Water Quality on the Toronto-Mississauga Waterfront after the July 8, 2013 Deluge

Transcription

1 Water Quality on the Toronto-Mississauga Waterfront after the July 8, 213 Deluge November 4, 214 Todd Howell and Peter Nettleton Environmental Monitoring and Reporting Branch Ontario Ministry of the Environment and Climate Change Toronto, Ontario

2 On the evening of July 8, 213 heavy thunderstorms passed the largest urban centre in Canada dropping exceptional amounts of rain 126 mm of rain fell at Pearson Airport that day, breaking the record at Pearson of mm on Oct. 15 th, 1954 due to Hurricane Hazel 2

3 Outline The Runoff Event Weather Conditions Tributary Discharge Immediate Effects on Nearshore Water Quality Measured patterns of suspended solids, phosphorus and fecal indicators Water column stratification Loaded phosphorus Where Did the Runoff distribute? Modelled nearshore circulation features in the days after the event 3 Ministry of the Environment and Climate Change

4 Environment Canada Radar Imagery of Thunderstorms on July 8 th, pm EDT: Thunderstorm development along stationary frontal zone and warm moist air mass Track of thunderstorms 4:5 pm EDT: Slow moving thunderstorms arrive in the Toronto area dropping 126. mm of rain at Pearson in a few hours. 4

5 River Discharge (Daily Mean) July 2 to July 15, 213 Discharge (m3/s) Don River Discharge (m3/s) July 2 July 4 July 6 July 8 July 9 Duffins Creek July 11 July 13 July 15 July 2 July 4 July 6 July 8 July 9 July 11 July 13 July 15 1 Discharge (m3/s) Rouge River Discharge (m3/s) Discharge (m3/s) July July 4 July 2 July 4 July 6 July 6 July 8 July 9 July 8 July 9 Fourteen Mile Creek July 11 July 11 July 13 Bronte Creek July 13 July 15 July 15 Discharge (m3/s) July 2 July 4 July 6 July 8 July 9 Credit River Discharge (m3/s) July 11 July 13 July 15 July 2 July 4 July 6 July 8 July 9 July 2 July 11 July 4 July 13 July 6 Humber River July 15 July 8 July 9 July 11 July 13 July 15 Based on Environment Canada Water Survey of Canada data 5

6 July 9, 213 Water Quality Survey Methods City of Toronto City of Mississauga Lake Measuremenst and Sampling Plan: continuous surface measurement over track for conductivity, temperature, turbidity, nitrate, fluorescence features water samples (red squares) for lab analysis (nutrients, major ions, fecal indicators, physical features) 6 water column profiles of temperature, turbidity, beam attenuation, conductivity, fluorescence features

7 Toronto Waterfront July 9, 213 7

8 Toronto Harbour Surface waters highly turbid (except SW Toronto Island) Apparent shore-parallel flow towards the east Note: sensor was out of range >13 FTU Secchi Depth 8

9 Water Column Strongly Stratified: But Variable With Location Temperature (oc) Temperature (oc) m m Depth (m) Attenuation Coefficient Beam Attenuation - 66 nm (m -1 ) Temperature (oc) Temperature West End P3 Depth (m) Sinking mid-depth plume Temperature (oc) East End Beam Attenuation - 66 nm (m -1 ) P m m Depth (m) 1 15 Floating Plume Depth (m) West End Beam Attenuation - 66 nm (m -1 ) P East End Beam Attenuation - 66 nm (m -1 ) P35 9

10 Credit River Water Column Temperature Structure interpolated from Profiles Etobicoke Creek Humber River Toronto Harbour Profiles used to interpolate 3D model of water column by kriging (EVS software) Profile Sites n = 39 Wide temperature gradient with depth; complex pattern of stratification with multiple density gradients Suspect upwelling in recent past 1

11 Discharge Loaded to Nearshore in Surface and Mid-depth Layers Toronto Harbour Credit River Credit River Etobicoke Creek Humber River Toronto Harbour River Discharge Floating Discharge Sinking Offshore 11

12 Lab measured Total Phosphorus (TP) highly enriched in surface waters TP levels over track estimated from linear regression with turbidity and interpolated by kriging Note: TP estimates are under estimates >12 FTU due turbidity sensor out of range 12

13 Percent Dissolved Phosphorus Estimating Total Phosphorus Loaded to Survey Area by Event ( as July 9) TP was well correlated with suspended solids Field surrogates of suspended solids (i.e. turbidity) can be used to estimate TP concentration TP Against % Dissolved Phosphorus Total Phosphorus ( g/l) Total Phosphorus ( g/l) Total Phosphorus Plotted Against Suspended Solids TP(ug/L)= * suspended solids (mg/l) R 2 = Suspended Solids (mg/l) Much of the phosphorus discharged was bound to particulate material 13

