Transcript No Slide Title

Carp River Model Update
July 2009 Storm
Planning and
Environment
Committee
October 13, 2009
Council Motion – Model Update
•On September 23rd, Council approved the following:
•“1. Staff be directed to run the modeling for water levels
in the Carp River with data updated to reflect the storm of
July 24, 2009 and the super-saturated soil conditions and
assess whether this new data is consistent with
expectations produced by the model under such
conditions;
•2. Staff report back to Planning and Environment
Committee on October 13, 2009 on the results of running
the model with the updated data;”
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Model Keeper Role
• On May 27th, 2009, in conjunction with the Third
Party Review (TPR), Council approved the
following recommendation:
• “Approve a budget of $75,000 to retain Greenland
International as the model keeper through 2009
and waive the provisions of the Notice By-law with
respect to this budget amendment;”
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Model Keeper Role
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The Model Keeper assignment is a dynamic
assignment which involves:
Maintaining the models that were previously
developed for the upper Carp River and
overseeing any changes to reflect new
development features,
Overseeing model adjustments as additional
monitored data becomes available, and
Review any changes to ensure the Third
Party Review recommendations are not
impacted.
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Work in Relation to Model
Keeper Role
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In early August, Greenland was instructed to
commence an update of the models to simulate
conditions present in July 2009. In keeping with the
Model Keeper Role, this assignment has included:
Updating data on new/active developments not
included in the model,
Updating new Storm Water Management facilities
not included in the model,
Inputting rainfall records from the July 2009 storm
event, and
Inputting data measured in the field (one monitor,
staked high water marks, etc).
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Rainfall Analysis – July 24th/25th
Event
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The weather radar data collected for the July
24/25 2009 storm event indicated a series of
pockets of intense rainfall that were localized.
There was considerable variation in rainfall
patterns within a few kilometers.
Advances in state of art science has enabled the
use of the weather radar data, which has been
applied with success elsewhere in the Province.
The City provided weather data that had been
calibrated with the 5 rain gauges in the
watershed.
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Rainfall Analysis – July 24th/25th
Event
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Rainfall Analysis – July 24th/25th
Event
Nine rainfall patterns were used to represent various
pockets of rain in the overall drainage area.
Most stringent pocket rainfall event:
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The worst rainfall was measured at grid no 11926
(near Amberwood Village).
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The July 24/25 event had two pulses in a 12 hr
period.
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From 3:10 PM to 5:15 PM - 66.72 mm (greater than
100 year 2 hour event – Provincial Std is 1:100yr).
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From 9 PM to 12 AM - 24.64 mm
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Important consideration: Thursday July 23rd there
was 16.27 mm of rain over the entire day carrying
over into early July 24th.
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Rainfall Preceding Event
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Important Note
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The model findings are preliminary. Greenland
follows a rigorous Quality Assurance and Control
process that requires an internal review of
results. To respond to the Planning and
Environment Council motion within the Council
directed timelines, Greenland has forwarded this
information prior to finalizing its full internal
review process. (1-2 weeks)
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Model Run Scenarios
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Adjusting soil moisture conditions from normal
to saturated to supersaturated.
Varying hydraulic parameters to mimic summer
vegetation.
Adjusting starting water levels in Glen Cairn
facility.
Adjusting base flow conditions at the start of
event.
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July Storm – Field Observations
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Measured high water marks close to 100 year
flood levels upstream of Hwy 417.
Measured water levels were 0.9m below 100 year
flood levels at the Village of Carp.
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Model Findings
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Glen Cairn facility bottom appears to be low in
original model. Overbank areas appear to be higher
from topography on City emap. Adjusting facility
bottom causes water levels to be closer to measured
high water marks.
Slight water level changes using different hydraulic
parameters for summer vegetation.
The slight difference in water levels from the
hydraulic model could be adjusted bringing in the
timing of the response from certain key areas with
future data collected from the two additional
monitors.
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Third Party Review
Recommendations
The following TPR recommendations were
approved by Council on May 27th, 2009:
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Interim SWM facilities are to be designed for
post to pre conditions up to and including the 100
year storm event.
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SWM Ponds located adjacent to the Carp River
flood plain are not to be used as interim sediment
control facilities.
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Third Party Review
Recommendations
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The fringe areas proposed for filling in the
vicinity of Pond 1 should not be filled until such
time as the Restoration Plan has advanced to
provide sufficient overall flood storage volume in
the study corridor.
Without any monitored data to validate the
original hydrology models, limit the interim
development to 34.0% of the development area
including future Fernbank Community lands.
Each development should provide additional at
source volume prorated on contributing area
based on 100 to 120 m³/ha.
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Third Party Review
Recommendations
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The development can proceed to full build out
with the completion of the Restoration Plan and
with monitored data to validate the original
model or the proposed development has
incorporated the additional features to account
for the 85,600 m³ identified as a supplemental
volume to account for a worst case scenario
defined in Phase 1 Section 5.
The Fernbank lands, in the developed condition,
do not need to be incorporated in the models now
because it is sufficient to require that peak flows
not exceed existing conditions in the upper Carp
River and that runoff volume not exceed the
suggested 40,000 m³ above existing conditions for
the 100 year event.
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Third Party Review
Recommendations
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Sediment volume can only be identified with
analyses for a variety of phasing schemes for
development due to the variability of material
that will comprise the sediment found in the
runoff.
The SWM facilities proposed will deal with water
quality by treating the typical urban runoff
anticipated after development. The clay and silt
particles present with undeveloped conditions
that normally will not settle out with standard
pond designs will be less prevalent with future
development once stabilized.
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Carp River Model Update –
July Storm
Recommendations and
Conclusions
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The worst two hour portion of the July 2009 storm was only
greater than the 100 year statistical 2 hour storm from
Ottawa weather records in less than 30% of the watershed.
The 100 year two hour volume is significantly greater than
the two hour storm volume recorded in the remainder of
the watershed. Therefore, the TPR Worst Case scenario
volume of 85,600 m³ is still valid.
Since the TPR, the July 2009 storm has shown a
vulnerability of municipal infrastructure in the Glen Cairn
community. A range of possible solutions are being
considered as part of the investigation. This review has
followed a worst case scenario approach to provide for
flexibility in developing an appropriate solution.
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Carp River Model Update –
July Storm
Recommendations and
Conclusions
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The Hazeldean Road Widening is not impacted.
Development can still proceed to the levels stated
in the City staff recommendations during the
TPR.
Revised modeled water levels to be applied to set
outlet conditions for interim facilities and
hydraulic gradelines for new developments.
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Next Steps
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Confirm Glen Cairn facility bottom model
assumptions with field survey,
Coordinate efforts between Model Keeper and
Flooding Investigation,
Continue data collection to build robust model,
Adjust, where warranted, widening alternatives
presently being reviewed to optimize benefit
through the Carp River corridor based on
potential Glen Cairn solutions, and
Provide adjusted water levels to active
applications (Trinity, Hazeldean Rd Widening).
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Questions?
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