Background
As part of their implementation of the North Dakota Map Modernization Plan, the North Dakota State Water Commission (NDSWC) selected HEI to perform floodplain map modernization or Risk MAP projects for 17 counties in North Dakota. The projects include preparing countywide digital flood insurance rate maps (DFIRM) or DFIRM updates for each county along with flood insurance studies (FISs) for several streams. These projects have included the production of more than 400 DFIRM panels as well as post-preliminary processing activities through map adoption.
The Project
HEI’s responsibilities for the projects include scoping, base map acquisition, topographic data acquisition, field survey, hydrologic and hydraulic analysis, floodplain mapping, DFIRM database creation, preliminary map production and distribution, post-preliminary processing, and outreach.
GIS and DFIRM
Geographic information system (GIS) is used throughout each phase of the DFIRM project. When gathering the scoping data, ArcMap is used to develop the maps to help show the project areas. The topographic data is normally stored in GIS databases. When working on the base map acquisition phase, data is gathered from various local and state sources and stored in an ESRI file geodatabase. Our engineers use several different mapping tools to help plot the flood areas during the hydrologic and hydraulic modeling analysis. Both the models and shapefiles are sent to FEMA partners for review and data storage. The flood mapping phase is one of the most intensive uses of GIS.
Once the models are complete, ESRI models and scripts that were developed for mapping the models are used to get the final polygons to show the flood areas. These will eventually become zones within the DIFRM database. Other items that are required in the database are made at this point to help fill out the FEMA DFIRM database.
Once the DIFRM database is built using ArcMap, the panels can be built. The panels will eventually be used to show the public where flooding is occurring for the 1% and 0.02% chance flooding events, also known as the 100- and 500-year flood events. These will be categorized within the DFIRM database as ZONE AE and ZONE X with varying attributes. These panels will be made with all the data from the newly made DFIRM database. Using all the tools ArcMap offers to make this process go smoothly and efficiently is key to getting these panels done correctly. The panels will be considered preliminary and will go out to the public for comment and review.
After the review period, changes will be made depending on public comments. After the edits from the public comments are incorporated into the panels, they are then released back for final commenting before becoming effective. This means they will now be the official flood maps for the area.
This whole process heavily uses GIS from survey and engineering to building the DFIRM database and making maps. Many Arc tools are used with models and scripts throughout the process.
Client Benefits
- Production of more than 400 DFIRM panels for North Dakota counties.
- Deeper insight from an experienced water resources firm that understands every aspect of floodplain management.
- Additional services were provided for some counties, such as floodway analyses and Flood Insurance Studies.
- Understanding of the development of floodplain maps help us better navigate FEMA requirements for project implementation.