Dry and Wet Weather Modelling of Water Quality Under ...trca.on.ca/dotAsset/25939.pdfDry and Wet Weather Modelling of Water Quality Under Alternative Land Use Scenarios in the Duffins

Dry and Wet WeatherModelling of Water QualityUnder Alternative Land UseScenarios in the Duffins andCarruthers CreekWatersheds: A SimpleSpreadsheet Approach

Report Prepared by:

Stantec Consulting Ltd.14 Abacus RoadBrampton, Ontario, L6T 5B7

and

Aquafor Beech Limited14 Abacus RoadBrampton, Ontario, L6T 5B7

Report Prepared for:

The Toronto and Region ConservationAuthority5 Shoreham DriveDownsview, Ontario, M3N 1S4

Project No. 631 22714.1January 2003

SPREADSHEET MODEL FOR WET AND DRY WEATHER FLOW

Stantec Consulting Ltd./Aquafor Beech LimitedRef. 22714.1 i

TABLE OF CONTENTS

Page

1.0 BACKGROUND 1

2.0 STUDY AREA 2

3.0 METHODS 4

4.0 FINDINGS AND INTERPRETATION 6

4.1.1 Wet Weather Sediment Load 11

4.1.2 Dry Weather Sediment Load 11

4.2.1 Wet Weather Sediment Concentration 11

4.2.2 Dry Weather Sediment Concentration 11

4.3.1 Wet Weather Phosphorous Load 11

4.3.2 Dry Weather Phosphorous Load 2

4.4.1 Wet Weather Phosphorous Concentration 12

4.4.2 Dry Weather Phosphorous Concentration 12

4.5.1 Wet Weather Chloride Load 12

4.5.2 Dry Weather Chloride Load 13

4.6.1 Wet Weather Chloride Concentration 13

4.6.2 Dry Weather Chloride Concentration 13

5.0 COMPARISON OF RESULTS WITH PAST STUDIES 14

6.0 CONCLUSIONS 15

7.0 REFERENCES 16

APPENDIX A: Unit Conversion and Sample Load Calculations

APPENDIX B: Graphs of Pollutant Concentrations and Loads


Stantec Consulting Ltd./Aquafor Beech LimitedRef. 22714.1 1

1.0 BACKGROUND

The Toronto and Region Conservation Authority (TRCA) has the mandate for protectingand preserving land, water, flora, and fauna in the watersheds as well as executingplans and policies related to the health of watersheds within its jurisdiction. Onecomponent of these watershed plans has been the characterization and prediction ofwater quality under existing and future land use scenarios. Analyses of water qualitymonitoring data (TRCA, 2002a; TRCA, 2002b) and modelling of agricultural non-pointsources of contaminants (TRCA, 2002c) are the subject of earlier reports.

Currently, water chemistry sampling conducted through the TRCA’s Regional WatershedMonitoring Network is not of sufficient frequency to calculate pollutant loads during bothwet and dry weather conditions. Hence, this study estimates loads and concentrationsof selected contaminants using a simple spreadsheet modelling approach. Estimatesare made for total suspended solids (TSS), phosphorus and chloride during wet and dryweather conditions in the Duffins and Carruthers Creek watersheds. The following threeland use scenarios were evaluated:

i) existing land cover,ii) projected land cover under the official plan (OP), andiii) projected land cover under the OP overlain with TRCA’s proposed

enhanced natural heritage (NH) cover for these watersheds.

These three alternative land use/management scenarios were selected to help guidemanagement actions within the watersheds. To provide a larger context for this study,results of the model are compared to similar estimates in other local watersheds.



2.0 STUDY AREA

The whole Duffins Creek watershed has been divided into six sub-watersheds for thisstudy. The loads and concentrations for the contaminants are estimated for each of thesub-watersheds of Duffins Creek, whole Duffins Creek watershed, and the wholeCarruthers Creek watershed. A general map of the sub-watersheds of the Duffins Creekand Carruthers Creek watershed with rivers and road network is shown in Fig. 2.1. TheDuffins and Carruthers Creek watersheds cover total areas of 28,305 and 3,810hectares, respectively.

In addition to private and public lands within these watersheds, about 7,350 hectares ofland within the municipalities of Pickering, Markham, and Uxbridge (“Pickering Lands”)were expropriated in the early 1970s by the Government of Canada to develop aninternational airport for the Greater Metropolitan Toronto Area (Transport Canada,2002). A majority of the Pickering Lands falls within the Duffins Creek watershed andsome portions of this land are currently under leased agricultural land use. Shortly afterthe expropriation of these lands, the Seaton community lands (11% of the watershed),and others in Markham, were purchased or expropriated by the Government of Ontariowith the intention of building a new city of 250,000 people adjacent to the new airport.However, plans to build the international airport were put on hold, and after a lengthyconsultation process, the targeted area for urban development was reduced to one thatwould support a community of only 45,000 people.





3.0 METHODS

The following data were used in the spreadsheet calculation of annual loads for TSS,Phosphorous, and Chloride under the three alternative land use scenarios discussedabove:

(i) percent area in rural, wooded, and urban land use;(ii) total wet / dry weather flow (runoff / baseflow) volumes for each study area;(iii) mean concentrations for three pollutants under each of the three land use categories(rural, wooded, and urban) during wet and dry weather.

