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Humber River

State of the Watershed Report –

Surface Water Quantity

2008

Humber River State of the Watershed Repor t – Surface Water Quanti ty

Humber_SW_Quantity_FINAL_062508F.doc ii

EXECUTIVE SUMMARY

• As of 2002, only one quarter (25%) of the total urban area in the Humber River watershed had stormwater management controls in place to treat urban run-off prior to it being released to receiving watercourses.

• The majority of annual stream flow in both the Main and East Humber subwatersheds is generated by groundwater discharge (baseflow) due to the permeable soils and hummocky terrain of the Oak Ridges Moraine area, predominantly rural land uses and presence of aquifers.

• The Oak Ridges Moraine, particularly its southernmost extent, and the Iroquois Sand Plain are major influences on the distribution of baseflow in the watershed. Both of these physiographic regions are characterized by highly permeable soils and underlying geology (sand and gravel) which produce high rates of infiltration and groundwater discharge to streams.

• Half (50%) of the total stream flow in the Humber River during baseflow conditions originates from within the Main Humber and East Humber subwatersheds. Secondary subwatersheds observed to be major contributors to baseflow are Upper Main, Centreville Creek and Purpleville Creek.

• Baseflows in the West Humber subwatershed are low with large tributaries becoming dry during summer months. The majority of stream flow is generated by surface run-off due to low permeability soils, impervious surfaces, and in some areas no aquifers being present.

• The majority of baseflow in the West Humber originates from the west branch.

• Seasonal variations in baseflow and minimum sustained baseflow rates at long term stream gauge sites have not changed significantly since continuous monitoring began in the late 1950s. August is typically the time of year when stream flow and water levels are at their lowest.

• Risk of flooding remains an important issue in portions of Bolton, Woodbridge, Oak Ridges (Richmond Hill) and Toronto.

• The Black Creek and Lower Humber subwatersheds have been almost entirely developed prior to the adoption of stormwater quantity and quality control measures. As a result, flooding is an issue of concern in some areas. Some reaches have been transformed into concrete channels to increase the conveyance capacity of the system. Stream flow tends to increase rapidly during storm events due to high rates of run-off from impervious surfaces and lack of stormwater controls.

• Significant increasing trends in average annual and seasonal stream flow volumes have been observed in the East Humber and in urbanizing watersheds like Highland Creek and the Rouge River, which are indicative of the hydrologic impacts of urban development (i.e., impervious surfaces) and not climate variability.


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• Increases in annual and seasonal stream flow caused by urbanization may be creating long term problems in some watercourses as they adjust to accommodate the changed pattern of flow. If nothing is done, excessive channel migration could impair sensitive aquatic ecosystems and expose municipal infrastructure in valley lands, leading to costly repairs and maintenance.

• Overall, water use in the Humber is predominantly for agricultural irrigation which accounts for 42% of the total annual withdrawals. Withdrawals for commercial use and water supply are also major water use sectors, comprising 30% and 18% respectively.

• Reaches of the West Humber are most at risk of negative downstream impacts on aquatic habitat and water availability from permitted surface water takings, with more than 18% of average annual baseflow allocated for withdrawal.

• Many water users in the Greater Toronto Area are switching from surface sources to groundwater sources as indicated by trends in MOE permits issued over the past four decades.


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TABLE OF CONTENTS

1.0 INTRODUCTION............................................................................................................ 1

2.0 UNDERSTANDING SURFACE WATER QUANTITY...................................................... 1

3.0 SURFACE WATER IN THE RURAL AND URBAN LANDSCAPE.................................. 3

4.0 MEASURING SURFACE WATER QUANTITY............................................................... 4

4.1 Stream Gauges............................................................................................................... 4 4.2 Field Measurements ....................................................................................................... 8 4.3 Assessment of Water Use............................................................................................... 9 4.4 Hydrologic and Hydraulic Models................................................................................ 11

5.0 EXISTING CONDITIONS............................................................................................. 11

5.1 Overview of Humber River Subwatersheds ................................................................. 11 5.2 Stream Flow.................................................................................................................. 15 5.2.1 Annual and Seasonal Stream Flow ..................................................................... 15 5.2.2 Baseflow Index...................................................................................................... 22 5.2.3 Minimum In-stream Flow Requirements .............................................................. 23 5.2.4 Seasonal Baseflow ............................................................................................... 25 5.2.5 Hydrologic Models................................................................................................ 28 5.2.6 Field Measurements of Baseflow ......................................................................... 31

5.3 Water Use...................................................................................................................... 39 5.4 Flooding ........................................................................................................................ 44

6.0 MANAGEMENT CONSIDERATIONS.......................................................................... 48

6.1 General.......................................................................................................................... 48 6.2 Baseflow........................................................................................................................ 49 6.3 Surface Water Use........................................................................................................ 49 6.4 Flooding ........................................................................................................................ 50

7.0 WATERSHED REPORT CARD RATINGS................................................................... 51 7.1 Stream Flow.................................................................................................................. 51 7.2 Flooding ........................................................................................................................ 53 7.3 Surface Water Use........................................................................................................ 54

8.0 REFERENCES............................................................................................................. 57

LIST OF FIGURES Figure 1: Planned levels of stormwater controls – Humber River Watershed............................... 6 Figure 2: Historical and current stream flow and precipitation gauges ........................................ 7 Figure 3: Locations of Baseflow Sampling................................................................................... 10 Figure 4: Primary and secondary Humber River subwatersheds ............................................... 13 Figure 5: Physiographic Regions in the Humber River Watershed............................................. 14 Figure 6: Historical Trends in Mean Annual Stream Flow at Selected Stream Gauges ............. 18 Figure 7: Historical Trends in Mean Summer Stream Flow at Selected Stream Gauges........... 21 Figure 8: Percentage of Total Annual Flow Volume Occurring in May to October at Selected

Gauges.................................................................................................................................. 22 Figure 9: Historical Mean Monthly Baseflow Rates Showing Seasonal Fluctuations (East

Humber, Stream Gauge #02HC009)– ................................................................................. 26 Figure 10: Mean Monthly Baseflow Rates (spring-summer) For Selected Humber River Stream

Gauges.................................................................................................................................. 27 Figure 11: Baseflow Contributions by Primary Humber River Subwatersheds, 2004 ................ 32


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Figure 12: Baseflow Normalized to Stream Length – Humber River Watershed, 2004 .............. 35 Figure 13: Geologic Model Cross-Section (West Humber)………………………………………...37 Figure 14: Geologic Model Cross-Section (East Humber)…………………………………………37 Figure 15: Water Abstractions by Purpose – Humber River Watershed ..................................... 40 Figure 16: Percent of PTTW’s Issued by Year and Water Source (TRCA Jurisdiction) .............. 44 Figure 17: Flood Vulnerable Areas and Roads - Humber River Watershed................................ 47 Figure 18: Surface Water Use ...................................................................................................... 55

LIST OF TABLES

Table 1: Portion of existing urban areas with stormwater controls - Humber Watershed, 2002 .. 4 Table 2: Historical and Existing Stream Gauges in the Humber River Watershed ....................... 5 Table 3: Mean Annual Stream Flows at Humber River Stream Gauges, Full Period of Record. 16 Table 4: Median Stream Flows During Spring-Summer Months* at Humber River Stream

Gauges and Minimum In-stream Flow Criteria .................................................................... 24 Table 5: Humber River HSP-F Model Outputs at Selected Locations (2002 land use/land cover

conditions; 1991 to 1996 climate data; HCCL, 2008) .......................................................... 30 Table 6: Contribution to Overall Baseflow Discharge by Humber River Subwatersheds, 2004. 33 Table 7: Surface Water Withdrawals as a Percentage of Baseflow Discharge, 2004 ................. 40 Table 8: Classification System for Assessment of Risk of Downstream Impacts From Surface

Water Withdrawals ................................................................................................................ 41 Table 9: Water Withdrawals By Subwatershed – Humber River Watershed, 2004..................... 42 Table 10: Number of Flood Vulnerable Areas and Roads by Flood Stage – Humber River

Watershed (TRCA, 2005)...................................................................................................... 46 Table 11: Percent Change in Median Summer Baseflow (1997 to 2003) and Report Card

Ratings .................................................................................................................................. 52 Table 12: Surface Water Use, High Risk Takings and Report Card Ratings .............................. 55


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1.0 INTRODUCTION

In 1997, the Humber Watershed Task Force released the Humber River Watershed Strategy, Legacy: A Strategy For A Healthy Humber (MTRCA, 1997), which provided thirty objectives for a healthy, sustainable watershed, and a set of actions necessary to achieve them. It also provided an overview of the state of the Humber River watershed at that time. Since the release of the watershed strategy, a significant amount of new information has become available through monitoring, special studies and the experiences of watershed partners. In 2004, the Toronto and Region Conservation Authority (TRCA), in partnership with watershed municipalities and the Humber Watershed Alliance initiated a study to develop an integrated watershed management plan for the Humber River. This study was initiated to fulfill the watershed planning requirements of the Oak Ridges Moraine Conservation Plan, 2002, and to update the strategies and recommendations of Legacy, in light of new information, a stronger scientific foundation and better understanding of the effects of human actions on natural ecosystems. The watershed plan is intended to inform and guide municipalities, provincial and federal governments, TRCA, non-governmental organizations and private landowners regarding management actions needed to maintain and improve watershed health. This State of the Watershed Report provides updated information on current conditions, emerging trends and identifies key watershed management issues and opportunities in the Humber pertaining to surface water quantity. Indicators of watershed health and associated targets are used to rate current conditions. Ratings for a full suite of indicators of watershed health are summarized in, Listen to Your River: A Report Card on the Health of the Humber River Watershed (TRCA, 2007). This State of the Watershed report also provides an overview of current management strategies and introduces some innovative approaches to address key issues, which will be considered for inclusion in the Humber River Watershed Plan. It begins with an overview of factors that influence watershed conditions and the indicators being used to track current conditions and evaluate watershed health.

2.0 UNDERSTANDING SURFACE WATER QUANTITY

The accounting of the total quantity of water and its distribution within a watershed is known as the water budget. The components of this budget include: the total amount of precipitation input to the system, both rain and snow; the percentage of precipitation which returns to the atmosphere through both evaporation and transpiration; the percentage which enters the groundwater system through infiltration; and the percentage which runs overland to rivers and streams. How these components move through the atmosphere and over and through the ground is known as the hydrologic cycle. Surface water quantity deals with the components of water within the hydrologic cycle that move over land or within surface systems of lakes, rivers and streams. Surface flow includes normal low flows in rivers and streams which are generated by groundwater discharge, overland flow from rain and snow melt, and precipitation that falls directly into lakes and rivers.



Climate and surficial geology are key factors in determining the quantity of rainfall and snowmelt that ends up as surface flow within a watercourse, primarily through their effect on evaporation and infiltration. Although surface flow varies throughout the year, there is a general tendency for the highest annual stream flows, or peak flows, to occur in the spring due to the spring melt or late fall when large amounts of precipitation occur and for the lowest stream flows to occur in the summer when precipitation is at a minimum and evapotranspiration is highest. Flooding is a natural, common occurrence in all watersheds. The presence of relatively small stream channels with wide floodplain areas extending beyond their banks in the Humber River watershed attests to the fact that flows often exceed their channel and spill out into the floodplain zones during periods of high stream flow. In mostly undeveloped watersheds, typically where agricultural or urban land uses account for a minor portion of the total watershed area, a significant portion of annual precipitation is cycled back to the atmosphere through evapotranspiration, while much of the remaining portion infiltrates into the soil, leaving a relatively small surface run-off component. Under these conditions, a significant portion of surface water flow originates from groundwater discharge and flows released from wetlands. The term low flow, or baseflow, refers to the amount of stream flow that is sustained in a watercourse during extended periods of dry weather. Baseflow conditions represent the lowest stream flows that typically occur in a watercourse and are usually supplied primarily by groundwater discharge occurring along the stream corridor and the gradual release of water from wetlands. Other sources of water that can contribute to baseflow include shallow groundwater seeping into or flowing alongside storm sewers that is discharged to the watercourse and run-off from outdoor water use in urban areas. In a typical rainfall year, approximately 70% of total annual stream flow in the Humber River occurs during baseflow conditions. This consistent and relatively clean source of water maintains aquatic habitat and recreational opportunities (e.g., fishing, swimming, boating) during periods of dry weather and in some instances represents a potentially sustainable source of water for human use. Seasonal fluctuations in stream flow influence the life cycle activities of aquatic species, such as fish spawning, hatching and migration. Rainbow trout, for example, migrate upstream and spawn in the spring when flows are at their highest and water levels the deepest. The fry then emerge from the gravel in the late spring as flows and water levels are dropping and congregate in lower velocity areas such as stream edges or pools during the early stages of their life. Alterations to stream flow patterns (e.g., through changes in land use or water takings) can have significant detrimental effects on aquatic populations that have adapted to the natural flow regime. Extreme stream flow events can put human life and property at risk, but storm events of the magnitude necessary to produce severe flooding are typically uncommon. In undeveloped or rural watersheds, wetlands, vegetated floodplains and natural, sinuous river and stream channels attenuate flood flows by detaining run-off and flood waters, resulting in longer but more controlled flood periods with much lower peak flows and maximum water levels.



