Duffins CreekState of the Watershed Report

Fluvial GeomorphologyJune 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� Surface Water Quantity� Stormwater Management� Hydrogeology� Aquatic Habitat and Species� Terrestrial Natural Heritage

Cover photographs: Meandering Stouffville Creek in winter, just south (downstream) of Stouffville.Inset: Bank erosion by West Duffins Creek near Whitevale and the Seaton Trail.Photo credit: TRCA

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Toronto and Region Conservation, 5 Shoreham Drive, Downsview, Ontario M3N 1S4Telephone: (416) 661-6600 � Fax: (416) 661-6898 � www.trca.on.ca

Prepared by:John Parish of Parish Geomorphic Ltd.and Bruce Robertson of the Ministry ofNatural Resources for the Toronto andRegion Conservation Authority.

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Table of ContentsIntroduction to Fluvial Geomorphology . . . . . . . . . . . . . . . . . . . . . . . .2Characterization of the Watershed . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3Basin Scale Geomorphological Assessment . . . . . . . . . . . . . . . . . . . .5Channel Function of Duffins Creek and its Tributaries . . . . . . . . . . .8

Channel Stability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8Existing Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8Channel Erosion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13

Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16Table and Figures

Table 1: Channel Characteristics for Various Streams of the Duffins Creek Watershed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10

Figure 1: Three levels of Geomorphic Investigation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4Figure 2: Digital Elevation Model of the Duffins Creek Watershed. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6Figure 3: Slope Model of the Duffins Creek Watershed. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7Figure 4: Drainage Area vs Bankfull Using Data from the Wilmot Creek

Watershed, East GTA Streams and Streams located in the Duffins Creek Watershed. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9

PhotographsPhoto 1: Ganatsekaigon Creek Upstream of Taunton Road. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11Photo 2: Urfe Creek Downstream of Taunton Road. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11Photo 3: Spring Creek Upstream of Highway 7. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12Photo 4: West Duffins South of Highway 7. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12

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Introduction to FluvialGeomorphologyWe all recognize that water moves downhill and that the more waterthere is, the deeper and faster it travels. Some of us have played withmoving water, such as temporarily blocking the flow of small runoffchannels (e.g., on driveway, garden) to observe what happens. If welooked carefully, we would find different flow patterns and changes inthe speed of flow, sometimes even causing some dirt to be moved. Thisis essentially the science of fluvial geomorphology.Fluvial geomorphology is a science that assesses the shape and form ofwatercourses. A key component of the science is identifying theprocesses responsible for the form of the channel. There are manydifferent processes that may be at work within channels. The mostimportant of these are physical, namely the movement of sediment(e.g., silt, sand, gravel) and water. Application of fluvialgeomorphology is beneficial to watershed studies as the processes atwork within the channels can be identified and quantified. Thisprovides a better understanding of the form (shape and pattern) andfunction of the stream system. This understanding can be used alongwith knowledge from other disciplines such as hydrology and biologyto assess the implications of change. Therefore a multi-disciplinaryapproach that includes fluvial geomorphology can be drawn upon todevelop guidelines for proposed land use changes that will promoteintegrated management and minimize changes to existing processes.

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Characterizationof the WatershedUnderstanding the fluvial geomorphology of awatershed involves examination of the watershedat various spatial and temporal scales. This isnecessary due to the natural complexity of streamsystems. The three common levels of examination,as shown in Figure 1, are the watershed, followedby stream reaches and then the site or channelcross-section scale. A stream can be influencedby the upstream drainage basin (spatial effect)and changes that have occurred in the past(temporal effect). It should be recognized thatthe dynamic response of a channel to a changecan take years to decades to be fully experienced.In other words, the fluvial geomorphology of awatercourse is part of a series of linkages orrelationships that compose the stream ecosystem.These linkages can be seen in many directionsthrough a watershed. For instance, longitudinalor long profile linkages (following the trend ofthe watershed) include the flow and movementof water, movement of sediment and locations ofsediment supply (e.g., eroding banks) andlocations of sediment storage (e.g., point bars).Lateral linkages are generally seen at the reach orcross-section scale and incorporate the tablelands, valley side slopes and riparian vegetation.Through these linkages, food and energy issupplied to the stream and distributed by theflowing water. Another linkage is a vertical flowand encompasses the interaction between surfacewater and ground water.At the watershed scale (the upstream basin),controls and modifying factors that influenceprocesses operating in the drainage basin can beidentified and assessed. Geology and climateexert the principal controls on the function andform of a drainage basin. The controls of geologyand climate are modified by other factors presentin the watershed. Climate controls the amount of water deliveredto the drainage basin and how and when it is

