& Special Flood Plain Policy Update

2.0 FLOOD PLAIN ANALYSIS
2.1 Existing Flood Plain Policy and Secondary Plan
Riverine hazard lands exist within the Dunnville Secondary Plan area. Flooding originates from the Grand River under
extreme flow events, this flooding potential is recognized in various past flood plain mapping studies and within the existing
Special Policy Area (SPA) that addresses a portion of lands within the Secondary Plan area and along the waterfront.
Existing SPA delineation in relationship to the Secondary Plan area is indicated in Figure 2.1. Also indicated in the Figure is
the extent of predicted flooding as outlined on existing Grand River Conservation Authority (GRCA) flood plain mapping for a
Regulatory event (additional details outlined in Section 2.2).
The SPA applicable to Dunnville and currently adopted within County planning documents is contained in Section 2.C.1.11 of
the Official Plan and shown in Figure 2.1. In summary, the three zones within the existing SPA (labeled as Area 1, 2 & 3)
ensure protection of new buildings, structures and major additions by requiring flood-proofing to the following levels:
Area 1: to the level of the Regulatory Flood - to an elevation of 179.0 m
Area 2: to the level of the Regulatory Flood - to an elevation of 176.5 m
Area 3: to the level of the 100 Year Flood - to an elevation of 178.7 m
As indicated, the existing SPA does not extend to all Regulatory flood inundated portions of the Secondary Plan area. Most
notably lands located east of SPA Area 3 and north of SPA Area 2 are not included in an SPA. Additionally, it is clear that
where Areas 1, 2 and 3 of the SPA converge, determining the correct protection level to use will require further analysis
(discussed further in Section 4.1.)
The Provincial Policy Statement requires that significant development be excluded from areas prone to flood inundation
unless those areas are addressed within an approved SPA (or a Two-Zone Flood Plain Policy). Areas that lie outside of an
SPA (or Two-Zone Flood Plain Policy) are generally subject to a One-Zone policy approach whereby all new development is
restricted from areas subject to flood inundation.
Given the opportunity to address a larger and contiguous area of historical flood plain development, such as lands located
within the Dunnville Secondary Plan area, consideration is usually given to applying a common policy across the lands – i.e.,
a Special Policy Area. An SPA sets common rules for development that have been agreed to by the flood plain regulator (i.e.
GRCA), the County and the Province. The Province is party to the agreements, and is ultimately the approval authority
through an Official Plan Amendment. It is based upon recognition of a given additional level of flood risk, with this determined
DUNNVILLE SECONDARY PLAN AND SPECIAL FLOOD PLAIN POLICY UPDATE: ISSUES AND OPTIONS REPORT | 5