3.0 SURFACE WATER IN THE RURAL AND URBAN LANDSCAPE

Extreme variations in surface water flow in urban and urbanizing watersheds occur more frequently and are more severe than those in undeveloped or rural watersheds. Similar to historical settlement patterns in other parts of southern Ontario, major land use changes in the Humber River watershed were initially to allow for settlement and agricultural activities. Flow stabilizing features such as forested lands were cleared, wetlands were drained and small streams channelized with riparian zones removed or altered. These activities altered the hydrologic cycle by reducing interception, evapotranspiration and infiltration, which in turn generated increased surface run-off and more frequent high flows in rivers and streams. While these changes in stream flow patterns caused by human settlement and rural land uses were significant, in general the typical seasonal flow variations and overall flow patterns were maintained and continued to define the watershed’s hydrologic response. The growth of urban settlements has caused the most significant stresses on the hydrologic system. Urbanization typically increases the portion of land within a watershed that is covered by impervious surfaces (e.g., roads, parking lots, driveways, roofs, etc.). As urban settlements grow and the watershed becomes increasingly impervious, precipitation cannot infiltrate into the soil to the same extent as it would have before urbanization. Instead, rainfall and snowmelt runs off impervious surfaces and is quickly conveyed through stormwater management systems to receiving watercourses. Urbanization and the increase in impervious cover that accompanies it causes major changes in the hydrology of receiving watercourses, including increased peak stream flows during wet weather, elevated stream flows after even minor rainfall events, and in some instances, decreased baseflows during dry weather (Shuster et al., 2005). These changes result in increases in stream channel erosion and instability, impaired water quality, and reductions in the quality of aquatic habitat and health of aquatic communities (CWP, 2003). As urban settlements grow, seasonal variations in stream flow in urban watercourses become less defined. Stream flow response to a rainfall or snow melt event, regardless of the season, is more rapid compared to rural watercourses. Reduced infiltration in urban watersheds can lower local groundwater levels, which can in turn reduce groundwater discharges to baseflow. A discussion of surface water responses to land use changes cannot entirely be separated from an understanding of how water management policies have also guided activities and influenced flow conditions. Beginning in the early 1970s, the Province developed floodplain planning policies aimed at minimizing the risk to life and property damage due to flooding. Land use planning tools were used to limit new development in delineated floodplains. Engineering practices prior to the early 1980s focused on conveying the increased volumes of surface run-off in urban areas as quickly as possible off the land through storm sewers. This management approach often led to the practice of channelizing watercourses, whereby natural stream channels were lined with concrete and engineered to convey stormwater away from urban areas in a more efficient manner. However, this proved to be counterproductive as the elimination of the storage and attenuation properties of natural channels and floodplains resulted in greater peak stream flows and more downstream flooding and stream channel erosion. In addition, the removal of wetlands, loss of small surface drainage features and encroachment of urban land uses within the floodplain zone further reduced or eliminated the natural capacity of the watershed to attenuate peak stream flows.



Stormwater management policies were introduced in the 1980s to mitigate the impacts of increased run-off on peak flood flow rates (MTRCA, 1980). Since then, stormwater management policies have evolved to address erosion control, water quality and, most recently, water balance and groundwater concerns (e.g., OMOE, 1991, 1994 and 2003). In the order of 250 stormwater management facilities have been constructed or proposed in the Humber River watershed in response to these policies. These facilities at least partially mitigate the impacts of urban run-off for the areas they treat and continue to influence watershed hydrology. As of 2002, some level of stormwater management controls were in place in approximately one quarter (25%) of the total urban area in the Humber River watershed. Table 1 provides a breakdown of the portion of urban areas with different levels of stormwater management controls within each primary Humber River subwatershed and for the whole watershed. Ponds designed to address all of the above noted stormwater management issues are typically only found in urban areas that have been developed since the early 1990s at which time requirements for modern stormwater controls came into effect (Figure 1). However, many municipalities have undertaken stormwater retrofit studies to identify and prioritize projects to improve the quality of storm run-off from older development areas. Stormwater retrofit projects typically involve modifications to existing ponds to improve water quality and new stormwater management controls at existing uncontrolled storm sewer outfalls. Detailed retrofit studies have been completed for the municipalities of Toronto, Brampton, Richmond Hill, and Vaughan. A preliminary stormwater retrofit opportunities study has been completed for the Town of Caledon (Figure 1).

Table 1: Portion of existing urban areas with stormwater controls - Humber Watershed, 2002

Primary Subwatershed

Portion of urban

areas with Quantity

controls only

Portion of urban

areas with Quantity

and Quality controls

Portion of urban

areas with

Retrofitted controls

Portion of urban

areas with some

level of SW controls

Main Humber 11.6% 25.3% 0.0% 36.9%

East Humber 10.8% 25.1% 0.0% 35.9%

West Humber 2.6% 19.5% 5.0% 27.1%

Black Creek 6.9% 7.1% 2.0% 16.0%

Lower Humber 2.3% 4.7% 10.6% 17.6% Total 6.4% 14.7% 4.2% 25.3%

4.0 MEASURING SURFACE WATER QUANTITY

4.1 Stream Gauges

Measurement of stream flow is accomplished by establishing a relationship between water levels in the river and the corresponding rate of flow at specific locations within the watershed. Stream gauges are then installed at these locations which, through constant measurement of water level, allow determination of stream flow to be made at any given time. Flow data collected at stream gauges can be used to calculate stream flow statistics that help to characterize the stream flow regime at that location. Examining long term and recent trends in stream flow at stream gauge locations can provide insight into watershed management issues such as increasing frequency of flood events, accelerated streambank erosion, and declining health of aquatic communities. Data from stream flow gauges also provide the detailed



information needed to calibrate hydrologic simulation models so that they are representative of the actual flood flow regime within the watershed. These modeled flows are critical for developing the floodplain mapping used for flood risk management. In the Humber River watershed, stream flow is measured continuously at fourteen (14) stream gauges (Figure 2). While several of the stream gauges have been recently installed or re-activated, there are a number of gauges which have been in continuous operation for a substantial length of time. Several date back to the 1960s, with data collection at the oldest site (East Humber gauge in Pine Grove) going as far back as 1956 (Table 2). Of the current active gauges, nine are operated as a part of the Federal/Provincial flow monitoring network and operated and maintained by the Water Survey section of Meteorological Services of Canada (WSC), which is part of Environment Canada (Environment Canada, 2000). Three are the property of the Town of Richmond Hill and the remaining two gauges belong to the Toronto and Region Conservation Authority (TRCA), and are maintained and operated either by TRCA staff or a private contractor. Data at the TRCA gauges is collected and maintained to the WSC standards. The TRCA’s Regional Watershed Monitoring Program has identified a need for more stream gauges within the watershed, and several additional gauge sites are proposed.

Table 2: Historical and Existing Stream Gauges in the Humber River Watershed

TRCA

Site # Gauge #

Gauge

Operator Subwatershed Location

Period of

Record

1 02HC031 Water Survey of Canada

West Humber West Humber @ Hwy. 7, W of Hwy. 50 1965 – present


Lower Humber Lower Humber @ Weston Rd, S of Lawrence Ave, W of Weston Rd.

1958 – present


Black Creek Black Creek @ Weston Rd, Smythe Park off Scarlett Rd.

1966 - present

15 n/a Town of Richmond Hill

East Humber East Humber @ Bathurst St., N of King Rd.

1999 - present


East Humber Inlet to Lake Wilcox, Sunset Beach Park., off Bayview Ave.

1998 - present


Main Humber Main Humber @ Palgrave, Albion Hills C.A. Campground.

1983 – 1998, 2002 - present


Main Humber Cold Creek @ King Rd. and King-Vaughan Townline

1962 – 1993, 2004 - present


Main Humber Main Humber@ Elder Mills, Rutherford Rd. E of Hwy 27

1966 – 2003


East Humber East Humber @ Pine Grove, Thistlewood and Islington Ave.

1956 – present


East Humber East Humber @ King Creek, King Rd. and Mill St.

1965 - 1993, 2002 – present


Main Humber Upper Humber @ Hwy.9, 5th Line N of Hwy.9.

2005 - present


Main Humber Centreville Creek @ Albion Hills, near Albion Hills Field Centre

2002 - present

41 n/a TRCA West Humber West Humber @ Goreway Rd., N of Hwy.7

2004 - present


East Humber Outlet of Lake Wilcox, at dam off Sylvan Cres.

1998 - present

71 n/a TRCA Main Humber Rainbow Creek @ Rainbow Creek Park, Hwy.7 W of Islington Ave.

2004 - present

n/a = not applicable

Figure 1: Planned levels of storm

water controls – Humber River Watershed

Figure 2: Historical and current stream flow and precipitation gauges



Information about low stream flows or baseflow conditions can also be derived from stream gauge data. By correlating information from stream gauges with information from nearby precipitation gauges, periods of low flow can be identified and used to characterize the baseflow regime. Baseflow separation was performed on mean daily data, obtained from Water Survey Canada long term gauging locations. The separation methodology is an amalgamation of methods referred to as a 6-day floating minimum (Pilgrim and Cordery, 1993; Viessman et al., 1989; Clarifica Inc., 2002). The floating minimum method finds the average minimum flow for a 6-day period. Flows above the minimum are considered run-off and the average minimum is considered baseflow. It is important to note that the stream gauge network was originally designed to collect data at a watershed scale and gauging sites were generally situated in the lower reaches of larger watercourses, where flooding is an important watershed management issue. This makes it difficult to detect subtle changes to baseflow using available stream gauge data, especially in headwaters reaches where aquatic communities are most sensitive to such changes. Also, the rating curves used to convert raw water level readings from stream flow gauges into stream flow rates are primarily intended to quantify high stream flow rates. For some Humber stream flow gauges, the stream flow information generated during low flow conditions does not accurately represent actual low flow conditions. Recently, new stream gauges have been installed and inactive gauges re-activated in the headwater reaches of the Humber River. As information from these gauges accumulates, more subtle trends in baseflow in these more sensitive reaches may be identified and tracked.

4.2 Field Measurements

To better understand the distribution of stream flow within the watershed during periods of low flow (extended dry periods), baseflow monitoring studies have been undertaken where field measurements are timed specifically to eliminate effects of surface run-off from precipitation events. Numerous, well-distributed field measurements during baseflow conditions provide insight into where groundwater-surface water interactions are occurring in the watershed, and help to identify natural and human influences on these flows. The Geological Survey of Canada (GSC) began baseflow studies in the Humber River watershed in 1995 as part of a collaborative research agreement with the TRCA (Hinton, 1996 and 1997). The purpose of these studies was to document the rationale and recommended method for conducting such studies, and also to report on preliminary findings. GSC undertook a reconnaissance survey of the Humber River watershed in 1995 where a total of 164 sites were visited. Of these 164 sites, baseflow was measured at 38 locations and water chemistry samples were collected at 40 locations. This reconnaissance survey continued in 1996, where a total of 476 sites were visited. Of the 476 sites visited in 1996, baseflow was measured at 199 locations and water chemistry samples were collected at 49 locations. Findings from the GSC baseflow studies helped to select monitoring sites for TRCA’s Low Flow Program and have been included in subsequent analyses performed to characterize the low flow regime of the Humber River (TRCA, 2006). A total of 192 sites were sampled by TRCA in 2004. Measurements at 25 long-term indicator sites have been undertaken annually, on a monthly basis through the summer, and are now part of the Regional Watershed Monitoring Program (Figure 3). TRCA applies WSC flow measurement standards (Terzi, 1981) and the GSC sampling protocol



(Hinton, 1997) to ensure accurate sampling is done during baseflow conditions. Given the geology and climate in the TRCA jurisdiction, a 72 hour period has been established as the minimum time to wait following any precipitation event before measuring, to ensure all surface run-off has cleared the system and the measured flow only reflects baseflow.

4.3 Assessment of Water Use

An understanding of major human withdrawals from and input to stream flow is needed to interpret baseflow field measurements and to evaluate the impacts of those influences on the surface water regime. The Ontario Ministry of Environment (OMOE) is the agency responsible for approving and permitting water withdrawals of more than 50,000 litres per day, through their Permit to Take Water (PTTW) Program. The TRCA obtained the PTTW database in 2002 and began to update and improve the information for records in TRCA watersheds. The database was edited and updated through interpretation of recent air photos. Expired PTTW records were removed from the database if the land use for that location did not match that of the permit. If the land use remained the same as the specific permitted use, the expired permit was retained and assumed active until its status could be field verified. An initial analysis was carried out that compared updated database information on water users with measured baseflow discharge of each Humber River subwatershed. This analysis provided estimates of the maximum portion of total stream flow during baseflow conditions that could be withdrawn based on maximum water taking permit allocations. Unfortunately, actual volumes and durations of water takings are often not tracked after a permit to take water has been issued. Hence, the relationship between actual and permitted water takings may be very weak. Therefore, calculations of total baseflow allocated for withdrawal were used to indicate potential stresses on the low flow regime and aquatic system. Further investigations into actual water use within TRCA watersheds were required to improve our understanding of water users and their influence on low flow regimes. In 2003 work was undertaken to locate and identify all water users in the TRCA jurisdiction. A water use survey form was developed with an attached newsletter promoting rural and commercial water conservation practices. The surveys were distributed in person by field technicians, and filled out on-site when contact with the landowner or business proprietor was made. Questions posed by the water use survey included:

• Water source; • Daily pumping rate; • Days pumping per year; • Hours pumping per day; • Water use purpose; and, • Contact information (Confidential).

Actual water use information was entered into the database, including improved information about the geographic locations of water takings.

