Hydrogeomorphological mapping on satellite images for deciphering regional groundwater prospective zones of the Luni river basin, Western Rajasthan, India M. Rajesh kumar Research Assistant Department of Earth Sciences Indian Institute of Technology Powai, Mumbai – 76, India rajgeo@iitb.ac.in AS Rajawat Scientist ‘SF’ ESHD/MWRG/RESIPA Space Applications Centre (ISRO) Ahmedabad, India T.N. Singh Student Symbosis Institute of Technology Pune Rajashree Chowdary Student Symbosis Institute of Technology Pune ABSTRACT Hydrogeomorphic mapping has been carried out regionally using satellite images to understand the major variations in morphology for the identifying the groundwater prospective zones in Luni river basin, western Rajasthan. Distinctive hydrogeomorphic units identified on images are playa, flood plain, palaeochannel, valley fill, intermontane valley, alluvial plain, buried pediplain, aeolian plain, dune complex, pediplain, buried pediment, pediment, structural hill, residual hill, and denudational hill. These units have been found to control the groundwater regime. Twenty-five sites were selected on the basis of integrated study of lineaments, geomorphology, drainage and hydrogeological maps for detailed geophysical, hydrogeological and exploratory drillings. Geo-technical investigations are also suggested at these locations for assessing the feasibility of suitable recharge structures. INTRODUCTION Luni river basin, located in the semi - arid zone of Thar desert in western Rajasthan has distinct morphological variations ranging from high extensive ridges of hard rocks to the vast alluvial plain blanketed by sand dunes and dotted with hills in the west. Deposition in the basin has taken place on an uneven basement and is net result of the streams supplying material of all size grades, typical of arid / semi-arid zone, and the active tectonic conditions operating along major lineaments. The basin well known for its major Luni-Sukri lineament (Dhir et al., 1992) and seismic activity along the same (Ramasamy et al., 1991) Several graben structures filled with sediments are found coincident with the major tectonic lineaments in the basin (Bhajpai et al., ms). Lineaments have also influences considerably the morphological process and continue to exercise control on the present day channel behavior (Kar, 1992, 1994). Geologically, the basin has the rocks of the Arvalli and Delhi Supergroups (Precambrian) along its eastern boundary, rocks of Malani Igneous suit (Post Delhi: Precambrian) right from the north to south, and rocks of Marwar Supergroup (Cambrian) in the northeast. The western and central part of the basin is occupied by desert sand, which overlies Quaternary alluvium (Taylor et al., 1955; G.S.I. 1976; Gupta et al., 1980; Pareek 1981, Dasgupta et al., 1993). In the present work, hydrogeomorphic mapping has been carried out using satellite images to understand the major variations in morphology all over the basin. STUDY AREA Luni River Basin lies to the west of the Aravalli hills in the state of Rajasthan and forms part of the Thar desert. It is located between latitudes 23º 41' N and 27º 05' N and longitudes 71º 04' E and 74º 42' E. River Luni originates from the western slopes of the Aravalli range at an elevation of 550 m, near Ajmer. After flowing for about 495 km in a southwesterly direction in Rajasthan, the river disappears in the marshy land of Rann of Kachchh. The total catchment of the Luni river basin in Rajasthan covers parts of the districts of Ajmer, Pali, Jodhpur, Nagaur, Barmer, Jalore and Sirohi. Fig. 1 shows the location map of the study area.  Fig 1: Location Map MATERIALS AND METHODS First of all, the published literature and map were collected and studied to get familiarized with the study area. The maps were digitized and then geo-corrected using ERDAS Imagine S/W 8.5 and then mosaiced using mosaic tool. First of all Luni basin boundary was digitally traced. An Area of Interest (AOI) layer was prepared and saved as a separate file. This was utilized later on for extracting data for the study area from IRS-P4 OCM and IRS01C/1D LISS-III mosaiced data. Drainage covering the Luni basin was traced on a tracing sheet using light table and Survey of India topographical maps on 1:250, 000 scale. The tracings were made using SOI Map sheets: 40 N, 40 O, 40 P, 45 B, 45 C, 45 D, 45 F, 45 G, 45 H, 45 I, 45 J, 45 K, 45 M & 45 N. The tracings were digitized using an A-0 size scanner and then geocorrected and mosaiced using ERDAS Imagine 8.5. Drainage was traced digitally and a drainage map was prepared. Hydrogeological maps and Ground Water Potential Maps were studied using Ground Water Atlas of Rajasthan, prepared by Ground Water Department, Jodhpur and State Remote Sensing Applications Centre, Jodhpur. The district wise maps covering the Luni region (Barmer, Jodhpur, Pali, Jalore, Sirohi, Nagaur & Ajmer) were scanned using A-3 Color scanner. The maps were geocorrected and mosaiced using ERDAS Imagine 8.5 s/w. All the lines and polygons were traced and given symbology. Final map was prepared using Map Composition tool. 3.2 Analysis of Satellite data IRS-P4 OCM and IRS-1C/1D LISS-III data (CDs) was analysed in the present study. Table-1 shows data utilized in the present study.  