Thompson Creek Flood Study Report - City of Peterborough

Thompson Creek Detailed Flood Reduction Study
City of Peterborough
These systems will be detailed further in the section describing the OTTSWMM
modelling of their major/minor system flow characteristics (Section 4.4.3).
To the best of our knowledge, there are no existing stormwater management facilities
within this part of the study area. However, there is low area east of Armour Road just
north of Franmor Drive which may be functioning as a stormwater storage area.
4.4 MODELLING CHARACTERISTICS OF MAJOR/MINOR SYSTEMS
As noted above, three different computer modelling tools were used to complete the
analysis of existing flood vulnerability. The following sections describe first the
analysis of water course related flood vulnerability then local flood vulnerability.
4.4.1 OTTHYMO Modelling of Thompson Creek Drainage Area
The first step in analysing vulnerability to flooding from the Thompson Creek
watercourse was to estimate the flows carried by the creek under various rainfall events.
To do this, the Visual OTTHYMO computer model was used. It transforms rainfall
data into flow estimates using equations which represent the response of the watershed.
The response is represented by parameters such as the drainage area, watershed slope,
watershed length, soil characteristics, imperviousness of the surface and initial wetness
of the basin. Together, these dictate how much runoff will occur for a particular rainfall
and how fast that runoff will be transformed into flow in the creek. The following
describes the development of the OTTHYMO model and its verification using
monitored flow data.
4.4.1.1 Model Development
Existing Land Use
The Thompson Creek watershed was subdivided into four sub-areas to facilitate
modelling its response under existing land use conditions. Figure 4.4.1 shows the
drainage boundaries of the sub-areas and their actual drainage areas in hectares. It also
shows the locations along the creek at which flows were calculated by the model.
Table 4.4.1 shows the other parameters used in the model to represent existing
conditions. Documentation of the model is included in Appendix H. This model was
used to estimate flows for measured rainfall/flow events monitored during the period
April to June 2006 to verify that the model was a good representation of the watershed
(see Section 4.4.1.2). However, it was not used to simulate the “design events” to
investigate flood vulnerability since land use changes are imminent within the
Thompson Creek watershed. To do so, the existing conditions model was modified to
represent future land use conditions.
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