Duffins Creek State of the Watershed Report Surface Water Quantity June 2002

Other topics in this series for both the Duffins Creek and the Carruthers Creek include:

• Introduction • Study Area • Human Heritage • Greenspace, Trails and Recreation • Land Use • Air Quality • Climate • Surface Water Quality • Stormwater Management • Fluvial Geomorphology • Hydrogeology • Aquatic Habitat and Species • Terrestrial Natural Heritage

Cover photographs: The beauty of Duffins Creek in winter.

Photo credit: TRCA

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Toronto and Region Conservation, 5 Shoreham Drive, Downsview, Ontario M3N 1S4 Telephone: (416) 661-6600 • Fax: (416) 661-6898 • www.trca.on.ca Table of Contents

Introduction to Surface Water Quantity ...... 2

Current Conditions ...... 4 Physical Characteristics ...... 4 Watershed Response ...... 6 Stream Gauges ...... 7 Flooding ...... 9

Summary ...... 13

References ...... 14

Figures Figure 1: The Hydrologic Cycle ...... 3 Figure 2: Duffins Creek Watershed, Municipal Boundaries and Physiographic Regions ...... 5 Figure 3: Duffins Creek and the Don River, May 12/13, 2000 Storm Event ...... 7 Figure 4(i): Duffins Creek Annual Flow ...... 8 Figure 4(ii): Highland Creek Annual Flow ...... 8 Figure 5: Annual Flow Volumes of the Duffins Creek ...... 9 Figure 6: Stream Gauge Locations – past, present and proposed ...... 10 Figure 7: TRCA Flood Vulnerable Areas – Stage 5 ...... 12

1 Introduction to Surface Water Quantity

Water quantity refers to the drainage of water through the Duffins Creek watershed under various rainfall and snowmelt conditions. There are many complex factors at play in determining the amount of precipitation that eventually ends up flowing in Duffins Creek. These factors include: soil types (with varying abilities to both hold and transfer water), topography, and land use. Obeying the laws of gravity, water above and below the ground surface flows down gradient eventually entering Lake Ontario at the Ajax waterfront.

Figure 1 illustrates the linkages between the major water components of a watershed and the factors or processes controlling this movement of water. A significant component of the precipitation falling on the watershed cycles back into the atmosphere through evaporation or transpiration (moisture released by plants). When the land surface is impermeable (e.g. urban built and paved), surplus water runs directly towards depressions (i.e. ponds, swales, swamps) and streams or evaporates back into the atmosphere. On permeable soils, however, the runoff component of precipitation is very small. Water that remains after evapotranspiration drains overland or into the ground. The subsurface movement of water begins the complex sequence of events associated with the groundwater flow system.

In managing the Duffins Creek watershed, great care is taken to ensure a natural balance to the movement of water. The study of the movement of water through the hydrologic cycle is an important element of our conservation work in the watershed. In the same manner, as one manages household or business finances, the amount of water flowing through the watershed is carefully accounted for in a water budget. As a result, the monitoring of precipitation, along with surface and groundwater levels, is an essential component of water quantity management in the Duffins Creek.

2 Figure 1: The Hydrologic Cycle. Adapted from the Oshawa Creek Watershed Management Plan, Central Lake Ontario Conservation Authority (2001) and Gerber (1999).

Human uses of the watershed can have significant impacts on all of the components of the water cycle, thus altering the water budget. Changes in the volumes and pathways of surface water flowing in the Duffins Creek can alter the size and shape of stream channels, the stability of streambanks, and dependent fish and wildlife habitats. Reductions in groundwater flow systems can have serious consequences to wetlands and aquatic communities (e.g., brook trout) and rural domestic groundwater supplies.