Figure 3: Locations of Baseflow Sampling



4.4 Hydrologic and Hydraulic Models

TRCA has been using hydrologic and hydraulic models on the Humber River watershed since 1979 (McLaren, 1979) to aid in enforcing policies and regulations intended to ensure that new developments are located outside of the flood risk area and that existing condition peak flood flows are maintained through the implementation of stormwater management practices. Models allow the simulation of flood flows under theoretical land use and precipitation conditions to determine, for example, the impact of development on flood flows and the stormwater management measures that are required to mitigate those impacts. Through calibration with flow data at the sites where it is collected, the model can predict flood flows at other locations throughout the watershed where flow gauges are not present. Regular updates, which typically incorporate technological advancements and additional climate and stream flow monitoring data, ensure that the models are kept current. In 1996, the TRCA retained a consultant to undertake a comprehensive update of the existing Humber River watershed hydrology model, using new computer modelling software, new flow data, updated land use conditions and integration of existing and approved offline stormwater controls (Aquafor Beech, 1997). A further update of the Humber River watershed hydrology was completed in 2002, taking into account additional calibration data from a series of severe storm events in the spring of 2000 and a considerable amount of additional development and planned development in the watershed (Aquafor Beech Ltd., 2002). Flows from the updated Humber River Hydrology model were used to update hydraulic models in order to generate a new digital set of flood plain maps. While flood plain mapping in the Humber River dates back to the 1950s, the first watershed wide flood plain mapping exercise was completed in 1979 (Proctor and Redfern, 1979). The recently completed flood plain mapping updates and extensions for the Humber River watershed reflect the latest land use conditions through the watershed, and have been completed using the latest hydraulic modelling computer software (Acres International, 2004a and 2004b; Clarifica, 2004; Greck and Associates, 2002 and 2003; Hatch-Acres, 2005; JF Sabourin and Associates, 2004) . An updated database of flood vulnerable areas and roads has also been prepared based on the updated flood plain information (TRCA, 2005; also see section 5.4 - Flooding).

5.0 EXISTING CONDITIONS

5.1 Overview of Humber River Subwatersheds

The Humber River watershed is the largest of the TRCA watersheds, draining an area of approximately 903 km2 (90255 hectares). For the purposes of the Humber Watershed Planning Study, the watershed has been broken down into 5 primary subwatersheds and 24 secondary subwatersheds (Figure 4). The Main Humber subwatershed drains an area of approximately 357 km2 that includes Centreville Creek, Cold Creek and Rainbow Creek subwatersheds. The headwaters of this system originate from the Niagara Escarpment, from which flow continues across the Oak Ridges Moraine and then down the South Slope into the Peel Plain (Figure 5).



Stream slopes are quite steep on the escarpment, moderate across the Oak Ridges Moraine, and become quite flat along the South Slope and Peel Plain. The permeable soils and hummocky terrain through the Oak Ridges Moraine result in higher baseflow rates and lower surface run-off in this area. As one moves down into the lower reaches of this system and Rainbow Creek, the soils of the Peel Plain tend to have much lower permeability and a larger portion of precipitation is converted to surface run-off. The West Humber subwatershed has its headwaters in the South Slope, while the majority of the 204 km2 subwatershed is within the Peel Plain. Soils throughout the subwatershed tend to be poorly drained clays and clay tills with relatively low infiltration capacity. As a result of low infiltration within the subwatershed, and because there are few sources of groundwater discharge from regional aquifers, baseflow in the West Humber tributaries tends to be low, with even large tributaries often dry in the summer months. The upper half of the watershed within the Town of Caledon remains primarily agricultural, while the majority of the lower half of the subwatershed in Brampton has been or soon will be developed. The downstream portion of the subwatershed in Rexdale in the City of Toronto was developed some time ago for residential and industrial uses. The Claireville Flood Control Dam and Reservoir is located where the main channel of the West Humber crosses from Brampton into Toronto, and is operated by TRCA as part of the Flood Warning Program. The East Humber subwatershed, which contains the King Creek and Purpleville Creek subwatersheds, comprises an area of approximately 200 km2, with its headwaters in the Oak Ridges Moraine. There are a number of kettle lakes and other internally drained areas within the upper watershed in Richmond Hill and Aurora. Soils through the watershed tend to be clay loams, with large pockets of sandy loam, loam and silt. Land use in the East Humber River subwatershed remains predominantly agricultural, though the settlements of Oak Ridges, King City, Nobleton and a portion of Woodbridge are within the subwatershed. The Black Creek subwatershed, draining an area of approximately 65 km2, has been almost entirely developed. The majority of the older residential and industrial development in the City of Toronto occurred prior to the adoption of stormwater quantity and quality control measures. As a result, flooding became a significant hazard through the Black Creek watershed and large reaches of Black Creek were transformed to concrete channels to increase the conveyance capacity of the system. Run-off therefore tends to be flashy with relatively high peak flows. The Lower Humber River drains an area of approximately 78 km2, and carries the Humber River flows off the Peel Plain through the Iroquois Sand Plain to Lake Ontario. Stream slopes are quite mild on the Peel Plain, and are nearly flat through the lower reaches and the Humber Marshes near the outlet to Lake Ontario. The subwatershed is entirely developed, with several large pockets of older industrial lands. Similar to the Black Creek, the majority of the subwatershed was developed with little to no modern stormwater management controls, although some major stormwater management retrofit projects are being implemented.

Figure 4: Primary and secondary Humber River subwatersheds

Figure 5: Physiographic Regions in the Humber River Watershed


15

5.2 Stream Flow

5.2.1 Annual and Seasonal Stream Flow

Data from active and historical Humber River stream gauges were used to calculate average annual rates of total stream flow, baseflow and ratios of baseflow to total stream flow. Table 3 summarizes mean annual stream flow rates over the full period of record for each Humber River stream gauge, which provides an indication of the long term average, or baseline conditions. The normalization of total flows and baseflows on the basis of a 100 km2 unit areas and the calculations of baseflow index in Table 3 provide insight into the characteristics of the surface flow regime of each subwatershed. The Main Humber River generates relatively large flows per unit of upstream drainage area, and unit baseflows and baseflow index are high. These levels suggest that the flow regime is dominated by groundwater inputs and that there is relatively little surface run-off from the pervious soils that cover the majority of the subwatershed. The West Humber River generates lower total flow per unit area but unit baseflows and the baseflow index suggest that the majority of flow results from surface run-off, which is consistent with the less permeable soils of the subwatershed and observations of dry streams during summer months. The East Humber River generates lower unit flows again than the Main or West branches but with a relatively high proportion of baseflow and less surface run-off than the West branch, which reflects the moderately permeable soils and retention of run-off in internally drained areas. Total unit flows in Black Creek are much higher than the remainder of the watershed, due to the near-complete development of the subwatershed and the generation of large quantities of run-off from impervious surfaces. Unit flows in the Lower Humber at the Weston Gauge reflect an average of upstream conditions, although the complete effects of development are not observed as the gauge is located upstream of the confluence with Black Creek and the dense development in the lower watershed within the City of Toronto. At present, average stream flow data from Humber River stream gauges is of limited use in examining trends over time. There are few gauges with a long and continuous period of record from which to conduct meaningful analyses of trends. Those Humber River stream gauges with a period of record greater than 30 years are typically located on watercourses with very large drainage areas that encompass diverse physiography and mixtures of land use. This makes it difficult to detect patterns of change in stream flow characteristics that could be attributed to human impacts such as land use change or water taking. Most of these gauges were originally installed at their respective locations to provide information on high stream flow rates to support TRCA floodplain management and flood warning programs rather than intended to monitor changes resulting from specific developments. As more data is accumulated from recently installed stream gauges, which are located in smaller drainage areas, and from a denser network of precipitation gauges, our ability to detect influences of physiography and land use change on stream flow patterns should improve.

Humber River State of the W

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16

Table 3: Mean Annual Stream Flows at Humber River Stream Gauges, Full Period of Record

Mean Total Flow

Mean Baseflow

Site #

Gauge #

Subwatershed

Location

Period of

Record

Drainage

Area (km

2)

Total

(m3/s)

Per

100km

2

Total

(m3/s)

Per

100km

2

Baseflow

Index (BFI)

24

02HC025

Main Humber

Main Humber @ Elder Mills

1966 – 2003

303

2.44

0.81

1.64

0.54

0.674

n/a

02HC012

Main Humber

Main Humber @ Cedar Mills

1957 – 1981

169

1.48

0.88

1.01

0.60

0.686

22

02HC047

Main Humber

Main Humber @ Palgrave

1983 – 1998,

2002 – 2004

167

1.55

0.93

1.12

0.67

0.722

23

02HC023

Main Humber

Cold Creek @

King Rd. and King-

Vaughan Townline

1962 – 1993,

2004

62

0.479

0.77

0.318

0.51

0.663

n/a

02HC034

West Humber

West Humber, d/s of Claireville

1965 - 1985

194

1.27

0.65

0.398

0.21

0.314

1

02HC031

West Humber

West Humber @ Hwy. 7

1965 – 2004

148

1.03

0.70

0.343

0.23

0.334

25

02HC009

East Humber

East Humber @ Pine Grove

1956 – 2004

197

1.20

0.61

0.703

0.36

0.585

26

02HC032

East Humber

East Humber @ King Creek

1965 – 1993

2002 – 2004

95

0.598

0.63

0.354

0.37

0.591

9

02HC027

Black Creek

Black Creek @

Weston Rd.

1966 – 2004

58

0.803

1.38

0.298

0.51

0.371

8

02HC003

Lower Humber

Lower Humber @ W

eston Rd.

1958 – 2004

800

6.03

0.75

3.29

0.41

0.545


17

Figure 6 presents trends in mean annual total stream flow rates at six Humber River stream gauge locations with long periods of record. The mean annual total stream flow rates at all six stations exhibit upward trends of varying magnitude over the period of record. However, only one station, on the East Humber River at King Creek, has recorded a trend that is statistically significant (p value < 0.05) according to the Kendall tau rank correlation. Trends at all other gauges have a p value greater than 0.05, meaning they have a greater than 5% probability that the trend is the result of random variability, and therefore are not considered statistically noteworthy. The presence of a significant trend (a 1.5% increase per year) on the East Humber River at King Creek likely reflects the effects of development upstream in King City and Oak Ridges (Richmond Hill) that has occurred over the period of record. The development occupies a substantial portion of the upstream catchment area to the gauge and the increase in flow volumes recorded were likely the result of increased run-off from new impervious surfaces, amplified by the location of portions of the development on soils that are highly impervious and which would otherwise have generated little run-off. For comparison, Figure 6 also presents results of analyses for the Highland Creek, which experienced major watershed development over the period of record and corresponding rapid increase in annual flows, and for the Rouge River, which experienced more moderate development over the period of resulting in flow increases similar in magnitude as those at the East Humber at King Creek gauge. Other gauge locations in the Humber River watershed also suggest upward trends in annual flows, such as on the Lower Humber at Weston. A lack of statistical significance does not necessarily prove that development has not altered stream flow patterns at these locations but rather may indicate that the effect of the impact is at present too small relative to the scale of natural flow variability to distinguish. It can be concluded that the increases observed at the East Humber at King Creek gauge are not the result of changes to rainfall patterns and meteorological variability. Analyses for gauges located where upstream land use was relatively static over the period of record, such as the nearby Little Rouge River and Duffins Creek as well as the Main Humber River at Elder Mills and Black Creek in the current study, show negligible or absent upward trends with very poor statistical significance. As such, it is reasonably certain the upward trends in annual flow volumes observed in developing watersheds such as the Humber River are due to the hydrologic impacts of development (i.e., impervious surfaces) and not to climate variability.


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Figure 6: Historical Trends in M

ean Annual Stream Flow at Selected Stream Gauges

Historical Stream Flow Data

Water Survey of Canada Station 02HC025

Main Humber River at Elder Mills

0.00

1.00

2.00

3.00

4.00

5.00 1950

1955

1960

1965

1970

1975

1980

1985

1990

1995

2000

2005

Average Annual Discharge (m3/s)

Slope of Linear Trend: +0.03%/yr

p-value: 0.964 (not significant)



West Humber River at Highway 7

0

0.51

1.52

2.5

1950

1955

1960

1965

1970

1975

1980

1985

1990

1995

2000

2005






East Humber River at Pine Grove

0.00

0.50

1.00

1.50

2.00

2.50 1950

1955

1960

1965

1970

1975

1980

1985

1990

1995

2000

2005






East Humber River at King Creek

0.00

0.50

1.00

1.50

2.00

2.50 1950

1955

1960

1965

1970

1975

1980

1985

1990

1995

2000

2005



p-value: 0.042 (significant)


atershed R

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ater Quantity

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ean Annual Stream Flow at Selected Stream Gauges (continued)



Black Creek at Weston Road

0.00

0.50

1.00

1.50

2.00

2.50 1950

1955

1960

1965

1970

1975

1980

1985

1990

1995

2000

2005






Lower Humber River at Weston

0.00

3.00

6.00

9.00

12.00

15.00 1945

1950

1955

1960

1965

1970

1975

1980

1985

1990

1995

2000

2005






Highland Creek at West Hill

0.00

0.50

1.00

1.50

2.00

2.50 1950

1955

1960

1965

1970

1975

1980

1985

1990

1995

2000

2005



p-value: 2.0e-7 (significant)



Rouge River Near Markham

0.00

1.00

2.00

3.00

4.00

5.00 1950

1955

1960

1965

1970

1975

1980

1985

1990

1995

2000

2005





20

In addition to changes in total annual flow volumes, urban development may also affect the seasonal distribution of flows. This is particularly evident in summer months, when natural stream flows are at their lowest and the increase in run-off volume caused by urban development is most apparent. Impervious surfaces in urban areas eliminate the exposed soil and vegetation that utilize water for infiltration and evapotranspiration during the growing season. This phenomenon is well documented in urban areas; for example, Hollis (1975) noted that even low levels of impervious cover between 5% and 10% can cause stream flows in response to moderate rainfall events to increase by an order of magnitude. In contrast, flows in winter and early spring periods are much less affected by urbanization as infiltration and evapotranspiration are minimal due to frozen or saturated ground and dormant or absent vegetation. Examples of this change are observed in flow records from both the East Humber River and Lower Humber River as illustrated in Figure 7. Data from the East Humber at King Creek gauge shows a major upward trend in average summer flow volumes. Although this trend is not statistically significant due to a relatively short record with high variability, the increase in summer flows on the East Humber River is apparent in the form of a statistically significant trend further downstream at the gauge at Pine Grove. A similar trend is apparent on the Lower Humber River at Weston, despite the relatively small proportion of upstream development in the catchment area of both these gauges. For comparison, increasing trends of 4% and 8% were observed in data from the more developed Rouge River and Highland Creek watersheds, respectively. Results from the gauge on the Main Humber at Elder Mills are also provided to illustrate the absence of trends on summer flows in catchments with little or no land use change.


