Floodplain Mapping

FEMA Regulatory Requirements and Compliance: PACE has a tremendous background of experience in working with FEMA staff and their consultants for the approval of projects.  In addition, we have completed numerous floodplain investigations for different communities and have worked with the regulatory requirements that include developing floodplain management guidelines, regulatory floodways, erosion hazard zones, and processing of numerous map revisions.  Numerous guidance documents related to flood insurance studies or floodplain mapping are available or have been published by FEMA, and PACE is familiar with their application.  Working knowledge of these documents ensures that the analysis meets the minimum FEMA requirements and satisfies the community’s objectives.  Some of these documents include: (1) Flood Insurance Study – Guidelines and Specification for Study Contractors, (2) Guidelines for Preparing Technical Support Data Notebook, and (3) Guidelines for Scoping Flood Insurance Studies.  Many of these guidelines included numerous criteria for hydraulic analysis and acceptable procedures that are not necessarily described in the NFIP regulations.  PACE is familiar with the key aspects to the re-study of an FIS which includes the processing and communication with FEMA to facilitate the review.   Understanding the FEMA NFIP regulations as outlined 44 CFR Part 65 provides guidance to ensure that the FIS meets all the necessary requirements and the community’s objectives.

FEMA Map Revisions (CLOMR/LOMR): PACE routinely prepares numerous technical flood hazard map revisions annually for locations throughout the nation and implemented processes with FEMA that have included many levee systems.  A detailed process has been developed by PACE for preparation of the CLOMR/LOMR submittal packages to ensure completeness and accuracy. Our extensive background on the map revision process has provided PACE with extensive experience with the current changes to the NFIP regulations and assisted in developing relationships with the FEMA staff in Washington and the Region IX office in Oakland.  In addition, this has also provided background relative to the hydraulic analysis techniques associated with levee systems required by FEMA.  Specialized hydraulic issues include: (1) ineffective flow areas, (2) non-regulatory levees eliminated from modeling one side at a time, (3) additional freeboard requirements at upstream, and (4) flow impingement.

Floodplain Analysis / River Hydraulics: Floodplain hydraulics is one of the primary areas of specialization of our stormwater engineers. PACE applies sophisticated hydraulic models to analyze the physical process of natural alluvial and urbanized floodplains.  The approach that PACE utilizes for Floodplain Information Studies (FIS) and floodplain mapping studies follows a logical work sequence of the technical analysis to ensure the accuracy of the final delineation.  The PACE staff has a tremendous working knowledge of the HEC models including HEC-2, HEC-RAS, and GEO-RAS that are routinely utilized in floodplain analysis.  In addition, some of the staff has taught university level courses on Computer Assisted Floodplain Modeling, which ensures a good solid technical background in floodplain analysis. The background in floodplain analysis includes (1) correct interpretation of model results, (2) correctly determining the characteristics of the floodplain which includes cross section location, orientation, roughness values, bridge modeling, culvert modeling, use of ineffective flow areas, and floodway modeling. PACES routinely has been involved in unique floodplain analyses including alluvial fan flooding, urbanized flooding, and overflow floodplains.  PACE routinely applies FLO-2D for the analysis of complicated floodplain hydraulics to develop a better understanding of the hydraulic characteristics from the one-dimensional model. The overland flow floodplain or split flow is more appropriately evaluated through the use of a two dimensional model.  We have successfully applied FLO-2D for several flow split evaluations and urbanized floodplains where the use of HEC-RAS did not clearly define the solution or the flow paths.