delivered. Typically, this results in high flowevents in the spring in conjunction withsnowmelt, while low flow conditions characterizewinter and summer. Most of the precipitation inthe basin is due to convection and frontal airmass activity, producing rainfall events in the falland summer (please see the Climate chapter fora more thorough discussion). Geology exerts a fundamental control on howthe water, once supplied to the watershed fromthe local climate, is delivered to the stream.Properties, described in the Hydrogeologychapter, such as infiltration, evapotranspirationand runoff are applicable here in order tounderstand what the water does once it reachesthe watershed. In general, the geology of thewatershed affects the drainage pattern, thevolume and properties of sediment supplied tothe channel, and the erosion and transportpotential of the creek. One of the means ofassessing the effect of climate and geology aremorphometric analyses, which are variousparameters measured at the watershed scale thatprovide a means of explaining how surface watertravels through watersheds. The next scale of analyses focuses on streamreaches, which are lengths of channel exhibitingsimilar physical characteristics (e.g., slope,planform). At the reach scale, detailed mappingand historic assessments are completed. Theseprovide insight into how the channel haschanged over time and allow a broad levelidentification of channel adjustments, such asrates of erosion and migration patterns. At thesite or cross-section scale, an assessment wouldinclude field investigations to examine thephysical characteristics of the river�s form, andgreater detail on properties comprising thechannel, such as bed and bank material. Elements within the watershed can modify thecharacteristics of the drainage basin that arecontrolled by geology and climate. Theseelements can be divided into either natural orunnatural factors. Natural modifying factorsinclude debris dams from the accumulation of

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woody material, beaver activity, and the extentand quality of the riparian vegetation (e.g., trees,shrubs and grasses that are adjacent to achannel); these factors tend to be temporary.Ponds or backwater areas behind debris dams orbeaver dams are zones of deposition. Accordingly,the area downstream of the dam has an increasedcarrying capacity, which may lead to increasederosion. These dams and associated backwaterareas modify the drainage process and may causeshifts in channel pattern. Modifying effects ofriparian vegetation include the ability to protect

the channel banks (i.e. root depth, root density),resulting in narrower, but deeper channels thanwould normally be expected given flowsproduced from the upstream area. This isespecially true in meadows, where the rootdensity from grasses and sedges is greater thanroots from mature trees. Unnatural modifying factors, such as changes inland use, tend to be more permanent and,consequently, produce a more dramatic influenceon the receiving streams. Land use in the basin

Figure 1Three levels of geomorphic investigation.

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primarily affects the hydrological cycle byinfluencing the amount of runoff, infiltration andevapotranspiration. Changes in land use andriparian vegetation within the basin, andespecially along the stream corridor, can affectthe intricate functions between the channel andits floodplain, as well as the primary functionsregarding the movement of water and sediment.

Basin ScaleGeomorphologicalAssessmentThe Duffins Creek basin extends from the southslope of the Oak Ridges Moraine to itsconfluence with Lake Ontario in the Town ofAjax. As described in an earlier chapter, thegeology or physiography of the basin is quitecomplex. This complex geology is also seen inthe topography (Figure 2) and slope classification(Figure 3) maps. These figures are the product ofa computed Digital Elevation Model (DEM)from 1:50,000 topographic mapping.The DEM was used to better understand thecurrent morphometric parameters at thewatershed scale. As discussed in the previoussection, morphometric analyses provide a meansof assessing how surface water travels throughthe basin. Two of the main parameters aredrainage density and the bifurcation ratio.Drainage density is a ratio of the total length ofall streams divided by the drainage area. Thusthe more streams within the watershed, thehigher the value. Bifurcation ratio measures thedegree of branching from the all the tributariesin the watershed. Results indicated that thedrainage density is relatively low at 1.5. This lowvalue is appropriate given the extent of sand andgravel within the watershed, which permits moreinfiltration and less runoff, accounting for fewersurface channels. The bifurcation ratio is also low(2.2), indicating that the basin has numeroustributaries and is well branched and distributed.These values provide some insight into the

