Thompson Creek Flood Study Report - City of Peterborough

Thompson Creek Detailed Flood Reduction Study
City of Peterborough
4.5.1.3 Return Period Events for Flood Damage Estimation
For the purpose of estimating average annual flood damages, it is necessary to calculate
flood damages for events with a known probability. To facilitate this, flows and water
levels must be calculated for events of known probability (or equivalently return
period). Hence a series of rainfalls with return periods of 1 in 2 years, 1 in 5 years, 1 in
10 years, 1 in 25 years, 1in 50 years and 1 in 100 years were required. The rainfall
volumes for these events were derived from the intensity-duration-frequency (i-d-f)
curves from the Peterborough Airport since it has the longest period of record in the
area. Table 4.5.1 shows the total rainfall amounts (mm) for one and six hour durations
for the noted return periods. In order to simulate the required hydrographs with the
hydrologic models described earlier, a hyeotograph (volume-time distribution) was
required for each event. As in the case of the volume events discussed above, the “AES
distribution” was used for both the one and six hour distribution. The 1 in 100 year six
hour storm is shown on Figure 4.5.4. The actual rainfall amounts used for each storm
are tabulated in Appendix K.
Table 4.5.1
Total Rainfall Volumes for 1 hour and 6 Hour Storms (Peterborough Airport)
Return Period
6 Hour
Volume
(mm)
1 Hour
Volume
(mm)
2 Year 37.36 23.75
5 Year 48.65 32.26
10 Year 57.49 38.96
25 Year 65.65 45.53
50 Year 76.13 51.66
100 Year 81.73 56.25
4.5.2 Results of Thompson Creek Watercourse Simulations
The results of the Visual OTTHYMO and HEC-RAS simulations for the Thompson
Creek watercourse are described in the following sections.
4.5.2.1 Return Period Events for Flood Damage Estimation
Table 4.5.2 shows the calculated peak flows for Thompson Creek for future land use
conditions (described in Section 4.4.1.1) for the six return period events (1 in 2 year to
1 in 100 year) for the six hour AES storm distribution at the locations on the creek
indicated on Figure 4.4.2. It should be noted that a constant outflow of 0.1 m 3 /s was
assumed from the Thompson Creek Dam based upon the flow measurements taken
during the study. The model includes the proposed Waverly Heights SWM pond which
attenuates flows from that subdivision before they discharge to Thompson Creek.
However, it does not include the flood plain storage upstream of Armour Road.
14-06605-01-W01 City of Peterborough 58