a comparison of methods for evaluating instream flow ...

RIVER RESEARCH AND APPLICATIONS

River Res. Applic. 19: 123–135 (2003) Published online in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/rra.701

A COMPARISON OF METHODS FOR EVALUATING INSTREAM FLOW NEEDS FOR RECREATION ALONG RIVERS IN SOUTHERN ALBERTA, CANADA STEWART B. ROOD,a * WILCO TYMENSENb and RON MIDDLETONc b

a Department of Biological Sciences, University of Lethbridge, AB, Canada T1K 3M4 Chinook Environmental Resources, RR9 Site 1 Box 1, Lethbridge, AB, Canada T1J 4R9 c Alberta Transportation, Edmonton, AB, Canada T6B 2X3

ABSTRACT Four methods were compared for determining recreational instream flow needs (R-IFN) for paddling canoes, kayaks and rafts on ten river reaches in the Oldman River Basin of southern Alberta. Two flow criteria were evaluated: ‘minimal flow’—the low flow that still provides a reasonable quality river trip; and ‘sufficient flow’—the lower end of the favoured flow range. A voluntary, mail-in user survey from 1983 to 1997 produced 394 responses (4251 paddler days) relative to flow suitability. An expert judgment approach considered flow recommendations from three regional paddling guides that were considered comprehensive and credible. A flow comparison involved about 20 paddle trips per reach by the authors with differing groups, boats and flows. These subjective approaches produced quite consistent results (r 2 = 0.63) and these were compared to results from an objective, hydraulic modelling method, the ‘depth, discharge method’ (DDM), that applied stage–discharge functions to determine flows that would satisfy depth criteria of 60 and 75 cm. The DDM minimal flows were closely correlated with the means of the subjective methods (r 2 = 0.73). Thus, all four approaches produced generally consistent results, indicating that all methods were valid. Typical minimal and sufficient flows were about 15 and 30 m3 s−1 , respectively, for the medium-sized river reaches that had average annual discharges (mean Q) of about 20 m3 s−1 . A close correlation (r 2 = 0.90) between the minimal flow and mean Q suggests that mean Q can provide an initial estimate for R-IFN for rivers of this type and size. We recommend that R-IFN studies commence with the DDM since it is quick, inexpensive and objectively defensible. This would provide guidelines for subsequent subjective assessments that should involve more than one approach to increase the breadth of subjective consideration. Copyright  2003 John Wiley & Sons, Ltd. KEY WORDS:

instream flow needs; paddling; recreation

INTRODUCTION In recent years there have been major changes in the appreciation of environmental, aesthetic and recreational values provided by rivers (Gillilan and Brown 1997; Jackson et al., 2001). In Alberta, Canada, changes in public opinion were particularly catalysed by the controversy surrounding the Oldman River Dam that impounded reaches of the Oldman, Castle and Crowsnest rivers in southwestern Alberta in 1993 (Figure 1). During that controversy, it became clear that non-consumptive uses of Alberta’s streams were poorly understood and that this hindered comprehensive river resource management. The concept of instream flow needs (IFN), flows that were required particularly for environmental aspects such as fisheries, water quality, and riparian ecosystems, have also emerged as prominent concerns. Analyses of environmental IFN were considered in the development of the operations plans for the Oldman Dam (Rood et al., 1998) and such analyses also led to changes in river regulation along adjacent streams (Rood and Mahoney, 2000). * Correspondence to: Stewart B. Rood, Department of Biological Sciences, University of Lethbridge, Lethbridge, AB, T1K 3M4, Canada. E-mail: [email protected] Contract/grant sponsor: Natural Sciences and Engineering Council of Canada.

Copyright  2003 John Wiley & Sons, Ltd.

Received 16 May 2001 Revised 18 February 2002 Accepted 22 March 2002

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Figure 1. Map of southern Alberta showing principal rivers including the Oldman River tributaries and other streams that were investigated in the present study. Triangles indicate major dams. For the southern tributaries of the Oldman River, L and U indicate lower and upper, respectively