atershed R

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ater Quantity

21


ean Summer Stream Flow at Selected Stream Gauges



Main Humber River at Elder Mills

0.00

1.00

2.00

3.00

4.00

5.00 1950

1955

1960

1965

1970

1975

1980

1985

1990

1995

2000

2005

Average Summer Discharge (m3/s)





East Humber River at King Creek

0.00

0.40

0.80

1.20

1.60

2.00 1950

1955

1960

1965

1970

1975

1980

1985

1990

1995

2000

2005






East Humber River at Pine Grove

0.00

1.00

2.00

3.00

4.00

5.00 1950

1955

1960

1965

1970

1975

1980

1985

1990

1995

2000

2005






Lower Humber River at Weston

0.00

3.00

6.00

9.00

12.00

15.00

18.00 1945

1950

1955

1960

1965

1970

1975

1980

1985

1990

1995

2000

2005





22

Figure 8 provides an additional illustration of the effects of urbanization on seasonal flow patterns, by comparing semi-annual total flow volumes at a number of gauges in the watershed over two separate decades. Comparison is provided for the months from May to October, a period during which flow is typically lowest in natural and rural watercourses. Both time periods considered (1969 to 1978; and 1988 to 1997) experienced similar annual rainfall amounts and distribution of rainfall. Between one time period and the other, May to October flows increased from 5% to 7% on the East Humber and Lower Humber Rivers, reflecting increased run-off from urban surfaces associated with upstream development over that time. In comparison, the proportion of May to October flows was essentially unchanged on the Main Humber River where little development took place upstream of the Elder Mills gauge. Data from the Black Creek gauge shows that approximately 50% of total annual flows are generated from the highly urbanized subwatershed between May to October, in contrast to much lower proportions for rural catchments within the watershed.

Figure 8: Percentage of Total Annual Flow Volume Occurring in May to October at Selected

Gauges

Percentage of Total Annual Flow in May-October

0

0.1

0.2

0.3

0.4

0.5

0.6

Main Humber

at Elder Mills

East Humber

at Pine Grove

East Humber

at King Creek*

Black Creek at

Weston

Lower

Humber at

Weston

Percent of Total Annual Flow

1969-1978

1988-1997

*1966-1974 and 1985-1993 used for comparison on East Humber at King Creek due to incomplete data

5.2.2 Baseflow Index

The ratio of baseflow to total flow, or Baseflow Index (BFI) helps to characterize the baseflow regime of Humber River subwatersheds. At stream gauges located in the Main Humber subwatershed, ratios of baseflow to total flow are significantly higher than those calculated for stream gauges in the West Humber, East Humber Black Creek, and Lower Humber subwatersheds (Table 3). This suggests that groundwater discharge is likely occurring at a


23

greater rate and extent in the Main Humber subwatershed than in other primary subwatersheds of the Humber River and that reaches in the Main Humber are more likely to support cold water aquatic habitats. Very low ratios have been calculated for the West Humber and Black Creek subwatershed stream gauges, indicating that reaches in these subwatersheds are likely receiving very limited inputs to stream flow from groundwater discharge. Furthermore, these ratios suggest that the stream flows are more strongly influenced by patterns of precipitation and more likely support cool or warm water aquatic habitats. It is also notable that Black Creek subwatershed is highly urbanized and that soils of very low permeability make up much of the West Humber subwatershed, both of which are factors that limit groundwater and surface water interactions. The ratios calculated at East Humber stream gauges suggest that groundwater discharge is occurring along some East Humber reaches, but not to the same extent as in the Main Humber subwatershed. These findings are consistent with field measurements of baseflow made in 1995/96 and in 2004 (see Section 5.2.4), and known geological characteristics of the watershed (TRCA, 2008). The ratio of baseflow to total flow can also provide insight into influences of land use and land cover on the stream flow regime. Generally, highly urbanized subwatersheds are expected to have lower ratios of baseflow to total flow than subwatersheds with predominantly rural land uses or natural land cover. This is based on assumptions that the predominant influences of urban development on stream flows are the reduction of baseflow (increased impervious cover reduces infiltration capacity of the land which reduces groundwater levels which reduces groundwater discharge rates), and the increase of total annual flow (increased impervious cover reduces infiltration capacity of the land which increases run-off which increases stream flow). The low ratio of baseflow to total flow calculated at the Black Creek subwatershed stream gauge reflects the fact that this subwatershed is nearing complete urbanization and is indicative of a stream flow regime that has been impacted by the proliferation of impervious surfaces associated with urban development.

5.2.3 Minimum In-stream Flow Requirements

The TRCA has adopted interim criteria for determining minimum in-stream flow requirements which are currently utilized by the Ontario Ministry of the Environment (OMOE), Central Region, when reviewing applications for permits to take water affecting surface water sources. The interim criteria use historic stream gauge records to identify the 40th percentile of mean daily stream flows during spring-summer months. The 40th percentile flow (or 60% durational flow) for Humber River stream gauges are shown in Error! Reference source not found.Table 4. It has been found that the 60% durational flow generally encompasses 100% or greater of the mean daily baseflows during spring-summer months, suggesting that this criterion is suitable for ensuring that existing baseflow conditions are not impacted by surface water takings. Work is currently underway which will enable the 60% durational flow to be estimated throughout the watershed based on stream gauge data and the understanding of the distribution of baseflows that has been gained through recent field measurements (TRCA, 2006).


atershed R

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ater Quantity

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Table 4: Median Stream Flows During Spring-Summer Months* at Humber River Stream Gauges and M

inim

um In-stream Flow Criteria

WSC Stream Gauges

Median of Mean Daily Flow Rate

(1997- 2003, spring – summer)

Gauge #

Location

Total Flow

(m3/s)

Baseflow

(m3/s)

60% Durational Flow Rate

(Interim M

OE Environmental Flow

Threshold Criteria, m

3/s)

7Q10 Flow Rate

(Extreme Low Flow

Conditions, m

3/s)

02HC003

Lower Humber @ W

eston

2.01

1.47

1.670

0.651

02HC009

East Humber @ Pine Grove

0.331

0.252

0.271

0.099

02HC023

Main Humber, Cold Creek @

King Rd.

No data

0.225

0.139

02HC025

Main Humber @ Elder Mills

0.966

0.810

1.080

0.584

02HC027

Black Creek @

Weston

0.275

0.196

0.251

0.119

02HC031

West Humber @ Hwy. 7

0.075

0.047

0.045

0.001

02HC032

East Humber @ King Creek

No data

0.109

0.056

02HC047

Main Humber @ Palgrave

Insufficient data

0.766

0.419

* Spring-summer months are defined as May, June, July and August.


25

Where stream flow data was available, median values for mean daily total flow and mean daily baseflow rates were calculated for the period of 1997 to 2003, during the spring and summer months (May, June, July and August). These seven year median flows can then be compared to the 60% durational flow to identify reaches of the Humber River that may be under stress from surface water takings during baseflow conditions (Table 4). Through this analysis only the gauge located in the Main Humber subwatershed at Elder Mills (02HC025) recorded mean daily total flow rates lower than the 60% durational flow. Available information regarding water takings indicates that upstream of this stream gauge there are several large water takings, but that this portion of the Main Humber is not under significant stress from surface water withdrawals (TRCA, 2006). Also provided in Table 4 for comparison is the 7Q10 flow rate for each gauge. The 7Q10 is a measure of the lowest seven-day flow rate over a ten-year period. This number represents extreme low flow conditions, and is usually used for assessing the assimilative capacity of watercourses for Sewage Treatment Plants and other operations discharging effluents into watercourses. 5.2.4 Seasonal Baseflow Monthly fluctuations in baseflow rates were determined from stream gauges operated on the Humber River since the mid-1950’s. This analysis was done to examine changes in mean baseflow rates on a monthly basis, and trends over time. Through this analysis, graphs of mean monthly baseflow discharge were created that illustrate seasonal variations in baseflow discharge rates for each stream gauge location (e.g., Figure 9). For the purpose of examining trends over time, 10 year data sets were created by calculating the mean monthly baseflow rates for the periods of 1955-61, 1961-71, 1971–81, 1981-91, and 1991-2001. From these graphs, it is apparent that distinct seasonal fluctuations occur. Moreover, these seasonal variations have not changed significantly over the period of record. August is typically the time of year when stream flow and water levels are at their lowest. By examining seasonal fluctuations on a long term basis at stream gauges it is clear that minimum sustained baseflow rates have not changed significantly since gauging records began (Figure 10).


atershed R

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ater Quantity

26

Figure 9: Historical Mean M

onthly Baseflow Rates Showing Seasonal Fluctuations (East Humber, Stream Gauge #02HC009)–

Humber River @ Pine Grove

Mean Monthly Baseflow 1955 - 2001

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

May

June

July

Aug

Sep

Oct

Month

m3/s

1955-61

1961-71

1971-81

1981-91

1991-2001


27

Figure 10: Mean Monthly Baseflow (spring-summer, m3/s) For Selected Humber Stream Gauges

Cold Creek (02HC023)

Mean Monthly Baseflow (1963 - 1993)

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

MAY JUN JUL AUG SEP

1963 - 72

1973 - 82

1983 - 93

31 Yr. Mean

Humber River @ Elder Mills (02HC025)


0

0.5

1

1.5

2

2.5

MAY JUN JUL AUG SEP

1965 - 74

1975 - 84

1985 - 94

1995 - 2003

39 Yr. Mean

Black Creek @ Weston Rd. (02HC027)


0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

MAY JUN JUL AUG SEP

1968 - 77

1978 - 87

1988 - 97

1998 - 2002

35 Yr. Mean

West Humber @ Hwy. 7 (02HC031)


0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

MAY JUN JUL AUG SEP

1975 - 84

1985 - 94

1995 -2003

29 Yr. Mean

East Humber @ King Creek (02HC032)


0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.45

0.50

MAY JUN JUL AUG SEP

1966 - 72

1973 - 79

1980 - 86

1987 - 93

28 Yr. M ean

Humber @ Palgrave (02HC047)


0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

MAY JUN JUL AUG SEP

1981 - 86

1987 - 92

1993 - 98

18 Yr. Mean

Humber River @ Weston Rd. (02HC003)


0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

MAY JUN JUL AUG SEP

1955 - 64

1965 - 74

1975 - 84

1985 - 94

1995 - 2003

49 Yr. Mean


28

5.2.5 Hydrologic Models

Another available tool for characterizing stream flows in the Humber River is the continuous hydrologic simulation model that has been developed of the Humber watershed (the Humber River Watershed HSP-F model). The Humber River HSP-F (Hydrologic Simulation Program - Fortran) model is a powerful and complex computer model, capable of simulating numerous aspects of urban and rural run-off in a number of different ways. The original HSP-F model of the Humber River watershed was developed to support preparation of the City of Toronto’s Wet Weather Flow Management Master Plan (WWFMMP) (XCG, 2003a and 2003b). The model was set up to evaluate the effectiveness of a number of different stormwater management strategies, primarily based on the ability to reduce contaminant concentrations and loadings in the portion of the watershed within the City of Toronto. As the focus of the study was the City of Toronto, the large portion of the watershed beyond the City was not modelled to the same level of detail as the portion within the City. The primary use of the model was to assess average annual rates of infiltration, evapotranspiration and run-off, collectively known as the water budget, on a watershed basis. In order for the TRCA to use the HSP-F model as an effective tool for watershed management, a second study was commissioned to refine the portion of the HSP-F model outside the City of Toronto to be consistent with the modeling approach and level of detail used in the City of Toronto portion of the model, and to make use of additional meteorological and hydrologic data to refine the calibration of the model. Particular attention was paid to the Oak Ridges Moraine area in order to better reflect the soils, hummocky terrain and internally drained areas that are prevalent in this area.


29

The refinements made to the HSP-F model make it a useful tool for evaluating the watershed’s response to a number of different future development and management scenarios with regard to more than just the water budget. Refinements have been made to the model in order to more accurately simulate water quality parameters, stream temperature and stream bank erosion potential (HCCL, 2008). The HSP-F model of the Humber River watershed has been set up to reflect watershed conditions as of 2002. The simulation period, or climate data period, that is being input to the model to predict watershed response to each scenario is from 1991 to 1996, with 1990 simulated as a ‘model initialization year’. Model outputs have been compiled and summarized at 31 locations within the watershed, including the outlets of each of the twenty-four (24) secondary subwatersheds. Model outputs for 2002 conditions will be compared with outputs from several different scenarios of future land and resource use and alternative management approaches in order to assist with identifying preferred management strategies to be recommended in the Humber River Watershed Plan. Model outputs for 2002 conditions also help to characterize current conditions regarding stream flow regimes in Humber River subwatersheds. Table 5 summarizes the model outputs at three different locations with similar upstream drainage areas. The first is the outlet of Cold Creek subwatershed, a tributary to the Main Humber. Cold Creek is almost entirely rural, with small pockets of large lot estate residential development. The majority of the subwatershed is located on the Oak Ridges Moraine. Although the soil in the Cold Creek subwatershed is primarily clay till with isolated exposed sand layers, the topography is quite hummocky in areas located on the Oak Ridge Moraine, which is conducive to high rates of infiltration and evapotranspiration, and low rates of run-off. The second is the outlet of the Main Branch of the West Humber subwatershed. Land use again is predominantly agricultural, with a mix of older estate residential development and modern residential development in the lower reaches of the sub basins. This subwatershed contains very little natural land cover. The area is located almost entirely in the Peel Plain physiographic region, which is characterized by low permeability clay till soils and relatively flat terrain, which is more conducive to low rates of infiltration and high rates of run-off. The Black Creek subwatershed is almost entirely developed for residential, commercial and industrial uses. The majority of built-up areas in the City of Toronto portion of the subwatershed were developed prior to the requirement for modern stormwater water quality and quantity controls. The limited amount of pervious area that remains in the subwatershed is underlain by low permeability clay soils.