movement of water through the basin. A typicalstorm hydrograph would be more broad andelongated as the tributary network drains theland. It should be noted that if the land use werechanged, such that there would be more runoff(i.e. urbanization), the hydrograph would changeas, typically, there would be higher peaks andlower baseflow.The Duffins Creek watershed is comprised ofseveral prominent tributaries. Reesor Creek islocated along the northwest margin of the basin.Just to the west is West Duffins Creek. Bothcreeks are similar with respect to physicalcharacteristics. Reesor Creek, due to the growthof the village of Stouffville, has experienced someadjustment in its flow regime. Between WestDuffins Creek and the main branch of DuffinsCreek, are Ganatsekaigon, Urfe and Broughamcreeks. These three tributaries all have similarlysized drainage areas and geology, but have quitedifferent physical characteristics, due largely tochanges in land use. The larger the watershed,the more gradual the effects of changing landuse. Therefore, Reesor Creek may quicklyundergo some change due to the growth ofStouffville, while Duffins Creek, which has moreurbanization, would not necessarily experience thesame effects to the relative proportion of urbanarea to basin size and due to the location of theurban areas. Urban growth in the headwaterareas is generally more detrimental than urbangrowth near the lower end of the watershed.

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Figure 2Digital Elevation Model of the Duffins Creek Watershed. The elevation ranges from approximately 78 metresabove sea level at the lake to approximately 405 metres above sea level on the moraine.

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Figure 3Slope Model of the Duffins Creek Watershed. The model indicates areas of steeper slope. However this is derived from asurface with and accuracy of perhaps +/- 5m. Generally steeper slopes exist in a band across the mid-southern extentand up to the north-eastern extent.

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Channel Functionof Duffins Creekand its TributariesThe main geomorphological function of allwatercourses is the efficient movement of waterand sediment through the system. This functionentails both conveyance and storage components,which are critical to the healthy function of thestream. The term �efficient� is used to describe akey concept relating to the use of energy by astream. A stream will find a shape, form or patternthat permits the necessary movement of waterand sediment, with the energy available (e.g.,slope). When this occurs, the system is referredto as being in a state of dynamic equilibrium. Channel StabilityDynamic equilibrium is generally synonymouswith channel stability and suggests a channelform (planform and cross-section) that is inbalance with the flow and sediment regimes thatare operative within the system. Further, as theword �dynamic� infers, it is understood that thechannel will shift and adjust to variations ineither sediment or flow, but remains within sometheoretical threshold limit. Once this limit isexceeded, a substantial channel adjustment isnecessary and it enters a period of instability as ittries to regain a dynamic balance. When changesoccur in one of the parameters that influencechannel form, then the channel will makeadjustments through one of its degrees offreedom. Channel gradient is one of these degreesof freedom, although a change in gradient isunlikely to occur as quickly as changes to channelcross-sectional area. This concept was expressedby Mackin (1948) who described a �gradedstream� as follows:

A graded stream is one in which, over a period ofyears, slope is delicately adjusted to provide, withavailable discharge and with prevailing channelcharacteristics, just the velocity required for the

transportation of the load supplied from thedrainage basin. The graded stream is a system inequilibrium.

Based on this definition, it is implied that achange in a stream�s discharge or sediment supplycan result in a dramatic change in the gradientand, if possible, the substrate within the channel.Existing ConditionsIt should be stated that most streams in southernOntario have been altered and consequently havebeen experiencing various levels of adjustment.It is important to understand these fundamentalconcepts of fluvial geomorphology, such that someinterpretation is possible when looking at data fromthe Duffins Creek watershed. Through reviewingvarious existing reports, some geomorphologicaldata were found, which provided some insight onthe physical characteristics of the variouswatercourses. Due in part to the complexity of the underlyinggeology and land use distribution, the movementof water and sediment through the system is quitevariable. For example, in the GanatsekaigonCreek and Urfe Creek catchments, which have asimilar geology, but different land use practices,the movement of water and sediment throughthem varies. The reverse is also true, in thatcatchments with similar land use but differentgeology will produce different channel forms. From a basin perspective, the use of regionalcurves or databases can provide some insight intothe delivery and movement of water through thesystem. A regional curve illustrating therelationship between upstream drainage area andbankfull flow is shown in Figure 4. Bankfull flowis a flow stage that exerts the most influence onchannel form. Typically, this discharge occurs onceevery year to once every two years in a naturalenvironment. The data shown in Figure 4 comefrom a variety of sources. Fluvial geomorphologicaldata from the Duffins Creek watershed wereavailable from two reports, one by ORTECH(1997) on the Seaton Lands and the other from