However, IFN for other non-consumptive uses were often neglected and in the 1980s we recognized that the consideration of recreational uses in flow scenario evaluation was hindered by the lack of understanding of recreational instream flow needs (R-IFN). R-IFN methodology has lagged behind environmental IFN analyses and in the early 1980s there were no broadly accepted methodologies. Consequently, as an initial investigation, Alberta Environment sought to gather input regarding flow sufficiency for recreation and established a voluntary, mail-in user survey programme that commenced in 1983. The survey continued through to 1997 but there have been criticisms of this survey method and concerns about the defensibility of a solely subjective approach. Through the 1990s, a number of approaches were developed to evaluate R-IFN, particularly for regulated rivers in the western United States (Brown et al., 1991; Shelby et al., 1992b). The general approaches have been reviewed by Shelby et al. (1992a) and Whittaker et al. (1993) and may be broadly categorized as subjective approaches that investigate human use or preference, or objective approaches that involve analyses of physical stream characteristics. The subjective approaches are diverse and can involve analyses of historical use, judgment by one or more experts, or survey approaches that involve input from many users (Whittaker et al., 1993; Shelby and Whittaker, 1995). A specialized survey approach is the ‘controlled flow study’ or ‘systematic field evaluation’ that involves comparisons of suitability under different flows that are deliberately provided (Giffen and Parkin, 1993; Shelby et al., 1998). The objective approaches often involve hydraulic modelling to determine the discharges that provide appropriate depth, width, velocity and/or other physical characteristics. A number of previous researchers Copyright  2003 John Wiley & Sons, Ltd.

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have applied such methods for R-IFN analysis and Whittaker et al. (1993) categorized these approaches as ‘prediction-based modelling methods’. The prior methods by Tennant (1976) and Corbett (1990) sought simple quantitative relationships that would identify particular proportions of mean annual flow that would offer suitable conditions for recreational boating and other uses. Whittaker et al. (1993) conclude that these approaches offer useful initial estimates but have significant weaknesses, and Burley (1990) provides additional reasons why simple R-IFN methods would fail. Subsequently, more sophisticated hydrometric methods have involved approaches such as instream flow incremental methodology (IFIM), in which depth, width and velocity criteria are applied and changes in usable areas satisfying these criteria are determined for different discharges (Whittaker et al., 1993). Previous studies usually applied a single approach for R-IFN determination and consequently the consistency and accuracy of different approaches have only occasionally been considered (Clipperton, 1998). During the collection of the 1983 to 1997 mail-in user survey for the streams in southern Alberta we recognized an opportunity to compare this survey approach with other subjective and objective methods. Consequently, the present study was conducted to assess, compare, and develop different subjective and objective methods for RIFN determination. It simultaneously applied these methods to define R-IFN for the rivers of the Oldman River Basin and thus contributes information for a current comprehensive assessment of river resource management in southern Alberta.

MATERIALS AND METHODS The study investigated all of the rivers of Oldman River Basin and the adjacent Milk River of southwestern Alberta, Canada (Figure 1, Table I). There are three large dams in the Oldman Basin and additional weirs (lowhead dams) and these are primarily managed to permit water storage and diversion for agricultural irrigation. Hydrologic data Historical discharges (Q) were obtained for the river reaches from HYDAT, the Water Survey of Canada hydrologic database. Discharge data involved daily mean flows that were considered appropriate since no hydroelectric dams exist that would impose diurnal flow pulsing. Table I. Characteristics of river reaches of the Oldman River Basin and the Milk River, Alberta. The rivers are sequenced north to south and then west to east. Grade of difficulty is in accordance with the International Canoe Federation difficulty classification Discharge (mean Q) (m3 s−1 )

Upper Oldman Middle Oldman Lower Oldman Willow Creek Crowsnest Carbondale Castle Upper Waterton Lower Waterton Upper Belly Upper St. Mary Lower St. Mary Milk Total

Gradient (m km−1 )

13.1 37.7 83.7 3.2 4.9

5.75 1.39 0.86 1.71 4.54

15.9 18.2 26.7 8.7 20.7 15.1 9.1

5.11 3.05 2.9 4.79 3.4 2.41 1.91

Copyright  2003 John Wiley & Sons, Ltd.

Grade of difficulty

II/III I + /II I II II III/III+ II/III II/II+ II II II I + /III I

Hydrometric gauge name

Waldron Brocket Lethbridge Lane Ck Frank Non-gauged Beaver Mines Waterton Park Glenwood Mountain View International Border Near Lethbridge Milk River

