Summary of Changes for Appendix C
Guidance for Riverine Flooding Analyses and Mapping


The Summary of Changes below details updates to Appendix C, which were made 
subsequent to the publication of this appendix in April 2003.  These changes represent 
new or updated guidance for Flood Hazard Mapping Partners.  Appendix C was 
reformatted to be consistent with the Mapping Activity Statements and the study workflow 
steps in the Mapping Information Platform (MIP).  As a result, a summary of the new and 
updated information is presented below for each major section rather than updates 
incorporated into the April 2003 layout.    

In addition to the changes outlined below, the revised Appendix C summarizes 
requirements at the beginning of each section and later describes the analysis procedures in 
greater detail.  The use of the word "must" has replaced the word "shall" consistent with 
other updates to Guidelines and Specifications. 

The major changes in the hydrologic analyses, hydraulic analyses, floodway analyses and 
floodplain boundary sections are summarized in the table below.  
 



Date
Affected 
Section/Subsection 
Description of Changes
November 2008
C.1 Introduction
Definitions are provided for Approximate, Limited 
Detailed and Detailed Studies.  More details are 
provided on the documentation required for flood 
insurance studies than in the April 2003 version of 
Appendix C.
November 2008
C.2 Hydrologic 
Analyses
Plus or minus one standard error (68-percent 
confidence interval) is adopted for determining 
statistical significance rather than the 90- and 50-
percent confidence intervals (as used in the April 2003 
version) in order to reduce the subjective judgment in 
this process. 
The Hydrologic Analysis Requirements that must be 
met are first summarized and then the hydrologic 
procedures are described.
For rainfall-runoff models, each hydrologic process is 
described in detail.  The processes include rainfall, 
rainfall losses, sub-basin responses, routing, input 
hydrographs, channel and reservoir storage and 
calibration of hydrologic models.
November 2008
C.3 Hydraulic Analyses
The Hydraulic Analysis Requirements that must be 
met are summarized first and then the hydraulic 
procedures are described.
New sections are provided on 1-D steady flow, 1-D 
unsteady flow, and 2-D models.  In each section the 
hydraulic modeling process is described in more detail 
than given in the requirements section.  The hydraulic 
processes include a discussion of cross sections, 
topographic data, hydraulic structures, non-conveyance 
area, loss coefficients, initial and boundary conditions, 
split flows, supercritical flow and calibration of 
hydraulic models.
November 2008
C.4 Floodway Analyses
The Floodway Analysis Requirements that must be 
met are summarized first and then the floodway 
procedures are described.
New sections are provided on floodway analyses for 
steady state and unsteady state modeling including the 
use of 2-D models.  More detailed is provided on 
floodway analyses for unsteady flow modeling than in 
the April 2003 version of Appendix C.
An example is provided for a floodway data table for a 
link-node type model.  
November 2008
C.6 Floodplain 
Boundaries
The Floodplain Boundary Determination Requirements 
that must be met are summarized first and then the 
floodplain boundary determinations for 1-D and 2-D 
models are described.