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Journal of Hydrology (2006) 327, 55–67
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Hydrological characteristics of the GangotriGlacier, central Himalayas, India
Pratap Singh a,*, Umesh K. Haritashya b, Naresh Kumar a, Yatveer Singh a
a National Institute of Hydrology, Roorkee 247 667, U.A., Indiab Department of Earth Sciences, Indian Institute of Technology, Roorkee 247 667, U.A., India
Received 5 September 2004; received in revised form 14 September 2005; accepted 2 November 2005
Summary The present study describes the hydrological characteristics of the Gangotri Glacier(286 km2), which is one of the largest Himalayan Glaciers. The study involves collection andanalysis of streamflow records near the snout of the Gangotri Glacier during four consecutiveablation seasons (May–October) (2000–2003). Discharge increases from May onward, reachesits highest value in July and then starts decreasing. Daily mean discharge during the study per-iod varied between 8 and 194 m3 s�1. The distribution of runoff has shown that July contributesmaximum runoff (30.2%) followed by August (26.2%). Maximum diurnal variability in runoff wasobserved in the month of May and September. The strong storage characteristics of the studyglacier are reflected by a comparable magnitude of runoff observed during daytime and night-time. Diurnal variations in hydrograph suggested almost similar pattern from year to year, beingmaximum runoff in the evening and minimum in the morning. Melt-runoff delaying character-istics reflected that over the melt season time lag (tl) varied between 4.00 and 7.30 h, whereastime to peak (tp) varied between 9.00 and 12.30 h. Relationship between mean monthly dis-charge and temperature was found to be much better (R2 = 0.76) than that on daily scale(R2 = 0.50).ª 2005 Elsevier B.V. All rights reserved.
KEYWORDSGangotri Glacier;Storage characteristics;Delaying runoff;Diurnal variation;Flow duration
0d
2
Introduction
Ice is considered as most widespread of all rocks on theearth surface, which presently covers about 10.7%(15.9 · 106 km2) of the total land area (148.3 · 106 km2) orabout 3.1% of the global area (509.6 · 106 km2). Two majorice sheets, namely, Antarctica (13.6 · 106 km2) and Green-
022-1694/$ - see front matter ª 2005 Elsevier B.V. All rights reservedoi:10.1016/j.jhydrol.2005.11.060
* Corresponding author. Tel.: +91 1332 272906; fax: +91 133272123.E-mail address: [email protected] (P. Singh).
land (1.7 · 106 km2) cover the largest extent of the world’sice. These two ice sheets, respectively, covers about 85.6%and 10.9% area of the total available ice extent in the world.The rest of ice surface, which represents about 3.5% area(550,000 km2) of the total ice covered area, is available inthe form of mountain glaciers and ice caps and distributedin different mountain ranges worldwide including south-central Asia, where glacier melt is one of the primary sourceof fresh water (Sharp, 1988; UNEP, 1992; NASA, 2003).About 75% of the world’s total freshwater, out of the avail-able 2.8%, is stored in the form of glacier ice and out of this
.
56 P. Singh et al.
about 90% is stored in Antarctica alone. However, the smallquantity accumulated over mountains outside the Polar Re-gions is of great importance for humankind because of itsproximity to populated areas. The glaciers also respondquickly to changes in the climatic environment, and theiradvancement or retreat can influence the sea level withindecades. This is the reason glaciers are considered as bestindicator of climatic change.
Snow and ice are very good source of water. Most of largeriver systems of the world originate from mountains where asignificant quantity of fresh water is stored in the form ofsnow and glaciers. In the context of India, all three majorriver systems (Ganga, Brahmaputra and Indus) originatefrom the Himalayas, and have substantial contribution fromthe melting of snow and glaciers. The Indian Himalayan re-gion contains total of about 5000 glaciers covering an areaof about 38,000 km2 (GSI, 1999). Now Himalayas are underincreasing pressure due to growing demand for fresh waterin the country due to population growth, urbanization andindustrial development. Hydrological investigations ofHimalayan Glaciers become inevitable because of theirimportance in terms of source of water for irrigation, drink-
Figure 1 Map showing location of the stud
ing water supply and hydroelectric power generation. Anumber of important multipurpose projects in India existon Himalayan rivers and many are under construction orproposed. The power generation from several projects likeSalal, Bhakra, Tehri, Maneri Bhali etc. depends heavily onthe melt runoff generated from melting of snow and glacier.The streamflow characteristics of the glacierized basin aredifferent from those of only rainfed basins or rainfed andsnowfed basins because of snow accumulation and trans-forming into ice, runoff generation, melt water storage,drainage characteristics and water compensation effect(Ferguson, 1985; Rothlisberger and Lang, 1987; Singh andSingh, 2001).