30

Table 5: Humber River HSP-F Model Outputs at Selected Locations (2002 land use/land cover

conditions; 1991 to 1996 climate data; HCCL, 2008)

Parameter Cold Creek West Humber –

Main Branch Black Creek

Drainage Area (km2) 63.8 79.6 75.9

Average Annual Stream Flow Volume (Mm3)

Baseflow 6.4 5.5 13.9

Storm Run-off 6.1 14.1 20.9

Total 12.6 19.6 34.8

Seasonal Stream flow Volume (Mm3)

January-March 3.9 7.1 8.7

April-June 4.2 6.5 9.8

July-September 2.1 2.7 8.5

October-December 2.4 3.4 7.8

Peak Flow (flow rate exceeded 0.1%

of the time, m3/s)

12.1 21.5 31.3

Extreme Low Flow (flow rate exceeded 99% of the time, m3/s)

0.1 0.0 0.2

The Cold Creek subwatershed, with its sandier soils and hummocky terrain, is predicted to have the lowest average annual total stream flow volume, which is evenly split between baseflow and storm run-off. This contrasts with the Main Branch of the West Humber subwatershed, where the model predicts there is more total stream flow and more of the flow is in the form of storm run-off, due to the tight soils and more gently sloping terrain. The extent of impervious cover in the Black Creek subwatershed results in model predictions of almost twice as much stream flow as in the main branch of the West Humber. The high baseflow volume predicted in Black Creek is somewhat misleading as a result of the baseflow separation routine used in the analysis of the model results. Rather than baseflow due to groundwater discharge, much of the dry weather flow volume predicted to occur in Black Creek is likely due to the extended detention and slow release of storm run-off from stormwater management facilities in the upper portion of the Black Creek subwatershed. While the model outputs for the outlets of the Cold Creek and West Humber subwatersheds may differ in total stream flow and baseflow volumes, the seasonal distribution of stream flow volume in the two subwatersheds are quite similar. Much more stream flow is predicted to occur in the late winter and spring seasons, due to snowmelt and saturated or frozen soil conditions. In the summer months, the dry land is able to absorb much of the water from storm events, reducing peak flow rates and run-off volumes. This is typical of the stream flow regime of an undisturbed, natural system. Native aquatic species have evolved such that their life stages are in harmony with the natural stream flow regime. In contrast to the model output from these rural subwatersheds are those from the Black Creek subwatershed, where the model predicts little difference in seasonal run-off volumes. Snowmelt and spring precipitation contribute to high flows in the spring months, while the lack of permeable land cover to store


31

and infiltrate water from rainfall events contributes to much higher total surface flow volumes in the summer and fall months. In addition to an unnatural seasonal distribution of stream flow, this also leads to higher peak flow rates from severe storm events, with the potential for flood hazards.

5.2.6 Field Measurements of Baseflow

In all comparable TRCA watersheds, a general pattern has developed in regards to major influences on the baseflow regime. It has been found that the chief contributing factor to overall baseflow is the Oak Ridges Moraine (ORM), in particular, the southernmost extent of this formation (Figure 5). The second major influence common among TRCA watersheds is the presence of the Iroquois Sand Plain (Figure 5). Both of these geological formations have extensive areas of highly permeable materials (sand and gravel). The ORM can be likened to a giant underground rain barrel, collecting precipitation through infiltration and gradually releasing a portion of this precipitation to the creeks and rivers as baseflow. The porous deposits associated with the ORM continue well beyond the physical boundaries of the above ground features and into the physiographic area referred to as the South Slope. It is in these areas that the largest contributions to baseflow generally occur.

The Iroquois Sand Plain is comprised predominantly of sandy deposits and is consistently an area of high infiltration in higher elevation areas, with discharge occurring mainly in the lower elevation areas. In the Humber River watershed, the Iroquois Sand Plain occurs only in the Lower Humber subwatershed. Baseflow measurements in the Lower Humber remain limited, due to the size and depth of the watercourse, and because of this, the influence of the Iroquois Sand Plain on the baseflow regime of the Humber River is still not well understood. Through baseflow measurements in 2004 it was found that more than 50% of the total stream flow of the Humber River during baseflow conditions originates from within the Main Humber and East Humber subwatersheds. The West Humber, Black Creek, and Lower Humber contribute the remaining 50% of total stream flow during baseflow conditions (Figure 11). Baseflow contributions can be further broken down according to Humber River secondary subwatersheds (Table 6). An examination of baseflow contributions at this scale reveals that the Upper Main, Centreville Creek, Purpleville Creek, Lower – Woodbridge to Rexdale, and Lower – Lambton to Mouth subwatersheds are major contributors to total baseflow in the Humber River. Centreville Creek contributes more than 25% of total baseflow discharge from the Main Humber, while Cold Creek contributes 15%. In the East Humber, it was found that almost 20% of the East Humber’s baseflow discharge is derived from Purpleville Creek (Table 6).


32

Figure 11: Baseflow Contributions by Primary Humber River Subwatersheds, 2004

The same analysis was completed with data acquired from the Geological Survey of Canada, which dates back to 1995 (Figure 11). A similar picture emerged in 1996 where a total of 74% of the total baseflow was derived from the Main and East Humber subwatersheds. Low values were observed for Black Creek and the West Humber subwatersheds, similar to those observed in 2004. TRCA field data showed a significant contribution from the Lower Humber subwatershed, which was not found in the GSC dataset. Ongoing monitoring at subwatershed outlets will further validate these contributions.

Humber River Watershed Percent Contribution by Subwatershed

GSC Data 1995 - 1996

8%

21%

11% 54%

6%

Black Creek East Humber Lower Humber Main Humber West Humber

TRCA Data 2004

8% 19%

34% 32%

7%


atershed R

eport –

Surface W

ater Quantity

33

Table 6: Contribution to Overall Baseflow Discharge by Humber River Subwatersheds, 2004

GSC 1996

GSC 1996

TRCA 2004

TRCA 2004

Primary

Subwatershed

Secondary Subwatershed

% Contribution

Net Change

% Contribution

Net Change

1.

Upper Main

29.6%

Gain

18.9%

Gain

2.

Palgrave to Bolton

-0.1%

Loss

-4.9%

Loss

3.

Centreville Creek

9.4%

Gain

14.2%

Gain

4.

Cold Creek

11.4%

Gain

8.0%

Gain

5.

Bolton to W

oodbridge

3.0%

Gain

-4.3%

Loss

Main Humber

6.

Rainbow Creek

0.7%

Gain

0.0%

Gain

7.

West Branch

1.8%

Gain

7.5%

Gain

8.

Main Branch

0.2%

Gain

1.4%

Gain

9.

East Branch

0.0%

N/A

0.8%

Gain

10. Lower

3.9%

Gain

-2.6%

Loss

West Humber

11. Albion Creek

N/A

N/A

0.0%

Gain

12. Upper East

9.1%

Gain

6.6%

Gain

13. King Creek

0.2%

Gain

0.2%

Gain

14. Nobleton to Kleinburg

-3.8%

Loss

-4.5%

Loss

15. Purpleville Creek

4.3%

Gain

13.3%

Gain

East Humber

16. Kleinburg to W

oodbridge

11.6%

Gain

3.2%

Gain

Black Creek

17. Black Creek

7.6%

Gain

7.9%

Gain

18. Woodbridge to Rexdale

1.6%

Gain

13.7%

Gain

19. Emery Creek

N/A

N/A

N/A

N/A

20. Rexdale to W

eston

N/A

N/A

1.3%

Gain

21. Berry Creek

0.2%

Gain

0.4%

Gain

22. Humber Creek

1.2%

Gain

0.0%

N/A

23. Silver Creek

0.8%

Gain

0.6%

Gain

Lower Humber

24. Lambton to M

outh

7.4%

Gain

18.5%

Gain


34

To better visualize the spatial distribution of groundwater recharge and discharge areas, mapping products were created to show the measured increases and decreases in baseflow normalized to the stream length between sampling stations. Figure 12 shows the normalized distribution of baseflow discharge for the Humber River watershed. Examining baseflow information in this way allows for quick identification of specific areas where increases or decreases in baseflow are occurring and provides insight into reaches where surface water takings may have been occurring during the period of measurement. Correlation of the normalized distribution of baseflow discharge with information on locations of known surface water takings also provides insight into reaches where water takings may be impacting stream health. The following sections provide an overview of some of the key findings from analysis of field measurements of baseflow at the subwatershed and reach scales. Main Humber The Main Humber subwatershed covers approximately 35,700 hectares. Not only is the Main Humber the largest of the Humber River primary subwatersheds, but it is also the largest contributor to overall baseflow discharge, contributing 32%of the total baseflow discharge from the Humber River. The majority of the Main Humber subwatershed is on the ORM and includes a portion of the Niagara Escarpment. Baseflows in the Main Humber primarily originate from the Upper Main, Centreville Creek and Cold Creek (subwatersheds 1, 3 and 4 respectively). Centreville Creek, located where the ORM and Niagara Escarpment meet, was observed to contribute 26% of total baseflow discharge from the Main Humber subwatershed and 14.2% of total Humber River baseflow discharge. Within the Centreville Creek subwatershed 80% of the baseflow discharge originates from the Bracken, Boyce’s and Evans Creek tributaries. Cold Creek, which is entirely on the ORM, contributes approximately 15% of the baseflow discharge from the Main Humber. Supporting previous findings, the major inputs within Cold Creek occur along reaches located on the southern portion of the ORM (Figure 12). Cold Creek was also identified in the GSC study as a significant groundwater discharge area, with baseflow resulting from regional groundwater flow along deeper flow paths (Hinton, 1997). A tributary that flows through Cold Creek Conservation Area, upstream from site MH-082, was found to contribute 42% of the total baseflow discharge from Cold Creek and 6% of the total baseflow discharge from the Main Humber. The stream drops in elevation by approximately 40 metres between the 16th and 15th Sideroads. The Oak Ridges aquifer likely outcrops along the stream corridor in this area. In the Upper Main subwatershed, the area above the Niagara Escaprment also appears to be a significant contributor to baseflow, as approximately 5% of the total baseflow discharge from the Main Humber occurs upstream of site MH312 at Airport Road. There are two possible sources for these baseflow discharges, both related to local geology. As glaciers receded along the Niagara Escarpment they left behind large sand and gravel deposits, which are known to be highly permeable. These sand and gravel deposits may be areas of positive hydraulic gradient where groundwater is discharged into the surface water system. The second possible explanation is that while the Niagara Escarpment is not porous like the ORM, infiltration does occur through cracks and fissures in the shale and sandstone, and as this water is released slowly, could be contributing to baseflows in these reaches.

Figure 12: Baseflow Norm

alized to Stream Length – Humber River Watershed, 2004


36

Rainbow Creek (subwatershed 6) is not a major contributor to overall baseflow, inputting less than 1% to the Main Humber subwatershed. Rainbow Creek tributaries were observed to be dry in the headwaters, and sampling was not possible throughout much of these reaches due to site specific conditions. Data collected by the GSC in 1996 showed slightly higher baseflow contributions, ranging from 3 – 10 L/s. East Humber

While the East and West Humber subwatersheds are similar in size, the East Humber’s contribution to overall baseflow was observed to be more than double that from the West Humber in 2004. This can be explained by the major differences in physiography and local geology. The headwater tributaries of the East Humber are located on the ORM while the majority of the West Humber tributaries are not. Baseflow measurements in 2004 show that more than 40% of the baseflow within the East Humber subwatershed is derived from tributaries and reaches located on the southernmost portion of the ORM and northernmost portion of the South Slope. Reaches along the main channel between King-Vaughan Rd. and Kirby Rd.were also observed to be major contributors to baseflow, likely due to groundwater discharge inputs from the Oak Ridges Aquifer. Purpleville Creek (subwatershed 15), an East Humber tributary, was observed to be a significant source of baseflow, providing 18% of the total baseflow discharge from the East Humber. The majority of the baseflow inputs to Purpleville Creek appear to originate from the eastern branch, between Kirby Rd. and Major Mackenzie Dr. and are likely due to groundwater discharge inputs from the Oak Ridges Aquifer. Based on reverse particle tracking analysis using the regional groundwater flow model, it is likely that a significant portion of groundwater discharging to Purpleville Creek infiltrated in the Upper East Humber (subwatershed 12), indicating that land use change and management measures in new developments in the Upper East Humber may have an influence on baseflow rates in Purpleville Creek, as well as locally. A significant increase in baseflow was also observed along reaches of the main channel downstream of Rutherford Rd., which is likely due to groundwater discharge inputs from the Thorncliffe Aquifer Complex (see Figure 13). West Humber

Baseflow in the West Humber subwatershed is not as strongly influenced by the ORM as it is in the East and Main subwatersheds. This is evident in the relatively small contribution the West Humber makes to total baseflow discharge from the Humber River (approximately 3% in 2004, 6% in 1996). Stream flow in many reaches of the main and east branches (subwatersheds 8 and 9 ) is intermittent, with periods of no flow occurring during dry months, particularly in reaches north of Mayfield Rd. Stream flow in the headwater reaches of the west branch (subwatershed 7) are influenced by groundwater discharge inputs from the Oak Ridges Aquifer, where 7%-12% increases in baseflow were measured along the uppermost reach (WH145). This area was also recognized as a moderate groundwater discharge zone by the GSC in a 1997 report (Hinton, 1997). A significant increase in baseflow was observed along the main channel between Martin Grove Rd. and Albion Rd. which may be due to groundwater discharge inputs from both the Oak Ridges Aquifer Complex (or equivalent) and the Scarborough Aquifer Complex (see Figure 14).