The mean wet weather concentrations for rural, wooded, and urban land uses in theDuffins Creek watershed represent an average of annual land use specific event meanconcentration (EMC) data from several studies of stormwater quality, most of which wereconducted in the City of Toronto (Aquafor Beech, 2001). Dry weather concentrationswere derived from observed baseflow concentrations for monitoring stations with similarupstream land cover types in the Duffins Creek watershed and other Southern Ontariowatersheds (Hinton, 1996; Beak, 1993). The wet and dry weather concentrations usedin this study for each land use category were as follows:

Table 3.1: Phosphorus, TSS, and Chloride Concentrations Under Three LandUse Categories During Wet and Dry Weather

Rural Wooded Urban

Wet weather

Phosphorus (mg/L) 0.20 0.12 0.30

TSS (mg/L) 100 70 170

Chloride (mg/L) 30 5 98

Dry weather

Phosphorus (mg/L) 0.020 0.016 0.015

TSS (mg/L) 6 6 6

Chloride (mg/L) 17 5 32

Note: Rural land use includes both open space and agricultural land, and wooded areas include wetlands,Meadows, and forests. Wet weather event mean concentrations represent an average concentration fromseveral studies for specific land uses. (Aquafor Beech, 2001).

Estimates of annual loads for TSS, phosphorus, and chloride were calculated as:

Annual loadi = runoff [LUr * Cri + LUw * Cw

i + LUu * Cui]

where: LU = percent land useC= wet or dry weather event mean concentrations



runoff = total runoff volume or total baseflow for the sub-watershedsubscript i represents the individual pollutant listed above; andsuperscripts r,w, and u represent rural, wooded, and urban land uses,

respectively.

The land use percentages were determined from air photo interpretation and projectedland use assuming full build out of the current, approved Regional, and Local OfficialPlans and assumed vegetation cover where such opportunities were expected to existand where other watershed management objectives were likely to be realized (TRCA,2002d). Wet weather runoff was determined from water budget model outputs for eachwatershed / sub-watershed and each scenario (Clarifica Inc., 2002). Dry weather runoffwas determined for the same watershed / sub-watershed and scenarios from dischargerates generated by a groundwater model, MODFLOW (Gerber Geosciences Inc., 2002).

Annual runoff and baseflow volumes were not available for the Carruthers Creekwatershed. Hence, Carruthers Creek runoff volumes were calculated from MillersCreek sub-watershed runoff volumes, as follows:

Carruthers Creek runoff (m3) = C * Millers Creek runoff (m3)

where: C = Carruthers Creek area (3810 ha )/Millers Creek area (1698 ha)

Millers Creek was chosen for this purpose because it is immediately adjacent toCarruthers Creek and has similar physical characteristics (e.g. slope, soils, land use). Asample spreadsheet calculation on load estimates and unit conversion is provided inAppendix A.

It should be noted that this simple approach assumes that runoff generated for a givenland use is directly proportional to the percent area this land use covers in a specificwatershed or subwatershed. Since, urban land uses contribute proportionally moresurface runoff and higher pollutant concentrations (see Table 3.1) for a given arearelative to other land uses during wet weather, this method will tend to underestimate thetotal wet weather pollutant loads in areas with significant urban land uses. For theDuffins and Carruthers Creek watersheds, this error associated with overlooking thehigher relative runoff contribution from urban areas was thought to be relatively smallbecause these watersheds have only 7 and 18% urban land use respectively. The erroris likely to be greater in some of the more urbanized sub-watersheds of Duffins Creek,especially under future land use scenarios, and therefore, should be considered carefullyin interpreting the results.



4.0 FINDINGS AND INTERPRETATION

Summaries of pollutant loads, concentrations, and land use percentages for the studyareas during wet and dry weather are presented in Table 4.1 and 4.2, respectively. Unitarea loads (kg/ha/day) for each watershed /sub-watershed are provided in Table 4.3 and4.4 for wet and dry weather conditions, respectively. Graphs of the unit area load andconcentration data are provided in Appendix B. The following discussion of resultscompares wet and dry weather concentrations and loads for three alternate land usescenarios: (i) existing conditions; (ii) future Official Plan (OP), and (iii) future OP overlainwith enhanced natural heritage (NH) cover.



Table 4.1: Estimated Wet Weather Loads and Concentrations for a) Existing LandUse; b) Projected Land Use Under the Official Plan; and c) ProjectedLand Use Under the OP Overlain with Enhanced Natural Heritage Cover

Loads(kg/day)

Concentrations(mg/L)

Land use (%)Basins|Scenario

TP TSS Cl TP TSS Cl Rural Wooded UrbanRunoff(m3/yr)

a 8.5 4477.2 1174.0 0.18 92.8 24.3 64.5 32.0 3.5 17609789

b 9.9 5228.0 1511.8 0.18 96.4 27.9 59.5 31.9 8.6 19778548

West Duffins(13,539 ha)

c 8.8 4716.4 1235.1 0.17 91.9 24.0 44.2 47.2 8.6 18737994

a 5.3 2802.4 666.0 0.17 89.0 21.1 51.1 45.3 3.6 11499156

b 5.5 2920.8 715.6 0.17 89.8 22.0 49.2 45.7 5.1 11869204

East Duffins(9,202 ha)

