Flood Risk and Vulnerability Analysis Project - Atlantic Climate ...

Standards Association 21 recommends that IDF relationships be updated every 5 years due to
projected climate change. As such, the following priority factors were applied:
Weighting Description
0 Maps up to 5 years old were flagged as low priority for update
1 Maps up to 10 years old were flagged as high priority for update
2 Maps older than 20 yrs were flagged as urgent for update
4.1.2 Topographic Map Base
Table 4-1. Age of Flood Study Weighting
Base mapping has changed significantly since the wide availability of sophisticated GIS
platforms and analytical tools. Provincial base mapping including topography and digital
elevation/terrain models (DEM‟s/DTM‟s) are generally updated every few years.
The age/vintage of the base mapping used to delineate flood plains may be a trigger to initiate a
re-mapping exercise. Upon reflection, the general approach is to use the most up to date
mapping available at the time of the flood study. As such, the age of the flood plain map study is
considered a sufficient recognition of base map age. As such, base map vintage was not given
separate consideration in this evaluation.
4.1.3 Analytical Methods
Approximate vs. Engineered Methods
Flood plains are typically delineated using one of two basic methodologies, namely:
approximate and engineered.
Approximate methods: as name implies, use simplified approaches for estimation of hydrology
and hydraulics to estimate flood plains. Accuracy for approximate methods is generally
accepted as 1 or 2 contour intervals. Approximate flood plains are meant to provide an “idea” of
where the flood plain limit is.
Engineered methods: are much more rigorous and detailed in their analysis of hydrology and
hydraulics. Engineered flood plains are used for development regulation.
21 Technical guide: Development, interpretation and use of rainfall intensity-duration-frequency (IDF)
information: Guideline for Canadian water resources practitioners, 1 st ed., Canadian Standards
Association, 2010. Available at http://shop.csa.ca/en/canada/infrastructure-and-public-works/plus-4013-
1st-ed-pub-2010/invt/27030802010/
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