Review of August 7, 2018 Storm Event

Transcription

1 Review of August 7, 2018 Storm Event Toronto and Region Conservation Authority August 10, 2018 Executive Committee Presented by: Dan Hipple, P.Eng. Senior Manager, Water Resources Engineering Chief Flood Duty Officer August 10, 2018

2 Overview Prior to August 7 th Storm Event August 7 th Storm Event Post Event Observations Moving Forward Toronto and Region Conservation Authority 2

3 Prior to August 7 th Storm Event Morning assessment indicated maximum potential of 19mm of rainfall for the day Call into Ontario Storm Prediction Centre (OSPC) indicated very low possibility of isolated showers/thunderstorms, with rainfall amounts of 10mm or less. 6:45pm Phone call to OSPC again, where they advised of a small rainfall cell over Highway 404 and Steeles Avenue area OSPC discussion focused on potential event for following day (August 8 th ), and advised to call back the following morning Continued to monitor as normal. Toronto and Region Conservation Authority 3

4 August 7 th Storm Event 8:45pm First low level alarm for Black Creek at Highway 401 gauge was received, showing very sudden increase in water levels. Rainfall gauges surrounding stream gauge showed little to no precipitation; felt it may have been interference in stream (branch, etc.). Rainfall noted in Mississauga, but decided to wait to confirm. 9:00 9:30pm Black Creek at 401 continued to rise, Black Creek at Alliance began to increase, and staff discussed options and action plan. Radar showed rainfall over Black Creek. Call to OSPC at 9:25pm indicated slow moving tropical rainstorm formed with possible rainfall amounts of 20-75mm, and EC was just releasing a Special Weather Statement for Toronto, Mississauga and Brampton during phone conversation. Toronto and Region Conservation Authority 4

5 August 7 th Storm Event 9:55pm Began drafting Flood Watch Message, and contacting City of Toronto. Call went to Toronto Central Dispatch, warning of high water levels in the Jane/Wilson area, and that Alliance/Rockcliffe area increasing. Dispatch was made aware that the Alliance area is prone to basement flooding, but Dispatch did not provide any recommendations. Staff tried contacting 311, but call couldn t get through and connection was lost. 10:00 10:30pm Black Creek at Alliance gauge peaked just under the High-High Alarm. Flood waters rose 3.5m in 1.5 hours, but precipitation gauges still showing little response; Flood Message draft was approved and began issuing; Further call to 311 was unsuccessful. Toronto and Region Conservation Authority 5

6 August 7 th Storm Event Toronto and Region Conservation Authority 6

7 August 7 th Storm Event By 11:05pm, Flood Watch Message posted to TRCA website, twitter page, and text messaged to municipal partners. Issues with mail distribution program delayed release to 11:20pm. Internal Situation Report distributed by 11:05pm. Further calls to partners, including Brickworks, Toronto Dispatch, and GO Transit Control. Follow-up return calls to those who left messages on the Flood Line. Staff continued to monitor events and coordinate with partners into the night. Black Creek at Alliance gauge was receding, with peak suggesting that the banks were not overtopped at the gauge location. Toronto and Region Conservation Authority 7

8 Post Event Observations Reports on preliminary rainfall amounts were being sent out: Environment Canada (EC) issued a statement at 3:43am confirming that 50-75mm of rainfall fell very in a localized are in Toronto from North York to the Island over 2-3 hours; EC s Billy Bishop Airport gauge showed 72mm; and News outlets and social media reporting amounts higher than 100mm from unknown/unconfirmed sources. TRCA rain gauges: Underwhelming, with ~20mm at the nearest gauge and 1.4mm at Pioneer Village, and 0mm in Mississauga; All decision making and reactions were based on stream gauges and information from OSPC/EC. Further radar imagery showed storm formed and hit in area of no rain gauges. Toronto and Region Conservation Authority 8

9 Post Event Observations Toronto and Region Conservation Authority 9

10 Post Event Observations Toronto and Region Conservation Authority 10

11 Post Event Observations Toronto and Region Conservation Authority 11

12 Post Event Observations Toronto and Region Conservation Authority 12

13 Post Event Observations Toronto and Region Conservation Authority 13

14 Post Event Observations Wednesday, August 8 th Hydrometrics staff visited the Alliance Avenue, Rockcliffe Boulevard and Hillside Drive area, looking for signs of high water; In the area of the TRCA gauge, the Black Creek did not overtop its banks, as indicated in our gauge information. Noted debris in several locations indicating areas where Black Creek overtopped its banks downstream of TRCA gauge location. Due to our gauge location and information, this was not known on the evening of August 7 th. Toronto and Region Conservation Authority 14

15 Post Event Observations 501 Rockcliffe Boulevard, rear driveway adjacent to Black Creek Toronto and Region Conservation Authority 15

16 Moving Forward Re-evaluate Black Creek Overtop Criteria Investigate if adjustments required to High-High Alarm associated with Black Creek at Alliance gauge; Investigate potential for rain gauge in area; Discuss with City of Toronto staff on protocols related to future flooding in area. Toronto and Region Conservation Authority 16

17 Questions? Dan Hipple, P.Eng. Phone: x dhipple@trca.on.ca TRCA website: TRCA Gauging website: beta.trcagauging.ca