Hydrological Studies of the Slims River, Yukon, June-August 1970

Transcription

1 " J CEFELD RANGES RESEARCH PROJECT, SCENTFC RESULTS: VOLUME 4 (AMERCAN GEOGRAPHCAL SOCETY-1974 '\ Hydrologial Studies of the Slims River, Yukon, June-August 197 Albert P. Barnett* "_/ "' ABSTRACT. Hydrologial studies were onduted on the Slims River during the summer of 197. The purpose was to determine fators ausing diurnal and seasonal variations in disharge. Disharge measurements were taken during periods whih displayed different limatologial onditions; diurnal variations were measured within seleted twenty-four hour periods. A ontinuous stage reorder was used to measure seasonal variations in stream flow. Tributary stream disharge was also measured. Climatologial data reorded at the nearby Kluane Lake Station were utilized for hydro-limatologial analysis. Available measurements inluded temperature, wind diretion and veloity, loud over and type, preipitation, atmospheri pressure, humidity, and inoming short-wave radiation. Shifts of Kaskawulsh Glaier meltwater drainage from the Slims to the Kaskawulsh River are the major fator in intraseasonal variations of disharge. Otherwise, Slims River drainage was found to vary diurnally and seasonally in aordane with ertain limatologial and physiographi fators. These inlude glaier ablation, exposure diretion and surfae area of the watershed surfae, ie-dammed lake drainage, short-wave radiation absorption, loud over, preipitation, and temperature. Disharge varied diretly with the general inreases and dereases in short-wave radiation and seasonal temperature. ntensity of rainfall does not always have a diret relationship to disharge. ' j " j lntrodution Hydrologial studies were onduted on the Slims River during the summer of 197. This river is important to an understanding of the regional environment beause: ( 1 it is the major soure of water for Kluane Lake, the largest lake in the Yukon Territoty; (2 it behaves anomalously from summer to summer, thus affeting lake levels and shoreline morphology; and ( 3 it is one of the two meltwater outlets of the Kaskawulsh Glaier. Geomorphi studies have previously been onduted in the Slims River area. Fahnestok (1969 desribed harateristis and hronology of the Slims valley train, providing supporting evidene to Bostok's (1952; 1969 hypothesis that the Slims River has experiened drainage reversal in postglaial time. The purpose of the study reported here was to determine fators ausing diurnal and intraseasonal variations in disharge. To aomplish this, disharge measurements of the river were taken during periods whih displayed different limatologial onditions. n order to gain insights into diurnal variations, a series of measurements wete-takert within-seleted twentyfour nour periods; - seasonal hanges were ompiled ontinuously by stage reorder. Disharge measurements of tributary streams were also taken to determine what perentage (or remainder of the Slims' disharge was omposed of Kaskawu,lsh Glaier meltwater. *Department of Geography, University of Mihigan, at time of writing. Present address: North Carolina-Central Univerity, Durham Climatologial data from the Kluane Lake meteorologial station utilized in this study inluded daily measurements of temperature, wind diretion and veloity, loud over and type, preipitation, atmospheri pressure, humidity, and inoming short-wave radiation. nterpretation of the limati data was useful in the identifiation of fators whih influene disharge variations. Study area. The Kaskawulsh Glaier in the efi.eld Ranges of the St. Elias Mountains drains eastward a distane of 72 km to its end moraine (Plate 1 1 At this point two meltwater streams-the Kaskawulsh and Slims Rivers-emerge from the glaier snout and drain 'divergent valleys. The Slims River flows from the north edge of the Kaskawulsh Glaier's end moraine into Kluane Lake. t enters the lake at mile of the Alaska Highway, eventually draining to the Bering Sea via the Yukon River system. The Slims River strethes 22.5 km over a valley floor omposed of glaial outwash. ts floodplain is about 18 m wide, exept in areas where tributaries have built alluvial fans whih onstrit the valley floor. The Slims and Kaskawulsh Rivers share the runoff from a21_km_drainage_hasin in_thejefi.eld Ranges.Ap- _ proximately 145 km 2 of this watershed is overed by Kaskawulsh Glaier ie (Rihard Rangle, personal ommuniation, in Fahnestok, 1969, p Tributary streams (Fig. 1, whih enter the river below the glaier terminus, supply the Slims with snowmelt as late as July, depending on both the amount of winter snow aumulation and limati-onditions. On the up- - per portions of fans, whih are developed from the 1 Plate 1 is a map inside the bak over of this volume. 143

