Journal of Radioanalytical and Nuclear Chemistry, Vol. 257, No. 1 (2003) 5-9
Use of isotopes in search of Lost River
S. M.Rao
15, Sarovar, Sector 9A, Vashi, Navi Mumbai 400 703, India (Received November 6, 2002)
Ample evidence exists from ancient lndian texts, geomorphology and sedimentology that a mighty river that once originated in the Himalayas flowed in the North-west lndia during 7000-3000 BP and disappeared in the sands of the Rajasthan desert. Remote sensing combined with ground search identified part of the buried channel of the ancient river in the Jaisalmer region of Rajasthan. Isotope study showed that the fresh groundwater in that region was indeed ancient and slowly moving southwest and probably had headwater connection in the lower ranges of Himalayas, but not to any glacier. The isotope data CZH,180, 3H and 14C) compare weil with the data in a similar study on another bral1ch of the buried channel in the Cholistan part of the Thar Desert in Pakistan.
Introduction
The 'Lost River' of Northwest India generally considered as the legendary Sarasvati River of Vedic times has been discussed in large detail in a recent publication!. The subject evokes strong feelings of reverence, curiosity and scientific enthusiasm in people of different pursuits. Scholars and students of the Vedas consider it as their spiritual enquiry, historians and archeologists like to investigate the Lost River as the cradle of a civilization preceding the Indus Valley and finally water resources specialists would like to locate the buried channel of the river and develop it as a groundwater sanctuary. It is not then surprising that there is tremendous active interest today to search for a river, which disappeared thousands of years back.
Background
Rigveda describes the birth and glory of the Sarasvati River. God Indra was praised by the Rigvedic sages for killing the serpent demon Ahi with his Thunderbolt and releasing the waters held by the demon.
They say "Oh Indra! On your being born and with fear of your rage, heavens trembled. Huge mountains were fearful and river waters started flowing moistening the desert. Oh Indra! You struck down barriers and broke open mountains."
In fact, Rigveda mentions release of seven rivers:
Sarasvati, Sutlej, Chenab, Ravi, Jhelum and Indus, but gives pride of place to Sarasvati as the biggest and most majestic of all. Whereas all the others are still major rivers in Northwest India and Pakistan, Sarasvati dwindled down to a small monsoon rivulet and is a mere tributary to a small river Ghaggar that disappears into the sands of the Thar Desert.
The question is whether it was the melting of the glaciers at the end of the last ice age ten thousand years back or whether it was the tectonics that was responsible
*E-mail: smraol@myiris.com
for the release of the seven rivers. The Rigvedic descrip- tion of the sudden appearance of the rivers following the breaking up of mountains distinctly points out tectonics being responsible for the birth of Sarasvati and other rivers. Glacier melting would have taken thousands of years for the river to attain the Rigvedic description of its majesty and its tempestuous roar while cascading down the Himalayan slopes and reaching the ocean.
Let's look at a brief chronology of events in Northwest India2 during the Holocene (extracted from cited reference) given in Table 1.
The birth of Sarasvati probably occurred around 6000-7000 BP.
The flow in the river started dwindling by about 4000-3000 BP. The epic Mahabharata refers to it as a sluggish river, meandering and migrating. The Puranas give its place of birth as Plaksa Prasravana (lower Himalayas) and disappearance as Vinasana (Rajasthan).
These are similar to the source and place of disappearance of the present day Ghaggar River. They also refer to its flow through a series of lakes towards the end of its life.
How did Sarasvati disappear?
Though the wet c1irnate ended around 4000 BP in large parts of Northwest India, it does not fully explain the disappearance of the Himalayan River Sarasvati.
Something catac1ysmic happened around 3000 BP. It could be tectonics and rise of the Aravali hill range. This drastically changed river drainage pattern of Northwest India. Desertification must have preceded the tectonic disturbance. Ancient texts refer to the river as flowing into the desert.
Tectonics3 must have cut off the main tributaries Jamuna and Sutlej from Sarasvati. Sutlej migrated west and joined Indus whereas Jamuna migrated east and joined Ganges near Allahabad.
