FEMA Flood Hazard Geodatabase Design
Shane Walker, CRWR
Table of Contents
The National Flood Insurance Program (NFIP) was initiated by the U.S. Congress in the late 1960’s with the purpose of assessing flood risk and collecting insurance fees under the supervision of the Federal Emergency Management Agency (FEMA). In the 1990’s, FEMA administrators realized that the NFIP system was financially overextended and most of the Flood Insurance Rate Maps (FIRMs) were outdated. Thus, with financial support from Congress, FEMA initiated the Map Modernization program to restudy and/or convert existing FIRMS to Digital Flood Insurance Rate Maps (DFIRMs). FEMA developed the Guidelines and Specifications for Flood Hazard Mapping Partners to guide the engineering firms performing the studies. Appendix L: Guidance for Preparing Draft Digital Data and DFIRM Database of the Guidelines specifies the database format in which engineering firms are required to submit Geographic Information System (GIS) data contained in the DFIRMs. Subsequently, FEMA issued Appendix N: Data Capture Standards to define the database format in which engineering firms are required to submit engineering, GIS, and modeling data used to create the DFIRM details.
Appendix L specifies a relational database with three types of tables: spatial, lookup, and domain. These DFIRM database tables are used to store cartographic information within DFIRMs. The spatial, lookup, and domain tables have a name prefix of “S_”, “L_”, and “D_”, respectively. The spatial tables store tabular information associated with a set of geometric features (e.g., a shapefile). The lookup tables are simple database tables that store supplemental information. The domain tables are lists of valid entries for particular fields within spatial and lookup tables. Appendix N specifies a relational database with the same types of tables as Appendix L: spatial, lookup, and domain. These DCS database tables are used to store information about terrain, survey, hydrologic, and hydraulic data used to create DFIRMs. However, there is some overlap between DFIRM database tables and DCS database tables, and Flood Hazard Mapping Partners are required to submit these two separate databases with similar, but slightly different data.
The objectives of this research are to:
1) Merge the DFIRM and DCS databases into a single database,
2) Convert the merger database into a Flood Study Geodatabase, and
3) Connect the Flood Study Geodatabase to the water resources community.
The thought model for meeting the objectives of this project are as follows:
1) Eliminate duplication of information between the DFIRM and DCS databases by eliminating DFIRM tables that are superseded by DCS tables, and convert all primary key fields to short integer to allow relationships to be created.
2) Convert DFIRM and DCS spatial, lookup, and domain tables to geodatabase feature classes, object classes, and coded value domains, respectively
3) Create a linear event table to relate the Flood Study Geodatabase to the National Hydrography Dataset - High Resolution (NHD 24K).
Procedure
of Application [back to top]
The Flood Study Geodatabase (FSG) schema was developed using a Microsoft Excel spreadsheet, a custom VBA script, and the ESRI Geodatabase Designer 2 Toolbar for ArcCatalog. The FSG Excel spreadsheet contains four worksheets describing the attributes of the geodatabase components: coded value domains, feature classes, object classes, and relationships (Figure 1 through Figure 4). An Excel VBA macro was written to translate the data stored in the FSG spreadsheet into an XML schema file that is compatible with the Geodatabase Designer 2 Toolbar (Figure 5). The “Import from XML” tool in the ESRI Geodatabase Designer 2 Toolbar (shown in Figure 5) was used to create an ESRI Flood Study Geodatabase (FSG) from the XML schema file.
Figure 1 FSG Spreadsheet – Domains Worksheet
Figure 2 FSG Spreadsheet – Feature Classes Worksheet
Figure 3 FSG Spreadsheet – Object Classes Worksheet
Figure 4 FSG Spreadsheet – Relationships Worksheet
Figure 5 ESRI Geodatabase Designer 2 Toolbar
Results and
Conclusions [back to top]
The Flood Study Geodatabase contains 56 feature classes partitioned into six feature datasets containing (Figure 6) and also contains 37 object classes (Figure 7). Feature class correlation between the Arc Hydro data model and the Flood Study Geodatabase is illustrated in Figure 8. A Flood Study Geodatabase diagram (thumbnail shown in Figure 9) was produced using the ESRI Geodatabase Diagrammer Toolbar.
Figure 6 Flood Study Geodatabase Feature Class List
Figure 7 Flood Study Geodatabase Object Class List
Figure 8 Arc Hydro and Flood Study Geodatabase Feature Class Correlation
Figure 9 Flood Study Geodatabase Diagram
The Flood Study Geodatabase
successfully combines the data contained in the DFIRM and DCS database, employs
geodatabase technology, and is related to the water resources community through
the NHD linear event table.
Primary contact for FEMA Flood Hazard Geodatabase Design: [back to top]
Shane Walker
Center for Research in
These materials may be used for study, research, and education, but
please credit the authors and the Center for Research in Water Resources, The