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PARISH Geomorphic (1999) on proposedstream crossings of Highway 407. These data areplotted against regional data from Wilmot Creek(Robertson et al., 1999) and from data collectedby PARISH Geomorphic over the last few yearsin the eastern part of the GTA (from the RougeRiver eastward to Harmony Creek in Oshawa). The relevance of the regional data is that itrepresents other systems with similar geologicand physiographic settings. While the WilmotCreek data primarily represent a rural land use,the GTA East data include both rural and urbansites, which largely explains the differences in thetrend line from these two sets of data.Specifically, the plots indicate that streams fromthe GTA East data set receive more water from asmaller drainage area, a function of impervioussurfaces. Another important observation fromFigure 4, is the variability in the data, whichsupports the discussion regarding how differentgeology and land use can influence the amountof water moved through the system. In all threedata sets, when looking at one drainage area, arange in discharge of three-to ten-fold can beseen. From Figure 4 it is apparent that the Duffinsdata are quite similar to the GTA East values,

suggesting that the basin characteristics are lesslike Wilmot Creek. Caution should be usedwhen reviewing the Duffins data, as it is fromonly nine sites in the central part of the basin. The data plotted in Figure 4 are presented inTable 1. Review of the actual data is useful to obtaina better understanding of some of the channelcharacteristics within the Duffins Creek basin.While the data come from four different catchments,there are some similarities. First, the gradient fromthese sites is fairly steep, except the West Duffinssite AL1630. The sites lie between Highway 7and Rossland Road and, as a consequence, crossesthe glacial Lake Iroquois shoreline. This steepertopography is shown in Figures 2 and 3, whichalso indicate that other parts of the basin exhibitfairly steep gradients. Another similarity is thesize of substrate materials, which is typically smallto large gravel, a reasonable reflection of theunderlying geology. Some of this similarity is seenin the attached photos. The substrate seen inPhoto 1 from Ganatsekaigon Creek and Urfe Creek(Photo 2) is quite similar. Photo 3 from SpringCreek (a tributary of Brougham Creek) illustratesa narrow creek width and the abundantherbaceous vegetation that lines the channel.

Figure 4Drainage area vs bankfull using data from the Wilmot Creek Watershed, East GTAStreams and Streams located in the Duffins Creek Watershed.

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Within the Seaton Lands Study (ORTECH,1997) is a description of the Ganatsekaigon, Urfeand Brougham creeks. The basins of these creekshave similar geology and drainage area.Unfortunately, Urfe does not have coldwaterfishery and water quality is more suspect. From afluvial geomorphology perspective, there may bean explanation. Land use practices within theUrfe Creek basin have been more detrimental tothe channel. This includes some realignment and

removal of riparian vegetation. Further, therehave been numerous ponds constructed alongthe creek. Removal of riparian vegetation canlead to more sediment entering the stream, asthere is less vegetation to trap material; less foodand nutrients reaching the creek; and more solarradiation reaching the creek, thereby raising watertemperatures. The ponds regulate flow, disruptsediment transport and increase water temperature.

Table 1: Channel Characteristics for Various Streams of theDuffins Creek Watershed

Creek Name Bankfull Drainage Substrate Bank GradientArea (km2) (D50-cm) (%)

Width Depth Discharge Height Angle(m) (m) (cm) (m) (º)

West Duffins Creek 11.33 0.50 8.07 99.08 5.9 0.86 41.6 0.31

(south of Hwy 7) West Duffins

Creek 11.40 0.72 23.00 108.00 3.2 N/A N/A 1.88(north of Taunton) West Duffins Trib.(south of Hwy 7) 3.67 0.28 1.62 2.42 5.5 0.69 44.4 1.67