River Trip Report Cards submitted No. cards

No. boaters

52 43 43 5 31 4 40 12

409 450 295 32 968 15 346 147

25 37 18 84 394

217 361 78 933 4251

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Following from the categorization of Whittaker et al. (1993), the study compared four methods for R-IFN determination. 1. User survey. The River Trip Report Card provided the basis for a voluntary, mail-in survey. Postcard style surveys were developed in 1983 (Figure 2) and distributed to paddling clubs in Alberta along with letters inviting participation. The cards were self-addressed with pre-paid postage to encourage paddler response. Ratings from River Trip Report Cards were converted to numerical scores from 1 to 7 with the two ratings for ‘river’ and ‘rapids’ being averaged. A suitability score was thus provided with ‘4’ representing ‘optimal’ flow. The current study determined low flow criteria and consequently a regression method commenced by recognizing the range of flows that were considered by some respondents as lower than ideal. Flows that were consistently judged as ‘just right’ or higher were above this threshold and were omitted from subsequent curve fitting. The remaining data were evaluated through linear and polynomial regression (CA-Cricket Graph III, Version 1.5.3, Computer Associates International Inc., Islandia, NY) and the lowest order function was selected that produced a near-maximal coefficient of determination (r 2 ). A curved response function was expected since it was anticipated that low flows would provide little improvement over the no-flow point up to the discharge at which the stream was approaching the depth that would consistently float a boat over riffles and permit full paddle blade immersion in most areas. Thereafter, it was expected that the suitability function would progressively increase and then flatten out as the ideal flow range was approached. Following from the regression analysis, the intercepts of the regression line with suitability ratings of 3.0 and 3.5 were identified and the associated discharges were interpolated to reflect the minimal and sufficient flows, respectively. 2. Expert judgment. To obtain expert judgment (Brown et al., 1991; also referred to as ‘professional judgment’—Whittaker et al., 1993), guidebooks and maps for the regional streams were obtained and guides

RIVER TRIP REPORT PLACE OF RESIDENCE PUT IN POINT

RIVER(S)

DATE

PULL OUT POINT

Covered Canoe

NO. OF EACH CRAFT: Open Canoe

Impossibly Low

WATER LEVEL GENERAL:

A Little High

WATER LEVEL AT RAPIDS: Just Right ACTIVITIES:

Impossibly Low

A Little High Fishing

Swimming

TIME

TIME Novice

NO. AT EACH SKILL LEVEL: Beginner

Just Right

DATE

NO. IN PARTY

Intermediate

Advanced

Kayak

Other

Raft

Much Too Low Much Too High

Dangerously High

Much Too Low Much Too High

Low

Low Dangerously High

Camping (locations)

Other CLARIFICATIONS AND COMMENTS:

05/92/5M

Figure 2. The River Trip Report Card used for the user survey in the present study. The reverse side included the return address along with postage payment authorization Copyright  2003 John Wiley & Sons, Ltd.

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127

were selected that were comprehensive (included numerous rivers and reaches) and credible, providing accurate maps and descriptions of major features and consistent ratings of rapids. The flow assessments of these credible guides were utilized. 3. Flow comparison. From 1982 to 2000, we (Rood and Tymensen) paddled all river reaches in the Oldman River Basin. Records were kept with reference to sufficiency of flow with numerical ratings as follows: 0 = insufficient for boating, 1 = much too low (numerous scrapes and frequent grounding) or much too high (overbank flows), 2 = very low (common scrapes and occasional grounding) or very high (features flushed out), 3 = low (passable with few scrapes but limited hydraulic features and/or slow travel time) or high (hydraulic features lose definition or substantial turbidity), 3.5 = slightly low (some limitations in hydraulic features and/or travel time) or slightly high (some loss of hydraulic features or increased turbidity), or 4 = optimal. We paddled most reaches more than 20 times in open canoes, river kayaks and rafts. To generate a plot describing suitability versus discharge, data were grouped into discharge categories with values from trips with discharges within 3 m3 s−1 being grouped. Suitability and discharge values for the groupings were averaged, and these means were plotted and linked to produce the suitability plot. 4. Hydraulic modelling—depth, discharge method (DDM). We refer to an objective, hydraulic modelling approach as the depth criteria, stage–discharge method or more concisely as the depth, discharge method (DDM). This method commenced with the determinations of sufficient depths for paddling. Depths of 50 cm or 60 cm were initially considered for determinations of minimal flows based on published reports (McGill, 1982; Simmons et al., 1977) and paddle measurements, with the expectation that the depth should be sufficient to immerse a typical paddle blade. For sufficient flow determination, depths of 75, 90 and 100 cm were initially considered with the expectation that increased depth would improve the appeal of many hydraulic features, reduce the chances of hitting rocks, permit the kayak Eskimo roll, and provide less obstructed conditions for a paddler who swims following a capsize. The comparisons of R-IFN estimates from the subjective methods to the DDM estimates using different depth values permitted the selection of the appropriate minimal and sufficient depth criteria. Stage–discharge ratings tables were obtained for Water Survey of Canada gauging stations and those stations were visited to investigate the physical context of the gauging site to determine whether the channel form at the gauging site was typical of the reach or alternatively, confined or otherwise impacted by an adjacent bridge or other artificial structure. Subsequently, stage–discharge ratings curves were plotted and discharges that would satisfy the different depth criteria were interpolated. As a final consideration, we conducted regression analyses to investigate the possible relationship between minimal or sufficient R-IFN values and mean annual discharge (Q) for the different stream reaches. Linear, polynomial and logarithmic regressions were applied and associated coefficients of determination (r 2 ) were calculated (CA-Cricket Graph III, Version 1.5.3, Computer Associates International Inc., Islandia, NY).