c 4.6 2495.4 513.9 0.15 84.2 17.4 30.5 64.4 5.1 10812808

a 0.8 417.9 101.2 0.17 89.8 21.7 57.7 39.8 2.5 1698791

b 2.0 1113.3 472.3 0.22 120.2 51.0 23.4 33.4 43.2 3380821

Ganetsekiagan(1,305 ha)

c 2.0 1107.6 468.9 0.22 119.9 50.8 22.5 34.3 43.2 3371259

a 1.0 526.2 118.6 0.17 87.5 19.7 53.7 44.9 1.4 2195203

b 2.1 1158.0 440.4 0.20 110.9 42.2 30.6 37.6 31.8 3809847

Urfe(1,437 ha)

c 2.1 1151.3 436.7 0.20 110.7 42.0 29.8 38.4 31.8 3795484

a 2.6 1425.5 593.2 0.22 119.1 49.5 37.6 24.6 37.8 4369051

b 3.2 1814.8 879.3 0.24 136.0 65.9 16.0 22.8 61.2 4872120

Millers(1,698 ha)

c 3.2 1811.2 877.0 0.24 135.8 65.8 15.5 23.3 61.2 4867174

a 2.0 1140.9 467.6 0.20 115.6 47.4 0.0 54.5 45.6 3603906

b 2.7 1571.9 738.7 0.23 130.6 61.4 0.0 39.4 60.6 4392176

Lower MainDuffins(1,124 ha)

c 2.7 1571.6 738.5 0.23 130.6 61.4 0.0 39.4 60.6 4391273

a 19.9 10509.7 2847.6 0.18 93.6 25.4 55.1 37.8 7.1 40975895

b 24.5 13159.6 4135.0 0.19 99.9 31.4 48.1 36.5 15.4 48102717

Whole Duffins(28,305 ha)

c 22.1 12066.9 3526.5 0.18 95.8 28.0 34.6 50.0 15.4 45975992

a 5.1 2751.3 910.1 0.19 102.6 33.9 47.6 34.1 18.3 9786674

b 6.2 3388.1 1325.1 0.21 113.3 44.3 33.3 33.4 33.3 10913549

Carruthers(3,810 ha)

c 6.0 3322.7 1271.7 0.20 111.2 42.5 27.4 39.6 33.0 10902470



Table 4.2: Estimated Dry Weather Loads and Concentrations for a) Existing LandUse; b) Projected Land Use Under the Official Plan; and c) ProjectedLand Use Under the OP Overlain with Enhanced Natural Heritage Cover

Loads (kg/day)Concentrations

(mg/L)Land use (%)Basins|Scenario

TP TSS Cl TP TSS Cl Rural Wooded Urban

BaseFlow

(m3/yr)

a 1.01 326.7 744.3 0.02 6.0 13.7 64.5 32.1 3.5 19870965

b 0.97 317.6 766.2 0.02 6.0 14.5 59.5 31.9 8.6 19324560

West Duffins(13539 ha)

c 0.94 317.6 668.6 0.02 6.0 12.6 44.2 47.2 8.6 19324560

a 1.08 359.5 725.3 0.02 6.0 12.1 51.1 45.3 3.6 21867515

b 1.06 356.0 728.2 0.02 6.0 12.3 49.2 45.7 5.1 21656545

East Duffins(9202 ha)

c 1.02 356.0 595.3 0.02 6.0 10.0 30.5 64.4 5.1 21656545

a 0.12 39.1 82.1 0.02 6.0 12.6 57.7 39.8 2.5 2380530

b 0.09 32.4 105.4 0.02 6.0 19.5 23.4 33.4 43.2 1975380

Ganetsekiagan(1305 ha)

c 0.09 32.4 104.8 0.02 6.0 19.4 22.5 34.3 43.2 1975380

a 0.09 29.5 58.3 0.02 6.0 11.8 53.8 44.9 1.3 1798355

b 0.07 25.5 73.3 0.02 6.0 17.2 30.6 37.6 31.8 1552345

Urfe(1437 ha)

c 0.07 25.5 73.0 0.02 6.0 17.2 29.8 38.4 31.8 1552345

a 0.07 24.3 79.8 0.02 6.0 19.7 37.6 24.6 37.8 1478615

b 0.06 23.3 91.1 0.02 6.0 23.4 16.0 22.8 61.2 1418390

Millers(1698 ha)

c 0.06 23.3 90.8 0.02 6.0 23.4 15.5 23.2 61.2 1418390

a 0.03 13.0 37.6 0.02 6.0 17.3 0.0 54.5 45.6 793510

b 0.03 10.9 38.9 0.02 6.0 21.4 0.0 39.4 60.6 665395

Lower MainDuffins(1124 ha)

c 0.03 10.9 38.9 0.02 6.0 21.4 0.0 39.4 60.6 665395

a 2.39 792.1 1785.6 0.02 6.00 13.5 55.1 37.8 7.1 48189490

b 2.27 765.8 1906.6 0.02 6.00 14.9 48.1 36.5 15.4 46592615

Whole Duffins(28305 ha)

c 2.20 765.8 1699.5 0.02 6.00 13.3 34.6 50.0 15.4 46592615

a 0.2 54.5 142.1 0.02 6.00 15.6 47.6 34.1 18.3 3312098

b 0.2 52.2 156.6 0.02 6.00 18.0 33.3 33.4 33.4 3177194

Carruthers(3810 ha)

c 0.2 52.2 149.7 0.02 6.00 17.2 27.4 39.6 33.0 3177194



Table 4.3: Estimated Wet Weather Unit Area Loads and Concentrations for a)Existing Land Use; b) Projected Land Use Under the Official Plan; andc) Projected Land Use Under the OP Overlain with Enhanced NaturalHeritage Cover

