CHAPTER 7 HYDROLOGICAL STUDIES - Ministry of Environment and

134 Pages·2011·5.37 MB·English

CHAPTER 7

HYDROLOGICAL STUDIES

7.1 General Appraisal of Hydrology of the Study Area

Although the headwaters region of Ganga in the Himalaya is dotted by a
number of mighty tributaries, the Bhagirathi River that rises from the Gangotri glacier
at Gomukh at an elevation of about 4000 m is traditionally considered to be the source
of Ganga River. The other main stream that originates in the Ganga basin in
Uttarakhand is the Alaknanda originating from Satopanth and Bhagirath Kherag
glaciers. Flowing downhill, Bhagirathi and Alaknanda river meet at Devprayag to
form Ganga River. Thus, the Ganga river basin up to Devprayag has two distinct sub-
basins: Bhagirathi and Alaknanda basins. The Alaknanda – Bhagirathi river basins up
to Devprayag cover a catchment area of 19,600 sq. km. A map showing the main
rivers and their catchment areas in the basin is given in Fig. 7.1.

To understand the hydrologic behavior of the area, it is important to describe
its physiography. Fig. 7.2 shows the physiography of the study area and a description
of the same follows.

7.1.1 Physiography of the Bhagirathi Basin

A channel emerging from the Gangotri glacier at Gomukh is considered to be
the source of the Ganga River. Gangotri glacier is located at an elevation above 4000
m in Uttarkashi district. The Ganga River bed up to Gangotri is filled up with debris
left behind due to recession of glaciers. Further downstream of Gangotri, the evidence
of broad U shaped valley of glacial origin is seen only at the higher elevation and the
river has cut a narrow V-shaped fluvial valley at the lower evlevation up to Kharali.
The bed slope is steep in the upper reaches and is of the order of 50.0 m to 3.0 m per
km from Gangotri to Loharinag Dingad. It decreases to 20.0 m per km in its descent
from Loharinag to Tehri. The total catchment area of Bhagirathi River is 8846.64 sq.
km and lies in Uttarkashi and Tehri Garhwal districts.This catchment can be sub-
divided into the watershed of the Bhagirathi, Bhilangana and Asi Ganga rivers.

In the Bhagirathi sub-basin, the highest and the most fascinating zone is above
4000 m elevation. Most of it is snowbound. This zone is the principal source of water
and major tributaries of Ganga River emanate from this zone. No vegetation grows in
this area. This zone is not inhabited by man. Occasionally shepherds visit some places
with flocks of sheep. Between 4000 m and 3000 m elevation the valleys and
amphitheatres are filled with glacial debris which is being slowly removed by rivers.
This zone has plenty of alpine meadows which provide pastures for semi-nomadic
tribes. This zone supports sub-alpine type trees.

Between elevation 3000 m and 2000 m occur tremendous gorges. Truncated
spurs rise steeply to dizzy heights. Over them descend water falls from hanging
valleys. This zone is also sparsely populated. The habitation and communication lie
along valley bottom. The area is extremely rugged. This zone has some of rich
temperate forests and generally good vegetation. It has reasonable concentration of

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Fig. 7.1 Drainage Network and Catchments of Major Rivers

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Fig. 7.2 Physiography of Alaknanda and Bhagirathi Basin

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trees. The fields are generally scattered, small and in steps. Between elevation 2000 m
and 1000 m river terraces are quite common. The valleys are open. Terraces provide
fertile land for intensive cultivation and as such this zone has comparatively high
density of population. This zone also supports sub-tropical chir forests. Most of the
project area falls between the slope 33% to 100%. This reflects its vulnerability to soil
erosion and thus emphasizes the need to protect the area against soil erosion.

Bhilangana and Asiganga are the major tributaries of Bhagirathi River.
Asiganga joins Bhagirathi River upstream of Uttarkashi. Bhilangana River originates
from Khatling glacier and joins Bhagirathi River at Tehri. It has its own sub-
tributaries, namely Balganga and Dharni Ganga.