RESULTS The streams included in the study varied by more than 20-fold in size (mean discharge) and ranged from flat-water streams of grade I difficulty to intermediate whitewater streams (grade III) with rapids up to class VI (Table I; Smith, 1995). As evidenced by the River Trip Report Cards and guidebooks, the rivers were used for recreational paddling and not for commercial transportation. The types of recreational paddling reported ranged from downstream travel trips of 20 km or more per day, to ‘park and play’ whitewater boating in which the paddlers remain at a rapid or short river reach. The present study did not attempt to resolve R-IFN values for the different types of recreational boating. User survey–River Trip Report Card (‘Trip Card’) A total of 395 Trip Cards were submitted for the Oldman Basin (for convenience the Milk River will be grouped with the Oldman Basin) with 394 submissions for the 12 streams listed in Table I and one additional submission for Lynx Creek. The number of submissions per reach varied from four for the Carbondale River to 84 for the Milk River. Copyright  2003 John Wiley & Sons, Ltd.

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Of the other streams, the Oldman River was generally well represented, as was the Castle River, a popular stream largely situated within the provincial (public) lands of the Bow Crow Forest Reserve (Table I). The lower reaches of the St. Mary and Waterton rivers were minimally represented, probably due to severe flow diversions that restricted paddling opportunities through the summers of most years. The Trip Cards represented an average of 11 boater days per card (Table I). The Carbondale and Lower St. Mary groups were small while the largest groups represented by the Trip Cards were for the Crowsnest River that was the site of an annual provincial whitewater slalom race and river rendezvous. The Trip Card data plot generally produced rather scattered distributions that did not indicate clear thresholds relative to flow suitability (Figure 3). Regression analysis was applied and a second-order polynomial provided a near-maximal coefficient of determination for each data set and was thus the function that was chosen to determine minimal and sufficient flows (Figures 3 and 4). Expert judgment For the subjective R-IFN approach involving expert judgment (Brown et al., 1991), six regional guides were considered and three of these provided accurate maps and spatial references and relatively consistent whitewater ratings that indicated careful consideration (Table II). The flow recommendations were fairly consistent across the three guides but the earlier Buhrmann and Young (1982) estimates displayed less variation than the subsequent estimates by Smith (1995) and SABDC (1998) (Table II). Two particular values from Buhrmann and Young (1982) were inconsistent with the other estimates; the estimate for the Upper Oldman was very low whereas the estimate for the Crowsnest River was inconsistently high. Flow comparisons Consistent with the functions described by other R-IFN investigators (Shelby et al., 1992a), the suitability versus discharge function that we observed based on multiple-flow comparisons produced a skewed bell-curve with a broad apex (Figure 5). Flows were insufficient for paddling up to the point where the boats would be floatable over the typical riffle sections. This would be the ‘much too low’ limit for paddling and above this discharge, the suitability improved rapidly. The ‘minimal’ flow value of 3 would provide a measure of suitability that we considered provided a reasonably favourable recreational experience (Figure 5). A relatively small increase in discharge brings the stream up to the ‘sufficient’ or ‘preferred’ flow and thereafter, the suitability function flattened out through the broad range of flows that were considered ‘optimal’. There was no specific optimum since the flows were considered ideal over a fairly broad range.

5

A Little High optimal

Suitability

4

Just Right

sufficient minimal

3

Low

2

Much Too Low

1 0

5

10

15

20

25

30

35

40

45

Discharge (m3/s) Figure 3. Plotted data for the River Trip Report Cards (RTRC) submitted for the Milk River. The best-fit second-degree polynomial regression curve is plotted and the coefficient of determination (r 2 ) was 0.32. R-IFN minimal and sufficient flows were determined by interpolating the discharges associated with suitabilities of 3.0 and 3.5, respectively, from the regression curves. The ‘optimal’ flow is also indicated as the intercept associated with the suitability of 4.0 Copyright  2003 John Wiley & Sons, Ltd.