Unit Area Loads(kg/ha/day)

Concentrations(mg/L)

Land use (%)Basins|Scenario

TP TSS Cl TP TSS Cl Rural Wooded UrbanRunoff(m3/yr)

a 0.0006 0.3307 0.0867 0.18 92.8 24.3 64.5 32.0 3.5 17609789

b 0.0007 0.3861 0.1117 0.18 96.4 27.9 59.5 31.9 8.6 19778548

West Duffins(13,539 ha)

c 0.0006 0.3484 0.0912 0.17 91.9 24.0 44.2 47.2 8.6 18737994

a 0.0006 0.3045 0.0724 0.17 89.0 21.1 51.1 45.3 3.6 11499156

b 0.0006 0.3174 0.0778 0.17 89.8 22.0 49.2 45.7 5.1 11869204

East Duffins(9,202 ha)

c 0.0005 0.2712 0.0558 0.15 84.2 17.4 30.5 64.4 5.1 10812808

a 0.0006 0.3202 0.0775 0.17 89.8 21.7 57.7 39.8 2.5 1698791

b 0.0015 0.8531 0.3620 0.22 120.2 51.0 23.4 33.4 43.2 3380821

Ganetsekiagan(1,305 ha)

c 0.0015 0.8488 0.3593 0.22 119.9 50.8 22.5 34.3 43.2 3371259

a 0.0007 0.3662 0.0825 0.17 87.5 19.7 53.7 44.9 1.4 2195203

b 0.0015 0.8059 0.3065 0.20 110.9 42.2 30.6 37.6 31.8 3809847

Urfe(1,437 ha)

c 0.0015 0.8012 0.3039 0.20 110.7 42.0 29.8 38.4 31.8 3795484

a 0.0015 0.8395 0.3494 0.22 119.1 49.5 37.6 24.6 37.8 4369051

b 0.0019 1.0688 0.5178 0.24 136.0 65.9 16.0 22.8 61.2 4872120

Millers(1,698 ha)

c 0.0019 1.0667 0.5165 0.24 135.8 65.8 15.5 23.3 61.2 4867174

a 0.0018 1.0150 0.4160 0.20 115.6 47.4 0.0 54.5 45.6 3603906

b 0.0025 1.3985 0.6572 0.23 130.6 61.4 0.0 39.4 60.6 4392176

Lower MainDuffins(1,124 ha)

c 0.0025 1.3982 0.6571 0.23 130.6 61.4 0.0 39.4 60.6 4391273

a 0.0007 0.3713 0.1006 0.18 93.6 25.4 55.1 37.8 7.1 40975895

b 0.0009 0.4649 0.1461 0.19 99.9 31.4 48.1 36.5 15.4 48102717

Whole Duffins(28,305 ha)

c 0.0008 0.4263 0.1246 0.18 95.8 28.0 34.6 50.0 15.4 45975992

a 0.0013 0.7221 0.2389 0.19 102.6 33.9 47.6 34.1 18.3 9786674

b 0.0016 0.8893 0.3478 0.21 113.3 44.3 33.3 33.4 33.3 10913549

Carruthers(3,810 ha)

c 0.0016 0.8721 0.3338 0.20 111.2 42.5 27.4 39.6 33.0 10902470



Table 4.4: Estimated Dry Weather Unit Area Loads for a) Existing Land Use; b)Projected Land Use Under the Official Plan; and c) Projected Land UseUnder the OP Overlain With Enhanced Natural Heritage Cover

Unit Area Loads

(kg/ha/day)Concentrations

(mg/L)Land use (%)Basins|Scenario

TP TSS Cl TP TSS Cl Rural Wooded Urban

BaseFlow

(m3/yr)

a 0.0001 0.0241 0.0550 0.02 6.0 13.7 64.5 32.1 3.5 19870965

b 0.0001 0.0235 0.0566 0.02 6.0 14.5 59.5 31.9 8.6 19324560

West Duffins(13539 ha)

c 0.0001 0.0235 0.0494 0.02 6.0 12.6 44.2 47.2 8.6 19324560

a 0.0001 0.0391 0.0788 0.02 6.0 12.1 51.1 45.3 3.6 21867515

b 0.0001 0.0387 0.0791 0.02 6.0 12.3 49.2 45.7 5.1 21656545

East Duffins(9202 ha)

c 0.0001 0.0387 0.0647 0.02 6.0 10.0 30.5 64.4 5.1 21656545

a 0.0001 0.0300 0.0629 0.02 6.0 12.6 57.7 39.8 2.5 2380530

b 0.0001 0.0249 0.0807 0.02 6.0 19.5 23.4 33.4 43.2 1975380

Ganetsekiagan(1305 ha)

c 0.0001 0.0249 0.0803 0.02 6.0 19.4 22.5 34.3 43.2 1975380

a 0.0001 0.0206 0.0405 0.02 6.0 11.8 53.8 44.9 1.3 1798355

b 0.0001 0.0178 0.0510 0.02 6.0 17.2 30.6 37.6 31.8 1552345

Urfe(1437 ha)

