PALAEOCHANNELS AND THEIR RECHARGE AS DROUGHT PROOFING MEASURE : STUDY AND EXPERIENCES FROM RAJASTHAN, WESTERN INDIA . A.K.Sinha * , K.S. Raghav # and Anoop Sharma* *Environmental geology Lab, Department of Geology, University of Rajasthan, Jaipur 302004. Email: email@example.com and firstname.lastname@example.org # Geological Survey of India, Western region, Jaipur ABSTRACT Rajasthan is India’s largest state. Major part of this country fall in arid to semi arid hydroclimatic zone and suffers due to drought frequently fastly eroding the coping capacity and economic potential of the people and severely impacting the bare survival needs of the people including food availability , safe drinking water and adequate nutrition . As the every cloud has silver lining so the findings of the of Palaeochannel provides an array of hope for the survival of the humanity and livestock in this part of the world in view of the recurring onslaught of the drought menace. Palaeochannels belong to past riverine environment which are today found in form of the geomorphic signature in a location representing drainage, streams , rivers which were flowing either ephemeral or perennial during the past time and now stand , either buried or lost and shifted due to tectonic , geomorphic as well as anthropogenic activities and climatic vicissitudes . Numerous Impression of such palaeochannels are present in this part of the world . In the present paper water prospect of palaeochannel as well its recharge prospects by means of rainfall –runoff water as well as canal water has been discussed. The study shows that the palaeochannel are not only having potable quality of ground resource which is manifested in the comparative yield of the wells as well as chemical study of the water samples but their favorable hydrological conditions revealed by the Resistivity survey points toward their being good rechargeable aquifer The remote sensing study supplemented by ground checks and Resistivity Survey has identified Palaeochannels in the semiarid to arid regions of Rajasthan, India which have very favorable geohydrological conditions and are amenable to recharge by rain water harvesting techniques as well as imported water through canal quite economically and environmental friendly way..The recharge would not only further augment the ground water availability in the region which may be used to mitigate the adverse impacts of the drought but may also rejuvenate the lost river and ephemeral river system leading to regeneration of the deranged ecological system. Further , India receives a rainfall of 4000 billion cubic meter every year out of which 1869 billion cubic meter appears as surface run off in the various river basin of the country and about 432 billion cubic meter goes to the replenishment of the Groundwater resources and the remaining are lost to sea as run off. Even if part of the run off lost to sea is conserved on land in identified natural storage such as Palaeochannel as well as in ephemeral river basin it would considerably ease the problem of arid region and would act as effective drought proofing measures in arid to semi arid regions. INTRODUCTION There is growing concern for the depleting water resources and increasing frequencies of drought all over the globe . The SCOPE- an international body survey reveals that water scarcity is the second most (Table-1) important environmental issues next to Climate Table –1: Major Global Environmental Issues Change threatening humanity .According to IWMI Indicator of relative water Scarcity , by 2025 , 44 percent of the world’s population will leave in countries with physical water scarcity and 26 percent will leave in countries with economic scarcity ( Fig-1). There has been reduction of about water user sector to grab the maximum share and benefit out of the depleting and deteriorating water regime. 40 percent decline in per capita water availability on global basis taking 1970 as baseline. Various agencies and individuals at local , national , regional and global level have forewarned us of worsening water scenario at local, national, regional and Global level mainly due to population explosion as well as imbalanced and unhealthy competitions among various Fig-1: IWMI indicator showing Relative water Scarcity by 2025 Notwithstanding the prediction of the many agencies , the Water Scarcity in fact has started unfolding up in arid regions of India ( Sinha 2001) even now . There is considerable decline in per capita availability of water ( Table- 2) . The worst affected regions( Fig-2) are Table-2: Per Capita Water Availability YEAR POPULATION PER CAPITA WATER AVAILABILITY (In Millions) ( In Cubic Meters) 1951 361 5177 1955 395 4732 1991 846 2209 2000 1002 1865 2025 1393 ( Projected ) 1342 1. East Flowing rivers basin area between Mahanadi and Pennar 2. East Flowing rivers between Pennar and Kanyakumari 