Hydrology of mountainous areas, especially snow andglacier hydrology, is lagging behind in proportion due togreater difficulty in collection of data at higher altitudes.However, the status of hydro-meteorological data has beenimproved in the recent times for few selected glaciers,more extensive work on some selected representative gla-ciers is needed. Melting and runoff generation processes,water yield and its temporal distribution for the snow andglacier fields are the key issues to be addressed. In the high
y area with the Gangotri Glacier system.
Ele
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)
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Area (km2)
Total zone area
Glacier area
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<3800
3800
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Figure 2 Altitudinal distribution of glacierized and non-glacierized area of Gangotri Glacier basin.
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Stage (cm)
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Dis
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)
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Hydrological characteristics of the Gangotri Glacier, central Himalayas, India 57
altitude, Himalayan glacierized basins very limited hydro-logical investigations have been done. The purpose of thepresent work is to understand discharge characteristicsincluding melt water storage behaviour, diurnal variationand delaying parameters. The study also includes develop-ment of relationship between discharge and temperatureand flow–duration curve for the Gangotri Glacier using flowrecords of four years (2000–2003).
Study area
Gangotri Glacier (30�43 N–31�01 N and 79�00 E–79�17 E)is the largest glacier of the Garhwal Himalayas. This gla-cier is located in Uttarkashi district of Uttaranchal stateand classified as valley type glacier. It covers the uppermost part of the Bhagirathi River basin. Although com-monly it is known as Gangotri Glacier, but in fact it isthe Gangotri Glacier system consisting of a cluster ofmany large and small glaciers (Fig. 1). This system com-prises of three major glacier tributaries, namely, Chatu-rangi Glacier (length 22.45 km; area 67.70 km2), RaktvarnGlacier (length 15.90 km; area 55.30 km2) and Kirti Glacier(length 11.05 km; area 33.14 km2) with main GangotriGlacier (length 30.20 km; area 86.32 km2) as trunk partof the system. Besides these three major glaciers othertributary glaciers draining directly into Gangotri Glaciersystem are Swachand, Maindi, and Ghanohim.
The approach to the snout of the glacier includes a trekof about 18 km distance starting from the Gangotri town.The major part of the trekking is along the Bhagirathi River.The shape of the snout keeps on varying due to the breakingapart of large pieces of ice blocks from the terminus of theglacier. Some times these detached glacial blocks float forfew kilometres in the melt water before melting. A largenumber of crevasses are present in the ablation zone. Thesecrevasses are well exposed when seasonal snow accumu-lated in the ablation zone is depleted. Major part of theablation area of the glacier is covered by sediment materiallike boulders, debris and moraines. Total catchment area ofthe Gangotri Glacier study basin up to discharge gauging siteis about 556 km2, out of which glacierized area is about286 km2 (51.4%). The elevation range of the study basin var-ies between 3800 and 7000 m. The altitudinal distribution ofglacierized and non-glacierized area of Gangotri Glacier isshown in Fig. 2.
Figure 3 Stage–discharge relationship developed for gaugingsite near the snout of Gangotri Glacier during melt season 2000.
Data collectionFor hydro-meteorological study of any glacier the first andforemost requirement is availability of continuous and reli-able flow data of at least ablation period (May–October)every year. In India, regular streamflow monitoring sitesare not available in the high altitude region, as is also thecase of Gangotri Glacier until 2000. Most of the studied gla-ciers are monitored only during specific project duration.Thus, keeping all these things in consideration a dischargeobservation site and a meteorological observatory wereestablished near the snout of the Gangotri Glacier in theyear 2000. Details of establishment of site and data collec-tion area given below. Further, analysis is based on thesedata collections.
The selection and establishment of a gauging site was oneof the challenging tasks. Keeping in view several demands,such as, round the clock accessibility to the site, flow ofwater in a single channel, minimum turbulence in flowetc. a suitable gauging site was selected about 3 km down-stream of the snout of glacier (Fig. 1). A concrete wall anda stilling well were constructed on the right bank of the riv-er. An automatic water level recorder was installed on thestilling well to record continuously variations in the waterlevel. A graduated staff gauge is also installed on the gaug-ing site near the stilling well for manual observations ofwater level. For estimation of discharge, the velocity-areamethod was used and to compute the velocity of flow,