37

Figure 13 Geologic model cross-section, East Humber between Rutherford Rd. and Islington Ave.

Figure 14 Geologic model cross-section, West Humber between Highway 27 and Albion Rd.


38

Black Creek In 2004, Black Creek was observed to contribute 7.9% of the total baseflow discharge from the Humber River. The headwaters of Black Creek begin just north of Major Mackenzie Drive. By the time the creek crosses Steeles Ave, Black Creek already comprises more than 35% of its total baseflow discharge. In 1996 it was observed that approximately 50% of baseflow from Black Creek originates from reaches north of Hwy 7 (Hinton, 1996). Along the reach downstream of Sheppard Ave, a significant reduction in baseflow was measured, which totaled more than 50% of the total baseflow discharge from Black Creek. Additional measurements along this reach are needed to confirm the location and magnitude of this measured decrease in baseflow. As Black Creek continues to flow south towards Wilson Ave, the creek flows over large sand and gravel deposits. This reach of Black Creek is predicted to be a groundwater discharge area due to the presence of these deposits. An increase in baseflow of more than 30% was measured at Wilson Ave, followed by another 24% increase measured upstream of Eglinton Ave. Just before the confluence with the Lower Humber, a small 8% reduction in baseflow was measured. This reach is concrete lined for flood control, ruling out a natural downward hydraulic gradient. Additional measurements along this reach are needed to confirm the location and magnitude of this measured decrease in baseflow.

Lower Humber The main channels of the East and Main Humber merge to form the Lower Humber just upstream of Woodbridge Ave at Islington Ave. A major increase in baseflow (approximately 50%) was observed between Woodbridge Ave. and Highway 407, likely due to an outcropping of bedrock material which routes groundwater from both the Oak Ridges Aquifer Complex (or equivalent) and the Thorncliffe Aquifer Complex, upwards, resulting in major groundwater discharge inputs to the stream along this reach (see Figure 12). Where the Lower Humber flows south of Steeles Avenue a 7% decrease was measured in baseflow. A similar decrease in baseflow was not observed in 1996. A large area of sand and gravel may exist along the top portion of this reach in which a negative hydraulic gradient may be present. There are also two known water takings along this reach, both for golf course irrigation. One of these users relies on groundwater for irrigation purposes, and is not likely having significant effects on the surface water flow. The second of these golf courses draws water directly from the Humber River but does not appear to be the sole cause of this decrease. The TRCA Water Use Assessment survey shows that their average withdrawal is about 1.14 million litres per day at an estimated rate of 23 litres per second, which is less than 1/3 of the measured decrease. Further spot measurements are required to pinpoint the cause of this decrease. Downstream from this measured decrease, a large increase of about 20% was observed, which supports the suspicion that individual or multiple water withdrawals may have been affecting stream flow while the upstream measurement was taken. A significant increase in baseflow was observed in the Lower – Lambton to Mouth subwatershed. Several factors could be causing this increase in baseflow. Reaches in this subwatershed could be receiving groundwater discharge from the Thorncliffe or Scarborough Aquifers outcropping along the deeply incised river valleys and from lower elevations of the Iroquois Sand Plain. As this subwatershed is completely urbanized, the observed increase could also be partly due to shallow groundwater seeping into or along storm sewers or other underground infrastructure and being released to the stream. Further field investigations and


39

correlation of field measurements of baseflow with the outputs of the York-Peel-Durham-Toronto regional groundwater flow model need to be undertaken to provide insight into the major factors influencing baseflow in this subwatershed.

5.3 Water Use

Water use can be broken down into two major groups: surface water use and groundwater use. While there are users withdrawing from combined sources, these will be discussed as groundwater use only, as this is usually the predominant source. Surface water use statistics for the Humber River watershed are summarized on a subwatershed basis in Table 7 and described in more detail in Table 9. Surface water use water budgets are developed on a watershed and subwatershed basis to provide a general indication of the potential for stress on baseflow regimes from surface water use. Surface water use water budgets are calculated using measured baseflow discharge information and estimates of average daily surface water withdrawals, as reported by individual surface water users. If actual water use information was not available, this analysis used the maximum permitted withdrawal, as stated in the Ontario Ministry of Environment Permit to Take Water database (OMOE, 2002). Allocation estimates are calculated both on a watershed and subwatershed basis, and provide a rough estimate of the percentage of total baseflow discharge that is being removed or permitted to be removed from the system as surface water withdrawals. A total of 262 individual water withdrawals were identified within the Humber River watershed, with complete water taking information available for 165 of these users. From these data, total allocation of surface water from the Humber River on an average year is approximately 2.3% of available baseflow. Surface water withdrawals are usually most active during dry periods between rain events, and these dry periods are concurrent with baseflow conditions. While 2.3% of the total baseflow being withdrawn in an average year does not seem to be a significant portion, when these allocations are examined on a subwatershed basis, a different picture emerges. The West Humber subwatershed appears to be the most at risk of negative impacts due to surface water use, with more than 18% of the average annual baseflow discharge allocated for withdrawal (Table 7). This subwatershed assessment of risk of impacts from surface water use is by no means definitive. Even in a subwatershed with a low percentage of the total baseflow discharge allocated for withdrawal, individual water takings from small headwater streams have the potential to cause significant impacts downstream during baseflow conditions. Overall, water use in the Humber is predominantly for agricultural irrigation, which accounts for 42% of the total annual withdrawals (Figure 15). Commercial use and water supply withdrawals are also major use sectors, comprising 30% and 18% respectively.


40

Figure 15: Water Abstractions by Purpose – Humber River Watershed

Table 7: Surface Water Withdrawals as a Percentage of Baseflow Discharge, 2004

Subwatershed

Annual Baseflow

Discharge

(Million L/yr)

Annual Surface

Withdrawals

(Million L/yr)

Percent Baseflow

Allocated

(%)

Black Creek 5651.3 12.4 0.2

East Humber 13686.6 160.3 1.2

Lower Humber 63166.6 20.9 0.03

Main Humber 46137.2 378.2 0.8

West Humber 5014.2 890.4 17.8

Humber River Watershed 63166.6 1462.1 2.3

Water Abstractions by Purpose

42%

30%

1%

18%

3%

5%

1.2%

Agricultural

Commercial

Institutional

Livestock

Miscellaneous

Recreational

Unknown

Water Supply


41

Results of the TRCA Water Use Assessment are summarized in Table 9. Water Use Assessment surveys indicate that 55% of agricultural water withdrawals are for market garden operations. Commercial use of water in the Humber River is predominantly for golf course irrigation, making up 60% of the total commercial water use. Irrigation practices like those used for crop farming or golf course maintenance are highly consumptive water uses, where 78% - 90% of water withdrawn is not returned to the local system, but is consumed through evaporation and transpiration (Conservation Ontario, 2003; Golder Associates and Marshall, Macklin, Monaghan Ltd., 2003). An assessment of potential risk of downstream impacts from known surface water takings was also conducted. For this assessment, surface water users were separated from the data set, and average withdrawal rates in litres per second were estimated based on daily withdrawal rates and the duration of these withdrawals. By correlating withdrawal information for each surface water taking with measured baseflow rates in affected reaches, risk of negative downstream impacts from surface water use was assessed on a reach basis. A classification system of Low, Medium or High risk was used as means of identifying priority areas for further investigation and possible management action (Table 8).

Table 8: Classification System for Assessment of Risk of Downstream Impacts From Surface

Water Withdrawals

Risk Rating Percentage of Total Baseflow Discharge Allocated

for Withdrawal

No known risk 0%

Low Less than 5%

Medium 5% to 25%

High greater than 25%


42

Table 9: Water Withdrawals By Subwatershed – Humber River Watershed, 2004

Daily Withdrawals (L)

Subwatershed Purpose Surface Ground Both Total

Agricultural 11744 0 0 11744

Commercial 2040000 91000 0 2131000 Black Creek

Recreational 0 130000 0 130000

Sub-total 2051744 221000 0 2272744

Agricultural 13444744 211000 189250 13844994

Commercial 2870213 3370000 0 6240213

Recreational 0 147000 0 147000

Livestock 1170 233000 3813 237983

Miscellaneous 640000 66000 0 706000

Unknown n/a n/a n/a n/a

Water Supply 9729 3834000 0 3843729

East Humber

Institutional 0 720000 0 720000

Sub-total 16965856 8581000 193063 25739919

Commercial 1635624 109000 0 1744624 Lower

Humber Livestock 0 500 0 500

Sub-total 1635624 109500 0 1745124

Agricultural 454152 2258000 2247775 4959927

Commercial 4838501 1401000 45461 6284962

Recreational 50000 648000 590946 1288946

Livestock 6747 382000 54974 443721

Miscellaneous 2263908 71000 6000 2340908


Main Humber Water Supply 908400 5629000 0 6537400

Sub-total 8521708 10389000 2945156 21855864

Agricultural 5963993 181000 75803 6220796

Commercial 420000 591000 0 1011000

Livestock 0 38000 0 38000

Miscellaneous 0 0 0 0

West Humber


Sub-total 6383993 810000 75803 7269796

Agricultural 19874633 2650000 2512828 25037461

Commercial 11804338 5562000 45461 17411799

Institutional 0 720000 0 720000

Livestock 7917 653500 58787 720204

Miscellaneous 2903908 137000 6000 3046908

Recreational 50000 925000 590946 1565946


Total Humber Water Supply 918129 9463000 0 10381129

Total 35558925 20110500 3214022 58883447 n/a = Not available

Reaches in the West Humber subwatershed are currently at highest risk of downstream impacts from surface water use. Baseflow discharge from this subwatershed is highly variable,


43

ranging from 18 l/s to 160 l/s. Two high risk water takings exist in this subwatershed and the percentage of baseflow that is allocated for withdrawal is greater than 10%. The East Humber subwatershed has the largest number of surface water users in the Humber River, with a total of 18 users, seven of which have a high potential risk of downstream impacts. The withdrawal purposes for these seven users vary from small aesthetic ponds, to larger operations such as agricultural and golf course irrigation. One of these golf courses is already beginning to implement a fixed elevation intake system, and will be shown to have a very low risk of downstream impacts once the system is in place. There is a single high-risk surface water taking in each of the Black Creek and Main Humber subwatersheds. The percentage of total baseflow discharge allocated for withdrawal in both the Black Creek and Main Humber subwatersheds is quite low. In the Lower Humber River, surface water takings are limited to two golf course operations. Due to the large volume of baseflow found in the lower reaches of the Humber (2000 – 2300 L/s), the individual withdrawal amounts have very low risk of downstream impacts (represent ing less than 5% of the measured baseflow discharge). In the last thirty years, a major shift in water taking permit applications from surface sources to groundwater sources has become apparent. During the 1960s, 68% of all permits issued by MOE to take water were for surface water sources. This trend continued into the late 1970s, but by 1990 the ratio of groundwater to surface water permits was about equal (50% ground, 45% surface). In response to recent concerns regarding allocation of surface water resources, MOE is issuing far more permits for groundwater takings and, in some cases, recommending that users switch from surface water sources to groundwater sources. During the 1990s, 64% of all permits issued were for groundwater sources, and only 28% were for surface water takings (Figure 16).

Source Water Protection legislation requires full water budgets and water use stress assessments for all watersheds, including the Humber. This study will further assess the cumulative impacts of ground and surface water use, which will also include stress assessments for future (2031) projected water demand.