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Crowsnest

5 4 3 2 1 0

10

15

20

25

30

Castle

5

Suitability

5

4 3 2 1 0

10

20

30

40

50

60

70

Upper St. Mary

5 4 3 2 1 10

20

30

40

50

Discharge

(m3/s)

60

70

Figure 4. Plotted data for River Trip Report Cards (RTRC) submitted for the Crowsnest (top), Castle (middle) and Upper St. Mary (bottom) rivers, Alberta. Only the low discharge (flow) range is presented and additional RTRC had been submitted for higher discharges than plotted. The regression for the Castle was restricted to the range indicated by the line; data indicated by square symbols were not included since they reduced the regression fit in the range of interest. Coefficients of determination (r 2 ) were 0.66, 0.56 and 0.74, respectively. Dashed lines indicate the minimal and sufficient flows that correspond to suitabilities of 3.0 and 3.5, respectively. Note the different x-axis scales for the different plots

Hydraulic modelling—the depth, discharge method (DDM) For the DDM, the sites of hydrometric gauging stations were visited and all were considered to be reasonably typical of the respective river reaches relative to overall channel geometry. Consequently, stage–discharge ratings curves for these gauging sites were applied for DDM analyses (Figure 6). Across the streams, the ratings curve depths of 60 cm and 75 cm provided values closest to the subjective method estimates of minimal and sufficient flows, respectively, and these were consequently adopted as the two DDM depth criteria. Copyright  2003 John Wiley & Sons, Ltd.

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Table II. ‘Minimal flows’ (in (m3 s−1 ) for recreational paddling along ten southern Alberta river reaches as determined by various subjective methods Buhrmann and Young (1982) Upper Oldman Lower Oldman Crowsnest Castle Upper Waterton Lower Waterton Upper Belly Upper St. Mary Lower St. Mary Milk Average

Smith (1995)

8 28 11 16 14 14 7 14 14 14 14.0

SABDC (1998)

20

20

7 20 22 30 15 15 20

8 22 15 25 15

18.6

17.5

River Trip Report Card

Flow comparison

11 25 7 20

14 27 6 15 16

8 21 18 11 15.1

16 20 16.3

Average 14.6 26.7 7.8 18.6 16.8 23.0 11.3 16.5 18.0 12.5 16.6

SABDC, Southern Alberta Business Development Center.

Lower St. Mary River

Suitability

optimal 4 3 2 1 0 0

10

20

30

Discharge

40

50

60

70

(m3/s)

Figure 5. The results of the flow comparison for recreational paddling along the Lower St. Mary River, Alberta. The river was visited at differing discharges and the padding suitability was evaluated by the authors

Comparisons across R-IFN methods The River Trip Report Card determinations of minimal flows were generally consistent with the expert judgment assessments and the flow comparison values (Table II). The average coefficient of determination (r 2 ) across the subjective assessments was 0.54 (n = 10, P < 0.001). Of the subjective methods, the Buhrmann and Young (1982) determinations were least consistent and the r 2 without these values increased to 0.63. The subjective method estimates for sufficient flows were also very consistent across different approaches (Table III). For these values the flow comparison consistently provided slightly lower flow estimates and this may have reflected our particular views about flow sufficiency. The depth, discharge method (DDM) estimates for both minimum and sufficient flows were consistently very close to the mean estimates from the subjective methods. Some specific comparisons are plotted in Figure 7 and the values are fully listed in Table IV. The full range of streams is represented in Figure 8 with the mean subjective minimal flows plotted against the DDM determinations. There was a close correlation between these estimates and the overall coefficient of determination (r 2 ) was 0.66. The lower Oldman reach represented the combined flow of all of the other reaches and was thus much larger than the other streams. The DDM method underestimated the lower Oldman minimal flow relative to the estimate from the subjective methods and this data point was furthest from the Copyright  2003 John Wiley & Sons, Ltd.

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Lower St. Mary

1.2

Stage (m)

1

sufficient minimal

0.8 0.6 0.4 0.2 0 0

20

40

60

80

100

120

Discharge (m3/s) Figure 6. The stage versus discharge or ‘ratings’ curve for the site of the stream flow gauge along the Lower St. Mary River, Alberta. The depth, discharge method (DDM) is applied, whereby the discharge associated with depths (stages) of 60 cm (0.6 m) and 75 cm are interpolated to provide R-IFN estimates for minimal and sufficient flows, respectively

Table III. ‘Sufficient’ or ‘preferred’ flows (in m3 s−1 ) for recreational paddling along ten southern Alberta river reaches as determined by various subjective methods and by the depth, discharge method (DDM), using a depth criterion of 75 cm Buhrmann and Young (1982)

Upper Oldman Lower Oldman Crowsnest Castle Upper Waterton Lower Waterton Upper Belly Upper St. Mary Lower St. Mary Milk Average Excluding Lower Oldman