58 P. Singh et al.
wooden floats were used. The cross-section area of thechannel was determined with the help of sounding rods atthe beginning of the melt season and was rechecked at theend of the season. To measure velocity, the channel was di-vided into four segments and velocity was measured at eachplace. The surface velocity of streamflow as determined byfloats was found to be in the range of 0.5–4.5 m s�1, beingmaximum during peak melt period. Because the surfacevelocity is higher than the mean velocity, the mean velocitywas determined by multiplying the surface velocity by a fac-tor of 0.90 (Singh and Ramasastri, 2003). After calibratingthe water levels observed from the staff gauge and thewater level recorder, a stage–discharge relationship (ratingcurve) was developed for each ablation season (2000–2003)to convert water levels into discharges. Collection of datafor various stages of flow covering both high and low flowstages and discharges helped in developing the stage–discharge relationship. Fig. 3 shows a stage–discharge rela-tionship developed for summer 2000. The range of dischargeused for constructing stage–discharge relationships for dif-ferent years was 8–194 m3 s�1. Because of the large size ofthe glacier, the discharge was very high, particularly duringthe peak melt period (July and August) therefore the possi-bility of errors in the flow measurements is in the range of±5% (Haritashya et al., in press).
Results and analysis
Distribution of streamflow and water yield
The main sources of runoff from the Gangotri Glacier areaare the melting of ice and snow, and rainfall. Since, rainfallis less, in the study region, therefore, most of the stream-flow is generated from the melting of ice and snow. Meltwater hydraulic systems of the glacier include supraglacial
Figure 4 (a) Daily mean discharge, and (b) monthly discharge obseduring four consecutive melt seasons.
system, englacial and subglacial system. The first two sys-tems exhibit considerable fragility, being easily susceptibleto rapid change, whereas the third system is more resistantto alteration unless ice conditions are dramatically trans-formed (Hooke et al., 1989; Menzies, 1995; Benn and Evans,1998). Finally, total melt water emerges out as integratedrunoff through the snout of the glacier. In the present case,the runoff drained from the well established snout of glacierinto a single melt stream.
Streamflow data was collected at the established gaugingsite for all the study years. Continuous records of the flowprovided hourly flow data. These hourly data were usedto get daily mean flow at the gauging site. Daily meanstreamflow recorded for 2000, 2001, 2002 and 2003 are gi-ven in Fig. 4(a). Distribution of discharge shows increasingtrend from May onward, reaches to its highest value in Julyand then starts reducing. Based on collected records, meanmonthly discharge for May, June, July, August, Septemberand October is observed to be 27, 74, 122, 106, 61 and22 m3 s�1, respectively. In terms of volume, averagemonthly flow for corresponding months is 71, 192, 326,283, 157 and 51 · 106 m3 (Fig. 4(b)). Distribution of runoffindicates maximum runoff in July (30.2%) followed by Au-gust (26.2%). As such, July and August receive about 56.4%of the total melt runoff. Hodgkins (1997) observed similardistribution of runoff in Austre Brøgrerbreen (Svalbard),Arctic region where July and August contributed about80% of the total melt runoff.
Over the whole ablation season (May–October), dailymean discharge varied from 8 to 194 m3 s�1. Maximum meandaily runoff from the basin in 2000, 2001, 2002 and 2003 wasobserved to be 174, 177, 194 and 168 m3 s�1, respectively.Estimations were also made in terms of specific water yieldfrom the study basin. The average monthly specific wateryield is estimated to be 0.13, 0.35, 0.59, 0.51, 0.28 and0.09 m for May, June, July, August, September and October,
rved for different months near the terminus of Gangotri Glacier
Hydrological characteristics of the Gangotri Glacier, central Himalayas, India 59
respectively. The total melt water yield for 2000, 2001,2002 and 2003 was computed to be 1.82, 2.02, 1.90 and2.04 m, respectively. Average melt water yield during thecomplete study period is about 1.91 m. In terms of volume,the total melt water from the Gangotri Glacier for the abla-tion period 2000, 2001, 2002 and 2003 is estimated to be993, 1106, 1036 and 1115 · 106 m3, respectively. Resultsshow that during four ablation period there is only a smallvariation from year to year. In order to understand the run-off generation trends and its variability from year to year, along-term discharge series is required. It is suggested that abroader database must be established for the Gangotri Gla-cier, which contributes a substantial quantum of runoff inthe Bhagirathi River.