2 144 ALBERTP.BARNETT Q!illillTil Moraine Bedrok Alluvial flats Alluvial fans Ablation moraine D Valley train / Feet _...,_N Sale in miles Fig. 1. The Slims River valley (from Fahnestok, 1969, p. 163; loations of ross setions disussed by Fahnestok should be disregarded. tributaries, runoff infiltrates the fans but reappears at the edge of the river as small springs. Throughout the summer months the larger fans supply the Slims with snow and glaial melt. Of the larger tributaries, Canada and Bullion Creeks are glaially fed, whereas Vulan and Sheep Creeks are supplied with snowmelt from high neve fields. The anyon walls of the lower segments of these streams exeed 3 m and large boulders luster in their narrow flood plains. Canada Creek, the largest of the tributaries, enters the Slims some 9 m downstream from the Kaskawulsh Glaier end moraine on the west slope of the valley. The upper portion of the fan is omposed of oarse material; the lower two-thirds of the fan onsists of gravel to siltsize material and has no vegetation over. Bullion and Sheep Creeks enter approximately 14 km and 13 km downstream on the west side of the valley. The upper two-thirds of their fans are wooded. The lower thirds are partially overed with thik grasses and muskeg. On the Bullion Creek floodplain lso/v-2% of the surfae has been reently reworked by-migrating, braided flow; major hanges have ourred during peak runoff periods. Mining and road alterations aross Bullion Creek have also modified its migration pattern. Vulan Creek, a snowmelt stream, drains the eastern slope of the Slims River and enters the main stream approximately 16 km below the Kaskawulsh Glaier terminus. On the upper portions of the Vulan fan, stream flow infiltrates gravel-sized alluvium to reappear on grass and muskeg lower on the fan. Field methods. Disharge and stage measurements were taken at the Slims River bridge. This is the most onvenient loation for disharge observations beause a 122-m long bridge funnels all water into two narrow hannels. Beause there is a high permafrost table (less than 1 m below the surfae subsurfae flow is negligible. Vertial markings painted on the downstream side of the bridge provided referene planes to measure the vertial angle reated by the fore of the water on a handline-suspended urrent meter and sounding weight. Starting at the west bank, depth readings were taken at 1.5-m intervals and veloity readings were taken at 3-m intervals. Water height was measured by stage reorder. Water temperature was also reorded prior to eah disharge measurement. Observations of tributary stream flow were made at Bullion, Sheep, and Vulan Creeks. Steam disharge, water temperature, maximum and minimum air temperature, and preipitation were measured at these

3 HYDROLOGCAL STUDES OF THE SLMS RVER 145 DATE 3JUN7 8JU L7 15JUL7 6AUG7 TME 3PM 7PM 3AM 3PM Q(h A(ft o38 G.H.(ft SYMBOL ;A CHANNEL 2. L-----_.--L--L-- Fl / DATE TME Q(ls A( ft2 G. H.(ft SYMBOL 3JUN7 3PM JU L7 7PM JUL7 3AM AU G 7 3PM : : :: :,:,.--,: :: o; _,.,,: : o o:o :, :.:o,:: :: oo :oj ;j;i;:,....--/,... ' / \. - \''. -/ \.:: / :''.;:::>......_ ',- ', ',, ,.---.J 25. '". t ' / / '"'""" " -. // -;- - : - -:- -- -;--- :... FT Fig. 2. Cross setions of the two Slims River hannels showing depth variations throughout the two months of observation. TABLE 1. Cross-Setional Data, June 3 and August 6 -, '" " j./ ' CHANNELl CHANNEL DP* Depth (m.dp* Depth (m (m (ft June 3 Aug. 6 (m (ft June 3 Aug *DP: distane from initial point.

