Thompson Creek Flood Study Report - City of Peterborough

Thompson Creek Detailed Flood Reduction Study
City of Peterborough
4.5.2.4 Thompson Creek Dam Flows
All the storm event simulations previously described assumed a typical constant
baseflow seepage rate of 0.1 m 3 /s from the Thompson Creek Dam. This is an
appropriate assumption when dealing with local storms centred over the relatively small
Thompson Creek watershed (approximately 75 hectares). The Thompson Bay on the
upstream side of the dam is fed by the Otonabee River which has a drainage area in
excess of 7,500 km 2 . At the time of year when local high intensity storms would occur,
the Otonabee River would generally be at low levels and any local storm would have no
effect on its flows. Hence it is unlikely that a large flow would occur at the dam
simultaneously with the local flow in the Thompson Creek watershed.
On the other hand, however, there is a potential flood risk in the Thompson Creek
watershed from a release of water from the Thompson Creek Dam itself. This could
occur for a number of reasons, such as:
high water levels on the Otonabee River during an extreme event might overtop
the dam and cause high flows in Thompson Creek
during high flow periods on the Otonabee River, the Trent Severn Waterway
(TSW), operators of the dam, may be forced to open the dam by removing some
of the stop logs to release flow from Thompson Bay down Thompson Creek
under extreme conditions, a dam break might occur which would release high
flows down Thompson Creek. There is no evidence that such an occurrence is
likely to happen but it is a potential scenario which should be considered.
It is not feasible to predict the probability of the above events because they involve
various human interventions which may or may not occur in different circumstances.
However, in order to understand the implications of such situations, two simulations
were completed to identify the flows which might occur in Thompson Creek and the
possible water levels and extent of flooding that might occur. The first scenario
involved removing 3 stop logs from the dam. This might be equivalent to the second
type of situation described above. The second scenario involved removing 7 stop logs
from the dam. This might be considered to be equivalent to the third situation where a
breach of the dam occurred. In both cases there would be a sudden release of water
from the dam with the latter being much larger.
The Visual OTTHYMO model was used to simulate the flows which would occur in
Thompson Creek in these two situations. It was assumed that the water level in
Thompson Bay would remain constant since there is a large volume of water in that
system. This effectively generates a constant outflow which is then routed downstream.
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