Thompson Creek Flood Study Report - City of Peterborough

Thompson Creek Detailed Flood Reduction Study
City of Peterborough
4.5 SIMULATION OF FLOOD VULNERABILITY DESIGN EVENTS
Based upon the city-wide “Flood Reduction Master Plan,” the overall Terms of
Reference for the “Detailed Flood Reduction Studies” were developed. These defined
an overall set of storm events which were to be used during the detailed studies to
evaluate flood vulnerability. These “design rainfalls” were selected to: simulate
conditions as they occurred during the July 2004 storm, address mapping of flood
plains and overland flow routes and provide a basis for flood damage estimation. Each
rainfall was simulated with the three models described above to calculate flows, water
levels and extent of flooding. The following sections describe this process.
4.5.1 Definition of Design Rainfalls
As noted, the “design rainfalls” fall into three groups:
the actual storm of July 14 -15, 2004 which led to such extensive flooding
a set of storms with pre-defined total rainfall volumes (40mm, 60mm, 80mm,
100mm, 120mm and 193mm) to be used for mapping the extent of flood plains
and overland flow spills routes
a set of storms with specific return periods (1 in 2 year, 1 in 5 year, 1 in 10 year,
1 in 25 year, 1in 50 year and 1 in 100 year) to be used to evaluate the numerical
value of average annual flood damages. This is required as part of the benefitcost
evaluation of any proposed remedial measures.
The following sections describe in detail the storms used based upon discussions held
between City staff, MMM and consultants for the parallel detailed flood reduction
studies underway on other City watersheds (see Appendix K for documentation).
4.5.1.1 Peterborough Storm of July 14 - 15, 2004
Given the significance of the July 2004 storm, a detailed investigation of its
characteristics was commissioned by ORCA. This report was summarized in Section
3.2.1 and the general characteristics of the storm were described. Based upon that
initial analysis, a detailed temporal-spatial analysis of the storm was completed by
UMA-AECON (2006) (see Appendix K for summary report). This analysis was
completed to permit the best estimate of the storm’s rainfall volume – time distribution
(hyetograph) over any particular watershed within the City to be computed.
Information from that report was initially used to define a hyetograph for the Thompson
Creek study area. Figure 4.5.1 shows the study area boundary overlaid upon a map of
the total rainfall distribution from the radar analysis across the study area.
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