Storage characteristics: day and nighttime flows
The storage characteristics of the glaciers are responsiblefor delayed response of melt water generated over the gla-cier surface into runoff. Broadly, melt water storage in aglacier can be classified as (i) long-term storage: includesstorage of water as ice and snow and storage or release ofwater depending on climate, (ii) intermediate-term stor-age: includes seasonal runoff variations and seasonal waterbalance, (iii) short-term storage: includes diurnal storage ofmeltwater in snow, firn and englacial and subglacial chan-nels. Short-term storage or diurnal storage, which controlsthe magnitude of the water runoff, depends on the dynam-ics, size, drainage network, seasonal snow cover and firncover, and size of the bare ice area which generally growsduring ablation season. Water can be stored in the glacierin a number of ways: in surface snow and firn, crevasses,surface pools, englacial pockets, subglacial cavities, engla-cial and subglacial drainage network and in basal sediments(Jansson et al., 2003).
Short-term melt water production and storage character-istics cause a diurnal variation of discharge from the glacier.This short-term storage and release of melt water is trig-gered both by the diurnal cycles of melt water input and cor-responding water pressure variations (Jansson et al., 2003).Due to this storage only part of the melt water produced in aday drains out same day as runoff from the snout. Theremaining melt water emerges gradually on subsequentdays. Thus, runoff observed at particular time is generatedby a combination of melting occurred on the same day andon previous days. Runoff delay varies with the intensityand maturity of the snow and firn on the glacier. The occur-rence of maximum streamflow in the glacierized rivers in thelate afternoon or evening clearly suggests that a major partof the melt water produced during the day period reachesthe snout after few hours (Singh et al., 2005).
To understand the melt water storage behaviour of theGangotri Glacier, continuous streamflow records were di-vided into daytime flow (0900–2000 h) and nighttime flow(2100–0800 h), respectively. Monthly daytime and night-time discharges for the different years are presented inFig. 5. The ratio of monthly daytime discharge to that ofnighttime discharge was computed and is given in Table 1.It was found that this ratio varies to a small extent frommonth to month and year to year.
Streamflow at Gangotri Glacier during daytime andnighttime indicates that in the beginning and at the end
of the melt season, volume of the nighttime flow is veryclose to the daytime flow, but during the peak meltingseason, nighttime flow reduces in comparison to the day-time flow. As shown in Fig. 5, similar trends of daytimeand nighttime flows were observed for all the years.Although very little or no melting takes place during thenighttime, but still there has been significant flow ob-served from the glacier during the nighttime. Such distri-bution of runoff evidently shows the strong melt waterstorage characteristics of the Gangotri Glacier, which ispossible due to its large size. Stronger storage componentof the glacier especially during the beginning of the meltseason also reflects the presence of larger extent ofseasonal snow cover and the firn over the glacier. As theseason progresses the efficiency of the glacier drainagesystem increases (Seaberg et al., 1988). Further investiga-tions are needed to understand whether changes in thedrainage characteristics over the melt season also affectthe runoff behaviour of this glacier or whether storagein snow and firn are dominant.
Changes in diurnal variations in discharge over themelt season
A variation in discharge occurs on hourly, daily and annualcycles, on an irregular basis because of the passage ofweather systems. Mean changes in discharge on diurnalscale for different months are depicted in Fig. 6. It is ob-served that discharge starts rising from May onwards,reaches its maximum in July and then starts reducing. Bothlimbs of hydrograph are almost flat during early and laterpart of melt season. Rising and falling limbs of the hydro-graph become steeper with advancement of the melt sea-son, but the rising limb of the hydrograph is alwayssteeper than the recession limb. Such diurnal variations inhydrograph with season can be explained by the changesin physical features of the basin with time. In the beginningof the melt season, less pronounced diurnal fluctuation indischarge from the glacierized basin may be because ofthe depth and large extent of seasonal snow over the gla-cier, which can have dampening effect on the melt runoff.Under such conditions, runoff can have much delayed re-sponse because melt water passes through the snowpackand flows as interflow after reaching the ice surface. Conse-quently, in the early and later part of the season, both limbsof hydrograph are almost flat. The flatness of the hydro-graph representing no significant changes in the later partof seasons is because of little or no melting due to cold tem-peratures during this period. During mid part of melt season(July–August) intense melting takes place due to availabil-ity of higher radiation and larger extent of exposed glacierice. It results in faster response of melt runoff producingwell distinguished diurnal change in discharge. At this stage,without being significant storage of melt water at the gla-cier surface, melting contributes rapidly to the diurnal hyd-rograph, and system becomes more responsive to diurnalforcing. As shown in Fig. 6, the distribution of hourly dis-charge indicates that maximum runoff (Qmax) is observedin the evening (1700–1900 h) and minimum flow (Qmin) inthe morning (0700–1000 h).