44

Water Use by Source

0

10

20

30

40

50

60

70

80

1960-69 1970-79 1980-89 1990-01

% of perm

its issued

Surface

Ground

Both

Figure 16: Percent of PTTW’s Issued by Year and Water Source (TRCA Jurisdiction)

5.4 Flooding

Flooding is a natural component of any watershed’s hydrologic regime. The Humber River, like all watercourses, periodically experiences levels that overflow its banks. Early accounts of flooding date back to the early 1800s. The most serious flooding in the recorded history of the Humber River occurred in 1954 as a result of Hurricane Hazel which brought approximately 210 millimeters of rain to the Toronto region in less than 12 hours. Of all of the TRCA watersheds, the Humber was the hardest hit by the storm, in terms of both storm magnitude and severity of damage. Numerous bridges were washed out, and over 1200 families in the Humber watershed were left temporarily homeless. One of the most dramatic events during the Hurricane Hazel flood occurred in the Humber River Watershed at Weston, where an entire section of Raymore Drive containing 14 homes was completely swept away, taking the lives of 31 people. As a result of the destruction caused by Hurricane Hazel, the 1959 Plan for Flood Control and Water Conservation (MTRCA, 1959) identified the need for 15 large control dams as well as four major flood control channels within the TRCA. Among the works implemented from the plan are the Claireville Dam on the West Humber River and flood control channels on the Humber River through Woodbridge and on the Black Creek at Weston. More importantly, the Plan noted the relative effectiveness of acquisition of flood prone lands in the Humber River valley systems as a means of reducing flood risks. To date, more than 6500 hectares of hazard land in the Humber River watershed has been acquired by the TRCA. In addition to reducing


45

potential flood damages, the secured open space in the Humber River valley provides the public with highly valued recreational opportunities. In south central Ontario, the regulatory flood event is the greater of the 100 year storm (largest storm that has occurred in the past 100 years) or Hurricane Hazel (Government of Ontario, 2002). The objective of the TRCA Floodplain Management Program is to minimize the risk of, or prevent flooding through the protection of valley and stream corridor systems, the restriction of any development activities in floodplain areas necessary to convey flood flows, and the operation of the Flood Forecasting and Warning Program. The watershed has been undergoing a significant degree of urbanization over the last two decades, especially in the cities of Richmond Hill, Vaughan and Brampton. Many of the smaller streams are beginning to exhibit the impacts of urbanization, evident in the changes in their hydrologic response during precipitation events. While regulations exist to ensure that new development is located away from flood prone areas, older urban areas in the watershed, mostly within the City of Toronto, will continue to be susceptible to flooding. Several flood damage centres were identified within the Humber River watershed through the Flood Control Program of the 1980 MTRCA Watershed Plan. Flood control works in Bolton and Woodbridge have greatly reduced the potential flood risk in these communities, but in the event of a storm comparable to Hurrican Hazel they would be flood-susceptible. There are two sizeable flood damage centres on Black Creek in the City of Toronto, at Wilson Avenue and another below Weston Road, where a large number of structures are subject to flooding during events as frequent as the predicted 1 in 25 year return period storm event. Other flood damage centres in the Humber include the Lake Wilcox area of Richmond Hill, the confluence of the West and Main Branches near Albion Road in Toronto and the main branch at Scarlett Road in Toronto. In addition to those areas subject to severe flood damage during an event the size of Hurricane Hazel, there are a number of areas within the Humber River watershed subject to nuisance flooding during more frequent events. Flooding due to ice jams occurs with some regularity in Bolton, along Highway 27 at Rutherford Road in Vaughan, on the Main Humber through Woodbridge, and between Dundas and Bloor Street in the Lower Humber. Flooding also occurs regularly in Oak Ridges, in part due to the extremely flat stream gradient between Lake Wilcox and Bathurst Street. Snowmelt occasionally leads to flooding when wetlands and submerged culverts along the East Humber River remain frozen, and even flooding behind beaver dams has threatened structures in the past. An important tool for managing flood risks in the watershed is the Humber River hydrology model which is periodically updated to represent current watershed conditions (Aquafor Beech, 2002). The hydrology model outputs, along with watershed mapping and hydraulics information, allow locations of flood-vulnerable structures (or areas) and roads to be identified. The current location of flood vulnerable areas and roads within the Humber River watershed, as predicted by the outputs of the Humber River hydrology and hydraulic models (TRCA, 2005) is illustrated in Figure 17. Statistics summarizing the number of structures vulnerable to flooding during different stages of flooding (TRCA, 2005) are provided in Table 10. These findings confirm that the risk of flooding remains an important watershed management issue in portions of the City of Toronto, Bolton, Woodbridge, and Richmond Hill.


46

This information provides a baseline assessment of the number of flood vulnerable areas and roads in the Humber River watershed. As the hydrology and hydraulic models are updated in the future, outputs from the updated models could be compared with the findings from this assessment to track whether or not the target of maintaining or reducing the number of flood-vulnerable areas and roads is being achieved. Maintaining or reducing flood risks at these sites is achieved through implementation of stormwater management controls in development areas that mitigate potential impacts of increased flows caused by urbanization. To ensure that peak flow rates are maintained throughout the watershed, and not just at the outlet of a development area, unit flow rate equations have been established for Humber River watercourses. These equations are used during the planning and design of new urban areas to set acceptable stormwater release rates from new developments. The limited differences that were observed between peak flow rates predicted during the 1997 hydrology model update (Aquafor Beech Ltd., 1997) and the 2002 hydrology update (Aquafor Beech Ltd., 2002) demonstrate that the unit flow rate approach has been largely successful in maintaining or reducing peak flow rates through the Humber River watershed.

Table 10: Number of Flood Vulnerable Areas and Roads by Flood Stage – Humber River

Watershed (TRCA, 2005)

Main Humber West Humber East Humber Black Creek Lower Humber Total

Watershed

Stage 1 (10 year storm event)

# of FVAs 39 5 14 111 2 171

# of FVRs 18 5 7 23 9 62

Sub-total 57 10 21 134 11 233


# of FVAs 63 5 16 205 7 296

# of FVRs 28 7 11 37 13 96

Sub-total 91 12 27 242 20 392


# of FVAs 90 5 23 327 9 454

# of FVRs 38 9 13 44 13 117

Sub-total 128 14 36 371 22 571


# of FVAs 105 5 25 385 11 531

# of FVRs 41 10 18 54 14 137

Sub-total 146 15 43 439 25 668

Stage 5 (regional storm event, Hurricane Hazel)

# of FVAs 420 48 187 1138 299 2092

# of FVRs 99 34 34 99 38 304

Sub-total 519 82 221 1237 337 2396

NB: # of FVAs = number of flood vulnerable areas (structures) # of FVRs = number of flood vulnerable roads (locations)

Figure 17: Flood Vulnerable Areas and Roads - Humber River Watershed


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6.0 MANAGEMENT CONSIDERATIONS

6.1 General

Urbanization has resulted in changes to watershed hydrology, including increases in the volume, severity and frequency of surface flows along with a potential for localized reductions in baseflows. These impacts threaten the specialized habitats of aquatic species as well as human lives and property. Variability in flow is monitored and analyzed using flow measurements from stream gauges and by conducting baseflow measurements. Water users can have significant local and watershed-wide effects on flow and must be included in any analysis of flow conditions, both existing and future. Flood flow information developed by watershed hydrology and hydraulic models are used to create floodplain mapping, which in turn can be used to ensure development is restricted to lands outside the Regulatory floodplain to minimize the risk to life and property and to help maintain the natural hydrologic and ecological function of valley lands. The Humber River watershed continues to urbanize and, while past advancements in stormwater management have mitigated some impacts of urban development on the hydrologic response of the watershed, there continue to be concerns associated with higher peak flows, greater overall volume of surface run-off being conveyed by the streams and more uniform yearly distribution of peak flows unless new approaches are undertaken. Data from field monitoring, together with increased scientific study of watershed interrelationships, is confirming the importance of addressing water budget imbalances in addition to traditional stormwater management practices. Despite the use of end of pipe facilities to provide extended detention of storm run-off, the increase in the volume of storm run-off is predicted to increase erosion in the watercourses as they adjust to accommodate the changes in flow regime. If nothing is done, the potential excessive channel migration could impair sensitive aquatic ecosystems and expose municipal infrastructure in valley lands, leading to increased repair and maintenance requirements. Implementing innovative stormwater management practices to reduce run-off volumes and preserve the natural water balance will help to mitigate impacts of urbanization on the health of receiving stream systems. Innovative best management practices that would help to address water budget imbalance issues could include urban designs that minimize impervious surfaces, incorporation of more aggressive lot level and conveyance controls to maximize infiltration of clean run-off and increase evapotranspiration (e.g., rain gardens, pervious paving materials, green roofs, parking lot bioretention areas, perforated pipe stormwater conveyance systems, roadside swales), and the use of rain barrels or cisterns for harvesting rainwater for irrigation or other purposes that do not require treated drinking water (e.g., flushing toilets and washing clothes).


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6.2 Baseflow

The Oak Ridges Moraine (ORM) is an obviously important influence on the spatial distribution of baseflow discharge within the Humber River watershed. Based on comparison of field measurements from multiple years, a consistent pattern in the distribution of baseflows has been observed. To protect and manage baseflow in the Humber River, attention should be focused on protecting and maintaining the function of areas where high rates of groundwater recharge (infiltration) occur and which play a significant role in maintaining water levels in the aquifer units that contribute groundwater discharge to surface streams. Through the Oak Ridges Moraine Conservation Plan, much of the ORM is protected from urban development, thus helping to ensure that natural functions of the ORM are maintained.

6.3 Surface Water Use

Overall, surface water use in the Humber River watershed is not significantly affecting annual baseflow discharge. However, some reaches were identified where a high potential risk of impacts from surface water uses exists after local impacts from surface water use were observed in several of these reaches in 2004. Many of these local impacts could be reduced or eliminated by implementing alternate withdrawal methods or other best management practices through the MOE Permit to Take Water process. With the application of minimum in-stream environmental flow requirements, water withdrawal volumes and the number of users can generally continue without detrimental impacts to the low flow system. However, the timing of the withdrawals should be addressed. This would include altering withdrawal structures (fixing the intake at a specific elevation) and encouraging the practice of drawing on surface water sources during elevated stream flows (wet weather) combined with on-site storage (e.g., ponds). For livestock users or other low volume users who are not regulated under the Ontario Water Resources Act, downstream impacts from these small users can only be managed through stewardship programs, and therefore an incentive must exist to make the effort worthwhile to the user. The TRCA has been working with the MOE and surface water users within its jurisdiction to reduce the risk of downstream impacts from water use. Approaches to achieving this include, but are not limited to, promoting the use of multiple sources, establishing fixed elevation intakes, and constructing storage reservoirs that are filled during elevated stream flow events. These actions are not mutually exclusive, and major water users typically combine several approaches to meet PTTW and Conservation Authority requirements. Further field investigations of individual water takings in reaches assessed as being at high risk of impacts from surface water uses will be completed in order to identify options for improved management and to determine if these individual takings are directly affecting baseflow. The following recommendations for improving the management of baseflows in the Humber River are proposed:


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• Establish long term baseflow monitoring / indicator sites within the Humber River watershed as part of the TRCA Regional Watershed Monitoring Program to further characterize and monitor baseflow conditions and enable the analysis of trends and the effectiveness of management programs and impact mitigation measures.

• Work with MOE in a proactive manner through the PTTW program to modify surface water takings for major users to allow for an uninterrupted passage of baseflows to support the aquatic ecosystem and to maintain minimum in-stream ecological flow requirements.

• Undertake groundwater system investigations and soil testing to better characterize recharge and discharge areas that significantly contribute to baseflows and develop strategies for protecting significant recharge and discharge areas to protect the sustainability of baseflows within the Humber River.

• Undertake additional field measurements to fill remaining gaps in our understanding of the baseflow regime of the watershed, and further investigate reaches where major decreases in baseflow have been observed, and investigate dry weather discharges from storm sewers.

• Significant variations in annual baseflow discharge rates observed in the West Humber require further study.

6.4 Flooding

In the past, flooding of the Humber River has been primarily a result of large tropical storms, rain-on-snowmelt events or ice jamming. New information derived from hydrology and hydraulic modeling work provides a baseline assessment of the number of flood-vulnerable areas and roads in the Humber River watershed. As the hydrology and hydraulic models are updated in the future, outputs from the updated models should be compared with the findings from the 2005 assessment to track whether or not the target of maintaining or reducing the number of flood vulnerable areas and roads is being achieved. To improve our understanding of the surface water flow system and our ability to identify trends and develop appropriate management solutions, data collection needs to be expanded. TRCA continues to expand the stream flow and precipitation monitoring network to provide an improved base of information that will better enable us to track whether or not surface water flow objectives and targets are being met.


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7.0 WATERSHED REPORT CARD RATINGS

7.1 Stream Flow

Beginning with the 2000 Humber River watershed report card (TRCA, 2000), average annual stream flow was selected as an indicator of watershed health that could be tracked over time to evaluate existing conditions. Upon examination of available stream flow data, difficulties in detecting significant trends in average annual stream flow have been encountered. Average annual stream flow does not distinguish between storm flow volumes from precipitation, snowmelt events (wet weather) and baseflow volumes occurring during dry weather and, therefore, is not a very sensitive indicator of stream health. While trends in average annual stream flow can provide some insight into changes in watershed hydrology, there are other more appropriate stream flow parameters that can provide insight into more specific threats or impacts on stream health and that are more sensitive to changes in the landscape. Therefore, annual and seasonal stream flow volume, and annual and seasonal baseflow rates are recommended to be used in subsequent report cards to evaluate existing conditions. New objectives pertaining to stream flow, which were not part of the 1997 watershed strategy, Legacy: A Strategy For A Healthy Humber (MTRCA, 1997), are also proposed. The first is to “protect or restore the natural variability of annual and seasonal stream flow”, based on the impacts to stream flow already observed and the potential for additional impacts from on-going development. The second new objective is to “maintain and restore natural levels of baseflow”, acknowledging the need to address life cycle needs of aquatic communities and ensure surface water sources are sustainable. The objectives, indicators and targets, as well as an updated watershed report card rating for existing (2002) conditions are provided below (Table 11).

Objectives: Protect and restore the natural variability of annual and seasonal stream flow; and

Maintain and restore natural levels of baseflow

Overall Rating

C

Indicator Measure Target Rating

Average annual and seasonal stream flow volumes at stream gauge locations (m3/year)

Maintain or reduce baseline annual and seasonal flow volumes*

C Stream Flow

Average seasonal (spring-summer) baseflow discharge at indicator sites (May to August; m3/sec.)

Maintain or enhance baseline seasonal baseflows*

C

* Based on measurements at long-term stream gauge locations and additional gauges recommended for

installation.