c 0.0000 0.0178 0.0508 0.02 6.0 17.2 29.8 38.4 31.8 1552345

a 0.0000 0.0143 0.0470 0.02 6.0 19.7 37.6 24.6 37.8 1478615

b 0.0000 0.0137 0.0536 0.02 6.0 23.4 16.0 22.8 61.2 1418390

Millers(1698 ha)

c 0.0000 0.0137 0.0535 0.02 6.0 23.4 15.5 23.2 61.2 1418390

a 0.0000 0.0116 0.0335 0.02 6.0 17.3 0.0 54.5 45.6 793510

b 0.0000 0.0097 0.0347 0.02 6.0 21.4 0.0 39.4 60.6 665395

Lower MainDuffins(1124 ha)

c 0.0000 0.0097 0.0347 0.02 6.0 21.4 0.0 39.4 60.6 665395

a 0.0001 0.0280 0.0631 0.02 6.00 13.5 55.1 37.8 7.1 48189490

b 0.0001 0.0271 0.0674 0.02 6.00 14.9 48.1 36.5 15.4 46592615

Whole Duffins(28305 ha)

c 0.0001 0.0271 0.0600 0.02 6.00 13.3 34.6 50.0 15.4 46592615

a 0.0000 0.0100 0.0400 0.02 6.00 15.6 47.6 34.1 18.3 3312098

b 0.0000 0.0100 0.0400 0.02 6.00 18.0 33.3 33.4 33.4 3177194

Carruthers(3810 ha)

c 0.0000 0.0100 0.0400 0.02 6.00 17.2 27.4 39.6 33.0 3177194



4.1.1 Wet Weather Sediment Load

A substantial increase in unit TSS loadings occurs in Ganetsekiagan, Urfe, Millers,Lower Main Duffins, and Carruthers Creek with the conversion of mostly ruralagricultural lands to urban land uses (Table 4.1). TSS loads remain similar amongscenarios in the West and East Duffins sub-watersheds (Fig. 4.1) because these twosub-watersheds are subject to much smaller increase in urban development under futurescenarios.

4.1.2 Dry Weather Sediment Load

Unit area loads during dry weather are generally proportional to the relative base flowcontributions from each sub-watershed (Table 4.4). Thus, the East Duffins sub-watershed, which has the highest baseflow relative to other sub-watersheds (Fig. 4.1),also has the highest dry weather TSS loads. High baseflow in the East Duffins isattributed to preserved woodlands in its headwaters. Small changes in dry weather TSSloading across different scenarios reflects the correspondingly small changes inbaseflow (Table 4.1), and dry weather concentrations of 6 mg/L for all land usecategories (see Table 3.1)

4.2.1 Wet Weather Sediment Concentration

Changes in land use from existing conditions to the future OP scenario resulted in anincrease in wet weather TSS concentrations by 13, 14, 25 and 33 % in the Lower MainDuffins, Millers, Urfe, and Ganetsekiagan sub-watersheds, respectively (Table 4.1).Since the two future scenarios in these sub-watersheds were similar, modelled TSSconcentrations were also similar. The higher TSS concentrations in Ganetsekiagan andUrfe sub-watersheds are due to higher unit load contribution of TSS relative to othersub-watersheds within the whole Duffins Creek (Table 4.3).

All areas had wet weather TSS concentrations (85 to 135 mg/L) above therecommended concentration of 25 to 80 mg/L for maintenance of a good fishery (EIFAC,1965). However, these wet weather concentrations would typically be of relatively shortduration (not more than a few days), and are within tolerance limits of most fishcommunities.

4.2.2 Dry Weather Sediment Concentration

The dry weather TSS concentrations are constant among scenarios (Table 4.2) becausethe mean concentrations for dry weather conditions are the same for all land usecategories (Table 3.1).

4.3.1 Wet Weather Phosphorous Load

The increase in phosphorous loadings with the change in land use scenario during wetweather conditions is more pronounced in Ganetsekiagan, Millers, Lower Main Duffins,



and Carruthers than in other sub-watersheds (Table 4.3 and Fig. 4.3). The rationale forthis result is similar to that for TSS, with which phosphorus is strongly correlated.

4.3.2 Dry Weather Phosphorous Load

The trend of phosphorous loading (Fig. 4.3) is quite similar to that of TSS loading (Fig.4.1) during dry weather conditions. Hence, it is reasonable to assume that both the wetand dry weather phosphorous loadings are a function of sediment loads. Although nofunctional relationship between TSS and Phosphorous load was investigated in thisstudy, evidence of sediment as the predominant carrier of phosphorous in the GreatLakes System has been reported in the literature for Ontario conditions (Dickinson andGreen, 1988; Gartner Lee Ltd, 2002).

4.4.1 Wet Weather Phosphorous Concentration

Phosphorous concentrations among all the sub-watersheds and watersheds under wetweather conditions varied between 0.15 to 0.24 mg/L for the three land use scenarios(Table 4.1 and Fig. 4.4). This range is higher than the Provincial Water QualityObjective (PWQO) limit of 0.03 mg/L for total phosphorous (TP). The increase inphosphorous concentration under different land use scenarios varied between 5 and 29%, with the greatest change occurring in Ganetsekiagan (Table 4.1). A very similarrange of TP concentration (0.19 to 0.22 mg/L) has been reported for the Grand River insouthern Ontario, which has land use characteristics similar to the Duffins Creek (Ostry,1982).