3 Claremont. The southern limit of the till plain is Current marked by steep topographic gradients, which Conditions define the former shoreline of Lake Iroquois. The Lake Iroquois Shoreline is located near the The Duffins Creek watershed, shown in Figure 2, 5th Concession Road which cuts across Pickering is 283 km2 in size and is located east of Toronto and serves as the northern boundary where Ajax within the Regional Municipalities of York and meets Pickering. Approximately 12,800 years Durham. Local municipalities include the City of ago, glacial Lake Iroquois occupied the Lake Pickering, Town of Ajax, Town of Whitchurch- Ontario basin at a time when the Wisconsinan Stouffville, Township of Uxbridge and Town of glacier blocked the St. Lawrence outlet and Markham. water drained to the south-west. The glacial meltwaters overflowed the banks of this basin, so In 1991, The Toronto and Region Conservation that the waters filled what is now the lower third Authority (TRCA) retained Aquafor-Beech of the Duffins watershed. The Lake Iroquois Engineering Limited to undertake a hydrology Shoreline appears today as an irregular line study. This study is currently being updated by broken by strongly developed features such as Aquafor-Beech Engineering. embayments and river mouths, remnants of the once coastal environment. The wave action from Physical Characteristics the waters of this glacial lake deposited boulder pavement or beach gravels along the shoreline The Duffins Creek watershed can be divided into (Chapman and Putnum, 1984). four physiographic regions with distinct topography, soil conditions and range of land surface elevations. The Lake Iroquois Plain is located in the bottom These four physiographic regions include: third of the watershed and consists primarily of a gently rolling till plain. Soils in this region consist • the Oak Ridges Moraine of a mixture of clay, silt and sand deposits, overlaying • the Halton Till Plain the Halton Till. These stone-free lacustrine • the Lake Iroquois Shoreline (lake-bottom) soils are fertile and suitable for • the Lake Iroquois Plain horticulture and have typically fared well for orchard crops. The largest relief is provided by The Oak Ridges Moraine is located in the the deeply incised valleys of Duffins Creek. northern third of the watershed. This region is the headwaters of the Duffins Creek watershed, Duffins Creek has two major branches which join and is a distinctive area of high ridges and approximately one kilometre upstream of sand/gravel hills. Highway 2. The west branch originates northeast of Whitchurch-Stouffville and drains an area of The Halton Till Plain is centrally located in the approximately 135 km2. The east branch originates watershed. Topography is predominantly gently northeast of Claremont in the Oak Ridges Moraine rolling, low-relief hills with the largest relief and drains an area of approximately 143 km2. produced by the incised major stream valleys. Both the east and west branches have a number Sometimes refered to as the south slope of the of tributaries including the following: moraine, the Halton Till Plan contains a variety of soils, some of which have proven to be excellent West Duffins Creek through more than a century of agricultural use. • Stouffville Creek Several large areas with surficial clay deposits are • Reesor Creek located between Whitchurch-Stouffville and • Wixon Creek 4 Figure 2 Duffins Creek Watershed, Municipal Boundaries and Physiographic Regions.