14 Procedure Used to Estimate Event Water Column Load to Study Area Estimate TP concentration over depth profiles using TP to turbidity regression Interpolate TP water column model from profiles by 3D kriging Calculate water column volume of survey area; estimate TP mass in volume Estimate TP mass in same volume given background nearshore TP levels Subtract estimated background TP mass from mass estimated on July 9 Nearshore Background TP used is based on 213 data collected on June 11 and July 31 between 3 and 2 m in eastern Toronto Total P ( g/l) Mean 9.5 ug/l East Toronto Ajax Oshawa Cobourg 1 14 )

15 Interpolated Water Column Concentrations of Total Phosphorus Credit River Etobicoke Creek Humber River Toronto Harbour Volume of area monitored: 1.4 X 1 9 cubic meters Mass of P in volume: metric tons Estimated background phosphorus mass: 9.54 metric tons Amount attributable to event (as of July 9): metric tons 15

16 July 9, 213 Numbers indicate: E.coli (CFU/1mL) Fecal pollution indicator E.coli strongly elevated in surface waters Levels elevated in areas subject to greatest influence of runoff Fecal Pollution Indicator E. coli 16

17 Fecal Pollution Indicators: E.col and Fecal Streptococci 14 E.coli (cfu/1ml) E.coli (CFU/1ml) = * fecal strep (CFU/1mL) R 2 =.91 E.coli Levels of E.coli highly correlated with those of fecal streptococci Fecal streptococci counts generally higher than those of E.coli 2 Fecal streptococci Fecal Strep (cfu/1ml) E.coli (CFU/1mL) E.coli TP Levels of E.coli somewhat correlated with TP While other parameters (nitrate, turbidity, dissolved P) exhibited a degree of co-variation with E.coli, TP appeared to be the strongest single correlate Total Phosphorus (ug/l) 17

18 Hydrodynamic Modelling to Support Broader Interpretations of Runoff Event MIKE3 DHI hydrodynamic modelling software used to infer water column structure, lake circulation and nearshore mixing of tributary discharge over the period surrounding the July 8, 213 runoff event - whole lake circulation modeled in 3D for April 1 to December 1, 213 in parallel with additional modeling of tributary discharge mixing in GTA nearshore for time surrounding the storm event - horizontal grid scale areas with proximity to shoreline; enhanced in the GTA area - combined sigma and z layering scheme (16 strata with up to 12 extra in deeper water) - water inflows from 28 gauged tributaries and Niagara River; tributary temperatures available for selected GTA sites and otherwise estimated from published trends 18

19 Nearshore Circulation Directly Preceding the July 9, 213 Survey As inferred from field survey, weak to moderate shore-parallel flow towards the east occurred near the height of the discharge event Toronto Harbour Not shown is flow at depth which mostly was slower and also towards the east Surface July 9, hour 19

20 Surface July 9, hour 12 Etobicoke Creek Credit River Humber River Bottom July 9, hour 12 Toronto Harbour Preliminary Tracking of Distribution of Discharge by the Proportion of Tributary Water Contributed to Water Column Relative Concentration procedure used: concentration of water in the lake discharged by specific tributaries estimated Gauged tributaries between Credit River and Rouge River over period July 5 to 12 treated as combined runoff source Predicted distribution of tributary discharge over study area similar to that observed in the field survey Discharge mostly limited to a surface layer except at shallow depth along the shoreline 2

21 Surface July 1 Hour Surface July 11 Hour Some dilution, however, pattern similar to July 9 persists 1 3 Surface July 1 Hour 12 Surface July 11 Hour 12 Note strong dilution and offshore dissipation of discharge contribution

22 Surface July 11 Hour 12 MODIS Satellite Image July 11,

23 Surface Currents July 11, hour Bottom Currents July 11 Hour Note Offshore Flows Note Onshore Flow Near Shoreline Surface temperature July 11 Hour 12 Upwelling on July 11, 213 Upwelling on July 11 Brings hypolimnetic water into nearshore areas impacted by the July 8 storm Likely dilutes and disperses runoff from the event 22

24 Summary The Runoff Event Elevated tributary discharge associated with the July 8 storm appeared centred between Credit River and Toronto Island/Harbour Immediate Effects on Nearshore Water Quality Levels of suspended solids, phosphorus and fecal indicators highly elevated in surface water Water stratification confines runoff to surface layer and to a limited extent, mid-water column layers Where Did the Runoff distribute? Tributary discharge associated with the July 8 storm appeared to be largely focused between the Credit River and Toronto Island until about July 11 An upwelling event on July 11 appeared to dilute and push runoff offshore 23 Ministry of the Environment and Climate Change

25 Acknowledgments Wendy Page, EMRB, OMOE Chris Jackson, EMRB, OMOE Michelle Cassar, EMRB, OMOE Tessa Villeneuve, Central Region, OMOE Amanjot Singh, CVC Derek Smith and Jamie Duncan, TRCA