Download
1 / 21
210 likes | 375 Views
Carp River Model Update July 2009 Storm. Planning and Environment Committee October 13, 2009. Council Motion – Model Update. On September 23 rd , Council approved the following:
E N D
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;”
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;”
Model Keeper Role • 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.
Work in Relation to Model Keeper Role • 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).
Rainfall Analysis – July 24th/25th Event • 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.
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: • The worst rainfall was measured at grid no 11926 (near Amberwood Village). • The July 24/25 event had two pulses in a 12 hr period. • From 3:10 PM to 5:15 PM - 66.72 mm (greater than 100 year 2 hour event – Provincial Std is 1:100yr). • From 9 PM to 12 AM - 24.64 mm • Important consideration: Thursday July 23rd there was 16.27 mm of rain over the entire day carrying over into early July 24th.
Important Note • 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)
Model Run Scenarios • 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.
July Storm – Field Observations • 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.
Model Findings • 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.
Third Party Review Recommendations The following TPR recommendations were approved by Council on May 27th, 2009: • Interim SWM facilities are to be designed for post to pre conditions up to and including the 100 year storm event. • SWM Ponds located adjacent to the Carp River flood plain are not to be used as interim sediment control facilities.
Third Party Review Recommendations • 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.
Third Party Review Recommendations • 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.
Third Party Review Recommendations • 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.
Carp River Model Update – July Storm Recommendations and Conclusions • 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.
Carp River Model Update – July Storm Recommendations and Conclusions • 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.
Next Steps • 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).