4 146 stations. All tributary stations were loated above their alluvial fans to eliminate the omplexities involved in braided stream measurements. Observations on Vulan Creek were made 3 m above the head of the fan along a straight 15-m reah. Rod disharge measurements, using a number 622 Prie pygmy urrent meter, were made at these stations. Stream Geometry The Slims River is divided into two separate hannels by the enter pile and foundation of the Alaska Highway bridge, mile Channel has a width of 19.8 m from the west bank to the enter pile and Channel measures 32. m from the enter pile to the east bank. The depths of both hannels vary greatly (Fig. 2 and Table 1. The deepest point in Channel varies from 3.3 to 5.8 m and in Channel from 4.6 to 8.2 m. Although the ross-setional area of Channel is greater than that of Channel, the disharge of Channel is often less than that of Channel (Table 2. Channel is loated near the onave bank just downstream from the axis of bend in a meandering segment of the Slims River. This is the setion in the meandering stream that experienes the greatest veloity (Leopold, Wolman, and Miller, 1964, p t should be noted that although Channel has higher veloities and disharge, Channel experienes greater souring and filling. Studies of hydrauli geometry have shown that the mean bed elevation at a river ross setion depends not only on water disharge, but is related to hanges in width, depth, veloity, and sediment load (Leopold, Wolman, and Miller, 1964, p. 23. During periods oflow disharge and veloity (in August, the highest disharge shifts to the previously deepened Channel. Flow Charateristis Diurnal disharge variations. Diurnal disharge measurements were taken on different days as the summer progressed. Table 2 summarizes the observations. The data reveal that peak disharges our between 21 and 3 hours; lows our in early afternoon. Given normal onditions the greatest ablation ours when solar energy is most abundant; this generally ours between the hours of 13 and 15 mean solar time. The time lag between peak ablation and peak disharge readings an be attributed to the ombined length of the glaier ablation surfae and the distane between the gauging station and the terminus of the glaier. The magnitude of disharge during high flow periods is dependent on geomorphi fators suh as glaier type, slope and exposure, surfae area ofthe zone of ablation, glaier sediment over, and drainage of ie-dammed lakes. Climatologial fators inlude radiation absorption, loud over, preipitation, and temperature. Of these variables, only the limatologial fators are onsidered in this paper. ALBERTP. BARNETT t is found that although disharge varies during 24- hour periods, the fators ausing these variations are due to the general tendeny of the limatologial variables during the period of observation rather than to their absolute value during measurement. A trend, to be effetive, must extend a period of days prior to the disharge measurement. Exeptions to this are ases of intense preipitation and drainage of ie-dammed lakes whih initiate major disharge flutuations within twelve hours after ourrene. ntraseasonal variations. ntraseasonal flow variations are given in Table 2. Measurements were taken at the same hours on different days in order to establish a better piture of seasonal progression. Measurements taken at 14 and 15 hours show gradual variations in disharge and ross-setional area for three distint periods. The first two periods are haraterized by gradual inreases in area and disharge, eah followed by a deline. The spring warming trend and assoiated snowmelt is the apparent ause for the inrease in disharge for the first period (June 3-July 9. The invasion on July 5 of a storm system with assoiated preipitation ontributed to the high runoff. By July 9, high barometri pressures and dereasing temperatures ontributed to a derease in runoff (Figs. 3 and 4. Subsequently, temperatures remained relati.rely low for the rest of the summer. This, and the redution of snow available for melt, aounts for the disharge not reahing its previous level. The seond derease (from Period to Period ll was aused by a major shift to the Kaskawulsh Glaier meltwater from the Slims River to the Kaskawulsh River. This phenomenon is extraordinarily important to the regimen of the Slims River and has been observed on at least two other oasions during the 196's (Melvin Marus and Philip Lipton, personal ommuniations. The subjet is treated in a later setion. Effets of limate on disharge. Beause the Slims River is loated in a rain shadow on the leeward side of the St. Elias Mountains, the preipitation is low, On days when preipitation ourred, however, slight variations in disharge were reorded. On July 8, for example, there was 22.6 mm of preipitation. Two disharge measurements were taken on this day and one on the following day. Unfortunately, more measurements are not available for this period sine the ontinuous stage reorder malfuntioned. n omparing measurements taken at 22 hours on July 8 with measurements taken. on July 5 at a orresponding time with no preipitation, a July 8 inrease in disharge is apparent (Table 2. Although on July 9, 2.8 mm of preipitation was reorded, redution in disharge, ross-setional area, and veloity were measured. Redued short-wave radiation was reeived on July 8 and July 9. This, along with lower temperatures, redued ablation and net water runoff into the Slims River. The amount of preipitation on July 8, however, was more than enough to ompensate for the lost glaial meltwater disharge and thereby resulted in a G