4.4.2 Dry Weather Phosphorous Concentration

The dry weather phosphorous concentrations were constant (Table 4.2) becauseconcentrations for each of the land use categories during dry weather were similar. Themodelled phosphorus concentration during dry weather of 0.02 mg/L comparesfavourably with actual concentrations monitored between 2000 and 2001 (mean =0.01mg/L) during predominantly dry weather at the mouth of the Duffins Creek (OMOEE,2002).

4.5.1 Wet Weather Chloride Load

Since chloride loading is also a function of land use type, Carruthers, Ganetsekiagan,Urfe, Millers, and Lower Main Duffins sub-watersheds show higher loads than other sub-watersheds (Table 4.3 and Fig. 4.5). In these areas, there is almost a one half to twofold increase in chloride loads from existing conditions to future OP scenarios under wetweather conditions (Fig. 4.5). This trend indicates that future development willsignificantly increase chloride loading to the streams, thereby affecting the biological,chemical, and physical health of the watercourses.



4.5.2 Dry Weather Chloride Load

The dry weather unit area chloride loads at the East and West Duffins sub-watershedsare very much comparable to the wet weather chloride loads (0.05 to 0.1 kg/ha/day), butin other watersheds and sub-watersheds there are two to three fold differences (Table4.4 and Fig. 4.5). Overall, there is no significant increase in chloride loads amongscenarios in any of the sub-watersheds and watersheds during dry weather conditions.

4.6.1 Wet Weather Chloride Concentration

The chloride concentrations under wet weather conditions varied between 20 and65 mg/L under different scenarios (Table 4.1 and Fig. 4.6), which is well below theapproximate threshold of 250 mg/L suggested by a recent federal investigation into theaquatic impacts of road salts (Environment Canada and Health Canada, 2001).

4.6.2 Dry Weather Chloride Concentration

During dry weather conditions, chloride concentrations were less than 25 mg/L in all thesub-watersheds and watersheds (Table 4.2 and Fig. 4.6), suggesting that chloriderelated water quality impacts are not a significant concern during dry weather.



5.0 COMPARISON OF RESULTS WITH PAST STUDIES

Results from this study could not be compared directly with the Agricultural Non-pointsource (AGNPS) simulation performed for Duffins and Carruthers Creek watershedsbecause the spreadsheet model results are separated into wet and dry weather,whereas the AGNPS results are storm intensity specific (e.g., 25 mm in 12 hours, 15 mmin 9 hours). However, it should be noted that both models reported TP concentrationsabove PWQOs. The AGNPS model results indicated a phosphorus concentration rangeamong the Duffins and Carruthers watersheds and sub-watersheds between 0.06 to0.46 mg/L, which is wider than the 0.15 to 0.24 mg/L range determined throughspreadsheet modelling. One of the possible reasons for such wider range of TP wouldbe due to more discretized land use information in AGNPS than in spreadsheet model.Both AGNPS and spreadsheet model results, however, indicated that Ganetsekiagan,Urfe, and East Duffins sub-watersheds had higher TP concentrations than other sub-watersheds in the region.

Unit area load results of this study are compared to other studies in Table 5.1. ThePollution from Land Use Activities Reference Group (PLUARG) study in 1981 for theDuffins Creek watershed (Ostry and Tseng, 1981) reported higher loading estimates fortotal phosphorus and TSS, but similar estimates for chloride. Using export coefficientscited in the Nobleton Sewage Servicing report, and applied to the Duffins Creekwatershed, total phosphorus loads were only slightly higher than reported in this study.In the Lake Simcoe Region, north of Duffins Creek, Winter et al (2002) reported unit arealoads for total phosphorus in predominantly urban catchments of 0.65 kg/ha/yr. In mixedagricultural and forest/scrubland sub-catchments, the unit area load ranged between0.11 and 0.27 kg/ha/yr, and between 0.06 and 0.07 kg/ha/yr, respectively. When appliedto the Duffins Creek watershed, the weighted unit area load for phosphorus was 0.17kg/ha/yr, which is about 58% of the value calculated in this study.

Table 5.1: Wet Weather Unit Area Load Estimates (kg/ha/year) for the DuffinsCreek Watershed

Area(ha.)

Urban(%)

Rural(%)

Wooded(%)

TotalPhosphorous

TSS Chloride Reference

28305 7 55 38 0.29 145.7 59.8 This study24864 7 59 34 0.65 362.0 51.3 Ostry and

Tseng, 198128305 7 55 38 0.32 n/a n/a Gartner Lee,

2002*28305 7 55 38 0.17 n/a n/a Winter et al.,

2002***Calculations are based on export coefficients determined from a 4-year study of the Laurel Creekwatershed in Waterloo, Ontario. Export coefficients for urban, rural, and wooded land uses (as defined inthis report) were estimated at 0.72, 0.39 and 0.15 kg/ha/yr, respectively.**Based on measurements of total phosphorus loads for different land uses in the Lake Simcoe Region. Inthis study, unit area loads for urban, agricultural, and forest/scrubland were 0.65, 0.19, and 0.06 kg/ha/yr,respectively.



6.0 CONCLUSIONS

Among the three pollutants modelled, TSS and phosphorous levels in the Duffins andCarruthers Creek watersheds exceeded available guidelines for surface waters.Chloride levels were within acceptable limits, but may become a concern as urbangrowth continues. While significant reductions in phosphorus have occurred over thepast 30 years (Flemming and Fraser, 1999), problems related to non-point sources ofpollution have not disappeared, and will require increased attention as point sourcesdecrease in importance and land use changes continue to exert stress on receivingwaters (Logan, 2000).