Urfe Creek(near Hwy 7) 3.16 0.29 1.46 2.99 7.5 0.58 36.9 2.11 Urfe Creek

(south of Taunton) 8.40 0.52 3.80 10.84 3.5 N/A N/A 3.04 Urfe Creek

(north of Rossland) 3.60 0.53 4.70 13.33 1.4 N/A N/A 1.55 Ganatsekaigon

Creek 5.39 0.69 3.80 10.50 0.89 N/A N/A 1.91 (south of Taunton)

Ganatsekaigon Creek 4.99 0.35 2.60 6.50 3.4 N/A N/A 1.73

(north of Taunton)Spring Creek

Tributary 2.97 0.38 1.73 1.56 0.049 0.73 49.4 1.79

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Another result from the Seaton report discussedthe hydraulic geometry of the streams. Hydraulicgeometry is a series of relationships that help toexplain and predict the dimensions of the channelas discharge increases. The report found that asdischarge increases, there is an increase in channelwidth and depth, but a much more pronouncedincrease in flow velocity. This is important tounderstand, as with higher flows, these creekscan be quite effective in transporting sediment,due to the higher velocities. Therefore, if flowswere to change due to changes in land use, thecreeks could rapidly adjust and perhaps degrade. Channel degradation was not restricted to UrfeCreek, as reaches on Ganatsekaigon, Whitevaleand Brougham creeks were noted asexperiencing problems (ORTECH, 1997). Theseproblems were mainly in headwater areas ortributaries that had been straightened andriparian vegetation removed. Some degradationwas also observed approaching the urban areaalong Ganatsekaigon Creek. Urban problems are

Photo 1Ganatsekaigon Creek upstream of Taunton Road.Note the coarse substrate and low banks.

Photo 2 Urfe Creek downstream of Taunton Road. Note the coarse substrate and wood debris.

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Photo 3Spring Creek (a tributary of Brougham Creek) upstream of Highway 7. Note the dense vegetation.

Photo 4West Duffins south of Highway 7. Note the stratified layers of the eroded bank.

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typically associated with a changing flow regime,where more runoff volume enters the creek,leading to adjustments such as increasing cross-sectional area. These adjustments result in morebank erosion and bed scour. Additional problemsinclude confining the creek, thereby removing itfrom its floodplain and lining the creek witherosion control structures, which in turn reducesediment supply. Both of these problems result inmore energy within the stream, furtherexacerbating the initial impact. It should be reiterated that there is very littlegeomorphic information available for the DuffinsCreek system. With each passing year, more localstudies will likely be completed, but a broaderbasin-scale perspective will be lacking. Aconcerted effort is necessary to provide a moreholistic understanding of the basin. This could bereadily applied to management decisionsregarding resources and natural ecosystems.

Channel ErosionA detailed review from the Seaton Lands Study(ORTECH, 1997) revealed several findings thathelp to describe the fluvial geomorphology of thestreams within the Duffins Creek basin. Forinstance, bank erosion is an active process,especially along West Duffins Creek, south ofHighway 7, where numerous erosion scars arepresent as the creek meanders into the highvalley walls (Photo 4). These large erosion sitesshould not initially be considered as excessive ora negative feature. All stable creek systems erode(e.g., eroding banks, bed scour). Erosion isnatural process that helps deliver sediment to thesystem. Sediment supply, transport, anddeposition is necessary to help the creek systemdissipate stream energy and maintain a balancebetween flow and channel form. Channel erosion can be the result of numerousprocesses. Obviously, flowing water and thehydraulic processes active on the bank can be apowerful force. Erosion can also result fromgeo-technical processes causing slope failures. Ice

and freeze-thaw cycles can also produce erosion.Eroded banks can provide information on thehistory of the valley. These observations may alsohelp explain historical influences on the localecosystem. As shown in Photo 4, different layersof material in the bank can be seen. This includesa layer of gravel that may have been the oldstream bed, at some past period, at a higherelevation. Eroded banks can also reveal areas ofgroundwater discharge. This observation suggeststhat groundwater is likely reaching the channel,which has implications on water quality andaquatic habitat. The presence of groundwaterdischarge in a bank can also indicate a cause oferosion as the saturated material is typicallyweaker and more prone to failure.

