Presented By: Richard Rogers - Sr GIS Technician

Guidelines and Standards for Flood Risk Analysis and Mapping Appendix L: Guidance for Preparing Digital Data and Flood Insurance Rate Map Databases April 2003 – version available when HCFCD LOMR Delegation initiated October 2011 – latest version available on FEMAs website Attribute Field formats have changed in October 2011 version. HCFCD GIS Standards Document is still based on 2003 version. Revisions to HCFCD GIS Standards Document are noted on last page. Download and follow the available version of HCFCDs GIS Standards Document before any new FEMA submittal is made. Based on FEMA document -

1: Programs & Projects 2: Model and Map Management System 3: GIS Standards Document (PDF)

Support of studies that require preparation of a CLOMR or LOMR (revision or proposed revision to the effective Flood Insurance Rate Map [FIRM]), in addition to that required in direct support of hydrologic and hydraulic modeling. All submitted GIS data has to support/reflect what is contained in your processing reports, topographic work maps and hydrologic/hydraulic models.

Last FEMA issued paper maps are the 2007 Flood Insurance Rate Map (FIRM) panels. All revisions (post 2007) are incorporated and maintained in a Digital (DFIRM) Geodatabase by FEMA. Effective GIS data is available from the FEMA map service center By LOMR case # as a Firmette (pdf) Web Map Service (WMS) National Flood Hazard Layer (NFHL) DVD (shape files) HCFCD maintains its own version of current floodplains.

Watershed drainage area boundaries Subbasin drainage area boundaries FEMA Effective Floodplain limits FEMA Effective Floodway limits Cross section location map Update all relevant GIS data layers, including revisions to the 1% and 0.2% FEMA effective floodplains and FEMA floodway limits, for all submittals when proposed activities modify any or all of the following

1% annual chance (100-year) floodplain 0.2% annual chance (500-year) floodplain Floodway Revised base flood elevations Added cross sections Revised or added linear water features Revised or added hydraulic/other structures CLOMR / LOMR boundary feature Required layers (dependent upon CLOMR/LOMR submittal) S_FLD_HAZ_AR & S_FLD_HAZ_LN S_BFE S_XS S_WTR_LN S_GEN_STRUCT S_LOMR Associated GIS Submittal Shape File

FEMA FLOODPLAIN FEATURES

All submitted GIS shape files, supporting a CLOMR / LOMR, are to be in projected grid coordinates. PROJECTION: Data Type: ESRI Shapefile Geometry Type: Polygon, Line or Point Projected Coordinate System: NAD_1983_StatePlane_Texas_South_Central_FIPS_4204_Feet

TOPOGRAPHY: Use the HCFCD LIDAR dataset (2001) with 2-foot contours as the base topographic data set for modeling purposes. The 2001 LIDAR dataset meets the minimum accuracy requirements for use in FEMA studies. However, the data must be supplemented with survey data for use in hydraulic analysis. Only use the 2001 LIDAR dataset provided by HCFCD for CLOMR and LOMR submissions. All other LIDAR datasets are not allowed. Note: Mapping proposed sites developed since 2001 may not be able to use the 2001 LIDAR dataset because the 2001 LIDAR does not reflect the change. In these cases, for a CLOMR use the conceptual plan or proposed design plans for the project, and for a LOMR use field surveyed topography or as-built survey data.

TOPOLOGY: Area spatial features for a given theme must cover the entire study area without overlaps, under laps or sliver polygons between adjacent polygons. Files must be free of discontinuities such as overlapping lines, gaps, "turn backs," dangling lines and duplicate elements. Vertices should be placed conservatively when designing features so that only the minimal number of vertices or nodes is used to create the desired shape with appropriate smoothness Lines must begin and end at nodes, connect at nodes and not extend through nodes. S_FLD_HAZ_LN: Endpoints at Zone change S_FLD_HAZ_AR: Merge together contiguous same Zone types. (no sliver polygons)

TOPOLOGY: Coincident features are those that share the same location or boundary, such as flood zone boundaries. These coincident features must superimpose, vertex (shape point) for vertex, within the files. The following pair of shape files have both area features and line features: S_FLD_HAZ_LN (line) and S_FLD_HAZ_AR (polygon). All spatial elements in the S_FLD_HAZ_LN must match exactly with the boundaries of the elements in the S_FLD_HAZ_AR.