Variations in diurnal amplitude of discharge with seasonare given in Table 2. The diurnal amplitude are 4.6, 17.8,
Figure 5 Monthly distribution of daytime (0900–2000 h) and nighttime (2100–0800 h) discharges observed for different monthsnear the snout of Gangotri Glacier during four consecutive summer seasons.
Table 1 Variation in ratio of monthly daytime discharge tothat of nighttime discharge for different months during four-ablation period (2000–2003)
Month Ratio of monthly daytime discharge tonighttime discharge
2000 2001 2002 2003
May 1.04 1.04 0.99 1.05June 1.01 1.01 1.03 1.01July 1.03 1.06 1.08 1.02August 1.02 1.03 1.01 1.01September 1.00 0.99 0.98 0.98October 1.02 0.99 0.99 0.98
Hours
0
50
100
150
Dis
char
ge
(m3
s-1)
Oct.
May
Sept.
June
Aug.
July
8 12 16 20 24 4 7
Figure 6 Mean diurnal variation in discharge computed fordifferent ablation months using four years data.
60 P. Singh et al.
42.6, 30.2, 11.1 and 3.8 m3 s�1 for May, June, July, August,September and October, respectively, representing meandiurnal discharges as 8.4, 17.6, 32.9, 27.6, 17.2 and 12.7for the corresponding months. Fig. 7 shows that trends ofvariation in diurnal amplitude with season in Gangotri Gla-cier is comparable to the trend observed in Dokriani Glacier,
Himalayas (Singh et al., 2004) but opposite to the trends re-ported from an Arctic glacier (Hodgkins, 2001). It is impor-tant to note that, as opposed to Arctic glaciers, the
0
20
40
60
80
100
May June July Aug. Sept. Oct.
Dokriani (Himalayas)
Gangotri (Himalayas)Scott Turnerbreen (Arctic)
(Qm
ax-Q
min)
/ Qm
ean
(%
)
Figure 7 A comparison of variations in diurnal amplitude ofdischarge between Arctic Glacier and Himalayan Glaciers.
Hydrological characteristics of the Gangotri Glacier, central Himalayas, India 61
maximum discharge for the Himalayan Glaciers (for exam-ple, Gangotri Glacier observes maximum discharge in themonth of July, whereas Dokriani Glacier observes in themonth of August) was observed when the diurnal cycleswere very clear in the discharge. For the Arctic Glacier,the maximum discharge was observed during the early partof the melt season when diurnal cycles were not very evi-dent in the discharge.
Melt-runoff delaying characteristics: time-lag andtime to peak
There is a time-lag between melt water generation over theglacier and the appearance of this melt water as runoff atthe snout of the glacier. To understand the variations intime to peak (tp) and time-lag (tl) between generation ofmelt water and its emergence as runoff, the data collectednear the snout of glacier during the observation period2000–2003 was used. The altitude of meteorological stationwas 3800 m. As solar radiation directly influences the melt-ing, therefore, the necessary criteria for such study is thathydrograph should be of clear weather day which means:either there is no rain and if it is there than it should be lessthan 2 mm and clear sky, which brings maximum insolationand high air temperatures. In other words, clear days wereselected to exclude rain-induced cases. Other importantfactor in such analysis is the measurement of streamflowat or nearest to the snout to minimize the impact of timetaken by the water to travel from snout to gauging site
Table 2 Variations in amplitude of diurnal discharge observed d
Month Date Qmax (m3 s�1) Qmin (m3 s�1) Qmea
May 22.05.2000 56.8 52 54.23.05.2000 56.45 52.15 54.24.05.2000 56.55 52 54.25.05.2000 56.6 52.05 54.
June 11.06.2003 108.8 89.65 99.12.06.2003 109 91.9 100.13.06.2003 112.3 94.94 102.14.06.2003 112.2 94.54 102.
July 28.07.2002 151.7 111.26 129.29.07.2002 153.88 110.76 132.30.07.2002 151.39 109.41 127.31.07.2002 154.03 109.01 129.
August 27.08.2001 125.14 92.59 109.28.08.2001 126.92 95.26 109.29.08.2001 125.97 95.86 110.30.08.2001 123.62 97.26 107.
September 13.09.2000 70.12 59.11 65.14.09.2000 71.12 60.08 64.15.09.2000 70.18 59.13 64.16.09.2000 70.45 59.05 64.