7.1.1.1 Glaciers

Very large number of glaciers exist above the snow line. The factors
controlling the glacierization of an area include the height of ridges, the orientation of
slopes and the amount and type of precipitation in the area. The Gangotri system is a
cluster of glaciers comprising the main Gangotri glacier (length: 30.2 km; width:
0.20-2.35 km; area: 86.32 km2) as trunk part of the system. The other major glaciers
of the system are: Raktvarn (55.30 km2), Chaturangi (67.70 km2), Kirti (33.14 km2),
Swachand (16.71 km2), Ghanohim (12.97 km2), and a few others (13 km2). Depth of
the glacier is about 200 m and the elevation varies from 4,000-7,000 m. Satopanth and
Bhagirath Kharak glaciers in upper Alaknanda basin originate from the peaks of
Chaukhamba and Badrinath range. These glaciers are 13 and 18 km long respectively
with snouts at an altitude of 3800m.

Because of the large size of the Gangotri glacier, its melt water stream, the
Bhagirathi River is full-fledged river even as it emerges from the sub-glacial tunnel at
the glacier terminus the Gaumukh (Cow’s mouth).

7.1.1.2 Rainfall

The basic pattern of climate of our country is governed by summer and winter
monsoon systems of Asia. The winter rains are brought by the ‘Western disturbances’
and the summer rains by the summer monsoon winds. For all the seasonal regularity
of monsoon winds and rainfall, local climates (over much of the area) are quite
variable. Sometimes, the rains may come at the expected time or rainfall over an
entire monsoon season may be considerably diminished. By contrast, there will be
time when the rainfall is unusually heavy leading often to disastrous floods. In the
interior region of catchment, rainfall is very low. Annual rainfall is about 1500-2000
mm. Fig. 7.3 shows monthly rainfall at Uttarkashi and Tehri stations in the Bhagirathi
basin.

The maximum rainfall is observed in monsoon months due to south west
monsoon which normally strikes the Garhwal Himalayas towards the end of June and
withdraws from the region towards the end of September. The precipitation is due to
the passage of depressions and or cyclonic storms from the Bay of Bengal over the
region. After originating from the Bay of Bengal, the monsoon winds move in north
west direction and strike the Garhwal Himalayas. The winter precipitation in the basin
is due to western disturbances advancing from Afghanistan and West Pakistan.

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Fig. 7.3 Monthly rainfall at Uttarkashi (upper) and Tehri (lower) stations in the
Bhagirathi basin.

7.1.1.3 Temperature

Temperature varies greatly from place to place and from month to month.
Maximum temperature ranges from 30oC to 36oC while minimum between 0oC to
6oC. For every 1000 m rise in elevation, the mean temperature falls by approximately
6oC.

7.1.1.4 Wind

The wind pattern in the area is extremely complicated. The general direction
of the flow over the mountains in winter is from North-East to North-West. Over
mountains the actual wind may show considerable deviation due to local influences.
At higher levels, the winds are westerly of about 120 km per hour reaching 160 km
per hour or more. At low levels they are about 50-60 km per hour.

7.1.2 Physiography of the Alaknanda Basin

The Bhagirath Kharak and Satopanth glaciers serve as the major source of the
Alaknanda River. Besides this, Luri Glacier and Bhagnyu glacier feed the Alaknanda
channel. The Alaknanda flows from Mana just upstream of Badrinath and the

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Dhauliganga flows from Malari to its confluence with the Alaknanda immediately
downstream of Joshimath. Most of the catchment areas of the Alaknanda River and
its tributaries in the headwater regions are covered with snow and glaciers.

The Alaknanda catchment, upstream of Vishnuprayag, represents an
asymmetrical basin in which the right bank slopes cover larger land area. The river
flows from west to east from Satopanth/ Kharak Bhagirath glaciers and turns towards
south near Mana. On the other hand, its major tributary, the Saraswati river, flows
from north to south and confluences with the Alaknanda River on its left bank near
Mana at 3,120 m.