3. Sabarmati basin and 4. Inland drainage basin in Rajasthan ( Western India ) The present paper deals with the possibility of the augmenting water resources through exploiting and recharging the palaeochannels in the Rajasthan RAJASTHAN SCENARION Rajasthan is the largest state of India having geographical area of 342239 sq km . It is situated in the western part of India . It is driest state having only 1.15 % of the total water resources . The state enjoys semiarid to arid climate conditions ; the aridity increases westward and is witnessed as development of Thar desert and also salt lakes /depressions . The state occupies a wide spectrum of geomorphological features such as Aravalli hill ranges , Eastern plains , Vindhyan –Deccan plateau and western sandy dunal landscapes ( Fig-2: Present Water Scarcity regions of India Thar desert ). The average annual rain fall has been 416.15 mm during the last 30 years . The depth to water ranges from 1.7 to 27.87 mbgl( Jan 2000). The region lack perennial source of water and more than 70 % people depend upon ground water and remaining on canal and impounded water. The thirty one out of thirty two districts of the state has been under the drought which has drastically affected this part of the world both ecologically and economically so much so that food and drinking water availability has reached to its lowest ebb. Ground water table has shown widespread decline through out the state at the rate of 10 to 40 cm per year.. As the deleterious effects of water resource depletion and pollution and its consequences are surfacing out, a variety of responses are being forged to mitigate or even reverse these . One such response gaining popularity in the region is Rainwater Harvesting. Despite large number of dams and reservoir in India 1150Km3 of its rainwater precipitation still run off to the seas annually in the form of rejected recharge. If a fraction of this can be stored underground in an appropriate reservoir / storage system ,groundwater availability could be enhanced significantly which may provide great succor to semiarid and arid regions of western India which are highly water deficit .The growing incidence o f surface water pollution and enhanced dependence on ground water warrant the need for the search and development of aquifer to enhance the storativity of the rain fall – run off and imported water through canal which may serve as source for the artificial recharge . PALAEOCHANNELS Every cloud has silver lining and so the finding of the palaleochannels by various workers ((Ghosh et al 1979, Bakliwal et al 1983,Yashpal et al 1983, ,Ramasamy et al 1991 , Rakshit & Sinha1997,Raghav& Sinha1998 ,Raghav 1999, Raghav & Sinha 1999) ) have unfolded new vistas and provide a new array of hope for the survival of the humanity and livestock in this part of the country in view of the recurring onslaught of drought menace. Palaeochannels /Palaeodrainage / Lost River / Burried River are typical geomorphic features in a location representing drainage streams , streams , Rivers, rivuletes which were flowing either during the past time and now stands either burried or lost or shifted due (Fig-3) to tectonic , geomorphological , anthropogenic process / activities as well as climatic vicissitudes . They appear in plan as linier / curvilinear signature and shape on Remote Sensing data products. However various definition of Palaeochannel has emerged . Some of which are as follows: 1.Palaeochannles are the drainage/rivers / streams which were flowing either ephemeral or perennial during past but now these are lost due to tectonic activities, climatic changes and geomorphic activities. 2. Palaeochannles are the drainage/rivers / streams which were flowing either ephemeral or perennial during past time but at present time these are lost due to internal ( tectonic activities ) and external activities ( climatic , geomorphic and anthropogenic ) 3. Palaeochannels are the older river courses which were buried due to sedimentation . 5. Palaeochannels are the remnant scars of the shifting of the rivers such as Yamuna , Sutluz rivers. Fig-3: Palaeochannels due to Shifting of Rivers EVIDENCES IN FAVOUR OF PALAEOCHANNEL Initially for long time the inscriptions in mythological and historical literature provided clue about the existence of such past river system. However with the evolution in the thought processes and technological innovation many new evidences have emerged supporting the existence of river system in the past. There are many Mythological , Archeological , Geomorphological , Geological , Geophysical and Remote sensing evidences which points toward presence of well integrated drainage network in the Thar desert in recent past. However the evidences derived from geological ,Geophysical and Remote sensing methods have proved beyond doubt the existence of number of palaeochannels . Geological