October 07.10.2001 31.89 28.48 30.08.10.2001 31.89 27.79 30.09.10.2001 31.83 28.24 29.10.10.2001 31.8 27.71 29.
and to eliminate the possible contribution from any othersources within the reach from the snout to gauging site.Therefore, a detailed study considering clear weatherhydrographs of different months irrespective of the ablationseason is done because year-to-year variation in discharge isnot significant. For this purpose, hydrographs observed inthe field has been digitised on half hourly basis, which pro-vides close information on important parameters like timelag and time to peak.
For identifying the delaying characteristics, an analysisof hydrographs of three or four consecutive clear weather
uring different months
n (m3 s�1) Qmax � Qmin (m3 s�1) Qmax � Qmin/Qmean (%)
16 4.8 8.8615 4.3 7.9414 4.55 8.4016 4.55 8.40
18 19.15 19.3109 17.1 17.0885 17.36 16.8844 17.66 17.24
04 40.44 31.3459 43.12 32.5241 41.98 32.9552 45.02 34.76
34 32.55 29.7734 31.66 28.9666 30.11 27.2174 26.36 24.47
24 11.01 16.8845 11.04 17.134 11.05 17.1688 11.4 17.57
21 3.41 11.2903 4.1 13.6588 3.59 12.0185 4.09 13.70
62 P. Singh et al.
days rather provides a clear picture. Fig. 8(a) and (b) showscomparison between temperature and discharge at an inter-val of 30 min for four consecutive days in different months.The average values of both tl and tp for different monthsbeing presented in Fig. 9(a) and (b) reveals that they followthe similar trend of changes over the ablation period. They
50
52
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58
60
8 12 16 20 24 4 8 12 16 20 24
22.05.2000 23.05.2000
4 8
8
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11.06.2003 12.06.2003
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28.07.2002 29.07.2002
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4 8 12 16 20 24 4 88 12 16 20 24
27.08.2001 28.08.2001
50
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13.09.2000 14.09.2000
Hou
26
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34
Dis
char
ge
(m3
s-1 )
Dis
char
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(m3
s-1 )
Dis
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Dis
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(m3
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8 12 16 20 24 4 8 12 16 20 24 4 8
07.10.2001 08.10.2001
a
b
Figure 8 Diurnal variation in discharge (solid line) and temperatyears.
are higher in the beginning and end of melt season ascompared to the peak melt season. For Gangotri Glacier tlvaried between 4.00 and 7.30 h, whereas tp varied between9.00 and 12.30 h over the entire melt season (Table 3). Inthe study area, daily discharge peaks lag behind the timeof maximum melting (maximum temperature) on the glacier
0
5
10
15
Tem
per
atu
re (
OC
)T
emp
erat
ure
(OC
)T
emp
erat
ure
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)T
emp
erat
ure
(OC
)T
emp
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(OC
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emp
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(OC
)
16 20 24 4 8 12 16 20 24 4 8
5.2000 25.05.2000
0
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.2003 14.06.2003
0
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.2002 31.07.2002
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24.0
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2001 30.08.200129.08.
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rs
-5
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09.10.2001 10.10.2001
ure (dashed line) for selected clear weather days for different
10R2
May June July Aug. Sept. Oct.0
2
4
6
8
Tim
e-la
g (
ho
urs
) = 0.98
1.6
R2 = 0.94
0
3
6
9
12
15
Tim
e to
pea
k (h
ou
rs)
May June July Aug. Sept. Oct.
May June July Aug. Sept. Oct.
0.6
0.8
1.0
1.2
1.4
Qm
ax/Q
min
R2 = 0.86
a
b
c
Figure 9 Average values of: (a) melt-runoff time-lag, (b)time to peak, and (c) discharge ratios for different summerseasons observed near the snout of Gangotri Glacier.
0 5 10 15 20Temperature (oC)
0
25
50
Dis
char
ge
(mm
)
R2 = 0.5075
Figure 10 Relationship between daily discharges and meantemperatures observed during four consecutive summer sea-sons (2000–2003).
0 5 10 15 20
Temperature (oC)
0
10
20
30
40
50M
elt
dep
th (
mm
)R2 = 0.76
Figure 11 Relationship between mean daily melt depth andtemperatures observed during different months for four con-secutive melt seasons (2000–2003).