Estimates of the three pollutants modelled in this study were in reasonably goodagreement with results from other studies in Southern Ontario, suggesting that, givenreliable estimates of pollutant concentrations for different land uses and runoff, thissimple approach could be applied in other largely rural watersheds with similar success.

The current spreadsheet model assumes that runoff from urban areas is similar to otherland uses thereby underestimating the resultant loading and concentrations of thepollutants modelled, as urban land use cover increases. However, it has been reportedthat the conversion of rural /agricultural lands to urban lands results into two to three foldincrease in basic hydrograph parameters (Anonymous, 2002) such as:

• runoff coefficient increases by 1.5x,• peakflow increases by 3x,• peakflow lag time decreases by 3x, and• runoff volume increases by 3.5x.

These increased parameters would translate into a similar increase in loading andinstream concentrations for the spreadsheet model results.

United States Environmental Protection Agency’s (USEPA) Wet Weather FlowDocument (USEPA, 1999) revealed that there is an average percent impervious area(APIA) factor associated with each land use category that relates to different EMCs.For example, the APIA for agricultural and forest areas is around 1, whereas for urbanareas it varies from 25 to 98 for low density residential to major roadways respectively.Thus, the information on APIA for each land use would improve the loading estimatesfrom urban area better than the current spreadsheet model. Hence, in watersheds withsignificant urban cover, the model could be improved by including the APIA factor in thewet weather loading algorithm that compensates for the greater proportion of runoffgenerated from urban areas relative to other land uses.



7.0 REFERENCES

Anonymous, 2002. Course Notes on Urban Hydrology, Department of Civil Engineering,University of Waterloo, Ontario.

Aquafor Beech, 2001. Compilation of Stormwater Average Event Mean ConcentrationData, Working Paper developed for the City of Toronto’s Wet Weather FlowManagement Master Plan, June 11, 2001.

Beak Consultants Limited (Beak). 1993. Pilot Watershed Study Soil and WaterEnvironmental Enhancement Program (SWEEP), Report # 6: Evaluation ofConservation Systems, Water Quality. Agriculture Canada, Guelph, Ontario.

Bowen, G.S. and M.J. Hinton. 1998. The temporal and spatial impacts of road salt onstreams draining the Greater Toronto Area. In: Proceedings of: Groundwater in aWatershed Context, Canada Centre for Inland Waters, Burlington, Ontario,December 2-4, 1998. p. 303-309.

Clarifica Inc. 2002. Water Budget in Urbanizing Watersheds: Duffins Creek Watershed.TRCA. Ontario.

Dickinson, W.T., and D.R., Green. 1988. Characteristics of Sediment Loads in Ontario.Canadian Journal of Civil Engineering, 15:1067-1079.

Environment Canada and Health Canada, 2001. Road Salts: Priority Substances ListAssessment Report. Prepared for the Canadian Environmental Protection Act,1999 Priority Substances List. Internet Publication.

European Inland Fisheries Advisory Commission (EIFAC), 1965. Water quality criteriafor European freshwater fish. Report on finely divided solids and inland fisheries.International Journal of Air and Water Pollution, V.9, 151 -168.

Flemming, R. and Fraser, H. 1999. Nitrate and Phosphorus Levels in Selected SurfaceWater Sites in Southern Ontario – 1964 to 1994. Unpublished Paper.

Gartner Lee Ltd. 2002. Nobleton Sewage Servicing Follow-Up Studies: 2000 to 2001.The Regional Municipality of York.

Gerber Geosciences Inc. 2002. Duffins Creek Watershed Hydrogeology andAssessment of Land Use Change on the Groundwater Flow System . TRCA,Ontario.

Hinton, M.J. 1996. Measuring Stream Discharge to Infer the Spatial Distribution ofGroundwater Discharge. In Proceedings of the Watershed ManagementSymposium, Canada Centre for Inland Waters, Burlington, Ontario, Dec 6-8,1995, pp.27-32.



Logan, T. 2000. Nonpoint sources of pollutants to the Great Lakes: 20 years postPLUARG. In: Great Lakes Science Advisory Board, Nonpoint Sources ofPollution to the Great Lakes Basin: Based on the Findings of a Workshop toAssess the Status of Nonpoint Source Pollution Control in the Great LakesBasin., Toledo, Ohio, September 16-18, 1998. Chapter 3.

Ontario Ministry of Environment and Energy (OMOEE), 2002. Unpublished data fromthe Lake Ontario Tributary Priority Pollutant Monitoring Program.

Ostry, R.C., and T. Tseng. 1981. A Preliminary Method for Evaluation of Non-pointSources: An Assessment Procedure for Working Group II of the WaterManagement Steering Committee. The Ontario Ministry of Environment,Toronto, Ontario.

Ostry, R.C. 1982. Relationship of Water Quality and Pollutant Loads to Land Uses inAdjoining Watersheds. Water Resources Bulletin, 18(1):99-104.

Toronto and Region Conservation Authority (TRCA). 2002a. Duffins Creek State of theWatershed Report. Downsview, Ontario.

Toronto and Region Conservation Authority (TRCA). 2002b. Carruthers Creek State ofthe Watershed Report. Downsview, Ontario.