5 ' HYDROLOGCAL STUDES OF THE SLMS RVER 147 '".5 -'. -- l_ - 1 U PRECPTATON "' _ '';:: '" 5 ". "\... 9 "' -" E J MAY JUNE JULY AUGUST. Fig. 3. Mean daily preipitation, loud over, and barometri pressure at Khiane Lake meteorologial station, May-August 197. ' v '.., disharge inrease. The amount falling on July 9 was not enough to ompensate for redued glaial melt, and therefore a redution in disharge was experiened. With the rise in stage aompanying flood passage through a gauging station, there is an inrease in veloity and sheer stress on the stream bed. As a result there is a tendeny for souring to our during high flow periods. Figure 2 shows the hanges in ross u J. E {! 4 setion during passage of snowmelt inrease for the Slims River. Observations began on June 3, 197. t is seen that the bed level at this time was about 4.5 m below the gauging datum and the disharge was 38.2 and 7.2 m 3 /se, respetively, for Channels and. By July 8, the disharge inreased to 68.2 and 92.8 m 3 /se and the bed level dropped 1.5 to 3. m. On July 1-11, a notieable inrease in stage (from.58 to. 7 m was reorded (Table 3. A diurnal variation from.64 to r:.. 6/ May June July August Fig. 4. Mean daily temperature at Kluane Lake meteorologial station, May-August ,

6 ... TABLE 2. Slims River Disharge, Summer 197 Time Gauge Period Date (Eastern Yukon height Daylight (m Channell Channell Cross-setion Veloity Disharge Cross-setion Veloity area (m 2 (m/se (m 3 /se area (m 2 (m/se Disharge (m 3 /se Both hannels Cross-setion Disharge area (m 2 (m 3 /se June July ll July ' August i ' F; iii ::> >-i ""' Cl ( (l C r'"",j

7 HYDROLOGCAL STUDES OF THE SLMS RVER 149 TABLE 3. Slims River Gauge Height tation. t is speulated that a draining ie-dammed lake Date supplied the Slims River with additional water in suffi- Gauge height in meters ient quantities to ause an inrease in stage height. A 6 hr 12 hr 18 hr Midnight number of small ie-dammed lakes are loated along the June lateral margin of the Kaskawulsh Glaier. These have July been observed to drain in a matter of a few hours (Mel vin Marus, personal ommuniation. One of these lakes apparently drained on July 14 as shown by an in rease in stage from 64 to 76 mm within a period of minutes. On July 17, the last day of the high flow period, preipitation reated very small stage flutuations The period July 18-2 experiened a redution in stage. This was in part a response to the limited amount of inoming short-wave radiation (Fig. 5. Cross-setional area redution (filling ourred with the derease of ve loity and disharge For the three-day period, July 24 to July 26, a total of mm of preipitation fell, with 85% of this total o urring on July 25. Disharge measurements were not taken during this period, although stage reords reveal an inrease from.61 m on July 24 to 1.1 m.onjuly The aumulated preipitation for this period was not Aug enough to ause suh an inrease in stage. This inrease, therefore, must be attributed to some other ause. Tern perature and radiation data show that the period in whih the peak daily mean temperature ourred oin ided with the period that reeived the greatest short wave radiation (July 17 through August 1. The resulting inrease of snowfield and glaier melting is the apparent '.J ause of the stage inrease for this period The Shift in Glaier Runoff 5 Between July 3 and August 4, 197 the stage of the Slims River dropped from.76 to.49 m, ross-setional area dereased from 27.5 to m 2, and veloity in tl..:: two hannels dereased from.65 to.14 m/se (Channel and.5 to.9 m/se (Channel. This was the result of a major shift of Kaskawulsh Glaier meltwater into hannels of the Kaskawulsh River, de priving the Slims River of more than three-quarters of its previous disharge. A gradual drop in stage ontinued Note: Time is Eastern Yukon Daylight. for two weeks after the initial deline (Table 3. This.J "' event ourred at the end of the period that experiened. 73 m was maintained until July 13. A peak stage of the peak mean daily temperature (Fig m above the gauge datum was ahieved at 6 hr The diurnal disharge variations during August (Period on July 14, with a low stage of. 73 m at 18 hr. This were of smaller magnitude than those of the previous leyelwas_maintaineduntil_j uly 17. _The_ peak stage.dur".. period.-the.august.variation-pattem-more.truly-repre--- ".;; ing this period ourred between midnight and 3 sents the diurnal pattern for tributary streams than do hours and the low stage ourred between 14 and the June and July patterns. This is beause approximately 17 hours. 5% of the Slims River flow after the shift at the end of July was omposed of tributary meltwater, whereas only Previous to July 1, a major storm system moved 1% of its earlier disharge onsisted of tributary flow. through the area, aompanied by heavy loud over and high preipitation. The lowest reorded inoming Peak flow in August ourred around midnight. This is short-wave radiation ourred during this period. The similar to the disharge pattern in June and July before -' stage inrease on July 1 ourred in onjuntion with the drainage shift. However, it was observed that the learing weather and a jump in insolation. The inrease high flow periods in August were somewhat more exon July 14 was not due to intense insolation or preipi- tended than high flows in the earlier period. Although ""