Hydrological characteristics of the Gangotri Glacier, central Himalayas, India 63
by few hours. Generally, the magnitude of runoff delay de-pends on the distance the water has to travel through andbelow the glacier, and the configuration of the internal
Table 3 Timings of Tmax, Qmax, Qmin, time lag, time to peak and
Month Time of Tmax
(h)Time of Qmax
(h)Time of Qmi
(h)
May 1300–1400 1930–2030 0800–0830June 1300–1400 1800–1930 0800–0830July 1300–1400 1700–1800 0800August 1300–1400 1730–1830 0800–0830September 1330–1400 1830–1900 0800–0900October 1300–1400 2030–2100 0830–0900
drainage network (Benn and Evans, 1998). In the early partof the melt season both tl and tp are larger because of thedistributed drainage systems, such as linked-cavity
ratio of Qmax to Qmin for different months
n Time lagbetween Tmax
and Qmax, tl (h)
Time to peak,tp (h)
Ratio ofQmax to Qmin
6.00–6.30 11.30–12.30 1.08–1.095.00–5.30 10.30–11.30 1.18–1.224.00 9.00–10.00 1.38–1.414.30 9.00–10.30 1.31–1.355.00–5.30 10.00–11.00 1.19–1.206.30–7.30 11.00–12.00 1.12–1.15
64 P. Singh et al.
networks and strong storage characteristics of the glaciersdue to the presence of seasonal snow cover. The tl as wellas tp is reduced with the advancement in melt season be-cause of the efficient and well developed drainage network(Willis et al., 1990; Hock and Hooke, 1993). The channelizednetwork system changes with season as does the exposedice surface, snowpack area and snow depth. Towards theend of the melt season, diurnal variations are more pro-nounced and follow fluctuations in available energy formelting. It is observed that during this period both tl andtp are higher, which may be due to little melting and majorcontribution rises from the water already stored in theaccumulation area. In order to investigate the inter rela-tionship between the variation in runoff and delaying char-acteristics of the glacierized basin, changes in the dischargeratio, i.e., Qmax/Qmin were computed over the melt period.As illustrated in Fig. 9(c), this discharge ratio for the Gango-tri Glacier varied between 1.08 and 1.41, indicating a largevariation in the runoff over the melt period. A comparisonof runoff delaying parameters with discharge ratio clearlyindicates that changes in tl and tp during the melt seasonare inversely correlated with variations in discharge.
Mel
t d
epth
(m
m)
Mel
t d
epth
(m
m)
0 5 10 15 20
Temperature (oC)
0
10
20
30
40
50 2000 R2 = 0.60
0 5 10 15 20
Temperature (oC)
0
10
20
30
40
2002 R2 = 0.7850
Figure 12 Relationship between mean daily melt depth and tempseasons.
Relationship between discharge and temperature
The melt water discharge from glaciers into proglacial riversis primarily controlled by the energy available for meltwhich is linked to air temperature. Most glaciers exhibitstrong seasonal variations in water runoff, following annualfluctuations in glacier surface ablation due to changes inincoming solar radiation and air temperatures (Benn andEvans, 1998). Therefore, it is important to find out theempirical relationship between discharge and air tempera-ture. For this purpose mean daily discharge is converted intomean depth of melt water over the glacierized area of thestudy basin. In the present study, first a relationship be-tween daily depth of discharge and daily mean temperatureis attempted considering data of all the years (2000–2003)(Fig. 10). For this daily data set, the coefficient of determi-nation (R2) was 0.50. Further, as shown in Fig. 11, relation-ship between mean monthly depth of discharge and meanmonthly temperatures for the entire data set is also investi-gated. A better relationship was observed for mean monthlydata set. At the same time, attempts were also made toinvestigate relationship between mean monthly depth of
0 5 10 15 20
Temperature (oC)
0
10
20
30
40
50M
elt
dep
th (
mm
)
2001 R2 = 0.64
0 5 10 15 20
Temperature (oC)
0
10
20
30
40
Mel
t d
epth
(m
m)
2003 R2 = 0.8950
erature as a mean over individual months for different ablation
Hydrological characteristics of the Gangotri Glacier, central Himalayas, India 65
discharge and temperatures for individual years (Fig. 12).The value of R2 computed for 2000, 2001, 2002 and 2003was 0.60, 0.64, 0.78 and 0.89, respectively. These resultssuggest for a better relationship between discharge andtemperature on monthly scale. High correlation betweenmean monthly values may be due to reduction in variabilityof both discharge and temperatures on monthly scale (Cv fordischarge = 0.27; Cv for temperature = 0.19) as compared todaily scale (Cv for discharge = 0.56; Cv for temperature =0.28).
Variability in runoff and temperature
The monthly variation of runoff through hydrograph andtemperature through thermograph is calculated for different
May June July Aug. Sep. Oct.
2000
2002
0
0.1
0.2
0.3
0.4
0.5
Cv
0
0.1
0.2
0.3
0.4
0.5
Cv
0
0.1
0.2
0.3
0.4
0.5
Cv
2
May June July Aug. Sep. Oct.