A combination of tectonics and onset of aridity might have caused the disappearance of Vedic Sarasvati.
S. MRAo:USEOFISOTOPESINSEARCHOFLOSTRIvER
Table 1. Brief chronology of events in Northwest India Period
(HP) 10,000
8,000 7,000 6,000 5,000 4,000 3,000 2000
Events
End oflast ice age/ Advent ofwet phase End of aridity
Wet spell-break up ofHimalayas (tectonics)-release of seven rivers (Sarasvati +) Rivers in Ml flow-agriculture commenced
Sarasvati valley civilization at its height (archeological sites) End ofwet c1imate
Tectonics - uplift of the Aravali hill range - Sarasvati flow disrupted before being lost Aridity in Indus valley- tectonic activity in llth/13th century
Search
Search for the location of the buried channel of the Lost River has been going on for more than a hundred years. Max MUELLER'S translation of the Rigveda appears to have set the trend. Two geologists,
R
D.OLDHAM (1886)4 and C. F. OLDHAM (1893)5 of the Geological Survey of India were probably the first to independently look for the buried channel in the Thar Desert in late nineteenth century. They were not sure . whether they had located the Sutlej, the Jamuna or the Sarasvati. They supported the view that the disappearance of the river was more related to tectonics rather than reduction in rainfall.
More than 1000 pre- Harappan and Harappan archeological sites located along the dry Ghaggar and Hakra riverbeds is further evidence of the existence of a mighty river in the pasto
With the availability of new technological tools like remote sensing and isotope geochemistry, there is resurgence of enthusiasm to search for the Lost River (Sarasvati) in the recent decades.
Remote sensing
There is an obvious advantage of looking at any terrain from a height. Higher one goes up and looks down and has tools of high resolution, better is the chance to identify discontinuities. Aerial photography was used in the sixties. LANDSAT and IRS satellite imageries were made available from the seventies.
Palaeochannels are usually associated with dense vegetation and are detectable with multispectral optical sensors. Mineral deposits on the surface interfere with
Advanced facilities in remote sensing satellites enabled the Indian Space Research Organisation and other agencies detect a number of palaeochannels, undetected earlier.5 The Rajasthan desert is seen strewn with buried channels. Which one is that of the Lost River/Sarasvati?
The Ghaggar - Hakra - Nara dry riverbed extending from Ganganagar district in Rajasthan, entering Pakistan and reentering India at Tanot in the Jaisalmer district attracted special attention. Remote sensing detected two courses6 in the Ganganagar district; one westward towards Fort Abbas in Pakistan and the other in Southwest direction towards Khangarh in Pakistan. The SW course enters India at Tanot in the Jaisalmer district of Rajasthan along the Indo-Pakistan border. Here again it has two branches, one north of Tanot and the other 14 km south of Tanot. It is the latter, which generated maximum interest. In the Kishangarh - Ghantiyali - Ghotaru region (Fig. 1)through which it passes, fresh groundwater occurs at a depth of 30 m and below, dug wells do not dry up in sunnner and the water level in the tube wells does not go down even after good pumping activity. This region was thus selected for isotope study.
The hydrogeological formation comprises Quatemary alluvium covered with thick sand dunes. The water table, as mentioned earlier, is very deep. The sand dunes are predominantly transverse oriented in the NW- SE direction. There is no conspicuous drainage system.
The interdunal depressions and fiats are the sites for scattered settlement, vegetation and used as routes for travel through the region.
Isotope stndy
S. M RAo: USE OF ISOTOPES IN SEAReR OF LOST RIvER
,..
.
JO" • .... .... ...
...
.
