Flood Plain Information

DELAWARE COUNTY FLOOD PLAINS (POLYGON COVERAGE OF 100 & 500 YEAR FLOODS):

Introduction:

In 1999, the Delaware County Auditor’s office received two sets of digital coverages from Dewberry & Davis of Fairfax, Virginia (a consulting company under contract with the Federal Emergency Management Agency (FEMA)) in ArcInfo Export file format. These sets contained no polygon topology and were originally created with Intergraph GIS software. Both sets were created using a different grid scheme. The first scheme corresponded to the United States Geological Survey (USGS) 7.5 minute quadrangles and the second corresponded to the FEMA Flood Insurance Rate Map (FIRM) scheme. The flood plains were delineated by FEMA. Both sets of digital coverages were used to extract the 100-year and 500-year flood plains, base flood elevation, cross section lines, and floodways for Delaware County, Ohio.

The digital base maps were originally georeferenced to Universal Transverse Mercator (UTM), Zone 17, Horizontal Datum NAD27, Vertical Datum NGVD29, Clarke 1866 Spheroid, Units Meters and were distributed as ARC/INFO export files. The original scale of these maps were 1": 500", 1": 1,000", and 1": 2,000". The export files were brought into the Delaware County GIS and georeferenced to the County wide standard of State Plane North, Zone 4976, Horizontal Datum NAD83, Ohio North and Vertical Datum NAVD88, GRS 1980 Spheroid, Units Feet. This matches Delaware Appraisal Land Information System (DALIS) databases. For additional information regarding DALIS databases and/or FEMA and DFIRM original code levels contact our office at (740) 833-2070.

Flood Plains Metadata:

Flood Plain information is obtained from FEMA and is administered by the Delaware County Building Department (740-833-2201)

The two digital base maps contained attributes that were coded with the FEMA Digitizing Levels or the DFIRM Digitizing Levels. The cross section lines (fpcs), base flood elevations (fpbfe), and floodways (fpfw) were extracted from the FEMA base map. The fpbfe and fpcs coverages include annotations. The FEMA defined levels used to extract the coverages are listed in Table 1.

The 100-year flood plain (fp100) and 500-year flood plain (fp500) coverages were extracted from the DFIRM base map. The DFIRM defined levels used to extract the coverages are listed in Table 2. See Table 3 for the DALIS defined level descriptions. In addition to the six flood plain related coverages, two more coverages containing the grid scheme used by FEMA and USGS are included. These coverages are femagrid (FEMA) and usgsgrid (USGS).

The femagrid and usgsgrid are polygon coverages. The polygons have been coded with one of the following items: PANEL_NO 3 3 i, QUADNAME 20 20 c

The fpfw, fp100, and fp500 are polygon coverages. The polygons have been coded with the following items: LEVEL 2 2 i , NAME 35 35 c

The fpcs and fpbfe are arc coverages. The arcs have been coded with the following item: LEVEL 2 2 i

All coverage’s were appended with the line option and were edge matched for continuity. The edge matching process of the fp100 has resulted in some minor spatial movement in approximately six of the arcs. The arcs that didn’t edge match correctly were shifted toward the arcs in the smaller scaled coverage. If both edge matched panels were of the same scale, the arcs were shifted half the distance toward each other until edge matching was complete. While elevations were not originally populated in the attribute files of Cross Section Lines and Base Flood Elevation coverages, annotations for those elevations were included. Therefore, fpcs and fpbfe coverages include elevation annotations.

Flood Plains Disclaimer:

The Delaware County Code Compliance Department provides this geographic data "as is". Code Compliance makes no guaranty or warranty concerning the accuracy of information contained in this geographic data. Code Compliance further makes no warranties, either expressed or implied, as to the condition of this product, or its fitness for any particular purpose. The burden for determining fitness for use lies entirely with the user. Although these types of data have been processed successfully on computers of Code Compliance, no warranty, expressed or implied, is made by Code Compliance regarding the use of this data on any other system, nor does the fact of distribution constitute or imply any such warranty. In no event shall Code Compliance or Delaware County have any liability whatsoever for payment of any consequential, incidental, indirect, special, or tort damages of any kind, including, but not limited to, any loss of profits arising out of use of or reliance on the geographic data.