May June
Figure 13 Changes in coefficient of variation (Cv) for
years (2000–2003) and as well as taking average for all themonths (Fig. 13). For comparative purposes, betweenmonths, coefficient of variation (Cv) is used here as a mea-sure of variability, rather than standard deviation. Cv is theratio of standard deviation to the mean. The result suggeststhat discharges observed during May and September showsmaximum variability, whereas October has least. Variabilityin discharge for June, July and August lies in between maxi-mum and minimum values. Analysis of temperature variabil-ity shows trends similar to the variability of discharge exceptin the month of October when the variability in temperatureis higher. This may be due to the fact that in the end of themelt season, temperature in the higher reaches becomesvery low which could not able to influence melting and dis-charge is mainly drained from the previously stored water.
0
0.1
0.2
0.3
0.4
0.5
Cv
2001
0.3
0.4
0.5
Cv
2003
Temperature
May June July Aug.
Discharge
0
0.1
0.2
000-2003
Sep. Oct.
May June July Aug. Sep. Oct.
July Aug. Sep. Oct.
discharge and temperature over the melt season.
0 20 40 60 80
Dependability (%)
0
50
100
150
Str
eam
flo
w (
m3 s
-1)
200
100
Figure 14 Flow–duration curve developed on the basis ofmean daily discharge data collected near the snout of theGangotri Glacier for four consecutive summer seasons (May–October) (2000–2003).
66 P. Singh et al.
Other possible reason of higher temperature variabilityin October is that the diurnal range of temperature(Tmax � Tmin) is higher in this month (Singh and Ramasastri,2003).
Flow–duration curve
Flow–duration curve have frequently been used in varioushydrological studies, such as hydropower, water supplyand irrigation planning, river and reservoir sedimentationstudies and low-flow augmentation (Vogel and Fennessey,1994). Streamflow variability can be studied through flowduration curve, which provides a graphical representationof the frequency distribution of the complete flow regime.These curves can be obtained by plotting discharge fromgauged river against various levels of dependability (% oftime) the flow is equalled or exceeded.
A flow–duration curve developed for Gangotri Glaciergauging site using daily streamflow data for the four consec-utive ablation period (2000–2003) is shown in Fig. 14. Theflow corresponding to 50, 75 and 90% dependability is foundto be 75.9, 35.5 and 21 m3 s�1. Flat curve observed in theupper portion of the flow–duration curve is typical charac-teristic of glacierized river, whereas relatively straightcurve in the lower portion indicates low baseflow at thesite. These values can be used for planning water resourcesprojects in the upper part of the Bhagirathi river. However,more studies based on larger database are needed for suchresults. Moreover, inclusion of winter runoff data will fur-ther improve such curves, which are currently not available.
Conclusions
Hydrological characteristics of the Gangotri Glacier, one ofthe largest glaciers of the Himalayas, have been investi-gated by collecting discharge data for four years by estab-lishing a gauging site very close to the snout of theglacier. The study has provided information on diurnal and
seasonal distribution of runoff. The maximum contributionto the total flow was recorded in July (30.2%) followed byAugust (26.2%). Similar trend of runoff distribution wasfound for all the years. The diurnal variations in the dis-charge were almost negligible in the beginning of the meltseason, but were well distinguished during peak melt period(July–August), and again gradually diminished towards theclose of the ablation season. One of the most importantcharacteristic feature of study area is very little rainfall(�260 mm), which suggests that most of the discharge hasbeen derived from the melting of glacier. The magnitudeof total seasonal runoff varied within 10% from year to year.The average specific water yield of the study basin is esti-mated to be 1.91 m.
Based on the comparable magnitude of daytime andnighttime flows, this study suggests for strong storage char-acteristics of the Gangotri Glacier. Hourly discharge patternshows that maximum discharge was observed in evening(1700–1900 h) and minimum discharge in the morning(0700–1000 h). Diurnal variations in discharge followeddiurnal variations in temperature with a certain lag of time.The value of time-lag varies over the melt season showedthat temperature was the most important factor and achange from clear skies to overcast resulted in a reductionof the ablation rate in early afternoon with an immediatereduction in the height of the daily peak discharge. Thetime-lag between temperature and discharge (4.00–7.30 h) and time to peak (9.00–12.30 h) were higher inthe beginning and towards the end of the season as com-pared to the peak melt season. Prevailing air temperaturesgoverned the magnitude and distribution of runoff.
Acknowledgement
The authors thank the Department of Science and Technol-ogy, Government of India for providing financial support tocarry out these investigations.
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