TOPOLOGY: New Personal or File Geodatabase New Feature Dataset, define Projection, use default fields for Tolerance In Feature Dataset -> Import Feature Class (multiple) : S_FLD_HAZ_AR, S_FLD_HAZ_LN, S_LOMR In Feature Dataset -> New Topology, Cluster Tolerance (use default) repairs minor errors Select feature classes, add Rules (may be easier to repair individually) S_FLD_HAZ_AR Must Not Overlap S_FLD_HAZ_AR Must Not Have Gaps S_FLD_HAZ_AR Boundary Must Be Covered By S_FLD_HAZ_LN S_LOMR Must Be Covered By Feature Class Of S_FLD_HAZ_AR S_FLD_HAZ_LN Must Not Overlap S_FLD_HAZ_LN Must Not Intersect Finish and Validate Topology

TOPOLOGY: Add Topology to ArcMap w/features, add Topology & Editor Toolbars, start editing session From Topology Toolbar - Map Topology (select features to participate) Topology name should appear in window If you need help with individual tools & editing features consult: ArcGIS Desktop Help (topology, editing features in) Validate topology after repair until either no errors are found or are explainable. Topologically correct feature classes can be exported to replace shape files.

DATA STRUCTURE: Shapefiles submitted should only cover the geographical extent of CLOMR / LOMR area. All Shapefile names and Attribute Fields are to be in Upper Case, Formatted, Named and Populated as described in the HCFCD GIS Standards Document. Any empty/Null Attribute Fields should be left blank. Not populated with. No MicroStation or AutoCAD files.

DATA STRUCTURE: Cross Section files, exported directly from HecGeoRAS, will need to have the correct/populated Attribute Fields as described in the manual for S_XS.

Added S_XS could be correctly located with incorrect STREAM_STN value or incorrectly located with correct STREAM_STN value.

In a Feature Dataset (with Topology) create a Feature Class of your S_XS and copy your channel alignment into it. The channel alignment should have no splits before copying. In Topology Properties (Feature Classes tab) add the new Feature Class Add Topology to ArcMap, start an edit session, select all features in the Feature Class At Topology Toolbar click the Planarize Lines button (use defaults) All Features are now split at intersections. Delete cross section features and save edits. You now should have a channel alignment, split at cross sections, to check Stationing with the [Shape_Length] Attribute Field. Open Attribute Table of S_XS file, Options – Export Data & save as dBASE Table Alternately: you could hand edit (split) the channel alignment at your S_XS locations XTools Pro – Feature Conversions – Split Polylines – Split polylines by another layer

Open dBASE Table in Excel and convert STREAM_STN to number and sort on field. Three columns are created: CH_Seg = channel segment (Shape_Length) between Effective XS and next XS location (up or downstream) cut by your S_XS file STN by CH_Seg = first effective XS + CH_Seg between next location cut by S_XS (B2+D2, B3+D3..) Diff = your S_XS STREAM_STN – STN by CH_Seg (calculated value) at that same location 5% map scale (50 FT max)

DATA STRUCTURE: Single bounding polygon to indicate LOMR areas that are to be incorporated into the Flood Insurance Rate Map (FIRM) or communicate areas of DFIRM data that were updated to reflect the results of LOMRs. Spatial extent should encompass the area where any of the following conditions have occured: modification of the existing regulatory floodway, modification of the Special Flood Hazard Area (SFHA), modification of the 0.2% annual chance flood hazard area, added or revised base flood elevations, added or revised lettered cross sections, added or revised hydraulic structures, added or revised channel alignments or detention/retention features.

DATA STRUCTURE: Generally it will cover the spatial extent of any areas/features that are being changed due to a CLOMR/LOMR. The S_FLD_HAZ_AR and S_FLD_HAZ_LN features are clipped by the S_LOMR boundary. S_LOMR usually will not have coincident S_FLD_HAZ_LN features. Exceptions would be, for example, if S_FLD_HAZ_LN (LN_TYP = LIMIT OF DETAILED STUDY) S_LOMR will have coincident S_FLD_HAZ_AR features.

Richard Rogers - Sr GIS Technician Harris County Flood Control District (direct) Please contact me directly if you have any questions or concerns with your GIS data before submittal.