ARMSTRONG COUNTY, PA Revised Preliminary DFIRM Mapping March 31, 2013 Kevin Donnelly, P.E., CFM GG3, Greenhorne & O Mara, Inc.
Presentation Agenda Armstrong County DFIRM Overview - June 25, 2010 DFIRM Countywide Format Vertical Datum Conversion Base Map Data New Floodplain Boundaries Incorporated Letters of Map Revision (LOMRs) GIS Products and Access Revised Preliminary Studies February 1, 2013 Enhanced (Detailed) Studies Base Level (Approximate) Studies Preliminary FIS and DFIRM Revisions
Base Map + Terrain Data + Flood Hazard Data
A DFIRM is Hardcopy Map and Flood Insurance Study (FIS) report Digital Flood Hazard Data Standard GIS database Horizontally and vertically controlled (known C.S.)
Countywide Format Countywide Production (45 communities) 1 Volume Flood Insurance Study (FIS) Report 13 effective FIS reports reduced to 1 volume New DFIRM Index based on USGS Quads Two map panel scales 1:6,000 - detailed studied streams (Zone AE) 1:12,000 - approximate studied streams (Zone A)
Countywide FIS Report Production Countywide Compilation Combined hazard information into a seamless countywide format Re-stationing and Re-lettering of Cross Sections Flood Profiles and Floodway Data Tables Vertical Datum Conversion (NGVD29 to NAVD88) Combined Effective FIS Reports 13 Effective FIS Reports combined into one countywide report
Vertical Datum Conversion NGVD 29 (old) Based on a mean sea level from 21 tidal stations in the US & 5 stations in Canada NAVD 88 (new) Based on the density of the Earth instead of varying values of sea heights Conversion in Armstrong County Varies NGVD29 + (vertical adjustment) = NAVD88 The vertical datum adjustment is 0.561 ft (negative) See page 20-21 of FIS for more information
Vertical Datum Conversion (-0.561 ft) NGVD 29 (old) NAVD 88 (new) 6 4 2 0 BFE = 4 ft 0.561 ft BFE = 3.439 ft 6 4 2 0
Base Mapping GIS Data Orthoimagery PAMAP program (1:19,200 scale and 1-ft ground resolution) Flown in Spring 2006 (Color to B/W) Transportation Road names from GIS data provided by PENNDOT and Effective FIRMs Stream Centerlines Developed from LiDAR data and Orthoimagery Vector lines with more than 1 square mile of drainage Stream names taken from USGS National Hydrography Dataset (NHD) and effective FIRMs
Base Mapping GIS Data Political Boundaries PENNDOT political boundaries NGS Benchmarks First or Second Order Vertical Benchmarks Stability C or better http://www.ngs.noaa.gov
Floodplain Boundary Changes June 25, 2010 No New Detailed Riverine Engineering Studies Detailed Studies (Zone AE and AE w/ BFEs) Re-delineation of approximately 87 stream miles using PAMAP LiDAR Approximate Studies (Zone A) New Hydrologic and Hydraulic analyses along 526 stream miles USGS Regression Equations (SIR 2008-5102) and HEC-RAS Flood boundaries mapped using PAMAP LiDAR
Redelineation (Zone AE w/bfes)
Approximate Zone A Floodplain
Improved Zone A Mapping
Improved Zone A Mapping
There were no LOMRs to be incorporated
DFIRM GIS Products and Access GIS files in a standard DFIRM database Shapefile (*.shp), Coverage (*.e00), MapInfo (*.mif) National Flood Hazard Layer (NFHL) KMZ, WMS, shapefiles Georeferenced FIRM panel images Map Store (http://msc.fema.gov) Download products: GIS database, FIS reports (pdf format), Georeferenced FIRM panels, FIRMettes Mapping Information Platform (MIP) https://hazards.fema.gov Digital Repository (Engineering Backup and DFIRM data) DFIRM Web Viewer and Training Materials Available after Effective Date (preliminary flooding available upon request)
NFHL and Google Earth NFHL Flood Hazard Zones/floodways BFEs Community Names/Boundaries Coastal Barrier Resources System Hydraulic and Flood Control Structures Cross Sections and Coast Transects (with labels) LOMRs
Revised Preliminary Study New/Restudy Using Enhanced (Detailed) Study Methodology Allegheny River two separate sections Campbell Run Redbank Creek New Base Level (Approximate) Study Methodology Buffalo Creek Tributary 1 Studies were conducted based on priority needs and funding
Enhanced (Detailed) Studies
Enhanced (Detailed) Studies Survey Six (6) structures and twenty six (26) channel cross sections were field surveyed Hydrology Peak Discharge Campbell Run - Regression equations from USGS Scientific Investigations Report 2008-5102 Redbank Creek - statistical analysis of 91 years of gage data from USGS gage at St. Charles, PA (03032500) using PEAKFQ following Bulleting 17-B Guidelines. Allegheny River Effective discharges used, calculated at USGS gage at Parker, PA (03031500). The hydrologic analysis was completed in 1974. After analysis of the calculated effective discharges, updating the effective discharges was not recommended.
Enhanced (Detailed) Studies Hydraulic Modeling HEC-RAS v4.1 steady flow model Channel cross section geometry includes field survey of the channel and PAMAP LiDAR for overbank and supplemental channel data Structures (Bridges, Culverts, etc.) Floodways modeled Water surface elevations computed for the following: 10% annual chance event (10-yr) 2% annual chance event (50-yr) 1% annual chance event (100-yr) 0.2% annual chance event (500-yr) Floodplain Mapping Delineated using PAMAP LiDAR
Base Level (Approximate) Studies Survey No Survey Performed Hydrology Peak Discharge Buffalo Creek Tributary 1 - Regression equations from USGS Scientific Investigations Report 2008-5102 Hydraulic Modeling HEC-RAS v4.1 steady flow model Channel and overbank cross section geometry from PAMAP LiDAR Impact of structures (Bridges, Culverts, etc.) not considered No floodways modeled Water surface elevations computed for the 1% annual chance event (100-yr) Floodplain Mapping Delineated using PAMAP LiDAR
Preliminary FIS and DFIRM Revisions Flood Insurance Rate Maps Revised floodplain and floodway delineation Base Flood Elevations Cross Sections FIS Report Hydrology and Hydraulics Sections Summary of Discharges Floodway Data Table Water Surface Profiles
Additional information regarding FIS reports, fact sheets, and FIRM index panels can be found at: http://www.rampp-team.com/public.htm
Questions?