HYDROGEOMOPHIC MAP Geomorphic mapping has been prepared by using the various band combinations of IRS-P4 OCM (acquired on November 25, 2002) and IRS 1C/1D LISS-III mosaiced data (acquired on November 16, 2001, October 13, 1998, November 30, 1998, October 08, 1998, October 03, 1988) due to better contrast and clarity of features on them. Regionally the basin has been classified into following geomorphic units (Fig 2 & 3). The relationship of these geomorphic units with the hydrogeological units can be compared (Fig 4). PLAYA Playa is a dry, vegetation free, flat area at the lowest part of an undrained dessert basin underlying by stratified clay, silt or sand and commonly by soluble salts. These are identified as white tone on satellite imageries and in the Luni basin these areas are at Pachpadra, Sambhar etc. Some times during rainy season they are filled with the water. Most of the Playas are saline depressions and they configuration is controlled by lineaments for example both at Sambhar and Pachpadra they form grabens and the ground water quality is saline. FLOOD PLAINS Flood plains areas are situated on either side of the rivers. In most part of the basin, they are represented by the dry beds. The major flood plain areas have been identified on satellite images along the main courses of the Luni and the Sukri-Jawai rivers and minor ones along the the Mithri, the Lilri, the Khari, the Bandi and the Sukri rivers. While the dry sandy beds appear white on FCC, most areas with vegetation appear as dark red tone on FCC. Flood plain areas have high potential of groundwater, however, only shallow water bearing zone must be tapped to avoid saline water, as salinity increases with depth, moreover, the areas near the confluences need to be particularly avoided as these are the locations of heavy silt depositions leading to hydraulic discontinuity with the main streams and promoting the salt concentration. Several such areas along the Luni, the Jawai-Sukri and the Khari rivers have been investigated for their high salt concentrations (Ghose, 1964). ALLUVIAL PLAINS/AEOLIAN PLAINS These are distributed in the northern and western part of the basin in the Jodhpur-Barmer-Jalore region. The vast flat regions of older alluvium having regional slope towards the Luni river are formed by alternating thick sequence of clay, sand, gravel and pebbles deposited by the drainages operative in the past. The deposition has taken place into deep seated and extensive faulted-grabens represented by major lineaments. The influence of the Lik river appears to be prominent in deposition of coarse-grained gritty gravels, indicated by southward palaeocurrent directions in cross-bedded gravels near Sindari and in the region to its north. The thickness of fluvial sediments range from around 40 m in the northwestern part to more than 300 m in the southwestern part of the basin. The alluvial regions are covered extensively by sand sheets and sand dunes, and are also dotted with salt-water depressions (ranns). As soon as the pediment zone is over due to abrupt increase in depth to bedrock, the zone of alluvial plain or the valley fill starts. The contact of the pediment with valley fill is marked by disappearance of streams coming from the rocky tract. The alluvial plain and the valley fill zone provide scope of development of deep groundwater reservoir particularly in alignment of geologic structure of the structural hills. The part of the alluvium further away from the hilly regions will have lesser content of granular material derived from the rocky tract and thus the hydraulic conductivity of the aquifers within the same would be considerably low as compared to that within the pediment. The occurrence and the quality of groundwater in this part of the alluvium due to the greater influx of clay would therefore be highly erratic. PALAEOCHANNELS These represent the former stream courses along which water may flow for a short distance during rainy season making the internal drainage. Such channels on the surface are almost disconnected with the main streams. The extent of channel continuity has been traced on band 3 and band 5 of OCM imagery by the typical light gray to white tone for the dry part and dark gray tone for the part with moisture and vegetation. On false color composite, the dry sections are indicated by their white to light greenish tone and the moist and vegetated sections by pinkish red tone. Several such channels have been identified along the tributaries of the Jawai-Sukri and the Luni rivers in the eastern part of the basin. It has been observed that in general the channels occupy the dissected pediments and get disorganized or extinct in the aeolian plain or dune complex. In the northern part of the basin these are represented by the former tributaries of the Mithri/Jojri river from its east and by an extensive network of the Jojri river from the NE of Jodhpur to W of Balotra. In the northwestern sector these are represented by the Lik river. The Lik river due to its bed being heavily occupied by sand dunes is almost extinct at present (Kar, 1998). The other abandoned channels of importance occur in the central part of the basin in the