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Rating Rationale Examination of historical stream flow data indicates that statistically valid trends in average annual stream flow volume have not been observed over the period of record at most long-term stream gauges. A single exception is the East Humber River at King Creek, where a significant increasing trend was observed, reflecting the influence of upstream development in King City and Richmond Hill. Despite the lack of statistical significance, a number of upward trends were observed that may not have had a sufficient period of record to demonstrate significance. Statistically significant upward trends in summer stream flow volume were observed in the East Humber and Lower Humber, downstream of developed or developing areas, reflecting the influence of impervious surfaces which have the greatest impact on surface flows during warm season rainfall events. A rating of C was assigned for the measures of average annual and seasonal stream flow volume, reflecting the significant increasing trends observed in the East and Lower Humber while acknowledging that no significant trends have been observed in other subwatersheds. Ratings were assigned for the measure of average seasonal baseflow based on the information and rating criteria shown in Table 11:

Table 11: Percent Change in Median Summer Baseflow (1997 to 2003) and Report Card Ratings

* Report Card Rating Criteria: A Increases by more than 10% B Increases by less than 10% C No change D Decreases by less than 10% F Decreases by more than 10%

The decreases observed in summer baseflow from the East and Main Humber subwatersheds between 1997 and 2003 suggest that changes in groundwater levels and groundwater discharge rates occurred during this time period. It is important to note that two years of drought conditions occurred in the late 1990s. Changes in summer baseflows over this time period were likely due to the short term drought conditions, but may also have been influenced by increases in groundwater withdrawals from municipal water supply wells in these subwatersheds. The increase in summer baseflow observed in the Lower Humber during this time period likely reflects influences from surrounding urban land uses and associated subsurface infrastructure. Aging storm sewers are prone to intercepting shallow groundwater and conveying it to receiving watercourses when installed below the water table. The cumulative effect can be an increasing trend in baseflows in some urban streams.

Subwatershed

% Change Rating*

East Humber ú 1.8% D

West Humber û 0% C

Black Creek ú 5% D

Main Humber ú 12.9% F

Lower Humber ü 2.6% B


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An overall rating of “C” was assigned with regard to the measure of average seasonal baseflow, representing an average of the ratings assigned to the five primary subwatersheds.

7.2 Flooding

The 1997 Humber watershed strategy, Legacy: A Strategy For a Healthy Humber (MTRCA, 1997) did not contain an objective pertaining to flooding. Acknowledging that risk of flooding remains an important watershed management issue in the Humber watershed. Based on current conditions, an objective to “eliminate or minimize risks to human life and property due to flooding” is needed to encourage initiatives for ongoing reduction of flood risk, as well as continuation of existing flood management policies and programs. This objective is indicated below, along with recommended indicators, measures and targets and a rating for existing conditions in the watershed.

Objective: Eliminate or minimize risk to human life and property due to flooding

Overall Rating

C

Indicator Measure Target Rating

Peak stream flow rates Maintain or reduce existing peak flows (2-100 year events)1

C Flooding

Number of flood vulnerable areas and roads

Maintain or reduce baseline number of flood vulnerable areas and roads2

C

1 Humber River Hydrology Model Update (Aquafor Beech Ltd., 2002) 2 TRCA Flood Vulnerable Areas and Roads Database (TRCA, 2005)

Rating Rationale A rating of C has been assigned for the flooding indicator reflecting that, while relatively recent development has been located outside the flood hazard area and stormwater management has been practiced to prevent increases in flood flow rates, there are large areas of older development that would be subject to flooding following a storm event the magnitude of Hurricane Hazel. There is clearly room for improvement through better management of run-off from developing areas, through the retrofitting of storm drainage systems in existing developed areas, through major structural improvements to increase the conveyance capacity of the valley systems and to remove or improve major obstructions to flows (i.e. undersized culverts), and through the further acquisition of flood-vulnerable lands. Information from hydrologic and hydraulic modeling work regarding the number of flood vulnerable areas and roads (TRCA, 2005) represents a baseline assessment that can be compared with findings from future updates to the Humber River hydrology and hydraulic models to assign report card ratings on the extent to which the target is being achieved.


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7.3 Surface Water Use

The Humber River watershed strategy of 1997 established an objective to “use groundwater and surface water at sustainable rates.” In the 2000 Humber Watershed Report Card, surface water and groundwater withdrawals were identified as potential indicators for evaluating current conditions, but there was insufficient information available at the time to assign report card ratings. Based on more recently available information regarding surface water use and stream flow rates during period of extended dry weather (i.e., baseflows), the following framework of measures and targets are proposed to be used. Using this framework of measures and targets, a watershed report card rating has been assigned for the indicator of surface water withdrawals.

Objective: Use groundwater and surface water at sustainable rates

Overall Rating

C

Indicator Measure Target

Portion of mean annual baseflow discharge allocated for withdrawal (by subwatershed)

Less than 10% Surface water withdrawals

Number of surface water takings representing low, medium and high risk of downstream impacts (by subwatershed)

No known risk of downstream impacts from surface water takings exists (i.e., all surface water takings are off-line and/or have intakes fixed at an elevation above baseflow water level)

Rating Rationale Ratings were assigned for each primary Humber River subwatershed for the indicator of surface water withdrawals based on the information shown in Table 12 and Figure 18.


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Surface Water UseHumber River Watershed

0.2% 1.2% 0.03% 0.8%

17.8%

0

5

10

15

20

25

30

Black

Creek

East

Humber

Lower

Humber

Main

Humber

West

Humber

Number of Users

0

10

20

30

40

50

60

70

80

90

100

Percent Baseflow Allocated (%)

Total Surface

Water Users

High Impact

Users

Percent of

Baseflow

Allocated for

Withdrawal

Table 12: Surface Water Use, High Risk Takings and Report Card Ratings

* Report Card Rating Criteria:

A No known risk of downstream impacts from surface water takings

B Low risk water takings exist

C Medium risk water takings exist

D High risk water takings exist

F High risk water takings exist and % total baseflow discharge allocated for withdrawal > 10%

Figure 18: Surface Water Use

The risk of downstream impacts from surface water withdrawals were examined at the local (reach) scale and subwatershed scale. Assessments of risk of downstream impacts from surface water withdrawals at the reach scale were based on the type of withdrawal and the volume used. The West Humber subwatershed is currently at highest risk of downstream impacts from surface water use. Baseflow discharge from this subwatershed is highly variable, ranging from 18 l/s to 160 l/s. Since high risk water takings exist in this subwatershed and the percentage of baseflow that is allocated for withdrawal is greater than 10%, a rating of “F” was assigned.

Subwatershed Total # of Users # of High Risk

Takings Rating*

East Humber 18 7 D

West Humber 3 2 F

Black Creek 3 1 D

Main Humber 16 1 D

Lower Humber 2 0 B


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There is only one high risk surface water taking in each of the Black Creek and Main Humber subwatersheds. The percentage of total baseflow discharge allocated for withdrawal in both the Black Creek and Main Humber subwatersheds is quite low (<1%). Since the target is to have zero risk of downstream impacts from surface water takings these subwatersheds were assigned a rating of “D”. In the Lower Humber River, surface water takings are limited to two golf course operations. Due to the large overall volume of baseflow found in the lower reaches of the Humber (2000 – 2300 L/s), the individual withdrawal amounts have very low risk of downstream impacts (represent less than 5% of the measured baseflow discharge). A rating of “B” was assigned to the Lower Humber because the risk of downstream impacts from these surface water takings is low. The East Humber subwatershed has the largest number of surface water users in the Humber River, with a total of 18 users, 7 of which have a high potential risk of downstream impacts. The withdrawal purposes for these 7 users vary from small aesthetic ponds, to larger operations such as agricultural and golf course irrigation. One of these golf courses is already beginning to implement a fixed elevation intake system and will be shown to have a very low risk of downstream impacts once the system is in place. A rating of “D” was also assigned to the East Humber due to the large number of high risk surface water takings. An overall rating of “D” was assigned for the current condition of the Humber River with regard to the water use objective, representing an average of the ratings assigned to the five primary subwatersheds.


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8.0 REFERENCES

Acres International. 2004a. Preparation of Digital Flood Plain Mapping for the East Humber

River Sub Watershed. Prepared for the Toronto and Region Conservation Authority. Acres International. 2004b. Preparation of Digital Flood Plain Mapping for the Main Humber

Watershed within the Region of York. Prepared for the Toronto and Region Conservation Authority.

Aquafor Beech Limited. 1997. Humber River Watershed Hydrology/Hydraulics and Stormwater

Management Study. Prepared for the Toronto and Region Conservation Authority. Aquafor Beech Limited. 2002. Humber River Watershed Hydrology Update. Prepared for the

Toronto and Region Conservation Authority. Center for Watershed Protection. 2003. Impacts of Impervious Cover on Aquatic Systems –

Watershed Protection Research Monograph No. 1, Ellicott City, Maryland. Clarifica Inc., 2002: Water Budget in Urbanizing Watersheds, Duffins Creek Watershed.

Prepared for The Toronto and Region Conservation Authority. Clarifica. 2004. Preparation of Digital Flood Plain Mapping for the West Humber River Sub

watershed. Prepared for the Toronto and Region Conservation Authority. Conservation Ontario. 2003. A Framework for Local Water-Use Decision-Making in a Watershed

Basis. Published by the Government of Ontario in partnership with the Credit Valley Conservation Authority and the Grand River Conservation Authority.

Environment Canada. Archived Hydrometric Data. http://www.wsc.ec.gc.ca/hydat/H2O/ Golder Associates Ltd. and Marshall Macklin Monaghan Ltd.. 2003. York Region - Water Use

Assessment (DRAFT) (incl. database). Produced for York Region. pp.29. Government of Ontario. 2002. Provincial Policy Statements (Section 3.1 Natural Hazards Policy)

under the Planning Act. Greck and Associates. 2002. Humber River Catchment 13 Floodline Mapping Update.

Prepared for the Toronto and Region Conservation Authority. Greck and Associates. 2003. Preparation of Digital Flood Plain Mapping for the Humber River In

Peel Region. Prepared for the Toronto and Region Conservation Authority. Hatch-Acres. 2005. Preparation of Digital Flood Plain Mapping for the Rainbow Creek Sub-

watershed. Prepared for the Toronto and Region Conservation Authority. HCCL. Humber River Watershed HSP-F Update and Future Scenarios Modelling - Draft Report,

January 2008. Prepared for the Toronto and Region Conservation Authority.


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Hinton M. 1996/97. Geological Survey of Canada. Baseflow Measurement Database. Hinton, M. 1997. Groundwater Discharge in the Humber River Watershed: Preliminary Report.

Prepared for the Toronto and Region Conservation Authority by the Geological Survey of Canada.

Hollis, G. 1975. The effect of urbanization on floods of different recurrence intervals. Water

Resources Research, 11(3), pp. 431-435. JF Sabourin and Associates. 2004. Preparation of Digital Flood Plain Mapping for the Humber

River Watershed in the City of Toronto. Prepared for the Toronto and Region Conservation Authority.

McLaren, T.F. 1979. Hydrologic Model Study Humber, Don and Rouge rivers, Highland, Duffins,

Petticoat and Carruthers creeks. Prepared for the Toronto and Region Conservation Authority.

Metropolitan Toronto and Region Conservation Authority (MTRCA). 1959. Plan for Flood Control and Water Conservation.

Metropolitan Toronto and Region Conservation Authority (MTRCA). 1980. Watershed Plan -

Flood Control Program. Metro Toronto and Region Conservation Authority (MTRCA). 1997. Legacy: A Strategy for a

Healthy Humber. Prepared for the Humber Watershed Task Force. Ontario Ministry of the Environment (OMOE). 1991. Interim Stormwater Quality Control

Guidelines. Ontario Ministry of the Environment (OMOE). 1994. Stormwater Management Practices

Planning and Design Manual. Ontario Ministry of the Environment (OMOE). 2002. Permit to Take Water Database. Ontario Ministry of the Environment (OMOE). 2003. Stormwater Management Planning and

Design Manual. Pilgrim, D.H., and I. Cordery Flood Run-off, in Handbook of Hydrology, ed. by D.R. Maidment,

McGraw-Hill Inc., New York, pp. 9.1-9.42, 1993. Proctor and Redfern Ltd. 1979. Floodline Mapping of the Humber River. Prepared for the

Metropolitan Toronto and Region Conservation Authority. Shuster, W.D., J. Bonta, H. Thurston, E. Warnemuende, and D.R. Smith. 2005. Impacts of

impervious surfaces on watershed hydrology: A review. Urban Water Journal, Vol. 2(4), pp. 263-275.


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Toronto and Region Conservation Authority (TRCA). 2004. Low Flow Measurements in the Humber River Watershed.

Toronto and Region Conservation Authority (TRCA). 2004. Water Use Assessment in the

Humber River Watershed

Toronto and Region Conservation Authority (TRCA). 2005. Flood Vulnerable Areas and Roads Database.

Toronto and Region Conservation Authority. 2007. Listen to Your River – A Report Card on the

Health of the Humber River Watershed. Prepared for the Humber Watershed Alliance. Toronto and Region Conservation Authority. 2008. Humber River State of the Watershed

Report – Geology and Groundwater Resources. Terzi, R.A. 1981. Hydrometric Field Manual – Measurement of Stream flow. Environment

Canada, Inland Waters Directorate, Water Resources Branch. Ottawa. pp.37. Viessman, W., Lewis, G.L., and Knapp, J.W. 1989. Introduction to Hydrology. 3rd ed. Harper

Collins Publishers, New York. XCG Consultants Ltd., 2003a. Toronto Wet Weather Flow Management Master Plan - Study

Area 3: Humber River. Prepared for the City of Toronto. XCG Consultants Ltd, 2003b. Humber River Watershed HSPF Model 905 Area Improvements.

Prepared for the Toronto and Region Conservation Authority.

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