Evidences Geological record indicates that during Late Pleistocene glaciating waters of the Himalayas were frozen and that in place of rivers there were only glaciers , masses of solid ice . At the outset of Holocene as climate became warmer the glaciers began to melt and break up and the frozen water held by them surged forth in great floods , inundating the alluvial plains in front of the mountain. The release of pent up water gave rise number of rivers flowing through the plains in front of Himalayas. The river deposits are identified and characterized on the basis of their typical geological and physical character. Following is one of the cross section( Roberts 1994) showing a typical river deposit ( Table-2) from Palaeochannel (unit 4-6) Table-2: A typical litholog of Palaeochannel (Pre-palaeochannel) Unit 1: light grey-yellow lake marl (maximum thickness >150 cm) Unit 2: Dark (?organic) marl (max. 20 cm) Unit 3: Backswamp clay (max. 160 cm) (Channel fill) Unit 4: Grey clay with manganese staining (max. 30 cm) Unit 5: Matrix supported gravel, locally part-cemented (max. 30cm) Unit 6: Fluviatile silts, sands and gravels, coarsening from west to east (max. 220 cm) Sub-unit 6a: Red-brown silts Sub-unit 6b: Buff silts Sub-unit 6c : Grey to orange fluviatile sands containing large freshwater bivalve shells Sub-unit 6d: Fluviatile gravels (Post-palaeochannel) Unit 7: Alluvial clay with manganese staining (max. 230 cm). This upper alluvium caps all the underlying units. Geophysical Evidences The geophysical sounding carried out in one of the inferred palaeochannel has also revealed the presence of typical coarse sand gravel bed which are alluvial in nature which has characteristic of being a good aquifer . Hydrogeological evidences : Lunkaransar, Didwana and Sambhar, the Ranns of Jaisalmer, Pachpadra, etc. are a few of the notable lakes, formed as a result of the changes; some of them are highly saline today,the only proof to their freshwater descent being occurrences of gastropod shells in those lake beds. Mr. Oldham accepted that there have been great changes in the hydrography of Punjab and Sind within the recent period of geology. Wilson has mentioned about the Sotar valley where “the soil is all rich alluvial clay such as is now being annually deposited in the depressions Freshwater pools are normally found encircled by saline water in palaeochannel zones. Remote Sensing Evidences The Advent of Remote Sensing technology could throw much light on the subject. With this technology it has now become possible to discover , delineate and understand the palaeochannel in regional context and in integrated manner. A remote sensing study of the Indian Thar desert reveals numerous signatures of palaeochannels in the form of curvilinear and meandering courses, which is identified by the tonal variations ( Bakliwal et al 1988). Its initial course flowed close to the Aravalli ranges and the successive six stages took west and northwesterly shifts till it coincides with the dry bed of the Ghaggar River. Yash Pal et al.(1980) found that the course of the river Saraswati in the states of Punjab, Haryana and Rajasthan is clearly highlighted in the LANDSAT imagery by the vegetation cover thriving on the rich residual loamy soil along its earlier course. Digital enhancement studies of IRS-1C data ,combined with RADAR imagery from European Remote Sensing satellites ERS 1/2, identified subsurface features and recognized the palaeochannels beneath the sands of the Thar Desert. A study of NRSA, based on satellite derived data, has revealed no palaeochannel link between the Indus and the Saraswati, confirming that the two were independent rivers; also, the three palaeochannels, south of Ambala, seen to swerve westwards to join the ancient bed of the Ghaggar, are inferred to be the tributaries of Saraswati/Ghaggar, and one among them, probably Drishadvati. Digital enhancement techniques using high resolution LISS-III data of IRS-1C satellite, together with pyramidal processing, identified two palaeochannels trending NE-SW in Jaisalmer districts. WATER RESOURCE POTENTIALITY OF PALAEOCHANNELS The palaeochannels considered as lost drainage are still having under flow of ground water evidenced by abnormally high pumpage discharge,fresh to low saline quality in comparison to water occurring in adjoining nonriverine environment and are also comparatively older in character ( Nair et al 1997) .This is a premise on the basis of which efforts are being made to trace the coarse of the Saraswati river- one of the very famous long river lost in the Thar Desert. Such palaeochannels are being looked upon as possible reservoir of ground water. If such basins are further identified and integrated, it is possible to rejuvenate it through recharge by Rainwater harvesting as well as by canal system. Such measures may initiate a blue revolution in the Thar