Thompson Creek Flood Study Report - City of Peterborough

Thompson Creek Detailed Flood Reduction Study
City of Peterborough
that the gauge level rose by about 5 cm during the event (although the rainfall was
approximately a 1 in 2 year storm). The simulation with HEC-RAS using the
OTTHYMO generated flows (including the storage upstream of Armour Road) was
able to reproduce the observed water level at the gauge. The summary output for the
event in included in Appendix I.
For the event of July 14 – 15, 2004, it was anticipated that some post-storm high water
marks might be available with which to verify the HEC-RAS model. However, as
indicated by ORCA in the “Thompson Creek Management Plan” (2004), there was
relatively little impact of the storm on Thompson Creek itself. There were some reports
of local drainage issues (at Scollard Drive, Eldon Court, Riverpark Village – see
Appendix B) but no information indicating flooding from the creek itself or of water
levels observed. City employees recollected that the culvert at Armour Road may have
overtopped for a short time. Simulations of the flows and water levels for the event
indicated that levels would have been similar to those for a Regional Storm and Armour
Road would have overtopped. The summary output from HEC-RAS is included in
Appendix I. Based upon this limited evidence, it was concluded that the HEC-RAS
model satisfactorily computes water levels in Thompson Creek.
4.4.3 OTTSWMM Modelling of Local Drainage Systems
As discussed in Section 4.3, within the study area, there are three local drainage
systems which outlet directly into Thompson Creek and a further six local systems
which drain directly into the Otonabee River. Each of these was modelled using the
OTTSWMM model. This tool has the ability to calculate both “major” and “minor”
system flows based upon a description of the drainage areas, street layout/width and
storm sewer systems. The “major” system flows are those which travel overland along
the streets, over parking lots, down grassed channels, etc. The “minor” system flows
are those which are contained in the sewer pipes. The model uses a hydraulic
description of the catchbasins in the system to determine how much of the flow is
actually “captured” by the sewer system and how much remains upon the streets, etc.
This allows analysis of whether the pipes are full or not and of the depth of flow on the
streets and in other overland flow routes throughout the system. Appendix J includes
information on the methods used by OTTSWMM to calculate major/minor flows.
4.4.3.1 Model Development
Drawing No. SS-1 shows the drainage plan, sewer system elements and major system
elements used to create the OTTSWMM models of the eight separate local drainage
systems in the study area. The details of the models are presented in a series of tables
included in Appendix J. The tables include:
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