The major glaciers present in the catchment are Khular Bank, Khuliagarvia
Gal, Anadeb Gal, Dakhni Nakthoni Gal, Uttar Nakthoni Gal, Paschimi Kamet Glacier,
Dakhni Chamrao Glacier, Uttar Chamrao Glacier, Balbala Bank, Tara Bank, Arwa
bank, Kalandani Bank, Vidum Bank, Bhagnyu Bank, Bhagirath Kharak and Satopanth
Bank. Arwa Tal, Rishi Kund, Sankunni and Satopanth Tal are four major lakes
present in the catchment.

In general, radial and rectangular drainage networks characterize the
catchment region and the small order basins show dendritic pattern. In particular a
radial drainage pattern is present around the important lake, Arwa Tal, in the
Alaknanda catchment.

The Saraswati River, which rises in the Tara glacier, is the major left bank
tributary of the Alaknanda River in its headwater region. Most part of the Saraswati
River catchment upstream of the confluence of Arwa nala (4,016 m) is covered with
snow. Glaciers and snow avalanches descend up to the river bed in this stretch.
Downstream of Mana, Kanchan Ganga, Rishi Ganga, Ghrit Ganga and Khirao Ganga
are important tributary streams of the Alaknanda River.

Rishiganga is a big tributary joining Alaknanda River on its right bank
downstream of Mana. Rishiganga has its source in the glaciated area and snowfields
on the northern flank of Nilkanth (6,596 m) peak. Flowing eastward, it confluences
with Alaknanda River on its right bank near Badrinath. Most parts of the catchment of
Rishiganga below 4200 m are either barren or covered with glacial moraines.

Originating from Khular bank glacier above 5400 m elevation Ghrit Ganga
joins the Alaknanda River at 2470 m near Hanuman Chhati. The Khirao Ganga
flowing from Panpatia glacier at 3800 m elevation joins the Alaknanda River on its
right bank at 2330 m elevation opposite to Benakulli village.

The Dhauliganga originates from Ganesh Parbat glacier lying above 6000 m.
At Phatatoli, the Dhauliganga receives water from the Silakangla (Urla) glacier.
Downstream, it maintains its south-westward course until it reaches Khal Kurans. In
this stretch the river receives a substantial input of water from a right bank tributary
near Shepak Kharak. This right bank tributary receives water from Uttari Raikana,
Raikana, Purbi Kamet, Deoban and Semkharak Ka glaciers. Upstream of Khal
Kurans the river receives water on its right bank from a small glacier which lies in the
south of Semkharak ka glacier. Downstream of Khal Kurans the river turns towards
southeast and flows following the northern flank of Ramkhulta Dhar till Janti Ghat. At

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Gamsali, Amrit Ganga rising in the Bankund glacier drains into the Dhauliganga
River on its right bank. At Kuikuti, the river receives water from Girthiganga on its
left bank.

Girthiganga is a major tributary of Dhauliganga. The river originates from
Naijgaon Peak and confluences with the Dhauliganga at Kurkuti. Dhauliganga, after
taking a hair-pin bend near the Bunga Peak (4331 m), flows towards the southwest
from Malari to Reni. At Reni, Rishi Ganga joins Dhauliganga River on its left bank.
Most parts of the catchment of the Dhauliganga River are either barren or covered
with snow and glaciers.

Birahi Ganga flows for 35 km up to its confluence point with Alaknanda
River. In its total length from Nanda Glacier to confluence with Alaknanda, it has a
drop of about 4950 m before joining Alaknanda. There are several important nallahs
joining this river from both banks. The main important left bank nallahs are Gudiyar
Gadhera, Biori Gadhera and Begar nalla. The main streams joining it from right bank
are Dhadhali gad, Shyam gad, Rogila gad and Pui Gadhera etc.

