Thompson Creek Flood Study Report - City of Peterborough

Thompson Creek Detailed Flood Reduction Study
City of Peterborough
4.4.1.2 Model Verification
Model verification consisted of simulating the flows from a measured rainfall event
from the monitoring period and comparing the results with measured flows in the creek
and at the outlet from the storm sewer system at the intersection of Scollard Drive and
Francis Stewart Road. The event selected occurred at about 2:00 am on June 1, 2006.
According to the rainfall gauge located at City Hall, about 30 mm of rainfall fell in
about 3 hours. This is approximately a 1 in 2 year rainfall for that duration. In contrast,
the rainfall gauge at Trent University (about 2.5 km north of the area) recorded only
about 4 mm of rain. At the outlet from the sewer system, a flow of 0.75 m 3 /s was
recorded. This is theoretically at or slightly above the capacity of the outlet pipe at that
location. Hence this was a significant event which produced a runoff volume of about
22 mm that is consistent with the observed rainfall at City Hall. The storm must have
been a localized event which passed through downtown and the study area but did not
reach as far north as the University. Hence the City Hall rainfall was used in the
simulation. Interestingly, as previously discussed in Section 4.2.3, the flow recorded at
the instream gauge near the corner of Ashdale Crescent West was only about 0.3 m 3 /s.
Theoretically, the flow downstream should be greater than upstream given the greater
drainage area. However, there appears to be significant overbank storage in the area
upstream of Armour Road (see for example, the discussion on Reach No. 2 in Section
4.2.3) which reduces the downstream flows. A similar “damped” response was
observed at this gauge for all other significant rainfalls during the monitoring period.
Only the normal seepage of flow through the Thompson Creek Dam was measured at
the upstream gauge, i.e. no flow spilled over the stop logs in the dam.
The results of the simulation of the verification event are summarized in Table 4.4.3.
As indicated, the outflow from subcatchment 11, is equivalent to the outflow from the
Scollard/Francis Stewart outfall flow. The observed and simulated flows match very
closely. The flow at the downstream gauge point also matches closely since a storage
element was added to the model just upstream of Armour Road. This required about
1,900 m 3 of storage. A review of the overbank topography in the area indicated that
this amount of storage is available in the riparian area and its utilization would be
promoted by the presence of a number of small dam structures which obstruct the creek.
The model output is included in Appendix G.
Based upon this close correspondence of observed and simulated flows for this
significant event, the model was judged to satisfactorily represent the hydrologic
response of Thompson Creek. The model parameters adopted were those originally
estimated from the physiographic data as shown in Tables 4.4.1 and 4.4.2. No other
flows of significance were found in the flow record from the gauge near the outlet of
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