8 15 ALBERT P. BARNETT z < 1\.-,.., >,..: :3 \ \ ; \ F \ \ \ 28JUL7 29JUL7 3JUL7 31JUL7 OAUG7 2AUG7 Fig. 5. nsolation at Kluane Lake meteorologial station, July 28 through August 2, 197. Eah division on the vertial sale represents.5 langleys. the time of day for peak ablation ours simultaneously for tributary soures in the watershed, the differenes in distanes between tributary soures and the Slims River gauging station ause peak meltwater from eah of the tributaries to reah the gauging station at different times. This lag effet results in extended high-flow periods that had been previously obsured by the Kaskawulsh Glaier runoff. Conlusions The most signifiant element in the summer 197 regimen of the Slims River was the shift of Kaskawulsh Glaier meltwater runoff in early August. Deprived of its prinipal water soure, the Slims River made only minimal ontributions to Kluane Lake during a normally high flow period. The impat of the drainage shift was aentuated by limati onditions during the summer and earlier aumulation season. The snowfield and glaier budget year was exeptionally dry along the ontinental front of the efield Ranges (see Marus, pp , this volume. Thus less snow was aumulated to feed tributary streams during the summer ablation period. Most of the neve fields were exhausted by the time the Kaskawulsh Glaier drainage shift ourred. Counterating this effet was the relative oolness and low insolation in June and July. This depression of inoming energy was insuffiient to prevent the melting of the shallow snowfields in the tributary watersheds; however, it did redue the usual rates of glaier ablation. The ombination of less glaier runoff and low tributary snow storage aounts for appreiably lower Slims River-dishargein--19'7-than-in-preeding-years;-Peak--- disharge values are, for example, less than half those reorded by Fahnestok in 1965 and Alford in earlier years (Fahnestok, 1969, Table 1. When the Kaskawulsh drainage shift ourred, extremely low disharges followed. Less than 25m 3 /se flowed past the Slims River bridge in August 197. n omparison, Fahnestok (1969 aounted for approximately 85m 3 /se from tributary soures in late July Thus it seems that regional limati events an also exert a major influene on year-toyear disharge of the Slims River. Beause the Slims is the prinipal feeder soure for Kluane Lake, these effets are inevitably signifiant to lake level and to shoreline development. Aknowledgments My gratitude is extended to the Arti nstitute of North Ameria and the Canadian Department of ndian Affairs and Northern Development for finanial and logisti support. The advie given by M. Leonard Bryan and Melvin G. Marus on observational proedures is truly appreiated. am sinerely grateful to the Commission on Geography and Afro-Ameria of the Assoiation of Amerian Geographers for its enouragement. Referenes Bostok, H. S. (1952 Geology of Northwest Shakwak Valley, Yukon Territory,Mem. 247, Geol. Surv. Can. Bostok, H. S. (1969 Kluane Lake: ts drainage and allied problems (115 G, and 115 F E,Paper 69-28, Geol. Surv. Can. Fahnestok, R. K. ( Morphology of the Slims River, in efield Ranges Researh Projet, Sientifi Results, edited by V. C. Bushnell and R. H. Ragle, Vol. 1, pp , Am. Geogr. So. and Arti nst. North Am., New York. Leopold, L. B., Wolman, M.G., and Miller,]. P. (1964 Fluvial -Proesses in Geomorphology,-Freeman Press,--S-an-Franiso- - - i! Oi

9 ,, ES U?CES l\'2-aar'l l... 1 f the nterior U.S. Departxnent o CEFELD RANGES RESEARCH PROJECT SCENTFC RESULTS VOLUME 4 PUBLSHED JONTLY BY THE AMERCAN GEOGRAPHCAL SOCETY AND THE ARCTC NSTTUTE OF NORTH AMERCA

10 Pr:prly of 2Uf AK. ftfsoorces lii&ry APR ! CEFELD RANGES RESEARCH PROJECT SCENTFC RESULTS. Volume 4 Edited by VVAN C.LBUSHNELL Amerian Geographial Soiety and MEL VN G. MARCUS Arizona State University AlA \':A r::r.:rr;::v-r r ' P'(!l'o.., +o._, li... t...,...,. '"''". w.._,..,... _.... \.1 t:; u_s_ fr.r'f' ;,t of -U.-. rh:,ior Published joint/y by AMERCAN GEOGRAPHCAL SOCETY, NEW YORK and ARCTC NSTTUTE OF NORTH AMERCA, MONTREAL 1974