Toronto and Region Conservation Authority (TRCA). 2002c. Agricultural Non-PointSource (AGNPS) Modeling of the Duffins and Carruthers Creek Watersheds :Draft Report, Downsview, Ontario.

Toronto and Region Conservation Authority (TRCA). 2002d. Technical Analysis andIntegration Process Background Report, Duffins and Carruthers CreekWatersheds Plan, Draft Report, Downsview, Ontario.

Transport Canada, 2002. Green Space Master Plan for the Federal Pickering Lands,Terms of Reference, September 9, 2002.

USEPA. 1999. Innovative Urban Wet-Weather Flow Management Systems, Report #EPA/600/R-99/029. National Risk Management Laboratory, USEPA, Cincinnati,Ohio.

Winter, J., Dillon, P., Futter, M, Nicholls, K., Scheider, W. and Scott, L. 2002. Totalphosphorus budgets and nitrogen loads: Lake Simcoe, Ontario (1990 to 1998),Journal of Great Lakes Research. 28(3): 301-314.

APPENDIX A

Unit Conversion and Sample Load Calculations


Stantec Consulting Ltd./Aquafor Beech LimitedRef. 22714.1 A.1

APPENDIX A: UNIT CONVERSION AND SAMPLE LOAD CALCULATIONS

UNIT CONVERSION

Pollutant Load (Metric Ton or tonne/Year) =

% Land Use (LU) * [Annual Runoff for Wet Weather OR Annual Base flow for DryWeather] m3/year * 1000 L/ m3 * [Event Mean Concentration, EMC] mg/L * 10-6 Kg/mg *10-3 Ton/Kg= % LU * 10-6

Pollutant Concentration (mg/L) = Pollutant Load / Runoff = [tonne/year*1000kg/tonne*1000 gm/kg*1000 mg/gm] * [year/m3*1000 L/ m3]

Unit Area Pollutant Load (Kg/ha/day) = (Metric Ton or tonne /Year * 1000/365)/ Sub-watershed Area in hectares

SAMPLE LOAD CALCULATIONSWest Duffins Creek (Area = 13539 ha)Existing Conditions /Wet Weather

Land Uses PercentRural 64.50Wooded 32.05Urban 3.45

Runoff volume/land use Total Runoff (m³/yr) 17,609,789

EMC's Rural Wooded UrbanPhosphorus (mg/L) 0.20 0.12 0.30Suspended solids (mg/L) 100 70 170Chloride (mg/L) 30 5 98

Annual Load (tonne/year) Unit Area Load (Kg/ha/day) Annual Load (Kg/day)Phosphorus 3.131 0.000633623 8.578620773TSS Load 1634.188 0.330691229 4477.228546Chloride 428.508 0.086712015 1173.993974

Concentration Data (mg/L)Phosphorus = 0.178TSS = 92.800Chloride = 24.334

APPENDIX B

Graphs of Pollutant Concentrations and Loads

Fig. 4.1 TSS Loadings (Unit Area Load) for Different Scenarios

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

1.10

1.20

1.30

1.40

1.50

West Duffins East Duffins Ganetsekigan Urfe Millers Lower MainDuffins

DUFFINSTOTAL

Carruthers

Basins

TS

S U

nit

Are

a Load

(Kg/h

a/day

)

Existing Wet Future Wet Fut+NH wet

Existing Dry Future Dry Fut+NH Dry

Fig. 4.2 TSS Concentrations for Different Scenarios

0

20

40

60

80

100

120

140


DUFFINSTOTAL

Carruthers

Basins

TSS

(W

et)

and

(Dry

) C

once

ntra

tion

, mg/

LExisting Wet Future Wet Fut+NH Wet


Fig. 4.3 Phosphorous Loadings (Unit Area Load) for Different Scenarios

0.0E+00

5.0E-04

1.0E-03

1.5E-03

2.0E-03

2.5E-03

3.0E-03


DUFFINSTOTAL

CarruthersBasins

P U

nit

Are

a L

oad

, Kg

/ha/

day



Fig. 4.4 Phosphorous Concentrations for Different Scenarios

0.00

0.04

0.08

0.12

0.16

0.20

0.24


DUFFINSTOTAL

Carruthers

Basins

Ph

osp

ho

uro

us

Co

nce

ntr

atio

n, m

g/L

Existing Wet Future Wet Fut+NH WetExisting Dry Future Dry Fut+NH Dry

Fig. 4.5 Chloride Loadings (Unit Area Load) for Different Scenarios

0.0E+00

5.0E-02

1.0E-01

1.5E-01

2.0E-01

2.5E-01

3.0E-01

3.5E-01

4.0E-01

4.5E-01

5.0E-01

5.5E-01

6.0E-01

6.5E-01

7.0E-01


DUFFINSTOTAL

Carruthers

Basins

Chl

orid

e U

nit

Are

a Lo

ad, K

g/ha

/day



Fig. 4.6 Chloride Concentrations for Different Scenarios

0

10

20

30

40

50

60

70


DUFFINSTOTAL

Carruthers

Basins

Chl

orid

e C

once

ntra

tion

, mg/

L



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Dry and Wet Weather Modelling of Water Quality Under ...trca.on.ca/dotAsset/25939.pdfDry and Wet Weather Modelling of Water Quality Under Alternative Land Use Scenarios in the Duffins