5 East Duffins Creek has happened with other watersheds that are • Mitchell Creek mostly urban. The Duffins Creek watershed is one • Brougham Creek of the last watersheds within TRCA’s jurisdiction • Urfe Creek to exhibit this annual response. Figures 4(i) and • Ganatsekiagon Creek 4(ii) illustrate the differences in annual flow that occurred in 1991 for the Duffins Creek and the highly urbanized Highland Creek watershed. Millers Creek, which originates in the lower eastern The relatively rural Duffins Creek watershed was section of the watercourse, drains a 17 hectare area able to absorb much of the annual moisture. In and joins the main branch between Highway 2 comparison, the highly urbanized Highland and Highway 401. The lower reaches of this 2 Creek watershed has a drainage area of 102 km , watercourse through Ajax have been channelized. of which 85 per cent of the total area is impervious. During a rain or melt event, the surface water In general, watercourse gradients north of runoff is virtually immediate, as evidenced by the Highway 2 are relatively steep and in the order of spikes in Figure 4(ii). one to two per cent. Downstream of Highway 2, watercourse gradients are mild and range from One way of understanding how a watershed 0.1 to 0.5 per cent. responds to changes over time in land use, management practices and precipitation is to Watershed Response plot measurements of total annual runoff. Flow data plotted in Figure 5 indicates that there have The rural nature of the Duffins Creek watershed not been significant charges in the Duffins Creek is clearly demonstrated by the hydraulic response watershed to result in a change in flow volumes. of the basin. This response was specifically observed during a large rainfall event of 50-60 mm that Figure 5 represents the change over time occurred on May 13, 2000. The Duffins Creek associated with the total volume of surface water took approximately 13 hours to peak with flows flow of the Duffins Creek watershed at the ranging from 5-83 cubic metres per second from historical stream gauge locations in the Highway 2 the beginning of the storm to the peak discharge, to Highway 401 reach. As can be seen in Figure respectively. In comparison, an urban watershed 5, the data charted indicate a flat trend line, (the Don River) of similar shape and only a slightly showing that the hydrologic response of the larger drainage area, peaked in approximately Duffins Creek watershed has not been altered 4-5 hours, with flows more than double those of appreciably enough at this point to reflect a change. Duffins Creek. While these watersheds have In other watersheds, such as the Don River, differences (e.g. size), enough physical similarities Highland Creek, Etobicoke Creek and Mimico exist within these basins to demonstrate the Creek, similar charts show definite upward difference in hydrologic response between a trends indicating an increase in the volumes of relatively rural basin like the Duffins Creek and surface flow amounts over time. In the case of one that is predominantly urban. Figure 3 the Don River watershed, volumes have doubled displays the hydrographs for the Duffins Creek over the last 40 years, reflecting the changes and Don River for the May 13, 2000 event. within the hydrologic response by the watershed as a consequence of changing land use. On an annual basis, the Duffins Creek clearly displays the hydrology of a typical rural The Aquafor Engineering Limited (1991) watershed, with the annual peak flow occurring hydrology study evaluated development for two solely in the spring. As a watershed urbanizes, major areas: the Ontario Realty Corporation Lands these peaks in runoff are anticipated to be more (or “Seaton lands”) and the Federal Pickering evenly distributed throughout the entire year, as Airport lands. The modelling results of land use 6 Figure 3 Duffins Creek and the Don River, May 12/13, 2000 Storm Event changes of these two areas show that while local through a private contractor. Historically, the impacts resulted from the development of the Duffins Creek has been the most extensively Seaton lands, no major downstream flooding gauged watershed in Canada, in part due to the impacts would be created, primarily due to the data gathering for either the Pickering Airport timing of the watershed response. However, the lands or for the Seaton land development modelling exercise clearly showed major hydrologic proposals. The five sites monitored by the TRCA changes within the watershed from urban were established in the mid-1990s to provide development of the Pickering Airport lands. The flow data for key subwatersheds draining federal study indicated that flood levels within the and provincial lands. With current resources, Pickering Village area could rise as much as one monitoring is anticipated to continue for only metre, given an uncontrolled urban development one more year unless further funding can be scenario for the Airport lands. Based upon these found. Two new stream gauges were installed in results, future land use changes within the the autumn of 2001, both located within the Duffins Creek watershed need to be carefully Claremont Conservation Area. The first was reviewed and studied in terms of flooding and installed on Mitchell Creek and the second on hydrological impacts. the East Duffins Creek at the confluence with Mitchell Creek. Figure 6 shows the locations of Stream Gauges past, present and proposed stream gauges. Streamflow in the Duffins Creek watershed is currently measured at seven sites. Two sites are maintained and monitored as part of the federal/provincial monitoring network, and the remaining five sites are measured by the TRCA 7 Figure 4(i): Duffins Creek Annual Flow

Figure 4(ii): Highland Creek Annual Flow

8 Figure 5: Annual Flow Volumes of the Duffins Creek, Measured Between Highways 2 and 401.

Flooding indicating a snowmelt or ice jam-related flood. In 1954, Hurricane Hazel produced the most Flooding is a common and natural occurrence in severe flooding in southern Ontario’s recorded all watersheds and should not be prevented from history. The most severe event along the Duffins happening. Problems with flooding arise when it Creek occurred on June 5, 1890. This event poses a risk to human lives or property. The best caused major flooding in the communities of way to prevent these risks is to establish an Greenwood and Pickering Village, with several adequate naturalized valley and stream corridor small dams being washed out and flooding of or floodplain and restrict any development many homes and roads within these communities. activities within this corridor. Hurricane Hazel produced the second most severe flooding event in the Duffins, causing Detailed historic accounts of flooding within the damage to buildings and roads within Stouffville, Duffins Creek watershed are scattered, with the Greenwood and Pickering Village. first recorded flood taking place in the late 1870s. This event occurred on September 13, The 1959 Plan for Flood Control and Water 1878 and involved damages to a mill. Since that Conservation identified no need for flood control time, the majority of flooding events were related works within the Duffins Creek. The only recorded either in the late winter or early spring, works referenced within the creek were recreational 9 Figure 6: Stream Gauge Locations – past, present and proposed.

