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

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 This document is intended to be shared for non-commercial use. We are promoting the electronic use of this document to minimize the consumption of paper resources. 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 TRCAs 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.

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