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SummaryFluvial geomorphology is a science that assesses the shape and form ofwatercourses. Application of fluvial geomorphology is beneficial to watershedstudies as the processes at work within the stream system can be identified andquantified. This understanding can be used in conjunction with other disciplinesto assist in developing guidelines for watershed management (i.e. existing landuses, proposed land use changes) to ensure existing processes with stream andriver systems are not impacted.Understanding the fluvial geomorphology of a watershed involves theassessment of various spatial and temporal scales occurring at the watershed orbasin level, stream reach scale and site or channel cross-section level. Climateconditions and basin geology are the primary factors that influence the processesaffecting the form and function of a drainage basin. Additional natural andhuman factors that can also impact or modify the characteristics of a drainagebasin can include beaver activity and the location and extent of riparianvegetation as well as the construction of dams, weirs and channelization.Changes in land use through urbanization of rural areas as well as agriculturalland use practices can also impact the form and function of streams and rivers.In order to understand these processes, a �morphometric� analysis is typicallycompleted to understand, at a basin scale, how climate influences the amountand distribution of water to the system (eg., rainfall and snow, location ofprecipitation, etc.) and how basin geology affects how the water is deliveredthroughout the basin (eg., drainage pattern, erosion and sediment supply, etc.).�Stream reach� assessments are completed which group channels into likereaches based on similar characteristics (eg., slope, planform). Reaches are thenexamined using detailed topographic mapping and historical information (i.e.aerial photographs) in order to gain insight into broad level channel adjustmentssuch as rates of erosion and migration patterns. Site, or cross-section informationis also compiled using data collected through field investigations in order toprovide further information on the physical characteristics of a watercourse suchas channel bed and bank material.A morphometric assessment was carried out for the Duffins Creek watershedusing available background information including topographic mapping, digitalelevation model (DEM) and surficial geology and surficial soils information. Twomain parameters used to characterize basin geomorphic conditions are drainagedensity and bifurcation ratio. A low drainage density value of 1.5 calculated forDuffins Creek watershed (i.e. total stream length over the basin area) isappropriate given the extent of sand and gravel within the basin which permitsgreater infiltration and a lower number of surface channels. The bifurcation ratioof 2.2 (i.e. degree of branching of tributaries) calculated for Duffins Creekwatershed is also low, which indicates numerous, well-branched tributary systems.

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A review of limited background information collected at nine locationswithin the southern portion of the watershed (i.e. Highway 7 to RosslandRoad) provides some additional geomorphic information. A comparison ofthis data with regional curves developed from collected information onstreams within the eastern Greater Toronto Area indicates a generalsimilarity. A review of bed slope and substrate material at these locationsalso indicates some consistency between tributaries located within thesubject reach. Notwithstanding, varying levels of channel degradation havebeen identified between tributaries such as Urfe, Ganatsekiagon, Whitevaleand Brougham creeks and can be attributed to previous modifications thathave been carried out within each subwatershed (eg., channel straightening,loss of riparian vegetation, construction of on-line ponds, etc.).Background data also confirms the presence of channel erosion alongportions of West Duffins Creek south of Highway 7. Factors attributing tothe erosion are a result of natural processes and stresses working on thebanks (e.g., weathering, high flows). Human activities may also contributeto accelerated erosion through urbanization, channelization and continuedagricultural practices carried out within the upstream basin.In summary, the geomorphic information available for the Duffins Creekwatershed is limited and somewhat site specific. As a result, further workwill be required to complete a basin-level assessment required to formulatefuture management decisions regarding resources and natural ecosystems.

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ReferencesMackin, J.H., 1948. Concept of the Graded River. Bulletin of the Geological

Society of America. 59: 463-512.ORTECH, 1997. Fluvial Geomorphology Baseline Study: Seaton Lands.

Submitted to the North Pickering Development Corporation. ReportNo. 96-T13-U004961-018.

PARISH Geomorphic Ltd., 1999. Highway 407 East � Markham Road to Eastof Brock Road Fluvial Geomorphology Assessment. Submitted to DillonConsulting Ltd. Report No. 98-007.

Robertson, B.L., C.H. Taylor and J.M. Buttle, 1999. A Comparison of theHydraulic Geometry Between a Low-Energy and a High-Energy DrainageSystem. Abstract from the 25th Annual Canadian Geophysical Unionmeeting, Banff.