~ STUDY AREA
sruovAREA, JAISA~MER
N
.AS.UlAR
~
8 5'01530 Km ••
Fig.1. Location map of the studyarea6
Table 2. Results of analyses of sorne representative groundwater samples from Jaisalmer Location
*DW/TWIHP0180,0/00E.c.,IlS/cm 3H., TU l4eage in years (uncorrected)
Dharmikua
2330DW -7-5 2 1800 Kishangarh
3500TW -5.6
<0.56000 Kuriaberi
2100DW -5.7
<0.54500 Nathurakua
3000DW -6.3
<0.53000 Ghantiyali
3700TW -6.6
<0.59500 Ghantiyali
2800DW -6.0
<0.55000 Ranau
1900TW -6.2
<0.56000 Sadewala tar
7600TW -3.4
<0.522000 Sadewala tar
2060DW -6.0 2 Longewala
2740TW -6.2
<0.519000 Ghotaru
2300TW -6.9
<0.513000 Ghotaru
3700DW -6.4 1 4000 Asutar
2600TW -6.3
<0.513000 Asutar
2400DW <0.5 Langtala
3400HP -5.0
<0.53000 Langtala
2380DW -6.0 1 3500 Dostmohkua
1400DW -6.5 1 6000
*DW/TWIHP refer to Dugwell/Tubewell/Hand pump.
s.M.RAo: USE OF ISOTOPES IN SEARCH OF LOST RIVER
The isotopic composition of the groundwater depends on its origin and any evaporation it had undergone before entering the ground. 2H and
180
are stable isotopes like IH and160
and their concentrations are indicated as per mille (%0) deviations from Standard Mean Ocean Water (SMOW) and represented as 82H and8180.
3H (tritium) is a radioactive isotope produced in the upper atmosphere by cosmic radiation. 1ts concentration is given in tritium UllÎts (TU). (1 TU=
1 atom of tritium in 1018 atoms of hydrogen). Since it is relatively short lived (T1I2=
12.3 y), its absence indicates that the water is not of recent origÎll. ln addition carbonates and bicarbonates dissolved Îll water have radioactive 14C, also produced naturally in the upper atrnosphere by cosmic radiation. Carbon-14 values are given as percentage Modem Carbon (pMC).Groundwater ages are then calculated using the half-life of 14C (T1I2
=
5730 y). Since carbon in water may exchange with carbon in the aquifer matrix, 14C ages need to be corrected suitably. Uncorrected ages are still valuable to identify palaeowaters, which are thousands ofyears old.The objective of the isotope investigation of the selected portion of the buried channel (Fig. lb), supposed to be oflhe Lost River, was to characterize the shallow and deep ground waters, determÎlle their ages, identify their sources of recharge and confinn headwater connection, if any in the Himalayas.
Results
A large number of samples from dug wells and tube wells have been analyzed7 for their isotopic and chemical composition. The reduced water levels vary from 62 m in the north to about 40 m in the south showing the flow in the NE-SW direction. The tube wells have screens at varying depths normally in the range of 73 to 150 m below the surface. Both the dug wells and the tube wells are in the same hydrogeological regime except that the tube wells represent deeper horizons with the consequent effect of stratification.
Chemically, both dug weIl and tube weIl waters are similar and evolve towards Na-CI type. Table 2 gives the data for sorne representative samples.
It is seen that the shallow and deep waters have
The tube wells as well as most of the dug wells have negligible tritium indicating absence of modem recharge. Sorne dug wells, however, have traces of measurable tritium showing sorne component of recent recharge.
Carbon-14 data indicate that waters are several thousands of years old. The dug well waters have 14C uncorrected ages of 5000 to1800 years. The youngest waters at Dharmi kua are weIl outside the buried channel and have more depleteci180and measurable tritium. The tube well waters, on the other hand, have 14C uncorrected ages of 22000 to 6000 years. Here again, the oldest waters at Sadewal, which is weIl outside the buried channel, have enriched
180
and are highly saline.The isotope data thus agrees reasonably well with the course of the buried channel identified by remote sensing. There is a trend of increase in the apparent 14C age of groundwater from Kishangarh to Ghotaru indicating that the ground waters are slow moving with a speed ofless than 5 rn/y.
From the above observations, it may be concluded that the isotope data when interpreted along with the available ground data and remote sensing information and the descriptions in ancient lndian texts supports the view that the buried channel in the Kishangarh - Ghantiyali - Ghotaru sector could be part of the Lost River. The buried channel waters are thousands of years old and appear to move slowly in the aquifer system.