Nandakini River is also an important tributary of Alaknanda River and meets
it on its left bank at an elevation of 870 m at Nandprayag. The Nandakini River has its
origin at an elevation of 6620 m in Nanda Ghungti glacier. The east to west drainage
is formed by the Nandadevi mountain range that is characterized by steep slopes
covered with dense forests. All these constitute water sources for the Nandakini River.
Nandakini flows from east to west direction till its confluence with Alaknanda. The
basin has a rectangular shape. The catchment of the Nandakini River lies between the
latitudes 30° 10' to 30° 21' N and longitudes 79° 25' to 79° 46' E. The highest
elevation in the basin is about 6620 m. Areas of the basin above 4000m are
considered to the permanent snow covered whereas those between 4000 to 2200 m are
dominated by forest. The areas below 2200 m are dominated by forest and agricultural
lands. The gradient of Nandakini River in initial reach is steep and becomes moderate
in later stages. There is no consumptive use of water in between the proposed intake
and powerhouse site.

Precipitation in the Nandakini catchment area is in the form of snow and rain.
The catchment receives moderate to heavy rainfall during monsoon whereas during
winter, it receives moderate snowfall at higher altitude and rainfall at lower altitude.
The Nandakini River runoff during monsoon is very high due to the heavy and
prolonged rains. The runoff during March to June is predominantly snow melt.

The Pinder River originates from Pindari Glacier at an elevation of 5,200 m.
The glacier lies between the Nanda Devi and Nanda Kot peaks and its snout is at an
elevation of 3,627 m. The glacier is 5 km long and 300 to 400 m wide. The permanent
snow cover is reported to be above EL 4,600 m. High elevation zone in catchment
area rises up to about EL 6,600 m. About 20% of the catchment area is covered by
snow/glacier, about 50 % is open forest, 12% dense forest. In its initial course, the
Pinder River flows through sedimentary rocks and then it meanders through quart
schists. Granite is found in abundance in this area. The Pinder River has cut a gorge in
thick glacial deposits up to nearly 10 km. The total length of the river is 124 km
flowing from east to west and drainage area is 1688 km2 till the confluence with
Alaknanda River at Karanprayag. The main tributaries of Pinder are Kail Ganga,

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Pranmati Gad, Meing, Gadhera, Kewar Gadhera, Chopta Gad and Ata Gad. Besides
these, there are many small streams and natural springs adding discharge in Pinder
River.

The Mandakini River is an important tributary of the Alaknanda River which
joins the latter at Rudraprayag. The length of Alaknanda River up to Rudraprayag is
180 km with an average slope of 24.0 m per km. The Mandakini river runs for a
length of 80.0 km up to the confluence at Rudraprayag with an average slope of 42.0
m per km. The famous shrine of Kedarnath is located in Mandakini sub-basin.

Flowing past the town of Srinagar, Alaknanda River meets Bhagirathi River at
Devprayag to form Ganga River. The total catchment area of Alaknanda River is
12587.23 sq. km and lies in Chamoli, Pithoragarh, Bageshwar, and Pauri Garhwal
districts. The total catchment area at Devprayag is 19600 sq. km. Some more
information about physiography of the area is given in Chapter 8.

7.1.2.1 Climate and Rainfall

The mountain topography plays a vital role in the weather and climate of the
area. The climate is ‘tropical monsoon’ type with most of the rainfall occurring in the
summer monsoon of June through October due to tropical storms and depressions
originating in the Bay of Bengal. The mean annual rainfall over the Alaknanda
catchment above Rudraprayag varies between 1000 mm and 2000 mm.

The annual rainfall in the Alaknanda basin ranges from 1000 to 1600 mm and
nearly 75% of the rainfall occurs during the monsoon months. Fig. 7.4 shows the
average monthly rainfall at Joshimath. Most river channels in this sub-basin are
deeply incised with steep valley slopes. Valley slopes in some segments, particularly
in the upper reaches are very steep and unstable. Landslides and sediment movement
as debris flow are frequent in these reaches. The mean annual rainfalls at Joshimath,
Munsyari, Rudraprayag, Okimath, Pauri, Chaukri and Tijjam are 1044 mm, 3005 mm,
1225 mm, 1757 mm, 1080 mm, 1729 mm and 2571 mm respectively. The annual
maximum temperature recorded at Rudraprayag is 45oC and the minimum
temperature is 2.5oC.