10 dams proposed upstream of the Village of Green point above the flood-vulnerable area several River and within the Greenwood Conservation hundred metres upstream. While both these Area. Neither of these recreational dams have works provide a high level of protection, both sites been constructed due to the implications for the remain flood vulnerable under a severe Hurricane aquatic habitat and wildlife species. Hazel-type event. This level of protection will have to be reassessed with updated hydrologic, Due to the extensive destruction caused by hydraulic and floodplain mapping. Hurricane Hazel throughout the entire TRCA region, flood protection along the watercourses Floodplain mapping for portions of the Duffins was deemed a necessity and continues to be Creek was originally undertaken in 1965 and based on minimizing damage caused by this type extended and updated in 1979. However, the of severe storm. Flood protection works were mapping has remained relatively unchanged undertaken in the Village of Stouffville and within the basins even with the land use changes Pickering Village areas to relieve the flood threats that have occurred. Therefore, there is a need to at these locations. Works in the Village of update the floodplain mapping in this watershed. Stouffville consisted of a small dam and reservoir Digital mapping will ease the work required for constructed in 1969. A gabion-lined flood any future updates. The TRCA has also identified control channel through the village was the need for more extensive and updated base completed in 1980. These two facilities provide mapping and floodplain mapping for the Millers a high degree of protection. Creek tributary because little mapping currently exists for the area. In Pickering Village, which is located at the confluence of the east and west tributaries of The current hydrology, hydraulics and floodplain Duffins Creek, a series of flood protection dykes mapping identify the potential locations of flood were constructed in 1982-83 to provide flood vulnerability within the watershed. Current protection to the community. Two dykes were mapping reveals approximately 64 structures and built, one from Brock Road east to the confluence 55 roads where flooding can still be anticipated. and then south connecting to Highway 2. The These flood-vulnerable areas can be seen on second dyke was constructed on the east side of Figure 7, however, these areas may change with the main branch of the creek from just above the the anticipated 2002 mapping update. creek’s crossing under Church Street to a high

11 Figure 7: TRCA Flood Vulnerable Areas – Stage 5. Current mapping reveals approximately 64 structures and 55 roads where flooding can still be anticipated.

12 Summary

The Duffins Creek watershed has a healthy flow regime with respect to flooding and water quantity. It is one of the last watersheds within the TRCA’s jurisdiction that exhibits typical rural watershed characteristics. Factors that contribute to this condition include the small amount of urbanization, the large number of natural features, the predominance of sandy soils, and the extensive forest cover and wetlands. All of these features result in the promotion of infiltration, and the reduction of stormwater runoff.

Historical accounts of flooding within Duffins Creek are scattered and rare. Flooding that has occurred has been principally due to ice jams and large storm events. Current mapping reveals that 64 structures and 55 roads are susceptible to flooding. These flood-vulnerable areas will be evaluated with future growth scenarios.

An extensive stream flow monitoring network has been established in this watershed. This network, coupled with low flow investigations and a detailed understanding of the hydrogeology, geology and geomorphology, provides an excellent position from which to manage the water resources of Duffins Creek.

The Toronto and Region Conservation Authority has recently undertaken an update to the watershed hydrology model and is developing a water budget model for the entire Duffins Creek watershed. These studies, along with the monitoring data, will be used to establish infiltration targets, flood and erosion control criteria as well as to design stormwater management systems.

13 References

Aquafor Engineering Limited, 1991. Duffins Creek Watershed Study, Phase 1: Hydrology. A Final Report for the Metropolitan Toronto and Region Conservation Authority.

Central Lake Ontario Conservation Authority, 2001. Oshawa Creek Watershed Management Plan (Existing Conditions Report). Draft, May 2001. Oshawa, Ontario.

Chapman, L.J. and Putnum, D.F., 1984. The Physiography of Southern Ontario. Third Edition. Ontario Geological Survey, Special Volume 2.

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