region from about 15 km west of Bilara to about 15 km northwest of Jalore. Through this sector upper Luni used to directly join the Sukri/Jawai river in the past (Kar, 1999). Extensive aquifer systems containing mostly fresh water have been formed along the palaeochannel belts, particularly along lineament controlled courses. The fresh water occurrence is because of the regular flushing of the channels during rainy season. Still, the water towards depth may be taken as brackish to saline. The promising aquifer in the channel belts of the Jojri in the Jodhpur district are being exploited for fresh water supply. The quality of water must be better in areas to the east of Jodhpur in the buried pediments if rhyolite and sandstone are fractured and criss-cross lineaments occur. VALLEY FILLS Valley fill zones are located adjacent to pediments/pediplains/buried pediments/buried pediplains. They vary in shape and extent. Wide and extensive valley fills are formed within the faulted grabens. These occupy the major lineaments of Luni-Sukri group with NE-SW trend and others with E-W trend. Minor and narrow valley fills are located along the dissected pediments. The valley fill zones are mostly occupied by major and minor streams. The streams show braiding, fanning, disorganization and disappearance in valley fill zones. They have been demarcated on the basis of their reddish tone or sometimes dark greenish blue tone on IRS FCC images. BURIED PEDIPLAIN /BURIED PEDIMENTS/PEDIPLAIN/PEDIMENT The rock cut plain erosional surfaces occur adjoining structural hills/denudational hills/residual hills and are known as pediments when their dimensions are small and as pediplain when they extend for larger regions. Some times these are covered with thin veneer of alluvium/aeolian sand and according to their dimensions are identifying as buried pediments or buried pediplains. Buried pediplains occur on both sides of the Luni flood plains. Buried pediments are basically the inclined rocky surfaces as extensions of ridges over which the alluvium and aeolian sand have been deposited. While extensive pediments all along the foothill region are observed close to the eastern boundary of the basin, the same of circular to oval and elongated shapes are commonly distributed right from the southern part to the northern part of the basin. The average altitude of the pediplain at foothills of Aravalli ranges is around 444 m in the northern part and 138 m in the southern parts of the Luni basin. The boundary pattern of the pediments varies according to the running behavior of ridges. The pediments of different ridges also appear as fused together. The gullies provide the media for transferring the surface water from hilly regions to the pediment zone, which also receives the groundwater runoff through the rocky tract. That is why the pediment zone is full of streams. On IRS images, the pediments are identified by their light greenish white tone in contrast to dark gray ridges on one side and dark greenish blue valley fill on the other. Several oval and elongated pediments of light gray tone are observed on images around ridges of granite situated to the south of Bhinmal, north of Bera between Jawai and Ugti rivers, and to the south of Siwana and Bhadrajun. DUNAL COMPLEX This tract consisting of sheets, sand dunes and interdunal depressions is mostly distributed in the northern and the northwestern parts of the basin. The northwestern part of the region is typical of its elongated sand dunes alternating with interdunal depressions. The interdunal depressions are the significant units as several of them are the sites of surface water reservoirs. The sand dunes and sand blanket the alluvial regions, western parts of the rocky ridges and their pediments. In fact, the peripheries of the sloping pediments are distinct on satellite images due to their sand cover appearing with light tone. The sand dunes in general are abundant in the western part of the basin in Barmer district. They rise to heights ranging from about 5 m to more than 50 m. The maximum height of about 70 m has been found in the vicinity of the Lik riverbed. Scattered sand dune ridges of about 25 m height are present near Sindari on either side of the Luni river and further down stream. The sand dunes are of linear and parabolic type and are also partly covered with vegetation. On false color composites, the sand dunes can be observed distinctly by yellowish green Colour and linear parabolic boundaries. The interdunal areas also appear dotted with pinkish red vegetation and light blue to dark blue water bodies. An extensive tract of parallel and linear dunal ridges has been identified on images in the region extending from west of the Gotan to the north of the Kankani. The aquifer potential is limited in the dunal tract is only the interdunal depressions. However, the infiltration through the sandy tract provides a good amount of recharge to the underlying aquifers. STRUCTURAL HILLS/DENUDATIONAL HILLS/RESIDUAL HILLS The Aravalli ranges predominantly constitute structural hills in the Luni basin. These ranges in general trend NE-SW and the altitude along their axis gradually decreases from the southern parts to the northern parts. The maximum