq. miles acquired
• in October 2003

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Phase I - Acquisition of LIDAR (cont)

• LIDAR - Products provided
• 1 foot contours
• Orthophotos
• Bare Earth DEM
• 3D Breaklines
• Raw LIDAR data
• Filtered LIDAR
• data set

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Phase II - HH Analysis and Floodplain Mapping

• Clay County Contracted with Houston Engineering,
  Inc. for Survey, Hydraulics and Floodplain
  Mapping in October, 2003
• Clay County contracted with Ulteig Engineers for
  work through Dilworth
• Hydrology was developed by the Buffalo-Red River
  Watershed District

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Phase II - HH Analysis and Floodplain Mapping

• Watershed Characteristics
• 1360 sq. mile
• Drainage Area
• Hydrology utilized stream-gage data and a HEC-HMS
  model developed by the Watershed District

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Phase II - HH Analysis and Floodplain Mapping

• Field Survey to Supplement LIDAR
• Structures
• 46 structures
• River Channel
• 153 sections
• Full Floodplain Cross Sections outside of LIDAR
  coverage
• 40 Sections
• Utilized GPS during ice conditions for survey

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GIS Integration
HEC-RAS Geometry
Hydrologic Parameters
Floodplain Delineation
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Phase II - HH Analysis and Floodplain Mapping

• Mapping done by GIS using HEC-geoRAS
• Work maps created in a format suitable for DFIRM
  generation

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Engineering Lessons Learned

• LIDAR provided an excellent source of topographic
  data
• LIDAR quality control extends beyond the initial
  accuracy checks and survey maintain contact with
  the mapping contractor.

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Engineering Lessons Learned

• Acquisition of survey data under ice conditions
  proved to be very efficient
• Utilization of GIS tools for model development
  and mapping significantly increases efficiency
• Expect the unexpected

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Benefits from CTP

• CTP project will provide a County-wide,
  up-to-date, Digital Flood Insurance Rate Map
  (DFIRM)
• The DFIRM will be easier to update when future
  studies are conducted or LOMAs and LOMRs are
  granted

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Benefits from CTP

• DFIRM can be placed on the Countys website for
  use by County residents, Realtors, bankers, and
  third-party map determination companies
• Orthophoto background allows structures and other
  features to be seen and more accurately
  referenced to flood zones

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CTP Lessons Learned

• If FEMA shows up at your door and offers you
  750,000 take it and run
• FEMA required no financial match from the County
• County was required to provide in-kind staff time
  to coordinate and administer the project

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CTP Lessons Learned

• FEMA transition to National Service Provider
  (Baker) but no change to our mapping contractor
• Possibly use local firm for map generation
• Things beyond our control
• Proposed improvements vs. in place
• Time extensions
• Short-change the mapping contractor

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CTP Lessons Learned

• Clay County would readily participate in another
  CTP project if the opportunity presented itself

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Things We Look Forward To

• Public review of PBSJs draft DFIRM in summer of
  2006
• Adoption of new DFIRM by Clay County Board of
  Commissioners in late 2006
• This project coming to a successful end!

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Questions?