GIS-Based Floodplain Submittal
Request in writing that a floodplain study be conducted by the county using GIS-based hydrology and hydraulic models with the property boundary (lot/parcel) highlighted on a tax map which clearly indicates the area of interest. The request should be sent to:
Program Support Section
Sustainable Initiatives Division
Department of the Environment
1801 McCormick Drive
Largo, MD 20774
Once a letter is received, along with the floodplain study fee (see Chapter 2.8.3 of the County’s Stormwater Management Design Manual for Fee Schedules), the request will be logged in and a 2-week turnaround time is anticipated unless there are extenuating circumstances or information is missing which precludes the study from being completed.
A county engineer will review the original request. In some cases, additional information may be required for the study to be completed. The county engineer will notify the applicant of any missing information. The existing or proposed stream crossing information necessary to complete the study is:
Federal Highway Administration chart number for the culvert
Federal Highway Administration scale number for the culvert
Headwall or wingwall type
Length of pipe/culvert
Minimum road elevations
Number of piers
Number of pipes
Pipe material and type
Upstream and downstream maximum low chord elevations of each pipe
Upstream and downstream stream invert elevations of each pipe
Width of piers
The information provided must be surveyed and tied into existing county topography. In addition, if there is a proposed stream crossing, the location should be clearly shown in the plan view.
If the study involves a balance of cut and fill, the area of cut as well as fill must be clearly defined.
Once a study is complete, a letter and map will be sent to the applicant with cross-section locations and 100-year floodplain elevations.
If the floodplain elevations are determined based on the County’s GIS topography, a freeboard will be added. However, if the applicant provides more detailed topography, no freeboard will be added.
The floodplain will need to be delineated (by the applicant) on a detailed site plan and submitted to the Department of Public Works and Transportation (DPW&T) for review and approval.
Note: Both FEMA and MDE will accept the County approved GIS-based floodplain.