The aquifer appears to have been recharged when the river was flowing. No modem recharge is apparent. But, the fact that the groundwater levels remain steady after copious exploitation indicates continued headwater connection. The stable isotope composition indicates that the Lost River originated at an altitude; probably in the lower Himalayas (Shivaliks) and the water had undergone sorne evaporation before recharging the aquifer.
Isotope study on the branch entering Pakistan
It may be recalled that the remote sensing detected two courses of ancient channel of Ghaggar-Hakra-Nara riverbed entering Pakistan from Ganganagar: one towards Fort Abbas and the other towards Khangarh.
The latter one reenters lndia at Tanot and the isotope
S.
M
RAo: USE OF ISOTOPESIN SEARCHOF LOST RIvER-2 o -4
----;...
,
02H= 6.44 0180-
4.04t= 0.75, n=7) 200
Dugwell
• Tubewell•. Precipitation 0
•
Hand pump
-MWL
---TW samples -20<0 cF-
NI
t<:>
-40
-60 -80
-10 -8 -6
Fig. 2. (52H--8180plot of Jaisalmer samples
Groundwater; fresh, brackish or saline has no measurable tritium (as in Jaisalmer study).
Stable comp<'lsition (8180=-5.7 to -4.20/00 and 82H=-44 to -37%0) is enrlched compared to Jaisalmer samples. The stable isotope values faH on an evaporation line with a slope of 4.8 and the line intercepts the Meteoric Water Line at 8180=-7.4%0 (Fig. 2).
Interpretation is that the 'fossil' groundwater was recharged as seepage from the ancient river under similar climatic conditions as today.
The groundwater ages, their stable isotopic composition including the evaporation signature are broadly similar to those found in the Jaisalmer branch of the buried channel.
Conclusions
The broad conclusion drawn from the remote sensing and isotope studies and from the references in the ancient texts is that the Kishangarh - Ghantiyali - Ghotaru section of the palaeochannel in the Jaisalmer district of Rajasthan could be part of the Lost River
(legendary Sarasvati River?). So also is the Fort Abbas- Fort Mojgarh sector of the ancient Hakra bed in Pakistan. More needs to be done to cover the entire dry bed of the Ghaggar - Hakra - Nara system since the search for the Lost River is far from complete.
References
L B. P. RADHAKRISHNA, S. S. MERH (Eds), Vedic Sarasvati, Evo1utionary History of a Lost River in Northwestem lndia, Memoir Geo1ogical Society oflndia, Vol. 42, 1999.
2. V. SRIDHAR, S. S. MERH, J. N. MALIK, Vedic Sarasvati, Evolutionary History of a Lost River in Northwestem lndia, Memoir Geo1ogical Society oflndia, Vol. 42,1999, p. 187 3.K.S. VALDIYA,Resonance, 1 (1996) No. 5, 19.
4. R. D. OLDHAM, J. Asiatic Soc. Bengal, 55 (1886) 322.
5.C. F.OLDHAM,J. Royal Asiatic Soc. (N.S), 34 (1893) 49.
6.A S. RAJAWAT,C.V. S. SASTRY,A NARAIN, Mem. Geol. Soc.
lndia,42 (1999) 259.
7. A. R. NAIR, S. V. NAVADA, S.
M
RAo, Mem. Geol. Soc. lndia, 42 (1999) 316.8. S.M RAo, S.K.JAIN, S. V. NAVADA, A. R. NAIR,K.SHIVANNA, Proc. lntern. Symp. on the Use of Isotope Techniques in Water Resources Development, IAEA, Vienna, 1987, p. 403.
9. S. V. NAVADA, S.
M
RAo, Isotopenpraxis, 27 (1991) 380. _ 10. M. A GEYH, D. PWETHNER, Applications of Tracers in AridZone hydrology (proc. of the Vienna Symp.), IAHS Publ. No.
232, 1995, p. 119.