height of the Aravalli ranges is around 1722 m at GuruShikhar, Mount Abu near the southern parts and around 782 m around Ajmer near the northern parts. A number of linear to curvilinear lineaments are observed. At number of places NW-SE trending faults dislocate these ridges and the western boundary of these ridges is reflected as a sharp break in relief and is represented by a tectonic dislocation. Mostly these ridges constitute of Delhi group of rocks. Apart from these isolated regions such as around Sirohi, Jodhpur, Jalore, Nagaur form low denudational hills and the vast pediplain around Pali shown regions dotted with isolated residual hills. Straight to curved and extensive ridges of quartzites of Delhi Super Group have been observed on imageries right from the southeast of Sendra to the north of Ajmer in Ajmer-Rir region, extending to the northeastern boundary of the basin. The ridges appear more straight and continuous than of granite and are in sharp contrast to their surrounding alluvium. In general, aquifer system in the hilly regions is located within shallow alluvium filled in intermontane valleys, in the vicinity of fracture controlled bedrock channels and within the fractured and weathered zone. Ridges also act as inhibitors of runoff and favor location of water bodies, providing recharge to the aquifers. In the hilly regions, the surface water percolates through the joint planes and also collects in structural depressions, where it acts as a recharge source for the aquifers. The extensive gullies developed especially along the axial joints and across the peripheral margin of the hilly regions act as channel ways through which the coarser material has been transported and deposited in the foothill region, where an extensive aquifer system has formed following channel trends.  Fig 2 Hydrogeomorphological interpretation of the Luni basin using OCM data  Fig 3: Hydrogeomorphological interpretation of the Luni basin using LISS III data  Fig 4: Hydrogeological Map of the Luni basin (Modified after Ground Water Atlas of Rajasthan, 1999) GROUNDWATER PROSPECTING Groundwater exploration in the arid terrain is extremely difficult due to lack of recharge conditions and aeolian sand cover. In the Luni basin, the Aravalli ridges in the east with semi-arid climate form the recharge zone. In the remaining parts of the basin, search for the ground water is confined to the most promising zones in terms of porosity and permeability. Porosity, the volume of available pore spaces in rocks determines the amount of water, which can be held in storage. Permeability determines the ease with which the water moves through the pores and fractures, and hence can be extracted for use. The clue to ground water search is the premise that sub-surface geologic elements forming aquifers have surface expressions, which can be discerned by remote sensing techniques. These surface expressions are drainage, landforms of depositional nature, moist pockets seen as anomalous vegetation patches, lineaments etc. Surface run-off and infiltration are both strongly affected by the steepness, length and roughness of the slopes. Drainage pattern and density gives useful indications. Ground water may occur where alluvial and/or colluvial deposits cover the bedrock. Valley fills, palaeochannels, alluvial plains, braided channels, flood plains, inter-dunal depressions, anomalous vegetation, underfit valleys, lineaments, lineament intersections, dyke-river confluences, buried pediments, pediplains etc. provide useful geomorphological indicators. Lineaments are the most useful input from satellite images reflecting lines of weakness in the earths’ crust as fractures, faults etc., which provide secondary permeability in hard rock terrain. They may be seen as linear tonal discontinuity, alignment of vegetation, and straight segments of stream courses, alignment of lakes, ponds, springs, linear scarps, rectilinear depressions or any combination of these. It can also be observed that the ground water prospective zones identified by remote sensing techniques can also be utilized as suitable sites for constructing suitable rain-water harvesting structures for recharge purposes. The source water from the distributaries of the Indira Gandhi Canal can be utilized for recharge purposes in the Luni basin. Table-2 summarizes characteristics of 25 sites selected on the basis of integrated study of lineaments, geomorphology, drainage and hydrogeological maps. Fig. 5 shows location of some 25 sites selected for detailed geophysical, hydrogeological and exploratory drillings. Geo-technical investigations are also suggested at these locations for assessing the feasibility of suitable recharge structures.      Fig 5: Ground water Prospective zones of the Luni basin, Western Rajasthan CONLUSIONS Following conclusions have been made in the present work:
The authors extremely happy to express my sincere thanks to Dr. K. N. Shankara, Director, Space Applications Centre, ISRO, Shri R.J.K. Jain, Head, HRDD, SAC and Dr. Shailesh Nayak, Group Director, Marine and Water Resources Group, Space Applications Centre, Ahmedabad for permitting me to work at SAC. REFERENCES
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