In the higher elevations of the Greater Himalayas, the snow accumulation
starts from the beginning of November and reaches maximum in January / February.
The snow-melt begins in March and reaches the maximum value in May-June
contributing substantially to the river flows. In winter snow-line comes down to near
about 2000 m – 3000 m rising to about 5000 m in August – September. The
contribution of the snow and glacier melt to the volume of river flows is rather limited
in the study area and progressively the contribution from rainfall increases as one
moves downstream. The rivers of the region show strong seasonal fluctuation in the
discharge.

The maximum and minimum discharges of the Ganga River at Devprayag
during 1990-91 were 4061 and 125 cumec, respectively (Singh and Hasnain, 1998).
During this period, the maximum and minimum contribution of the Alaknanda to the
total discharge was 3000 and 85 cumec, respectively. The flow of Alaknanda River at
Devprayag is nearly twice as big as that of Bhagirathi River.

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Fig. 7.4: Distribution of annual rainfall at Joshimath.

Figure 7.5 shows a line diagram of Ganga and its major tributaries (numbers in
the figure are average annual flows in MCM or million cubic meters) in virgin
conditions.
Yamuna Ganga
Tajewala 10,750 Devprayag 22,000
Delhi 13,700 Haridwar 23,900
Chambal 30,050 Narora 31,400
Betwa 10,000
Ken 11,300 15,620 Ramganga
93,020 Allahabad 152,000 58,980

Tons 5,910
7,390 Gomati
94,400 Ghaghara
Sone 31,800
52,200 Gandak
Patna 364,000
68,340 Kosi
Farakka 459,040

Fig. 7.5 Line diagram of Ganga and its major tributaries.
Numbers are average annual flows in MCM (million cubic meters).

7.1.3 Appraisal of Surface Water Resources

The purpose of appraising water resources is to determine the source, extent
and dependability of supply. Estimation of surface water availability (surface water
potential in the basin) is one of the prime requirements for planning and design of
works on any river system. Quantity of flow and associated dependability are the key
considerations.

7.1.4 Data Availability

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A line diagram of the Alaknanda and Bhagirathi basin up to Devprayag river
basin showing the locations of various river gauging stations is given in Fig. 7.11. A
water-year is defined as the period from the month of June to May in the following
year.

7.1.4.1 River gauging stations

Daily gauge and discharge data of 16 stations were collected from the Central
Water Commission (CWC), New Delhi. Fig. 7.6 shows location of the gauging sites
of CWC in the study area. After preliminary scrutiny of the data, length of time-series
and locating the gaps, it was seen that the data of only 9 gauging sites could be used
in the study. Out of these, two sites fall on the tributaries and the rest are on the two
main rivers Alaknanda and Bhagirathi basins.

Daily observed discharges data at nine stations as per details in Table 7.1 were
used for estimation of various quantities of interest.

Table 7.1 Availability of discharge data obtained from CWC

S. Name of Name of Catchment Period of Range of
No. Discharge River area (sq. Record discharge
Gauging Station km) (cumec)
1 Uttarkashi Bhagirathi 4555 1989-90 to 1.8 to 1011
2008-09
2 Tehri-G5 Bhagirathi 7208 1989-90 to 0.8 to 1907
2008-09
3 Deoprayag-A1 Bhagirathi 7813 1989-90 to 0.5 to 8255
2008-09
4 Badrinath Alaknanda 1285 1989-90 to --
2008-09
5 Joshimath Alaknanda 4508 1989-90 to 7.3 to 960
2008-09
6 Karnaprayag Pinder 2294 1989-90 to 11.5 to
2008-09 1640
7 Chandrapuri Mandakini 1297 1989-90 to 11.2 to
2004-05 1028
8 Rudraprayag -A5 Mandakini 1644 1989-90 to 49 to 2873
(before confluence) 2008-09
9 Rudraprayag -G5 Alaknanda 10675 1989-90 to 50.7 to
(after confluence) 2008-09 3762

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