Note
The information in this notice has been updated in IP-23-01.
Background
County Stormwater Practices and Procedures Manual (SWM Manual) requires the delineation of non-tidal floodplain when a floodplain exists on a site and this is typically required prior to the project final plan approval. A floodplain exists on-site and a determination of 100-year floodplain is required- If the total runoff, from the 10- year 24-hour storm, to any discharge point from a site is equal to or exceeds 100 cfs, or if a platted 100-year floodplain is located adjacent to or upstream of the site.
Purpose
When a floodplain exists on-site, the county requires delineation of floodplain. This delineation should meet section 7.8.2. of the SWM Manual. Currently, the county does map the delineated floodplain in the county GIS system. The purpose of this memo is provide notice that when floodplain delineation is required, the design professional should provide certain information to the county so it can be used to map the floodplain in the county GIS system. The Department of Public Works (DPW) maintains GIS mapping system and to assist with this effort, the Department of Inspections has reached to DPW, Bureau of Watershed Protection and Restoration (BWPR) regarding project submittal requirements.
Project Submittals – Floodplain Studies
After the approval of the floodplain study, the design professional should submit the below information to the county reviewer. This information should be submitted electronically (shared drives, drop box, ftp site, etc.):
- GIS shapefile of the modeled floodplain. If the design professional does not have access to GIS to add attributes to the floodplain shapefile, the Flood Data Description Memo below provides guidance on how this information should be submitted.
- PDF of the approved floodplain study
The Flood Data Description Memo below provides further guidance on the GIS shape file and instructions. In all cases, the design professional should ensure the data have the projected coordinate system NAD 1983 StatePlane Maryland FIPS 1900 (US Feet). The county reviewer will share this information with DPW BWPR.
Timing
This memo applies to all floodplain studies submitted after the date of this memo. I&P has coordinated with the development community regarding this information and I&P appreciates the collaborative effort to help add the floodplain information to the county GIS system.
Overview
To assist Inspections and Permits with the acquisition of modeled 100-year floodplain polygons by the development community, the Modeling and Analysis Unit of BWPR has provided a template shapefile ‘IP_FloodPolygons.shp’, an associated report information ‘ReportInformation.xlsx’. The attribute table for this shapefile can be seen in Figure 1.
Template Shapefile
Figure 1: Attribute table for IP_FloodPolygons.shp
The modeled 100-year flood polygon should either be appended to the template shapefile, or an existing shapefile should be formatted to include the fields in Figure 1, as described in Table 1. If the data preparer does not have access to GIS to add attributes to the floodplain shapefile, please see below. In all cases, the data preparer should ensure the data have the projected coordinate system NAD 1983 StatePlane Maryland FIPS 1900 (US Feet).
| Field | Description | Domain to be used |
|---|---|---|
| FID | Auto-populated by software | |
| Shape | Auto-populated by software | |
| ReportID | Report ID used to link associated table | |
| HH_Model | Hydraulic and/or hydrological model used | |
| ProjectNam | Name of project if applicable | |
| GradingPer | Grading Permit ID if applicable | |
| FloodOwner | Floodplain Owner | County, County-Easement, Private |
| Shape_Leng | Auto-populated by software | |
| Shape_Area | Auto-populated by software |
Each Shapefile should be named by combining the calendar year, company initials, and project location. For example, if the shapefile was prepared in 2021 by Morris & Ritchie Associates, Inc. for River Road Field Description Domain to be used FID Auto-populated by software Shape Auto-populated by software ReportID Report ID used to link associated table HH_Model Hydraulic and/or hydrological model used ProjectNam Name of project if applicable GradingPer Grading Permit ID if applicable FloodOwner Floodplain Owner County County-Easement Private Shape_Leng Auto-populated by software Shape_Area Auto-populated by software New Development, then the shapefile should be named “2021MRARiverRoadNewDevelopment.shp”. For floodplains that might not be contiguous but were modeled for the same project, a multipart polygon can be submitted.
Explanation of Fields in IP_FloodPolygons.shp
Although the basic information to be included in the shapefile is outlined in Figure 1, and described in Table 1, further explanation is provided below for greater clarity.
ReportID
The purpose of this field is to link a given flood polygon to each record in the table contained in ReportInformation.xlsx. It is critical that ReportInformation.xlsx is completed to document data sources. There is no required format for this field, but it should be unique for every polygon that is created by the data preparer.
HH_Model
The purpose of this field is to document the hydrologic and hydraulic models used to generate the flood polygon. For example, this could be “HEC-HMS and HEC-RAS”.
ProjectNam
This field should contain the project name, where applicable. For example, this could be “1234 New Office Road Construction”.
GradingPer
This field should contain the Grading Permit number associated with the study, where applicable.
FloodOwner
This field should note who owns the floodplain, either the County, privately held, or whether it is under a County-Easement.
Template Spreadsheet
In addition to the template shapefile, the Modeling and Analysis Unit of BWPR is also requesting that the template spreadsheet, ReportInformation.xlsx, be filled out. This will ensure documentation of data sources which will be critical long term.
Explanation of Fields in ReportInformation.xlsx
The purpose of the spreadsheet is to record details about the specific study that generated the modeled flood polygon. Data in the spreadsheet are linked to the shapefile via the ReportID field. Descriptions of these fields can be found in Table 2, and further explanation is provided below for greater clarity.
| Field | Description |
|---|---|
| ReportID | Report ID used to link to table to feature class |
| Authors | Authors of report or data |
| Title | Title of the report |
| EngineeringFirm | Name of engineering firm that created report/data |
| ReportDate | Date that report was published |
| FileLocation | Link to file on server, if applicable. I&P to complete. |
ReportID
This field should contain a report ID used to link each row in the table contained in ReportInformation.xslx to the associated flood polygon in IP_FloodPolygons.shp. As stated earlier, there is no required format for this field, but it should be unique for every polygon that is created by the data preparer.
Authors
This field should contain the names of the authors of any report associated with the flood polygons. If no report is available, this field should contain the names of the authors of the flood polygon.
Title
This field should contain the title of the report associated with the flood polygon.
EngineeringFirm
This field should contain the title of the report associated with the flood polygon. If no report is available, this should contain the name of the firm who created the data.
ReportDate
This field should contain the data of the report associated with the flood polygon.
FileLocation
This field should contain the file location of the report associated with the flood polygon. Field Description ReportID Report ID used to link to table to feature class Authors Authors of report or data Title Title of the report EngineeringFirm Name of engineering form that created report/data ReportDate Date that report was published FileLocation Link to file on server, if applicable. I&P to complete.
If Data Preparer Does Not Have Access to GIS
If the data preparer does not have access to GIS software, the shapefile can be submitted solely with geometry. However, shapefile attributes outlined in Table 1 should be provided as an Excel spreadsheet. In such cases, an extra field “ShapefileName” should be entered in the spreadsheet stating the name of the shapefile. This will allow Anne Arundel County to append these attributes to the geometry. A template is found in ‘ShapefileAttributes.xlsx’.