Background
When a floodplain exists on-site, the county requires delineation of floodplain. This delineation should meet section 7.8.2 of the SWM Manual.
On 3/18/2021, the Department of Inspection and Permits - Engineering Division (I&P) in collaboration with the Department of Public Works - Bureau of Watershed Protection and Restoration (BWPR) issued the original IP-21-06 notice outlining information that is needed from the design professionals to aid BWPR in mapping and subsequently publishing the floodplains in the County’s Geographic Information System. The original notice required the design professionals to provide the information in a polygon ArcGIS shapefile format following a prescribed shapefile template as outlined in the DPW-BWPR March 4, 2021 memo. Two issues arose during the implementation phase as follows:
- Design professionals typically prepared this information as polylines in CAD or other environments and did not consistently have access to ArcGIS licenses. Files submitted to the County by exporting the delineation directly from CAD as shapefiles did not follow the prescribed BWPR template; and Non-Tidal Floodplain Delineations – Development Projects January 5, 2023
- I&P engineers could not verify that the GIS shapefiles match the approved delineation before forwarding the information to BWPR. This revised project submittal requirements shown below are the result of collaboration between I&P and BWPR to address these issues.
Revised Required Project Submittals – Floodplain Studies
After the approval of the floodplain study and the preparation of the floodplain easement documents, the design professional should submit the floodplain delineation along with the approved study to the county engineer reviewer via email. For delineations that are based on base flood elevations, submit a PDF of the previously platted 100 year floodplain. For delineations that are based on proposed flood elevations, submit a PDF of the Plat easement exhibit (signed by the engineer manager) and a PDF file of the approved floodplain study. Larger file attachments (more than 10 MB) shall be uploaded to a Google drive location (to be made available by the I&P engineer).
This information is required before the final subdivision plans or the final site development plans are approved. The county reviewer will share this information with DPW BWPR. Subsequently, DPW BWPR shall utilize the X and Y coordinates for the three tick marks on the previously platted file or the proposed approved Plat exhibit to geo-reference and digitize the floodplain limits in the GIS environment. The delineated floodplain limit along with the study report will be published by DPW BWPR to the public through the County enterprise GIS system.
Timing
This memo applies to all floodplain studies submitted after the date of this memo.