River Trip Report Card

23 57 20 23 42 42 14 34 42 23 32.0

16 60 9 30 14 32 30 16 25.9

Flow comparison

22 45 9 25 26 30 28 26.4

Average subjective

20 54 13 26 34 42 14 32 33 20 28.1

Depth discharge method (DDM) 33 35 12 23 32 50 16 28 35 14 27.8

Subjective/ DDM

0.62 1.54 1.06 1.13 1.06 0.84 0.88 1.14 0.95 1.44 1.07 1.01

regression line. By excluding this reach the r 2 increased to 0.78; thus, 78% of the variation of the subjective method R-IFN estimate was associated with variation in the DDM estimate. In the final regression analysis, there was a close correlation between the estimates of minimal flows for recreational paddling and mean annual discharges (Q) (Table IV). Again excluding the much larger lower Oldman River, the coefficient of determination (r 2 ) was 0.90 for the linear regression for this relationship (Figure 9). The data were positioned close to the 1-to-1 line (unit slope, origin intercept) indicating that mean discharge could provide reasonable estimates of the R-IFN minimal flows for these streams (Figure 9). For the data set excluding the lower Oldman River, the regression fit was slightly improved with a seconddegree polynomial that described a diminishing curve (y = minimal flow, x = meanQ; y = −0.014x 2 + 1.170x + 1.765; r 2 = 0.92). Inclusion of the lower Oldman River considerably reduced the linear or polynomial regression fit (r 2 = 0.53 with linear regression) and this full data set was better described by a logarithmic function that represented a steeply diminishing curve (y = 16.173 log(x) − 3.039; r 2 = 0.89). Copyright  2003 John Wiley & Sons, Ltd.

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Figure 7. Estimates of minimal (open bars) and sufficient (shaded bars) discharges for recreational paddling along four river reaches in Alberta. For each river, the bars represent values from: River Trip Report Cards (RTRC), paddling guides by Buhrmann and Young (1982) (B & Y), Smith (1995), the multiple flow comparison, and the depth, discharge method (DDM)

DISCUSSION Different phrases have been used to describe the low end of the paddleable range of instream flows. ‘Minimum flow’ has frequently been used (Brown et al., 1991) but we disfavour this since it inappropriately implies a discrete threshold. Since the favourability or navigability progressively diminishes, we use the term ‘minimal flow’ to indicate a flow near the transition from a favourable to an unfavourable level. ‘Marginal’ has also been used for this transition (Whittaker et al., 1993) but we consider that this term presents a negative impression suggesting inadequate flow. Clipperton (1998) used ‘minimum acceptable flow’, a more informative phrase but one that may be misinterpreted as representing an acceptable flow objective. These semantic ambiguities emphasize the need to clarify designations both for analyses and for application in river resource planning (Brown et al., 1991). Relative to the River Trip Report Card, the inclusion of two ratings lines for ‘river’ and ‘rapids’ was useful since it provided respondents with two ratings opportunities. The different categories reflected the expectation that since rapids typically include swifter and shallower water along with boulders or bedrock outcrops, higher flows might be required at rapids than for pools. This expectation was frequently supported as a number of Trip Cards reported overall flows as ‘just right’ whereas flows at rapids were ‘low’. However, this was not a uniform pattern. For example, a bedrock-confined whitewater reach such as through Castle Canyon is paddleable at much lower flows than adjacent, broader, alluvial, gravel- and cobble-bed segments of the same stream. Copyright  2003 John Wiley & Sons, Ltd.

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Table IV. Minimal flows for recreational paddling along ten southern Alberta river reaches, as determined by subjective methods (Table II) and by the depth, discharge method (DDM), using a depth criterion of 60 cm, along with mean annual discharges (Q) and various ratios of these values Mean subjective (m3 s−1 ) Upper Oldman Lower Oldman Crowsnest Castle Upper Waterton Lower Waterton Upper Belly Upper St. Mary Lower St. Mary Milk Average Excluding Lower Oldman

Mean Depth minimal discharge method (DDM) (m3 s−1 ) (m3 s−1 )

14.6 26.7 7.8 18.6 16.8 23.0 11.3 16.5 18.0 12.5 16.6

21 22 7 14 15 30 9 17 20 9 16.4

Subjective/ DDM

17.8 24.3 7.4 16.3 15.9 26.5 10.1 16.8 19.0 10.5 16.5

0.70 1.21 1.11 1.33 1.12 0.77 1.25 0.97 0.90 1.47 1.1

Mean Q (m3 s−1 )

13.1 83.7 4.9 15.9 18.2 26.7 8.7 20.7 15.1 9.1 21.6

Mean Q/ mean minimal

0.74 3.44 0.66 0.98 1.15 1.01 0.86 1.24 0.79 0.86 1.17 0.92

Subjective Methods (m3/s)