desert. It is obvious that palaeochannels have comparatively better prospects of water storage in comparison to adjoining non-fluvial zone. The isopach map in case of other ephemeral basin( Sinha et al 2001) has revealed a comparatively thicker unconsolidated sedimentary pile which has potentiality of holding greater volume of water and as such on the basis of similar analogy palaeochannels may also be looked upon as comparatively thicker sedimentary pile having potentiality of holding larger volume of water to meet the demand during the drought situation. However there is need to identify , delineate and estimate the sedimentary thickness of all such paleochannels for precise planning of the water resources development and utilization program to effectively counter the menace of the drought. The palaeochannels of Quaternary may become major source of ground water in this region. Quality and semi-quantitative data of availability of ground water from few paleochannels of the region are tabulated herewith ( Table-3 ) Table 3: Distribution of sub surface water. Source Occurrence Aquifer Reservoir Depth Quality Ground i Sand dune sand Palaeochannel F1 Good 35 m to 50m Sweet water sheet ii Abandoned Palaeochannel F2 Moderately good 15m to 30 m Sweet playas and Good 30 m to 40 m Brackish lakes i Sand Palaeochannel F1 Moderately good 10 m to 15 m -do- dune/sand Poor 2 m to 5 m Sweet sheet ii Playas and Silty sand and Clay Very poor 1.5 m to 2.5m Brackish lakes iii Rivers Channel deposits -do- Sweet Quality of Water in Palaeochannel Further ,in order to assess the quality of the ground water in the palaeochannels a total of 37 water samples were collected from dug wells confined to different lithological units. The geochemical analyses of water samples are carried out and TDS, Ph, CO3, HCO3, Cl, SO4, NO3, F’ were calculated. Total hardness as CaCO3 and Ca++, Mg++, Na+, K’, SiO2 and B were determined. The epm % values and atomic ratio values of Na+ / K+ Cl+/HcO3+, 01-/F’ Cl-/So2-; Na+/Mg+; Mg+/Ca+ and total alkalinity of these samples were calculated .The percentage values of all these sample were plotted on the piper diagram which reveals that most of the water confined in abandoned playas and rocky pediplain areas is NaCl type. The water of the sand dune field areas is NaHCO3, type. The quality of water is potable and fit for irrigation purposes as well. No doubt it holds much hope for future as huge untapped reservoir of fresh water resources PALAEOCHANNEL- PROSPECTS In view of the adverse prediction of the various international and national agencies about the availability of the water resources during 2025 to 2050 and the surfacing water scarcity conditions in semi to arid region of the world including India , the delineation and identification of palaeochannel may be highly useful from the following point of view: i) source of the ground water , in general of good quality ii) possible locales for rainwater harvesting iii) possible locales for artificial recharge using excess of canal water etc SUMMARY AND CONCLUSION There are overwhelming evidences from various sources mainly from Satellite Imagery interpretations as well from archeological , geological , and Geophysical evidences that the rivers with well integrated drainage once flowed through Thar Desert , the remnants of which are found today as palaeochannels . These Palaeochannels are not only the abode of potable water but alos posses high volume of storativity which if utilized by recharging them by catching each and every droplets of the rainfall-runoff component and imported water through existing canal , may provide as relieve to drought affected people and livestock. Such measures may be adopted towards drought proofing in this state . These palaeochannels are not merely the imprints of the lost channels but are the riverine monument which need to to be understood in greater details and possibly stands out to provide not only needed water resource to the society but lesson too to modern humanity for taking proper care of their existing riverine environment and to take suitable measures to prevent them from turning into palaeochannels. REFERENCE Bakliwal PC,Ramasamy S.M,and Grover A.K,(1983) Use of remote Sensing in Identification of possible areas of Groundwater , Hydrocarbons, and Minerals in Thar Desert , Western India .Proc. Vol . 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Sens., v. 12 (12): 2597-2609 Robert Neis 1994 Çatal Hüyük palaeoenvironment project , Archive report Sridhar V ,Merh S.S and Mallik J.N 1999 : Late Quaternary Drainage Disruption in Northwestern India : A Geoarcheological Enigma .Geological Society of India Memoir No 42 pp 187-204 Yashpal, Sahai, B., Sood, R.K. and Agrawal, D.P. 1980. Remote sensing of the lost Sarasvati River. Proc. Acad. Sci. Earth Planetary Sci. V. 89: 317-331.
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