35 30

L. Oldman

25 U. Waterton Castle

20 15

Milk

L. Waterton L. St. Mary U. Oldman

Belly U. St. Mary

10

Crowsnest

5 0 0

5

10

15

20

25

30

35

Depth Discharge Method (m3/s) Figure 8. Average minimal flows for recreation as determined from the various subjective methods of the present study (Table III) versus the minimal flow as determined by the depth, discharge method (DDM). The dashed line has a unit (1) slope and origin (0,0) intercept. The solid line represents the best-fit linear regression of the data excluding the Lower Oldman (y = 0.52x + 7.6; r 2 = 0.779). The best fit including the Lower Oldman was y = 0.62x + 6.8; r 2 = 0.658

A second benefit from the provision of two response lines for river and rapids was that this provided respondents with an opportunity for intermediate assessments. For example, if a paddler group considered a flow as slightly low, they could provide ‘just right’ and ‘low’ for the two categories to reflect the intermediate assessment. This provided refinement for the regression analyses. Across all Trip Cards, more than one-half indicated that the flows were ‘just right’. This probably partially reflected the paddlers’ enjoyment of the overall paddling experience that resulted from favourable social (Heywood, 1987) and environmental conditions (Knopp et al., 1979). Additionally, prospective paddlers will attempt to choose a river reach with suitable flow. Particularly after an automated ‘flow phone’ was implemented in the early 1990s, it was easy for remote paddlers to identify reaches with suitable flows. The provision of Internet-based flows in 1998 and the addition of near-real-time flow data in 2000 should increase this trend. As a group, the paddling community is becoming more sophisticated about flow information Copyright  2003 John Wiley & Sons, Ltd.

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R-IFN Minimal Flow (m3/s)

30 L. Waterton 25 L. St. Mary

20

Castle

U. Oldman Milk

15 10

U. St. Mary U. Waterton

Belly Crowsnest

5

Willow Ck. 0 0

5

10

15

20

Mean Discharge

25

30

(m3/s)

Figure 9. Average minimal flows for recreation (mean of all methods, Table III) versus the mean annual discharge (Q) for rivers in the Oldman River Basin, Alberta, excluding the large Lower Oldman River but including Willow Creek. The dashed line has a unit (1) slope and origin (0,0) intercept. The solid line represents the best-fit linear regression: y = 0.77x + 3.97; r 2 = 0.901

and paddling clubs and outdoor equipment stores are increasingly tending to advertise flow information and provide recommendations about current paddling options. With respect to the expert judgments, the different guides were written by paddlers that used different boat types and have different ‘comfort zones’, a description of the whitewater difficulty in which the paddlers are comfortably proficient. These differences probably influenced flow assessments as Buhrmann and Young (1982) generally provided higher whitewater difficulty ratings and lower minimal flow recommendations than Smith (1995) or the SABDC (1998). The development of the depth discharge method provided an objective, hydraulic approach that was simple in principle and application and provided a complement to the subjective approaches. However, it relies on a representative channel cross-section at the hydrometric gauging site(s). We were cautious in the adoption of the ratings functions from the gauging sites in the present study since we anticipated substantial site-specific variation in hydraulic geometry that reflects position relative to rapids, bedrock confinement and other geomorphic features. In the present study, the confirmation of the suitability of this objective approach was its consistency with other R-IFN methods (Figure 8). However, the possible complexity due to non-typical channel cross-sections at gauging sites should be considered in future applications of the depth discharge method. As indicated in the final analyses, it was noteworthy that there was a close correlation between R-IFN and mean discharge (Figure 9). This probably results from fundamental relationships between stream flow and channel geometry. The size of the stream channel is a particular physical consequence of stream flow and associated with this size, typical depth characteristics result (Leopold, 1994). This simple relationship between R-IFN minimal flow and mean discharge was expressed across a range of streams although these drained adjacent watersheds and all tended to be small to medium in size. We expect that the relationship will not hold for larger streams but sufficient depth is less commonly a limitation for paddling along large rivers.

CONCLUSION AND RECOMMENDATIONS The present study demonstrated close agreement in estimates of R-IFN from different methods for most rivers in southern Alberta. Different subjective approaches generated similar values that were also consistent with estimates based on the hydrometric method involving a combination of depth criteria and stage–discharge analysis. The consistent assessments support the validity of all of the methods. Further, this consistency across methods strengthens the confidence in the values determined. Following from the present study, we recommend the depth discharge method (DDM) as an initial approach for R-IFN minimal flow determination. The method is objective, quick and inexpensive, requiring only the hydrometric ratings curve for relevant stream gauge sites and visits to those sites to ensure typical channel Copyright  2003 John Wiley & Sons, Ltd.

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geometry. We suggest that this DDM could be conducted at the onset of R-IFN studies and this would provide initial estimates that would be refined by subjective approaches involving paddler assessments. We do not recommend that any R-IFN determination is based solely on physical hydrometric analyses since there is great diversity across streams that influences the paddling experience. Since the ultimate objective is the determination of paddleable flows, paddler assessments must be included in R-IFN studies. Further, we recommend that multiple approaches be applied. This will strengthen the analysis, broaden the range of opinions, and also broaden the range of applications.

ACKNOWLEDGEMENTS

We acknowledge the substantial contribution of T. Dykstra (retired from Alberta Environment) on the River Trip Report Card programme. The input from K. Clipperton, J. Mahoney, R. Morrison, D. Ohrn and K. White of Alberta Environment is also gratefully acknowledged along with editorial assistance from D. Galat (USGS, MO) and helpful comments from two anonymous reviewers. This project was funded through a contract with Alberta Environment and a Natural Sciences and Engineering Council (NSERC) of Canada grant. REFERENCES Brown TC, Taylor JG, Shelby B. 1991. Assessing the direct effects of streamflow on recreation: a literature review. Water Resources Bulletin 27: 979–989. Buhrmann H, Young D. 1982. Canoeing Chinook Country Rivers. University of Lethbridge, AB. Burley JB. 1990. Advancing recreation assessments. Rivers 1: 236–239. Clipperton K. 1998. Integrating instream flow requirements into management of multiple use rivers. MEvDs Thesis, University of Calgary. Corbett R. 1990. A method for determining minimum instream flow for recreational boating. SAIC Special Report 1-239-91-01. Science Applications International Corporation: McLean, VA. Giffen RA, Parkin DO. 1993. Using systematic field evaluations to determine instream flow needs for recreation. Land and Water Associates: Hallowell, ME. Gillilan DM, Brown TC. 1997. Instream flow protection: seeking a balance in western water use. Island Press: Washington, DC. Heywood JL. 1987. Experience preferences of participants in different types of river recreation groups. Journal of Leisure Research 19: 1–12. Jackson RB, Carpenter SR, Dahm CN, McKnight MD, Naiman RJ, Postel SL, Running SW. 2001. Water in a changing world. Ecological Applications 11: 1027–1045. Knopp TB, Ballman G, Merriam LC Jr. 1979. Toward a more direct measure of river user preference. Journal of Leisure Research 11: 317–326. Leopold LB. 1994. A View of the River. Harvard University Press: Cambridge, MA. McGill JS. 1982. Whitewater - creating a river race course. Landscape Architecture July: 81–83. Rood SB, Mahoney JM. 2000. Revised instream flow regulation enables cottonwood recruitment along the St. Mary River, Alberta, Canada. Rivers 7: 109–125. Rood SB, Kalischuk AR, Mahoney JM. 1998. Initial cottonwood recruitment following the flood of the century of the Oldman River, Alberta, Canada. Wetlands 18: 557–570. Shelby B, Whittaker D. 1995. Flows and recreation quality on the Dolores River: Integrating overall and specific evaluations. Rivers 5: 121–132. Shelby B, Brown T, Baumgartner R. 1992a. The effects of streamflow on river trips on the Colorado River in Grand Canyon, Arizona. Rivers 3: 191–201. Shelby B, Brown T, Taylor JG. 1992b. Streamflow and recreation. USDA Forest Service General Technical Report RM-209. USDA: Fort Collins, CO. Shelby B, Whittaker D, Roppe J. 1998. Controlled flow studies for recreation: a case study on Oregon’s North Umpqua River. Rivers 6: 259–268. Simmons WP, Logan TH, Simonds RA, Brown RJ. 1977. Model studies of Denver Whitewater channel. American society of Civil Engineers, Journal of the Hydraulics Division 103: 763–775. Smith S. 1995. Canadian Rockies Whitewater—the southern Rockies. Headwaters Press: Jasper, AB. SABDC 1998. Adventure Guide and topographic map of Southwest Alberta. Southern Alberta Business Development Center: Pincher Creek Alberta. Tennant DL. 1976. Instream flow regimens for fish, wildlife, recreation, and related environmental resources. Fisheries 1: 6–10. Whittaker D, Shelby B, Jackson W, Beschta R. 1993. Instream Flows for Recreation: a Handbook on Concepts and Research Methods. US Department of the Interior, National Park Service. Copyright  2003 John Wiley & Sons, Ltd.

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